Journal of Applied and Computational Mechanics
https://jacm.scu.ac.ir/
Journal of Applied and Computational Mechanicsendaily1Sun, 01 Jan 2023 00:00:00 +0330Sun, 01 Jan 2023 00:00:00 +0330Optimization of Spark Ignition Engine Performance using a New Double Intake Manifold: Experimental and Numerical Analysis
https://jacm.scu.ac.ir/article_16030.html
In this study, the effect of different intake manifold geometries on the performance of a spark-ignited engine is investigated both numerically and experimentally. 1D and 1D-3D simulations are carried out to find the optimal dimensions of different intake manifold designs. The numerical simulations are successfully validated with real data. The results show that the manifold design utilizing two-valve throttle has a better performance. The superior design is constructed and mounted on the engine to compare the output result with the base design. The operation tests are performed at various rotational speeds in the range of 1000-6000 rpm. Regarding the experimental tests, the superior double intake manifold increases the engine brake power and torque by 6.814%.&nbsp;A New Approach for Exergoeconomics Evaluation by Considering Uncertainty with Monte Carlo Method
https://jacm.scu.ac.ir/article_16189.html
The exergoeconomics analysis combines thermodynamic assessments based on exergy analysis with economic concepts. this article suggests a new method for exergoeconomics analysis and evaluation of energy systems by considering uncertainty in economic parameters. As the first step, the future values of economic parameters that influence the operating cost of the energy system are forecasted by the Monte Carlo Method. Then, as a novel approach, principles of exergoeconomics analysis method are coupled with the Monte Carlo Method for exergoeconomics evaluation of energy systems. Also, three new parameters, i.e. Risk Factor (RF), Risk Factor Sensitivity (RFS), and Product Cost Sensitivity (PCS), are proposed. Two different approaches are considered in the evaluation process to improve the system: a) decreasing the total cost of products and b) reducing the risk of the cost of products. Also, the proposed method is applied to the CGAM system as a benchmark. Eventually, the results of the first and second approaches show that the total cost of products can be reduced 4.1% (from 22.270 $/GJ to 21.358 $/GJ) and also the risk of the cost of the products can be reduced 5.8% (from 25.8% to 24.3%).Numerical and Experimental Investigation on Post-buckling Behavior of Stiffened Cylindrical Shells with Cutout subject to Uniform Axial Compression
https://jacm.scu.ac.ir/article_16692.html
In this paper, post buckling behavior of thin steel and aluminum cylindrical shells with rectangular cutouts under axial loading was studied experimentally and also using the finite element method. Riks method is used for analyzing the cylindrical shells. The effect of longitudinal and circumferential stiffeners (ribs and stringer) was studied on the buckling load and the post buckling behavior as the stiffeners used individually and in combination with each other. It was shown that by adding stringer, the buckling load improves and the rib has a positive effect on the post buckling behavior of the structure. Some tests were performed by ZwickRoell tensile/compression testing machine and it was carried out for both types of steel and aluminum shells with and without stiffeners. Comparing the experimental results with the FEA results shows good agreement. Nonlinear analysis of cylindrical steel and aluminum shells with cutout have demonstrated that, in some cases, a local buckling called snap-back can be seen in the load-displacement path. Snap-back which is a decrease in the amount of both load and displacement indicates this local buckling. This phenomenon is because of appearing mode shapes sequentially during the numerical buckling analysis of shells. Although these local buckling happened, the structure is still endured the higher loads.Potential of Semi-Empirical Heat Transfer Models in Predicting the Effects of Equivalence Ratio on Low Temperature Reaction and High Temperature Reaction Heat Release of an HCCI Engine
https://jacm.scu.ac.ir/article_16712.html
In this paper, the influence of equivalence ratio on the low-temperature reaction heat release (LTR-HR) and high-temperature reaction heat release (HTR-HR) of homogeneous charge compression ignition engine has been experimentally and numerically examined. The numerical study was performed using zero-dimensional (0D) single-zone model by considering the chemical kinetic of fuel combustion. Annand, Woschni, Hohenberg, Chang (Assanis), and Hensel semi-empirical heat transfer models were employed in the 0D single-zone simulations. In this study, the in-cylinder pressure, rate of heat release, LTR-HR and HTR-HR were investigated. The Hensel heat transfer model was the only model that predicted the combustion in all of the operating conditions. The Hohenberg model properly recognized the effects of equivalence ratio changes on the HTR-HR.Calculation of Backscattered Ultrasonic Waves Field from a Copper-clad Steel Rod Immersing in Water and Effect of Clad Corrosion and Interfacial Disbond between Clad and Rod Defects on this Field using the Finite Element Method
https://jacm.scu.ac.ir/article_17135.html
Inspection and specificity of the intactness of multi-layer and small-size parts like copper-clad steel rod is a hard task and requires high accuracy. The intactness of these parts is crucial due to their importance. One of the inspection methods for these parts is using ultrasonic waves. The scattering phenomenon occurs when these waves impact curved shape bodies under a special condition. The ultrasonic scattering waves contain a lot of information from the physical conditions and mechanical properties of the part. However, using these waves requires high accuracy and attention due to their complexity. One result of the ultrasonic scattering waves is the far-field backscattered frequency spectrum, form function. For the first time in this research, the form function of a copper-clad steel rod that is immersed in water is calculated using the finite element method (FEM) available in the commercial ABAQUS software. For validating the proposed model, the simulation results are compared with analytical and experimental results in the normalized frequency range of 4 &pound; Ka &pound; 10. A good agreement is observed between the three methods at the resonance frequencies, and in the overall form of obtained form function. Furthermore, the effects of the two most common defects in these rods, i.e., the corrosion and interfacial disbond between the clad and steel rod, is studied. Results show that this method can properly specify the corrosion percentage and location, and also the length and location of the interfacial disbond defect.&nbsp;Numerical Simulation of Fuzzy Volterra Integro-differential Equation using Improved Runge-Kutta Method
https://jacm.scu.ac.ir/article_17145.html
In this research, fourth-order Improved Runge-Kutta method with three stages for solving fuzzy Volterra integro-differential (FVID) equations of the second kind under the concept of generalized Hukuhara differentiability is proposed. The advantage of the proposed method in this study compared with the same order classic Runge-Kutta method is, Improved Runge-Kutta (IRK) method uses a fewer number of stages in each step which causes less computational cost in total. Here, the integral part is approximated by applying the combination of Lagrange interpolation polynomials and Simpson&rsquo;s rule. The numerical results are compared with some existing methods such as the fourth-order Runge-Kutta (RK) method, variational iteration method (VIM), and homotopy perturbation method (HPM) to prove the efficiency of IRK method. Based on the obtained results, it is clear that the fourth-order Improved Runge-Kutta method with higher accuracy and less number of stages which leads the less computational cost is more efficient than other existing methods for solving FVID equations.Numerical Modeling of Fluid’s Aeration: Analysis of the Power Losses and Lubricant Distribution in Gearboxes
https://jacm.scu.ac.ir/article_17623.html
Aeration determines the entrainment of air in another fluid. In geared transmissions, this process affects the operating temperature of the mechanical system because the air&rsquo;s bubbles trapped in the lubricant act as an insulator. Lubricant&rsquo;s aeration occurs mainly because the gears&rsquo; teeth entering the oil sump and the oil impacting on free surface. Being able to numerically model aeration is fundamental to better describe the physics and the lubrication mechanisms which affect the behavior of the system. In this paper, a new solver that includes the aeration phenomenon was implemented in the opensource environment OpenFOAM&reg;. The simulations&rsquo; results were validated with torque measurements. Moreover, a comparison of the oil distribution between a standard multiphase- and the new aeration-solver is provided.An Exact Analytical Solution for Heat Conduction in a Functionally Graded Conical Shell
https://jacm.scu.ac.ir/article_16222.html
In this study, an exact analytical solution for the heat conduction problem in a truncated conical shell is presented. The cone is made of functionally graded materials and it is considered that the material properties vary according to power-law functions. The general thermal boundary conditions are applied to cover a wide variety of actual applications. The results are successfully validated. Two examples, which are tried to mimic practical conditions, are studied using the derived solution, and a parametric study is done to shed light on the problem. The outcomes of this research provide useful information for understanding the nature of heat transfer behavior in the specific geometry of a cone. Regarding the specific applications of conical shells, the results can be used in the prefabrication process of these shells and tailoring the design parameter of functionally graded materials.CFD Analyses and Comparison of the Effect of Industrial Heat Sinks in Subsea Control System (SCS)
https://jacm.scu.ac.ir/article_17638.html
This article is part of the e-cooling project which has been granted by OutoKumpu and Intel. The &lrm;author has been project manager aiming for optimization of the heat sink application. In this &lrm;regard, several articles through 2006 to 2012, have been published to explain the chain of the process &lrm;&lrm;(casting, machining, welding) using the Pin-Fin technology.&lrm; In 2011 to 2015, The project has been recapped and aiming to develop next design heatsink &lrm;&lrm;(combined copper- Aluminum heat sink) with special focus for the subsea application. The Risk &lrm;analyses of the new heat sink design have also been studied. A new model has been developed &lrm;for industrial production/ optimization process from casting to final processing.&lrm; The mathematical modeling has been primarily employed to solve the source code addressing the &lrm;energy of the dissipation rate using the 3D Navier-Stokes equations. The Ansys Fluent has been &lrm;employed as the modeling software to implement the source term as subroutine. In this industrial &lrm;research work the implementation of the mathematical modeling in the Ansys Fluent software is &lrm;a critical part of the work aiming for design and optimization of the heat sink within SCI &lrm;application&lrm;.Bifurcation of Fiber-Reinforced Cylindrical Membranes under Extension, Inflation, and Swelling
https://jacm.scu.ac.ir/article_17657.html
We analyze bifurcation for a cylindrical membrane capable of swelling subjected to combined axial loading and internal pressure. The material is conceptualized as an isotropic and absorbent matrix (it can swell when it is exposed to some swelling agent, for instance) containing nonabsorbing fibers. More in particular, fibers are symmetrically arranged in two helically distributed families which are (also) mechanically equivalent. Arterial wall tissue has been modeled using this theoretical framework. The matrix of the membrane is taken to be a swellable neo-Hookean material. The swollen membrane is then inflated and axially stretched so that the circular cylindrical geometry is initially preserved. Nevertheless, prismatic, bulging, and bending (composite) bifurcation conditions are analyzed. It is shown that for membranes with and without fibers, prismatic bifurcation does not play a major role. On the other hand, bending and bulging are feasible for fiber-reinforced membranes. Results capture the onset of bifurcation configurations corresponding to bending and bulging and highlight possible coupling during postbifurcation as it might occur, for example, in the formation and development of an abdominal aortic aneurysm.Multibody Modeling and Nonlinear Control of a Pantograph Scissor Lift Mechanism
https://jacm.scu.ac.ir/article_17659.html
In this paper, a new strategy for developing effective control policies suitable for guiding the motion of articulated mechanical systems that are described within the framework of multibody system dynamics is proposed. In particular, a scissor lift table having a pantograph topology is analytically modeled as a rigid multibody system by using a Lagrangian formulation. An operational approach is thus introduced in this investigation to design the control system that commands the motion of the lift table. In this vein, two dynamical models are developed in this investigation, namely a minimal coordinate multibody model and a redundant coordinate multibody model. While the minimal coordinate multibody model is used in the paper for the optimal design of a high-performing nonlinear controller, the redundant coordinate multibody model is employed to verify both the efficiency and the effectiveness of the control approach adopted in this work. More specifically, the nonlinear control system devised in this paper is based on the combination of an open-loop control architecture with a closed-loop control strategy. The open-loop control policy is determined by using a nonlinear quasi-static feedforward controller, whereas the closed-loop control action is obtained considering an error-based proportional-derivative feedback controller. With the use of both the pantograph scissor lift multibody models developed in this work, several numerical experiments are carried out in the paper, thereby demonstrating the readiness and the effectiveness of the control methodology proposed in this investigation.Bernoulli-Euler Beam Unsteady Bending Model with Consideration of Heat and Mass Transfer
https://jacm.scu.ac.ir/article_17682.html
The article describes the problem of unsteady vibrations of a Bernoulli-Euler beam taking into account the relaxation of temperature and diffusion processes. The initial mathematical model includes a system of equations for unsteady bending vibrations of the beam with consideration of heat and mass transfer. This model is obtained from the general model of thermomechanodiffusion for continuum using the D'Alembert's variational principle. The solution of the problem is obtained in the integral form. The kernels of the integral representations are Green's functions. For finding of Green's functions the expansion into trigonometric Fourier series and Laplace transform in time are used. The calculation example is investigated for a freely supported three-component beam made of zinc, copper and aluminum alloy under the action of unsteady bending moments, including the interaction of mechanical, temperature and diffusion fields.A Reduced-Order Simulation Methodology for Nanosecond-Pulsed Plasmas in a Backward-Facing Step Supersonic Combustor Configuration
https://jacm.scu.ac.ir/article_17683.html
This work presents a simplified methodology for coupling the physics of a nanosecond-pulsed discharge to the process of supersonic combustion within a backward-facing step combustor. The phenomena of plasma and supersonic combustion are simulated separately and then coupled. Based on results reported in the literature, a zero-dimensional plasma model is built, considering only the kinetic effects of the nanosecond-pulsed discharge. A set of Favre-averaged compressible Navier-Stokes equations, as well as finite rate chemistry, is used in the combustion model and solved with a control-volume based technique. The plasma-supersonic combustion coupling process only considers the discharge as a source of O and H radical species. The calculated densities of the radicals generated during each pulse from the plasma model are periodically seeded inside the domain of the combustor. The proposed methodology is used to perform a novel simulation that involved the application of plasma to a well-known supersonic combustion experiment. The temperature and species concentration contours show that the proposed methodology captures the main effects of the nanosecond-pulsed discharge on supersonic combustion. The ignition delay time is reduced when the plasma discharge was applied. In addition, the simulations show that the plasma causes a supersonic low-enthalpy mixture to ignite, confirming the capability of the methodology.A Novel Flexible Lane Changing (FLC) Method in Complicated Dynamic Environment for Automated Vehicles
https://jacm.scu.ac.ir/article_16757.html
Decision making and path planning in case of highly transient dynamics of the surrounding as well as the effect of road condition are the issues that are not completely solved in the previous researches. The goal is to perform a safe and comfortable lane change that includes flexible re-planning capabilities. In this paper, a novel structure for path planning and decision making part of a vehicle automatic lane change has been introduced which comprehensively considers both longitudinal and lateral dynamics of the vehicle. The presented method is able to perform re-planning even in the middle of a lane change maneuver according to new traffic condition. Inclusion of the dynamics of all involved vehicles and providing online performance are the other advantages of the proposed system. The algorithm is simulated and various scenarios are constructed to evaluate the efficiency of the system. The results show that the system has completely acceptable performance.Flow Structure when Filling a Channel with a Curable Liquid
https://jacm.scu.ac.ir/article_17686.html
The filling of a plane gap with a non-Newtonian fluid under non-isothermal conditions is considered by assuming viscous dissipation and curing reaction induced by the heat supplied through the walls of the gap. The rheology of the medium is described by the modified Cross-WLF model accounting for the effect of temperature, strain rate intensity, and the extent of a chemical reaction on the viscosity. The curing reaction kinetics is determined by the equation based on the n-th order reaction with self-acceleration. The problem is solved numerically using an original computational technique. The curable fluid flow structure is revealed to include three characteristic zones during the filling process: a fixed layer on the solid wall with a high degree of curing; a central &ldquo;core&rdquo; with an almost uniform distribution of characteristics; and a transition zone serving as a "lubricating" layer between two abovementioned zones. The structure is governed by heating of the fluid through the wall, since the heating affects the rheological characteristics of the medium and the rate of the cured layer formation. Analysis of the similarity criteria for the considered flow conditions shows that the fluid flows in a creeping regime (Re &lt; 0.01); the temperature distribution is mainly affected by convective heat transfer (Pe &gt; 100); the influence of dissipative heating and exothermic effect of the curing reaction is insignificant. The effect of curing on the mass distribution of the liquid portions entering through the inlet section is shown. The variation of the pressure distribution is analyzed at various flow conditions.Performance Investigation of Simple Low-dissipation AUSM (SLAU) Scheme in Modeling of 2-D Inviscid Flow in Steam Turbine Cascade Blades
https://jacm.scu.ac.ir/article_16773.html
This study evaluates the performance of the SLAU, AUSM+UP upwind schemes, and CUSP artificial dissipation scheme for the flow through the convergent-divergent nozzles and turbine stator blades under different pressure ratios by developing an in-house code. By comparing the results with analytical and experimental results, it is found that, despite the simplicity of the SLAU scheme in the absence of tuning variables, it provides reasonable predictions for different turbine blades in point of location and strength of the shocks. The SLAU scheme could converge at a much higher rate, leading to very much lower values of residuals. The SLAU scheme causes about 30% and 20% improvements over the prediction of the shock-induced losses in supersonic and subsonic outlet flows, respectively.Self-damping of Optical Ground Wire Cables: A Bayesian Approach
https://jacm.scu.ac.ir/article_17702.html
The empirical Power Law model has a long usage history in cable self-damping studies, and several types of research have been done to characterize its parameters for various types of cables. In this work, a novel Bayesian model calibration framework is proposed and applied to study self-damping Optical Ground Wire (OPGW) cables. This technique then combines experimental and statistical approaches to obtain the confidence intervals for each parameter and characterize the different regions where the model presents other behaviors. The results enable a better calibration of the model's parameters and agree with the trends already set in the literature. They also provide a new understanding of the model and estimate different uncertainties its application entices.Sweep Blade Design for an Axial Wind Turbine using a Surrogate-assisted Differential Evolution Algorithm
https://jacm.scu.ac.ir/article_17704.html
This paper presents an optimal design of a sweep blade for the axial wind turbine using a hybrid surrogate-assisted optimizer. The design problem is defined to maximize the ratio of the torque coefficient to the thrust coefficient of a turbine blade at a low wind velocity of 10 m/s. Pitch angle and leading-edge blade curve are considered as the design variables. For the aerodynamic analysis of the wind turbine blade, computational fluid dynamics has been used as a high-fidelity simulation. While the surrogate models including, the Kriging model (KG), the radial basis function model (RBF), and the proposed hybrid of KG and RBF (HyKG-RBF) models are applied for function approximation or low-fidelity simulation. In this study, to obtain a set of sampling points and surrogate models development, an optimal Latin Hypercube sampling (OLHS) technique is utilized in the design of the experiment (DOE). A differential evolutionary (DE) algorithm is used to solve the proposed design problem. The performance of the proposed hybrid surrogate assisted optimization method is contrasted with two conventional surrogate assisted optimization techniques. Results demonstrate that the proposed hybrid surrogate model viz. HyKG-RBF is the most efficient surrogate-assisted optimization method for solving the sweep blade optimization problem.Accuracy and Convergence Rate Comparative Investigation on Polytope Smoothed and Scaled Boundary Finite Element
https://jacm.scu.ac.ir/article_17707.html
Continuity and discontinuity of two-dimensional domains are thoroughly investigated for accuracy and convergence rate using two prominent discretization methods, namely smoothed and scaled boundary finite element. Because of their capability and versatility when compared to primitive elements, N-sided polygonal elements discretized from modified DistMesh and PolyMesher schemes are used. In terms of accuracy and convergence rate, NSFEM and SBFEM are found to be superior to CSFEM and ESFEM regardless of meshing alternative. The best accuracy occurs at NSFEM and SBFEM, and the obtained convergence rates are optimal. Particularly, in the smoothing domain, it is believed that DistMesh has more promising potential than PolyMesher does; yet, in the discontinuity domain, PolyMesher has been discovered to be more powerful while maintaining its efficiency.Static Buckling of 2D FG Porous Plates Resting on Elastic Foundation based on Unified Shear Theories
https://jacm.scu.ac.ir/article_17716.html
This article develops a mathematical model to study the static stability of bi-directional functionally graded porous unified plate (BDFGPUP) resting on elastic foundation. The power function distribution is proposed for the gradation of material constituent through thickness and axial directions. Three types of porosity are selected to portray the distribution of voids and cavities through the thickness of the plate. Unified theories of plate are exploited to present the kinematic fields and satisfy the zero-shear strain/stress at the top and bottom surfaces without shear correction factor. Hamilton&rsquo;s principle is employed to derive the governing equations of motions including the higher terms of force resultants. An efficient numerical method namely differential integral quadrature method (DIQM) is manipulated to discretize the structure spatial domain and transform the coupled variable coefficients partial differential equations to a system of algebraic equations. Problem validation and verification have been proven with previous works for bucking phenomenon. Parametric studies are exemplified to exhibit the significant impacts of kinematic shear relations, gradation indices, porosity type, and boundary conditions on the static stability and buckling loads of BDFGP plate. The proposed model is economical in different applications in nuclear, mechanical, aerospace, naval, dental and medical fields.Numerical Study on the Ferrofluid Droplet Splitting in a T-junction with Branches of Unequal Widths using Asymmetric Magnetic Field
https://jacm.scu.ac.ir/article_16956.html
Research on the microdroplet splitting phenomenon has intensified in recent years. Microdroplet splitting has numerous applications in chemical synthesis, biology, and separation processes. The current paper covers the numerical study of ferrofluid microdroplet splitting at various lengths and velocities inside the T-junction with branches of unequal widths under asymmetric magnetic fields. Microdroplet splitting can be controlled by using an asymmetric magnetic field and the asymmetry in the width of T-junctions branches. Three geometrical models of the T-junction with different widths ratio (0.7, 0.85, and 1), along with a magnetic field with various intensities are studied. This magnetic field is generated by a line dipole. In this study, the distance between the dipole and origin is kept constant. The splitting ratio of ferrofluid microdroplets at different velocities (different capillary numbers), different non-dimensional lengths and different magnetic force (different magnetic Bond numbers) at the center of T-junction are calculated for each amount of branch width. The results are verified with previous works and their correctness is proved. The splitting ratio is defined as the volumetric ratio of the larger daughter droplet to the mother droplet. The results indicate that generally, the stronger the asymmetric magnetic force is, the more asymmetric the splitting will become, with the splitting ratio becoming closer to 1. Also, as asymmetry increases between the widths of the two branches of the T-junction, the splitting ratio approaches 1.Two-node Curved Inverse Finite Element Formulations based on Exact Strain-displacement Solution
https://jacm.scu.ac.ir/article_17717.html
The inverse finite element method (iFEM) is an efficient algorithm developed for real-time monitoring of structures equipped by a network of strain sensors. The inverse element for modeling curved beams was previously developed using an approximate solution based on independently interpolated displacement components. In this study, a new formulation is proposed by the development of a least-squares variational principle using the kinematic framework of the curved beam theory. The library of existing iFEM-based elements is expanded by introducing three different inverse curved elements named iCB3, iCB4 and iCB5 respectively. This new formulation has been developed considering the exact solution of the curved beam theory that corresponds to the membrane-bending coupling and the explicit statement of the rigid-body motions. The three inverse elements, which require three, four and five measurement points respectively, extend the practical utility of iFEM for shape sensing analysis of curved structures according to the minimum available quantity of strain sensors. The effectiveness and higher accuracy of the iCB/iFEM methodology compared to other solutions present in literature are demonstrated considering numerical studies on curved beams under static transverse force and distributed loading conditions. For these problems, the effect of strain measurements error, number of sensors and discretization refinement on the solution accuracy is evaluated.Analytical Investigations for the Joint Impacts of Electro-osmotic and Some Relevant Parameters to Blood Flow in Mildly Stenosis Artery
https://jacm.scu.ac.ir/article_17750.html
The joint impacts of electro-osmotic, variable viscosity, magnetic field, chemical reaction, and porosity on blood flow in the artery slant from the axis at an angle with mild stenosis are investigated using Yang transform homotopy perturbation method (YTHPM). The mathematical model, solved by Tripathi and Sharma, is developed by adding the effect of electro-osmosis. The results of axial velocity, concentration, temperature, and the wall shear stress for blood flow are studied in two cases, the absence and presence of electro-osmosis. The results illustrate that an increase in the electro-osmotic parameter and Helmholtz Smoluchowski velocity leads to velocity increases, while the temperature increases when the Joule heating increases with constant values of electro-osmotic parameter and Helmholtz Smoluchowski velocity. On the contrary, it is noted that the electro-osmotic on concentration has no significant effect. Moreover, the importance of applying electro-osmotic is exhibited through proper use and explaining that how it can benefit physicians during surgical operations. Furthermore, a contour plot is created to show the difference in the profile of velocity to the flow of blood when the magnetic field is increased and the altitude of stenosis takes the larger values. The results exhibit that YTHPM is effective in finding the analytical approximate solutions for Newtonian blood flow under the electro-osmotic parameter influence, with good convergence. In addition, the new solutions' graphs demonstrate the truthfulness, utility, and exigency of YTHPM which are in excellent agreement with the results of earlier investigations.An Alternative Procedure for Longitudinal Vibration Analysis of Bars with Arbitrary Boundary Conditions
https://jacm.scu.ac.ir/article_17787.html
The present work aims at generating a systematic way for longitudinal vibration (LV) analysis of bars (or rods) with arbitrary boundary conditions (BCs) by mixed-type finite element (MFE) method using the G&acirc;teaux differential. Both materials and geometrical properties of the bar are uniform along the longitudinal direction. The problem is reduced to solution of the classical eigenvalue problem in dynamic analysis. The axial (normal) load and the displacement along the bar are the basic unknowns of the mixed element. The element formulation for the shape function must satisfy only C0 class continuity since the first derivatives of the variables exist in the functional. The functional governed with proper dynamic and geometric BCs of the problem. Results of the recommended method are benchmarked and verified via numerous problems present in the literature. The unique aspects of this study and the possible contributions of the proposed method to the literature can be summarized as follows: by using this new functional, displacements and internal force values can be obtained directly without any mathematical operation. In addition, geometric and dynamic BCs can be obtained easily and a field variable can be included to the functional systematically. To examine the effects of BCs on the longitudinal vibratory motion of a uniform elastic bar and to give a better insight into LV analysis of bars with arbitrary BCs, a set of numerical examples are presented.Numerical Simulations of Spoiler’s Effect on a Hatchback and a Sedan Car Exposed to Crosswind Effect
https://jacm.scu.ac.ir/article_17193.html
Numerical simulations of the airflow around a hatchback and a sedan vehicle without and with spoilers are carried out, besides, its effect on drag and lift coefficients are investigated with and without crosswinds. The effects of crosswind on aerodynamic forces are considered and its results are compared with the case without considering the effects of crosswind. For this purpose, the steady-state three-dimensional Navier-Stokes equations are solved by the Simple Method. Moreover, for turbulence modeling, the Realizable k-e model is implemented. The spoiler angle and its length are changed for both car models; furthermore, the effects of two spoilers on drag and lift coefficients are investigated in detail. All cases are simulated with and without crosswind. The results show that the impact of the spoiler for without crosswind conditions to decrease the lift coefficient in both models is significant; in addition, the drag coefficients are reduced for some cares. It can be concluded that the increase of spoiler length for both sedan and hatchback vehicles can increase the downward force and vehicle stability.Economic Evaluation of Supplying Commercial Thermal Load by a New CPVT System: A Case Study in Iran
https://jacm.scu.ac.ir/article_17234.html
This paper aims to provide a concentrated photovoltaic thermal (CPVT) system regarding the high potential of receiving solar energy in Iran. Generated thermal energy of the system supplies the average thermal load of a commercial building and also its generated electricity is sold to the grid according to Iran's feed-in tariff (FiT). In order to calculate the system profitability, an economic evaluation is done in 20 years that is regarded as a novel approach. Furthermore, sensitivity analyses are performed to develop the results to the other locations with different economic conditions and various potential of energy resources, and also to present an appropriate financial outlook. The results demonstrate that the system is highly profitable given net present value (NPV) of 551.55 k$, internal rate of return (IRR) of 150.79%, benefit to cost ratio (BCR) of 10.32, payback time (PBT) of 0.51 years, and levelized cost of energy (LCOE) of 0.1293 $/MWh. Moreover, sensitivity analyses show that the system profitability is greatly appropriate even regarding the variety of unpredictable parameters. For instance, if the generated energy decreases by 20%, IRR and PBT will equal 120.63% and 0.63 years respectively, and the system can still maintain its high profitability. Moreover, it has been revealed that the enhancement of FiT can increase the system's economic efficiency. According to the results, it is noticeably profitable to use the CPVT systems to produce electrical and thermal power in countries with a high potential of receiving solar energy (especially middle-eastern countries).Electrochemical and Mechanical Properties of Ni/g-C3N4 Nanocomposite Coatings with Enhanced Corrosion Protective Properties: A Case Study for Modeling the Corrosion Resistance by ANN and ANFIS Models
https://jacm.scu.ac.ir/article_17241.html
This work investigates the effect of electrolysis bath parameters on the corrosion, micro-hardness, and wear behavior of Ni coatings. The characterization of synthesized Graphitic carbon nitride (g-C3N4) was done by Fourier transform infrared, Raman spectroscopy, and transmission electron microscope. The surface morphology of coated samples with various amounts of current density was studied by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The corrosion prevention effect of Ni/g-C3N4 nanocomposite coatings was investigated by EIS and polarization techniques. The experimental outcome demonstrates that an electrolysis bath of 0.3 g/L g-C3N4 and 0.1 A.cm-2 presents a Ni coating with the highest corrosion protection, wear resistance, and microhardness. The corrosion current densities of Ni/g-C3N4 coatings obtained by electrochemical tests were used for training two machine learning techniques (Artificial neural network (ANN) and adaptive neuro-fuzzy inference system (ANFIS)) based on current density, g-C3N4 concentration, and plating time as an input. Various statistical criteria showed that the ANFIS model (R2= 0.99) could forecast corrosion current density more accurately than ANN with R2= 0.91. Finally, due to the robust performance of ANFIS in modeling the corrosion behavior of Ni/g-C3N4 nanocomposite coating, the effect of each parameter was studied.Temperature Effect on Moving Water Droplets at the Channel of PEMFC by Multi-component Multiphase Lattice Boltzmann Method
https://jacm.scu.ac.ir/article_17253.html
In this paper, a multi-component multiphase pseudopotential Lattice Boltzmann method with multi relaxation time (MRT) collision operator is presented to examine the dynamic behavior of liquid droplets movement and coalescence process in the gas channel of PEMFC. In the numerical method, the forcing term is improved to achieve a high-density ratio and thermodynamic consistency. First, the density ratio, Laplace law, and contact angle are validated with previous studies. Then, different parameters, such as operating temperature, pressure difference, surface contact angle, the radius of droplets, and distance between two droplets on the droplet movement and coalescence process are studied. The results revealed by rising temperature from 30 to 80 degrees, the speed of drop increases around 6 percent. The simulation results indicated that the rising of pressure gradient increases the gas flow velocity on the channel and leads to increasing the shear force and eventually faster movement of the droplet on the gas channel. Also, investigation of various contact angles shows that a hydrophilic surface causes a resistance force between the droplet and the wall and delays the removal of droplets. Moreover, droplet coalescence is useful for droplet movement because of increasing the velocity gradient on top of the droplet; consequently, the shear force on the droplet is raised during coalescence.Power Law Nanofluid through Tapered Artery based on a Consistent Couple Stress Theory
https://jacm.scu.ac.ir/article_17303.html
Based on couple stress theory, this study investigated non-Newtonian power-law nanofluid flows in converging, non-tapered, and diverging arteries. In addition to excluding gravity effects artery, geometry included mild stenosis. The momentum equation is solved via the Galerkin method, and the results are compared with experimental and classical findings. Although the power-law couple stress theory&rsquo;s relations are first used in the analysis of non-Newtonian blood flow, the results of this theory are far more consistent with experimental results than classical results. Comparison of the results of the study of blood flow velocity profiles in a non-tapered artery without stenosis by the mentioned theory with experimental and classical theory results shows the difference in velocity at the center of the artery between the experimental results and the results of the classical theory is 36%, while this value has been reduced to 14% for the results of the couple stress theory. The variations in velocity profile with the power-law index (n=0.8 and n=0.85) and the dimensionless Darcy number (Da=10-10 and Da=10-7) in all three geometries indicated a flat velocity distribution with the increase in the power-law index while increasing the velocity profile with increased Darcy number. Mass transfer and energy equations are solved using the extended Kantorovich method. The solution convergence is evaluated, and the influence of parameters such as Prandtl number, Schmidt number, and dimensionless thermospheric and Brownian parameters on concentration and temperature profiles is obtained.Stress-driven Approach to Vibrational Analysis of FGM Annular Nano-plate based on First-order Shear Deformation Plate Theory
https://jacm.scu.ac.ir/article_17712.html
Vibrational behavior of small-scale functionally graded annular plate based on the first-order shear deformation theory, and non-local stress-driven model is investigated. For the first time, generalized differential quadrature rule is utilized to solve the governing equation and related boundary conditions. The convergence, accuracy, and efficiency of the generalized differential quadrature rule are investigated using problem-solving for different situations. The effects of parameters such as size parameter, inhomogeneity coefficient of functionally graded materials, thickness to outer radius ratio, inner radius to outer radius ratio, and boundary conditions on the natural frequency of the structure have been investigated. Results show that, unlike the strain-driven model, the non-local stress-driven theory predicts the same behavior for all boundary conditions and increasing the size parameter has led to a stiffening behavior and an increase in the natural frequency of the structure.Automatic Structural Synthesis of Planetary Geared Mechanisms using Graph Theory
https://jacm.scu.ac.ir/article_17792.html
Graphs are an effective tool for planetary gear trains (PGTs) synthesis and for the enumeration of all possible PGTs for transmission systems. In the past fifty years, considerable effort has been devoted to the synthesis of PGTs. To date, however, synthesis results are inconsistent, and accurate synthesis results are difficult to achieve. This paper proposes a systematic approach for synthesizing PGTs depending on spanning trees and parent graphs. Trees suitable for constructing rooted graphs are first identified. The parent graphs are then listed. Finally, geared graphs are discovered by inspecting their parent graphs and spanning trees. To precisely detect spanning trees, a novel method based on two link assortment equations is presented. Transfer vertices and edge levels are detected without the use of any computations. This work develops the vertex matrix of the rooted graph, and its distinctive equation is used to arrange the vertex degree arrays according to the vertex levels and eliminate the arrays that violate the distinctive equations. The precise results of the 5-link geared graphs are confirmed to be 24. The disparity between the recent and previous synthesis results can be attributed to the fact that the findings of the current method, which employs rooted graphs, are more comprehensive than those obtained with graphs lacking multiple joints. A novel algorithm for detecting structural isomorphism is proposed. By comparing the vertex degree listings and gear strings, non-isomorphic geared graphs are obtained. The algorithm is simple and computationally efficient. The graph representation is one-to-one with the vertex degree listing and gear string representation. This allows for the storage of a large number of graphs on a computer for later use.Driveline Stability in Racing Motorcycles: Analysis of a Three Degrees of Freedom Minimal Model
https://jacm.scu.ac.ir/article_17795.html
Motorcycles under heavy braking conditions can experience a self-excited oscillation known as &lsquo;chatter&rsquo;. A simplified three degrees of freedom model of the rear of a motorcycle is developed to study the stability of this mode with the inclusion of lateral dynamics introduced by roll angle. Since motorcycles achieve high roll angles during operation, the study of chatter during these manoeuvres is a topic of interest. The equations of motion are linearised about a quasistatic equilibrium and simplified to accommodate symbolic inspection. Power analysis, eigensystem analysis, eigenvalue sensitivity and Routh-Hurwitz stability criterion are used to study the stability of the system in the braking region. It was found that a driveline mode can become unstable at about 19 Hz, and that its tendency towards instability is increased with added roll angle. This mode is sensitive to model parameters affecting the system inertia and stiffness, as well as the chain geometry. Finally, it is found that the lateral dynamics and roll angle play no direct role in chatter but have a significant indirect effect on it through the working point of the force characteristic function of the tyre.Influence of Thermal Radiation on Heat Transfer through a Hollow Block
https://jacm.scu.ac.ir/article_17808.html
Hollow blocks are widely used in construction to reduce the thermal resistance of building walls. The air within the blocks has a low thermal conductivity, which makes it possible to consider such hollow blocks as a good insulating material. This work presents a numerical investigation of the impact of thermal radiation on energy transport and airflow inside a hollow block. The coupled heat transport by free convection, thermal radiation and conduction through the solid walls is taken into account. The finite-difference procedure is applied to work out numerically the control equations of conservation of momentum, energy and mass in both solid walls and air filled enclosure. The main parameters governing the problem are surface emissivity, Rayleigh number and thermal conductivity of solid walls. The influence of these factors on the overall heat transfer through hollow block is presented and investigated. The outcomes show that the low emissivity of the inner walls inside the hollow blocks will significantly help to reduce the energy consumption of buildings.A Novel Approach to Fully Nonlinear Mathematical Modeling of Tectonic Plates
https://jacm.scu.ac.ir/article_17820.html
The motion of the Earth's layers due to internal pressures is simulated in this research with an efficient mathematical model. The Earth, which revolves around its axis of rotation and is under internal pressure, will change the shape and displacement of the internal layers and tectonic plates. Applied mathematical models are based on a new approach to shell theory involving both two and three-dimensional approaches. It is the first time studying all necessary measures that increase the accuracy of the obtained results. These parameters are essential to perform a completely nonlinear analysis and consider the effects of the Earth&rsquo;s rotation around its axis. Unlike most modeling of nonlinear partial differential equations in applied mechanics that only considers nonlinear effects in a particular direction, the general nonlinear terms are considered in the present study, which increases the accuracy of the amount of displacement of the Earth's inner layers. Also, the fully nonlinear and dynamic differential equations are solved by a semi-analytical polynomial method which is an innovative and efficient method. Determining the amount of critical pressure at the fault location that will cause phenomena such as earthquakes is one of the useful results that can be obtained from the mathematical modeling in this research.Numerical Study of the Dynamic Response of Elevated Steel Conical Tank under Vertical Seismic Excitation - Case Study
https://jacm.scu.ac.ir/article_17824.html
Elevated cylindrical and conical steel tanks are widely used to conserve water or chemical liquids. These important structures are required to stay protected and operative at any time. The wall angle inclination of conical tank part, as well as the presence of the vertical earthquake component, can cause damage to this structure and even lead to its failure. The purpose of this study is to examine the effect of wall angle inclination of the tank and the vertical earthquake acceleration component on the nonlinear dynamic stability of the elevated steel conical tanks under seismic excitation. The elevated steel conical tank is simulated utilizing the finite element analysis method using ANSYS software. The fluid-structure interaction is considered using a suitable interface that allows the fluid to apply hydrodynamic pressures on the structure. Three different models, namely Model &ndash;A-30&deg;, Model &ndash;B-45&deg;and Model &ndash;C-60&deg; are investigated; it has been concluded that the impact of inclination of the tank wall significantly affects the nonlinear stability of the elevated steel conical tank. While considering the vertical ground acceleration, inclination plays a significant role in the design of this type of structures. Therefore, it should be appropriately included in the seismic analysis of elevated steel conical tanks to satisfy the safety of the elevated steel conical tank response under seismic loading.A Note on the Discharge over Full-width Rectangular Sharp-crested Weirs and Weirs of Finite Crest Length
https://jacm.scu.ac.ir/article_17825.html
The head-discharge relationship for sharp-crested weirs is developed based on the energy consideration upstream and at the crest of the weir. The discharge for weirs of finite crest length is estimated by correlating the critical depth and total energy at the upstream of the weir. In both cases, discharge is linked with the total head. Therefore, prediction of discharge for both sharp-crested weirs and weirs of finite crest length requires an iterative solution method. The present technical note formulates the relationship between the discharge coefficients based on water and total heads to estimate the error associated with implementation of head-discharge equation based on the head. The proposed prediction curves are used to convert the iterative solution method based on the total head to a direct solution strategy based on the water depth at the upstream of sharp-crested weirs and weirs of finite crest length with either a sharped-edge or rounded entrance. Based on the similarity of velocity profiles in gate flow, it is concluded that a distance as short as 2.4 times of the water head is suitable enough to measure the upstream water depth. In sharp-crested weirs, the effect of velocity head is negligible for the approach velocity ratio smaller than 0.1. Different correction curves were developed for weirs of finite crest length based on the ratio of water head to the crest length of weirs.Numerical Investigation into the Effects of Orientation on Subcooled Flow Boiling Characteristics
https://jacm.scu.ac.ir/article_17839.html
The progress reached in the high heat flux systems has required the development of appropriate thermal management approaches for dissipating the high heat fluxes, especially for small-scale devices. One of the most advantageous thermal management techniques is the utilization of subcooled flow boiling. In this work, the subcooled flow boiling of FC-72 is numerically simulated in a minichannel using ANSYS Fluent to investigate the effects of system pressure and gravitational orientation on the subcooled flow boiling thermal transfer performances. Two different orientations (vertical downflow and vertical upflow) were examined in the same conditions of heat flux (q = 191553 W/m2), mass flux (G = 836.64 kg/(m2s)) and inlet temperature (Tin = 304.54 K), and under three different system pressures (102000, 120000, and 209900 Pa). The present computational study has been validated and a good agreement with the experimental data was demonstrated. The predicted results demonstrate that the increase in system pressure improves the thermal performance of subcooled flow boiling by an average enhancement of 15.94%. In addition, the vertical upflow orientation is more advantageous than the downflow orientation due to the buoyancy force that moves the bubbles towards the flow direction and leads to less chaotic liquid-vapor interactions. An average enhancement of 1.65% in the heat transfer coefficient is reached in the upflow orientation compared to the downflow orientation for the higher system pressure of 209900 Pa.Heat Transfer Improvement in a Thermal Energy Storage System using Auxiliary Fluid Instead of Nano-PCM in an Inclined Enclosure: A Comparative Study
https://jacm.scu.ac.ir/article_17846.html
Modern thermal energy storage (TES) systems rely laboriously on finding a low-cost method to improve heat transfer. In the present analysis, adding CuO nanoparticles and tilting the enclosure simultaneously is compared with a novel approach that employed water as a supplemental fluid to improve the melting process using the density difference between PCM and supplemental fluid. Oleic acid is selected as an immiscible PCM in water, which causes PCM and auxiliary fluid utterly separate at the end of the melting process to be usable in more additional TES cycles. By placing water as a heavier material directly on top of oleic acid, the melted oleic acid is replaced by water at the bottom of the enclosure when it melts because water has a heavier density than oleic acid. At first, adding 1% and 2% of CuO nanoparticles in an enclosure with different inclinations of 0&deg;, 45&deg;, and 90&deg; is studied to identify the energy storage rate. Continuity, momentum, and energy equations are used to formulate a mathematical model of the TES system. In the next step, the melting process of the combined system is analyzed to determine the energy storage rate of the combined system compared to the system, including CuO nanoparticles in the inclined enclosure. Comparing the combined system with the optimal case of nano-PCM in the inclined enclosure, it was found that the energy storage rate in the system using auxiliary fluid is 1.396 times higher.The Impact of Marangoni Convection and Radiation on Flow of Ternary Nanofluid in a Porous Medium with Mass Transpiration
https://jacm.scu.ac.ir/article_17847.html
The current paper examines the impact of radiation and Marangoni convective boundary conditions on the flow of ternary hybrid nanofluids in a porous medium with mass transpiration effect on it. Estimated PDEs are converted to ODEs with consideration of the corresponding similarity transformations. The obtained non-dimensional reduced equations are solved by analytical process. A unique access based on the Laplace transform (LT) is used to find analytical solutions to the resulting equations. With the use of graphs, the exact solution may be investigated in the presence of many physical parameters such as&nbsp;solid volume fraction parameter, mass transpiration, porosity, radiation. The fluid flow contains three types of nanoparticles: spherical Silver (Ag), cylindrical SWCNT, and platelet graphene. Because of the shape composition of ternary hybrid nanoparticles, variation in concentrations is a primary factor of thermal performance. The shape of nanoparticles in ternary hybrid nanofluids has a major impact, and its application has the advantage of improving the cooling system's thermo-hydraulic performance.A Novel BESO Methodology for Topology Optimization of Reinforced Concrete Structures: A Two-loop Approach
https://jacm.scu.ac.ir/article_17861.html
A new topology optimization methodology for reinforced concrete structures is proposed. The structures are optimized in two iterative loops, where different sensitivity criteria are used to determine the regions to be topologically optimized. For the first loop, the compliance criterion is used to determine the higher compliance elements and, consequently, remove the concrete from the computational domain. In the next loop, only failed concrete regions (Ottosen failure surface) are replaced by reinforcement, ensuring that complies with the von Mises criterion. In the end, the sizing of the reinforcements is obtained based on the principal forces in the steel regions. Results regarding the mechanical behavior, cost, volume, and mass of the optimized structures are presented in this study. A case study indicated that the proposed methodology can lead to volume, mass, and cost reductions of 20%, 21.5%, and 56%, respectively.Natural Magneto-velocity Coordinate System for Satellite Attitude Stabilization: Dynamics and Stability Analysis
https://jacm.scu.ac.ir/article_17868.html
The paper addresses the problem of attitude stabilization of an artificial Earth satellite with the aid of an electrodynamic control system. Our objective is to stabilize the satellite in a special coordinate system, whose axes are directed along the Lorentz force vector and the geomagnetic induction vector. Thus, natural magneto-velocity coordinate system (NMVCS) is used. We consider the general case of the satellite mass distribution. Therefore, the disturbing action of the gravitation torque is taken into account. The satellite moves along a circular near-Earth orbit. The nonlinear stability analysis based on the Lyapunov direct method is applied in the paper. The proposed approach gives us admissible domains of control parameters for which attitude stabilization in NMVCS is guaranteed without restrictions on the Earth&rsquo;s magnetic field model. Stabilization conditions are formulated in the form of explicit inequalities for the control parameters. As a result, a control strategy for the satellite attitude stabilization in the NMVCS is elaborated.Exact Solutions for Isobaric Inhomogeneous Couette Flows of a Vertically Swirling Fluid
https://jacm.scu.ac.ir/article_17871.html
The paper generalizes the partial class of exact solutions to the Navier&ndash;Stokes equations. The proposed exact solution describes an inhomogeneous three-dimensional shear flow in a layer of a viscous incompressible fluid. The solution is studied for the case of the motion of a steady-state isobaric fluid. One of the longitudinal velocity components is represented by an arbitrary-degree polynomial. The other longitudinal velocity vector component is described by the Couette profile. For a particular case (the quadratic dependence of the velocity field on two coordinates), profiles of the obtained exact solution are constructed, which illustrate the existence of counterflows in the fluid layer. The components of the vorticity vector and the tangential stresses are analyzed for this exact solution.A Systematic Computational and Experimental Study of the Principal Data-Driven Identification Procedures. Part I: Analytical Methods and Computational Algorithms
https://jacm.scu.ac.ir/article_17883.html
This paper is the first part of a two-part research work aimed at performing a systematic computational and experimental analysis of the principal data-driven identification procedures based on the Observer/Kalman Filter Identification Methods (OKID) and the Numerical Algorithms for Subspace State-Space System Identification (N4SID). Considering the approach proposed in this work, the state-space model of a mechanical system can be identified with the OKID and N4SID methods. Additionally, the second-order configuration-space dynamical model of the mechanical system of interest can be estimated with the MKR (Mass, Stiffness, and Damping matrices) and PDC (Proportional Damping Coefficients) techniques. In particular, this first paper concentrates on the description of the fundamental analytical methods and computational algorithms employed in this study. In this investigation, numerical and experimental analyses of two fundamental time-domain system identification techniques are performed. To this end, the main variants of the OKID and the N4SID methods are examined in this study. These two families of numerical methods allow for identifying a first-order state-space model of a given dynamical system by directly starting from the time-domain experimental data measured in input and output to the system of interest. The basic steps of the system identification numerical procedures mentioned before are described in detail in the paper. As discussed in the manuscript, from the identified first-order state-space dynamical models obtained using the OKID and N4SID methods, a second-order configuration-space mechanical model of the dynamic system under consideration can be subsequently obtained by employing another identification algorithm described in this work and referred to as the MKR method. Furthermore, by using the second-order dynamical model obtained from experimental data, and considering the hypothesis of proportional damping, an effective technique referred to as the PDC method is also introduced in this investigation to calculate an improved estimation of the identified damping coefficients. In this investigation, a numerical and experimental comparison between the OKID methods and the N4SID algorithms is proposed. Both families of methodologies allow for performing the time-domain state-space system identification, namely, they lead to an estimation of the state, input influence, output influence, and direct transmission matrices that define the dynamic behavior of a mechanical system. Additionally, a least-square approach based on the PDC method is employed in this work for reconstructing an improved estimation of the damping matrix starting from a triplet of estimated mass, stiffness, and damping matrices of a linear dynamical system obtained using the MKR identification procedure. The mathematical background thoroughly analyzed in this first research work serves to pave the way for the applications presented and discussed in the second research paper.A Systematic Computational and Experimental Study of the Principal Data-Driven Identification Procedures. Part II: Numerical Analysis and Experimental Testing
https://jacm.scu.ac.ir/article_17884.html
This paper is the second part of a two-part research work intended at realizing a systematic computational and experimental analysis of the principal data-driven identification procedures based on the Observer/Kalman Filter Identification Methods (OKID) and the Numerical Algorithms for Subspace State-Space System Identification (N4SID). More specifically, this second paper treats the presentation of the numerical analysis and the experimental testing carried out in this study. To perform a systematic comparison, the identification methods mentioned before are implemented in a general-purpose computer program developed in the MATLAB computational environment. To this end, a simple two-degrees-of-freedom dynamical model of a vibrating mechanical system is considered first as a demonstrative example. The demonstrative example is used to carry out a numerical analysis of the performance of the computational methods of interest for this investigation. Subsequently, an experimental analysis is carried out focusing on a three-dimensional structure that vibrates under the effect of an external source of impulsive excitation. To perform a thorough analysis, the flexible structure employed as an experimental case study is modeled starting from its CAD geometric model and assuming different levels of complexity, which range from a simple three-degrees-of-freedom lumped parameter model to a relatively more complex linear finite element model. In the paper, the mechanical models of the structural system considered as illustrative examples are principally employed for comparing the results arising from the modal analysis. The computational and experimental analysis of these structural models turned out to be useful to trace guidelines for evaluating the effectiveness and the efficiency of the numerical and experimental results obtained from the identification process. In this study, a numerical and experimental analysis of the OKID algorithms and the N4SID methods is developed. Both classes of techniques enable the time-domain state-space system identification, that is, they construct an estimation of the state, input influence, output influence, and direct transmission matrices which characterize the dynamic properties of a mechanical system. The present investigation demonstrates that, if properly tuned, both the OKID methods and the N4SID algorithms lead to consistent numerical and experimental results, even in the case when the input-output measurements used for performing the identification procedure are affected by a certain degree of noise. The numerical and experimental results found in this second part of the research work confirmed the efficacy of the time-domain system identification methodologies described in the first part of the paper.Time Distance: A Novel Collision Prediction and Path Planning Method
https://jacm.scu.ac.ir/article_17889.html
In this paper, a new fast algorithm for path planning and a collision prediction framework for two dimensional dynamically changing environments are introduced. The method is called Time Distance (TD) and benefits from the space-time space idea. First, the TD concept is defined as the time interval that must be spent in order for an object to reach another object or a location. Next, TD functions are derived as a function of location, velocity and geometry of objects. To construct the configuration-time space, TD functions in conjunction with another function named "Z-Infinity" are exploited. Finally, an explicit formula for creating the length optimal collision free path is presented. Length optimization in this formula is achieved using a function named "Route Function" which minimizes a cost function. Performance of the path planning algorithm is evaluated in simulations. Comparisons indicate that the algorithm is fast enough and capable to generate length optimal paths as the most effective methods do. Finally, as another usage of the TD functions, a collision prediction framework is presented. This framework consists of an explicit function which is a function of TD functions and calculates the TD of the vehicle with respect to all objects of the environment.2D Planar Simulation of Collisions between Liquid Droplets and Solid Particles in a Gas
https://jacm.scu.ac.ir/article_17907.html
Here we present a 2D planar simulation of the collisions between liquid droplets and solid particles that are most often used in industrial applications. The collisions are modeled using a combination of Volume of Fluid and Level Set methods. We study the impact of the particle-to-droplet size ratio and the shape of solid particles on the collision behavior and interaction regimes. The findings are presented in the form of collision regime maps. The interaction regimes are also distinguished for binary droplet collisions: deposition, separation, and disintegration. We show the impact of density, viscosity, and surface tension on the droplet collision regime maps as well as on the number of secondary fragments. The practical value of the research comes from the newly established differences of collision regimes between droplets and particles of different shapes and sizes.Even and Uneven Porosities on Rotating Functionally Graded Variable-thickness Annular Disks with Magneto-electro-thermo-mechanical Loadings
https://jacm.scu.ac.ir/article_17908.html
This paper investigates the porosity effect on rotating functionally graded piezoelectric (FGP) variable-thickness annular disk. Even and uneven porosity distributions for the disk are approximated. The porous annular disk is subjected to the influence of electromagnetic, thermal, and mechanical loadings. Material coefficients are graded and described as a power law in the radial direction of the annular rotating disk. The resulting differential equation with boundary conditions is solved using the semi-analytical technique. Two cases are studied for the porous annular disk, circular disk, and mounted disk. The effectiveness of the porosity factor and grading index on the temperature, stresses, and displacement are reported. Comparisons between non-porous and porous annular disks for even and uneven porosity are executed and discussed. The obtained results are presented to conclude the important role of porosity on the rotating variable-thickness annular disk for the purpose of engineering mechanical design.Local Thermal Non-equilibrium Analysis of Cu-Al2O3 Hybrid Nanofluid Natural Convection in a Partially Layered Porous Enclosure with Wavy Walls
https://jacm.scu.ac.ir/article_17926.html
A numerical study is performed to investigate the local thermal non-equilibrium effects on the natural convection in a two-dimensional enclosure with horizontal wavy walls, layered by a porous medium, saturated by Cu-Al2O3/water hybrid nanofluid. It is examined the influence of the nanoparticle volume fraction, varied from 0 to 0.04, the Darcy number (10-5 &le; Da &le; 10-2), the modified conductivity ratio (0.1 &le; &upsih; &le; 1000), the porous layer height (0 &le; Hp &le; 1), and the wavy wall wavenumber (1 &le; N &le; 5) on natural convection in the enclosure. Predictions of the steady incompressible flow and temperature fields are obtained by the Galerkin finite element method, using the Darcy-Brinkman model in the porous layer. These are validated against previous numerical and experimental studies. By resolving separately the temperature fields of the working fluid and of the porous matrix, the local thermal non-equilibrium model exposed hot and cold spot formation and mitigation mechanisms on the heated and cooled walls. By determining the convection cell strength, the Darcy number is the first rank controlling parameter on the heat transfer performance, followed by N, Hp and &gamma;. The heat transfer rate through the hybrid nanofluid and solid phases is highest when N = 4 at a fixed value of nanoparticle volume fraction.Impact Dynamics of Nonlinear Materials: FE Analysis
https://jacm.scu.ac.ir/article_17928.html
The paper presents an experimentally validated 3D finite element modelling impacts of viscoelastic and natural materials. It considers, in particular, the material set of ash wood and rubber in the context of the impact between the bat (the &ldquo;hurley&rdquo; made of ash wood) and the ball (the &ldquo;sliotar&rdquo; made of polyurethane-cork composite) in the Irish game of hurling. The hurley is highly anisotropic in its mechanical properties and this impact system therefore presents a unique modelling challenge. The FE models do not rely on either the assumption of linear materials models or on calibrated materials models. The FE models are able to take all three geometric, status and material nonlinearities into account yielding a close correlation with real-world impact scenario. The reported FE results were validated against experimental measurements showing an excellent correlation of more than 91% in term of maximum ball deformation.Prediction of the Supersonic Flow Base Pressure by Axisymmetric Direct Numerical Simulation
https://jacm.scu.ac.ir/article_17929.html
Axisymmetric direct numerical simulation (DNS) has been carried out to predict supersonic base flow behavior. Substantially fine grid has been used to perform calculations for the flow with Reynolds number up to 106. Optimal grid resolution was established through test calculations for affordable run time and solution convergence determined by the vorticity value. Numerical scheme provides fourth-order approximation for dissipative, fifth-order for convective and second-order for unsteady terms of conservation equations. Reynolds Averaged Navier-Stokes (RANS) approach has been employed to obtain input flow profiles for DNS calculations. Series of calculations have been carried out for Mach number 1.5 with Reynolds numbers 104, 105, 106 and for Mach number 2.46 with Reynolds number 1.65&times;106. It has been found that local base pressure coefficient calculated by DNS is a bit overestimated in a zone close to symmetry axis in comparison with experiment while integrated base drag coefficient shows good agreement with experimental data and noticeably better than one obtained by RANS approach.A Bridge Vibration Measurement Method by UAVs based on CNNs and Bayesian Optimization
https://jacm.scu.ac.ir/article_17936.html
A bridge vibration measurement method by Unmanned Aerial Vehicles (UAVs) based on a Convolutional Neural Network (CNN) and Bayesian Optimization (BO) is proposed. In the proposed method, the video of the bridge structure is collected by a UAV, then the reference points in the background of the bridge and the target points on the bridge in the video are tracked by the Kanade-Lucas-Tomasi (KLT) optical flow method, so that their coordinates can be obtained. The BO is used to find the optimal hyper-parameter combination of a CNN, and the CNN based on BO is used to correct the bridge displacement signal collected by the UAV. Finally, the natural frequency of the bridge is extracted by processing the corrected displacement signals with Operational Modal Analysis (OMA). Moreover, a steel truss is used as the experimental model. The number of reference points and the shooting time of the UAV with the optimal correction effect of the BO-based CNN are obtained by two groups of comparative experiments, and the influence of the distance between structure and reference points on the correction effect of the BO-based CNN is determined by another group of comparative experiment. The static reference points are not required for the proposed method, which evidently enhances the applicability of UAVs; the conclusion of this paper has great guiding significance for the actual bridge vibration measurement.Multilevel Modeling of 1-3 Piezoelectric Energy Harvester Based on Porous Piezoceramics
https://jacm.scu.ac.ir/article_18008.html
The paper presents a computer analysis of the properties of a piezoelectric composite consisting of porous piezoceramic rods regularly arranged in an elastic matrix (piezocomposite with a connectivity of 1-3). The porous piezoceramic PZT-4 is used based on porous piezoceramics as an active material. The calculation of material properties is carried out based on a multilevel approach. First, the effective moduli of porous piezoceramics are determined, and then a 1-3 piezocomposite with rods having the calculated homogeneous properties is analyzed. The simulation uses the homogenization method based on the Hill lemma and the finite element method, as well as approximate analytical models. The effective properties of 1-3 composite are determined for various percentages of porosity of piezoceramic rods, which are a composite of 3-0 connectivity. Calculations were performed in the software package ACELAN-COMPOS. The calculated properties are used in finite element models to evaluate the effectiveness of composite materials in sensors and energy harvesting devices. Two cases of stiffness of an isotropic matrix are considered, which correspond to the stiffness of a porous composite at 50% and 80% porosity. The electromechanical properties, such as electro-mechanical coupling coefficient and output potential, for different transducers models made from the proposed composite are analyzed.Smart Gas Sensors: Materials, Technologies, Practical Applications, and Use of Machine Learning – A Review
https://jacm.scu.ac.ir/article_18013.html
The electronic nose, popularly known as the E-nose, that combines gas sensor arrays (GSAs) with machine learning has gained a strong foothold in gas sensing technology. The E-nose designed to mimic the human olfactory system, is used for the detection and identification of various volatile compounds. The GSAs develop a unique signal fingerprint for each volatile compound to enable pattern recognition using machine learning algorithms. The inexpensive, portable and non-invasive characteristics of the E-nose system have rendered it indispensable within the gas-sensing arena. As a result, E-noses have been widely employed in several applications in the areas of the food industry, health management, disease diagnosis, water and air quality control, and toxic gas leakage detection. This paper reviews the various sensor fabrication technologies of GSAs and highlights the main operational framework of the E-nose system. The paper details vital signal pre-processing techniques of feature extraction, feature selection, in addition to machine learning algorithms such as SVM, kNN, ANN, and Random Forests for determining the type of gas and estimating its concentration in a competitive environment. The paper further explores the potential applications of E-noses for diagnosing diseases, monitoring air quality, assessing the quality of food samples and estimating concentrations of volatile organic compounds (VOCs) in air and in food samples. The review concludes with some challenges faced by E-nose, alternative ways to tackle them and proposes some recommendations as potential future work for further development and design enhancement of E-noses.Impact of Microbial Activity and Stratification Phenomena on Generating/Absorbing Sutterby Nanofluid over a Darcy Porous Medium
https://jacm.scu.ac.ir/article_18021.html
The present article discusses the impact of microbial activity by considering Sutterby nanofluid over a stretching surface with the Brownian motion and porous medium. Thermophoretic effects are the measure concerned to balance the temperature of the fluid to generate the improved results. We include these effects in our model with some other parameters like Brownian motion and microbial activity. The stratification phenomenon is considered for the evaluation of heat generation/absorption over the horizontal sheet in the Sutterby nanofluid. The porous medium and chemical reaction with microbial activity is further analyzed in an incompressible Sutterby nanofluid. With the help of some suitable similarity transformations, the initial boundary conditions and the governing partial differential equations of our model are converted into the coupled structure of ordinary differential equations and final boundary conditions. The Spectral quasilinearization method (SQLM) is used to numerically solve these ordinary differential equations to evaluate the impacts of various parameters taken in our model. The graphical representation of different parameters is analyzed for the flow, temperature, solutal and microbial distribution. The coefficients of physical interest are also analyzed and show good results in favor. The rise of nanofluid parameters declines the flow profile of the fluid while enhancing the temperature profile and falling for the thermal stratification phenomenon. The Sutterby nanofluid model also incorporates the behavior of dilatant solutions and pseudoplastic which is helpful in various engineering processes and industries. This model is ideal for polymeric melts as well as high polymer resolutions.Stability analysis of an inflated, axially extended, residually stressed circular cylindrical tube
https://jacm.scu.ac.ir/article_18023.html
Residual stress may have an important influence on the mechanical response of residually stressed materials. This paper is concerned with the effects of residual stress on the stability of inflated, axially extended, residually
stressed circular cylindrical tube. To this end, the theory of small incremental
deformations superimposed on a large underlying finite deformation is used.
Asymmetric and axisymmetric types of bifurcation are considered. It is found
that for residual stress parameter &circ;&gamma; of the same sign the effect of the residual stress is different depending on the type of bifurcation. For example, for
asymmetric bifurcations with mode number m = 1 and with positive &circ;&gamma; inclusion of residual stress makes the tube more stable, on the other hand, for
axisymmetric bifurcations inclusion of residual stress, corresponding to positive residual stress parameter &circ;&gamma;, leads to increase of instabilities. In all cases,
residual stress with positive and negative residual stress parameter &circ;&gamma; leads to
a symmetric character of bifurcation curves.Investigation of Driving Torques at the Joints of Industrial Robot Arms Based on the Topology Optimization Technique
https://jacm.scu.ac.ir/article_18028.html
This paper presents investigating the driving torques of industrial robot arm joints using the structural optimization method for Upper Arm (UA) link. The optimal criteria mention reducing the mass of UA link. The static and dynamic analysis problems are considered when robot moves in the vertical plane and in space. Results of these problems were used to perform the optimization of UA link structure. Stress and displacement values in statics and dynamics analysis of the optimized link with a weight reduction of 39% and over 45% in volume show that it ensures to meet the set optimal criteria. A mathematical model of 6 degrees of freedom (DOF) robot with is established to determine the kinematics and dynamics equations. The inverse kinematics and dynamics problems solving algorithm of the redundant robot is effectively applied to determine the input values with the given motion trajectory of the end-effector point in the workspace with two different trajectories in a plane and in space. The analysis results show that there is a change in driving torque values in a direction favorable for the operation of the joints for any trajectory when the mass of robot reduced. This is also verified by a simple 2DOF robot model presented in the Appendix with three different optimization methods. The reported results have essential implications for application of various topology optimization issues in order to positive change the driving torques at joints while well ensuring the functionality of robot arm.