numerical method

This study introduces a novel lattice structure, whose unit cell design draws inspiration from the fusion of honeycomb patterns and the DNA found at the core of cells, constructed from PLA material. This structure underwent tensile testing along the X and Y axes. Additionally, the paper presents a new analytical-numerical approach that combines Timoshenko beam theory, mechanics of materials principles, and finite element analysis to determine the mechanical properties and forecast failure in cellular structures. This method was corroborated using the ABAQUS commercial software. Research indicated that a closer ratio of thickness to unit cell length, specifically 1/10, leads to more precise predictions for the mechanical behavior of the cellular structure under tension along the X axis. The findings showed that, in comparison to the Y axis, the X direction exhibited a 7% increase in load-bearing capacity and an 8% increase in maximum yield stress, yet the equivalent stiffness was 75% lower

In this paper, the static behavior, instability and buckling in porous micro plates under electrostatic field are investigated based on the modified couple stress theory and with regard to modeling, determining equations and solution methods. The plate is considered to be porous and the porosity distribution is considered to be non-uniform. The equations are obtained considering the distributed support load. By using the definition of dimensionless parameters such as load, voltage and length scale, the equations of motion become dimensionless. It can be seen that in the special case, by removing the dimensionless non-classical parameters, the equation of the classical plate under the electrostatic field is obtained. Galerkin mode summation and numerical methods are utilized to solve the static deformation equation and assess the pull-in instability voltages and buckling loads. Convergence analysis is done and the number of approximation functions and elements required for both methods are calculated and the compatibility of the results obtained from the two methods is examined. In the results section, the difference between classical and non-classical theories is examined and the effect of dimensionless parameters of length scale and porosity ratio on maximum displacement, pull-in instability voltages and buckling load is studied. The results show that the use of modified stress couple theory leads to a very large stiffness prediction compared to classical theory. This result highlights the necessity of using the modified couple stress couple theory for the micro-scale. It is observed that the length scale parameter plays the role of stiffening. The change of porosity ratios also shows that as this ratio increases, the displacement increases and the stable areas decrease. Variations in this ratio lead to uniform changes in buckling load and pull-in instability voltage, and linear relationships are obtained to calculate buckling load and pull-in instability voltage versus porosity ratio. Also, in small values of support load, it is shown that the relationship between the instability voltage and the compressive load of the support is linear, but in the buckling range, this relationship is not linear.

One method to improve heat convection is to increase the heat transfer coefficient of the working fluid. Adding metal or non-metal nanoparticles into the base fluid, known as nanofluid, is a technique to enhance the heat transfer coefficient. Research in the field of nanofluids has grown significantly in the last two decades. In this study, the effects of a homogenous combination of Al2O3 and TiO2 nanoparticles with deionized water are investigated. The thermohydraulic performance of the nanofluid inside the vertical channel is analyzed by experimental and numerical methods for turbulent and laminar flow. The turbulence model utilized in computational fluid dynamics is the k-ε model. The heating rod in the test section produces 1 kW cosine heat flux. The results show that increasing the concentration of nanoparticles significantly reduces the maximum temperature of the rod. The use of 1% homogeneous nanofluid reduces the maximum temperature by 20% at the Reynolds of 950 and 9.5% at the Reynolds of 4200 compared to pure water. Also, the heat transfer coefficient increases with the addition of nanoparticles. The difference between the results obtained by the k-ε turbulence model and the experimental method shows a difference of 10% to 13%. This research shows that the combined nanofluid with suitable thermal performance can be one of the working fluids in future thermal cycles.

In this research, a meshless method has been developed to solve internal and axi-symmetric flows. In this method, the least squares of the Taylor series are used for spatial discretization and explicit multi-step Runge-Kutta method is used for temporal discretization. Governing equations are based on two-dimensional and axi-symmetric Euler equations. The second and forth order dissipation are used to solve the flows. In order to model boundary condition, subsonic and supersonic inlet and outlet boundary conditions as well as the wall boundary have been used according to the problem. To validate the results of the code, the inviscid flow inside a two-dimensional nozzle and the supersonic flow inside the channel along with bump have been simulated and the results have been compared with valid data. Also, the ability of the code to shock capturing in the two-dimensional and axi-symmetrical nozzle is presented. Finally, the simulation of the steady flow inside a axi-symmetric convergent-divergent supersonic nozzle with Mach 5 in outlet has been done to measure the accuracy of solving the numerical code at hypersonic speed. The results show that the developed code can simulate steady internal and axi-symmetric flows with very good accuracy. The code convergence process is also presented, which shows appropriate convergence of the developed code. The analysis time for shock capturing in the axisymmetric nozzle is about 64% faster than the Fluent-software.

In this study, the effect of transverse steps location on hydrodynamic components and the longitudinal stability of the vessel has been investigated. The vessel studied in this research is a planning catamaran, each demi-hull with two transverse steps. At first, vessel resistance with a weight of 5.3 kg within a range of length Froude number of 0.49 to 2.9 in calm water has been calculated. Then, craft behavior was evaluated at displacements of 5.3, 4.6, and 4 Kg using the numerical method. The numerical simulation results have been validated with similar experimental results. The craft in 4 and 5.3 kg weights, in Froude numbers greater than 2.43 and 2.9, respectively, has a Porpoising instability. In order to improve the longitudinal stability of the vessel, the Taguchi test design has been used to determine the optimal location of the transverse steps. The results showed that by placing the transverse steps in the optimum location, the Porpoising instability in the vessel has been resolved. In planing mode, vessel resistance decreased by 12%, 9.5%, and 6.6% in the optimum state of transverse steps compared to the base state for the mentioned weights. In similar conditions, the lift force on the vessel increased by 15, 10, and 7 percent for the mentioned weights, respectively.

In this paper, the buckling of rectangular sheets with variable thickness under in-plane loads is investigated. Each sheet structure under compressive load may buckle at a certain level of load and lose its stability. In analyzing the stability of a low-thickness structure, determining the buckling load is important and necessary. The buckling load depends on some parameters such as geometric features, boundary conditions and type of loading. In this paper, the amount of buckling load was obtained for changes in sheet thickness with different patterns and different boundary conditions. For thickness changes, various modes such as how the changes, starting location, and intensity of the changes are examined. The buckling load was calculated using the Galerkin method as well as numerical methods and compared with the available results. The results showed that the amplitude of thickness changes is the most important parameter affecting the reduction of buckling load. For sheets with trapped edges, the effect of these parameters is more noticeable. Also, asymmetric thickness changes will have a significant effect on the buckling load.

In the first part of this research, non-catalytic natural gas converter is analyzed numerically. The GRI-1.2 mechanism, which includes 177 basic chemical reactions, is used to calculate the reaction rate in natural gas oxidation processes. The EDC waste loss model is used to model combustion. Due to the fact that the calculations have been done for a very large natural gas converter, a symmetric axial model is used to reduce the computational costs. The results of the first phase of the study show that increasing the pressure increases the conversion of CH4 to hydrogen, but from a pressure of 3 MPa and above, the amount of hydrogen production remains almost constant. In addition, with increasing the ratio of water vapor to natural gas, the maximum flame temperature in the converter decreases and the molar fraction of H2 / CO in the output increases. In the second part of the research, a stable three-dimensional heterogeneous numerical model for studying the methane vapor vapor reforming process is investigated. The results show that by increasing the inlet temperature of heating pipes, the CH4 / H2O ratio increases to about 0.25 and the number of methane heat supply pipes increases. Also, by comparing the results of this simulation and the existing experimental research in this field, the results of this study can be used for the development of industrial.

Spin is one of the most important phases of aircraft design. Therefore one of the important tests for taking the pilot certification is entry and recovery from spin. The spin of PC-21 is investigated numerically and theoretically at the developed spin phase and is compared with results of flight test. The spin type of this airplane is counterclockwise and maximum rudder deflection is 25 degree. According to theoretical results, the spin of this aircraft should be happen at angle of attack 30 degree; however the flight test results show that spin must be happen at angle of attacks between 40 to 65 degrees. Numerical results show good agreement with flight test data. This research describes the ability of computational fluid dynamics to prediction of the behavior of airplanes in the spin conditions. The proper turbulence modeling, strong hardware, accuracy evaluation and significant experience in CFD procedures are requirements of the approach.

This paper aims at investigating the mechanical behavior of a nonlinear system consisting of two coupled beams and a PZT material attached on each beam, excited with a single resonant frequency, for energy harvesting. In order to model the beams, in-extensional assumption and Euler-Bernoulli beam theory are utilized. It is assumed that the beams undergo large amplitude vibrations; which necessitates the application of a nonlinear theory which is taking into account curvature-related and inertial-related nonlinearities. Numerical studies were carried out to study the effect of the different parameters such as external resistance load, gap distance between beams on the nonlinear behavior of the system. It was obtained that as the gap distance between beams decreases, the scavenged power increases and the system behavior tends to exhibit non-periodic response. In addition, a comparison was done between linear and nonlinear systems shown that considering nonlinearity in the system accompanies a shift in the resonance frequency and induces hardening nonlinear behavior in the system.

In this manuscript, in-plane normal and shear interlaminar stresses in composite Timoshenko beam under transverse loading placed on the elastic foundation are studied. The elastic behavior of interlaminar stresses at the interface of adjacent layers is modeled by radial and tangential springs of high stiffnesses. In the first, governing equations and boundary conditions are derived by the virtual work principle and then they are solved by generalized differential quadrature method. By calculating the displacements of the beam laminates, the interlaminar stresses, which are the reaction of radial and tangential springs between adjacent layers of the laminated beam, are obtained. Also, the other stresses of the beam are calculated and drawn by equilibrium equations. Comparison between the results of presented analysis for a beam the and the results of three dimensional elastic solution is shown that the presented method has good accurate to predict the in-plane stresses. The results showed that Winkler effects on interlaminar stresses are lower than Pasternak effects. Also, the elastic foundation caused decrease and increase for interlaminar shear stress and normal stress, respectively.

Composite conical shells have extensive industrial application and stability analysis is necessary for them. In this article, stability of composite conical shells subjected to dynamic external pressure is investigated by numerical and experimental methods. In experimental tests, cross-ply glass woven fabrics were selected for manufacturing of specimens. Hand-layup method was employed for fabricating the glass-epoxy composite shells. A test-setup that includes pressure vessel and data acquisition system was designed. For detecting the buckling load, pressure history of vessel during loading was used. Because of suddenly changing in volume of pressure vessel in instability moment, a disruption in pressure history can be observable. Also, numerical analyses are performed in Abaqus software. For doing this at a distinct loading time, we load composite cone with dynamic external loading and then draw displacement of a specific node versus time. And then with continuous changing of loads and drawing it versus time, the load on which variation of displacement become significant has been considered as dynamic buckling load.
In both of experiments and numerical studies, increasing of shell’s stability threshold in dynamic loading is recognizable. Finally, results are compared together while a good correlation is observed.

In this article, cavitation flow around axisymmetric projectiles with ringed and non-ringed cavitator has been investigated using control volume and boundary element methods. In the numerical method, the homogeneous equilibrium approach as well as the zwart model, for modeling the mass transfer and forming the system of equation, have been used. In the boundary element approach with dipole distribution on the body and cavity surfaces and source distribution on the cavity surface, the right conditions were set for using the Green's theorem in solving the potential flow. Moreover, some source components were imposed on the cavitator surface in order to add the hole effects. The validation procedure for both methods has been done by analytical and experimental data. In general, the results of this research are presented in two parts. In the first part, hydrodynamic properties of ringed cavitator such as cavity dimensions, intended forces, flow behavior and etc are analysed deploying the numerical methods based on Navier Stokes equations. In the second part, the boundary element method has been used for the analysis of the cavitation flow around practical geometries with ringed cavitator. The most important finding of this study is reduction of the cavity dimensions and also an increase in the force on the projectile during the use of annular cavitator. In addition, as a result of this study, two equations for maximum length and maximum diameter of the formed cavity on the cylindrical body in relation to the cavitation number and hole diameter have been provided.

In aircrafts with multiple wings, control surfaces, and stabilizers, the stabilizing fins located at the tail provide stability for the boosting. In such aircrafts, the vortices resulting from the flow around upstream wings and control surfaces usually weaken the stabilizers’ performance. The nature of the form of grid fins makes them less sensitive in comparison with planar fins. Accordingly, the performance can be improved by substituting grid fins for planar fins. This paper simulates the flow field around the different models of planar and grid fins by applying finite volume methods using hybrid grid near the airplane’s body. At first, the flow field around a model with available experimental results was simulated to achieve the appropriate model of turbulence model. Then, two set of planar stabilizers, i.e. PL1 and PL2 and one set of grid stabilizers were designed for an aircraft with wings and control surfaces in a way that aerodynamic coefficients of the fins are equal to each other. However, they demonstrate different aerodynamic coefficients when installed on the aircraft as stabilizers. The simulation was run at Mach numbers 0.6, 0.7, and 0.8 and attack angles 0, 2, 4, and 6 degrees. The results indicate that pitch moments and normal force coefficients of the planar fin are lower than the grid fin in both models. Moreover, the performance of the planar fin as a stabilizer will be improved if its chord’s length is decreased and its span is increased.

In this paper the flow on a finite wing with triangular damage is numerically and experimentally investigated to understand the influences of damage on the aerodynamic characteristics of wing. To study the effects of different span positions, the damage was considered in tip, middle and root position of the wing span. The aerodynamic coefficients and their increments due to damage were extracted and the results were compared to each other and also to the experimental results. Then flow visualizations were practiced to make evident the flow structure on the model and to help to understand the influences of each position of damage on the aerodynamic coefficients. There was the flow through the damage which was driven by the pressure difference between the upper and lower wing surfaces. The flow could take two forms dependent on the angle of attack. The first form was a "weak-jet" which formed an attached wake and resulted in small changes in force and moment coefficients. The second form resulted from increased incidence. This was the "strong-jet" where through flow penetrated into the free stream flow with large separated wake and reverse flow. The effect on the force and moment coefficients was significant in this case. Generally comparing to an undamaged model, increasing incidence for a damaged model resulted increase loss of lift coefficient, increased drag coefficient and more negative pitching moment coefficient.