مجله مکانیک سازه ها و شاره ها
سال سیزدهم شماره 6 (بهمن و اسفند 1402)

The importance of research in crashworthiness and the post-accident behavior and efforts to improve the behavior of the structure and reduce the accelerations to the occupants with the help of energy absorbers is determined by observing the increasing statistics of vehicle accidents, including cars, trains, and airplanes. In this research, the energy-absorbing behavior of a thin wall with an aluminum rectangular section will be investigated by numerical solution in finite element method and in Abaqus software, and to improve its energy absorption parameters, discontinuities were created on the geometry, which regularized the folding pattern. The primary research approach is to improve the energy absorption behavior without fundamentally changing the geometry. Discontinuities with different geometrical shapes, sizes, and numbers are placed in different places in the model to obtain the best energy absorption behavior. After evaluating and choosing the circular discontinuity among the other geometric shapes, for their proper placement, an initial guess of the location of the discontinuities was considered with the help of similar research. Then, the eigenvalues of the geometry extracted from the buckling solver have been used to place and increase the number of discontinuities.Finally, by examining 43 models with different numbers and placement of discontinuities, a model with a 13% improvement in the CFE criterion was proposed.

This article addresses the bi-level multi-objective optimization problems raised in reliability-based robust design optimization of mechanism synthesis through establishing a state-of-the-art game theoretic scenario. A novel bi-level decentralized decision-making approach is proposed using the synergy of reliability-based robust design optimization (RBRDO), Stackelberg/cooperative game theory, Monte Carlo simulation (MCS) and genetic programming (GP). The application of the proposed approach is elaborated in a case-study of multi-objective robust synthesis of high-speed path generating four-bar. The four performance criteria, namely, accuracy (), robustness ( and ), reliability () at upper level and quality of motion () at lower level are assigned to four players so that each of whom is in charge of one objective criterion being optimized. The peak input driving torque as the dynamic constraint is associated with the upper-level problem. The genetic programming (GP) metamodel is used to capture the Stackelberg protocol between two levels i.e., constructing the follower’s rational reaction set (RRS) and the Nash arbitration scheme is hired to model the cooperative behaviors in upper level. By this way, the four-objective optimization problem of four-bar linkage is reduced into a single-objective robust design problem. The obtained results show a considerable enhancement in reliability and robust behavior of mechanism, whilst the deterministic criteria of accuracy and quality of motion is preserved.

Ionic Polymer-Metal Composite (IPMC) strips are very thin actuators in the form of a sandwich composite with an electroactive polymer in the core and two metal electrodes on its sides. In this paper, a multi-scale electrochemical-mechanical analysis of actuation time response of an IPMC composite strip is performed. First, the electrochemical response of IPMC primary motion stemming from electrostatic force, viscous force of ionic cluster motion in the polymer matrix solvent, and diffusive force caused by the concentration potential are obtained by a hydraulic model. The solution methods in the space domain include finite element numerical analysis based on Glerkin's formulation, and Euler's integration method in the time domain. Then, the solvent transport equation is written, and the rate of eigen strain and bending moment of the IPMC actuator is obtained. By extracting the amount of cluster concentration in the boundary layer of cathode and anode, the displacement response of the end of the beam is determined. The results of the model are validated with previous available studies. The results show a reasonable fit between the response of the IPMC actuator and the electrical excitation, and confirm that the presented model provides the prediction of the fast response of IPMC strip.

In this research, the parameters of brazing temperature, time, and joint seam have been optimized in brazing joints of 420 stainless steel with BNi-2 filler metal on the shear strength of lap joint samples using response surface methodology. The parameters of brazing temperature, time, and joint seam were determined by the design of the experiment using the Benken box method. The thickness of BNi-2 filler metal was considered to be 0.04, 0.07, and 0.1 mm in this research. After preparing the samples, they were placed in a vacuum furnace at temperatures of 1000°C, 1070°C, and 1140°C for 10, 30, and 50 minutes. The mechanical tensile test was performed to determine the shear strength. It was observed that increasing the joint seam from 0.04 to 0.1 mm caused a 14% decrease in shear strength. Also, increasing the brazing temperature from 1000°C to 1140°C has increased the shear strength by 21%, and increasing the brazing time from 10 to 50 minutes has increased the shear strength by 27%. In the end, it was optimized that the maximum shear strength is 164.429 MPa in the joint seam of 0.04 mm, the temperature is 1109.84 °C and the time is 46.58 minutes.

The integrated design method for a missile guidance and control system is such that all the limitations of the subsystems are taken into account during the design in a bid to increase the accuracy and overall performance of the system in the final phase. This will improve efficiency, save time and implementation cost, and as a result, system performance will improve. This article describes the process of designing and simulating the performance of the neural sliding model controller, which was created to guide the missile in a two-dimensional engagement in minimizing the collision time and the miss distance to the target. In the design of the controller, a PID is first considered to evaluate the proposed controller, followed by the design of the neural sliding model controller discussed using neural networks. According to the simulations, it can be shown that the use of this proposed controller and the application of the integrated guidance and control model will reduce the final miss distance and the collision time compared to the PID controller.

Double-layer sheet forming methods are developed in various industries due to their dual properties and wide application. In this paper, the numerical and experimental investigation of the bowing defect in the flexible roll forming process of double-layer sheets have been discussed. Numerical analysis has been conducted using Abaqus finite element software and experimental tests using a single-station flexible roll forming machine. After validation of the numerical model, the effects of significant parameters on the bowing defect in the flexible roll forming process, including the forming angle, sheet thickness, sheet wing length, and the displacement of sheet layers have been investigated using full factorial design of experiments method and finite element simulations. The results were analyzed using the Analysis of Variance statistical method. The results showed that with increase of the forming angle and wing length, the amount of bowing defect increases while it decreases with the increase of the thickness of the sheet. Also, the arrangement of layers is also effective in the occurrence of the bowing defect. The results showed that the bowing defect in the Al-Cu layer material increased from 2.152 to 2.646 mm with the increase of the wing length from 18 to 25 mm.

Industrial effluents is one of the important sources of pollution in industrial activities, including power plants. With the basic control of industrial effluents, in addition to preventing its harmful effects, the consumption of limited water resources is also saved. Due to the high energy consumption of different desalination systems to produce fresh water, as well as the heat losses in power plants, a major part of the effluents can be desalinated for reuse in processes that require water. In this study, the simulation of a multi-effect distillation (MED) unit for a steam power plant is done by Thermoflow software. The required thermal energy of the unit is supplied from the boiler blowdown stream. Sensitivity analysis has been done on the basic parameters in the simulation to select the optimal values. In the premier scenario, considering the eavailability of 870 m3/day of effeluent from various units of IRANSHAHR steam power plant, a MED desalination plant with 12 effects with the ability to produce 290 m3/day of fresh water is proposed. The steam consumption rate is 1.1 ton/hr, which is about one seventh of the power plant's boiler capacity. The gain of ratio of the proposed system is equal to 10.2 and the recovery ratio is 33%. The investment cost of the proposed system is 3290 $ per cubic meter of fresh water per day.

In this paper, a combined cooling, heating and power system based on hybrid drive of internal sand external combustion engines with biomass power source with a gasification reactor with air gasification agent and of the counter flow type is discussed and the synthesis gas obtained from this equipment is used in a gas-burning internal combustion engine. This proposed system has been compared with a similar cogeneration system with a natural gas power source, and energy and economic perspectives have been used for the system. The results show that the proposed system that uses synthesis gas as input fuel will have a significant advantage from energy and economic viewpoints compared to the case where natural gas is used as the main fuel, where the parameter related to the percentage reduction of primary energy consumption shows that if synthesis gas is used as a fuel in the drive of the internal combustion engine, compared to natural gas, it will save 40.55% in input energy consumption. The proposed system with synthetic gas fuel has a significant advantage from the economic point of view and the percentage of fuel consumption reduction, so that the results show a savings of 83.98% in fuel consumption costs. The results also show that the total price of electricity production in the proposed system with biomass and synthesis gas power source in different rotational speeds of the internal combustion engine will be lower and more economical compared to the cost of electricity production with natural gas fuel.

Increasing the heat transfer rate in various industries in order to improve the efficiency of equipment, prevent damage to parts and reduce costs is one of the essential discussions in the industry. One of the solutions to increase heat transfer is the use of active heat sink. In this research, an active heat sink with Galinsten liquid metal fluid was used and the discretization of Navier-stokes equations was done using the second order upstream finite volume method. The effect of applying the magnetic field in the Y direction (perpendicular to the flow axis) to the heat sink has caused the creation of a force against the flow direction called the Lorentz force, which has caused the M-shaped velocity distribution. According to the constant flux boundary condition, increasing the flow velocity in the vicinity of the walls has caused the surface temperature to decrease and the heat transfer to improve. The results showed that the effect of applying a uniform external magnetic field in both Y and X directions with a Hartmann number of 517 improved the Nusselt number by 38% and 13%, respectively, compared to a Hartmann number of zero. The effect of applying a magnetic field in the Y direction to the heat well with a Hartmann number of 517, 38%, Hartmann number of 258, 22% and Hartmann number of 129, 13% has improved the heat transfer.

With increasing importance of flow measurement in industries, especially in petrochemical and water and wastewater, and their need to reduce the installation space and increase the accuracy, it is necessary to improve the existing flowmeters and produce new types. In the last two decades, the V-Cone flowmeter has received the special attention of researchers with features such as reducing the required initial length, lower pressure drop compared to other types, and the ability to be used in two-phase flows. Also, several researches were done to improve the flowmeter geometry. But one of the things that is less discussed is how to connect the flowmeter stand to the body (flowmeter nose). Therefore, in this research, experimental and numerical study of a new case that has a continuous nose, and comparing it with standard types including pointed, curved and elbow, have been done. Using test results, correlations were proposed to estimate the pressure drop between two flowmeter sensors and the pressure loss. Calculations showed that the relative error of pressure drop calculation in the range of Reynolds numbers investigated (5.88 × 104 to 9.80 × 104) is about -0.73%. Numerical simulation showed that the continuous type with the highest level of disturbance (about 3.5% more than the minimum value) causes the increase of fluctuations in the value shown by the pressure gauge located downstream and the error in the calculation of the discharge coefficient. Also, changing the shape of the flowmeter nose caused only minor changes in the size of the vortexes.

In this paper, three-dimensional code has been developed to simulate the partial cavitating flow around projectiles with various heads (blunt, hemispherical, and conical) using the BEM. For this purpose, after generating the geometry using quadrilateral elements with four control points, using the integral expression of Green's theory, source and dipole have been distributed on elements, and using an iterative algorithm, simulation is done and results are compared with the available experimental data and other numerical results. Despite the low computational cost of this method, the results have a high accuracy and convergence rate. One of the main contributions of this work is to present a correlation between the properties of cavity around projectiles with different heads (in the limit of 0.075≤σ≤0.5). Also, Analysis of the results shows that the method has a suitable ability to predict the properties of cavitation flow at non-zero angles of attack (up to 8° angle of attack) in the shortest time. Of course, by increasing the angle of attack and getting away from the potential assumption, the results are associated with some errors (15% in geometrical characteristics and 12% in aerodynamic coefficients). Due to high convergence rate and acceptable accuracy, this method can be used for initial design and optimization of subsurface projectiles with cavitation.

Flow-induced vibration is the effective factor in mechanical destruction of structures that are exposed to fluid flow. In this study, random vortex- boundary element methods (RVM-BEM), is used to simulate two-dimensional laminar fluid flow around four one/two-degrees-of-freedom cylindrical cylinders in a rectangular arrangemen. Hydrodynamic force coefficients, streamlines and cylinder displacements were plotted. The vorticity distribution is separated into blob-vortexes and its changes are studied by tracking these vortexes in the Lagrangian approach by considering two mechanisms of convection and diffusion in each time step. Satisfying no-slip boundary condition, vortex sheets were created on boundary. The cylinder vibrations were modeled as a system of mass, spring, and damper. The results showed that for 1 and 2DoF compared to the stationary cylinder, the average drag coefficient changes are 0.84 and 0.97, respectively. The rear cylinders vibrations amplitude were less than in the front cylinders. The y-amplitude was three times larger than x-amplitude. The maximum x-amplitude vibration of 1DoF cylinders was 1.51 times larger than 2DoF ones. Solving flow over 2DoF single cylinder by BEM(no need for homodis mapping or considering the vortexe images) with a similar solution in Ansys-Fluent software, showed 25% reduction in runtime and 2.3% increase in calculations accuracy.