نشریه مهندسی مکانیک مدرس
سال بیست و یکم شماره 9 (شهریور 1400)

In present study, the stress and strain distributions due to the radiant gradient in some radiant tube burners have been investigated. In the design of the burner, several outlet valves are mounted on the wall of the burner tube and the combustion-produced fluid is discharged by the outlets into the furnace. For this purpose, three cylindrical radiant tubes with the same length, diameter, thickness and material and difference in design of fluid outlets are modeled. To simulate the mechanical behavior of the pipes, after the geometric modeling and considering the pipe material and boundary conditions, ANSYS commercial software has been used. The boundary conditions for numerical solution are extracted from the results of the experimental tests. Due to the average fluid velocity within the radial tube, the fluid flow falls into the turbulent range. In order to obtain the stress-strain diagram of the tested alloy, the Ramberg-Osgood equation is used. Due to the solution of the fluid-solid interaction by ANSYS, the best design is concluded through the Von-Mises stress minimum values. Also, by removing the thermal load from the next load step, the residual stresses generated in the samples are calculated. To illustrate the accuracy of the solution, some specimens of the burner have been made and evaluated to verify the numerical solution.

Bistable composites have gained increased attentions in industry, especially in the aerospace industry, due to their unique feature of shape-changing without the need for continuous energy. The advantage of using these structures is their ability to package in small size, whilst deploying in long lengths and high stiffness ratio along the length. This unique feature, along with the advantages of other fiber reinforced composites such as high strength, light weight and high rigidity, has made them a good choice for many applications such as deployable booms and antennas for satellites. In this paper, the bistablility of shell structures at different time-temperature conditions are investigated. To explain the mechanical behavior of the Bistable Tape Springs (BiTSs) in different conditions, an analogous 2D model consist of rigid linkages, elastic springs and viscous dampers is proposed. The relationships between the force and energy through the transition path for the 2D model were established and the non-dimensional strain energy paths for different initial parameters were obtained, accordingly. As a case study, four BiTSs made of composite materials are fabricated and subjected to a particular thermo-viscoelastic condition to verify all stability behaviors of the 2D LSD model under thermo-viscoelastic conditions.

The aim of this paper is to investigate the growth of pitting corrosion in CUSTOM 450 stainless steel and to obtain strain values in growing pits at the maximum bending region. In this regard, a two-point bending specimen was made and subjected to a potentiostatic test under the potential of 350 mVSCE in the 3.5 wt% sodium chloride solution. Then, the depth of the grown pits is calculated using Eddy Current device. By simulating a sample under the pitting corrosion in COMSOL Multiphysics software and matching its results with the results of the Eddy Current device, it was found that the simulation can largely replace the laboratory test. To calculate the tensile stress distribution in the cross section of the sample under pitting corrosion, the Laplace equation governing the sample was discretized. The same results were obtained by solving the discrete equations and comparing them with the results of COMSOL Multiphysics software. According to the results, the pit tends to grow superficially. This means that the surface growth of the pit is greater than its growth in the direction of depth. This is due to the fact that near the sample surface, tensile stress and electrical potential are high, as well as chemical reactions and corrosion in areas near to the pit surface.

The magnitude of reaction forces in locating points is considered as one of the basic parameters in the fixture planning and element design stages of the fixture design procedure. The magnitude of these forces depends on the intensity, position, and orientation of the transient clamping and active machining forces and torque. Analysis of the effect of machining force and torque on reaction forces is a complex process because the magnitude, position, and orientation of machining loads change at any given time. In this paper, an analytical model is presented to investigate the effect of machining loads on online values​​ of reaction forces in the contact points between the workpiece and the fixturing elements. The magnitude ​​and direction of machining forces and torque are calculated on the tool path and using these parameters as inputs to the analytical model, the reaction forces are calculated in each of the six locators at each moment. A finite element analysis is performed to validate the values predicted by the analytical model. For this purpose, the necessary subroutines are prepared and the values ​​of the reaction forces obtained from the simulation are compared to their corresponding values ​​from the analytical model. A three-dimensional workpiece with a 3-2-1 locating system was used as a case study to evaluate the performance of the proposed model. The maximum error in calculating the reaction forces was obtained as 10.85% from the proposed analytical model which indicates the accuracy of the theoretical predictions.

In this paper, the mathematical modeling, construction, control, and implementation of a one-degree-of-freedom cube dynamic system with a reaction wheel actuator will be discussed. The innovation of this paper is the implementation of the proportional-integral-derivative controller on the experimental system of one degree of freedom with a reaction wheel. First, equations of system are expressed, then the system is analyzed in time and frequency domain. Then, the proportional-integral-derivative controller will be designed and implemented on the constructed system. The system response is compared in six steps for different control gains. The control gains of the best answer are proportional gain of -20, integral gain of -30 and derivative gain of 3- in system theory answers it has 1 degree of superiority and in experimental answer it has 7 degrees of overshoot. The steady-state error is zero for both experimental and theoretical system. The rise time of the simulation theory is 10 time steps, each time step is equal to 0.001 seconds, and the experimental response of the system is 10 time steps. The simulation session time is 180 time steps and the experimental response is 100 time steps.. In the next step, the stability of the control designed with the selected gains from the previous step is tested by inserting the perturbation, and the system is stabilized by 4 degrees overshoot. By changing the angle of the bottom plane, the response will have 3 degrees overshoot, but the system will remain stable.

Roll motion is one of the most important and dangerous motions of the ship and can even result in capsizing of the vessel. Therefore, its control has been always of interest for marine industry researchers. Among the various methods and equipment for controlling the roll motion, the use of free surface anti-roll tanks has been one of the most important methods and which used in many cases due to its simplicity in construction and design. The high efficiency of these tanks at all speeds and even without speed is another strength of these tanks. This study investigates the effect of the free surface anti-roll tank on the roll motion numerically and experimentally. In the numerical simulation, a CFD sloshing solver, based on the “Open source Field Operation And Manipulation”, known in short as Open-FOAM, and assuming 2D laminar flow conditions, is customized to calculate the sloshing loads from the tank. The predicted roll damping and moments due to the anti-roll tank are validated against experimental results. This simulator could be used as a sloshing simulator to couple with seakeeping solvers.