فصلنامه مکانیک هوافضا
سال بیستم شماره 1 (پیاپی 75، بهار 1403)

The target of this research is to investigate the amount of entropy production during natural convection inside a 2D chamber containing a non-Newtonian nanofluid using the lattice Boltzmann method. The chamber is exposed to uniform heat absorption/production and uniform and non-uniform magnetic field at different angles. The feature of the present work is to evaluate the effect of thermal radiation and the shape of the cavity cold wall in three shapes: smooth, curved and diagonal on the flow characteristics. Application in the design of electronic coolers and solar collectors is one of the practical cases of this numerical research. Acceptable agreement of the obtained results with previous related studies confirmed the validity of the presented results. Based on the results, the presence of radiation parameter leads to the improvement of heat transfer, which is more evident due to the increase of fluid power-law index. In addition to reducing the Nusselt value for enhancing the fluid power-law index, the effectiveness of the presence of the magnetic field in reducing the entropy and heat transfer rate enhances as the fluid power-law index decreases. It is feasible to attain the flow strength and the Nusselt value up to 40% and 61% more, respectively, by applying a vertical and non-uniform magnetic field. Although for heat production mode, there will be the lowest value of thermal performance index and the Nusselt value, the greatest influence of the magnetic field is observed in the heat production mode. By designing the wall in a smooth shape, in addition to increase the thermal performance coefficient, it is possible to decline the Bejan value.

This study deals with the design and experimental implementation of an adaptive actuator failure compensator for a spacecraft attitude control simulator in the presence of unknown actuator failures and uncertainties. The adaptive actuator failure compensation controller is designed using the backstepping method, which considers uncertainties in the time of occurrence, values, and failure patterns. The adaptive backstepping control method is designed to compensate for the uncertainties of the actuator failure by incorporating the inertia matrix and the distribution matrix. The stability analysis of the proposed adaptive controller for the dynamics of the spacecraft simulator with actuator failures has been carried out. Simulation results and laboratory studies are presented to show the effectiveness of the proposed controller in the presence of stuck, sinusoidal, and complete failures in the spacecraft attitude control simulator system. The results indicate the good performance of the proposed method in the presence of unknown actuator failures and model uncertainties in the system.

One of the special topics in the aeroelastic field is the flutter of the airplane wing at an index speed called the flutter speed, which, if this phenomenon is not controlled, there will be a possibility of destroying the structure (airplane wing). Various methods for wing control have been proposed in the last two decades. In the current research, two-way forced jet momentum embedded on the wing is used to control a pseudo three-dimensional wing with a simplified unsteady flow regime. The jet activation signal at the flutter speed is provided by the pulse width-pulse frequency modulator. The advantages of this modulator include its quasi-linear performance, high precision with the presence of fluctuations and flexibility. In this research, the double aeroelastic, non-reversible and rectangular (Hancock) wing model is considered, and the strip theory is used to develop the lift force during spinball. In the speed of the flutter ball, the swing of the wing is driven to damping by the jet activity, and according to the obtained aeroelastic graphs, satisfactory results have followed.

In this study, a new integrated control for the steering and braking of semi-trailer trucks for tracking in longitudinal and lateral combined maneuvers is proposed. For this purpose, a nonlinear model of a tractor semi-trailer with 10 degrees of freedom including the longitudinal, lateral and yaw motion of the tractor unit, the articulation angle and the rotational motion of each wheel is used. Then the active steering and braking controller is designed with the purpose of tracking and utilizing the sliding mode method. Also, for the yaw stability of the vehicle, a lateral stability controller is proposed using the sliding control method. Then, by utilizing multi-objective optimization, a new integrated control strategy is presented in order to optimally allocate the longitudinal and lateral forces of the tires. This strategy is designed based on achieving the purposes of tracking and stability by using the capacity of tire forces in the optimum slip range by using variable weight coefficients. In order to implement the integrated controller, the tractor semi-trailer model presented in the TruckSim software is used. The obtained results indicate the excellent performance of the integrated controller strategy designed for tracking by maintaining lateral stability when performing the lane change maneuver with braking. So, by using the proposed controller, the maximum tracking error of the longitudinal and lateral position, the yaw angle of the tractor and the articulation angle are equal to 1.83, 0.56, 4.42 and 9.53%, respectively. This is while in the case of a vehicle without a controller, due to lateral instability, the reference path is not tracked.

Shot peening is a cold working process that is used to increase the fatigue life of metal parts by creating compressive residual stress on their surface. The experimental investigation of the parameters of this process is very difficult and expensive, therefore, the finite element method is usually used to simulate and investigate the parameters of this process. However, most of the existing finite element models are not able to describe the real and random movement of the flow of particles and are also limited in terms of modeling the number of particles. Therefore, in this research, in the first stage, a finite element model of the shot pinning process is presented, which is capable of simulating the random and numerous states of this process, and in the next stage, the effect of different parameters of this process such as the size, velocity and angle of throwing the balls on the residual stress is investigated. the result of these investigations led to finding the optimal values of these parameters, so that the optimal value for the diameter of the shots was 1.5 mm, for the velocity of the shots was equal to 100 m/s and for the throwing angle of the shots was equal to 90 degrees. Also, the increase in the diameter of the shots had the greatest effect and the increase in the launch angle of the shots had the least effect in increasing the amount and depth of the residual stress. Also, we were able to numerically measure the important parameter " Shot peening intensity" which is usually measured experimentally by Almen gauge using this model. The obtained results were in good agreement with the experimental results obtained from the work of other researchers and therefore the validity of the presented model can be assured.

In this paper, effect of the different random road inputs in the form of combinatorial profile on the nonlinear and active quarter car model with two-degree of freedom has been analyzed. Bi-objective optimization processes using differential evolution algorithm with fuzzified mutation along with non-dominated sorting algorithm and crowding distance criterion have been carried out. Further, in current work, the hybrid usage of sliding mode control with skyhook and inertial delay control has been applied for modeling of the active suspension system with nonlinear parameters under the combination of three different random roads excitation, namely, class A, B and C. It is important to notice that the two objective functions which have been selected to be simultaneously optimized are, namely, vertical sprung mass acceleration and relative displacement between sprung mass and unsprung mass. The obtained results have been depicted in Pareto frontiers. Comparison of the results of this work with the ones in the literature has proved the superiority of methodology of this work. In fact, in 75% of outputs of application tests, the proposed design of this work has conquered the ones of previous works, and it shows the proper behavior of the suggested design of this work.

During the vehicle motion trajectory tracking process, there are uncertainty considerations in vehicle modeling, including parameter changes, modeling error, and external disturbance that have a significant effect on the tracking performance. Therefore, in this research, a control strategy for motion trajectory tracking of the in-wheel motor electric vehicle, which has a high capability, is proposed. At first, a dynamic model with two degrees of freedom is used to create a trajectory tracking error model, and then it becomes the problem of tracking yaw. Therefore, the amount of the steering angle as the input of the controller is obtained by controlling yaw tracking. In order to estimate and compensate the uncertainties related to the system, in this research, the design the nonlinear mode observer is applied. And also, the controller algorithm is designed to detect yaw tracking. In the next step, in order to stabilize the in-wheel electric vehicle, a sliding mode control algorithm is designed to achieve the desired yaw torque. Then, by designing the optimal torque distributor, the optimal force of the tires is allocated. Finally, simulation is done using Simulink Matlab/Carsim software. The results of the performed simulations show the performance and high capabilities of the proposed control algorithm in emergency situations and despite external disturbances.

High velocity impact resistance is a key requirement for advanced performance structures. This study focuses on experimental investigation of composite behavior made of Innegra fabric under high velocity impact. The targets are made by vacuum infusion method using Innegra fabric, which is a woven fabric composed of high modulus polypropylene fibers as reinforcement and epoxy as matrix.  These samples are subjected to high velocity impact test performed by gas gun. In the present article, the ballistic performance of two- and four-layer composites impacted by conical projectiles with different diameters of 5 and 10 mm are investigated and the effect of the projectile diameter and sabot is studied. The experimental tests have been performed in the velocity range from 30 m/s to 160 m/s for two- and four-layers composites. Ballistic limit, energy absorption and damage pattern have been investigated. The results show the appropriate ballistic performance of Innegra/epoxy composite compared to other composites such as Kevlar/epoxy. The ballistic limit velocity base on experimental tests for two-layer Innegra/epoxy composite with a conical projectile is 54 m/s and for four-layer composite with 52% increase, is 82 m/s and the energy absorption for two-layer composite is 27.33 J and for four-layer composite with 78% increase is 48.70J.

In this article, a method for designing a fault-tolerant optimal attitude tracking control (FTOATC) for a quadrotor UAV subject to component and actuator faults is presented. The proposed fault-tolerant method is based on safe reinforcement learning (SRL) and is capable of ensuring input and state constraints without the need for prior knowledge of the quadrotor dynamics. To this end, the proposed optimal method is presented with a dual neural network (NN) structure consisting of identifier-critic neural networks. In the identifier NN update law, in addition to considering the variable forgetting factor dependent on measurement noise, the experience response method is used, which increases convergence speed and robustness to measurement noise and reduces estimation error. In this method, solving the constrained FTOATC problem is equivalent to solving an unconstrained optimal stabilization problem for an augmented system, where control input constraints and states are guaranteed by selecting suitable cost functions on the input signal and appropriate control barrier functions (CBF)on the states, respectively. Furthermore, fault detection is performed without the need for any model or filter bank, simply by comparing the residual value of the Hamilton-Jacobi-Bellman (HJB) equation with a predetermined threshold. The Uniformly Ultimately Boundedness (UUB) of identifier and critic NN weight errors and, as a result, the convergence of the control input to the neighborhood of the optimal solution are all proved by Lyapunov theory and the performance of the method is validated through simulation results.

Presently there is not any known scaling method using scaled models to investigate mechanical behavior of cell which prepares executable scaled experiments for design of drug delivery systems by nanoparticles as a practical application. in this paper, for first time, based on the new finite-similitude scaling theory, scaled framework is developed for perforation behavior analysis of Red Blood Cell (RBCs) membrane subjected to impact loading by conducting experimental tests on large-scale models even made out of different materials such as rubbers with different hyperplastic constitutive laws.   Abaqus finite element software is employed to test the effectiveness of the finite-similitude theory. Validating numerical experiments under impact loading by experimental results, shows that behavior of red blood cell with Yeoh law can be predicted with good accuracy.  Among 8 selected trial material, number 7 with Mooney-Rivlin law is the best selection to scale RBC with error less than 5%. Also, if 10% error in result will be accepted, then number 2 with Yeoh law is the good choice for RBC scaling. Based on results, number 8 with Ogden law is the worst for RBC scaling.