Journal of Modeling and Simulation
Volume:53 Issue: 2, Summer-Autumn 2021

The Non Equal Channel Angular Pressing is one of the promising severe plastic deformation techniques which is used to produce ultra-fine grained and nanostructured materials. In the present investigation, the deformation behavior of Al1100 alloy during non-equal channel angular pressing was studied using two dimensional finite element simulation. Results showed when the ratio of the width of output to input channel is higher than 0.7, the corner gap is formed in the outer side of the intersecting area of two channels and the amount of plastic strain decreases in the lower part of the sample. In contrast, when the amount of this ratio is lower than 0.7, the dead metal zone is formed in the outer region of the intersecting area and the amount of strain is increased in the lower side of sample. It is also observed that the uniformity of the applied plastic strain is decreased with the formation of dead metal zone. In addition, the amount of damage factor is increased with increasing the ratio of the width of output to input channel and the region with higher amounts of damage factor is shifted from the lower side to the middle region of deformed sample. Finally, the results of FEM simulation showed that the amount of pressing force is decreased with increasing the width of output channel.

In this paper the Fourier transform combined with Adomian decomposition method (FTADM) is applied for solving the squeezed unsteady flow between parallel plates influenced by an inclined magnetic field. By moving these plates toward each other, the squeezing flow which is perpendicular to the plates is appeared. We assume that inclination varies from zero to ninety degrees. The momentum and energy equations are solved using the Adomian decomposition method with the combination of Fourier transform. The effect of the squeezed number, the angle of magnetic inclination, and the bottom plate suction/injection on the velocity and temperature are studied. The results show that by increasing the squeeze number, the intensity of the magnetic field and the magnetic inclined angle may increase the velocity near up and bottom plates in the longitudinal direction. However, the velocity near the midway of up and bottom plates may decrease. Moreover, our results show more accuracy and a smaller number of calculations when compared to the previous numerical simulations. This may be attributed to the fact that in the FTADM, one is able to incorporate all boundary conditions into the solution. However, in the semi-analytical methods, the solution may be accurate in a limited portion of the solution domain because only a part of boundary conditions is imposed into the solution.

Direct trajectory tracking of quadrotor system in the 3D space is not possible originating from the fact that control inputs are not independent in order to manipulate all flying degrees of freedom. The major concentration of the presented study is to describe the design procedure of a new intelligent algorithm for moving the quadrotor along a trajectory curve in space. The presented algorithm consists of two major parts where in the first one, the desired Euler angles and their associated rate are intelligently estimated by a fuzzy logic controller (FLC) working based on experimentally fuzzyfied rules. The second part of the proposed algorithm is the sliding mode control (SMC) designed for precise tracking of the commanded Euler angles while guaranteeing the robust stability of the quadrotor flight. For simulation of airborne performance of the quadrotor equipped with the proposed trajectory algorithm, a heavy-duty 6-DOF hardware-in-the-loop motion simulator (HILMS) by which all motions of a quadrotor either translational or rotational movements can be precisely evaluated, is designed and fabricated. The introduced HILMS employs one load cell for each arm of the quadrotor allowing the microcontroller to access to motors’ thrust during operation. In this way, while the translational motion is restricted, the position of the quadrotor can be computed along the governing mathematical motion equations. The empirical results confirm stability and trajectory tracking quality of the quadrotor by implementation of the proposed two-staged intelligent algorithm.

Several effects, such as optical nonlinear and thermal effects can change and reduce the output power of high-power fiber laser. In this paper, the photodarkening effect as an additional loss factor in the high-power fiber lasers was added in the rate equations, and the pump power variation relation was rewritten under the new conditions. By considering the complete form of the heat transfer function, including conductive and radiative heat transfer, the generated heat in the double clad fiber laser with the bidirectional pump scheme for different cavity geometry was determined. In this work, the photodarkening loss is added to the rate equations as power decreasing factor which is suggested as a stretched exponential function. The effects of core radius, the first clad size, input power, and output reflectors coefficient, and laser cavity length in the heat generation was calculated, also the contribution of each heat production factor including Quantum defect, photodarkening, and propagation loss was determined in heat generation. It was shown that the share of photodarkening heat caused from pump power and propagation loss affected from pump power in heat generation in the Double clad fiber laser is negligible. But the photodarkening heat affected from signal power is the main factor in heat generation at the central points of fiber laser.

Aimed at the nonlinear system identification of aeroelastic aircraft, the signal decomposition methods are required to extract the contributing natural and non-standard flight modes from flight test data, especially in the presence of flight noise. To this end, the SSA-EMD algorithm is proposed in this paper as a noise-tolerant signal decomposition method. The SSA-EMD is an improved Empirical Mode Decomposition (EMD) in which the sifting process is implemented by a direct approach to the signal trend extraction as a substitute for the envelope concept. In the proposed method, Singular Spectrum Analysis (SSA) is used for extraction of the signal trend in order to improve the mathematical foundation of the EMD. The proposed method is verified by decomposing some benchmark signals. Numerical results demonstrate that the proposed method outperforms the original one, especially in handling noisy signals. Then, a novel gray-box non-parametric system identification method is proposed for considering extracted flight mode in the aircraft dynamics. The performance of the SSA-EMD is studied for the aircraft system identification from real flight test data of an aeroelastic aircraft in the transonic regime. It can be observed that the average fitness values of 60.01% and 88.41% are obtained for the lateral flight parameters using the EMD and SSA-EMD, respectively. Also, the RMSE values of the flight parameters predicted by the EMD and SSA-EMD are 1.85 and 0.65, respectively. Therefore, the SSA-EMD can achieve better results than the original EMD for the aircraft system identification due to its noise rejection properties.

In this paper, a new hierarchical robust nonlinear control scheme is designed for the horizontal plane path following control problem of an underactuated autonomous underwater vehicle in the presence of the model uncertainties and fast time varying external disturbances. At first, the path following error model is established based on virtual guidance method. Then, the controller design starts at a kinematic level and evolves to a dynamic setting, building on the kinematic controller derived, using backstepping technique and a disturbance observer-based sliding mode control, respectively. A Lyapunov-based stability analysis proves that all the signals are ultimately bounded and path following errors converge to an arbitrarily small neighborhood of the origin. Following achievements are highlighted in this paper: (I) in order to simplify the control design, the derivative of the virtual control is estimated by the disturbance observer which avoids explosion of complexity without common filtering techniques; (II) the proposed controller can be easily implemented with no information of the bounds on the parameter uncertainties and external disturbances in a continuously changing environment. Furthermore, computer simulations have shown that the overall closed-loop system achieves a good path following performance which proves the feasibility and good robustness of the proposed control law.

Cloud computing provides a shared pool of resources in a distributed environment. It supports the features of utility-based computing. Task scheduling is a largely studied research topic in cloud computing, which targets utilizing cloud resources for tasks by considering the objectives specified in QoS. Optimal task scheduling is an NP-hard problem, which is time-consuming to solve with precise methods and depends on many factors such as completion time, latency, cost, energy consumption, throughput, and load balance on the machines. Therefore, using meta-heuristic algorithms is a good selection. This paper uses the Pathfinder optimization Algorithm (PFA) for the task scheduling problem; but when the dimension of a problem is extremely increased, the performance of this algorithm decreases. In the last iterations, fluctuation rate (A) and vibration vector (ε) converge to 0, and finding a new solution is impossible. We used fuzzy logic to overcome this shortcoming and named the new algorithm Fuzzy-PFA (FPFA). In this paper, makespan, energy consumption, throughput, tardiness, and degree of imbalance are considered as objective functions. Our goal is to minimize the makespan, energy consumption, tardiness, and degree of imbalance while maximizing throughput. Finally, different algorithms such as Firefly Algorithm (FA), Bat Algorithm (BA), Particle Swarm Optimization (PSO), and PFA are used for comparison. The experimental results indicate that the proposed scheduling algorithm can improve up to 34.2%, 16.2%, 15.9%, and 3.5% the objective function in comparison with FA, BA, PSO, and PFA, respectively.

Channel, as the medium for the propagation of electromagnetic waves, is one of the most important parts of a communication system. Being aware of how the channel affects the propagation waves is essential for the design, optimization, and performance analysis of a communication system. Along with conventional modeling schemes, in this paper, we present a novel propagation channel model. The proposed modeling strategy considers the color{red} 2-dimensional color{black} time-frequency response of the channel as an image. It models the distribution of these channel images using Deep Convolutional Generative Adversarial Networks (DCGANs). In addition, for the measurements with different user speeds, the user speed is considered as an auxiliary parameter for the model. StarGAN as an image-to-image translation technique is used to change the generated channel images with respect to the desired user speed. The performance of the proposed model is evaluated using a few existing evaluation metrics. Furthermore, color{red} as modeling the 2D time-frequency response is more general than the modeling of the channel only in time, the conventional metrics for evaluation of the channel models are not sufficient; color{black} therefore, a new metric is introduced in this paper. This metric is based on the Cepstral Distance Measure (CDM) between the mean autocorrelation of the generated samples and measurement data. Using this metric, the generated channels show significant statistical similarity to the measurement data.

This paper proposes a new method for accessing breast cancer risk called Hybrid High-order Interval Type-2 Fuzzy Cognitive Map (H-HIT2 FCM). In a simple Fuzzy Cognitive Map (FCM), the weights between nodes and activation functions are constant in each iteration. As an extension, in the high order FCM, each node has a different transformation function to make it more flexible. However, using FCM or high order FCM can not make a favorable response in uncertain situations. Applying type-2 fuzzy to obtain the weights of FCM, the resulted method will have much better responses in such uncertain situations. An H-HIT2 FCM is proposed in this work, assessing breast cancer risk in three modes of optimistic, realistic, and pessimistic. The proposed method has three levels. At the first level, patient profile, family history, and inherited factors are tested by high order FCM. At the second level, by examining the mass characteristics obtained from the mammograms, the disease risk is achieved by high-order interval type-2 FCM in three modes of optimistic, realistic, and pessimistic. The exact position of the tumor is obtained in the third level. Finally, a support vector machine predicts an overall breast cancer risk. Overall, by comparison with the existing methods, the accuracy of the results is desirable. The three-mode assessment will help the patients, and their physician run the best treatment. The proposed method is successfully tested on a real radiology dataset, and the corresponding results are reported.

This paper aims to identify a gray-box non-parametric model for the airplane nonlinear aerodynamics throughout high angle of attack maneuvers using the Adaptive Neuro-Fuzzy Inference System (ANFIS). The gray-box modeling is employed in this paper in which the force and moments are predicted rather than the flight parameters. Flight test data of a large-scale unpowered model of a fighter airplane is modeled by the ANFIS, and the results are compared with the traditional multi-layer feed forward Artificial Neural Network (ANN). The employed gray-box identification method considers both the nonlinearity and the longitudinal-lateral/directional coupling effects. The control commands and the flight conditions are the inputs to the system identification block while the force and moment coefficients are the targets. The optimal values for the ANFIS parameters are adjusted by the hybrid learning algorithm in order to minimize the Mean Squared Error (MSE) between the best estimated and the target force and moment coefficients; while the ANN is trained by several learning algorithms. The precision of the model is checked during the training and test phases for a single flight condition. Afterwards, the generalization of the model is checked for flight conditions dissimilar from the training one. The results indicate that the ANN has moderate precision in the test phase while the ANFIS has excellent precision in that phase. Furthermore, based on the results, the ANN predictions cannot follow the flight data in flight conditions dissimilar from the training ones while the ANFIS seems quite robust in those conditions.

While most balanced multiband band-pass-filters have some remarkable properties, they provide a trade-off between design goals. Also, few of them have provided a structure capable of satisfactory harmonic suppression. Stepped Impedance resonators (SIR) are famous and widely utilized to relocate or cancel high order harmonics, and they provide advantages when used in designing bandpass filters. They have shown benefits in achieving common mode (CM) suppression along with compact size and wide stopband. To design a tri-band balanced bandpass filter, a Ring-SIR structure is used as the main building block of the filter, the SIR is first analyzed and the design formulas are presented and based on that, design graphs are extracted. Using the graphs, it is possible to design a tri-band filter and have the ability to control its pass-bands’ center frequencies. To achieve high pass-band selectivity, coupled feeding configuration is chosen and external quality factor is analyzed and respective graphs are presented. Results show more than 20dB isolation with pass-bands centering at 1.7, 2.55, and 4.48 GHz, and insertion losses of 1.44, 1.77 and 2.11 dB respectively. The corresponding FBWs are 3.95%, 4.10% and 1.56% respectively. Great out-of-band performance is achieved with a wide stop-band stretching from 4.8 to 8.76 GHz. The CM rejection for three pass-bands are better than 12.9, 18.9 and 43.5dB, respectively.