Applied Mechanics and Materials Vols. 110-116

Abstract: A computational study performed for a canard guided spin stabilized projectile using finite volume TVD schemes is described in this paper. Computational Fluid Dynamics (CFD) modeling and analysis of the spinning projectile with fixed canard are conducted to determine the lateral-directional aerodynamic coefficients at three supersonic speeds and various angles of attack. The analyses provide a detailed understanding of the effects of canard with different circumferential position on lateral-directional aerodynamic coefficients, and the results show that side force coefficient and yaw moment coefficient vary periodically with the circumferential position angles of canard.

Abstract: Over the past decade, a lot of attention has been paid to plasma actuators because they are useful tools for flow control. Previous successes with plasma actuators include drag and noise reductions from a circular cylinder, one of representative bluff bodies, mainly through separation delay. However, to the best of authors’ knowledge, no attempt has been made to examine its capability to control square cylinder wake with fixed separation points. The purpose of this study is to numerically investigate whether or not the square cylinder wake can be controlled by means of plasma actuators. In particular, a linear plasma synthetic jet actuator is adopted and attached to the rear side of the cylinder. In this study, we use an immersed boundary method combined with an empirical plasma model for plasma-based flow control. The present method is second order accurate in time and space. Results show that the wake behind the square cylinder can be controlled effectively when the plasma-induced force is strong enough. With the plasma actuator on, the mean drag is reduced and the Karman vortex shedding is alleviated because the induced jet increases the base pressure and prevents the separating shear layers from interacting with each other.

Abstract: In order to solve the problem of complex faults of radar and bottleneck problem in the expert system, a fault diagnosis system based on hierarchical fault tree and a new method of knowledge storage for radar is developed. The radar faults are divided into subjective faults and objective faults through the analysis of knowledge for some types of radar faults. Aimed at objective faults, a knowledge base structure based on polychromatic sets theory is proposed, which solves the problems of inconvenient storage of fault tree and lacking unified mathematical model, puts forward the description method of knowledge base and realizes the intelligent knowledge reasoning. Aimed at subjective faults, a knowledge base structure based on the method of conventional production rule is founded. The system is verified using VC++6.0. The result shows that knowledge bases with different methods are built respectively according to different types of faults, which improves efficiency and accuracy of the location of faults, providing a new way on the research of radar fault diagnosis system.

Abstract: In this paper, we report an efficient numerical method to predict fluid flow behavior in a square and deep lid-driven cavities. The conventional continuity and momentum equations are transformed into stream-function and vorticity formulation to reduce the number of unknown spatial quantities. Numerical experiments were performed with different values of aspect ratio and Reynolds number to investigate the effect of these dimensionless parameters on the fluid flow behavior in the cavity. In the current study, we found that the dynamics and the structure of primary vortex are significantly affected by the Reynolds number and the aspect ratio of the cavity.

Abstract: A Fuzzy approach to backward movement control for trucks in a dynamic environment is presented in this paper. The approach is then extended and employed for conditions where Obstacles randomly are placed on the truck pathway. In the first case, Obstacles randomly are assumed to be fixed, while the second condition includes moving Obstacles randomly through which the truck should be directed toward the parking dock. The method is designed in a way to be used in conditions with infinite number of Obstacles randomly at arbitrary places. In any case, to find the parking dock, the truck movement must be adapted to that of Obstacles randomly. In the present paper, two separate fuzzy controllers are used for directing the truck: one for finding the target, and the other for avoiding the Obstacles randomly. While there is no Obstacles randomly around, the target finder controller is in use; and in the cases where the truck gets close to Obstacles randomly the Obstacles randomly avoider controller is activated. The proposed method is employed for parking a truck model through fixed and moving Obstacles randomly.

Abstract: An adaptive dynamic surface control scheme for actuator failures compensation in a class of nonlinear system is presented. Radial basis function neural networks (RBF NNs) are incorporated into our controller design, for approximating the nonlinearities around the known nominal model. The RBF NNs compensate the system dynamics uncertainties and disturbance induced by actuator failures. The closed-loop signals of the system are proven to be uniformly ultimately bounded (UUB) by Lyapunov analysis. The output tracking error is bounded within a residual set which can be made small by appropriately choosing the controller parameters. We show the effectiveness of our approach by simulating the longitudinal dynamics of a twin otter aircraft with half portion of the elevator failing at unknown value and time instant.

Abstract: This paper presents a new approach for tuning PID controller parameters in the control of nonlinear systems. The design is based on optimal tracking of step response for nonlinear systems. The problem is first restated as a non linear optimal control infinite horizon problem, then with a suitable change of variable, the time interval is transferred to the finite horizon [0 1). This change of variable, poses a time varying problem. This problem is then transferred to measure space, and it is shown that an optimal measure must be determined which is equivalent to a linear programming problem with infinite dimension. Then, using finite horizon approximations, the optimal control law as piece wise constant function is determined. Finally, PID controller parameters are Determined using the optimal control law. Simulations are provided to show the effectiveness of the proposed methodology.

Abstract: Numerical analysis by using Fluent® has been carried out to investigate the pressure drop of single phase flow in a 2 meter long of rifled tube and smooth tube which is placed horizontally. The rifled tube or also known as spiral internally ribbed tube that is used in this investigation has an outside diameter 45.0 mm and inside equivalent diameter1 of 33.1 mm while the smooth tube has an outside diameter 45.0 mm and inside diameter 34.1 mm. The working fluid that is used in this investigation is water. In this numerical analysis, realizable k-epsilon model has been chosen to solve the fully developed turbulence flow in both the tubes. The result of the pressure drop which is obtained from simulation shows that the pressure drop in rifled tube is about 1.69-1.77 times much higher than pressure drop in smooth tube. The high pressure drop in rifled tube comparing to smooth tube is due to the helical rib in the rifled tube which causes swirling effect near the wall. A correlation has been proposed for the single phase friction factor of the rifled tube.

Abstract: In order to detect and isolate orbiting satellite actuator faults, a decoupling parity space method was extended. The decoupling parity vector was obtained using this method by singular value decomposition. Sometimes this vector may not exist, then by singular value substitution or generalized Eigen value method was used for solving the optimal approximation. The vector can easily make satellite actuator fault detected and isolated. The simulation results showed the effectiveness of the proposed algorithm.

Abstract: In this paper, a new method for maneuvering target tracking (MTT) based on nonlinear input estimation (IE) is innovated and is employed for tracking of maneuvering targets. Proposed method augments the states and unknown inputs (maneuvers) in a higher order state space realization and estimates both of them simultaneously. The concurrent estimation of states and inputs eliminates the maneuver detection delay which is popular in the conventional IE methods. The proposed method has excellent performance for both maneuvering and non-maneuvering stages. Also, a model with highly nonlinear dynamics for maneuvering targets is given and is used in the numerical simulations to analyze the performance of the proposed maneuvering target tracking method. Furthermore the proposed method is compared with a conventional IE method and the simulation results show the effectiveness of the proposed method.