IRANIAN JOURNAL OF SCIENCE AND TECHNOLOGY TRANSACTION B- ENGINEERING
Year:2003 | Volume:27 | Issue:B3|Papers Count:14

This paper investigates the effect of structural damping on the chaotic behavior of nonlinear panels in supersonic flow. The nonlinear governing equations, based on Von Karman’s large deflection of isotropic flat plates, are considered with structural damping. A first order piston theory is utilized for aerodynamic panel loadings. The governing equation includes the effect of constant axial loading in the panel middle surface plus a static pressure differential. The Galerkin approach is used to transform the nonlinear governing equations into a set of nonlinear ordinary differential equations. The resulting system of equations is solved through a numerical integration scheme. Static and dynamic bifurcation boundaries as well as panel limit cycles are determined for various structural damping coefficients. Chaotic analysis is performed using several criteria, results indicate that structural damping highly influences the panel stability boundary and limit cycle amplitude as well as the domain of the chaotic region.

In this paper we present our modeling approach for studying the role of the shoulder muscles in the bowling (swinging) of a ten pin bowling ball and the moments, stresses and forces that are induced on the shoulder. Three experiments are conducted to obtain data on the positional relationship of the muscles in the shoulder, and the external moments from the ball and arm are compared to the moments that the muscles can create. Then, a mathematical model for a six degree of freedom in the human arm is developed for a given dynamic trajectory. The mathematical model of human arm kinematics is based on the experimental evaluation of selective movements in the sagittal, frontal, and horizontal plane. The developed model contains six revolute degrees of freedom for positioning the wrist and represents a redundant mechanism where each joint is dedicated to a specific task.

Feedback linearization is a systematic approach often applied to the dynamic model of mobile robots and ground vehicles. It transforms a nonlinear system into a (fully or partially) linear system, and then uses the well-known linear design techniques to complete the control design. This transformation divides the model dynamics into two parts: a) the external dynamics which is to be transformed into a linear system and b) the internal dynamics which becomes unobservable by the transformation. Nonholonomic systems have an internal dynamics with a dimension equal to the number of independent nonholonomic constraints. One of the main subjects in the vehicle’s motion control is trajectory tracking. To stabilize the vehicle around a trajectory, both external and internal dynamics of the system must be stable. Since feedback linearization only treats the external dynamics of the system, internal dynamics has to be examined separately. In this paper, the internal dynamics of a four-wheel vehicle is investigated and it’s stability is analyzed. It is shown that the internal dynamics of the vehicle is stable when the vehicle is moving forward.

Local bifurcation of the attitudinal dynamics of the torque free rigid body motion is discussed. Hamiltonian formalism is used to express equations of motion. To simplify attitudinal dynamics of a rigid body, six dimensional state space is reduced to a two dimensional one by Andoyer canonical transformation. Non-dimensional parameters of the system are defined and the effects of change in these parameters on the structural stability and the equilibrium points of the reduced space are discussed. The Poincaré surface of the section in the reduced phase space and heteroclinic orbits are derived. Based on the non-dimensional parameters of the system, two and three dimensional bifurcation diagrams are achieved. This study shows that various types of structural stability can be achieved for torque free rigid body attitudinal dynamics by changing relative magnitudes of the principal moments of inertia. These results are helpful when the chaotic behavior of a rigid body under perturbation is considered.

An analysis of rib-stiffened columns is made in the present study, employing the energy method with three sinusoidal terms in the assumed deflection function. A total of 325 design curves are determined and plotted showing the critical load for different lengths, widths and thickness of the stiffening ribs. The curves show an increasing trend in buckling load-carrying capacity up to 250 percent. Minimizing the material volume of the compound columns, the optimal portions of the design curves are determined. Using "NETS", a neural network has been designed which consists of two hidden layers with 15 nodes in each layer. 640 optimum input-output pairs have been selected and used to train the network. The network was successfully trained with a maximum error of 0.0075 and RMS error of 0.0014. The response of the network to new data entries (numerical values not used in the training process) of the variable parameters is examined and compared to those recorded in the design curves . Maximum error for new data entries is less than 4 %.

This paper presents a practical implementation of explicit self-tuning control to a hydraulic robot for trajectory tracking. The proposed control strategy is simple, however, adapts itself to system variations such as load changes, noise and disturbances and it may be suitable for non-minimum phase control systems. Computational complexity of self-tuning control is not a limitation anymore because of increased computing power of computers even for high speed applications. This situation makes the self-tuning control an important alternative to PID control, which is the most widely used controller in industrial processes. Extensive experiments conducted on hydraulic robots to demonstrate and verify the control performance of the proposed self-tuning control in comparison with the traditionally designed, PID control.

Pipes with non-circular cross sections made by reshaping processes are widely used as structural elements in almost all industries. Despite a long history of the process, because of the complicated deformation behavior of pipes during reshaping, the design procedures for forming rolls and pass-schedules mainly rely on experience-based knowledge. Thus, the fundamental and systematic approaches to the reshaping technology and the guidance for the design of rolls and processes have been required. In order to solve these serious problems, a new design method has been developed to determine ideal roll profiles and roll arrangement for the process. It is based on the simulation technique to analyze twodimensional elasto-plastic deformations of the cross sections of pipes. Furthermore, it is shown that there are good agreements between the results of the design method and the experimental results for the square and the oval pipes.

An analytical investigation of the buckling problem of composite shells with radius variation is presented. Different types of loading such as compressive and external can be applied. Flügge’s shell equations, modified for anisotropic laminated materials are used. The modal forms are assumed to have axial dependency in the form of simple Fourier series. To implement the present method to find the buckling load of composite tubes with different boundary conditions the derivatives of Fourier series are legitimized using Stocke’s transformation. The mathematical model presented includes the radius variations at the cross section of tubes in the form of functions including the imperfection factor. The analytical procedure developed in this work for finding the buckling loads yields an exact equation which is simpler than the exact method adopted by other research workers. The results are presented in the form of buckling diagrams and figures showing the mode shapes.

GMDH-type neural networks are used for the modelling of explosive welding process of plates. The aim of such modelling is to show how the geometric characteristics of the bonding interface such as amplitude and wave length change with the variation of important parameters involved in the explosive welding of plates, namely, standoff distance, mass of the explosive per unit weight of flyer plate, flyer plate thickness, and parent plate thickness. It is also demonstrated that Singular Value Decomposition (SVD) can be effectively used to find the vector of coefficients of quadratic sub-expressions embodied in such GMDH-type networks. Such application of SVD will highly improve the performance of GMDH-type networks to model the very complex process of explosive welding of plates.

Propagation of shock waves over a cylinder, sphere and projectile are numerically simulated. Time dependent full Reynolds averaged Navier-Stokes equations are solved numerically with Roe’s scheme. For cylinder and sphere, the diffraction pattern, loci of triple points and shape of diffraction shocks are obtained and compared with experimental results. It is shown that good agreement is obtained, and Roe’s method is capable of predicting those flows. Interaction of a moving shock wave with flow around a SOCBT projectile is simulated numerically and flow features, pressure coefficient distribution on the projectile surfaces and the time histories of the drag force are obtained. Results show that as the moving shock wave passes through the projectile, the flow field and aerodynamic forces are changed dramatically. The time history of the drag force shows that it decreases and even becomes negative while shock wave passes the projectile.

The purpose of this paper is to develop analytical-numerical solutions to work out the longitudinal temperature changes of flow in the passages of a plate heat exchanger. The solution for a general variation in U, except for some special cases, becomes so complicated as to be impractical. In this regard uniform heat flux, constant U, linearity between U and T and linearity between U and ؤ T will be studied. The results are then compared with the established experimental data available in the literature using similar plate dimensions and flow details.

High efficiency, environmental friendliness, low operation and maintenance costs, and the lowest possible impact on the environment are some of the requirements of sustainable energy production. In the selection of new power generation systems, a number of steps have to be taken into account in order to meet these requirements. Here, the first law analysis has been implemented and investigated, followed by a combination of the first and second law analyses (exergy analysis), and thermoeconomics. Finally, an exergetic life cycle assessment (ELCA) has been carried out for two different power cycles to show how the irreversibility of a process is coupled to environmental issues. The study involves two cycles, a two-pressure level combined cycle and a humid cycle, to demonstrate the usefulness of the three methods mentioned above in a pre-purchase process. The main goal of this study is to point out the advantages and the difficulties related to the implementation of each and every method, and to identify the target groups that can gain knowledge and information by using these methods. Since the operators of power plants often do not have access to detailed information about component materials, characteristics, etc., of the power cycle, assumptions have to be made when comparing different cycle configurations with each other. These limited types of data and information have also been used here to create a plausible scenario of how different pre-purchase methods can differ from each other

In this investigation, the instantaneous unsteady heat transfer within a pneumatically driven rapid compression-expansion machine that offers simple, wellcontrolled and known boundary conditions was studied. Values of the instantaneous apparent overall heat flux from the cylinder gas to the wall surfaces were calculated using a thermodynamics analysis of the experimentally measured pressure and volume temporal development. Corresponding heat flux values were also calculated through the application of a zero-dimensional k-ε turbulence model. In the zero-dimensional k-ε turbulence model (ZDM) the characteristic velocity is a contribution of turbulence kinetic energy, mean kinetic energy of charged air into cylinder and piston motion for the calculation of Reynolds, Nusselt and Prandtl numbers. Comparison of the zero-dimensional k-ε turbulence model prediction with experimental data shows good agreement for all compression ratios (8.4~24.3).

Streamline curvature is still a powerful method in predicting the performance of turbomachines whose results will be more realistic if a good estimation of losses and deviation is incorporated in the calculations. The present study improves the result of a single stage transonic compressor by incorporating shock and profile losses using previous correlations. Deviation is estimated on the basis of several correlations and results are then compared with the available experimental data. Looking at the effect of the above mentioned methods on outlet flow angle, meridian Mach number, pressure ratio and temperature, it is possible to recommend that one of the methods or a suitable combination of these methods be incorporated in the solution procedure.