MODARES TECHNICAL AND ENGINEERING
Year:2005 | Volume:- | Issue:20|Papers Count:13

Mutual interactions-between aerodynamic and structural forces cause aeroelasticity that is very important in aircraft wings. In this paper, instability of a wing in dynamic situation that is called flutter is considered for a composite wing in subsonic flows. The "Strip Theory" approach is used to calculate the aerodynamic forces along the wing. For this reason, displacements along the wing and flutter speed are determined using the "Assumed Mode Method ". In this method, the displacement along the wing is assumed by definite boundary conditions. The stored potential and kinetic energy in the wing, as well as the generalized aerodynamic forces and moments on the wing, are determined. By employing Lagrange’s equations, the wing motion is formulated. A Computer program has been developed to calculate the speed of the wing instability, the effects of the elastic axis and the center of gravity has been investigated on the stability of the wing. The flutter speed is calculated for a certain wing, which the data is available, and a suitable elastic axis has been determined for a specified center of gravity.

In this study, flow in a solid fuel ramjet is numerically simulated to calculate the regression rate of solid fuel. In spite of simple geometry of a solid fuel ramjet combustion chamber, due to presence of phenomena including formation of a recirculation zone, turbulent jet, reattachment zone, turbulence boundary layer, combustion, and evaporation of solid fuel in the boundary, a complex flow is encountered. Investigations reveal that the most important reason for discrepancy between the numerical results and experimental data is the weakness of turbulence models. For the first time, a new low Reynolds number k-ε model is used in solid fuel ramjet which is relevant to the flow behind a step. In present work, a new algebraic model for turbulent heat diffusion coefficient is proposed based on the modification of the constant Prt model. This modification is made using an empirical correlation between maximum Nusselt number and entrance Reynolds number. The model includes both the simplicity of Prt=0.9 assumption and the accuracy of the two-equation heat transfer model. Numerical results show better agreement to the experimental data compared with the previous works.

Active and semi active suspension systems provide good ride comfort for passengers and appropriate road holding for vehicle simultaneously. Model Reference Adaptive Control (MRAC) system is one of the control approaches of such systems. As there is no study on control of two degrees of freedom model of a quarter car active suspension system with MRAC based on a selected model reference through present reference models, in this paper, an ideal reference model is selected, and then a MRAC system is designed. The design procedure begins by selection of a control law and then an appropriate Lyapunov function is considered and the parameters of control law are adapted in such a way that the error signal between output of active system and reference model converges to zero. Simulation results show good improvement of active suspension performance over the traditional passive suspension systems.

In this work, modeling, of the complete rotor system including elastic shaft with distributed mass, rigid disks and effects of oil film in bearings and also flexibility of suspension are considered. A variety of innovations including modeling a complete rotor system with damping effects, solving vibration equations with damping terms, considering nonlinear effects and ultimately solving nonlinear equations are presented. This paper is a relatively complete work in modeling and vibration analysis of rotor considering gyroscopic effect, damping, dependency of stiffness and damping coefficients on frequency, non-linearity and solving vibration equations including these parameters. A MATLAB computer program is written based on the linear theory using finite element method. In this method four element types including shaft, disk, bearing and suspension are defined. The responses of system are obtained based on the linear theory and then, the program applies nonlinear effects and analyzes them. Finally linear and nonlinear responses of the system are compared with each other and also with the results of other papers.

In this paper, fabrication process, theoretical, control approach and evaluation of Robotic pruning machine with force control system are described. Force control system keep contact force between cutting tool and tree branch in certain limit. Operating process is such that the cutting force is measured by a load cell and the motion speed is changed by certain rate of contact force in software. In estimation of this machine motion speed of manipulator arms relation to loading rate and correction of kinematics equation, test of machine beside tree and the effect of sensitivity coefficient of the force control system on power and time consumption are investigated.

A physical modeling of mixing phenomenon for polymer/wood-fiber composites in twin extruder, is presented. An analytical method for obtaining length of mixing zone least-length is proposed. Experimental verification was conducted using a modeled twin-extruder with transparent polycarbonate cylinder and polyamide screws. Mixing phenomenon was visualized and photographed with various mixing zone lengths. Visual observations were shown to be in good agreement with the analytical results.

This paper presents a new theoretical analysis of normal penetration of projectiles into metallic targets. In this model, by assuming the plugging model of failure for target and by using conservation of mass, momentum and energy in front of the plastic stress wave in projectile and target, and Mie-Grunisen equation of state, the axial stress in front of plastic stress wave is determined. The penetration process considering deformation of projectile and plug, is divided into several stages. For each stage, the governing equations of motion are derived. The theory is also extended to oblique penetration. The results of this model are compared with the experimental results and the numerical results of LS-Dyna, software, showing good agreement.

If ground vibration caused by blasting exceeded from the specific amount, it will damaged the structures and rock mass which are adjacent to blasting site. There fore ground vibration should be under control. One of the methods for controlling the ground vibration is using peak particle velocity criteria. In underground power station complex of Masjed Soliman’s dam the structures of phase2 have been excavated by drilling and blasting in presence of the phasl structures. Hence, ground vibration which is the result of blasting, should be limited to such a degree that no damage caused to adjacent structures. For this reason more than 300 blasting have been registered by geophones. By using these data in terms of particle velocity criteria, Formulas for all areas of underground power station complex have been calculated. Then with regard to these formulas, blasting patterns for reduce of damage were redesigned.