Journal of Aerospace Science and Technology
Volume:4 Issue: 3, Autumn 2007

The purpose of this paper is concerned with the mathematical model development issues, necessary for a better prediction of dynamic responses of articulated rotor helicopters. The methodology is laid out based on mathematical model development for an articulated rotor helicopters, using the theories of aeroelastisity, finite element and the time domain compressible unsteady aerodynamics. The helicopter is represented by a set of coupled nonlinear partial differential equations for the main rotor within nonlinear first order ordinary differential equations representation, describing the dynamics of the rest of the helicopter. The complexity of the formulation imposes the use of numerical solution techniques for dynamic response calculations. The validation is performed by comparing simulated responses oppose to flight test data for a known configuration. The results show improvement in dynamic response prediction of both on-axis and cross-coupled responses of helicopter to pilot inputs

In this paper a general formulation for finding the maximum allowable dynamic load (MADL) of flexible link mobile manipulators is presented. The main constraints used for the algorithm presented are the actuator torque capacity and the limited error bound for the end-effector during motion on the given trajectory. The precision constraint is taken into account with two boundary lines in plane which are equally offset due to the given end-effector trajectory, while a speed-torque characteristics curve of a typical DC motor is used for applying the actuator constraint. Finite element method (FEM) is utilized for deriving the kinematic and dynamic equations which considers the full nonlinear dynamic of mobile manipulator. In order to verify the effectiveness of the presented algorithm, two simulation studies considering a flexible two-link planar manipulator mounted on a mobile base are presented and the results are discussed.

Engineers have a range of methods to estimate the fatigue life under multiaxial conditions. Each of these predictive methods is generally subjected to restrictions, related to the inherent simplified assumptions. The objective of this paper is to evaluate the validity of commonly used multiaxial fatigue criteria for different multiaxial loading conditions. The best criterion is identified through comparative analysis. The assessment is based on the experimental research findings of the SAE notched shaft, which is used as a benchmark [1]. The relative performance of three of existing multiaxial fatigue theories based on the strain criteria and the critical plane approaches are investigated. There is not any fixed strain life criterion that can predict the fatigue life best for different loading. Among all the critical plane models considered, Fatemi and Socie model [2] gives best fatigue life prediction for both multiaxial in phase and 90° out of phase loading cases.

In this paper, classical thin shell theory is used to analyze vibration and critical speed of simply supported rotating orthotropic cylindrical shell. The effects of centrifugal and Coriolis forces due to the rotation are considered in the present for mulation.. In addition, axial load is applied on cylinder as a ratio of critical buckling load. Finally the effects of orthotropic ratio, material and geometry of the shell as well as axial loads on bifurcation of natural frequency are investigated.

Thin-walled tube bending is still to be considered a new and advanced technique. The process has been adopted into several industries such as aero and automotive. This process may produce a wrinkling, bulking and tearing phenomenon if the process parameters are inappropriate, especially for tubes with large diameter and thin wall thickness. Push bending process is one of the methods used for bending tubular parts. It is a suitable technique to make considerably small bending radii. The method is performed using a rigid die to guide and form the tube into the required shape while the tube is pushed by a punch. A pressure media is used inside the tube to prevent its wrinkling and buckling. Hyper-elastic (rubber) materials are commonly used as the pressure media. This paper presents the pressure distribution within the tube, before and during the push bending process. Theoretical result of pressure distributions is compared with the finite element simulations. Effects of rubber properties on the tube quality are also studied. Finally optimum working conditions of process is predicted by the finite element method and is compared with previously published experimental observations.