Nguyen Phong Dien

On the compression softening effect of prestressed beams

The main objective of the present paper is to study the transverse vibration of the prestressed beams. The differential equation of the transverse vibration of the Euler-Bernoulli beam is developed , in which the initial axial strain in every cross section of the beam is taken into account, so that the initial normal stress is not equal to zero. We have proposed some formulae to determine the natural frequencies of the prestressed beam. The forced transverse vibration of the beam with a moving external force has been considered. From this it follows compression softening effect of prestressed beams. A detailed comparison between the calculating results for the prestressed and the non-prestressed beam is also presented.

Balancing conditions of planar mechanisms with multi-degree of freedom

One of the problems of the complete shaking force and shaking moment balancing of planar mechanism consist of the deriving the so-called balancing conditions. These balancing conditions will be used to determine the size and location of counterweights or supplementary links which must be added to the initial mechanism, in order to eliminate the shaking force and the shaking moment caused by all moving links. The balancing methods for planar mechanisms with one degree-of-freedom can be found in a large number of publications [2-7] . However , the development on the balancing theory of planar mechanisms with multi-degree of freedom is still limited and the literature on this respect therefore is very little. In the paper, we presents a new method for deriving the general balancing conditions of planar mechanisms with multi-degree of freedom and an arbitrary structure. The developed algorithm is suitable for the application of the widely accessible computer algebra systems such as MAPLE. In the following example, the conditions for complete shaking force and shaking moment balancing of a planar five-bar linkage are given .

Complete shaking force and shaking moment balancing of spatial multibody systems with open kinematic chains

This paper deals with a solution for the problem of full shaking force and shaking moment balancing of spatial multi body systems with open kinematic chains. Firstly, the general conditions for complete dynamic balancing of spatial multibody systems are formulated. These include formulae for complete elimination of the resultant inertia force and inertia couple caused by all moving bodies. In the following example, the equations of complete shaking force and shaking moment balancing of a nine-bar direct drive manipulator are given.

Damping identification in multi-degree-of-freedom systems using the continuous wavelet transform

The identification of damping in multi-degree-of-freedom vibration systems is a well-known problem and appears to be of crucial interest. Compared to an estimation of the stiffness and mass, the damping coefficient or, alternatively, damping ratio is the most difficult quantity to determine. In this paper, the continuous wavelet transform based on the Morlet-wavelet function is used to identify the modal damping ratios of multi-degree-of-freedom vibration systems. A new wavelet-based method for the damping identification from measured free responses is presented. The proposed method was also tested by experiments on a steel beam.

Dynamic force analysis of a six-link planar mechanism under consideration of friction at the joints

The dynamic analysis of mechanisms with joints friction is complex since the frictional force depends nonlinearly on the resultant reactive force between the two mating surfaces of the joint. In this paper a non-iterative approximate method is used for determining the joint reaction forces and the driving torque of mechanisms is considered. By using the computing program MATLAB the dynamic forces of a six-link planar mechanism are cakulated with this method.

Parametric Vibration Analysis of Transmission Mechanisms Using Numerical Methods

Transmission mechanisms are frequently used in machines for power transmission, varia‐ tion of speed and/or working direction and conversion of rotary motion into reciprocating motion. At high speeds, the vibration of mechanisms causes wear, noise and transmission errors. The vibration problem of transmission mechanisms has been investigated for a long time, both theoretically and experimentally. In dynamic modelling, a transmission mecha‐ nism is usually modelled as a multibody system. The differential equations of motion of a multibody system that undergo large displacements and rotations are fully nonlinear in n generalized coordinates in vector of variable q [1–4].

Inverse kinematic and dynamic analysis of redundant measuring manipulator BKHN-MCX-04

This paper deals with the problem of inverse kinematics and dynamics of a measuring manipulator with kinematic redundancy which was designed and manufactured at Hanoi University of Technology for measuring the geometric tolerance of surfaces of machining components. A comparison between the calculation result and the experimental measurement is also presented.