Nguyen Van Khang

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 .

A photonic band gap power-balanced asymmetrical T-junction

This paper aims to numerically propose a modern light power divider, operating at optical communication wavelength λ = 1.55 µm having unique feature on equality of two throughputs with asymmetrical structure. As a result, the divider has high potential for integrating into high-density optical circuits. Based on the analysis of dispersion and calculation of wave-vector k of electromagnetic fields, we produce a simple configuration, comprising two defect points, one defect line, and one reflex mirror, for equally dividing light power inside the asymmetrical divider. Simulated results by the Finite-Difference Time Domain (FDTD) method show a good performance with transmittance of over 98% for both TE and TM waves.

Optimal control of transverse vibration of Euler-Bernoulli beam with multiple dynamic vibration absorbers using Taguchi's method

Vibration absorbers are frequently used to suppress the excessive vibrations in structural systems. In this paper, an imposing nodes technique is applied for vibration suppression of Euler-Bernoulli beams subjected to forced harmonic excitations by means of multiple dynamic vibration absorbers. A procedure based on Taguchis method is proposed to determine the optimum absorber parameters to suppress the vibration amplitude of the beams. Numerical tests are performed to show the effectiveness of the proposed procedure.

Received signal strength prediction using Gaussian process

Gaussian Process (GP) is a statistical tool where observations are considered normally distributed random variables. The technique uses previous observations and their covariances or similarities to analyze and predict future data. In this paper, the Gaussian random variable is the Received Signal Strength (RSS) between one anchor and one mobile station. In the training phase, the positions of anchor and mobile station together with the RSS between them are known. GP will use these data to predict the RSS at any other location of the mobile station. Experiment is conducted to validate the algorithm.

Balancing Conditions of Planar and Spatial Mechanisms in the Algebraic Form

This chapter deals with an approach to formulate balancing conditions for the shaking force and shaking moment of planar mechanisms and spatial mechanisms. In the Mechanism Theory, every Mechanism has p moving members and a non-moving frame. According to tradition, a planar 8R-eightbar mechanism is a multibody system with 7 moving bodies.

A comparison study of some control methods for delta spatial parallel robot

A comparison between three methods applied to parallel robot control namely: computed torque controller, sliding mode control and sliding mode control using neural networks is presented in this paper. The simulation results show that PD control method is only accurate when model parameters are precisely identified. In case of uncertain parameters, sliding mode and neural network sliding mode control methods are applied instead. Three controllers are implemented in Matlab for simulation. The results show that the control quality is improved by using the neural network sliding mode control method in comparison with two others.

Flutter instability analysis of bridge decks using the step-by-step method

The branch switch characteristics of coupled flutter are clarified by use of Step-by-Step flutter analysis. In the case of typically coupled flutter instability, the branch switch characteristic from torsional branch to heaving branch is observed. In this paper, a revised step-by-step analysis method is proposed and a calculating program using MATLAB is built. Finally, the flutter behavior of the Cao Lanh Bridge, which is the long bridge in Vietnam, is studied from the point of view of flutter in two-degrees of freedom, namely torsional and heaving motion.

Parameter optimization of tuned mass damper for three-degree-of-freedom vibration systems

There are problems in mechanical, structural and aerospace engineering that can be formulated as Nonlinear Programming. In this paper, the problem of parameters optimization of tuned mass damper for three-degree-of-freedom vibration systems is investigated using sequential quadratic programming method. The objective is to minimize the extreme vibration amplitude of vibration models. It is shown that the constrained formulation, that includes lower and upper bounds on the updating parameters in the form of inequality constraints, is important for obtaining a correct updated model.

A novel multipath mitigation technique for gnss software receiver

In this paper, we introduce a novel multipath mitigation technique for binary offset carrier signals in global navigation satellite system (GNSS). The proposed technique is based on nonlinear operator called Teager - Kaiser Operator, which initially has been used to obtain energy of physical process. Moreover, the proposed multipath mitigation technique tries to reduce or remove the error caused by multipath signals. The technique was implemented in GNSS software receiver and improves the accuracy of code tracking loop in short -delayed multipath.