Key Engineering Materials Vols. 321-323

Abstract: In a mechanical system that has periodically repeated subcomponents, premature failures or malfunctions often occur. Due to slight irregularities of parameters of periodic systems, maximal frequency responses of a few subcomponents become often significantly larger than those of other subcomponents. These phenomena, called frequency response localization, need to be comprehended for reliable designs of the periodic systems. In the present study, the effects of parameter distribution patterns on the frequency response localization are investigated. Probabilistic results of the frequency response localization characteristics with two distinct parameter distribution patterns are exhibited.

Abstract: The operation error of a robot that occurs inevitably due to the manufacturing tolerance needs to be controlled within a certain range to achieve proper performance of the robot system. The reduction of manufacturing tolerance, however, increases the manufacturing cost in return. Therefore, design engineers try to solve the problem of maximizing the tolerance to reduce the manufacturing cost while minimizing the operation error to satisfy the performance requirement. In the present study, a revolute joint model considering uncertainties due to joint clearance is employed to perform a reliability analysis of the robot manipulator operation. The reliability analysis procedure employs single Monte-Carlo simulation and a statistical relation between the tolerance and the operation error. Significant reduction of computing time can be achieved with the proposed method. The present method is especially effective if sensitivity information is hard to be obtained for the analysis.

Abstract: As a number of aged fossil power plants recently increased, the precise life assessment of critical equipments gets to be important more than ever. Despite of infrequent likelihood of failure, the equipments in high pressure and temperature operation condition have traditionally been considered as critical because of huge consequence of the equipments and hence life assessment of fossil power plant has been focused on all of the severe operated equipments for past decades. Nowadays, with Risk-Based Inspection technology being developed rapidly, most of the power plant utilities get a chance to reduce the scope of the inspection and test and to extend the interval for the life assessment. This paper provides methodology based on Risk-Based Inspection technology to optimize the life assessment work scope and interval and also demonstrates the enhanced life assessment procedure including risk assessment of equipments.

Abstract: Zirconium alloys are used for many applications in nuclear components, such as the pressure tube material in a pressurized heavy water reactor, nuclear fuel cladding, etc. One of the problems during the operation of a nuclear reactor is the degradation of the zirconium alloys, which is due to an increase of the hydrogen content in the zirconium alloy. Therefore a non-destructive determination of the hydrogen concentration in zirconium alloy is one of the important issues that need to be addressed. The resonant ultrasound spectroscopy (RUS) technique is evaluated for a characterization of the hydrogen concentration in Zr-2.5Nb alloy. Referring to the terminal solid solubility for dissolution (TSSD) of Zr-2.5Nb alloy, the plot of the mechanical damping coefficient (Q-1) versus the temperature or the deviation of the resonant frequency for the temperature (df/dT) versus the temperature was correlated for the hydrogen concentration in Zr-2.5Nb alloy. It was found that the temperature at an abrupt change of the slope can be correlated with the hydrogen concentration of the Zr-2.5Nb alloy.

Abstract: This paper is focused on a probabilistic design of the honeycomb structure which is a constituent unit of satellite. The design is considering launching and space environments by kriging metamodel. The proposed methodology using the kriging metamodel is conducted by stochastic step-moving method (SSMM) as the criterion of a sequential approximate optimization to satisfy the global optimum value based on the local optimum value. Also, Design of Experiments (DOE) is used to reduce computation costs. The honeycomb structure is analyzed for reliability. For the optimal design, constraints are taken for natural frequency and several stresses that should be considered on the satellite platform in launching situations. Thermal effects of space environments and wrinkling are also considered since a structural sandwich is often poor at carrying in-plane compressive loads and may be inflicted with instability and thermal effect.

Abstract: In-plane characteristics of a single degree of freedom frictional system with a compressed spring are considered. The compressed spring is vertically installed to the mass moving horizontally along the friction interface. The compressed spring can introduce a nonlinear negative stiffness into the in-plane motion. The resulting system has a multiple equilibrium points; an unstable point at the center and two stable points on either side. It is shown that two stable equilibrium points can be separated far apart by increasing the compression ratio and the stiffness of the spring. The friction system is often characterized by stick and slip motions that cause unfavorable effects such as wear, noise, and chatter etc. It is demonstrated that increasing the compression ratio and the stiffness of the spring results in decreasing the size of the stick regions.

Abstract: Evaluation of the ride comfort for railway vehicles can be divided into two classes; the long-term evaluation of ride comfort and the momentary evaluation of ride comfort. In the present paper, the ride comfort of railway vehicles are investigated for high speed trains in Korea. The long-term ride comfort has been analyzed by a statistical method and the momentary ride comfort has been analyzed by using the longitudinal acceleration, the jerk and the stationary lateral acceleration.

Abstract: The Korean High Speed Train (KHST) has been tested on the Kyongbu high speed line and the Honam conventional line since 2002. A data acquisition system was developed to test and prove the dynamic performance of the KHST, and the system has been found to be very efficient in acquiring multi-channel data from accelerometers located all over the train. Also presented in this paper is an analysis procedure which is simple and efficient in analyzing the acceleration data acquired during the on-line test of the KHST. The understanding of system vibration mode for a railway vehicle is essential to evaluate the characteristics of a dynamic system and to diagnose the dynamic problems of the vehicle system during tests and operations. Methods based on homogeneous linear systems are not realistic because real systems have nonlinear characteristics and are strongly dependent on environmental conditions. In this paper an efficient method of vibration analysis has been proposed and applied for the KHST to evaluate its vibration mode characteristics. The results show that this method is suitable to estimate the system vibration modes of the KHST.

Abstract: Recently, the finite element absolute nodal coordinate formulation(ANCF) was developed for large deformation analysis of flexible bodies in multi-body dynamics. This formulation is based on finite element procedures and the general continuum mechanics theory to represent elastic forces. In this paper, a computational method, which predicts the dynamic and structural properties of a very flexible beam in a multibody system, is presented based on Euler-Bernoulli beam theory and ANCF. In order to consider the dynamic interaction between a continuous large deformable beam and a rigid multibody system, a combined system equations of motion was derived by adopting absolute nodal coordinates and rigid body coordinates. The efficiency and reliability of the computational results are verified by comparison with a commercial program. These methods can be applied for predicting the dynamic stress and fatigue life of the wire harness used in a robot system. The process of predicting the fatigue life using the proposed method in this paper may be applied to continuous mechanical parts of various dynamic systems.

Abstract: An Over Head Transportation (OHT) vehicle is used to transport large loads in a factory more efficiently. To maximize productivity, the speed and load requirement for the OHT vehicle is continually increasing. This may create a repetitive dynamic load and thus cause fatigue failure in related components. In this paper, a computer aided engineering (CAE) method is proposed for fatigue life prediction in the early design stage using multibody dynamic analysis and the linear damage rule. The process of predicting the fatigue life using the proposed computer models in this paper may be applied to structures of various mechanical systems.