Stiffness Of Spring Elements Research Articles

Finite Element Model refinement of powertrain mount brackets for estimating natural frequencies

Natural frequencies of powertrain mount brackets have great influences on NVH (Noise, Vibration, Harshness) performances of a Powertrain Mount System. Usually, large relative error between the measured- and the estimated natural frequencies using finite element analysis existed. In this paper, a methodology to refine the mount bracket finite element model is proposed based on global response surface method and optimization methods. The material parameters uncertainty and the constraint boundary (bolt joint) are taken into account for model update parameters, since they are the main factors affecting the accuracy of the calculated natural frequencies of bracket. The material parameters are optimized by minimizing the errors between calculated and measured un-constrained natural frequencies of the mount bracket. The bolt joint are modeled using the equivalent stiffness of spring element that are optimized by minimizing the deviations between the calculated and measured constrained natural frequencies of the bracket. Another mount bracket is used to obtain natural frequencies calculated using the refined finite element model and measured, and the comparisons of the calculated versus the measured natural frequencies shown that the refined finite element model of mount bracket with identified material parameters and boundary stiffness values exhibits high prediction precision for estimating natural frequencies of the brackets. This indicates that the proposed finite element model refinement methodology for mount bracket is effective and can help the NVH engineers to design larger natural frequencies of mount brackets.

Modal Damping Ratio and Optimal Elastic Moduli of Human Body Segments for Anthropometric Vibratory Model of Standing Subjects.

The present study aims to accurately estimate inertial, physical, and dynamic parameters of human body vibratory model consistent with physical structure of the human body that also replicates its dynamic response. A 13 degree-of-freedom (DOF) lumped parameter model for standing person subjected to support excitation is established. Model parameters are determined from anthropometric measurements, uniform mass density, elastic modulus of individual body segments, and modal damping ratios. Elastic moduli of ellipsoidal body segments are initially estimated by comparing stiffness of spring elements, calculated from a detailed scheme, and values available in literature for same. These values are further optimized by minimizing difference between theoretically calculated platform-to-head transmissibility ratio (TR) and experimental measurements. Modal damping ratios are estimated from experimental transmissibility response using two dominant peaks in the frequency range of 0-25 Hz. From comparison between dynamic response determined form modal analysis and experimental results, a set of elastic moduli for different segments of human body and a novel scheme to determine modal damping ratios from TR plots, are established. Acceptable match between transmissibility values calculated from the vibratory model and experimental measurements for 50th percentile U.S. male, except at very low frequencies, establishes the human body model developed. Also, reasonable agreement obtained between theoretical response curve and experimental response envelop for average Indian male, affirms the technique used for constructing vibratory model of a standing person. Present work attempts to develop effective technique for constructing subject specific damped vibratory model based on its physical measurements.

Modeling and Experimental Validation for Hammer-Driven Type Penetrators under Horizontal Condition

This paper proposed a method used to analyze the motion of hammer-driven type penetrators and built a testbed for validating the result of structure optimization of the penetrator in deep space exploration. This method gave a clear understanding of the working principle of the penetrator. The penetrator mainly comprises five components: hammer element, suppressor element, housing element, brake spring, and force spring. Based on the structure of the penetrator, the maximum forward movement of housing element was chosen as optimal object. In order to describe the working process clearly and properly, the working stroke was divided into three phases: unlocking phase, colliding phase, and penetrating phase. In each phase, the displacement and velocity of hammer element, suppressor element, and housing element were described with equation sets when numerically solved. Then, the corresponding parameters of the penetrator were obtained in the testbed with high-speed camera. At last, comparing the parameters obtained by theoretical analysis with that obtained by experiment test with high-speed camera, the perfect ratio of mass element (hammer element, suppressor element, and housing element) and perfect ratio of stiffness of spring element (brake spring and force spring) were obtained.

Structural behavior of cable anchorage zones in prestressed concrete cable-stayed bridge

Since the cable anchorage zone in a prestressed concrete cable-stayed bridge is subjected to a large amount of concentrated tendon force, it shows very complicated stress distributions which can cause serious local cracks. Accordingly, it is necessary to investigate the parameters affecting the stress distribution, such as the cable inclination, the position of the anchor plate, the modeling method, and three-dimensional effects. The tensile stress distribution in the anchorage zone is compared to the actual design condition by varing the stiffness of spring elements in the local modeling, and an appropriate position for the anchor plate is determined. The results provide elementary data for the stress state in the anchorage zones and encourage more efficient designs.Key words: finite element analysis, bursting stress, spalling stress, cable anchorage zone, cable-stayed bridge.