Volume 2: Automotive Systems; Bioengineering and Biomedical Technology; Computational Mechanics; Controls; Dynamical Systems
Latest Publications


TOTAL DOCUMENTS

100
(FIVE YEARS 0)

H-INDEX

4
(FIVE YEARS 0)

Published By ASMEDC

9780791848364

Author(s):  
Daniel Rabinovich ◽  
Dan Givoli ◽  
Shmuel Vigdergauz

A computational framework is developed for the detection of flaws in flexible structures. The framework is based on posing the detection problem as an inverse problem, which requires the solution of many forward problems. Each forward problem is associated with a known flaw; an appropriate cost functional evaluates the quality of each candidate flaw based on the solution of the corresponding forward problem. On the higher level, the inverse problem is solved by a global optimization algorithm. The performance of the computational framework is evaluated by considering the detectability of various types of flaws. In the present context detectability is defined by introducing a measure of the distance between the sought flaw and trial flaws in the space of the parameters characterizing the configuration of the flaw. The framework is applied to crack detection in flat membranes subjected to time-harmonic and transient excitations. The detectability of cracks is compared for these two cases.


Author(s):  
Raimond Grimberg ◽  
Adriana Savin ◽  
Shiu C. Chan ◽  
Rozina Steigmann ◽  
Lalita Udpa ◽  
...  

Prosthetic heart valves of the Bjork-Shiley Convexo-Concave (BSCC) type have long been used extensively in implants; however, there have been reports of cases where one component of the valves failed, leading to the demise of the patient. This paper presents a new method for noninvasive electromagnetic evaluation for this type of valve, using an eddy current transducer with orthogonal coils. In vitro experiments have shown that discontinuities of outlet strut with depths equal or larger than 0.4mm can be detected with a probability of detection (POD) of 86.4%, and in the case of discontinuities with depth equal or larger than 0.6mm with POD of 97%.


Author(s):  
Bohdan M. Diveyev ◽  
Zinovij A. Stotsko

The main aim of this paper is improved dynamic vibration absorbers design with taking into account complex rotating machines dynamic The is considered for the complex vibroexitated constructions. Methods of decomposition and the numerical schemes synthesis are considered on the basis of new methods of modal methods. Development of of complicated machines and buildings in view of their interaction with system of dynamic vibration absorbers is under discussion.


Author(s):  
M. Perl

The equivalent thermal load was previously shown to be the only feasible method by which the residual stresses due to autofrettage and its redistribution, as a result of cracking, can be implemented in a finite element analysis, of a fully or partially autofrettaged thick-walled cylindrical pressure vessel. The present analysis involves developing a similar methodology for treating an autofrettaged thick-walled spherical pressure vessel. A general procedure for evaluating the equivalent temperature loading for simulating an arbitrary, analytical or numerical, spherosymmetric autofrettage residual stress field in a spherical pressure vessel is developed. Once presented, the algorithm is applied to two distinct cases. In the first case, an analytical expression for the equivalent thermal loading is obtained for the ideal autofrettage stress field in a spherical shell. In the second case, the algorithm is applied to the discrete numerical values of a realistic autofrettage residual stress field incorporating the Bauschinger effect. As a result, a discrete equivalent temperature field is obtained. Furthermore, a finite element analysis is performed for each of the above cases, applying the respective temperature field to the spherical vessel. The induced stress fields are evaluated for each case and then compared to the original stress. The finite element results prove that the proposed procedure yields equivalent temperature fields that in turn simulate very accurately the residual stress fields for both the ideal and the realistic autofrettage cases.


Author(s):  
David H. Bassir ◽  
WeiHong Zhang ◽  
Jose´ L. Zapico

In this article, complexities related to the multicriteria (multiobjective) optimization of laminated composite structures subjected to technological constraints we will be presented. So, various technological constraints will be presented and a strategy of handling each constraint (in order to use the multiobjective optimization tools based on genetic algorithms) will be also introduced.


Author(s):  
U. Tasch ◽  
P. Moubarak ◽  
W. Tang ◽  
L. Zhu ◽  
R. M. Lovering ◽  
...  

We describe an instrument that assesses two features of the gait of rats, spatiotemporal paw movement variables (SPMV) and ground reaction forces (GRF) in the vertical direction. The GRF and the SPMV variables are measured electrically by eight single axis load-cells that support two floor plates. We can derive four gait parameters from the SPMV and GRF measured by the instrument: the stride length of individual limbs, the maximum and mean vertical ground forces, and the intensity of the vibrations created by each paw during locomotion. Measurements of the vertical GRF show errors of less than 3.5%; errors in the determination of the paw positions, used to derive stride lengths, are less than 9 mm. Here we report the stride length, maximum and mean GRF values, and the intensity of the floor vibrations of healthy adult mature rats. Our instrument is capable of evaluating changes in these gait parameters in rat models of injury and disease.


Author(s):  
S. Golan ◽  
D. Elata ◽  
U. Dinnar

The mechanical properties of compliant materials such as biological tissues and biocompatible soft polymers are essential in medical research and engineering applications. These properties are often determined using techniques that require costly instrumentation (e.g. pull test machines). Alternative and more accessible methods can significantly aid the characterization process. The bulge test determines a material elastic modulus by analyzing the pressure-deflection response of thin samples made of this material. The technique has been extensively employed in the characterization of metals and semiconductors (modulus ∼ 100 GPa). By employing plate rather than membrane mechanics, the present study extends bulge testing to characterize materials with a modulus that is five orders of magnitude lower (∼ 1 MPa). The novel method is demonstrated analytically using plate theory, numerically using finite element modeling and experimentally by successfully applying it to polydimethylsiloxane (modulus ∼ 1.33 MPa). The introduced technique does not require costly equipment, is simple to implement and presents an appealing alternative to current characterization approaches.


Author(s):  
Oliviero Giannini ◽  
Aldo Sestieri

The complex envelope vectorization (CEV) is a recent method that has been successfully applied to structural and internal acoustic problems. Unlike other methods proposed in the last two decades to solve high frequency problems, CEV is not an energy method, although it shares with all the other techniques a variable transformation of the field variable. By such transformation involving a Hilbert transform, CEV allows the representation of a fast oscillating signal through a set of low oscillating signals. Thanks to such transformation it is possible to solve a high frequency dynamic problem at a computational cost that is lower than that required by finite elements. In fact, by using finite elements, a high frequency problem usually implies large matrices. On the contrary the CEV formulation is obtained by solving a set of linear problems of highly reduced dimensions. Although it was proved that CEV is in general a successful procedure, it was shown that it is particularly appropriate when the modes of the system have a negligible role on the solution. Moreover, the numerical advantage of the CEV formulation is much more pronounced when full matrices are used. Thus, for the first time it is applied to a boundary element formulation (BEM). Both external and internal acoustic fields of increasing complexity are considered: the internal and external field generated by a pulsating sphere; the external field of a forced box, where the velocity field is determined by finite elements; a set of 4 plates that form an open cavity. The results are compared with those obtained by a BEM procedure (SYSNOISE), highlighting the good quality of the proposed approach. An estimate of the computational advantage is also provided. Finally it is worthwhile to point out that the reduction of the BE matrices allows for an in-core solution even for large problems.


Author(s):  
Eyal Buks

Nanomechanical resonators having small mass, high resonance frequency and low damping rate are widely employed as mass detectors. We study the performance of such a detector when the resonator is driven into a region of nonlinear oscillations [1]. We predict theoretically that the mass sensitivity of the device in this region may exceed the upper bound imposed by thermo-mechanical noise upon the sensitivity when operating in the linear region. On the other hand, we find that the high mass sensitivity is accompanied by a slow response of the system to a change in the mass. For experimental demonstration we employ homodyne detection (see Fig. 1) for readout of the output signal of an optical displacement detector, which monitors the motion of a doubly clamped nanomechanical resonator made of Pd-Au [2, 3]. The nanomechanical resonator is driven into the region of nonlinear oscillations (see Fig. 2) and the region of bistability is identified (see Fig. 3). As expected theoretically [1] we find that when operating close to the edge of the bistability region the device exhibits strong intermodulation amplification [2] (see Fig. 3). Moreover, strong noise squeezing in the output signal of the homodyne detector is observed in this region [3] (see Fig. 4). An alternative mass detection scheme, in which the resonator is driven into a stochastic resonance, will also be discussed [4].


Author(s):  
Vittorio Belotti ◽  
Roberto P. Razzoli ◽  
Rinaldo C. Michelini

The growth sustainability requires dramatic changes to lower the natural resources consumption and the surroundings pollution, by recovery/remediation processes. The EU policy aims at the extended producers/suppliers responsibility, with effective charges on the products allowed to be put on the market, used and called-back, in view of the properly small impact and transparent lifecycle acknowledgement. This leads to «extensions» in designing the new offers with integrated monitoring and service functions. The design for the lifecycle eco-effectiveness is accomplishment, better qualifying the far-seeing companies according to the EU eco-policy. The idea is to reach the duty visibility, by the extended plug-and-play concept, based on series of integrated design options, assigning the structural and functional modules, for the operation monitoring, the reliability assessment and the impact appraisal. This instrumental setting includes intangible information/communication aids, to confer ambient intelligence abilities. This way, the on-process visibility is assured, and exploited for on-duty servicing and end-of-life processing. The example case chosen deals with the critical situation of the parts manufactured in plastics, which are deemed to represent most relevant portion in the cars to come. The following recovery options are possible: - the reuse of the reconditioned items, according to suitably assessed life-extension opportunities; - the recycling of the warn-out components, with the regeneration and reusing of the materials; - the thermal recovery of residual stuffs, within careful handling and pollution-safe warnings; - the reduction to registered ASR, automobile shredding residue, within the EU directives limits. The on-board information system includes, as innovative feature, the resort to identifying tags or labels, to be read and written through wireless links. The technology exploits cheap and compact supports, allowing the labelling of the component, from production, to lifecycle, with an identifying code. The RFID, Radio Frequency Identification Device, is privileged, as ideal means for the component traceability and the history, use modes/styles and cumulated issues storing.


Sign in / Sign up

Export Citation Format

Share Document