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931.
In optimal topological design of structures one obtains the configuration of optimal structures when the design domain, the
displacement boundary conditions and the applied loads are specified. In the optimal structure one often notices a marked
difference between the main bearing structure and the load transfer zones. The latter are composed of relatively light elements
the exact nature of which is not always very distinct. The main purpose of this paper is to allow the main bearing part of
the structure to emerge. Moreover the actual location of the load along its line of action is not always a design requirement.
In order to include this relaxed condition regarding the loading position the concept of transmissible or sliding forces is
introduced in topological design of structures. A transmissible force is a force of given magnitude and direction which can
be applied at any point along the line of action of the force. The optimization formulation is similar to standard topological
design procedure in addition to the condition of transmissability of the forces. It is shown that this condition reduces to
an equal displacement constraint along the line of action of the forces. The method is illustrated by typical structural examples.
It is observed that this numerical method produces indeed crisp images of the main structural components, unblurred by the
secondary load transfer elements. It is also indicated that many results are often replicas of Prager structures which were
previously obtained by analytical methods.
Received March 3, 1999 相似文献
932.
Maximization of eigenvalues using topology optimization 总被引:24,自引:7,他引:17
N.L. Pedersen 《Structural and Multidisciplinary Optimization》2000,20(1):2-11
Topology optimization is used to optimize the eigenvalues of plates. The results are intended especially for MicroElectroMechanical Systems (MEMS) but can be seen as more general. The problem is not formulated as a case of reinforcement of an existing structure,
so there is a problem related to localized modes in low density areas. The topology optimization problem is formulated using
the SIMP method. Special attention is paid to a numerical method for removing localized eigenmodes in low density areas. The
method is applied to numerical examples of maximizing the first eigenfrequency. One example is a practical MEMS application;
a probe used in an Atomic Force Microscope (AFM). For the AFM probe the optimization is complicated by a constraint on the stiffness and constraints on higher
order eigenvalues.
Received June 10, 1999 相似文献
933.
H. Courteney 《Cognition, Technology & Work》2000,2(3):142-153
Cognitive engineering has developed enormously over the last fifteen years. Yet, despite many excellent research projects
and publications, its full potential has not been embraced into mainstream system design. This paper will examine the reasons
for this failure and argue that the problem is not simply inertia or lack of education. There are strong organisational influences
that cause resistance to this particular approach. The discipline itself has characteristics that make it fragile in the modern
corporate structure. In addition, the cognitive engineers themselves are not blameless in the equation. They appear to have
done exactly what they criticise the engineering community for doing: they have packaged their product in a manner that is
not ‘user friendly’ to its target population, not structured to suit its application, and not output in the format required.
Suggestions will be made to rectify the situation: a list of actions is proposed for practising cognitive engineers to make
their product more likely to enjoy widespread uptake. 相似文献
934.
Ride comfort optimization of a city bus is considered in this article, using stiffness and related damping of the power unit
mounts as design variables. The response of the bus, due to road irregularities, is calculated in the time domain by using
a finite element (FE) model describing the complete vehicle. The body of the bus is condensed, using a substructuring technique,
in order to reduce the simulation times. Operational deflection shapes (ODS) have been used to compare measured and calculated
vibrations and some corrections of the FE model have been done. The response, i.e. acceleration, at three locations in the
bus has been frequency-weighted according to the comfort standard ISO 2631:1997. The resulting root mean square (RMS) values
of these responses are then used in the objective functions in the optimization procedure. The computational results show
that it is possible to increase the ride comfort. However, the improvement of the ride comfort is probably too small to have
a substantial subjective impact on the passenger in the bus. The results show that the objective function, regarding the overall
ride comfort in the bus, has local optima.
Received October 10, 1999 相似文献
935.
U. Kirsch 《Structural and Multidisciplinary Optimization》2000,20(2):97-106
The Combined Approximations (CA) method developed recently, is an effective reanalysis approach providing high quality results.
In the solution process the terms of the binomial series, used as basis vectors, are first calculated by forward and back
substitutions. Utilizing a Gram–Schmidt orthogonalization procedure, a new set of uncoupled basis vectors is then generated
and normalized. Consequently, accurate results can be achieved by considering additional vectors, without modifying the calculations
that were already carried out. In previous studies, the CA method has been used to obtain efficiently accurate approximations
of the structural response in problems of linear reanalysis. It is shown in this paper that the method is most suitable for
a wide range of structural optimization problems including linear reanalysis, nonlinear reanalysis and eigenvalue reanalysis.
Some considerations related to the efficiency of the solution process and the accuracy of the results are discussed, and numerical
examples are demonstrated. It is shown that efficient and accurate approximations are achieved for very large changes in the
design.
Received July 7, 1999 相似文献
936.
一个设备管理系统的开发 总被引:2,自引:0,他引:2
黄崇斌 《计算机与数字工程》2000,28(1):39-40,45
本文针对学校设备管理的方式,开发了一个相应的设备管理软件系统,实现了设备管理计算机应用化,提高了管理质量、管理手段和管理效益,具有一定的实用价值。 相似文献
937.
C M Srivastava 《Bulletin of Materials Science》1984,6(2):273-281
An explanation has been offered for the mechanism of cooper pairing in thebcs theory of superconductivity on the basis of the relativistic Darwin interaction. The theory leads to an expression for critical
temperature which depends on a few atomic parameters. Calculated values ofT
c for elements and alloys are in good agreement with experiment. 相似文献
938.
Results of measurement of elastic modulii on As-Sb-Se glasses are reported and their composition dependence discussed. The
Young’s and the shear modulii lie in the range of 170–210 and 65–80 kb respectively. These values are typical of chalcogenide
glasses. For (As, Sb)40Se60 glasses, the modulii increase monotonically with increasing Sb2Se3 content. The observed composition dependence of the modulii for the As
x
Sb15Se85 −x
glasses is examined in terms of the chemically ordered structural units in the glasses. 相似文献
939.
940.
分析了溶解乙炔站火灾、爆炸的原因。根据“以防为主,以消力辅”的原则,在建筑设计中采取了一系列措施,以预防火灾、爆炸事故的发生,或使事故的损失和危害降至最低。 相似文献