A new scheme for imposing a minimum length scale in topology optimization

A new scheme for imposing a minimum length scale in topology optimization is presented. It guarantees the existence of an optimal design for a large class of topology optimization problems of practical interest. It is formulated as one constraint that is computationally cheap and for which sensitivities are also cheap to compute. The constraint value is ideally zero, but it can be relaxed to a positive value. The effect of the method is illustrated in topology optimization for minimum compliance and design of compliant mechanisms. Notably, the method produces compliant mechanisms with distributed flexibility, something that has previously been difficult to obtain using topology optimization for the design of compliant mechanisms. The term ‘MOLE method’ is suggested for the method. Copyright © 2003 John Wiley & Sons, Ltd.     

Topology optimization of hinge-free compliant mechanisms using level set methods

A new level set-based multi-objective optimization method is proposed for topological design of hinge-free compliant mechanisms. Firstly, the flexibility requirement of compliant mechanisms is formulated by using the mutual energy. Two types of mean compliance are developed to meet the stiffness requirement. Secondly, several objective functions are developed for designing hinge-free compliant mechanisms based on the weighting method in which a new scheme for determining weighting factors is used. Thirdly, several numerical examples are performed to demonstrate the validity of the proposed method. It is shown that the resulting compliant mechanism configurations contain only strip-like members which are suitable for generating distributed compliance and decreasing stress concentration.     

Compliant mechanism design with non-linear materials using topology optimization

In this paper, compliant mechanism design with non-linear materials using topology optimization is presented. A general displacement functional with non-linear material model is used in the topology optimization formulation. Sensitivity analysis of this displacement functional is derived from the adjoint method. Optimal compliant mechanism examples for maximizing the mechanical advantage are presented and the effect of non-linear material on the optimal design are considered.     

The effect of inter-factory linkage flexibility on inventories and backlogs in integrated process industries

A discussion on the multi-dimensional character of flexibility is presented and an approach is suggested to define and measure flexibility. Petri nets are used as a design representation of an FMS for the purpose of comparing different systems on a flexibility basis thus unveiling their desirable flexibility properties.     

Multi-physics design and optimization of flexible matrix composite driveshafts

Flexible matrix composites (FMCs) consist of low modulus elastomers such as polyurethanes which are reinforced with high-stiffness continuous fibers such as carbon. This fiber–resin system is more compliant compared to typical rigid matrix composites and hence allows for higher design flexibility. Continuous, single-piece FMC driveshafts can be used for helicopter applications. In the present investigation, an optimization tool using a genetic algorithm approach is developed to determine the best combination of stacking sequence, number of plies and number of in-span bearings for a minimum-weight, spinning, misaligned FMC helicopter driveshaft. In order to gain more insight into designing driveshafts, various loading scenarios are analyzed and the effect of misalignment of the shaft is investigated. This is the first time that a self-heating analysis of a driveshaft with frequency- and temperature-dependent material properties is incorporated within a design optimization model.     

Inverse finite element method for large‐displacement beams

A finite element model for the inverse analysis of large‐displacement beams in the elastic range is presented. The model permits determining the initial shape of a beam such that it attains the given design shape under the effect of service loads. This formulation has immediate applications in various fields such as compliant mechanism design where flexible links can be modeled as large‐displacement beams. Numerical tests for validation purposes are given, together with two design applications of flexible mechanisms with distributed compliance: a flexible gripper and a flexible S‐type clutch. Copyright © 2010 John Wiley & Sons, Ltd.     

Triple-resonant transducers

A detailed analysis is presented of two novel multiple-resonant transducers which produce a wider transmit response than that of a conventional Tonpilz-type transducer. These multi-resonant transducers are Tonpilz-type longitudinal vibrators that produce three coupled resonances and are referred to as triple-resonant transducers (TRTs). One of these designs is a mechanical series arrangement of a tail mass, piezoelectric ceramic stack, central mass, compliant spring, second central mass, second compliant spring, and a piston-radiating head mass. The other TRT design is a mechanical series arrangement of a tail mass, piezoelectric ceramic stack, central mass, compliant spring, and head mass with a quarter-wave matching layer of poly(methyl methacrylate) on the head mass. Several prototype transducer element designs were fabricated that demonstrated proof-of-concept.     

Ensuring Flexibility in the CIM Environment

ABSTRACT

Implementation and design of computer-integrated manufacturing (CIM) systems are complex and detailed processes. They require meticulous planning and prior analysis to ensure that a viable and profitable system is developed. One of the most fundamental factors to be considered for a CIM system is the flexibility of the proposed system. Many authors have addressed the issue of system level flexibility and in a variety of ways. Two new categories of flexibility, programming and communications flexibility, are presented along with illustrations of the relative importance of the different categories of flexibility in various situations. A comparison and summary of the relationships between the work of previous authors and this paper is included.     

Synthesis methodology of a compliant exact long dwell mechanism using elastica theory

Compliant exact dwell mechanism design and its synthesis methodology are investigated. This class of compliant dwell mechanisms incorporates the buckling motion of an initially straight fixed–fixed flexible member as a follower. The initially straight flexible beam is modeled using nonlinear exact inextensible Elastica theory. The output response of a compliant long dwell mechanism is obtained using design charts for a mechanism that complies with the desired dwell time, maximum rise height and mechanism space requirements.     

A Multi-Criteria Topology Optimization for Systematic Design of Compliant Mechanisms

This paper attempts to present a new multi-criteria topological optimization methodology for the systematic design of compliant micro-mechanisms. Instead of employing only the strain energy (SE) or the functional specifications such as mechanical efficiency (ME), in this study an alternative formulation representing multiple design requirements is included in the optimization to describe the performance of compliant mechanisms. In most conventional designs, SE is used to only measure the design requirement from the point of view of structures, while ME is usually applied to describe the mechanical performance of mechanisms. However, the design of a compliant mechanism is required to comprehensively consider both the structural and mechanical performance quantities. Displacement, material usage and dynamic response are imposed as three external constraints to narrow the searching domain. In doing so, the multi-criteria optimization problem involving the SE and ME can reasonably embody the mechanical structural characteristics of compliant mechanisms. A sequential convex programming, the method of moving asymptotes (MMA), is applied to solve the topological optimization problem, which can not only ensure numerical accuracy but also both the monotonous and non-monotonous structural behaviors. SIMP model (solid isotropic material with penalization) is used to indicate the dependence of elastic modulus upon regularized element densities. Several typical numerical examples are used to demonstrate the effectiveness of the proposed methodology, and the prototype of a resulting mechanism has also been manufactured to validate the design of the compliant mechanism.     

Buckling dynamics of imperfect Elastica subject to various loading conditions

Buckling dynamics of a pinned-pinned flexible imperfect beam attached to a sliding mass is investigated using nonlinear Elastica theory. Initially straight flexible buckling beam having pinned end boundary conditions loaded at one of its end with curved imperfection is considered. Large deflection analysis of flexible beam is studied using nonlinear Elastica theory. Imperfection analysis of the flexible beam is investigated considering the imperfection as an initial curvature. The governing differential equations are expressed in terms of nonlinear functions that are typical of flexible beams, generally leading to highly implicit relationships involving elliptic integrals and functions. Dynamic simulation of the flexible beam is studied using numerical simulation procedures with various types of loading (step, ramp, and sinusoidal) assuming this member buckles in its first mode. Dynamic response of the imperfect buckling Elastica has been obtained by using numerical Runge-Kutta methods. Load deflection characteristics of flexible beams are presented in polynomial curve fits. The polynomial curve fits obtained from nonlinear inextensible exact beam theory may then be used as the nonlinear lumped system stiffness. The buckling Elastica may find applications in compliant mechanism design. The motivation behind this research is not only to present the dynamic behavior of the buckling beam considering the magnitude of the imperfection but also to provide a tool to design new types of compliant mechanisms. Original compliant mechanism designs are presented demonstrating where the buckling dynamics of imperfect Elastica or flexible curved beams might be needed in mechanism design and synthesis.     

Using cognitive work analysis to explore system flexibility

The presented work describes a structured approach for identifying flexible working practices in complex socio-technical systems; further, it presents a framework for the elicitation of design changes capable of increasing system adaptability. The proposed approach uses the first three phases of the cognitive work analysis framework: work domain analysis; control task analysis; and strategies analysis. Functions are extracted from an abstraction hierarchy; these are then explored in a number of different situations using a contextual activity template. These functions are then explored in greater detail with the strategies analysis phase. The contextual activity template is used to identify situations where functions are unable to perform; in order to increase the flexibility of the system, new strategies are then proposed and represented in strategies analyses flow diagrams. To communicate the approach, it is introduced using the familiar, domestic domain of an ‘Apple iPod’. The paper presents a structured approach based upon cognitive work analysis for exploring system flexibility. The case study presented, an Apple iPod, shows how design changes to the system can be informed by this approach. This paper takes an existing approach and clarifies the link between analysis and design.     

Rapid simulation of impacts on composite sandwich panels inducing barely visible damage

The finite element based design tool, CODAC, has been developed for efficiently simulating the impact behavior of sandwich structures consisting of two composite face sheets and a compliant core. To achieve a rapid and accurate stress analysis, three-layered finite shell elements are used. A number of macromechanical damage models are implemented to model damage onset and damage growth.

The transient impact analysis is assessed via an experimental impact test program on honeycomb sandwich panels. Force–time histories and damage sizes are examined. The influence of distinct damage and degradation models on the impact response is analyzed. Results show that the presented time-efficient methodology is capable of accurately modeling core failure behavior and rapidly simulating low-velocity impacts which induce barely visible damage.     

A new level set method for topology optimization of distributed compliant mechanisms

A new level set method for topology optimization of distributed compliant mechanism is presented in this study. By taking two types of mean compliance into consideration, several new objective functions are developed and built in the conventional level set method to avoid generating the de facto hinges in the created mechanisms. Aimed at eliminating the costly reinitialization procedure during the evolution of the level set function, an accelerated level set evolution algorithm is developed by adding an extra energy function, which can force the level set function to close to a signed distance function during the evolution. Two widely studied numerical examples in topology optimization of compliant mechanisms are studied to demonstrate the effectiveness of the proposed method. Copyright © 2012 John Wiley & Sons, Ltd.     

A level set method for shape and topology optimization of large‐displacement compliant mechanisms

A parameterization level set method is presented for structural shape and topology optimization of compliant mechanisms involving large displacements. A level set model is established mathematically as the Hamilton–Jacobi equation to capture the motion of the free boundary of a continuum structure. The structural design boundary is thus described implicitly as the zero level set of a level set scalar function of higher dimension. The radial basis function with compact support is then applied to interpolate the level set function, leading to a relaxation and separation of the temporal and spatial discretizations related to the original partial differential equation. In doing so, the more difficult shape and topology optimization problem is now fully parameterized into a relatively easier size optimization of generalized expansion coefficients. As a result, the optimization is changed into a numerical process of implementing a series of motions of the implicit level set function via an existing efficient convex programming method. With the concept of the shape derivative, the geometrical non‐linearity is included in the rigorous design sensitivity analysis to appropriately capture the large displacements of compliant mechanisms. Several numerical benchmark examples illustrate the effectiveness of the present level set method, in particular, its capability of generating new holes inside the material domain. The proposed method not only retains the favorable features of the implicit free boundary representation but also overcomes several unfavorable numerical considerations relevant to the explicit scheme, the reinitialization procedure, and the velocity extension algorithm in the conventional level set method. Copyright © 2008 John Wiley & Sons, Ltd.     

Relaxing high-dimensional constraints in the direct solution space method for early phase development

Early phase distributed system design can be accomplished using solution spaces that provide an interval of permissible values for each functional parameter. The feasibility property guarantees fulfillment of all design requirements for all possible realizations. Flexibility denotes the size measure of the intervals, with higher flexibility benefiting the design process. Two methods are available for solution space identification. The direct method solves a computationally cheap optimization problem. The indirect method employs a sampling approach that requires a relaxation of the feasibility property through re-formulation as a chance constraint. Even for high probabilities of fulfillment, \(P>0.99\), this results in substantial increases in flexibility, which offsets the risk of infeasibility. This work implements the chance constraint formulation into the direct method for linear constraints by showing that its problem statement can be understood as a linear robust optimization problem. Approximations of chance constraints from the literature are transferred into the context of solution spaces. From this, we derive a theoretical value for the safety parameter \(\varOmega\). A further modification is presented for use cases, where some intervals are already predetermined. A problem from vehicle safety is used to compare the modified direct and indirect methods and discuss suitable choices of \(\varOmega\). We find that the modified direct method is able to identify solution spaces with similar flexibility, while maintaining its cost advantage.     

面向大规模定制的虚拟设计研究

综述了大规模定制的范围经济性和面向大规模定制的基本设计方法，并提出了一个虚拟设计框架，该框架改变了传统的设计模式，利用先进的设计方法学和仿真支撑技术为产品开发提供了最大柔性和敏捷性。同时，它提供了一个多学科合作的设计环境，用户直接参与进设计循环中。最后，结合新型剑杆织机的开发，展示了一个能够支持新产品快速成功开发的虚拟设计环境。     

一款低频Janus-Helmholtz顺性腔换能器

Janus-Helmholtz(JH)顺性腔换能器是在传统的JH换能器腔内加入顺性管堆,通过调节占空比实现谐振频率及带宽的控制。在"顺性腔"的设计中采用了压缩系数为3.2×10-8 Pa-1的顺性管,通过ATILA仿真软件对Janus-Helmholtz顺性腔换能器在不同占空比下的声发射性能进行预计且与测试结果进行对比,发现在占空比为12%时,可在300~700 Hz的频带内实现190 d B的声源级,且可实现600 Hz以下频段全向辐射。     

A note on: On controlling the controllable lead time component in the integrated inventory models

This paper develops an analytical approach to quantifying manufacturing system flexibility (MSF). Measures of flexibility, namely, producibility, processivity, transferability and introducibility are developed based on a state-transition formalism, the reachability graph. The uncertainty in system operating conditions is specified in terms of certain disturbing factors, external and internal to the system, which impinge on system performance. The contribution of each factor to the value of a given type of flexibility is estimated using the analytic hierarchy process (AHP). The individual flexibility measures are thus combined to give a measure of MSF under a given operating environment. A Petri net model is used to construct the reachability graphs used in flexibility measurement. Uses of the proposed measures at the design and operational analysis stages of FMS are presented