Redundancy Allocation Optimization for Multistate Systems With Failure Interactions Using Semi-Markov Process
Adding redundancy is a widely used method in engineering to improve the system reliability. How to add redundancy, (i.e., to meet the reliability requirement with the minimum cost), is an interesting topic in system design. Traditionally, the optimal redundancy allocation scheme is obtained under two simplified assumptions, i.e., binary states of each component and no failure dependency between components. The binary-state assumption assumes that each component and the entire system can only have two states: fully operational and completely failed. The failure independency assumption assumes no failure interaction between components, i.e., one component failure will not affect the failure process of other components. Although those two assumptions can simplify the analysis, they may lead to inaccurate reliability predictions and thus results in doubtful and misleading redundancy allocation scheme which in fact may not meet the reliability requirement. This work proposes a method to obtain the optimal redundancy allocation scheme by using the Semi-Markov process and optimization techniques without those two simplified assumptions. The target system is a type of commonly-seen system having multiple states and failure interactions. The target system contains a main subsystem providing the required output and an auxiliary subsystem helping the main subsystem function normally, such as the rotating subsystem and the lubricating subsystem, the computer mother board and the fan, and so on. A case study of a shipboard power electronic cabinet demonstrates the applicability of the proposed approach.
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Kazuko Fuchi, Philip R. Buskohl, Giorgio Bazzan, Michael F. Durstock, Gregory W. Reich, Richard A. Vaia and James J. Joo
J. Mech. Des 137(9), 091401; doi: 10.1115/1.4030876
Origami structures morph between 2D and 3D configurations, and their efficient shape reconfigurations show potential for many engineering applications. However, the enormity of the design space and the complex relationship between origami-based geometries and engineering metrics place a severe limitation on design strategies based on intuition. This work proposes a physics-based origami design method using topology optimization that determines an optimal crease pattern for a folding by adding or removing folds based on a design metric. Optimization techniques and mechanical analysis are also co-utilized to identify an action origami building block and determine the optimal network connectivity between multiple actuators.
Sen Lin Longyu Zhao James K. Guest Timothy P. Weihs Zhenyu Liu
J. Mech. Des 137(8), 081402 (Aug 01, 2015); doi: 10.1115/1.4030297
Fixed geometry fluid diodes are devices that allow fluid to flow in one direction but inhibit flow in the reverse direction. Unlike valves, which have moving parts, fixed geometry fluid diodes achieve this effect by using the inertia of the fluid to guide flow into tortuous paths in the reverse flow case. Topology optimization is used in this paper to design diodes of various aspect ratios, including an example to reproduce the Tesla valve, a fixed geometry diode originally designed and patented by Nicola Tesla. The objective function is to maximize diodicity, measured as the ratio of pressure drop in the reverse flow case to the forward flow case, and a gradient-based optimizer is used to solve the topology optimization formulation. An optimized design was 3D printed and experimentally tested to verify diode-like behavior.
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Systematic Design Optimization of the Metamaterial Shear Beam of a Nonpneumatic Wheel for Low Rolling Resistance
Authors: Christopher Czech, Paolo Guarneri, Niranjan Thyagaraja, Georges Fadel
J. Mech. Des.. 2015;137(4):041404-041404-9. doi:10.1115/1.4029518
Design requirements for engineered components are growing more complex and specific, with heavier emphases on efficiencies like weight and energy considerations. Often times, these considerations require the component to be constructed from materials that do not occur naturally. Instead, a metamaterial, one with properties not exhibited naturally by any known material, may be tailored to achieve the design requirements. Some examples include metamaterials with large strength to weight ratios, low energy loss moduli, or specified optical properties. However, designing these materials in a systematic manner has remained an engineering challenge, as linking the overall design requirements to the material requirements (a multiscale design problem) is not an elementary task. In this research, a method to design a shear layer metamaterial for a non-pneumatic wheel using a two-level optimization approach is presented. The design requirements for the shear layer metamaterial are determined in a top-level optimization, and mesostructures with the desired properties are designed using novel topology optimization methods at the material structure level. Inspired by honeycomb structures, a half-period staggered unit cell connectivity was utilized to change the inherent symmetry between unit cell layers. One geometry found using this staggered connectivity, the auxetic honeycomb (pictured below), is shown to be an optimum to the minimum volume topology optimization problem for materials subjected to pure shear boundary conditions. This is the first evidence supporting this structure as an optimum of a structural problem in shear deformation.
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In joint replacement surgery, Patient Specific Surgical Guides (PSSGs) are used for accurate alignment of implant components. PSSGs are designed preoperatively to have a geometric fit with the patient’s bone such that the incorporated guidance for drilling or cutting is instantly aligned (a). It is essential that the position of the PSSG is maintained, and hence, the influence of the location and direction of the pushing force should be minimal. The extent that the pushing force may vary is what we refer to as docking robustness. In this article, we present a docking robustness framework comprising quantitative measures and graphical tool. The contact efficiency and guide efficiency measures can successively be used to find appropriate contact locations and an appropriate location for the application surface. Robustness maps (b) graphically depict for a chosen contact set the allowed variation in the surgeons pushing force. An optimization of the PSSG dimensions for the distal femur shows that twelve contacts already result in a relatively high contact efficiency. The re-located application surface S2 (b) increases the guide efficiency as it is located in brighter parts of the robustness map.
This section includes brief descriptions of articles soon to be or recently published by the Journal of Mechanical Design. These featured articles highlight recent research developments and emerging trends in mechanical design. For Abstracts and Full Articles please see ASME's Digital Collection.