Accepted Manuscripts

Philip Odonkor and Kemper Lewis
J. Mech. Des   doi: 10.1115/1.4041629
The control of shared energy assets within building clusters has traditionally been confined to a discrete action space, owing in part to a computationally intractable decision space. In this work, we leverage the current state of the art in reinforcement learning for continuous control tasks, the Deep Deterministic Policy Gradient (DDPG) algorithm, towards addressing this limitation. The goals of this paper are twofold; (i) to design an efficient charged/discharged dispatch policy for a shared battery system within a building cluster, (ii) to address the continuous domain task of determining how much energy should be charged/discharged at each decision cycle. Experimentally, our results demonstrate an ability to exploit factors such as energy arbitrage, along with the continuous action space towards demand peak minimization. This approach is shown to be computationally tractable, achieving efficient results after only 5 hours of simulation. Additionally, the agent showed an ability to adapt to different building clusters, designing unique control strategies to address the energy demands of the unique clusters studied.
TOPICS: Design, Cycles, Batteries, Simulation, Algorithms
Daniel Hulse, Christopher Hoyle, Kai Goebel and Irem Tumer
J. Mech. Des   doi: 10.1115/1.4041571
Complex engineered systems can carry risk of high failure consequences, and it is desirable for complex engineered systems to be resilient such that they can avoid or quickly recover from faults. Ideally, this should be done at the early design stage where designers are most able to explore a large space of concepts. Previous work has shown that functional models can be used to predict fault propagation behavior and motivate design work. However little has been done to formally optimize or compare designs based on these predictions, partially because the effects of these models have not been quantified into an objective function. This work closes this gap by introducing the resilience-informed scenario cost sum (RISCS), a scoring function which integrates with a fault scenario-based simulation, to enable the optimization and evaluation of functional model resilience. The scoring function accomplishes this by quantifying the expected cost of a design's fault response using probability information, and combining this cost with design and operational costs such that it may be parameterized in terms of designer-specified resilient features. The scoring function is applied to a monopropellant system design-to the optimization of resilient features and the evaluation of possible design variants. Using RISCS as an objective for optimization, the algorithm generates the design solution which provides the optimal trade-off between design cost and risk. For concept selection, RISCS may be used to judge whether resilient concepts justify their design costs and to make direct comparisons between different model structures.
TOPICS: Design, Hazard analysis, Resilience, Optimization, Risk, Failure, Probability, Tradeoffs, Simulation, Algorithms
Yong Hu, David Talbot and Ahmet Kahraman
J. Mech. Des   doi: 10.1115/1.4041583
In order to accurately predict ring gear deformations and to investigate the effects of ring gear flexibility on quasi-static behaviors of planetary gear sets, a complete load distribution model of planetary gear sets having flexible ring gears will be formulated here based on the baseline model proposed by the same authors [1]. Direct comparisons to published experiments are provided to assess the accuracy of the proposed load distribution methodology. Example analyses with flexible ring gear rims are performed indicating that ring gear flexibility could influence gear mesh-level and planetary gear set system-level behaviors. Influence of spline supporting a ring gear is also investigated revealing that positions of planet branches with respect to external splines could influence ring deflections and resultant gear mesh load distributions.
TOPICS: Stress, Planetary gears, Splines, Gears, Deflection, Deformation
Guodong Sa, Zhenyu Liu, Chan Qiu and Jianrong Tan
J. Mech. Des   doi: 10.1115/1.4041573
Array structure is widely used in precise electronic products such as large phased array antennas and large optical telescopes, the main components of which are a large surface base and the massive high-precision discrete elements mounted on the surface base. The geometric error of discrete elements is inevitable in the manufacturing process and will seriously degrade product performance. To deal with the tolerance design of discrete elements, a region-division-based tolerance design method is proposed in this paper. The whole array was divided into several regions by our method and the tolerance of discrete elements was correlated with the region importance on performance. The method specifically includes the following steps: first, the sensitivity of product performance to geometric errors was analyzed and the statistical relationship between performance and geometric errors was established. Then, based on the sensitivity matrix, the regional division scheme was developed, and the corresponding tolerance was optimized according to the established relationship function. Finally, the optimal tolerance was selected among multiple solutions to achieve the best performance. Taking a large phased array as an example, a simulation experiment was performed to verify the effectiveness of the proposed method.
TOPICS: Design methodology, Errors, Simulation experiments, Telescopes, Electronic products, Manufacturing, Design
Wenjian Yang and Huafeng Ding
J. Mech. Des   doi: 10.1115/1.4041572
Planetary gear trains (PGT) are widely used as transmissions in machinery. The structure synthesis of PGTs is an effective way to create novel and excellent transmissions. In the structure synthesis of PGTs, the isomorphism detection (ID) is an essential and especially important process. The ID aims to avoid duplication and guarantee the uniqueness of each PGT. The reliability of the ID method directly determines the accuracy of the synthesis result. Unfortunately, when the existing ID methods are used to synthesize PGTs, the derived results are not consistent with each other. A very important reason is that the ID methods fail to work in some cases. This fact gives rise to the need of an extremely reliable ID method which may resolve the contradictory results in future. In this paper, our previous perimeter loop based ID method, which is applicable for linkage kinematic chains and has been proved to be reliable and efficient, is improved to detect isomorphic PGTs. The improvements relative to the previous method are discussed in detail. The method is fully automated with the aid of computer program, and verified by the atlas of PGTs with up to six links, as well as some example PGTs with seven, eight and ten links.
TOPICS: Planetary gears, Trains, Kinematic chains, Linkages, Computer software, Machinery, Reliability
Technical Brief  
Liang Cong, Fu Zhao and John Sutherland
J. Mech. Des   doi: 10.1115/1.4041574
The product end-of-use stage is the key to circulating materials and components into a new life cycle rather than direct disposal. Low economic return of end-of-use value recovery is a major barrier to overcome. To address the problem, a design method to facilitate end-of-use products value recovery is proposed. Firstly, product end-of-use scenarios are determined by optimization of end-of-use components flows. The end-of-use scenario depicts what modules (groups of components) will be allocated for reuse, recycling or disposal, the order of joint detachment (the joints for modules connection), and the end-of-use options for each module. Secondly, in the given study, bottleneck, improvement opportunities and design suggestions will be identified and provided following the end-of-use scenario analysis. Pareto analysis is used for ranking joints, according to their detachment cost, and for indicating what joints are the most suitable for replacement. Analytic hierarchy process is employed to choose the best joint candidate with trade-off among criteria from the perspective of disassembly. In addition, disposal and recycling modules are checked to eliminate hazardous material and increase material compatibility. A valued based recycling indicator is developed to measure recyclability of the modules and evaluate design suggestions for material selection. Lastly, based on heuristics, the most valuable and reusable modules will be selected for reconfiguration so that they can be easily accessed and disassembled. A hard disk drive is used as a case study to illustrate the method.
TOPICS: Design methodology, Economics , Recycling, Design, Flow (Dynamics), Hazardous substances, Optimization, Disks, Cycles, Pareto analysis, Tradeoffs
Review Article  
Qun Chao, Junhui Zhang, Bing Xu, Hsinpu Huang and Min Pan
J. Mech. Des   doi: 10.1115/1.4041582
The continued development of electro-hydrostatic actuators (EHAs) in aerospace applications has put forward an increasing demand upon EHA pumps for their high power density. Besides raising the delivery pressure, increasing the rotational speed is another effective way to achieve high power density of the pump, especially when the delivery pressure is limited by the strength of materials. However, high-speed operating conditions can lead to several challenges to the pump design. This paper reviews the current challenges including the cavitation, flow and pressure ripples, tilting motion of rotating group and heat problem, associated with a high-speed rotation. In addition, potential solutions to the challenges are summarized, and their advantages and limitations are analyzed in detail. Finally, future research trends in EHA pumps are suggested. It is hoped that this review can provide a full understanding of the speed limitations for EHA pumps and offer possible solutions to overcome them.
TOPICS: Hydrostatics, Actuators, Aerospace industry, Pumps, Pressure, Power density, Rotation, Flow (Dynamics), Design, Heat, Strength (Materials), Cavitation
Wei Chen
J. Mech. Des   doi: 10.1115/1.4041528
Editorial on the 2017 Editors' Choice Award and Honorable Mentions
Wenjian Yang and Huafeng Ding
J. Mech. Des   doi: 10.1115/1.4041482
The structure synthesis of planetary gear trains (PGT) is helpful for innovating transmission systems in machinery. Many researchers have devoted to the synthesis of 1-degree-of-freedom (DOF) PGTs in the past half century. However, most synthesis methods are limited to PGTs with no more than 8 links. Moreover, the synthesis results are not consistent with each other. Up to now, the controversy in the synthesis results is still not resolved, and the exact synthesis results are still not confirmed. This paper presents a systematic and fully automatic method based on the parent graph to synthesize 1-DOF PGTs. The complete database of rotation graphs (r-graph) and displacement graphs (d-graph) of 1-DOF PGTs with up to 9 links is established for the first time. All possible reasons for the contradictory synthesis results are analyzed, and the controversy in the existing synthesis results which has lasted for nearly half century is completely resolved. The exact results of 6, 7 and 8-link r-graphs are confirmed to be 27, 152 and 1070, respectively. The exact results of 6, 7 and 8-link d-graphs are confirmed to be 81, 647 and 6360, respectively. Besides, the new results of 8654 r-graphs and 71837 d-graphs of 9-link PGTs are provided for the first time.
TOPICS: Planetary gears, Trains, Databases, Displacement, Rotation, Machinery
Junfeng Ma, Raed Jaradat, Omar Ashour, Michael Hamilton, Parker Jones and Vidanelage Dayarathna
J. Mech. Des   doi: 10.1115/1.4041428
Manufacturing system design is a complex engineering field that requires cooperated and aggregated multiple-disciplinary theoretical and practical support. Thereby, the concepts and topics in manufacturing system design courses are not easy to grasp by students. Advances in virtual reality (VR) technology present a new opportunity that can provide the implementation of complex engineering theory from industrial real-life practice in a virtual 3D model. The authors developed a unique queuing theory VR teaching module that can be used in a manufacturing system design course. The module uses Oculus Rift headset, Oculus Touch and Unity 3D software package. The efficacy of this VR teaching module is measured through simulation sickness, system usability and user experience tools. The statistical analysis shows that VR teaching module is a user-friendly and efficient tool for delivering queueing theory. Approximately 91.7% of the participants experienced below moderate level simulation sickness and none of them withdrew from the study; 91.67% had "above average" satisfaction in terms of system usability. The average user experience was found to be 3.625 out 6. The results also show that the system usability has impact on students' knowledge gain but not motivation, while user experience can affect student's knowledge gain and motivation. VR teaching module outperforms the traditional teaching module in terms of knowledge gain and motivation. Overall, the findings of the study confirm the efficacy of VR technology in teaching queuing theory.
TOPICS: Design education, Teaching, Virtual reality, Manufacturing systems, Students, Simulation, Design, Computer software, Three-dimensional models, Statistical analysis
Xinpeng Wei and Xiaoping Du
J. Mech. Des   doi: 10.1115/1.4041429
The performance of a product varies with respect to time and space if the associated limit-state function involves time and space. This study develops an uncertainty analysis method that quantifies the effect of random input variables on the performance (response) over time and space. The combination of the first order reliability method (FORM) and the second order reliability method (SORM) is used to approximate the extreme value of the response with respect to space at discretized instants of time. Then the response becomes a Gaussian stochastic process that is fully defined by the mean, variance, and autocorrelation functions obtained from FORM and SORM, and a sequential single loop procedure is performed for spatial and random variables. The method is successfully applied to the reliability analysis of a crank-slider mechanism, which operates in a specified period of time and space.
TOPICS: Space, Uncertainty analysis, Reliability, Event history analysis, Stochastic processes
Dimitrios Papadimitriou, Zissimos P. Mourelatos and Zhen Hu
J. Mech. Des   doi: 10.1115/1.4041370
This paper proposes a new second-order Saddlepoint Approximation (SOSA) method for reliability analysis of nonlinear systems with correlated non-Gaussian and multimodal random variables. The proposed method overcomes the limitation of current available SOSA methods which are applicable to problems with only Gaussian random variables, by employing a Gaussian Mixture Model (GMM). The latter is first constructed using the Expectation Maximization (EM) method to approximate the joint probability density function of the input variables. Expressions of the statistical moments of the response variables are then derived using a second-order Taylor expansion of the limit-state function and the GMM. The standard SOSA method is finally integrated with the GMM to effectively analyze the reliability of systems with correlated non-Gaussian random variables. The accuracy of the proposed method is compared with existing methods including a SOSA based on Nataf transformation. Numerical examples demonstrate the effectiveness of the proposed approach.
TOPICS: Event history analysis, Approximation, Probability, Nonlinear systems, Density, Reliability
Alexandra Bloesch-Paidosh and Kristina Shea
J. Mech. Des   doi: 10.1115/1.4041051
Additive manufacturing (AM) has unique capabilities when compared to traditional manufacturing, such as shape, hierarchical, functional, and material complexity, a fact that has fascinated those in research, industry, and the media for the last decade. Consequently, designers would like to know how they can incorporate AM's special capabilities into their designs, but are often at a loss as how to do so. Design for Additive Manufacturing (DfAM) methods are currently in development but the vast majority of existing methods are not tailored to the needs and knowledge of designers in the early stages of the design process. Therefore, we propose a set of process-independent design heuristics for AM aimed at transferring the high-level knowledge necessary for reasoning about functions, configurations, and parts to designers. Twenty-nine design heuristics for AM are derived from 275 AM artifacts. An experiment is designed to test their efficacy in the context of a re-design scenario with novice designers. The heuristics are found to positively influence the designs generated by the novice designers and are found to be more effective at communicating DfAM concepts in the early phases of re-design than a lecture on DfAM alone. Future research is planned to validate the impact with expert designers and in original design scenarios.
TOPICS: Design, Additive manufacturing, Manufacturing, Shapes
Amy Suski
J. Mech. Des   doi: 10.1115/1.4025965
TOPICS: Design

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