Accepted Manuscripts

Yafeng Han and Wen Feng Lu
J. Mech. Des   doi: 10.1115/1.4040546
Lattice structures are broadly used in lightweight structure designs and multi-functional applications. Especially, with the unprecedented capabilities of additive manufacturing (AM) technologies and computational optimization methods, design of nonuniform lattice structures has recently attracted great research interests. To eliminate constraints of the common "ground structure approaches" (GSAs), a novel topology optimization based method is proposed in this paper. Particularly, the structural wall-thickness in the proposed design method was set as uniform for better manufacturability. As a solution to carry out the optimized material distribution for the lattice structure, geometrical size of each unit cell was set as design variable. The relative density model, which can be obtained from the solid isotropic microstructure with penalization (SIMP) based topology optimization method, was mapped into a nonuniform lattice structure with different size cells. Finite element analysis (FEA) based homogenization method was applied to obtain the mechanical properties of these different size gradient unit cells. With similar mechanical properties, elements with different "relative density" was translated into unit cells with different size. Consequently, the common topology optimization result can be mapped into a nonuniform lattice structure. This proposed method was computationally and experimentally validated by two different load-support design cases. Taking advantage of the changeable surface-to-volume ratio through manipulating the cell size, this method was also applied to design a heat sink with optimum heat dissipation efficiency. Most importantly, this design method provides a new perspective to design nonuniform lattice structures with enhanced functionality and manufacturability.
TOPICS: Design methodology, Optimization, Topology, Design, Mechanical properties, Finite element analysis, Density, Heat, Stress, Energy dissipation, Wall thickness, Additive manufacturing, Heat sinks, Lightweight structures
Murtuza Shergadwala, Ilias Bilionis, Karthik Kannan and Jitesh H. Panchal
J. Mech. Des   doi: 10.1115/1.4040548
Many decisions within engineering systems design are typically made by humans. While decision theory is increasingly being used from a normative standpoint to develop computational methods for engineering design, there is still a significant gap in our understanding of how humans make decisions within the design process. Particularly, there is lack of knowledge about how an individual's domain knowledge and framing of the design problem affects information acquisition decisions. To address this gap, the objective of this paper is to quantify the impact of a designer's domain knowledge and problem framing on their information acquisition decisions and the corresponding design outcomes. The objective is achieved by (i) developing a descriptive model of information acquisition decisions based on an optimal one-step look ahead sequential strategy, and (ii) using the model in conjunction with a controlled behavioral experiment. The domain knowledge of an individual is measured in the experiment using a Concept Inventory, whereas the problem framing is controlled as a treatment variable in the experiment. A design optimization problem is framed in two different ways: a domain-specific track design problem, and a domain-independent function optimization problem. The results indicate that when the problem is framed as a domain-specific design task, the design solutions are better and individuals have better knowledge about the problem, as compared to the domain-independent task. The design solutions are found to be better when individuals have a higher knowledge of the domain and they follow the modeled strategy closely.
TOPICS: Structural frames, Engineering design, Framing (Construction), Design, Optimization, Performance, Computational methods, Engineering systems and industry applications
Benliang Zhu, Qi Chen, Rixin Wang and Xianmin Zhang
J. Mech. Des   doi: 10.1115/1.4040547
Moving morphable component(MMC)-based method is a new developed approach for topology optimization. In the MMC-based method, the design problem is formulated using a set of morphabe components and the optimized structural topologies are obtained by optimizing shapes, sizes and locations of these components. However, the optimization process often tends to break the connection between the load area and the supported boundary. This disconnection has a strong influence on the convergence, especially when the large deformation effects are considered. In this paper, a method is developed for topology optimization of geometrically nonlinear structures by using MMC-based method. A scheme is developed to deal with the disconnection issue in the optimization process. Several numerical examples are used to demonstrate the validity of the proposed method.
TOPICS: Optimization, Topology, Shapes, Deformation, Stress, Design
George Cheng, Timothy Gjernes and Gary Wang
J. Mech. Des   doi: 10.1115/1.4040485
Expensive constraints are commonly seen in real-world engineering design. However metamodel based design optimization (MBDO) approaches often assume inexpensive constraints. In this work, the Situational Adaptive Kreisselmeier and Steinhauser (SAKS) method was employed in the development of a hybrid adaptive aggregation-based constraint handling strategy for expensive black-box constraint functions. The SAKS method is a novel approach that hybridizes the modeling and aggregation of expensive constraints and adds an adaptive strategy to control the level of hybridization. The SAKS strategy was integrated with a modified Trust Region Based Mode Pursuing Sampling (TRMPS) algorithm to form the SAKS-Trust Region Optimizer (SAKS-TRO) for single-objective design optimization problems with expensive black-box objective and constraint functions. SAKS-TRO was benchmarked against five popular constrained optimizers and demonstrated superior performance on average. SAKS-TRO was also applied to optimize the design of an industrial recessed impeller.
TOPICS: Optimization, Design, Modeling, Impellers, Engineering design, Algorithms
Zefang Shen, Garry Allison and Lei Cui
J. Mech. Des   doi: 10.1115/1.4040486
Exoskeletons can assist wearers to reproduce natural movements when attached to the human body. However most current such devices are bulky and heavy, which limits their application. Compact and lightweight devices are needed to boost the availability of therapy services for at-home application. In this paper, we integrated type synthesis and dimensional synthesis to design 1-DOF linkages consisting of only revolute joints with multiple output joints for compact exoskeletons. Type synthesis starts from a 4-bar linkage where the output link generates the first angular output. Then an RRR dyad is connected to the four-bar linkage for the second angular output while ensuring the overall DOF of the new mechanism is 1. A third output joint is added in a similar manner. During each step, dimensional synthesis is formulated as a constrained optimization problem and solved via genetic algorithms. In the first case study, we designed a leg exoskeleton based on an 8-bar-10-joint linkage to reproduce a natural walking gait at hip and knee joints. The second case study presents a finger exoskeleton based on a 10-bar-13-joint linkage for a natural curling motion. We manufactured the exoskeletons to validate the proposed approach.
TOPICS: Linkages, Degrees of freedom, Design, Exoskeleton devices, Optimization, Genetic algorithms, Patient treatment, Knee
Ping Hu, Lei Yang and Baojun Li
J. Mech. Des   doi: 10.1115/1.4040487
This study reports a parameterization technique based on a skeleton-section template for shape optimization of beam components. The skeletal curve and the cross-sectional profiles consist of the template, and are used as design variables to generate global shape variants as well as local reinforcements on the surface model. To validate applicability of the proposed template-based parameterization technique to general shape optimization frameworks in automotive engineering, two proof-of-concept numerical studies pertaining to crashworthiness design of an S-shaped frame were implemented. The first case study considered the skeletal curve as design variables, and led to global change of the shape; the second treated the cross-sectional profiles as design parameters and yielded local reinforcements on the shape. Both studies showed the efficiency of the proposed method in generation of high-quality shape variants for optimization and design space exploration. From the numerical results observed were considerable amount of improvements in crashworthiness performance of the structure measured by the peak crushing force and the energy absorption. We conclude that the proposed template-based parameterization technique is suitable for shape optimization tasks.
TOPICS: Shape optimization, Design, Shapes, Crashworthiness, Optimization, Automotive engineering, Absorption
Technical Brief  
Xiaobang Wang, Yuanzhi Liu, Wei Sun, Xueguan Song and Jie Zhang
J. Mech. Des   doi: 10.1115/1.4040484
Battery thermal management system (BTMS) is a complex and highly-integrated system which is used to control the battery thermal conditions in electric vehicles (EVs). The BTMS consists of many sub-systems that belong to different disciplines, which poses challenges to BTMS optimization using conventional methods. This paper develops a general variable-fidelity based multidisciplinary design optimization (MDO) architecture and optimizes the BTMS by considering different systems/disciplines from the systemic perspective. Four sub-systems and/or sub-disciplines are modeled, including the battery thermodynamics, fluid dynamics, structure, and lifetime model. To perform the variable-fidelity based MDO of the BTMS, two computational fluid dynamics (CFD) models with different levels of fidelity are developed. A low fidelity surrogate model and a tuned low fidelity model are also developed using an automatic surrogate model selection method, the Concurrent Surrogate Model Selection (COSMOS). An adaptive model switching (AMS) method is utilized to realize the adaptive switch between variable-fidelity models. The objectives are to maximize the battery lifetime and to minimize the battery volume, the fan's power, and the temperature difference among different cells. The results show that the variable-fidelity MDO can balance the characteristics of the low fidelity mathematical models and the computationally expensive simulations, and find the optimal solutions efficiently and accurately.
TOPICS: Design, Optimization, Thermal management, Electric vehicle batteries, Batteries, Engineering disciplines, Computational fluid dynamics, Engineering simulation, Electric vehicles, Switches, Fluid dynamics, Thermodynamics, Temperature, Universe, Simulation
Technical Brief  
Mohsen Kolivand, Victor Sun, Douglas Chemelli, Joe Balenda and Zhenghong Shi
J. Mech. Des   doi: 10.1115/1.4040425
Automotive differential gears are usually operating at very low speed and high load conditions and hence are usually designed to be protected against the root bending fatigue failure. Depending on application requirements and lubrication regime surface failures may occasionally be encountered as well. Mainstream existing design procedures published by AGMA is based on analyzing one single gear pair engagement while up to four potential engagements, between two side gears and two differential pinions, exist. There are also differential designs with three or four differential pinions that increases potential number of engagements to respectively six and eight. Usually the hypoid gear loading is divided by number of side gears, two, also differential pinion loads are also usually assumed to be equal; this is a good estimate when no misalignments are present. When misalignments are present however, load sharing between the differential pinions become greatly imbalanced. This study tries to come up with a simplified analytical approach to evaluate overload factor between the differential pinions as a result of misalignments realized by differential gears inside a differential case. The total indexing runout quality of gears is also studied through treating it as a source of misalignment. This study will help designers to evaluate the effects of tolerancing limits and differential case machining errors on differential gear bending lives.
TOPICS: Differential gears, Bending (Stress), Gears, Stress, Indexing (Machining), Lubrication, Machining, Errors, Failure, Fatigue failure, Spiral bevel gears, Design
Esraa Abdelall, Matthew C. Frank and Richard Stone
J. Mech. Des   doi: 10.1115/1.4040424
This study assessed the effectiveness of 3D visual feedback from design for manufacturability (DFM) software on mitigating design fixation on non-producible manufacturability features. Whereas design fixation studies focus on fixation caused by exposure to prior solution and its effect on novelty and functionality of designs, a recent study showed that migrating design between manufacturing processes (e.g. Additive to Conventional manufacturing) can cause fixation on non-producible manufacturability features. In this work, a fixation group and a defixation group were asked to design a basic product for additive manufacturing (DFAM) and then to modify the next iteration for conventional machining. The fixation group relied on their self-assessment while modifying, while the defixation group utilized DFM software feedback. Results showed that 3D feedback reduced design fixation on non-producible features and improved the machinability of modified designs. Findings suggest the use DFM software for treating the design fixation related to additive manufacturing and for facilitating migration of designs from additive to conventional manufacturing. This work could be applied to manufacturing industries, particularly where AM is used for prototyping, or when demand for part changes and an AM part needs to migrate to conventional methods.
TOPICS: Design, Feedback, Design for Manufacturing, Computer software, Manufacturing, Additive manufacturing, Machinability, Manufacturing industry, Machining
Guanglei Wu
J. Mech. Des   doi: 10.1115/1.4040351
This paper presents the parametrically excited lateral instabilities of an asymmetrical spherical parallel manipulator by means of monodromy matrix method. The linearized equation of motion for the lateral vibrations is developed to analyze the stability problem, resorting to the Floquet theory, which is numerically illustrated. To this end, the parametrically excited unstable regions of the manipulator are visualized to reveal the effect of the system parameters on the stability. Critical parameters, such as rotating speeds of the driving shaft, are identified from the constructed parametric stability chart for the manipulator.
TOPICS: Universal joints, Manipulators, Reactor protection systems, Stability, Equations of motion, Vibration
Marta Perez Mata, Saeema Ahmed-Kristensen and Kristina Shea
J. Mech. Des   doi: 10.1115/1.4040169
The user experience of a product is recognized as of increasing importance in particular in consumer products. Current approaches to designing user experiences are not easily translated to languages that a computer can understand. This paper examines a particular aspect of user experience, namely perception of the aesthetics of a product, to formalize this to rules which are embedded into a tool to generate design. Investigating the perception of consumers is key for designing for their aesthetic preferences. Previous research has shown that consumers and designers often perceive the same products differently. This paper aims to embed rules on perception into a tool to support designers during design synthesis. Aesthetic design rules connecting perceptions with aesthetic features were integrated into a set grammar and a parametric modelling tool, and applied to the particular case of vases. The generated tool targeted the creation of vases with the perception of beautiful, elegant and exciting. Results show that it is possible to generate beautiful, elegant and exciting vases following the three aesthetic design rules, i.e. tall, simple and curves. The main contribution of this paper is the method used to incorporate information on perception into the set grammar and the parametric model. The tool is additionally proposed for supporting designers during design synthesis of shapes. The results are valid for vases but the method can be applied to other perceptions and product categories.
TOPICS: Design, Shapes, Preferences, Modeling, Computers
Srinivasan Venkataraman, Binyang Song, Jianxi Luo, Karupppasamy Subburaj, Mohan Rajesh Elara, Lucienne Blessing and Kristin Wood
J. Mech. Des   doi: 10.1115/1.4040165
Identifying relevant stimuli that will help generate solutions of desired novelty and quality is challenging in analogical design. To quell this challenge, this research studies the multifaceted effects of using stimuli located at various analogical distances to the design problem domain(s) on the novelty and quality of concepts generated using the stimuli. Data from a design project involving 105 student designers, individually generating 226 concepts of spherical rolling robots are collected. From these data, 138 concepts generated with patents as stimuli and the patents used as stimuli are analyzed. Analogical distance of a patent is measured in terms of knowledge similarity between technology classes constituting the patent and design problem domain of spherical rolling robots. The key observations are: (a) technology classes in closer rather than farther distances from the design problem are used more frequently to generate concepts, (b) as analogical distance increases the novelty of concepts increases, and (c) as analogical distance decreases the quality of concepts increases.
TOPICS: Robots, Design, Patents, Students
Jokin Aginaga, Xabier Iriarte, Aitor Plaza and Vicente Mata
J. Mech. Des   doi: 10.1115/1.4040168
Rehabilitation robots are increasingly being developed in order to be used by injured people to perform exercise and training. Parallel robots can be an ideal solution for this purpose due to its inherent properties for lower mobility tasks. This paper presents the design of a new four degree-of-freedom (DOF) parallel robot for knee rehabilitation. Needed four DOFs are two translations in a vertical plane and two rotations, one of them around the direction perpendicular to the vertical plane and the other one with respect to a vector normal to the mobile platform. These four DOFs are reached by means of two RPRR limbs and two UPS limbs linked to an articulated mobile platform. Kinematics of the new mechanism are solved and the direct Jacobian is calculated. A singularity analysis is carried out and the gained DOFs of the direct singularities are calculated. Some of the singularities can be avoided by selecting suitable values of the geometric parameters of the robot. Moreover, among the found singularities, one of them can be used in order to fold up the mechanism for its translation. It is concluded that the proposed mechanism reaches the desired output movements in order to carry out rehabilitation manoeuvres.
TOPICS: Kinematics, Robots, Degrees of freedom, Design, Knee, Mechanical admittance
John Meluso and Jesse Austin-Breneman
J. Mech. Des   doi: 10.1115/1.4039494
Parameter estimates in large-scale complex engineered systems affect system evolution yet can be difficult and expensive to test. Systems engineering uses analytical methods to reduce uncertainty, but a growing body of work from other disciplines indicates that cognitive heuristics also affect decision-making. Results from interviews with expert aerospace practitioners suggest that engineers bias estimation strategies. Practitioners reaffirmed known system features and posited that engineers may bias estimation methods as a negotiation and resource conservation strategy. Specifically, participants reported that some systems engineers ``game the system'' by biasing requirements to counteract subsystem estimation biases. An agent-based model simulation which recreates these characteristics is presented. Model results suggest that system-level estimate accuracy and uncertainty depend on subsystem behavior and are not significantly affected by systems engineers' ``gaming'' strategy.
TOPICS: Engineers, Systems engineers, Simulation, Systems engineering, Aerospace industry, Analytical methods, Engineering disciplines, Decision making, Uncertainty, Negotiation
Steffen Hau, Alexander York, Gianluca Rizzello and Stefan Seelecke
J. Mech. Des   doi: 10.1115/1.4039104
State of the art actuator technologies, e.g., solenoids or pneumatic cylinders, are available in nearly infinite variations to address every specific application. However, for a large number of applications, dielectric elastomers (DE) represent a more energy efficient, lightweight, and low-cost solution with respect to the established technologies mentioned above. In addition to large strain, low power consumption, and high flexibility, DE actuators (DEA) have also highly scalable performance, which allow to adapt them to a large variety of applications. An effective means to scale DE performance is represented by the scaling of material geometry. In fact, a DE membrane can be easily designed in different sizes and shapes. However, in order to perform a successful design, the relation between material geometry and performance has to be properly investigated. In this paper, performance scaling by means of geometry is studied for circular out-of-plane DEAs. Such actuators consist of a silicone elastomer membrane sandwiched between two electrodes (carbon black silicone mixture). DEAs with six different geometries are manufactured, and a model-based strategy is used to find an experimental relationship between geometry and electro-mechanical characteristics. In addition, an effective and computationally simple method for predicting force-displacement characteristics of different geometries, given by a specific material combination (elastomer and electrode), is presented. The proposed method allows to easily adapt DEAs to different applications in terms of stroke and force requirement, while minimizing at the same time both characterization and prototyping effort.
TOPICS: Elastomers, Scaling laws (Mathematical physics), Actuators, Membranes, Geometry, Silicones, Electrodes, Displacement, Energy consumption, Shapes, Design, Pneumatic cylinders, Carbon black pigments, Solenoids
Design Innovation Paper  
Rami Alfattani and Craig Lusk
J. Mech. Des   doi: 10.1115/1.4037621
This paper presents a new Bistable Collapsible Compliant Mechanism (BCCM) that is utilized in a Lamina- Emergent Frustum. The mechanism is based on transforming a polygon spiral into spatial frustum shape using a mechanism composed of compliant links and joints that exhibits bistable behavior. A number of mechanism types (graphs) were considered to implement the shape-morphing spiral, including 4-bar, 6-bar, and 8-bar chains. Our design requirements permitted the selection of a particular 8-bar chain as the basis for the BCCM. Bistable behavior was added to the mechanism by introducing snap-through bistability as the mechanism morphs. Parametric CAD was used to perform the dimensional synthesis. The design was successfully prototyped. We anticipate that the mechanism may be useful in commercial small animal enclosures or as a frame for a solar still.
TOPICS: Compliant mechanisms, Chain, Design, Shapes, Computer-aided design, Solar stills
Amy Suski
J. Mech. Des   doi: 10.1115/1.4025965
TOPICS: Design

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