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Accepted Manuscripts

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research-article  
Xianda Li, Jie Zhao, Ren He, Yaobin Tian and Xiangzhi Wei
J. Mech. Des   doi: 10.1115/1.4038300
Additive manufacturing allows a direct fabrication of any sophisticated mechanism when the clearance of each joint is sufficiently large to compensate the fabrication error, which frees the designers of cumbersome assembly jobs. Clearance design for assembly mechanism whose parts are fabricated by subtractive manufacturing has been well defined. However, due to the fabrication error and the diversity of materials the related standard for parts fabricated by additive manufacturing is still under exploration. For saving time and materials in a design process, a designer may fabricate a series of small mechanisms to examine their functionality before the final fabrication of a large mechanism. As a mechanism is scaled the joint clearance may be reduced, which affects the kinematics of the mechanisms. Maintaining certain clearance for various joints during the scaling process, especially for gear systems, is an intricate problem involving intense analysis of nonlinear systems. In this paper, we give a systematic study on the parametric design problem for the major types of joints, which allows the mechanisms to be scaled to an arbitrary level while maintaining the kinematics of the mechanisms. Simulation and experimental results are present to validate our designs.
TOPICS: Parametric design, Additive manufacturing, Manufacturing, Clearances (Engineering), Design, Kinematics, Errors, Machining, Simulation, Gears, Nonlinear systems
research-article  
Ana-Maria Olteteanu and L.H. Shu
J. Mech. Des   doi: 10.1115/1.4038264
Functional fixedness refers to a cognitive bias that prevents people from using objects in new ways, and more abstractly, perceiving problems in new ways. Supporting people in overcoming functional fixedness could improve creative problem solving and capacities for creative design. A study was conducted to detect whether a relationship exists between participants' tendency to reorient objects presented as stimuli in an Alternative Uses Test and their creativity, also measured using the Wallach Kogan pattern meanings test. The Alternative Uses Test measures creativity as a function of identifying alternative uses for traditional objects. The Wallach Kogan pattern-meanings test detects the ability to see an abstract pattern as different possible objects or scenes. Also studied is whether Kruglanski's Need for Closure scale, a psychological measure, can predict the ability to incorporate reorientation cues when identifying uses. This study revealed highly significant, high correlations between reorientation and several creativity measures, and a correlation between reorientation and the predictability subscale of the Need for Closure scale. A qualitative exploration of participants' responses reveals further metrics that may be relevant to assessing creativity in the Alternative Uses Test.
TOPICS: Creativity, Design
research-article  
Yuki Sato, Kentaro Yaji, Kazuhiro Izui, Takayuki Yamada and Shinji Nishiwaki
J. Mech. Des   doi: 10.1115/1.4038209
This paper proposes an optimum design method for a two-dimensional micro-channel heat sink under a laminar flow assumption that simultaneously provides maximal heat exchange and minimal pressure drop, based on a topology optimization method incorporating Pareto front exploration. First, the formulation of governing equations for the coupled thermal-fluid problem and a level set-based topology optimization method are briefly discussed. Next, an optimum design problem for a micro-channel heat sink is formulated as a bi-objective optimization problem. An algorithm for Pareto front exploration is then constructed, based on a scheme that adaptively determines weighting coefficients by solving a linear programming problem. Finally, in the numerical example, the proposed method yields a Pareto front approximation and enables the analysis of the trade-off relationship between heat exchange and pressure drop, confirming the utility of the proposed method.
TOPICS: Design methodology, Optimization, Thermofluids, Topology, Microchannels, Pressure drop, Heat sinks, Heat, Laminar flow, Algorithms, Design, Linear programming, Approximation, Tradeoffs
research-article  
Vasileios Geroulas, Zissimos P. Mourelatos, Vasiliki Tsianika and Igor Baseski
J. Mech. Des   doi: 10.1115/1.4038212
A general methodology is presented for time-dependent reliability and random vibrations of nonlinear vibratory systems with random parameters excited by non-Gaussian loads. The approach is based on Polynomial Chaos Expansion (PCE), Karhunen-Loeve (KL) expansion and Quasi Monte Carlo (QMC). The latter is used to estimate multi-dimensional integrals efficiently. The input random processes are first characterized using their first four moments (mean, standard deviation, skewness and kurtosis coefficients) and a correlation structure in order to generate sample realizations (trajectories). Characterization means the development of a stochastic metamodel. The input random variables and processes are expressed in terms of independent standard normal variables in N dimensions. The N-dimensional input space is space filled with M points. The system differential equations of motion are time integrated for each of the M points and QMC estimates the four moments and correlation structure of the output efficiently. The proposed PCE-KL-QMC approach is then used to characterize the output process. Finally, classical MC simulation estimates the time-dependent probability of failure using the developed stochastic metamodel of the output process. The proposed methodology is demonstrated with a Duffing oscillator example under non-Gaussian load.
TOPICS: Stress, Event history analysis, Differential equations, Random vibration, Chaos, Failure, Polynomials, Probability, Stochastic processes, Dimensions, Reliability, Simulation
Design Innovation Paper  
Pulkit Shamshery and Amos G. Winter, V
J. Mech. Des   doi: 10.1115/1.4038211
This study presents the design and validation of on-line pressure-compensating (PC) drip irrigation emitters with a substantially lower minimum compensating inlet pressure (MCIP) than commercially available products. A reduced MCIP, or activation pressure, results in a drip irrigation system that can operate at a reduced pumping pressure, has lower power and energy requirements, requires a lower initial capital cost, and facilitates solar-powered irrigation systems. The technology presented herein can help spread drip irrigation to remote regions and contribute to reducing poverty, particularly in developing countries. The activation pressures of drip emitters at three flow rates were minimized using a genetic algorithm-based optimization method coupled with a recently published fluid-structure interaction analytical model of on-line PC drip emitter performance. The optimization took into account manufacturing constraints and the need to economically retrofit existing machines to manufacture new emitters. Optimized PC drip emitter designs with flow rates of 3.3, 4.2, and 8.2 lph were validated using precision machined prototype emitters. The activation pressure for all was = 0.2 bar, which is as low as 16.7% that of commercial products. A limited production run of injection molded 8.2 lph dripper prototypes demonstrated they could be made with conventional manufacturing techniques. These drippers had an activation pressure of 0.15 bar. A cost analysis showed that low MCIP drip emitters can reduce the cost of solar-powered drip irrigation systems by up to 40%.
TOPICS: Pressure, Optimization, Shapes, Trickle irrigation, Engineering prototypes, Flow (Dynamics), Solar power, Manufacturing, Fluid structure interaction, Developing nations, Machinery, Irrigation (Agriculture), Algorithms, Design
research-article  
Bo Lin, Chinedum E. Okwudire and Jason S. Wou
J. Mech. Des   doi: 10.1115/1.4038071
Accurate modeling of static load distribution of balls is very useful for proper design and sizing of ball screw mechanisms (BSMs); it is also a starting point in modeling the dynamics, e.g., friction behavior, of BSMs. Often, it is preferable to determine load distribution using low order models, as opposed to computationally unwieldy high order finite element (FE) models. However, existing low order static load distribution models for BSMs are inaccurate because they ignore the lateral (bending) deformations of screw and do not adequately consider geometric errors, both of which significantly influence load distribution. This paper presents a low order static load distribution model for BSMs that incorporates lateral deformation and geometric error effects. The ball and groove surfaces of BSMs, including geometric errors, are described mathematically and used to establish a ball-to-groove contact model based on Hertzian contact theory. Effects of axial, torsional and lateral deformations are incorporated into the contact model by representing the nut as a rigid body, and the screw as beam FEs connected by a newly-derived ball stiffness matrix which considers geometric errors. Benchmarked against a high order FE model in case studies, the proposed model is shown to be accurate in predicting static load distribution, while requiring much less computational time. Its ease-of-use and versatility for evaluating effects of sundry geometric errors, e.g., pitch and ball diameter errors, on static load distribution are also demonstrated. It is thus suitable for parametric studies and optimal design of BSMs.
TOPICS: Screws, Stress, Deformation, Errors, Modeling, Design, Finite element analysis, Dynamics (Mechanics), Friction, Finite element model, Stiffness
research-article  
Mehmet Unal, Gordon P. Warn and Timothy W. Simpson
J. Mech. Des   doi: 10.1115/1.4038005
Recent advances in simulation and computation capabilities have enabled designers to model increasingly complex engineering problems, taking into account many dimensions, or objectives, in the problem formulation. Increasing the dimensionality often results in a large trade space, where decision-makers must identify and negotiate conflicting objectives to select the best designs. Trade space exploration often involves the projection of non-dominated solutions, that is, the Pareto front, onto two-objective trade spaces to help identify and negotiate tradeoffs between conflicting objectives. However, as the number of objectives increases, an exhaustive exploration of all of the 2D Pareto fronts can be inefficient due to a combinatorial increase in objective pairs. Recently, an index was introduced to quantify the shape of a Pareto front without having to visualize the solution set. In this paper, a formal derivation of the Pareto Shape Index is presented and used to support multi-objective trade space exploration. Two approaches for trade space exploration are presented and their advantages are discussed, specifically: (1) using the Pareto Shape index for weighting objectives and (2) using the Pareto Shape Index to rank objective pairs for visualization. By applying the two approaches to two multi-objective problem, the efficiency of using the Pareto Shape Index for weighting objectives to identify solutions is demonstrated. We also show that using the Index to rank objective pairs provides decision-makers with the flexibility to form preferences throughout the process without closely investigating all objective pairs. The limitations and future work are also discussed.
TOPICS: Shapes, Tradeoffs, Preferences, Dimensions, Simulation, Space, Visualization, Computation
research-article  
Xian-long Peng, Qin-yu Niu, Wei Guo and Zong-de Fang
J. Mech. Des   doi: 10.1115/1.4037762
The application of a Gleason coniflex cutter (plane-cutter) on a modern Phoenix bevel gear machine tool in face gear manufacturing has a advantage: involving a universal cutter or grinder and an available existing machine, it is valuable to research this method for face gear generation. The principle of the application of the plane-cutter in face gear manufacturing is presented first. Then, the geometry of the cutter is defined, and the model of the face gear generated by this method in abstract is established. Third, a method that uses a pre-designed contact path for synthesis with the motion parameters of the plane-cutter is proposed; controllable transmission errors are taken into consideration in this process. Fourth, based on the equivalence principle of the position and direction, the computer numerical control (CNC) motion rules of all spindles of the machine are determined, and the surface generated by the machine is presented. Finally, numerical simulation of an example demonstrates that although the surface generated by the plane-cutter, to a certain extent, deviates from the theoretical surface generated by the traditional method, the surface, in meshing with the standard involute surface of the pinion, presents good geometry meshing performance based on tooth contact analysis (TCA), except for a shortened contact ellipse.
TOPICS: Manufacturing, Gears, Machinery, Geometry, Computer numerical control machine tools, Bevel gears, Computers, Errors, Machine tools, Computer simulation, Tool grinders
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
Announcements  
Amy Suski
J. Mech. Des   doi: 10.1115/1.4025965
TOPICS: Design

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