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Editorial

J. Mech. Des. 2017;139(8):080201-080201-1. doi:10.1115/1.4037093.

I am pleased to announce the Journal of Mechanical Design's (JMD's) Editors' Choice Paper Awards for the years: 2014, 2015, and 2016.

Topics: Performance
Commentary by Dr. Valentin Fuster

Research Papers: Design Automation

J. Mech. Des. 2017;139(8):081401-081401-8. doi:10.1115/1.4036778.

Previous work in air transportation system-of-systems (ATSoSs) design optimization considered integrated aircraft sizing, fleet allocation, and route network configuration. The associated nested multidisciplinary formulation posed a numerically challenging blackbox optimization problem; therefore, direct search methods with convergence properties were used to solve it. However, the complexity of the blackbox impedes greatly the solution of larger-scale problems, where the number of considered nodes in the route network is high. The research presented here adopts a rule-based route network design inspired by biological transfer principles. This bio-inspired approach decouples the network configuration problem from the optimization loop, leading to significant numerical simplifications. The usefulness of the bio-inspired approach is demonstrated by comparing its results to those obtained using the nested formulation for a 15 city network. We then consider introduction of new aircraft as well as a larger problem with 20 cities.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2017;139(8):081402-081402-9. doi:10.1115/1.4036836.

The center shift, a common problem existing in rotating flexural pivots, is diminished in a multibeam flexural pivot by the internal interaction among these beams. The objectives of this paper are to develop a model for this flexural pivot and to analyze the interaction. First, the calculus of variations with a Lagrange multiplier is exploited to develop the model based on energy approach. Then, the properties of a conservative system are utilized to analyze the constraint characteristics of these beams, and two different load sequences are taken into account to formulate the rotating stiffness of the flexural pivot. The three methods that are used to develop the same model are compared to show their respective advantages, and the analysis of the internal constraints offers several significant qualitative and quantitative design insights. Furthermore, the circular arc motion is expanded to the elliptic arc motion, and an approximate replacement is therefore presented. Furthermore, the circular arc motion is expanded to the elliptic arc motion, and an approximate replacement is therefore presented.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2017;139(8):081403-081403-11. doi:10.1115/1.4036999.

The stiffness of plate structures can be significantly improved by adding reinforcing ribs. In this paper, we are concerned with the stiffening of panels using ribs made of constant-thickness plates. These ribs are common in, for example, the reinforcement of ship hulls, aircraft wings, pressure vessels, and storage tanks. Here, we present a method for optimally designing the locations and dimensions of rectangular ribs to reinforce a panel. The work presented here is an extension to our previous work to design structures made solely of discrete plate elements. The most important feature of our method is that the explicit geometry representation provides a direct translation to a computer-aided design (CAD) model, thereby producing reinforcement designs that conform to available plate cutting and joining processes. The main contributions of this paper are the introduction of two important design and manufacturing constraints for the optimal rib layout problem. One is a constraint on the minimum separation between any two ribs to guarantee adequate weld gun access. The other is a constraint that guarantees that ribs do not interfere with holes in the panel. These holes may be needed to, for example, route components or provide access, such as a manhole. We present numerical examples of our method under different types of loadings to demonstrate its applicability.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2017;139(8):081404-081404-11. doi:10.1115/1.4036998.

Large wind turbines typically have variable rotor speed capability that increases power production. However, the cost of this technology is more significant for small turbines, which have the highest cost-per-watt of energy produced. This work presents a low-cost system for applications where cost and reliability are of concern. The configuration utilizes the fixed-speed squirrel cage induction generator. It is combined with a variable ratio gearbox (VRG) that is based on the automated-manual automotive transmission. The design is simple, low cost and implements reliable components. The VRG increases efficiency in lower wind speeds through three discrete rotor speeds. In this study, it is implemented with active blades. The contribution of this work is a methodology that synthesizes the selection of the gearbox ratios with the control design. The design objectives increase the power production while mitigating the blade stress. Top-down dynamic programming reduces the computational expense of evaluating the performance of multiple gearbox combinations. The procedure is customizable to the wind conditions at an installation site. A case study is presented to demonstrate the ability of the strategy. It employs a 300 kW wind turbine drivetrain model that simulates power production. Two sets of wind data representing low and high wind speed installation sites were used as the input. The results suggest a VRG can improve energy production by up to 10% when the system operates below the rated wind speed. This is also accompanied by a slight increase in the blade-root stress. When operating above the rated speed, the stress decreases through the optimal selection of gear combinations.

Commentary by Dr. Valentin Fuster

Research Papers: Design for Manufacture and the Life Cycle

J. Mech. Des. 2017;139(8):081701-081701-10. doi:10.1115/1.4036777.

Consumers might be willing to repair their broken devices as long as the associated repair costs do not exceed an undesirable threshold. However, in many cases, the technological obsolescence actuates consumers to retire old devices and replace them with new ones rather than extending the product lifecycle through repair. In this paper, we aim to investigate the impact of components' deterioration profiles and consumers' repair decisions on the lifespan of devices, and then assesse the anticipated life cycle environmental impacts. A Monte Carlo simulation is developed to estimate the life cycle characteristics such as the average lifespan, the number of failed components' replacement, and the total repair cost per cycle for a laptop computer. The lifecycle characteristics estimated from simulation model further have been used in a life cycle assessment (LCA) study to quantify the environmental impact associated with different design scenarios. The results reveal the impact of product design as well as consumers' repair decisions on the product lifespan and the corresponding environmental impacts.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2017;139(8):081702-081702-13. doi:10.1115/1.4036996.

Traditional origami structures fold along predefined hinges, and the neighboring facets of the hinges are folded to transform planar surfaces into three-dimensional (3D) shapes. In this study, we present a new self-folding design and fabrication approach that has no folding hinges and can build 3D structures with smooth curved surfaces. This four-dimensional (4D) printing method uses a thermal-response control mechanism, where a thermo shrink film is used as the active material and a photocurable material is used as the constraint material for the film. When the structure is heated, the two sides of the film will shrink differently due to the distribution of the constraint material on the film. Consequently, the structure will deform over time to a 3D surface that has no folding hinges. By properly designing the coated constraint patterns, the film can be self-folded into different shapes. The relationship between the constraint patterns and their correspondingly self-folded surfaces has been studied in the paper. Our 4D printing method presents a simple approach to quickly fabricate a 3D shell structure with smooth curved surfaces by fabricating a structure with accordingly designed material distribution.

Commentary by Dr. Valentin Fuster

Research Papers: Design Education

J. Mech. Des. 2017;139(8):082001-082001-9. doi:10.1115/1.4036566.

This study compares the potential of the methods of inventive principles (IPR) of TRIZ (MIPT) and BioTRIZ (MIPB) in relation to stimulating creativity in problem solving. The two methods were applied to different issues by groups of undergraduate students. The solutions were evaluated in terms of creativity, which was defined by the criteria of originality and utility. Quantitative analysis provided evidence that the two methods are equal in terms of creative contributions. However, further analyses indicate that the IPs derived from biological systems tend to provide a greater creative contribution compared to those based on technical systems. In addition, it was found that repeated inventive principles (IPR), that is, those indicated more than once by the applied methods, tend to introduce a greater potential for stimulating creativity compared to inventive principles (IPs) indicated only once.

Commentary by Dr. Valentin Fuster

Research Papers: Design of Mechanisms and Robotic Systems

J. Mech. Des. 2017;139(8):082301-082301-10. doi:10.1115/1.4036781.

The sketching of kinematic chains is important in the conceptual design of mechanisms. In general, the process of sketching kinematic chains can be divided into two steps, namely sketching topological graphs and converting them into the corresponding kinematic chains. This paper proposes a new method to automatically sketch topological graphs including both planar and nonplanar graphs. First, two parameters called moving sign (MS) and moving sign string (MSS) are defined, based on which a new algorithm is proposed to acquire all feasible layouts of the contracted graph by moving inner edges. All topological graphs synthesized from the same contracted graph are identified to have the shared feasible layouts, and another algorithm is proposed to determine the optimal layout for each topological graph. Then, topological graphs are sketched automatically by determining the location of vertices. The method has low complexity and is easy to be programmed using computer language.

Commentary by Dr. Valentin Fuster

Research Papers: Design of Direct Contact Systems

J. Mech. Des. 2017;139(8):083301-083301-11. doi:10.1115/1.4036583.
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Most of the prior studies on power-split hybrid electric vehicle's (PS-HEV) design focused on the powertrain configuration optimization. Yet, depicting the selected configuration is highly required for further design steps, ultimately manufacturing. This paper proposes an automatic approach to generate all the feasible kinematic diagrams for a given configuration with a single planetary gear (PG) set. While the powertrain configuration, which is the output of prior studies, illustrates the connection of the powertrain components to the PG, the kinematic diagram is a schematic diagram depicting the connections and arrangements of the components. First, positioning diagrams, specifying the position of the components with respect to each other and to the PG, are used to find all the possible arrangements. Then, given that the positioning diagrams have a one-to-one relationship with the kinematic diagrams, the feasible kinematic diagrams are identified using a set of feasibility rules applicable to the positioning diagrams. Finally, few guidelines are introduced to select good kinematic diagrams that best suit the overall vehicle design. Various configurations were investigated, and three of them including Prius and Voltec first-generation single PG configurations are discussed. The study reveals that the kinematic diagrams that have been patented are only a subset of all the feasible kinematic diagrams, and that even some good kinematic diagrams with better manufacturability are identified using this methodology. Thus, this methodology guarantees the search of the entire design space and the selection of kinematic diagrams that best suit the desired vehicle.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2017;139(8):083302-083302-5. doi:10.1115/1.4036782.

Graph theory is a powerful tool in structural synthesis and analysis of planetary gear trains (PGTs). In this paper, a new algorithm has been developed for detecting degenerate structure in planetary gear trains. The proposed algorithm is based on the concept of fundamental circuits' rotation graphs. Detection of degeneracy is entirely based on finding one key element. The key element or link that makes planetary gear train into two groups is found in this work. The main advantage of the proposed method lies in the drastic reduction in the required combinatorial analysis compared to other methods available.

Commentary by Dr. Valentin Fuster

Design Innovation Paper

J. Mech. Des. 2017;139(8):085001-085001-9. doi:10.1115/1.4036779.

A new hypoid gearing using a common crown rack is introduced. The proposed hypoid gear has no unloaded gear transmission error. The common crown rack is located at a neutral position between the pinion and gear blanks. An arbitrary generating surface inclined at a pressure angle is prescribed. The proposed hypoid gearing is in point contact, fulfilling a constant speed ratio along the curved line of action. The synthesis feasibility is numerically verified for the entire range of hypoid gears, including parallel-, intersecting-, and crossed-axis gear systems. The proposed hypoid gear is compared with the hypoid gear by Gleason method and the differences between the two are discussed.

Commentary by Dr. Valentin Fuster

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