The volume of metal hydride packed bed changed by the influence of the expansion during hydrogen absorption and by the contraction during hydrogen desorption was measured by direct observation. The metal hydride used in the experiment are newly developed nano-structured FeTi (n-FeTi) by mechanical alloying. In the authors' previous study of LaNi5, the volume of the packed bed gradually increased according to the hydrogen absorption and desorption cycles because of the influence of particle breakup. On the other hands, in n-FeTi produced by mechanical alloying, particle breakup hardly occurred, and the volume of the whole packed bed decreased according to the hydrogen absorption and desorption cycles. Then, the volume change of the whole packed bed due to hydrogen absorption / desorption was small, and the expansion ratio was 5% or less. The porosity data of the metal hydride packed bed obtained in this experiment is considered to be useful for numerical analysis of n-FeTi and design of practical hydrogen tanks.
The extended subloading surface model is capable of describing cyclic loading behavior accurately. The elastoplastic deformation analysis by the finite element analysis can be executed efficiently by the complete implicit stress integration method with the return-mapping and the consistent tangent modulus tensor. The subloading surface model has been applied to the FEM analysis with the return-mapping method. However, the implicit stress integration procedure with the loading criterion used in the past works is applicable only to the description of monotonic loading process so that it causes the erroneous calculated result in the cyclic loading process. The rigorous loading criterion is adopted in this article. The validity of the implicit stress integration procedure adopting the loading criterion will be verified in forward and inverse loading processes for strain increments to various directions. The implicit calculations by the return-mapping method are performed adopting the past and the rigorous loading criterions in the monotonic and the reverse loadings under the bi-axial loading state in this article. Eventually, it may be stated that the accurate numerical solution can be attained by adopting the rigorous loading criterion for the general loading process in the multi-axial stress and/or strain state.
A parameter Ustar (U*), which is independent of stress or strain, was previously developed by the authors to express load transfer. The connectivity between the loading point and an arbitrary point is represented by U*. The most serious problem encountered while calculating U* using FEM is the high computation time required. For a large-scale model, computation would take several weeks even if a supercomputer is used. To overcome this difficulty, we had previously developed the inspection loading algorithm, which is adopted to several available programs (e.g., Nastran U*Toolkit). However, the previous algorithm is not applicable to structures that have slidable supports due to the complexity of the stiffness modeling contraction. In the present study, the stiffness modeling was exchanged and a new algorithm was introduced. The basic equation was extended to include the previous equation. The computation time reduction is over 90 percent. In usual FEM calculations considering the slidable ends, it is easy to obtain results by removing the degree-of-freedom of the stiffness matrix. Our goal is not there. The purpose of the present study is to develop a fast U* calculation algorithm that can avoid a huge number of iterative FEM calculations. In an actual calculation involving a passenger car body, the results obtained by the new algorithm coincided with the accurate values.
The present paper proposes a shape optimization of the adhesive interface to improve the strength of adhesive structure under a multiaxial stress state. Its strength was evaluated by the failure function based on the first invariant of stress tensor I1 and the second invariant of deviatoric stress tensor J2, which has been discussed in the related previous paper. We defined a sum of squares of the failure function as an objective function in the optimization. Two types of the adhesive material properties, which put the major weights on only I1 and J2, respectively, were numerically examined. As a multi-material structure model bonded by the adhesive, a thin-walled butt-jointed cylinder was employed to avoid stress concentration at free edges in the adhesive layer. Three kinds of loadings were applied: only tension, only torsion, and a tension-torsion combined load. The shape of optimal adhesive layer according to each condition was in good agreement with the simplified theoretical solution. The kinked part of the optimal adhesive interface necessary for the pipe configuration was also reasonable to diminish the stress concentration around the corner. The obtained optimal shapes for the two typical adhesive material properties suggest that the present optimization method would be applicable dependent to the adhesive material parameters under multiaxial stress states.
Tasks using a multi-fingered hand are performed by sequentially applying functional finger actions to an object. We refer to a functional finger action as a “primitive action.” Various manipulations can be realized by coordinating the primitive actions. Multi-fingered hands are expected to realize various tasks, and for this purpose, it is necessary to configure software which has high reusability and efficiently for implementing many tasks. In this paper, we describe primitive actions as highly reusable software modules, and we outline the process of implementing tasks through a coordination of these primitive actions. First, we describe the configuration of a multi-fingered hand system and demonstrate how coordinations of the primitive actions are performed within the system. Then, we provide symbolic descriptions of coordination of primitive actions, and we describe tasks for the multi-fingered hand by an action network of which the nodes show coordination of primitive actions. This facilitates reuse of the task description, and provides efficient implementation of the task. As an example, the task of picking up a towel from a stack is described. Furthermore, we demonstrate that the basic specification of the robotic hand required for the task can be derived by analyzing the primitive action sequence.
This paper addresses the cascading design method of NVH (Noise, Vibration and Harshness) performance between an OEM (Original Equipment Manufacturer) and suppliers. The increasing trend toward electric vehicles requires the exploring of cascading design method, because of the easiness of the assembly of the electric vehicles. However, there are difficulties for the cascading design of NVH performance to overcome the coupling problem among each subsystem. It is generally difficult to divide key evaluation characteristics of a whole structure to individual characteristics of each subsystem because of the coupling resonance. In this paper, cascading design method which utilizes the MMC (Mutual Mean Compliance) was proposed. The MMC is used as an index to meet the final NVH target levels of a whole structure. Then, the MMC is cascaded to each subsystem or component. Finally, the cascaded MMC is achieved by improving individual MMCs of each separate subsystem, while being careful about the resonance of a whole structure caused by strong coupling. In the paper, it is shown that the recalculation of MMCs after subsystem’s structural modification is feasible using FBS (Frequency response function Based Sub-structuring). In addition, MMC based cascading design method using FBS was defined and organized as a procedure. The method was also verified by a numerical case study.
This paper presents theoretical consideration of a travel route and speed profile while turning at an intersection. These two are important for vehicle movement and ride comfort. The curvature distribution of a travel route is an important physical quantity that generates a traveling track. The formulation and characteristics of a transition curve at connection points for a non-interpolation curve, a single clothoid curve, and a multiple clothoid curve are investigated. The physical variable derived from a curvature distribution function is demonstrated, and the features of the three types of transition curves are explained. The integration value of a curvature distribution function represents an azimuthal angle. Therefore, the curvature distribution curve is the velocity of the azimuthal angle. Then, the first-order differential value of the curvature distribution curve is the acceleration of the azimuthal angle, and the second-order differential value of the curvature distribution curve is the jerk of the azimuthal angle. The theoretical equation of a traveling path is derived from the curvature distribution curve of the three types of transition curves, and their characteristics are formulated. Theoretical expressions of a speed profile of a real running vehicle at a traffic intersection are also proposed. Theoretical values agreed well with the measurement results. The validity of the multiple clothoid curve is discussed analytically as compared with the other two cases where it is interpolated by the non-interpolation curve or the single clothoid curve. It was also found that the influence of the multiple clothoid curve on vehicle movement and ride comfort was superior to those of the non-interpolation and single clothoid curve. Some results are presented in the form of parametric plots.
This study aims to suggest a method for achieving an autonomous gait transition according to speed for a four-legged robot pacing at medium speeds. Our quadruped robot is simply designed and applies a central pattern generator (CPG) for each leg. Each leg is controlled by a PD controller based on a rhythmic output from the CPG. The four CPGs are coupled, and a hard-wired CPG network is constructed to generate a default pace pattern. In addition, we apply feedback of the body tilt to the CPG as vestibular sensory feedback. As a result, our robot safely locomotes at various speeds by autonomously changing the gait from walking to pacing to rotary galloping according to speed, despite the fact that the walk and rotary gallop are not predefined. A factor that causes the gaits' emergence is considered the body oscillation that changes according to the speed. The body oscillation exhibits a double peak per leg frequency at low speeds, no peak at medium speeds, and a single peak at high speeds. The phase differences between the four legs are adjusted according to the body oscillation by feeding the body tilt back to the CPG. The gait transition is triggered only by the body tilt angle, we expect that the suggested method can be generally used for quadruped robots.
This study presents a method of determining the macroscopic viscoelastic properties as well as the macroscopic coefficients of thermal expansion and cure-shrinkage of fiber-reinforced plastics (FRP) in consideration of the dependence of the viscoelastic properties of the resin used in the matrix phase on the degree of cure (DOC). The DOC-dependent viscoelastic material behavior of the resin is represented by the generalized Maxwell model and is accompanied with non-mechanical strains such as thermal strain and cure shrinkage. Within the framework of computational homogenization, a series of numerical material tests (NMTs) are conducted on a representative volume element (microstructure) with different DOCs to discretely evaluate the macroscopic viscoelastic properties. On the assumption that the macroscopic material behavior can be represented by the anisotropic version of the generalized Maxwell model, we originally propose a method to determine the macroscopic viscoelastic properties and the macroscopic coefficients of thermal expansion and cure-induced shrinkage, both of which are functions of DOC. After numerical examples to determine these properties for a specific unit cell of FRP are presented, a simple numerical verification is carried out to demonstrate that the proposed method is capable of determining the DOC-dependent macroscopic viscoelastic properties associated with mechanical and non-mechanical strains.
We implement and perform large-scale LES analysis for running groups of cyclists. The mesh-refined lattice Boltzmann method (LBM) and coherent-structure Smagorinsky model (CSM) are adopted for the simulations to achieve a high performance computing on the recent GPU supercomputer. In the simulation with 16 cyclists, the mesh spacing around cyclists is 4 mm, and the total number of the mesh is up to 8.1×108 and the number of GPUs utilized is up to 64. Each calculation took 4 or 5 days for the 8～11 seconds of physical duration. The flow around 16 cyclists in various arrangement is calculated, and the results show that the in-line arrangement is more effective than the rhomboid arrangement in the viewpoint of the total aerodynamic drag of the group; however, a specific person in rhomboid arrangement can obtain larger drag reduction and save the endurance. Results on two groups also suggest that the frontal group in rhomboid arrangement will be exploited as the wind protection of the backward groups.
In order to improve the efficiency of combustion engines, variable compression ratio (VCR) engine is researched. VCR engine changes the compression ratio according to its mechanical configuration. One of the solutions to construct VCR engine is the multi-link type. Multi-link type has an advantage for reducing high order shaking force which is the source of mechanical vibration. Since piston motion strongly influences shaking force, it is required to make the piston displacement profile close to sine curve. However, conventional combustion engine is designed based on four-link piston crank mechanism. Because of the design constraint due to four-design parameters regarding the four-link piston crank mechanism, piston displacement profile diverges from sine curve. In order to solve this problem, six-link piston crank mechanism is applied to VCR engine. Since six-link piston crank mechanism has six-design parameters, the piston displacement profile becomes closer to sine curve than that of the four-link piston crank mechanism. A Stephenson type six-link piston crank mechanism whose constitute four-bar mechanism is the double-crank mechanism is newly designed. And, this mechanism is applied to VCR engine model. We want to put this VCR engine model to practical use. We show basic characteristic of mechanical vibration. First, we measure frame displacement of VCR engine model when the compression ratio vary high compression ratio. Next, we compare frame displacement of VCR engine model with frame displacement of four-link engine model. As a result, tendency of basic characteristic of mechanical vibration almost equate to tendency of dynamics analysis.
To improve the fuel efficiency of automobiles, the development of lightweight and high-strength material is required. Silicon, as a raw material for this purpose has attracted attention. So as method using silicon, Si alloys have been developed. Combustion synthesized β/O’-SiAlON powders were sintered by the hot pressing. Combustion synthesis is known as a self-propagating high-temperature synthesis (SHS). It is possible to design various materials with different properties by varying the ratio of Si, Al, O, and N because the composition of Si alloys is similar to that of SiAlON. In the present study, we prepared five types of Si alloys (S1, S2, O25, O75 and O100), which are similar to material design concept of β/O’-SiAlON having heat resistance and oxidation resistance, and used Si3N4 as a comparative material. We investigated the surface strength by performing the scratch test. In scratch tests, the load at which the fracture progresses to large-scale brittle fracture becomes larger in the order of O100, S1, O75, Si3N4, O25 and S2. The crystallite size of O25 is the smallest in Si alloys. Then, the composition of Al in S2 is the largest in Si alloys. Therefore, it found that Si alloy, which has small crystallite and contains more Al, shows high critical fracture load.
Recently, crowdsourced manufacturing concept highly attracts attention. In crowdsourced manufacturing, each participant shares their manufacturing resources to improve asset efficiency. To realize this concept, it is important how to make matching between resource requests and resource offers which achieve high efficiency improvement in fair way. Previously, some authors show production efficiency improvement with some resource matching algorithm. But, as shown in market design research field, matching stability is important in resource matching problem not only efficiency. In this research, we propose two stability indices 'number of blocking pairs' and 'loss caused by blocking pairs' for resource matching. The concept of blocking pair is well known, but to utilize it for resource matching problem, there are some obstacles. So, we propose analysis method of resource matching stability. And, we evaluate efficiency of the crowdsourced manufacturing system and matching stability of some representative optimization methods. The computational experiments give the following conclusions. (1) M:n type matching methods improve efficiency of the crowdsourced manufacturing system compared with the conventional dispatch method. (2) Resource matching method should be selected with consideration of features of crowdsourced manufacturing system, because distribution of profit among participants differs according to resource matching method, and matching stability differs according to stability analysis term length. (3) In the case of profit maximization of whole crowdsourced manufacturing system, a polite discussion is necessary, because profit of each participant might be reduced. In the future, we will develop new resource matching method with good balance between management effect and matching stability.
Configure-to-order (CTO) production is introduced for satisfying various individual customer requirements closely while saving various engineering efforts. In CTO, manufacturing companies modularize their products and customize them according to individual customer needs. A variety of modules and options must be provided for meeting various customer needs accurately. However, the more choices of modules and options are provided, the more customers and manufacturers have difficulties in arranging products which meet customer needs with them. In order that a manufacturer arranges optimal products more effectively for customers by means of CTO production paradigm, product architecture and order receiving procedure must be sophisticatedly designed with considering co-occurrence relations originated from customer needs. This paper proposes a novel method for designing product architecture and receiving order procedure with integrating customer needs, physical functions and entity structure through three design structure matrixes (DSMs) and two domain mapping matrixes (DMMs). The evaluation function that optimizes the degree of coherence between DSMs is formulated with a series of DSMs and DMMs. A simulated annealing based method is introduced to explore optimal modular architectures. A case study of an industrial three-axis linear-type robot is demonstrated. The design result by the proposed method is compared with ones that consider only physical functions and entity structure. Its result shows the validity and promises of the proposed method.
Recently, the use of portable terminals with touch screens such as smartphones has spread rapidly. Many users have used these devices to browse the internet or social networking services (SNS). There are many link texts (hyperlinked texts) to navigate between pages or to download files. However, interacting with link text in a portable terminal with a touch screen can often be difficult because link texts that have low text height and narrow space between lines (set by web designers who wanted to display as much information as possible on a screen of limited size) can cause accidental interactions. Many studies have evaluated usability when using portable terminals with touch screens and most of these studies have focused on Button, which is a basic GUI component. In contrast, GUI design approaches for link text have not been received sufficient attention. This study is aimed at evaluating the influence of two factors, namely the text height and the line spacing of link text, on the error rate and pointing time to overcome the usability problems associated with link texts. User experiments on pointing tasks were conducted for seven text heights (1.0, 1.5, 2.0, 2.5, 3.0, 3.5, and 4.0 mm) and five ratios of line spacing to text height (0.1, 0.3, 0.5, 0.7, and 1.0). The result shows that when the text height is 4.0 mm and the ratio of line spacing is 1.0 (the height of touch-sensitive area is 8.0 mm), rapid and accurate pointing the link text can occur. We hope that these findings contribute to an easy-to-use design for link texts.