A Calculation Method for the Deformation Behavior of Warp-Knitted Fabric

In this paper, a new method to simulate the structure and loop deformation behavior of double-bar reflex-lapping warp-knitted fabrics based on the structural characteristics is proposed. A simplified mass-spring model was built in which loops knitted by filaments were considered as particles with the uniform mass distribution connected by structure springs for overlaps and shear springs for underlaps. Deformation forces and direction on particles were analyzed to describe the displacement and deformation behavior of particles. A loop model with eight control points was established, and the relationship between control points and particles was studied combining the quadratic Bezier curves. The deformation simulation was implemented by a simulator program with C# and JavaScript via web technology on Visual Studio 2015. The stereoscopic sense of filaments was realized by changing the direction and intensity of the light. The results show that the fabric deformation and the loop shape can be accurately achieve using the simplified mass-spring model compared with the real sample.

An improved dynamic modeling approach of aerostatic thrust bearing considering frequency-varying stiffness and damping of air film

The damped mass-spring model is often employed for the dynamic modeling and vibration analysis of aerostatic bearing systems by taking the air film as equivalent springs. However, the stiffness and damping of the air film are frequency-dependent, making the commonly used approach of taking static stiffness or fixed value as the spring coefficient no longer applicable for a bearing subject to a complex external force containing different frequencies. To address this issue, this paper develops the damped mass-spring model for the aerostatic thrust bearing considering the frequency-varying stiffness and damping by means of the linear superposition method. It indicates that the air bearing is still a linear system despite the frequency-dependent character of dynamic coefficients because the bearing vibration satisfies the superposition principle. The improved dynamic modeling approach is able to accurately and efficiently predict the overall dynamic response of the thrust plate when the it is subjected to a multi-frequency vibration. In solving the overall dynamic response, the stiffness and damping associated with the responses of the transient part and steady part correspond to the natural vibration frequency and external disturbance frequencies, respectively. The feasibility and accuracy of the improved modeling approach are partly or completely verified by the direct trajectory calculation method, the CFD dynamic mesh simulation and a modal test. The proposed modeling method provides an effective way for the vibration analysis of air bearings, and in the meantime avoids the possible numerical errors caused by the traditional modeling approach.

Real-Time Cloth Simulation for Hula Costume CAD Development

In recent years, 3D computer graphics (3DCG) technology has been applied in various fields such as AR technology, VR technology, movies, games, and virtual fitting of clothes. Among them, there is the problem of contact between clothing and other objects (such as the body). In this paper, we focus on that problem. Since this research is part of the development of CAD for the design of hula costumes, and since we assume that the users of the CAD will have PCs with not very high performance, we took an approach that does not require a large amount of computation. As a representation of the cloth, we used a mass-spring model in which springs and mass points are connected in a grid. We also compared how the three methods of calculating position and velocity, Euler method, FB Euler method, and Runge-Kutta method, affect the simulation results.

Discrete scattering and meta-arrest of locally resonant elastic wave metamaterials with a semi-infinite crack

Previous investigations on wave scattering and crack propagation in the discrete periodic structure are concentrated on the conditional mass–spring model, in which the internal mass is not included. In this work, elastic wave metamaterials with local resonators are studied to show the scattering of elastic waves by a semi-infinite crack and the arrest behaviour. The influences of internal mass–spring structure are analysed and the discrete Wiener–Hopf method is used to obtain the displacement solution. Numerical calculations are performed to show that the dynamic negative effective mass and band gaps can be observed owing to the local resonance of the internal mass. Therefore, the scattering of an elastic wave with a specific frequency by a semi-infinite crack can be avoided by tuning the structural parameters. Moreover, the energy release ratio which characterizes the splitting resistance is presented and the meta-arrest performance is found. It is expected that this study will increase understanding of how to control the scattering characteristics of elastic waves by a semi-infinite crack in locally resonant metamaterials and also help to improve their fracture resistance.

Development of Simplified Wear Estimation Method Considering Rolling Motion Between Mooring Chain Links for Floating Structures

For the development of floating offshore wind turbines (FOWTs) in Japan, reliability assessment and cost reduction by efficient maintenance on mooring chains are part of the key issues because sites deeper than 60 m require mooring systems for station keeping. In this paper, attempts have been made to simplify the wear estimation method which was previously proposed by using a 3-D rigid-body link model for improvement of accuracy. These investigations are performed about a spar-type floating structure moored with three catenary lines at Goto, Nagasaki prefecture, Japan. In the previous study, it was confirmed that the estimation method using the 3-D link model can calculate the interlink wear amount closer to the chain diameter measurements and more reasonable than the method using the conventional mass-spring model by removing the rolling distance from the displacement of contact points. However, the estimation method has technical difficulty in terms of calculation of contact properties and analysis costs for the mooring chain design. For this reason, the wear estimation method is simplified and verified by considering the rolling motion between mooring chain links modeled by the widely employed mass-spring model based on the method proposed by Mooring Integrity JIP. Firstly, the wear due to the rolling is reproduced by a three-dimensional FE analysis to investigate the actual wear phenomenon including the effect of the proof load test as well as the idealized configuration. Secondly, the application method is proposed against the response of the mooring chain subjected to irregular waves Finally, a comparison with the measurement is conducted to verify the proposed wear estimation method.

Review on the 3-D simulation for weft knitted fabric

There are different kinds of geometrical models and physical models used to simulate weft knitted fabrics nowadays, such as loop models based on Pierce, piecewise function, spline curve, mass-spring model, and finite element analyses (FEA). Weft knitting simulation technology, including modeling and yarn reality, has been widely adopted in fabric structure designing for the manufacturer. The technology has great potentials in both industries and dynamic virtual display. The present article is aimed to review the current development of 3-D simulation technique for weft knitted fabrics.

Design and construction of multi-cylinder type liquid piston Stirling engine

In a multi-cylinder type liquid piston Stirling engine (MCLPSE), liquid columns in U-shaped tubes play the role of solid pistons in a mechanical Stirling engine. Besides the straightforward structure, advantages of the MCLPSE are a relatively low operation temperature difference below 100 K and use of harmless working fluids of air and water. This study presents a mass spring model for the MCLPSE, from which we determine geometrical parameters of MCLPSE to achieve a target acoustic power production under a given temperature condition. The preliminary test results will be presented.