• Journal of Institute of Convergence Technology
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• v.6 no.2
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• pp.15-20
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• 2016

This paper presents the effects of a virtual mass on the stability boundary of a virtual spring in the haptic system. A haptic system consists of a haptic device, a sampler, a virtual rigid body and zero-order-hold. The virtual rigid body is modeled as a virtual spring and a virtual mass. According to the virtual mass and the sampling time, the stability boundary of the virtual spring is analyzed through the simulation. As the virtual mass increases, the value of the virtual spring to guarantee the stability gradually increases and then decreases after reaching the maximum value. These simulation results show that the addition of the virtual mass enables to expand the stability boundary of the virtual spring.

• Journal of Institute of Convergence Technology
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• v.10 no.1
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• pp.41-45
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• 2020

This paper presents the effects of a virtual mass on the stability boundary of a virtual spring in the haptic system with first-order-hold. The virtual rigid body is modeled as a virtual spring and a virtual mass. When first-order-hold is applied, we analyze the stability boundary of the virtual spring through the simulation according to the virtual mass and the sampling time. As the virtual mass increases, the stability boundary of the virtual spring gradually increases and then decreases after reaching the maximum value. The results are compared with the stability boundary in the haptic system with zero-order-hold. When a virtual mass is small, the stability boundary of a virtual spring in the system with first-order-hold is larger than that in the system with zero-order-hold.

• Journal of Institute of Convergence Technology
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• v.7 no.2
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• pp.25-30
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• 2017

This paper presents the effects of a virtual mass with a low-pass filter on the stability boundary of a virtual spring in the haptic system. In general, a haptic system consists of a haptic device, a sampler, a virtual impedance model and zero-order-hold. The virtual impedance is modeled as a virtual spring and a virtual mass. However the high-frequency noise due to the sampling time and the quantization error of sampled data may be generated when an acceleration is measured to compute the inertia force of the virtual mass. So a low-pass filter is needed to prevent the unstable behavior due to the high-frequency noise. A finite impulse response (FIR) filter is added to the measurement process of the acceleration and the effects on the haptic stability are simulated. According to the virtual mass with the FIR filter and the sampling time, the stability boundary of the virtual spring is analyzed through the simulation. The maximum available stiffness to guarantee the stable behavior is reduced, but simulation results still show that the stability boundary of the haptic system with the virtual mass is larger than that of the haptic system without the virtual mass.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.10a
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• pp.229-230
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• 2012

The free flexural vibration of a cantilever plate partially submerged in a fluid is investigated. The fluid is assumed to be inviscid and irrotational. The virtual mass matrix is derived by solving the boundary-value problem related to the fluid motion using elliptical coordinates. The introduction of the elliptical coordinates naturally leads to the use of the Mathieu function. Hence, the virtual mass matrix which reflects the effect of the fluid on the natural vibration characteristics is expressed in analytical form in terms of the Mathieu functions. The virtual mass matrix is then combined with the dynamic model of a thin rectangular plate obtained by using the Rayleigh-Ritz method. This combination is used to analyze the natural vibration characteristics of a partially submerged cantilever plate qualitatively. Also, the non-dimensionalized added virtual mass incremental factors for a partially submerged cantilever plate are presented to facilitate the easy estimation of natural frequencies of a partially submerged cantilever plate. The numerical results validate the proposed approach.

• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.957-966
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• 2020

This paper presents the virtual mass method to implement the prediction of total resistance for ice-going ship in floe ice region based on the combined method of CFD and DEM. Two ways of floe ice distribution are adopted for the analysis and comparison. The synthetic ice model test has been conducted to determine the optimal virtual mass coefficients for the two different floe ice distributions. Moreover, the further verification and prediction are developed in different ice conditions. The results show that, the fixed and random distributions in numerical method can simulate the interaction of ship and ice vividly, the trend of total resistance varying with the speed and ice concentration obtained by the numerical simulation is consistent with the model test. The random distribution of floe ice has higher similarity and better accuracy than fixed distribution.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.4
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• pp.807-815
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• 2017

For liquid rocket engine(LRE)-based space launch vehicles, longitudinal instability, often referred to as the pogo phenomenon in the literature is predicted. In the building block of system-level task, accurate dynamic modeling of a fluid-filled tank is an essential. This paper attempts to apply the virtual mass method that accounts for the interaction of the vehicle structure and the enclosed liquid oxygen to LOX-filled tanks. The virtual mass method is applied in a modal analysis considering the hydroelastic effect of the launch vehicle tank. This method involves an analysis of the fluid in the tank in the form of mass matrix. To verify the accuracy of this method, the experimental modal data of a small hemispherical tank is used. Finally, the virtual mass method is applied to a 1/8-scale space shuttle external tank. In addition, the LOX tank bottom pressure in the external tank model is estimated. The LOX tank bottom pressure is the factor required for the coupling of the LOX tank with the propulsion system. The small hemispherical tank analysis provides relatively accurate results, and the 1/8-scale space shuttle external tank provides reasonable results. The LOX tank bottom pressure is also similar to that in the numerical results of a previous analysis.

• The International Journal of Costume Culture
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• v.13 no.2
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• pp.118-129
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• 2010

Digital technology introduced into the clothing and fashion industry is evolving to digital virtual fashions and consumer-centered mass-customized production systems. Today the application of such 3D virtual try-on systems is being expanded gradually in the clothing industry. This study purposed to make virtual avatars and virtual garments using OptiTex and V-stitcher virtual software and compared the appearance of the virtual garments put on the virtual avatars. For this, we created virtual avatars and virtual garments using body measurements obtained from jive subjects of top jive body shapes, respectively, using $[TC]^2$ body scanner. According to the results of comparing the outcomes of the two different virtual software systems, virtual avatar II of V-Stitcher tended to have a more round and lifted hip and the waist line at a higher position. In addition, the body curves and shapes of a virtual avatar affect the appearance of virtual garments. This study applied the same body measurements to virtual avatars and the same pattern to virtual garments, but when different kinds of virtual software were used, the virtual avatars and virtual garments showed different appearance and fit. This result may mean that when customers buy apparel products using different kinds of virtual try-on systems, their evaluation of appearance can vary depending on the virtual try-on system. Therefore, research needs to be made actively for the development and use of linkage programs that can reflect actual body measurements between virtual software systems and 3D body scanning systems.

• Journal of Institute of Convergence Technology
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• v.3 no.2
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• pp.23-29
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• 2013

When a human operator interacts with a virtual wall that is modeled as a virtual spring model, the lager the stiffness of the virtual spring is, the more realistic the operator feels that the virtual wall is. In the previous studies, it is shown that the maximum available stiffness of a virtual spring to guarantee the stability can be increased when the first-order-hold method is applied, however the effects of a human impedance on the stability are not considered. This paper presents the effects of a human impedance on stability of haptic system with a virtual spring and a first-order-hold (FOH) method. The human impedance model is modeled as a linear second-order system model. The relations between the maximum available stiffness of a virtual spring and the human impedance such as a mass, a damping and a stiffness are analyzed through the MATLAB simulation. It is shown that the maximum available stiffness is proportional to the square root of the human mass or damping respectively.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.36 no.1
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• pp.60-65
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• 2000

The virtual mass of net is an important parameter in the analysis and control of net movement in the water. This experiment was performed with the purpose of getting a relation on the quantity of netting and virtual mass of trawl nets using the circulating water channel that can control flow speed. Twelve types of conical nets were examined. Resistance of the conical net at the steady and acceleration state was recorded as text on the personal computer through the tension meter and current meter. The results were obtained as follows ;1. Resistance(R) of the conical net is proportional to the degree of attack angle in the sam e amount of twine material.2. Coefficient of the resistance(Cd)could be defined by the following regression model as a function of Reynolds Number(Re). Cd=0.039Re-0.14743. Resistance(R) is proportional to TSA(Twine surface area) and defined as follows; R=21.398TSA-0.12194. Coefficient of virtual mass(CM) could be calculated by the following first order regression model. CM=37.557U-8.96845. Virtual mass is directly proportional to Volume of net(V) or d/l.

• Journal of Institute of Convergence Technology
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• v.4 no.2
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• pp.17-21
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• 2014

This paper presents the effects of the time delay on the stability of the haptic system that includes a virtual wall and a first-order-hold method. The model of a haptic system includes a haptic device model with a mass and a damper, a virtual wall model, a first-order-hold model and a time delay model. In this paper, the time delay is considered as the computational time delay that is assumed to be as much as the sampling time. As the time delay increases, the maximal available stiffness of a virtual wall model is reduced reversely. The relation among the time delay and the maximum available stiffness, the mass and the damper of the haptic device are analyzed using the MATLAB simulation.