• 한국방재학회 논문집
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• 제8권2호
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• pp.97-103
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• 2008

Determination of stress-strain relationship in torsional tests is complicated due to nonuniform stress-strain variation occurring linearly with the radius in a soil specimen in torsion. The equivalent radius approach is adequate when calculating strain at low to intermediate strains, however, the approach is less accurate when performing the test at higher strain levels. The modified equivalent radius approach was developed to account for the problem more precisely. This approach was extended to generate the plots of equivalent radius ratio versus strain using modified hyperbolic and Ramberg-Osgood models. Results showed the effects of soil nonlinearity on the equivalent radius ratio curves were observed. Curve fitting was also performed to find the stress-strain relationship by fitting the theoretical torque-rotation relationship to measured torque-rotation relationship.

• 한국방재학회 논문집
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• 제8권2호
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• pp.39-43
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• 2008

Determination of strain associated with shear modulus and damping ratio during torsional test is complicated. This is due to nonuniform stress-strain variation occurring linearly with radius in a soil specimen in torsion. A conventional equivalent radius approach proposed by Chen and Stokoe appears to be adequate for evaluating strain associated with shear modulus at low to intermediate strain levels. This approach is less accurate for damping measurement, particularly at high strain. Modified equivalent radius approach was used to account for the nonuniform stress-strain effect more precisely. The modified equivalent radius approach was applied for hyperbolic, modified hyperbolic, and Ramberg-Osgood models. The results illustrate the usefulness of the modified equivalent radius approach and suggest that using a single value of equivalent radius ratio to calculate strains is not appropriate.

• Coupled systems mechanics
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• 제6권1호
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• pp.55-74
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• 2017

The evaluation of torsional effects on multistory buildings remains an open issue, despite considerable research efforts and numerous publications. In this study, a large number of multiple test structures are considered with normally distributed topological attributes, in order to quantify the statistically derived relationships between the torsional criteria and response parameters. The linear regression analysis results, depict that the center of twist and the ratio of torsion (ROT) index proved numerically to be the most reliable criteria for the prediction of the modal rotation and displacements, however the residuals distribution and R-squared derived for the ductility demands prediction, was not constant and low respectively. Thus, the assessment of the torsional parameters' contribution to the nonlinear structural response was investigated using artificial neural networks. Utilizing the connection weights approach, the Center of Strength, Torsional Stiffness and the Base Shear Torque curves were found to exhibit the highest impact numerically, while all the other torsional indices' contribution was investigated and quantified.

• Composites Research
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• 제27권2호
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• pp.37-41
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• 2014

섬유강화복합재료는 비강도와 비강성이 뛰어나 여러 분야에 걸쳐 사용량이 증가하고 있으며 자전거와 같은 스포츠 용품에도 사용량이 점점 증가하고 있다. 복합재료는 다양한 형상의 구조부품으로 만들어져 사용되고 있다. 특히 자전거 프레임의 일부에는 사각형 복합재 튜브 형태로 제작되어 사용되고 있으나 이에 관한 연구는 많지 않다. 사각 복합재 튜브의 경우에 모서리에 적절한 라운드 값을 주어 굽힘과 비틀림에 견디도록 설계된다. 본 연구에서는 모서리의 곡률반경이 R5, R10, R15인 세 개의 그룹에 가로-세로 1:1, 1:1.5, 1:2의 형상비를 갖는 아홉 종류의 사각 복합재 튜브를 제작하였다. 탄소섬유강화복합재료가 튜브제작에 사용되었으며 단면적은 모두 같도록 설계되었다. $[0/90/{\pm}45]s$으로 적층하여 제작한 사각 복합재 튜브에 굽힘과 비틀림 하중을 가하여 실험평가를 수행하였다. 실험결과 사각 복합재 튜브의 R 값과 형상비에 따라서 굽힘 및 비틀림 특성이 크게 다름을 알 수 있었다.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2000년도 춘계학술대회논문집 - 한국공작기계학회
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• pp.629-634
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• 2000

Generally, the accuracy of motion control systems is strongly influenced by both the mechanical characteristics and servo characteristics of feed drive systems. In the fed drive systems of machine tools that consist of mechanical parts and electrical parts, a torsional vibration is often generated because of its elastic elements in torque transmission. Especially, a torsional vibration caused by the elasticity of mechanical elements might deteriorate the quick movement of system and lead to shorten the life time of the mechanical transmission elements. So it is necessary to analyze the electromechanical system mathematically to optimize the dynamic characteristics of the feed drive system. In this paper, based on the simplifies feed drive system model, radius errors due to position gain mismatch and servo response characteristic have been developed and an optimal criterion for tuning the gain of speed controller is discussed. The proportional and integral parameter gain of the feed drive controller are optimal design variables for the gain tuning of PI speed controller. Through the optimization problem formulation, both proportional and integral parameter are optimally tuned so as to compensate the radius errors by using the genetic algorithm. As a result, higher performance on circular profile tests has been achieved than the one with standard parameters.

• 대한기계학회논문집A
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• 제33권12호
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• pp.1471-1481
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• 2009

In diesel engines, it is inevitable that the torsional vibration is produced by the fluctuation of engine torque. Therefore, it is necessary to establish preventive measures to diminish the torsional vibration. The sleeve spring type damper is one of the preventive measures for reducing the torsional vibration. In this study, the closed form equations to predict the spring constant of a sleeve spring and the torsional characteristics of the torsional vibration damper are proposed to calculate stiffness of the damper and verified their availability through the finite element analysis and experiments. And the stability of the sleeve spring torsional vibration damper is verified by analyzing the inner star and outer star, which are the core parts of the damper, and 2-roll bending process is proposed to manufacture sleeve spring. The program to calculate the initial radius including spring-back effect is developed, and the FEA method to analyze elasto-plastic problem was verified through analysis of 90$^{\circ}$bending process. The results of the analysis are in good agreements with those of the experiments. The newly proposed method can be used as an advanced technique that remarkably curtails cost of production and replaces the conventional forming.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2013년도 춘계학술대회 논문집
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• pp.492-497
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• 2013

In this study, a parametric study is performed to investigate the squeal noise of an automobile water pump. The squeal noise studied in this paper is generated by the self-excited torsional resonance of the rotating shaft, and this noise is related to the stick-slip phenomenon of the mechanical seal in the water pump. The mechanical seal friction has the characteristics of the negative velocity-gradient. The equations of motion of multiple-degree-of-freedom torsional vibration model is constructed by the Holzer's method and then the equation is transformed to an equivalent single-degree-of-freedom torsional resonance simulation model. A squeal noise criteria is determined by the simulation model to perform the parametric study. The design parameters(the mass moment of inertia of the pulley, the mass moment of inertia of the impeller, the length of the shafts, the radius of the shafts, spinning speed of the shafts, the position of the mechanical seal, radius of the mechanical seal, and normal load of the mechanical seal) are investigated to confirm the stability for the squeal noise.

• 한국소음진동공학회논문집
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• 제23권7호
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• pp.624-630
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• 2013

In this study, a parametric study is performed to investigate the squeal noise of an automobile water pump. The squeal noise studied in this paper is generated by the self-excited torsional resonance of the rotating shaft, and this noise is related to the stick-slip phenomenon of the mechanical seal in the water pump. The mechanical seal friction has the characteristics of the negative velocity-gradient. The equations of motion of multiple-degree-of-freedom torsional vibration model is constructed by the Holzer's method and then the equation is transformed to an equivalent single-degree-of-freedom torsional resonance simulation model. A squeal noise criteria is determined by the simulation model to perform the parametric study. The design parameters(the mass moment of inertia of the pulley, the mass moment of inertia of the impeller, the length of the shafts, the radius of the shafts, spinning speed of the shafts, the position of the mechanical seal, radius of the mechanical seal, and normal load of the mechanical seal) are investigated to confirm the stability for the squeal noise.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2000년도 추계학술발표대회 논문집
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• pp.9-12
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• 2000

This paper deals with the torsional buckling behavior of plain weave GFRP composite cylindrical shells having comparatively small length-to-diameter ratio. Boundary conditions corresponding to clamped ends and simply supported ends are considered. Torsional buckling loads and circumferential mode numbers according to the variation of shell length-to-radius ratio are conformed. To verify the availability of the theoretical results, comparison with the theoretical and experimental results are made.

• 한국지진공학회논문집
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• 제12권1호
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• pp.43-55
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• 2008

비틂시험에서 전단탄성계수와 감쇠비에 상응하는 변형률 산정의 복잡성은 여러 방법에 의하여 해결되어 왔다. 특히, 수정 등가반경법은 공진주/비틂전단 시험의 모든 변형률 영역에서 변형률에 따른 등가반경비 곡선을 보다 효과적으로 나타내는데 적합하다. 감쇠비 산정시 수정 등가반경법을 쌍곡선 모델, 수정 쌍곡선 모델, 램버그오스굿 모델등에 적용시켜 보았다. 연구결과는 감쇠비 산정시 재래식 등가반경법에 의한 하나의 등가반경 수치를 사용하는 것은 적절치 않다는 것을 보여주었다. 이력감쇠뿐 아니라 미소변형률 영역에서의 흙의 감쇠 현상을 고려하기 위하여 새로운 모델이 개발되었고, 이러한 두 가지 복합감쇠에 상응하는 변형률 산정시 부가적 조정이 필요한지 검토해 보았다.