• 전산구조공학
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• 제9권4호
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• pp.219-228
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• 1996

힌지가 발생하는 철근콘크리트 골조구조물의 비선형해석시에 부재강성값을 사용하는 새로운 방법에 대한 연구이다. 본 연구에서는 부재의 비선형상태에서 힌지영역의 접선강성을 평가하고 효율적으로 이용하는 방법을 제시하였다. 비선형응답을 얻기위해 고유벡터를 이용하는 해석법은 비선형범위에서 시각증분에 따라 강성이 변하고 따라서 고유벡터군도 그 변하는 수만큼 재산정 하여야 하기 때문에 일반적인 해석방법이 아니다. 그러나 부재의 비선형상태를 나타내는 강성값, 즉 고유벡터의 산정횟수를 줄이며 산정된 기존값을 적절하게 재사용하여 해석의 효율성을 입증하였다. 지진하중을 받는 철근콘크리트 골조구조물의 비선형 해석의 경제성은 고유벡터의 산정횟수에 의존되기 때문에 고유벡터의 산정횟수를 감소시키며 신뢰성있는 응답을 구하여 본 해석법의 효율성을 입증하였다.

• The Journal of Korean Physical Therapy
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• 제22권1호
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• pp.1-7
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• 2010

Purpose: Stretching exercises are commonly used in conjunction with sports and rehabilitation. Weassessed the immediate effects of stretching on passive stiffness of the hamstring muscles and knee range of motion (ROM) using three stretching techniques. Methods: A total of 45 participants were recruited. Isokinetic equipment was used to measure the passive stiffness of hamstring muscles and an inclinometer was used to measure active and passive ROM of the knee joint pre and post stretching. Stiffness was then calculated based on the incline of the torque-angle relationship. The test conditions for Group I were $3{\times}30$ seconds of static stretches using the hamstring muscle, Group II were $3{\times}30$ seconds of static stretches using the hamstring muscle with ankle dorsiflexion, and Group IIII had $3{\times}30$ seconds of active stretching. Results: Group II had significantly higher excursion of active ROM and Group IIIhad significantly higher excursion of passive muscle stiffness. All of the groups had significantly higher active and passive ROM and significantly lower muscle stiffness after stretching. The participants showed no change in hamstring muscle stiffness on the following day. Conclusion: Stretching has significant acute effects on ROM and muscle stiffness and canbe used in warm-up protocols for reducing muscle stiffness before a variety of exercise programs.

• 펄프종이기술
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• 제39권4호
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• pp.21-28
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• 2007

A simple method of on-line stiffness measurement using the wrinkling behavior of paper web between two rollers was presented. The theory and the equation were presented, and lab and mill tests were executed. We called the stiffness measured by Taber tester as 'Taber stiffness', and by tension wrinkling measurement as 'wrinkle stiffness', respectively. Lab experimental results showed Taber and wrinkle stiffness are almost equivalent. In the mill experiment, we could measure the stiffness in the wet state and in the dry state. The dry wrinkle stiffness was close to the taber stiffness, but the wet wrinkle stiffness was much lower than the corresponding taber stiffness.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 학술대회 논문집 전문대학교육위원
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• pp.216-220
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• 2006

This paper is presented for the measurement of the bearing stiffness for the spindle motors. BLDC Spindle Motors for the Hard Disk Drive are used by several kinds of the bearings, such as ball bearing, fluid dynamic bearing, and aero dynamic bearing. The spindle motors are attached the platters to read and write the data. Because the platter rotates at high end speed with the load and can be shocked from a suddenly moving, the bearing needs the rated stiffness with the pressure. By the way, it has not been realized to measure the real stiffness for each bearing types. In this paper, we proposed the method of measuring the stiffness for the bearings by using the magnet force. Experimental results show the performance to measure the bearing stiffness of the BLDC spindle motors for an HDD.

• 대한건축학회논문집:구조계
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• 제34권12호
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• pp.3-10
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• 2018

Recently, severe damage to domestic horticultural structures is frequently observed due to extreme climate effects. To minimize the structures' damage, a study on the structural stability of multi-span vinyl greenhouses is needed. This paper presents to measure the rotational stiffness of different connectors to improve the design capacities of the specification. The paper investigated fourteen types of the different connectors, which was commonly used in the multi-span greenhouses, and three different types of the connectors predicted to be under moment-connection were selected: i) T-clamp, ii) U-clamp, iii) C-clamp. Static loading tests for three different connectors were performed to measure the rotational stiffness. Additionally, the boundary condition for the structural design was proposed based on the experimental results of the rotational stiffness. One of three connectors, C-clamp had larger rotational stiffness than other connectors, and the experimental results presented the three connectors had boundary conditions; i) T-clamp was pinned-connection, ii) U-clamp was semi-rigid connection, iii) C-clamp was semi-rigid connection.

• Structural Engineering and Mechanics
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• 제44권3호
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• pp.363-378
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• 2012

The stiffness of a suspension system is provided by the bushings and the stiffness of the wheel center controls the suspension's elasto-kinematic (e-k) specification. So the stiffness of the wheel center is very important, but the stiffness of the wheel center is very hard to measure. The paper give a new method that we can use the stiffness of the bushings to calculate the equivalent stiffness of the wheel center, which can quickly and widely be used in all kinds of suspension structure. This method can also be used to optimize and design the suspension system. In the example we use the method to calculate the equivalent stiffness of the wheel center which meets the symmetric and positive conditions of the stiffness matrix.

• 비파괴검사학회지
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• 제33권3호
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• pp.276-282
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• 2013

This paper proposes an ultrasonic method for measurement of linear and hysteretic interfacial stiffness of contacting surfaces between two steel plates subjected to nominal compression pressure. Interfacial stiffness was evaluated by the reflection and transmission coefficients obtained from three consecutive reflection waves from solid-solid surface using the shear wave. A nonlinear hysteretic spring model was proposed and used to define the quantitative interfacial stiffness of interface with the reflection and transmission coefficients. Acoustic model for 1-D wave propagation across interfaces is developed to formulate the reflection and transmission waves and to determine the linear and nonlinear hysteretic interfacial stiffness. Two identical plates are put together to form a contacting surface and pressed by bolt-fastening to measure interfacial stiffness at different states of contact pressure. It is found from experiment that the linear and hysteretic interfacial stiffness are successfully determined by the reflection and transmission coefficient at the contact surfaces through ultrasonic pulse-echo measurement.

• 대한기계학회논문집A
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• 제29권4호
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• pp.563-569
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• 2005

This paper develops a finite element model of a cabover type large truck. The finite element model is for evaluating torsional stiffness of the frame of the large truck. The torsional test of the frame is conducted in order to validate the developed finite element model. A load cell is used to measure the load applied to the frame. An angle sensor is used to measure the torsional angle. An actuator is used to apply a load to the frame. A vertical upward load and a vertical downward load are applied to the frame in the torsional test. The frame's torsional stiffness is computed with the measured load and torsional angle in the torsional test. The finite element model of the large truck includes cab, deck and payload, suspension, and tire. Cab, deck, and suspension are modeled not to affect the frame's torsional stiffness. The simulation is performed with the developed finite element model for evaluating the frame's torsional stiffness. The simulation results show a very good correlation with the torsional test results in the tendency of changing of the frame's torsional stiffness not only with the direction of the applying load but also with the amount of the applying load. In addition, the simulation results predict the measured torsional stiffness of the frame with about $5{\%}$ error.

• 한국자동차공학회논문집
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• 제11권1호
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• pp.121-127
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• 2003

The stiffness of a bushing in a suspension is extremely important for the overall performance of the suspension system. A new measurement system including the flexible jig was developed to measure the multi-directional stiffness of bushings. To overcome the disadvantage of building each individual jig for each type and size of a bushing, we designed the flexible jig which can accommodate numerous bushings of similar shapes and sizes. Upon using the novel design of the flexible jig in the industry, we could successfully measure the torsional and conical stiffness of many bushings and apply the data for the prediction and evaluation of the performance of a suspension system, which would assist designing the optimal suspension system.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.844-849
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• 2006

Accurate modeling of complex dynamic stiffness of the pneumatic springs is crucial for an efficient design of vibration isolation tables for precision instruments such as optical devices or nano-technology equipments. Besides pressurized air itself, diaphragm made of rubber materials, essentially employed for prevention of air leakage, plays a significant contribution to the total complex stiffness. Therefore, effects of the diaphragm should be taken care of precisely. The complex stiffness of an inflated diaphragm is difficult to predict or measure, since it is always working together with the pressurized air. In our earlier research, the complex stiffness of a diaphragm was indirectly estimated simply by subtracting stiffness of the pressurized air from measurement of the total complex stiffness for a single chamber pneumatic spring. In order to reflect dynamic stiffness of inflated diaphragm on the total stiffness at the initial design or design improvement stage, however, it is required to be able to predict beforehand. In this presentation, how to predict the complex stiffness of inflated rubber diaphragm by commercial FE codes(e.g. ABAQUS) will be discussed and the results will be compared with the indirectly measured values.