• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 2007년도 정기 학술대회 논문집
• /
• pp.757-762
• /
• 2007

The lining segment which is the main structure of the shield tunnel consists of joints, not continua. Past international and domestic design data have been commonly used for design practices without specific verification about the structural analysis model, design load, and affection of the soil constant of the lining segment. In this study, the propriety is estimated through the comparison between analytical solution and numerical solution for segment analysis and design models of the shield tunnel which is being used internationally and domestically. As a result, the full. circumferential beam jointed spring model (1R-S0) is suggested by considering aspects of convenient use, application to field condition, and accuracy of analysis result. With suggested model, the parameter analysis was conducted for joint stiffness, ground rigidity, joint distribution, and joint number.

• 한국철도학회:학술대회논문집
• /
• 한국철도학회 2002년도 추계학술대회 논문집(II)
• /
• pp.1065-1073
• /
• 2002

A new damage identification technique using static displacement data is developed to assess the structural integrity of bridge structures. In the conventional damage assessment techniques using dynamic response, it is usually difficult to obtain a significant natural frequencies variation from the measured data because the natural frequencies variation is intrinsically not sensitive to the damage of a bridge. In this proposed identification method, the stiffness reduction of the bridges can be estimated using the static displacement data measured periodically and a specific loading test is not required. The static displacement data due to the dead load of the bridge structure can be measured by devices such as a laser displacement sensor. In this study, structural damage is represented by the reduction in the elastic modulus of the element. The damage factor of the element is introduced to estimate the stiffness reduction of the bridge under consideration. Finally, the proposed algorithm is verified using various numerical simulation and compared with other damage identification method. Also, the effect of noise and number of damaged elements on the identification are investigated. The results show that the proposed algorithm is efficient for damage identification of the bridges.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2007년도 제38회 하계학술대회
• /
• pp.1916-1917
• /
• 2007

Aortic AIx(augmentation index) has been used to measure aortic stiffness and evaluate ventricular load quantitatively. Algorithm for the detection of augmentation point gradually increases the differential order to detect inflection point rather than detects the distinctive point that appears after a specific time. Developed algorithm for AIx is proved to provide more accurate results than the ones developed by previous studies with the deviation from $-11.5{\pm}14.34$ points to $-3.75{\pm}1.26$ points. Results could provide the basis for the measurement of aortic stiffness using easily-measurable radial artery pulse waves, and could be extended to develop a system for early diagnosis of various vascular diseases.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2004년도 추계학술대회논문집
• /
• pp.709-712
• /
• 2004

A study of the coupled flexural-torsional vibrations of thin-walled beams with monosymmetric cross-section is presented. The governing differential equations for free vibration of such beams are solved numerically to obtain natural frequencies and their corresponding mode shapes. The beam model is based on the Bernoulli-Euler beam theory and the effect of warping is taken into consideration. Numerical results are given for two specific examples of beams with free-free, clamped-free, hinged-hinged, clamped-hinged and clamped-clamped end constraints both including and excluding the effect of warping stiffness. The effect of warping stiffness on the natural frequencies and mode shapes is discussed and it is concluded that substantial error can be incurred if the effect is ignored.

• Earthquakes and Structures
• /
• 제3권3_4호
• /
• pp.271-295
• /
• 2012

This paper presents the solution scheme of using the continuous formulation of 1-D linear member for the dynamic analysis of structures consisting of axially loaded members. The context describes specific applications of such scheme to the verification of experimental data obtained from field test of bridges carried out by a microwave interferometer system and velocimeters. Attention is focused on analysis outlines that may be applicable to in-situ assessment for cable-stayed bridges. The derivation of the dynamic stiffness matrix of a prismatic member with distributed properties is briefly reviewed. A back calculation formula using frequencies of two arbitrary modes of vibration is next proposed to compute the tension force in cables. Derivation of the proposed formula is based on the formulation of an axially loaded flexural member. The applications of the formulation and the proposed formula are illustrated with a series of realistic examples.

• 한국전문물리치료학회지
• /
• 제30권4호
• /
• pp.275-280
• /
• 2023

Background: Although warm-ups before exercise are widely accepted, research on sex differences in improving hamstring flexibility is limited. Differences in the physical and physiological characteristics between males and females may result in different responses to warm-ups. Objects: This study aimed to examine sex differences in the effects of specific warm-up on hamstring flexibility. Methods: This study included 24 young adults with hamstring tightness. The participants performed five maximal knee extensions and flexions at 90° flexion of the hip, and the maximal knee extension angle was measured in real-time using a smartphone clinometer application. Results: The groups did not significantly affect the maximal knee extension angle but showed a significant effect for repetition (p = 0.002) and group-repetition interaction (p = 0.002). Males had no significant change in hamstring flexibility; however, females showed a significant increase in flexibility in the 5^th trial compared with the 1^st trial (p = 0.041). These results demonstrated sex-specific differences in flexibility improvement over time. Conclusion: The findings of this study suggest that specific warm-up can successfully improve hamstring flexibility in females. This may be due to various factors, such as muscle stiffness of the lower extremity, estrogen levels, and temperature sensitivity. In clinical settings, specific warm-up might be helpful for females who participate in sports or activities, such as running or jumping, which require a full range of motion in the hip and knee joints.

• Tribology and Lubricants
• /
• 제34권3호
• /
• pp.75-83
• /
• 2018

Microturbomachinery (< 250 kW) using gas foil bearings can function without oil lubricants, simplify rotor-bearing systems, and demonstrate excellent rotordynamic stability at high speeds. State-of-the-art technologies generally use bump foil bearings or leaf foil bearings due to the specific advantages of each of the two types. Although these two types of bearings have been studied extensively, there are very few studies on leaf-bump foil bearings, which are a combination of the two aforementioned bearings. In this work, we illustrate a simple mathematical model of the leaf-bump foil bearing with leaf foils supported on bumps, and predict its static and dynamic performances. The analysis uses the simple elastic model for bumps that was previously developed and verified using experimental data, adds a leaf foil model, and solves the Reynolds equation for isothermal, isoviscous, and ideal gas fluid flow. The model predicts that the drag torques of the leaf-bump foil bearings are not affected significantly by static load and bearing clearance. Due to the preload effect of the leaf foils, rotor spinning, even under null static load, generates significant hydrodynamic pressure with its peak near the trailing edge of each leaf foil. A parametric study reveals that, while the journal eccentricity and minimum film thickness decrease, the drag torque, direct stiffness, and direct damping increase with increasing bump stiffness. The journal attitude angle and cross-coupled stiffness remain nearly constant with increasing bump stiffness. Interestingly, they are significantly smaller compared to the corresponding values obtained for bump foil bearings, thus, implying favorable rotor stability performance.

• Composites Research
• /
• 제19권2호
• /
• pp.13-19
• /
• 2006

본 논문에서는 미세 방전가공(Electrical Discharge Machining; EDM) 기계를 위한 샌드위치 구조를 설계하기 위해 복합재료의 적층 순서, 두께, 그리고 리브의 형상 등을 고려한 파라메트릭 연구를 수행하였다. 샌드위치 구조는 면재인 섬유강화 복합재료와 심재인 레진 콘크리트 및 고분자 포움으로 이루어졌다. 컬럼은 정적 굽힘강성과 비굽힘강성을 높이기 위해 십자 리브를 가진 형상으로 설계하였으며, 적층 순서와 두께를 조절하였다. 베드의 경우 양방향의 강성을 동시에 향상시키기 위해 적층 순서와 리브 형상을 조절하였다. 최적의 고강성을 얻기 위하여 리브의 두께와 면재의 두께 등 설계 파라메터의 최적치를 제안하였다. 각 설계 파라메터의 변화에 따른 구조의 정적, 동적 강성의 변화를 확인하기 위해 유한요소해석을 수행하였으며, 진동 실험을 통하여 각 요소의 고유진동수와 감쇠비를 측정하여 비교하였다. 이러한 결과로부터 고정밀 미세 방전가공 기계 구조를 위한 최적의 형상조건을 제안하였다.

• 한국복합재료학회:학술대회논문집
• /
• 한국복합재료학회 2002년도 춘계학술발표대회 논문집
• /
• pp.215-218
• /
• 2002

In this paper, we applied composite material of high specific stiffness and strength to the fabrication of a folding wheelchair frame for the replacement of conventional metal wheelchair frames. A one-body composite frame was designed and the finite element analysis was performed on this design. Some specimens of joint parts were manufactured and strength test was done. With the results of analysis and test, some modification was done and a prototype was produced.

• Composites Research
• /
• 제13권3호
• /
• pp.1-8
• /
• 2000

Excellent environmental durability and handy installation procedure as well as high specific strength and stiffness have introduced fiber-reinforced polymeric composite materials into the civil and architectural engineering field. This study presents the considerably enhanced strength characteristics of the mortal beams by being reinforced with epoxy-bonded carbon fiber sheets(CFS). Three point bending and Charpy impact tests were performed on both of bare and reinforced mortar specimens. The influences of length, and the number of reinforcing plies were investigated. Strength reduction due to pre-existent notch was lessened dramatically. The acoustic emission(AE) measurement revealed the progressive damage process in reinforced specimens.