• 한국철도학회논문집
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• 제14권3호
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• pp.262-270
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• 2011

궤도지지강성은 차량이 주행함에 있어 궤도와 차량에 매우 큰 영향을 미치며, 이는 궤도 파괴이론에 근거한 궤도유지관리와 승객의 승차감에 영향을 준다. 또한 궤도설계 시 고려되는 궤도지지강성은 이론에 근거한 계산치이며 이는 공용중인 궤도에서의 실제 궤도지지강성과는 상이하다. 따라서 본 연구에서는 현장측정을 통해 동적 윤중과 레일수직변위, 레일저부응력을 측정하여 궤도지지강성을 산출하였고 이를 이론 궤도지지강성과 비교 분석하였다. 현장측정결과 자갈도상궤도에서의 궤도지지강성은 자갈의 상태에 직접적인 영향을 받으며 콘크리트궤도의 경우 궤도구조별(일반적인 침목매입식, 레일플로팅, 침목플로팅) 궤도구조특성에 직접적인 영향을 받는 것으로 나타났다. 그러나 자갈 및 콘크리트궤도 모두 설계 시 적용되는 궤도지지강성이 측정된 궤도지지강성에 비해 과소평가되는 것으로 분석되었다. 이는 공용중인 궤도의 상태평가 시 현장의 궤도상태를 반영하지 못한 예측 및 평가가 될 소지가 있을 것으로 판단된다. 이에 본 연구에서는 궤도구조형식 및 궤도상태별 궤도지지 강성의 범위를 실험적으로 제시하였다.

• 한국의류학회지
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• 제10권1호
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• pp.47-57
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• 1986

The purpose of this study is to investigate fatigue phenomema of woven fabric. In order to obtain the basic data which is available for predicting the fabric fatigue phenomena, the change of mechanical properties of woven fabrics caused by the wearing and the changes of mechanical properties of woven fabrics which were subjected to repeated tensile-shearing deformation using fabric testing machine has been investigated and compared. The fatigue of woven fabrics was examined with the value of basic mechanical properties of specimens measured by the KES-F fabric testing system and their hand value and wearing ability. The results were as follows. 1) The fatigue phenomena of woven fabrics by the wearing for 800 hours are different on the position of the body: On the portion of hip, the change of surface property was the greatest, bending hysterisis was greatly increased, thickness weight, stiffness, fullness shearing hysterisis were more increased than original fabric and T.H.V. was decreased. On the portion of knee, decreasing of tensile resilience and increasing of bending, shearing hysterisis were observed greater than any other part, and increasing of stiffness, crispness was more than original fabric. On the bottom area, the changes of mechanical property was comparatively small, H.V. and T.H.V. showed near the value of the original fabric. 2) By drycleaning most of mechanical properties showed the tendency to recover the value of the original fabric, but bending hysterisis and thickess were increased, tensile and com-pression resilience were decreased more than original fabric in all parts. 3) The fatigue phenomena caused by fabric fatigue testing machine were as follows. The decreasing of hystersis in the repeated deformation such as bending, shearing was appeared at the $10^2$ deformation, but with the increasing cycle, the tendency was slightly regained. Handle value was also appeared the lowest value at the $10^2$ deformation.

• 한국소음진동공학회논문집
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• 제23권10호
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• pp.869-877
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• 2013

Tension force of hanger ropes has been recognized and utilized as an important parameter for health monitoring of suspension bridges. Conventional vibration method based on string theory has been utilized to estimate tension forces of relatively long hanger ropes without any problem, however it is convinced that the vibration method is not applicable for shorter hanger ropes in which the influence of flexural stiffness is not ignorable. Therefore, as an alternative of vibration method, a number of feasibility studies of system identification(SI) technique considering flexural stiffness of the hanger ropes are recently performed. In this study, the influence of support condition of the finite element model utilized for the SI method is investigated with numerical examples. The numerical examples are prepared with the specification of the Kwang-Ahn bridge hanger ropes, and it is revealed that the estimation result of the tension force can be varied from -21.6 % to +35.3 % of the exact value according to the consideration of the support condition of FE model. Therefore, it is concluded that the rotational stiffness of the support spring should be included to the list of the identification parameters of the FE model to improve the result of tension estimation.

• Coupled systems mechanics
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• 제4권2호
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• pp.173-189
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• 2015

In reality, masonry infill modifies the seismic response of reinforced concrete (r.c.) frame structures by increasing the overall rigidity of structure which results in: increasing of total seismic load value, decreasing of deformations and period of vibration, therefore masonry infill frame structures have larger capacity of absorbing and dissipating seismic energy. The aim of the paper is to explore and assess actual influence of masonry infill on seismic response of r.c. frame structures, to determine whether it's justified to disregard masonry infill influence and to determine appropriate way to consider infill influence by design. This was done by modeling different structures, bare frame structures as well as masonry infill frame structures, while varying masonry infill to r.c. frame stiffness ratio and seismic intensity. Further resistance envelope for those models were created and compared. Different structures analysis have shown that the seismic action on infilled r.c. frame structure is almost always twice as much as seismic action on the same structure with bare r.c. frames, regardless of the seismic intensity. Comparing different models resistance envelopes has shown that, in case of lower stiffness r.c. frame structure, masonry infill (both lower and higher stiffness) increased its lateral load capacity, in average, two times, but in case of higher stiffness r.c. frame structures, influence of masonry infill on lateral load capacity is insignificant. After all, it is to conclude that the optimal structure type depends on its exposure to seismic action and its masonry infill to r.c. frame stiffness ratio.

• Advances in nano research
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• 제10권2호
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• pp.115-128
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• 2021

In this article, free vibration behavior of electro-magneto-thermo sandwich Timoshenko beam made of porous core and Graphene Platelet Reinforced Composite (GPLRC) in a thermal environment is investigated. The governing equations of motion are derived by using the modified strain gradient theory for micro structures and Hamilton's principle. The magneto electro are under linear function along the thickness that contains magnetic and electric constant potentials and a cosine function. The effects of material length scale parameters, temperature change, various distributions of porous, different distributions of graphene platelets and thickness ratio on the natural frequency of Timoshenko beam are analyzed. The results show that an increase in aspect ratio, the temperature change, and the thickness of GPL leads to reduce the natural frequency; while vice versa for porous coefficient, volume fractions and length of GPL. Moreover, the effect of different size-dependent theories such as CT, MCST and MSGT on the natural frequency is investigated. It reveals that MSGT and CT have most and lowest values of natural frequency, respectively, because MSGT leads to increase the stiffness of micro Timoshenko sandwich beam by considering three material length scale parameters. It is seen that by increasing porosity coefficient, the natural frequency increases because both stiffness and mass matrices decreases, but the effect of reduction of mass matrix is more than stiffness matrix. Considering the piezo magneto-electric layers lead to enhance the stiffness of a micro beam, thus the natural frequency increases. It can be seen that with increasing of the value of WGPL, the stiffness of microbeam increases. As a result, the value of natural frequency enhances. It is shown that in hc/h = 0.7, the natural frequency for WGPL = 0.05 is 8% and 14% less than its for WGPL = 0.06 and WGPL = 0.07, respectively. The results show that with an increment in the length and width of GPLs, the natural frequency increases because the stiffness of micro structures enhances and vice versa for thickness of GPLs. It can be seen that the natural frequency for aGPL = 25 ㎛ and hc/h = 0.6 is 0.3% and 1% more than the one for aGPL = 5 ㎛ and aGPL = 1 ㎛, respectively.

• 구강회복응용과학지
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• 제19권4호
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• pp.291-296
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• 2003

The use of resonance frequency analysis (RFA) provides a possibility to clinically measure implant stability and osseointegration. The implant stability quotient (ISQ) value of RFA is well known that influenced by effective abutment length and stiffness of the implant in the surrounding tissues. Among these factors stiffness is not accurately defined histologically yet. And the purpose of this study was to find the histolgical relationship of RFA. 17 implants in 3 beagle dogs were used for this study. Among these implants 10 were survived for 7 months, 4 were survived for 3 months and 3 were immediate status after placement. Resonance frequency analyses were conducted and the dogs were sacrificed. Percentage of the bone to implant contact (BIC) in the interface, percentage of the mineralized bone (bone area) within the threads of the implant, and marginal bone level were measured under light microscopy. The correlation between resonance frequency and histomorphometric measurements were analysed and following results were obtained. 1. There was statistically significant correlation between ISQ value and BIC on healed implants. But ISQ value and BIC of all implants were not significantly correlated. (P<0.01) 2. Significant correlation between ISQ value and bone area was not found in this study. 3. There was statistically significant correlation between ISQ value and marginal bone level on all implants as well as on healed implants. (P<0.01).

• 한국산학기술학회논문지
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• 제20권6호
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• pp.396-401
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• 2019

가상환경 속 가상 강체는 가상 스프링과 가상 댐퍼의 병렬구조로 모델링되며 가상 강체의 현실감을 증강시키기 위해서는 가상 모델로부터의 반력을 안정적으로 최대한 크게 제시해야 한다. 따라서 햅틱 인터페이스의 안정성을 유지시킬 수 있는 가상 스프링과 가상 댐퍼의 영역을 분석하여 가상 강체모델을 선정하는 것이 중요하다. 기존에는 영차홀드를 이용하는 시스템에 대해 안정성 영역이 분석되었으나, 본 논문에서는 일차홀드 방식과 가상 댐퍼를 이용하는 햅틱 시스템에 대한 안정성 영역을 분석한다. 안정적인 가상 댐퍼 영역의 경계값은 샘플링 주기와 반비례 관계를 가지며, 안정적인 가상 스프링 영역의 최대값은 샘플링 주기의 제곱에 반비례 관계를 갖는다. 그리고 그 최대값은 일차홀드 방식을 이용하여 기존의 영차홀드의 경우보다 약 110% 향상시킬 수 있다. 가상 댐퍼의 크기가, 일차홀드 방식에서의 안정적인 가상댐퍼 경계값의 약 50% 보다 작다면, 일차홀드를 이용함으로써 기존의 영차홀드의 경우보다 안정적인 가상 스프링의 영역을 수 배 더 크게 할 수 있다.

• Structural Engineering and Mechanics
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• 제83권6호
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• pp.835-851
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• 2022

This paper analyzes the variation law of the pipe lateral vibration characteristics, it was treated as a beam model, and was dispersed into several subunits based on the FEM. The corresponding stiffness and mass matrix of the pipe was deduced by using Hermite interpolation function, and the overall dynamic balance equation was established. The lateral vibration under different pipe lengths, thicknesses and towing speeds are solved by integral method. The results show that the pipe vibration trend decreases first and then increases, and the vibration value at the ore bin is larger than that at the pump set, and the value at the top is the largest, and the least value location can change with the length increase. Increasing length and thickness can reduce lateral vibration value, while increasing speed can increase the value. Neither the thickness nor the towing speed will change the location where the least value occurs. The vibration intensity will increase with the decrease of pipe length and thickness and the increase of towing speed.

• Structural Engineering and Mechanics
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• 제6권5호
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• pp.543-554
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• 1998

Space truss structures may be fabricated in any of several common grid configurations. With different configurations, the truss performance varies considerably affecting both its competitiveness and suitability for specific applications. The work presented in this paper is an assessment of the most commonly adopted truss configurations and their effect on truss characteristics such as the stiffness/weight value, member stress distribution, number of joints and members, degree of redundancy and cost. The study is parametric and covers wide variations of truss aspect ratios, boundary conditions and span/depth ratios. The results of this study could be of significant value to the design of space truss structures.

• 콘크리트학회논문집
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• 제23권5호
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• pp.683-692
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• 2011

필로티형 저층 RC 집합주택에서는 지진 발생 시 필로티층에 손상이 집중된다. 따라서, 이 연구에서는 필로티층의 비틀림과 X, Y방향의 강도와 강성을 증가시키기 위해 좌굴방지가새를 설치함과 동시에, 과도한 변형과 축력의 변동이 발생하는 외부기둥의 연성과 축성능, 전단 성능을 증가시키기 위해 외부기둥을 FRP로 보강하였다. 이와 같은 보강 효과를 실험적으로 검증하기 위해 순수 골조와 FRP와 좌굴방지가새로 보강된 골조에 대한 반복 횡하중 실험을 수행하였다. 실험 결과 항복강도(43.2 kN)는 설계항복강도(30 kN)와 압축부의 강도 증가 때문에 차이가 나타났고, 강성(11.6 kN/mm)은 설계강성(24.2 kN/mm)에 비하여 절반의 값을 가졌다. 이러한 강성의 차이는 골조와 가새의 접합부 사이의 미끄러짐과 기초의 회전 및 횡변위가 원인으로 나타났다. 보강된 골조의 에너지 흡수 능력은 순수 골조에 비해 7.5배 향상되었다. 기초당 설치된 로드셀의 개수를 2개에서 1개로 변화시키면, 횡강성이 11.6 kN/mm에서 6 kN/mm로 줄어 들었고, 이것은 단지 순수 골조의 강성에 3배에 지나지 않는다(2.1 kN/mm).