• 대한기계학회논문집
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• 제19권2호
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• pp.374-381
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• 1995

In this paper, integration methods for stiff constrained mechanical systems are studied to analyze dynamic response of the stiff mechanical system efficiently. The stiff, non-stiff systems are identified by using eigenvalues of the Jacobian of the systems. To integrate both stiff system and non-stiff system efficiently a new switching method between the non-stiff differential equation solver and the stiff differential equation solver is presented.

• 한국강구조학회 논문집
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• 제17권4호통권77호
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• pp.395-405
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• 2005

본 논문은 고항복비-고강도강의 효율적인 이용을 위하여 유강혼합구조 시스템의 실험결과를 요약한 것이다. 최근 건축구조물에서도 대형화 및 초고층화 되어감에 따라 사용강재에 대하여 높은 성능을 요구하게 되었고, 고강도강을 사용해야 하는 경우가 늘고 있다. 하지만 고강도강은 항복비가 높고 최대 응력시 변형도가 작고 탄성계수가 연강과 같다는 단점으로 인하여 수요가 증가하고 있지 못한 실정이다. 이러한 고항복비를 가지는 고강도강의 결점을 보완하고 효과적인 사용을 위해서는 새로운 구조시스템이 필요하다. 본 연구에서는 고항복비를 가지는 고강도강을 건축구조물에 효과적으로 적용할 수 있는 방안으로 유강혼합구조 시스템을 제안하고, 고강도강이 포함된 유강혼합기둥 실험을 통하여, 고강도강을 효율적으로 사용할 수 있는 가능성을 제시하고자 하였다. 내력비와 강성비를 포함할 수 있는 강요소 (stiff element)와 유요소 (flexible element)의 항복변형비를 변수로 하여, 유강혼합구조시스템 적용시 적절한 항복변형비를 찾고자 하였다. 실험결과 제안된 유강혼합구조시스템은 연강만으로 이루어진 시스템에 비해 높은 에너지 흡수능력을 보여주었고, 강요소에 대한 유요소의 항복변형비가 2.7~3.3일 때 가장 큰 에너지 흡수능력을 갖는 것을 확인할 수 있었다.

• Geomechanics and Engineering
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• 재33권6호
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• pp.583-596
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• 2023

The interlayers, either softer or stiffer than the surrounding layers, are usually overlooked during field investigation due to the small thickness. They may be neglected through the analysis process for simplicity. However, they may significantly affect the dynamic behavior of the soil-foundation system. In this study, a series of 3D finite-element Direct-solution steady-state harmonic analyses were carried out using ABAQUS/CAE software to investigate the impacts of interlayers on the dynamic response of a cast in place pile group subjected to horizontal harmonic load. The experimental data of a 3×2 pile group testing was used to verify the numerical modeling. The effects of thickness, depth, and shear modulus of the interlayers on the dynamic response of the pile group are investigated. The simulations were conducted on both stiff and soft soils. It was found that the soft interlayers affect the frequency-amplitude curve of the system only in frequencies higher than 70% of the resonant frequency of the base soil. While, the effect of stiff interlayer in soft base soil started at frequency of 35% of the resonant frequency of the base soil. Also, it was observed that a shallow stiff interlayer increased the resonant amplitude by 11%, while a deep one only increased the resonant frequency by 7%. Moreover, a shallow soft interlayer increased the resonant frequency by 20% in soft base soils, whereas, it had an effect as low as 6% on resonant amplitude. Also, the results showed that deep soft interlayers increased the resonant amplitude by 17 to 20% in both soft and stiff base soils due to a reduction in lateral support of the piles. In the cases of deep thick, soft interlayers, the resonant frequency reduced significantly, i.e., 16 to 20%. It was found that the stiff interlayers were most effective on the amplitude and frequency of the pile group.

• Smart Structures and Systems
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• 제15권5호
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• pp.1293-1309
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• 2015

3D two adjacent buildings with different heights founded in different kinds of soil connected with viscous dampers groups, with especial arrangement in plane, were investigated. Soil structure interaction for three different kinds of soil (stiff, medium and soft) were modeled as 3D Winkler model to give the realistic behavior of adjacent buildings connected with viscous dampers under various earthquake excitations taking in the account the effect of different kinds of soil beneath the buildings, using SAP2000n to model the whole system. A range of soil properties and soil damping characteristics are chosen which gives broad picture of connected structures system behavior resulted from the influence soil-structure interaction. Its conclusion that the response of connected structures system founded on soft soil are more critical than those founded on stiff soil. The behavior of connected structures is different from those with fixed base bigger by nearly 20%, and the efficiency of viscous dampers connecting the two adjacent buildings is reduced by nearly 25% less than those founded on stiff soil.

• 대한의용생체공학회:의공학회지
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• 제32권2호
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• pp.105-108
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• 2011

The purpose of the present study was to analyze the lower stiffness over the difference between soft and stiff landings during hopping. Five male subjects performed hopping on two legs at 2.5 Hz. During the experiments, 3D motion capture system was used to obtain the kinematic data and two force plates were synchronized to calculate the kinetic data. We determined lower extremity stiffness of the knee and ankle from kinetic and kinematic data. Leg stiffness was approximately 1.2-times significantly higher in stiff landing than in soft landing_ There was no significant difference in knee joint stiffness between soft and stiff landings. Ankle joint stiffness was approximately 1.34-times significantly higher in stiff landing than in soft landing. These results suggest that humans adjust lower extremity stiffness over the comparison of two different landing methods we evaluated.

• Journal of applied mathematics & informatics
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• 제8권1호
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• pp.165-180
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• 2001

This paper presents a new difference scheme for numerical solution of stiff system of ODE’s. The present study is mainly motivated to develop an absolutely stable numerical method with a high order of approximation. In this work a double implicit A-stable difference scheme with the sixth order of approximation is suggested. Another purpose of this study is to introduce automatic choice of the integration step size of the difference scheme which is derived from the proposed scheme and the one step scheme of the fourth order of approximation. The algorithm was tested by means of solving the Kreiss problem and a chemical kinetics problem. The behavior of the gas explosive mixture (H₂+ O₂) in a closed space with a mobile piston is considered in test problem 2. It is our conclusion that a hydrogen-operated engine will permit to decrease the emitted levels of hazardous atmospheric pollutants.

• 콘크리트학회논문집
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• 제23권4호
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• pp.511-520
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• 2011

최근 국내에서는 고분자 화합물인 폴리우레아를 이용하여 보강 성능의 향상을 위한 연질형 폴리우레아를 개발하여 구조물에 적용하였지만 보강 성능은 미비한 것으로 나타났다. 따라서, 이 연구에서는 폴리우레아를 구조물의 보강재로 사용하기 위하여 연질형 폴리우레아의 구성 요소를 변화시켜 경질형 폴리우레아를 개발하였다. 개발된 경질형 폴리우레아는 연질형 폴리우레아에 비해 경도와 인장강도가 향상된 성능을 나타내었다. 경질형 폴리우레아를 일반 구조물의 보강재로 사용하기 위하여 RC 슬래브 시험체를 제작하여 보강 성능을 평가하였으며, 현재 보강재로 사용되는 섬유 시트와 적층하여 보강한 후 성능을 평가하였다. 실험 결과 경질형 폴리우레아만으로 보강한 시험체가 무보강 시험체보다 우수한 강성 증진 효과와 연성 증진 효과를 나타내는 것으로 나타났다. 또한, 섬유 시트를 부착한 후 경질형 폴리우레아를 외부에 도포하여 보강한 시험체는 섬유 시트만으로 보강한 시험체보다 보강 성능이 매우 우수한 것으로 나타났다. 그러나 경질형 폴리우레아를 도포한 후 섬유 시트를 부착한 시험체는 경질형 폴리우레아의 변형을 강성이 높은 섬유 시트가 억제하여 하중이 가해지며 생기는 응력이 한곳에 집중되어 취성적인 파괴 거동을 보이는 것으로 나타났다.

• Transactions on Electrical and Electronic Materials
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• 제14권3호
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• pp.116-120
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• 2013

This paper proposes a novel RF MEMS dc-contact switch with stiff membrane on a quartz substrate. The uniqueness of this work lies in the utilization of a seesaw mechanism to restore the movable part to its rest position. The switching action is done by using separate pull-down and pull-up electrodes, and hence operation of the switch does not rely on the elastic recovery force of the membrane. One of the main problems faced by electrostatically actuated MEMS switches is the high operational voltages, which results from bending of the membrane, due to internal stress gradient. This is resolved by using a stiff and thick membrane. This membrane consists of flexible meanders, for easy movement between the two states. The device operates with an actuation voltage of 6.43 V, an insertion loss of -0.047 dB and isolation of -51.82 dB at 2 GHz.

• Structural Engineering and Mechanics
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• 제38권3호
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• pp.315-332
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• 2011

The Combined Deterministic Stochastic Subspace based System Identification Technique (CDSSSIT) is a powerful input-output system identification technique which is known to be always convergent and numerically stable. The technique determines a Kalman state sequence from the projection of the output-input data. The state space matrices are determied subsequently from this Kalman state sequence using least squares. The objective of this paper is to examine the efficiency of the CDSSSIT in identifying the modal parameters (frequencies and mode shapes) of a stiff structure. The results show that the CDSSSIT predicts the modal parameters of stiff buildings quite accurately but is very sensitive to the location of sensors.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1996년도 가을 학술발표회 논문집
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• pp.239-246
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• 1996

Very stiff floor system in a residential-commercial building causes some problems in the numerical analysis procedure due to significant difference in stiffness with adjacent structural elements. Static analysis of structure with a stiff transfer-floor can be peformed approximately in two steps for upper and lower pons for the structure. However, it is impossible to perform dynamic analysis in two steps with separate models. An efficient method for dynamic analysis of a structure with a rigid floor system is proposed in this study. The matrix condensation technique is employed to reduce the degree of freedom for upper and lower parts of the structure and a beam elements with rigid bodies of both ends are introduce to model the rigid floor system. Efficiency end accuracy of the proposed method ore verified through analysis of several example structures.