• 한국초전도ㆍ저온공학회논문지
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• 제5권1호
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• pp.118-122
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• 2003

Pulse tube refrigerator, which has no moving parts at its cold section, is attractive fer obtaining higher reliability, simpler construction and lower vibration than Stilting refrigerator or Gifford-McMahon refrigerator. Commonly used means to achieve optimum performance of Stilting type pulse tube refrigerator is an inertance tube. The use of inertance tube is a simple way to generate the phase shift needed to make pulse tube refrigerator operate as efficiently as Stilting refrigerator. In this study, the performance of the inertance pulse tube refrigerator (IPTR) was investigated experimentally. An in-line type IPTR consists of a linear compressor with two reciprocating pistons driven by linear motors, which makes pressure waves, a regenerator a pulse tube with the inertance tube, and a reservoir, The dynamic pressures (the compressor, pulse tube, reservior) and the temperature at the cold heat exchanger are measured to explore the dependence of the inertance tube on the performance of the IPTR. The experimental results show the dependency of cool-down characteristics, no-load temperature and amplitude of the pressures on the length and diameter of the inertance tube.

• 화약ㆍ발파
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• 제28권2호
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• pp.119-132
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• 2010

각종 토목공사가 수행됨에 유발되는 소음 및 진동에 관한 민원사례가 증가하고 있다. 일반적으로 육상부보안물건에 대한 관리기준과 피해 발생시 분쟁을 해결하는 객관적 기준자료는 다수 확보된 상태이다. 그러나 수중 소음에 관한 객관적 자료나 기준은 부족한 상태이다. 수중 생태의 환경 검토는 국외의 경우 수중소음계를 이용한 수중소음계측 방식 및 계측 결과값에 대한 항목(최대소음레벨, 실효치, 노출소음레벨)별 관리기준을 제시하고 있으며, 청각역치 연구 결과를 토대로 관리기준을 제시하고 있다. 그러나 국내에서는 수중생태에 관한 연구자료 및 피해정도를 판단할 수 있는 관리기준의 설정이 미흡한 상태이다. 따라서 본 연구는 수중 소음 측정 장비를 활용한 합리적인 수중소음 관리기준 설정을 위한 방향을 모색하고자 한다.

• 한국도로학회논문집
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• 제15권3호
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• pp.17-22
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• 2013

PURPOSES: Current theories for composite structures are too difficult for design engineers for construction. The purpose of this paper is to demonstrate to the practicing engineers, how to apply the advanced composite materials theory to the road structures. METHODS: Some laminate orientations have decreasing values of $D_{16}$, $B_{16}$, $D_{26}$ and $B_{26}$ stiffnesses as the ply number increases. The plate aspect ratio considered is from 1 to 5. In order to study the effect of $M_x$ on the equilibrium equations, two cases are considered. $M_x$ term is considered or neglected. RESULTS: Most of the road structures have high aspect ratios, for such cases further simplification is possible by neglecting the effect of the longitudinal moment terms. CONCLUSIONS: Most of the road structures have plate aspect ratios higher than 2. It is concluded that, for all boundary conditions, neglecting the longitudinal moment($M_x$) terms is acceptable if the aspect ratio (a/b) is equal to or higher than 2. This conclusion gives good guide line for design of the road structures.

• 한국압력기기공학회 논문집
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• 제12권1호
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• pp.11-16
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• 2016

Fuel assembly's mechanical characterization test facility (FAMeCT) in KAERI was constructed with upgraded functional features such as increased loading capacity, underwater vibration testing and severe earthquake simulation for extended fuel design guideline. This facility is designed and developed to provide out-pile fuel data for accident analysis model and fuel licensing. Functional tests of FAMeCT were performed to confirm functionality, structural integrity, and validity of newly-built fuel assembly mechanical test facility. Test program includes signal check of data acquisition system, load delivering capacity using real-sized fuel assemblies and a standard loading cylindrical rigid specimen. Fuel assembly's lateral bending test was carried out up to 30 mm of pull-out displacement. Limit case axial compression loading test up to 33 kN was performed to check structural integrity of UCPS (Upper Core Plate Simulator) support frame. Test results show that all test equipment and measurement system have acceptable range of alignment, signal to noise ratio, load carrying capacity limit without loss of integrity. This paper introduces newly constructed fuel assembly's mechanical test facility and summarizes results of functional test for the mechanical test equipment and data acquisition system.

• Smart Structures and Systems
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• 제13권3호
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• pp.389-406
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• 2014

Optimal sensor placement techniques play a significant role in enhancing the quality of modal data during the vibration based health monitoring of civil structures, where many degrees of freedom are available despite a limited number of sensors. The literature has shown a shift in the trends for solving such problems, from expansion or elimination approach to the employment of heuristic algorithms. Although these heuristic algorithms are capable of providing a global optimal solution, their greatest drawback is the requirement of high computational effort. Because a highly efficient optimisation method is crucial for better accuracy and wider use, this paper presents an improved simulated annealing (SA) algorithm to solve the sensor placement problem. The algorithm is developed based on the sensor locations' coordinate system to allow for the searching in additional dimensions and to increase SA's random search performance while minimising the computation efforts. The proposed method is tested on a numerical slab model that consists of two hundred sensor location candidates using three types of objective functions; the determinant of the Fisher information matrix (FIM), modal assurance criterion (MAC), and mean square error (MSE) of mode shapes. Detailed study on the effects of the sensor numbers and cooling factors on the performance of the algorithm are also investigated. The results indicate that the proposed method outperforms conventional SA and Genetic Algorithm (GA) in the search for optimal sensor placement.

• Wind and Structures
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• 제20권3호
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• pp.363-388
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• 2015

For controlling the vibration of specific building structure with large span, a practical method for the design of MTMD was developed according to the characteristics of structures subjected to wind loads. Based on the model of analyzing wind-induced response of large-span structure with MTMD, the optimization method of multiple tuned mass dampers for large-span roof structures subjected to wind loads was established, in which the applicable requirements for strength and fatigue life of TMD spring were considered. According to the method, the controlled modes and placements of TMDs in MTMD were determined through the quantitative analysis on modal contribution to the wind-induced dynamic response of structure. To explore the characteristics of MTMD, the parametric analysis on the effects of mass ratio, damping ratio, central tuning frequency ratio and frequency range of MTMD, was performed in the study. Then the parameters of MTMD were optimized through genetic algorithm and the optimized MTMD showed good dynamic characteristics. The robustness of the optimized MTMD was also investigated.

• Structural Engineering and Mechanics
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• 제30권1호
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• pp.1-20
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• 2008

The dynamic characteristics of the passive, semi-active, and active tuned-liquidcolumn dampers (or TLCDs) are studied in this paper. The design of the latter two are based on the first one. A water-head difference (or simply named as water head in this paper) of a passive TLCD is pre-set to form the so-called semi-active one in this paper. The pre-set of water head is released at a proper time instant during an earthquake excitation in order to enhance the vibration reduction of a structure. Two propellers are installed along a shaft inside and at the center of a passive TLCD to form an active one. These two propellers are driven by a servo-motor controlled by a computer to provide the control force. The seismic responses of a five-story shear building with a passive, semiactive, and active TLCDs are computed for demonstration and discussion. The responses of this building with a tuned mass damper (or TMD) are also included for comparison. The small-scale shaking-table experiments of a pendulum-like system with a passive or active TLCD to harmonic and seismic excitations are conducted for verification.

• Structural Engineering and Mechanics
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• 제61권6호
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• pp.737-746
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• 2017

The touch down zone (TDZ) and top connection point of the vessel are most critical part of fatigue damage in the steel catenary riser (SCR). In general, the linear soil model has been used to evaluate fatigue performance of SCRs because it gives conservative results in the TDZ. However, the conservative linear soil model shows the limitation to accommodate real behavior in the TDZ as water depth is increased. Therefore, the riser behavior on soft clay seabed is investigated using a nonlinear soil model through time domain approach in this study. The numerical analysis considering various important parameters of the nonlinear soil model such as shear strength at mudline, shear strength gradient and suction resistance force is conducted to check the adoptability and applicability of nonlinear soil model for SCR design.

• 한국지진공학회논문집
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• 제18권6호
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• pp.279-289
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• 2014

Considering a rigorously fluid-structure interaction, a method for an earthquake response analysis of a floating offshore structure subjected to vertical ground motion from a seaquake is developed. Mass, damping, stiffness, and hydrostatic stiffness matrices of the floating offshore structure are obtained from a finite-element model. The sea water is assumed to be a compressible, nonviscous, ideal fluid. Hydrodynamic pressure, which is applied to the structure, from the sea water is assessed using its finite elements and transmitting boundary. Considering the fluid-structure interaction, added mass and force from the hydrodynamic pressure is obtained, which will be combined with the numerical model for the structure. Hydrodynamic pressure in a free field subjected to vertical ground motion and due to harmonic vibration of a floating massless rigid circular plate are calculated and compared with analytical solutions for verification. Using the developed method, the earthquake responses of a floating offshore structure subjected to a vertical ground motion from the seaquake is obtained. It is concluded that the earthquake responses of a floating offshore structure to vertical ground motion is severely influenced by the compressibility of sea water.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2007년 가을학술발표회
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• pp.334-344
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• 2007

This paper performed a comprehensive evaluation of the results of the 2007 Ground Response Analysis Round Robin Test, at which 14 institutions and individuals participated. The submitted results showed significant discrepancies. The main reason for this difference has been attributed to the dispersion in the estimated shear wave velocity profiles and dynamic soil curves. It is therefore concluded that accurate evaluation of the material properties is of primary importance for reliable estimation of the ground vibration. Evaluation of the effect of the analysis method showed that the equivalent linear analysis overestimates the peak ground acceleration, but overall the results are similar to a total stress nonlinear analysis. However, the total and effective stress nonlinear analyses show distinct discrepancies, the effective stress analyses consistently resulting in a lower response due to the development of the excess pore water pressure and thus softer response.