• 비파괴검사학회지
• /
• 제20권5호
• /
• pp.402-411
• /
• 2000

이 연구에서는 점탄성 재료중의 하나인 아스팔트 세멘트의 점탄성 특성을 초음파를 이용하여 측정하는 방법에 대하여 고찰하였다. 2.25MHz의 주파수에서 $-20^{\circ}C$부터 $60^{\circ}C$까지의 온도변화에 따른 파속도와 감쇠를 측정한 후, 선형 점탄성 이론에 근거하여 저장 및 손실 종탄성율, 손실 탄젠트, 저장 및 손실 종컴플라이언스와 같은 물성변화를 구하였다. Maxwell과 Voigt-Kelvin 점탄성 모델을 이용하여 응력완화 및 크리프 거동과 점도의 변화도 예측하였다. 또한 중첩원리와 이동인자의 타당성을 문헌에 보고된 결과와 비교함으로써 입증할 수 있었다.

• 설비공학논문집
• /
• 제9권1호
• /
• pp.43-54
• /
• 1997

This paper presents an approximate analytical solution to a two-region one-dimensional model for the charging process of stratified thermal storage tanks with variable inlet temperature in the presence of momentum-induced mixing. Based on the superposition principle, an arbitrary-varying inlet temperature is decomposed into inherent discontinuous steps and continuous intervals approximated as a finite number of piecewise linear functions. This approximation allows the temperature of the upper perfectly-mixed layer to be expressed in terms of constant, linear and exponential functions with respect to time. Applying the Laplace transform technique to the model equation for the lower thermocline layer subject to each of three representative interfacial conditions yields compact-form solutions, a linear combination of which constitutes the final temperature profile. A systematic method for deriving solutions to the plug-flow problem having polynomial-type boundary conditions is also established. The effect of adiabatic exit boundary on solution behaviors proves to be negligible under the actual working conditions, which justifies the assumption of semi-infinite domain introduced in the solution procedure. Finally, the approximate solution is validated by comparing it with an exact solution obtained for a specific variation of inlet temperature. Excellent agreements between them suffice to show the necessity and utility of this work.

• Structural Engineering and Mechanics
• /
• 제62권4호
• /
• pp.443-453
• /
• 2017

The performance of bolted side-plated (BSP) beams is affected by the degree of transverse partial interaction, which is a result of the interfacial slip caused by transverse shear transfer between the bolted steel plates and the reinforced concrete beams. However, explicit formulae for the transverse shear transfer profile have yet to be derived. In this paper, a simplified piecewise linear shear transfer model was proposed based on force superposition principle and simplification of shear transfer profiles derived from a previous numerical study. The magnitude of shear transfer was determined by force equilibrium and displacement compatibility condition. A set of design formulae for BSP beams under several basic load cases was also derived. Then the model was verified by test results. A worked example was also provided to illustrate the application of the proposed design formulae. This paper sheds some light on the shear force transfer mechanism of anchor bolts in BSP beams, and offers a practical method to evaluate the influence of transverse partial interaction in strengthening design.

• Journal of Mechanical Science and Technology
• /
• 제20권10호
• /
• pp.1691-1701
• /
• 2006

The scan type magnetic camera is proposed to improve the limited spatial resolution due to the size of the packaged magnetic sensor. An image of the scan type magnetic camera, ${\partial}B/{\partial}x$ image, is useful for extracting the crack information of a specimen under a large inclined mag netic field distribution due to the poles of magnetizer. The ${\partial}B/{\partial}x$ images of the cracks of different shapes and sizes are calculated by using the improved dipole model proposed in this paper. The improved dipole model uses small divided dipole models, the rotation and relocation of each dipole model and the principle of superposition. Also for a low carbon steel specimen, the experimental results of nondestructive testing obtained by using multiple cracks are compared with the modeling results to verify the effectiveness of ${\partial}B/{\partial}x$ modeling. The improved dipole model can be used to simulate the LMF and ${\partial}B/{\partial}x$ image of a specimen with complex cracks, and to evaluate the cracks quantitatively using magnetic flux leakage testing.

• 조명전기설비학회논문지
• /
• 제13권1호
• /
• pp.102-110
• /
• 1999

제어용 스피커 및 검출용 마이크로폰 등 트랜스듀서들의 위치는 능동 소음제어 시스템의 성능에 큰 영향을 미친다. 능동 소음제어 시스템의 음향 특성이 매우 복잡하고, 유체 밀도, 복소 전파계수 등 음향 파라미터들의 값을 실제 적용 시에는 알 수 없는 경우가 많아 트랜스듀서들의 위치가 능동 소음제어 시스템의 성능에 미치는 영향을 해석적으로 구하기는 매우 어렵다. 본 논문에서는 트랜스듀서들 간의 전달함수들을 중첩의 원리를 이용하여 유도하였으며, 트랜스듀서들 간의 거리가 능동 소음제어 시스템의 성능에 미치는 영향을 컴퓨터 시뮬레이션을 통해 연구하였다. 단일극 시스템은 소음원과 제어 음원 사이의 거리에 영향을 받으며, 이중극 시스템은 두 제어 음원 사이의 거리와 소음원과 1차 제어 음원 사이의 거리에 많은 영향을 받는 것을 알 수 있었다.

• International Journal of Internet, Broadcasting and Communication
• /
• 제13권2호
• /
• pp.43-51
• /
• 2021

As the number of mobile devices has been increasing tremendously, system capacity should be enlarged in future next generation communication, such as the fifth-generation (5G) and beyond 5G (B5G) mobile networks. For such future networks, non-orthogonal multiple access (NOMA) has been considered as promising multiple access technology. In this paper, to reduce both latency and complexity in existing NOMA, we propose non-successive interference cancellation (SIC) NOMA with asymmetric binary pulse amplitude modulation (2PAM), nearly without bit-error rate (BER) loss. First, we derive the closed form of BER expressions for non-SIC NOMA with asymmetric 2PAM, especially under Rayleigh fading channels. Then, it is shown that the BER performance of the stronger channel user who is supposed to perform SIC in conventional NOMA can be nearly achieved by the proposed non-SIC NOMA with asymmetric 2PAM, especially without SIC. Furthermore, we also show that the BER performance of the weaker channel user in conventional NOMA can be more closely achieved by the proposed non-SIC NOMA with asymmetric 2PAM. These BERs are shown to be achieved over the part of the power allocation range, which is consistent with the NOMA principle of user fairness. As a result, the non-SIC NOMA scheme with asymmetric 2PAM could be considered as a promising NOMA scheme toward next generation communication.

• Smart Structures and Systems
• /
• 제28권6호
• /
• pp.827-838
• /
• 2021

The dynamic displacement is considered to be an important indicator of structural safety, and becomes an indispensable part of Structural Health Monitoring (SHM) system for high-speed railway bridges. This paper proposes an indirect strain based dynamic displacement reconstruction methodology for high-speed railway box girders. For the typical box girders under eccentric train load, the plane section assumption and elementary beam theory is no longer applicable due to the bend-torsion coupling effects. The monitored strain was decoupled into bend and torsion induced strain, pre-trained multi-output support vector regression (M-SVR) model was employed for such decoupling process considering the sensor layout cost and reconstruction accuracy. The decoupled strained based displacement could be reconstructed respectively using box girder plate element analysis and mode superposition principle. For the transformation modal matrix has a significant impact on the reconstructed displacement accuracy, the modal order would be optimized using particle swarm algorithm (PSO), aiming to minimize the ill conditioned degree of transformation modal matrix and the displacement reconstruction error. Numerical simulation and dynamic load testing results show that the reconstructed displacement was in good agreement with the simulated or measured results, which verifies the validity and accuracy of the algorithm proposed in this paper.

• 한국도로학회논문집
• /
• 제17권4호
• /
• pp.53-61
• /
• 2015

PURPOSES : The objective of this study is to evaluate the SDAR (solvent deasphaltene residue), which is obtained from the solvent deasphalting (SDA) process, as a pavement material. METHODS : The physical properties of the SDAR were evaluated based on its chemical composition, and asphalt mixtures with the SDAR were fabricated and used for the evaluation of mechanical properties. Firstly, the chemical composition of SARA (saturate, aromatic, resin and asphaltene) was analyzed using the TLC-FID (thin-layer chromatography-flame ionization detector). Moreover, the basic material properties of the asphalt binder with the SDAR were evaluated by the penetration test, softening point test, ductility test, and PG (performance grade) grade test. The rheological properties of the asphalt binder with the SDAR were evaluated by the dynamic shear modulus ($G^*$) obtained using the time-temperature superposition (TTS) principle. Secondly, the mechanical properties of the asphalt mixtures with the SDAR were evaluated. The compactibility was evaluated using the gyratory compacter. Moreover, the tensile strength ratio (TSR) was used for evaluating the moisture susceptibility of the asphalt mixtures (i.e., susceptibility to pothole damage). The dynamic modulus $E^*$, which is a fundamental property of the asphalt mixture, obtained at different temperatures and loading cycles, was used to evaluate the mechanical properties of the asphalt mixtures. RESULTS AND CONCLUSION : The SDAR shows stiffer and more brittle behavior than the conventional asphalt binder. As the application of the SDAR directly in the field may cause early failures, such as cracks on pavements, it should be applied with modifiers that can favorably modify the brittleness property of the SDAR. Therefore, if appropriate additives are applied on the SDAR, it can be used as a pavement material because of its low cost and strong resistance to rutting.

• 한국산학기술학회논문지
• /
• 제14권2호
• /
• pp.850-857
• /
• 2013

본 논문의 목적은 다중 셀 OFDMA 시스템에서 효율적인 부채널 할당에 근거하여 서비스 연속성을 제공하는 것이다. 특히 지연 및 손실에 의해 서비스 지속성에 악영향을 야기할 가능성이 있으므로 다양한 이동 멀티미디어 서비스의 QoS 요구사항을 유지하기 위하여 핸드오버를 위한 자원 관리 방안이 필요하다. 따라서 본 연구에서는 두 개의 부채널 할당 방법을 제안한다. 우선, 동일 부채널 간섭 원리를 사용하여 주파수 재사용 기법을 확장함으로서 간섭 채널의 중첩 할당 방식이 제안되고, 둘째로 핸드오버 요구를 위하여, 이동 멀티미디어의 서로 다른 서비스 특성과 서비스의 질에 따라서 할당된 채널의 수를 조정하는 새로운 부채널 할당 방법을 제안한다. 시뮬레이션을 통하여, 제안된 방법이 데이터 처리량을 20%까지 증가시키며, 핸드오버 실패율을 25% 정도 감소시킬 수 있음을 보인다.

• 한국재난관리표준학회지
• /
• 제3권1호
• /
• pp.33-42
• /
• 2010

본 논문에서는 전체해석과 국부해석 조합방법을 이용하여 국부손상 또는 균열의 영향을 반영한 트러스교의 전체지간에서의 응력거동을 예측하였다. 이를 위해서 전체 구조체는 프레임요소에 의한 해석을 수행하고 국부 상세부분은 쉘요소에 의한 해석을 수행하여 두 결과를 조합함으로써 교량의 연결부처럼 응력분포가 복잡한 부분에서 이동하중에 따른 응력이력을 손쉽게 산정하게 된다. 트러스 연결부의 실제 기하학적 형상 및 강성을 전체 프레임해석에 고려하기 위해 국부 쉘모델과 프레임모델의 변위 비교를 통해 프레임 모델의 단면수정계수를 산정하였으며, 실제 공용중인 트러스교의 실험값과 해석값을 비교하여 전체해석-국부해석 조합방법을 검증하였으며, 더 나아가 국부손상의 영향이 반영된 국부 쉘모델 해석결과를 전체해석에 반영시켰다.