• 대한조선학회지
• /
• 제18권3호
• /
• pp.11-27
• /
• 1981

This paper is prepared to solve the problem of two-dimensional sinusoidal motion of hydrofoil, which can be related not only to the prediction of unsteady forces acting on the marine propeller blade but to the study of aquatic animal's undulatory mode of propulsion. For convenience's shake, this manuscript can be devided into two parts. In the first part, the lift and moment coefficients have been calculated by the method of conformal transformation. In the other part, the thrust and the hydromechanical efficiency have been evaluated, using Lagally's technique having extended to the unsteady case, they also have been compared with the results, which had been obtained by Lighthill[6] and Wu[7] using Prandtl's acceleration potential.

• 기계저널
• /
• 제33권10호
• /
• pp.861-870
• /
• 1993

여기서는 차량의 구동 성능을 예측하기 위하여 대우자동차에서 최근에 개발한 프로그램에 대하여 설명하고자 한다. 이 프로그램의 특징으로는 기능의 다양화 및 사용의 편리함을 들 수 있다. 이 프로그램은 수동 및 자동 변속기 장착 차량의 가속 성능과 연비를 예측할 수 있게 하였다. 정속 주행 시험과 같이 일정 속도의 주행 상태와, 가속 성능 시험에서와 같이 정해진 드로틀개도 변화에 따르는 주행 상태뿐 아니라, LA-4모두, Tokyo-10모드와 같이 시간에 따라 변화하는 속 도에 따른 주행 상태의 시뮬레이션도 가능하게 하였다. 주행 저항 계산방법으로는 풍동시험을 이용한 방법뿐 아니라 타행 (Coastdown) 시험을 이용하는 방법을 추가하였다. 예측 결과의 정 확도에 별로 영향을 주지않는 부분은 단순화시켜 모델링함으로써 입력 데이터 수를 작게 하였고 이로 인하여 사용자의 편리성을 높게 하였다.

• Computers and Concrete
• /
• 제16권4호
• /
• pp.643-667
• /
• 2015

3-dimentional precast recycled aggregate concrete (RAC) finite element models were developed by means of the platform OpenSees to implement sophisticated nonlinear model subjected to seismic loads. Efforts were devoted to the dynamic responses (including dynamic characteristics, acceleration amplifications, displacements, story drifts) and capacity curve. In addition, this study extended the prediction on dynamic response of precast RAC model by parametric study of material properties that represent the replacement percentage of recycled coarse aggregate (RCA). Principles and assumptions that represent characteristics of precast structure and influence of the interface between head of column and cast-in-place (CIP) joint on the stiffness of the joints was put forward and validated by test results. The comparison between simulated and tested results of the precast RAC frame shows a good correlation with most of the relative errors about 25% in general. Therefore, the adopted assumptions and the platform OpenSees are a viable approach to simulate the dynamic response of precast frames made of RAC.

• Journal of Industrial and Engineering Chemistry
• /
• 제67권
• /
• pp.266-275
• /
• 2018

Herein, a novel operating life (OL) test method was evaluated with 200 mAh pouch-type lithium-ion batteries. By combining the calendar life (CL) test with intermediate pulse power cycling, more realistic life prediction was possible, which encompassed real operation of batteries accompanying with thermal acceleration. Larger capacity decrease and resistance increase of pouch cell were observed in the OL test, which was well explained using the SEI film growth model. After dissemble of pouch cell, capacity loss and resistance increase mostly occurred within anode, reflecting that SEI film growth on anode surface was highly attributable to cell degradation.

• Geomechanics and Engineering
• /
• 제29권5호
• /
• pp.583-598
• /
• 2022

The Compaction effect is important for evaluating the subgrade construction. However, there is little research exploring the compaction quality of deep soil using hydraulic compaction. According to reinforcement effect analysis, dimensional analysis is adopted in this work to analyze subgrade compactness within the effective reinforcement depth, and a prediction model is obtained. A hydraulic compactor is then employed to carry out an in-situ reinforcement test on gravel soil subgrade, and the subgrade parameters before and after reinforcement are analyzed. Results show that a reinforcement difference exists inside the subgrade, and the effective reinforcement depth is defined as increasing compactness to 90% in the depth direction. Layered compactness within the effective reinforcement depth is expressed by parameters including the drop distance of the rammer, peak acceleration, tamping times, subgrade settlement, and properties of rammer and filler. Finally, a field test is conducted to verify the results.

• 대한원격탐사학회지
• /
• 제37권5_1호
• /
• pp.927-938
• /
• 2021

편대 비행하는 저궤도위성에는 비슷한 크기의 비중력 섭동이 일정한 시간 차이를 두고 가해진다. 이러한 시간상관관계를 이용하면 한 개 위성의 가속도계에서 측정된 가속도 값으로 다른 편대비행 저궤도위성의 비중력가속도를 추정할 수 있다. 편대비행 저궤도위성인 GRACE 및 GRACE-FO 위성에서 한 개 위성의 가속도계 데이터를 사용할 수 없는 기간이 존재하는데, 앞서 기술된 시간 이식 기법이 JPL (Jet Propulsion Laboratory)에서 공식적으로 가속도계 데이터 복원 시 사용되고 있다. 본 논문에서는 기존의 시간 이식 기법의 가속도계 추정 정확도를 개선하기 위하여 신경망 (neural network; NN) 모델 기반 편대비행 저궤도위성 가속도계 데이터 추정 방법을 제안하였다. 시간 이식 기법은 위성의 위치 및 우주환경요소 등을 반영할 수 없지만, NN 모델은 이를 모델 입력으로 사용할 수 있으므로 예측 정확도를 높일 수 있다. 1개월간 NN 모델을 사용하여 가속도계 예측 시험을 수행하고 시간 이식 기법과 예측 정확도를 비교하였다. 그 결과 along-track 및 radial 방향에서 NN모델의 가속도계 데이터의 예측 오차는 시간 이식 기법에 비해 각각 55.0%, 40.1% 감소하였다.

• 한국소음진동공학회논문집
• /
• 제23권6호
• /
• pp.527-536
• /
• 2013

In order to predict structural vibration and radiated noise of high-voltage transformer in operation, it is necessary to precisely find the excitation force generated by the coils and core. However, finding the excitation force through experiments of high voltage transformer in operation is not possible. Therefore, this paper deals with identifying the excitation force by using the acceleration data measured through experiments and the transfer function estimated through finite element model. A method to predict structural vibration and radiated noise was also proposed. Three-phase windings and the core are the source of high-voltage transformer. The excitation forces were identified using the acceleration data and the transfer function of the surface of the tank. Structural vibration and radiated noise from the surface of the tank was predicted by using the identified excitation force. As a result of the interpretation of the experimental and computational analysis of structural vibration from the surface of the tank and radiated noise from the field point, the interpretation of the computational analysis showed relatively good accordance with the experiment.

• 한국지진공학회논문집
• /
• 제24권6호
• /
• pp.277-283
• /
• 2020

In order to improve the ground-motion prediction equation, which is an important factor in seismic hazard assessment, it is essential to obtain good quality seismic data for a region. The Korean Peninsula has an environment in which it is difficult to obtain strong ground motion data. However, because digital seismic observation networks have become denser since the mid-2000s and moderate earthquake events such as the Odaesan earthquake (Jan. 20, 2007, M_L 4.8), the 9.12 Gyeongju earthquake (Sep. 12, 2016, M_L 5.8), and the Pohang earthquake (Nov. 15, 2017, M_L 5.4) have occurred, some good empirical data on ground motion could have been accumulated. In this study, we tried to build a ground motion database that can be used for the development of the ground motion attenuation equation by collecting seismic data accumulated since the 2000s. The database was constructed in the form of a flat file with RotD50 peak ground acceleration, 5% damped pseudo-spectral acceleration, and meta information related to hypocenter, path, site, and data processing. The seismic data used were the velocity and accelerogram data for events over M_L 3.0 observed between 2003 and 2019 by the Korean National Seismic Network administered by the Korea Meteorological Administration. The final flat file contains 10,795 ground motion data items for 141 events. Although this study focuses mainly on organizing earthquake ground-motion waveforms and their data processing, it is thought that the study will contribute to reducing uncertainty in evaluating seismic hazard in the Korean Peninsula if detailed information about epicenters and stations is supplemented in the future.

• 한국해안해양공학회지
• /
• 제6권1호
• /
• pp.23-33
• /
• 1994

서해안 사질토매립지반을 대상으로 지진응답해석 및 반복삼축압축시험 결과를 통하여 지진 및 예측방법에 따른 액상화특성에 대하여 검토하였다. 지수응답해석 결과, 입력지진과 지반특성에 따라 지표면에 도달하는 최대가속도의 크기가 다르게 나타남을 알았으며 간역예측법으로 해안매립지반의 액상화 평가시 적용 가능한 지진계수를 제시하였다. N치가 작고 느슨한 상부층에 대한 액상화강도는 반복삼축압축시험 결과에 비하여 Seed법에 의한 결과가 작게 나타났고 Iwasaki 방법과 S파속도 이용법은 크거나 유사한 결과를 얻었다. 또한 간역예측법들은 상세법에 비해 액상화 가능성을 과대 평가하는 경향이 있었으며 액상화 한계심도(안전율 1일때)는 입력가속도(0.1g-0.2g)에 따라 7m-14m정도로 추정되었다.

• Structural Engineering and Mechanics
• /
• 제23권4호
• /
• pp.409-430
• /
• 2006

The aim of this study is to investigate the reliability of strong motion records processed by causal and acausal Butterworth filters in comparison to the results obtained from a synthetic accelerogram. For this purpose, the fault parallel component of the Bolu record of the Duzce earthquake is modeled with a sum of exponentially damped sinusoidal components. Noise-free velocities and displacements are then obtained by analytically integrating the synthetic acceleration model. The analytical velocity and displacement signals are used as a standard with which to judge the validity of the signals obtained by filtering with causal and acausal filters and numerically integrating the acceleration model. The results show that the acausal filters are clearly preferable to the causal filters due to the fact that the response spectra obtained from the acausal filters match the spectra obtained from the simulated accelerogram better than that obtained by causal filters. The response spectra are independent from the order of the filters and from the method of integration (whether analytical integration after a spline fit to the synthetic accelerogram or the trapezoidal rule). The response spectra are sensitive to the chosen corner frequency of both the causal and the acausal filters and also to the inclusion of the pads. Accurate prediction of the static residual displacement (SRD) is very important for structures traversing faults in the near-fault regions. The greatest adverse effect of the high pass filters is their removal of the SRD. However, the noise-free displacements obtained by double integrating the synthetic accelerogram analytically preserve the SRD. It is thus apparent that conventional high pass filters should not be used for processing near-fault strong-motion records although they can be reliably used for far-fault records if applied acausally. The ground motion parameters such as ARIAS intensity, HUSID plots, Housner spectral intensity and the duration of strong-motion are found to be insensitive to the causality of filters.