• 한국추진공학회지
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• 제25권1호
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• pp.1-11
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• 2021

포고 현상은 액체추진 로켓에서 발생하는 축방향의 동적 불안정 진동이다. 동체의 고유진동수와 추진제 공급계의 주파수가 가까와 지면 전체 시스템이 불안정 현상을 보인다. 포고 현상을 예측하기 위해 1단의 추진제 (산화제 및 연료) 탱크는 쉘 요소로, 나머지 구성 요소인 엔진 및 상단은 mass-spring으로 모델링하여 구조해석을 수행하였다. 추진제 공급계의 압력 및 유량 섭동예측에는 transmission line model이 사용되었다. 본 논문에서는 이와 같이 수행된 구조 및 유체 모델링을 통합하여 폐루프 전달함수를 구성하였다. 포고 억제기는 수동적인 방법으로 압력 섭동을 흡수하는 분 기관 및 accumulator로 구성되며 추진제 공급계 중간에 위치한다. 발사체의 비행과정 동안 포고현상을 억제하는 설계 최적화를 위한 설계변수로는 분기관 및 accumulator의 직경 및 길이로 설정하였다. 목적함수로는 포고 억제기의 질량, 그리고 추진제 질량에 따른 폐루프 전달함수의 에너지 최소화로 설정하여 다목적함수 최적화를 수행하였다.

• 대한토목학회논문집
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• 제26권5A호
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• pp.861-872
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• 2006

본 연구에서는 이차원 연속체에 존재하는 점성균열을 무요소법에서 국부 단위분할 원리에 근거하여 정식화하였다. 균열이 한 절점의 영향영역(domain of influence)을 완전히 통과하는 경우 그 절점의 형상함수는 계단함수로 확장되고, 균열 끝이 영향영역 내에 위치하는 경우 특이성이 제거된 가지함수(branch function)로 확장된다. 이러한 해의 영역의 확장은 국부 단위분할 원리를 만족하는 변위계에서만 이루어지므로, 약형 정식화는 표준 Galerkin방법에 의해서 얻어진다. 균열과 상호작용하는 영향영역만 확장되기 때문에, 성긴 형태의 시스템의 행렬을 유지하게 된다. 그러므로 확장에 의해 발생하는 계산비용의 증가는 최소화된다. 동적인 문제에서 균열성장에 관한 조건은 재료안정론으로부터 얻어졌다. 즉, 재료 한 점에서 어느 방향으로든 변형열화가 집중하게 되면, 그 방향에 점성균열을 삽입하여 연속체가 비연속체로 되도록 하였다. 균열의 성장속도도 같은 조건으로부터 자연스럽게 얻어졌다. 전통적인 무요소법보다 더 나은 정확도와 빠른 수렴성을 보이는 것이 확인되었으며, 이 기법의 적용성을 보이기 위해 잘 알려진, 정적 및 동적문제에 적용하였다.

• Steel and Composite Structures
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• 제23권5호
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• pp.571-583
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• 2017

A kind of accordion-web RBS connection, "Tubular Web RBS (TW-RBS)" connection is proposed in this research. TW-RBS is made by replacing a part of web with a tube at the desirable location of the beam plastic hinge. This paper presents first a numerical study under cyclic load using ABAQUS finite element software. A test specimen is used for calibration and comparison of numerical results. Obtained results indicated that TW-RBS would reduce contribution of the beam web to the whole moment strength and creates a ductile fuse far from components of the beam-to-column connection. Besides, TW-RBS connection can increase story drift capacity up to 9% in the case of shallow beams which is much more than those stipulated by the current seismic codes. Furthermore, the tubular web like corrugated sheet can improve both the out-of-plane stiffness of the beam longitudinal axis and the flange stability condition due to the smaller width to thickness ratio of the beam flange in the plastic hinge region. Thus, the tubular web in the plastic hinge region improves lateral-torsional buckling stability of the beam as just local buckling of the beam flange at the center of the reduced section was observed during the tests. Also change of direction of strain in arc shape of the tubular web section is smaller than the accordion webs with sharp corners therefore the tubular web provides a better condition in terms of low-cycle fatigue than other accordion web with sharp corners.

• Parasites, Hosts and Diseases
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• 제55권6호
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• pp.607-611
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• 2017

Primary maternal infection with toxoplasmosis during pregnancy is frequently associated with transplacental transmission of the parasite to the fetus. This study was conducted to test the utility of PCR assay to detect recent infections with Toxoplasma in aborted women at various gestational ages who referred to Obstetrics and Gynecology Department of Alavi Hospital in Ardabil during 2014 and 2016. Two hundred women with a history of single or repeated abortion were investigated in this study. Blood samples were tested for specific anti-Toxoplasma IgM and IgG antibodies by ELISA. According to the results, 53.5% of the women under study were positive for anti-Toxoplasma antibodies: 4.0% of them had IgM, 43.0% had IgG, and 6.5% had both IgM and IgG. Subsequently, Nested-PCR analysis was used to detect T. gondii DNA in the placenta of subjects. In 10.5% of the women, the results were positive for 529 bp element of T. gondii. Among them, 5 (23.8%) cases were IgM positive, 1 (4.8%) case was IgG positive, and 11 (52.4%) were both IgM and IgG positive. In 4 (19.0%) patients, none of the antibodies were found to be positive. In total, 16 patients had positive results in both ELISA and PCR methods, and 174 cases had negative results for new infection. The findings of this study revealed that T. gondii might be one of the significant factors leading to abortion, and that the analysis of placenta can be important in order to achieve increased detection sensitivity.

• 한국산학기술학회논문지
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• 제11권9호
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• pp.3599-3609
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• 2010

연안개발과 해안매립을 사용하여 개발된 새로운 도시 건설의 수요가 증가하면서 해안구조물과 고층구조물의 시공이 증가하는 추세이다. 이러한 구조물에서 수평력과 인발력을 받는 구조물의 기초의 적용이 증가하고 있으며, 특히 구조물에서 인발력에 효과적으로 저항하기 위한 기초형식으로 선단확장형말뚝의 사용이 증가하고 있는 실정이다. 압축력을 받는 기초에 관한 많은 연구들이 이루어지고 있으나, 선단확장형말뚝의 인발저항에 관한 연구는 미비한 상태이다. 따라서 본 논문에서는 국외 4개 현장을 대상으로 선단확장형말뚝을 시공하고 정재하시험을 실시하여 말뚝의 지지력 및 하중-변위특성과 주면마찰력을 고려한 하중분담을 고찰하였다. 또한 3차원 유한요소해석 및 이론에 의해 산정된 극한인발력과 현장시험의 극한인발력을 비교 평가하였다.

• 정보과학회 컴퓨팅의 실제 논문지
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• 제23권8호
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• pp.498-503
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• 2017

SIMD(Single Instruction Multiple Data)는 대표적인 병렬화 아키텍처 중 하나로, SIMD 레지스터에 적재된 여러 개의 데이터들을 하나의 명령어로 처리하는 기술이다. 퀵정렬(Quicksort)은 데이터 값들이 리스트로 저장되어 있을 때, 임의의 위치에 있는 데이터 값을 피봇으로 하여 그것보다 작은 값은 왼편으로, 큰 값은 오른편으로 분할하여 생성된 두 개의 서브리스트에 대하여 같은 작업을 반복함으로써 데이터 값들을 정렬하는 정렬 알고리즘이다. 본 연구에서는 SIMD 명령어를 이용하여 파이프라인 아키텍처에서 조건 예측 실패에 따른 성능 저하를 유발하지 않도록 분기 조건을 최소로 사용하는 효율적인 퀵정렬(Quicksort) 알고리즘을 제안한다. 또한, VBP(Vertical Bit Parallel) 기법과 얼리 프루닝(early pruning) 기법을 적용하여 SIMD 레지스터에 데이터를 바이트 단위로 적재함으로써 퀵 정렬 알고리즘의 성능을 향상하였다.

• 대한한의학원전학회지
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• 제31권1호
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• pp.1-14
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• 2018

Objectives : This paper reviews the possibility of confusing wind-cold and cold dryness that can be found in the critical discussion revolving Wu Jutong's concept of cold dryness. With this, the paper aims to refresh the understanding of the concept of cold dryness as put together by Wu Jutong. Methods : The paper reviews the concept of Wu Jutong's cold dryness based on today's critical discussions on the topic. At the same time, the paper searches for additional theoretical basis that can be proposed with regards to Wu Jutong's concept of cold dryness. Results : The core element of the criticisms against Wu Jutong's cold dryness is that cold dryness's cold dryness pattern proposes cold fluid as one of the main symptoms, and that Xiaoqinglongtang is referred to as a cure. However, the problem of the dryness and dampness that can be found in Wu Jutong's cold dryness seems that it can be explained by the discussions regarding Shenkuzao as written in Neijing. Moreover, considering the fact that the connection between cold paathogen and Shenkuzao that surfaced in historical medical theories can also be applied to the concept of cold dryness, it seems that it can be helpful in understanding the characteristics of disease mechanism of cold dryness. Conclusions : The discussion on the concept of cold dryness originally derives as a branch of the discussion on cold. Acknowledging this, it seems that reconsideration is required on the assertion that Wu Jutong confused the symptoms of wind-cold with that of cold dryness.

• Earthquakes and Structures
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• 제11권3호
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• pp.517-538
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• 2016

This paper presents a probabilistic fragility analysis for two groups of bridges: simply supported and integral bridges. Comparisons are based on the seismic fragility of the bridges subjected to accelerograms of two seismic sources. Three-dimensional finite-element models of the bridges were created for each set of bridge samples, considering the nonlinear behaviour of critical bridge components. When the seismic hazard in the site is controlled by a few seismic sources, it is important to quantify separately the contribution of each fault to the structure vulnerability. In this study, seismic records come from earthquakes that originated in strike-slip and reverse faulting mechanisms. The influence of the earthquake mechanism on the seismic vulnerability of the bridges was analysed by considering the displacement ductility of the piers. An in-depth parametric study was conducted to evaluate the sensitivity of the bridges' seismic responses to variations of structural parameters. The analysis showed that uncertainties related to the presence of lap splices in columns and superstructure type in terms of integral or simply supported spans should be considered in the fragility analysis of the bridge system. Finally, the fragility curves determine the conditional probabilities that a specific structural demand will reach or exceed the structural capacity by considering peak ground acceleration (PGA) and acceleration spectrum intensity (ASI). The results also show that the simply supported bridges perform consistently better from a seismic perspective than integral bridges and focal mechanism of the earthquakes plays an important role in the seismic fragility analysis of highway bridges.

• Advances in Energy Research
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• 제5권2호
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• pp.91-105
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• 2017

Thermal hydraulic (TH) analysis of nuclear power reactors is utmost important. In this way, the numerical codes that preparing TH data in reactor core are essential. In this paper, a subchannel analysis of a Russian pressurized water reactor (WWER1000) core with enhanced numerical code is carried out. For this, in fluid domain, the mass, axial and lateral momentum and energy conservation equations for desired control volume are solved, numerically. In the solid domain, the cylindrical heat transfer equation for calculation of radial temperature profile in fuel, gap and clad with finite difference and finite element solvers are considered. The dependence of material properties to fuel burnup with Calza-Bini fuel-gap model is implemented. This model is coupled with Isotope Generation and Depletion Code (ORIGEN2.1). The possibility of central hole consideration in fuel pellet is another advantage of this work. In addition, subchannel to subchannel and subchannel to rod connection data in hexagonal fuel assembly geometry could be prepared, automatically. For a demonstration of code capability, the steady state TH analysis of a the WWER1000 core is compromised with Thermal-hydraulic analysis code (COBRA-EN). By thermal hydraulic parameters averaging Fuel Assembly-to-Fuel Assembly method, the one sixth (symmetry) of the Boushehr Nuclear Power Plant (BNPP) core with regular subchannels are modeled. Comparison between the results of the work and COBRA-EN demonstrates some advantages of the presented code. Using the code the thermal modeling of the fuel rods with considering the fission gas generation would be possible. In addition, this code is compatible with neutronic codes for coupling. This method is faster and more accurate for symmetrical simulation of the core with acceptable results.

• Steel and Composite Structures
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• 제28권4호
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• pp.439-447
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• 2018

The structural behaviors of cylindrical barns as a specific engineering structure have been considered as a complicated computing process. The structure design against the earthquake load, to protect by using the code, is an urgency avoiding unexpected damages. The situation has been subjected to the applied design method if there would be no failure across the construction procedures. The purpose of the current study is to clarify the behaviors of cylindrical reinforced concrete barns through the analytic methods across the mass and Lagrangian approaches through the whole outcomes comparison indicating that the isoparametric element obtained from the Lagrangian approach has been successfully applied in the barns earthquake analysis when the slosh effects have been discarded. The form of stress distributions is equal with $s_z$ closed distributions to one another.