• 한국음향학회지
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• 제39권4호
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• pp.351-363
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• 2020

발사체는 비행 중 공기역학적 현상에 기인하는 음향하중의 영향을 받는데, 특별히 천음속 영역에서 그 영향이 증가된다. 음향하중으로 인한 페어링 내부 소음진동은 탑재물의 오작동을 유발할 수 있어 이를 예측하고 저감하는 과정이 필수적이다. 본 연구에서는 발사체 외부에 작용하는 공기역학적 음향하중에 의한 페어링 내부 음향 진동환경을 예측하고, 음향 블랭킷과 헬름홀츠 공명기를 이용하여 소음저감 설계를 구현하는 프로세스를 개발하였다. 음향하중 예측은 Reynolds-Averaged Navier-Stokes(RANS) 유동해석 결과와 난류 경계층 내부 압력섭동에 관한 준 경험식을 이용하였고, 음향진동 연성해석은 ANSYS APDL과 VA One SEA의 Finite Element Statistical Energy Analysis(FE-SEA) 하이브리드 해법을 이용하였다. 개발된 절차를 천음속 해머 헤드형 발사체에 적용하여 음향하중 저감효과를 확인하고 개발된 절차의 유효성을 검증하였다. 본 연구에서 개발된 절차는 타당한 수준의 정확도로 신속한 결과를 얻을 수 있어 발사체 초기설계 단계에 유용하게 쓰일 수 있을 것으로 예상된다.

• 대한환경공학회지
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• 제28권11호
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• pp.1207-1212
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• 2006

본 연구는 담수 퇴적물 중 유기물의 척도가 되는 화학적산소요구량, 염양염류인 총질소와 총인 및 금속류인 철과 망간에 대해 국내 외 분석법을 적용하여 분석을 실시함으로서 각 분석법간의 상관성을 파악하고 그 적용성을 알아보고자 하였다. 화학적산소요구량은 국내 해양환경공정시험방법과 일본의 위생시험법을 적용하였는데 두 방법 모두 측정범위가 넓고, 생물학적산소요구량이나 유기물질과 상관관계가 좋은 과망간산칼륨법을 이용하고 있기 때문에 분석법간 편차가 크지 않음을 확인하였다. 총질소와 총인의 경우 국내 식품공전에 의한 시험법과 일본의 위생시험법을 적용하여 분석을 실시하였다. 총질소는 두 방법 모두 중화 적정법이지만 시료 분해 및 증류 과정의 차이에 의해 일본의 위생시험법에 의한 분석 값이 약간 낮은 경향을 보였다. 총인의 경우 두 방법 모두 질산과 과염소산에 의한 분해 후 값을 측정하는 방법으로 비슷한 결과를 보였다. 철과 망간과 같은 금속류의 실험은 크게 용출방법과 산분해법을 실시하였다. 용출법에서 얻은 결과값은 산분해한 값에 비하여 적은 값을 나타내었는데 그 이유는 용출조건보다 산분해 조건에서 금속류가 더 잘 녹아나오기 때문이다.

• Structural Engineering and Mechanics
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• 제68권1호
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• pp.1-15
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• 2018

In ocean industry, free surface type ART (Anti Roll tank) system has been widely used to suppress the roll motion of floating structures. In those, various obstacles have been devised to obtain the sufficient damping and to enhance the controllability of freely rushing water inside the tank. Most of previous researches have paid on the development of simple mathematical formula for coupled ship-ARTs analysis although other numerical and experimental approaches exist. Little attention has been focused on the use of 3D panel method for preliminary design of free surface type ART despite its advantages in computational time and general capacity for hydrodynamic damping estimation. This study aims at developing a potential theory based hydrodynamic code for the analysis of floating structure with baffled ARTs. The sloshing in baffled tanks is modeled through the linear potential theory with FE discretization and it coupled with hydrodynamic equations of floating structures discretized by BEM and FEM, resulting in direct coupled FE-BE formulation. The general capacity of proposed formulation is emphasized through the coupled hydrodynamic analysis of floating structure and sloshing inside baffled ARTs. In addition, the numerical methods for natural sloshing frequency tuning and estimation of hydrodynamic damping ratio of liquid sloshing in baffled tanks undergoing wave exiting loads are developed through the proposed formulation. In numerical examples, effects of natural frequency tuning and baffle ratios on the maximum and significant roll motions are investigated.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2014년도 추계학술대회 논문집
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• pp.975-977
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• 2014

Recently, As portability of storage device has been increased, it is important to analyze the precise anti-shock analysis. For non-operational shock analysis, the accuracy of non-operational shock simulation has been improved. However, because operational shock analysis includes nonlinear process, it is hard to get clear result from operational shock simulation. In this paper, by using Lagrange multiplier method, the FE model including ramp-disk contact of nonlinear process will be analyzed. Through this, we find ramp-disk contact affect the dynamic of slider. Additionally, for the more accurate analysis, we should include ramp-disk contact process at the FE model.

• Structural Engineering and Mechanics
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• 제55권5호
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• pp.1037-1053
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• 2015

This paper presents finite element (FE) based pushover analysis of a reinforced concrete structure with a two-leaf cavity wall (TLCW) to estimate the performance level of this structure. In addition to this, an unreinforced masonry (URM) model was selected for comparison. Simulations and analyses of these structures were performed using the DIANA FE program. The mentioned structures were selected as two storeys and two bays. The dimensions of the structures were scaled 1:1.5 according to the Cauchy Froude similitude law. A shake table experiment was implemented on the reinforced concrete structure with the two-leaf cavity wall (TLCW) at the National Civil Engineering Laboratory (LNEC) in Lisbon, Portugal. The model that simulates URM was not experimentally studied. This structure was modelled in the same manner as the TLCW. The purpose of this virtual model is to compare the respective performances. Two nonlinear analyses were performed and compared with the experimental test results. These analyses were carried out in two phases. The research addresses first the analysis of a structure with only reinforced concrete elements, and secondly the analysis of the same structure with reinforced concrete elements and infill walls. Both researches consider static loading and pushover analysis. The experimental pushover curve was plotted by the envelope of the experimental curve obtained on the basis of the shake table records. Crack patterns, failure modes and performance curves were plotted for both models. Finally, results were evaluated on the basis of the current regulation ASCE/SEI 41-06.

• 한국강구조학회 논문집
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• 제30권1호
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• pp.25-35
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• 2018

균일 외압을 받는 링 보강 원형단면 강재 쉘에 대하여 재료 및 기하학적 비선형 유한요소법(GMNIA)을 적용하여 외압강도를 평가하였다. 링 보강 쉘의 기하학적 초기결함의 진폭, 반경 대 두께 비, 링 보강재 간격 대 반경비 등이 외압강도에 미치는 영향을 분석하였으며, Eurocode 3과 DNV 설계기준에 의한 설계 외압 강도와 유한 요소해석으로 구한 외압강도를 비교 평가하였다. 기하학적 초기결함의 형상은 선형탄성 좌굴해석에 의한 좌굴모드를 적용하였으며 보강 쉘의 반경 대 두께 비는 250~500범위를 고려하였다.

• 소성∙가공
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• 제19권8호
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• pp.508-516
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• 2010

Thickening process in sheet metal forming is being increased to improve the strength as well as to reduce manufacturing process such as welding. This process can make it possible to obtain part locally thicker than that of initial sheet thickness. In this study, design method for manufacturing the component which has double sinks with local thickened wall is proposed. Deep drawing and upsetting processes are applied in order to form double sinks and thicken its walls. Used material is SPHC440 with the thickness of 2.0mm and initial blank size is determined on the basis of the final product. Distance between the center of double sinks and first drawing ratio to avoid fracture are the most significant factors during deep drawing. FE-analysis is implemented in order to determine the appropriate values. Progressive die is designed based on the proposed method and FE-analysis. As a result of experiment, locally thickened component can be manufactured, which has double sinks with the thickness about 3mm at the corner and wall.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 춘계학술대회논문집
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• pp.645-650
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• 2004

There have been lots of efforts to analyze the dynamic characteristics of mechanical systems. However, it is difficult to know the dynamic characteristics of mechanical systems composed of many parts with joints. Specially, in case of a bolted joint structure, no effective modeling method has been defined to acquire dynamic characteristics of the structure, using the finite element (FE) analysis. In this research, a linear dynamic model is developed for bolted joints and large interfaces using con frusta method and linear spring elements, respectively. The developed modeling method for bolted joints is verified based on the experimental result.

• 한국소음진동공학회논문집
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• 제14권10호
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• pp.990-998
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• 2004

There have been lots of efforts to analyze the dynamic characteristics of mechanical systems. However, it is difficult the know the dynamic characteristics of mechanical systems composed of many parts with joints. Specially, in case of a bolted Joint structure, no effective modeling method has been defined to acquire dynamic characteristics of the structure using the finite element (FE) analysis. In this research, a linear dynamic model is developed for bolted feints and large interfaces using con frusta method and linear spring elements, respectively. The developed modeling method for bolted joints is verified based on the experimental result.

• 한국자기학회지
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• 제12권1호
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• pp.1-6
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• 2002

Sol-gel법을 이용하여 $Y_3$Fe$_{5-x}$Al$_{x}$O$_{12}$ (x = 0.0, 0.25, 0.50, 0.75, 1.0) 분말을 합성하였다. 열시차 중량 분석장치(TG-DTA), x선회절기, 시료진동 자화율 측정기(VSM) 및 Mossbauer 분광기를 이용하여 물질의 결정구조 및 자기적 성질을 연구하였다. $Y_3$Fe$_{5-x}$Al$_{x}$O$_{12}$ 의 결정구조는 cubic이며, 격자상수는 x = 0.0에서 1.0까지 치환되었을 때 12.381부터 12.304 $\AA$으로 선형적으로 감소함을 보였다. Mossbauer spectrum을 13K부터 600K가지 여러 온도에서 측정을 하였다. x=0일 때 Mossbauer spectrum은 2 set으로 잘 구분할 수 있지만 치환량이 증가함에 따라 바깥쪽 팔면체 자리의 선폭이 점점 넓어지는 것을 관측할 수 있다. 이러한 현상은 사면체 자리에 존재하는 Fe$^{3+}$ 과 $Al^{3+}$ 이온의 확률적 분포에 따른 것으로 해석된다.