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기하학적 비선형 판재 해석을 위한 혼합형 FE Model 연구
김우람(Wooram Kim),최윤대(Youn Dae Choi) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.5
A mixed finite element model was developed using the classical plate theory to analyze nonlinear bending of plate. The Lagrange multiplier method and the principal of minimum virtual energy were employed to find proper weight functions for the constraints which state the constitutive relations of force like variables and strains. All detail terms of element wise coefficient matrices and associate tangent matrices are presented to use the Newton iterative method. Then, linear solutions of the current model and traditional displacement model under the SS(simple support) boundary conditions were compared along with existing analytic solution. Post processed images of the nonlinear result of force like variables are presented to show the continuity of the solutions at the joint of the element boundaries. Finally, converged nonlinear finite element solutions of the current model are compared with those of existing traditional displacement model.Put Abstract text here.
김우람 ( Wooram Kim ),권윤자 ( Younja Kwon ),조영민 ( Youngmin Jo ) 한국공업화학회 2016 공업화학 Vol.27 No.4
새로운 고체산화제 화합물인 pyridinium dinitramide (Py-DN)는 환경 및 인체에 독성이 적은 비염소계의 에너지물질로서 고체 추진제 뿐만 아니라 단일계 추진제로 활용이 가능한 high performance green propellant (HPGP) 물질이다. 합성반응은 술팜산칼륨(potassium sulfamate, NH2SO3K)을 출발물질로 시작하였으며, 합성된 Py-DN의 화학적인 구조특성을 적외선분광법과 가시광선-자외선분광법으로 관찰하였다. 또한, 유사한 물성의 친환경 고체산화제인 ammonium dinitramide[ ADN, NH4N(NO2)2]와 guanidine dinitramide[GDN, NH2C(NH2)NH2N(NO2)2]의 열특성을 TG/DSC로 분석하여 상대비교하였다. 본 연구에서 합성한 Py-DN염의 흡열온도는 77.4 ℃, 분해온도는 144.7 ℃, 발열에너지는 1739 J/g으로 기존의 DN계열 물질보다 열적 반응이 빠르므로 분해온도가 상대적으로 낮아 단일계 추진제의 촉매 분해 시 촉매의 예열온도를 낮출 수 있어 로켓추력기의 연료로 활용할 경우, 낮은 분해온도 적용성에 장점이 있다. A new solid oxidizer, pyridinium dinitramide (Py-DN) is a low toxic energetic material which can be utilized as a HPGP (high performance green propellant). In this work, Py-DN was synthesized using various starting materials including potassium sulfamate, pyridine hydrochloride, strong nitric acid and sulfuric acid. Physical and chemical properties of the Py-DN were characterized using UV-Vis, FT-IR and a thermal analyzer and their properties were compared to those of previously prepared salts including ammonium dinitramide[ADN, NH4N(NO2)2] and guanidine dinitramide[GDN, NH2C(NH2)NH2N(NO2)2] in our lab. Endothermic and exothermic decomposition temperatures of Py-DN were 77.4 ℃ and 144.7 ℃, respectively. The combustion caloric value was 1739 J/g, which is thermally more sensitive than that of conventional dinitramides. It may enable to lower the decomposition temperature, which can reduce preheating temperature required for satellite thruster applications.
김우람 ( Wooram Kim ),권윤자 ( Younja Kwon ),조영민 ( Youngmin Jo ),박영철 ( Youngchul Park ) 한국공업화학회 2015 공업화학 Vol.26 No.6
An environmentally favorable solid oxidizer, guanidine dinitramide (H2C(NH2)NH2N(NO2)2), with high purity and synthesis yield was prepared using guanidine carbonate (NH2C(=NH)NH2·1/2H2CO3). Two different crystalline forms (α-form and β-form) were obtained depending on the solvent used and synthesis process. Despite of the same chemical composition, Raman-IR and TGA-DSC revealed that different structures existed between them. In particular, the thermal analysis showed the exothermic temperature of α-form at 155.7 ℃ while 191.6 ℃ for β-form. The caloric value of α-form was 536.4 J/g which was 2.5 times larger than that of β-form, 1310 J/g. In addition, α-form was steeply decomposed with one-step variation, but β-form followed a two-step thermal decomposition pattern.
영농형 태양광 구조물 활용 고부가가치 작물의 이상기후 영향 분석
김우람(Wooram Kim),남재우(JaeWoo Nam),김근호(Geun Ho Gim),김덕성(Deok Sung Kim),임철현(Cheolhyun Lim) 한국태양광발전학회 2021 Current Photovoltaic Research Vol.9 No.2
Agrovoltaic system is a concept that combines agriculture and photovoltaic (PV) system by applying a PV system to the upper part of farmland. In this study, we developed a folding drive system for an agrophotovoltaic (agroPV) module (150 Wp/4×9 cell) exclusively for pear farming with 10 kW capacity. The system was installed in 2018, and the growth characteristics and quantity of pears under the agroPV folding system have been investigated for 2 years. We found that thare is no differences of the characteristics of pears grown under the agroPV system compared to the pears grown without the system (control) except the percutaneous color L of pear. However, the weight and sugar content of the pear grown under the agroPV system were decreased by 4.5% and 1.3°Bx compared to that of the control, respectively. We assume that this is mainly due to the influenced of the delay in flowering as upper PV module block some of sunlight. However, interestingly, when we deleyed the pear harvesting by 2 weeks, the weight of pears increased by 8.5% and they became nearly the sample as the control pears harvested 2 week earlier. In addition, we also found that the agroPV modules decrease the fall rate of pear when the typoon struck, also it mitigates cold damage by 38% during April by protecting from frost. In conclusion, it can be said that the agroPV system help to protect target crops from the environmental conditions and the quality of the crops are similar to the that of control.
기하학적 비선형 판재 해석을 위한 혼합형 FE Model 연구
김우람(Wooram Kim),최윤대(Youn Dae Choi) 대한기계학회 2010 大韓機械學會論文集A Vol.34 No.10
전통 판재이론을 이용하여 기하학적 비선형성을 갖는 판재의 휨해석을 위한 혼합형 유한요소모델을 구성하였다. 혼합형 유한요소 모델의 구성에 포함되는 변형률과 합성력의 관계에 대한 적절한 가중함수를 찾기 위하여 라그랑지 승수법과 최소가상에너지 원리를 사용하였다. 각 요소별 유한요소 방정식의 계수행렬과 뉴턴 반복법 사용을 위한 접선 행렬에 대한 구체적 값을 제시하였다. 구성된 유한요소 해석모델의 선형 해에 대한 정확도 분석을 위하여, 여러 경계조건하에서의 수학적 해와 제시된 모델과 기존 모델의 유한요소해를 비교하여 현재 모델의 정확도의 향상을 확인하였다. 또한 수렴된 비선형해를 이용하여 제시된 모델의 경우, 각종 합성력들에 대한 요소 경계에서의 연속성이 기존의 모델의 합성력에 비해 개선됨을 제시하였다. 최종적으로 수렴한 비선형해에 대한 유효성을 보이기 위하여 기존 모델의 비선형 수렴해와 현재 모델의 비선형 수렴해를 비교하여 제시하였다. A mixed finite element model was developed using the classical plate theory to analyze the nonlinear bending of a plate. The appropriate weight functions for the constraints integrated over the domain were determined by the Lagrange multiplier method by using the principle of minimum virtual energy; which provides the constitutive relations between force-like variables and strains. All of detail terms of element wise coefficient matrices and associate tangent matrices to be used in the Newton iterative method are presented. Then, the linear solutions of the current model and those of the traditional displacement model under the SS (simple support) boundary conditions were compared with the existing analytical solution. The post-processed images of the nonlinear results of the force-like variables are presented to show the continuity of the solutions at the joint of the element boundaries. Finally, the converged nonlinear finite element solutions of the current model are compared with those of existing traditional displacement model.