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부유식 재생에너지 플랜트의 개념설계를 통한 계류라인의 피로설계
정준모(Joonmo Choung),이민성(Min-Sung Lee),전상익(Sang-Ik Jeon) 대한조선학회 2011 대한조선학회 학술대회자료집 Vol.2011 No.6
This paper presents the concept design precedure of floating-type combined renewable energy platform based on hydrodynamic analyses and the fatigue design procedure of taut-type mooring lines. Two types of combined renewable energy platforms are taken into account: first combination of wind, wave, and photovoltanic energies and second combination of wind , current, photovoltanic energies. The concept design is from the literature survey, but main dimensions have been decided based on the basic hydrostatic calculation. Fully coupled hydrodynamic analyses have been carried out to identify motion characteristics of the floating body and tension histories of each mooring lines. Further fatigue lives using rainflow cycle counting method, API stress-life diagram, and Palmgren-Miner rule are predicted for chain link-type taut mooring system. Finally mooring lines satisfying design life of twenty years are proposed.
정준모(Joonmo Choung),심천식(Chun-Sik Shim) 대한조선학회 2011 대한조선학회 학술대회자료집 Vol.2011 No.11
This is the third of several companion papers dealing with derivation of material constants for ductile failure criterion under hydrostatic stress. It is observed that ultimate engineering stresses and elongations at fracture from tensile tests for round specimens with various notch radii tend to increase and decrease, respectively, due to stress triaxiality. The engineering stress curves from tests are compared with numerical simulation results, and it is proved that curves from two approaches are very closely coincide each other. Failure strains are obtained from equivalent plastic strain histories from numerical simulations at the time when the experimental engineering stress falls down suddenly. After introducing a new concept of average stress triaxiality and accumulated average strain energy, material constants of Johnson-Cook failure criterion for critical energies of 100%, 50%, and 15% are presented. Experimental results conducted for EH-36 steel are relatively good agreement with 100% critical energy whereas literature states that aluminum fits with 15% critical energy. Therefore it is expected that a unified failure criterion, available for most kinds of ductile materials, of critical energy according to the used materials can be provided.
부유식 복합 재생에너지 플랫폼 계류선의 효과적 배치에 관한 연구
정준모(Joonmo Choung),전기영(Gi-Young Jeon),김유일(Yooil Kim) 한국해양공학회 2013 韓國海洋工學會誌 Vol.27 No.4
This paper presents the conceptual design procedure for the taut?leg mooring lines of a floating?type combined renewable energy platform. The basic configuration of the platform is determined based on an understanding of floating offshore plants. The main dimensions and mass distribution are determined based on a hydrostatic calculation. To identify the motion history of the floating platform and the tension history of the mooring lines, a hydrodynamic analysis is executed using Ansys.Aqwa. This helps in the selection of the best configuration for the mooring system such as the number of mooring lines, wire types, anchored positions, etc. In addition, the fatigue life of the mooring lines can be predicted from the tension history using the rain?flow cycle counting method.
국내 연안 카페리 차량 고박 장치 안전성에 관한 연구 제2부
정준모(Joonmo Choung),조희상(Huisang Jo),이경훈(Kyunghoon Lee),이영우(Young Woo Lee) 한국해양공학회 2016 韓國海洋工學會誌 Vol.30 No.6
For a carferry with a displacement of 1,633 tonf, a seakeeping analysis-based direct load approach (DLA) was used in Part I of these series, where the final deliverable was the long-term probabilistic acceleration components. In Part II of these series, the tangential acceleration components are explained based on two approaches: a standard called the IMO CSS code and simple formulas with the probable maximum roll and pitch rotations. The subsequent tangential acceleration-induced external force components are also introduced for these two approaches. The lashing strength components were selected from the IMO CSS code. It was assumed that two different vehicles (a car and a truck) were stowed at the most distant locations on the main deck to assume the largest tangential acceleration components and were secured with four steel wires with longitudinal and transverse lashing angles of 45∘. Four cases were considered, with different methods for predicting the acceleration components and different tools for the external loads and lashing strengths involved: cases Rule-LS (rule-based maximum probable roll and pitch angles for predicting the acceleration components in conjunction with LashingSafety), DLA-LS (seakeeping-based long-term acceleration components with LashingSafety), CSS-LC (IMO CSS code-based acceleration components using LashCon), and CSS-LS (IMO CSS code-based acceleration components using LashingSafety). In terms of the acceleration and external force components, the CSS-LC and CSS-LS results are more than two times the results of Rule-LS. Thus, when the external forces and lashing strengths are evaluated using CSS-LC and CSS-LS, the truck needs more lashing wires, while Rule-LS and DLA-LS predict that the present lashing configuration is on the safe side.
조선 해양 구조물용 강재 변형률 경화 및 변형률 속도 경화의 이론적 배경
정준모(Joonmo Choung),심천식(Chun-Sik Shim),김경수(Kyung Su Kim) 대한조선학회 2011 대한조선학회 학술대회자료집 Vol.2011 No.6
In this paper, global study trends of material behaviors are investigated regarding static and dynamic hardenings and final fractures of marine structural steels. Especially, after reviewing all papers published in the 4th and 5th ICCGS (International Conference on Collision and Grounding of Ship), the used hardening and fracture properties are summarized explicitly presenting material properties. Although some papers have tried to employ new plasticity and fracture models, it is obvious that most papers still employed ideal hardening rule such as perfect plastic or linear hardening and simple shear fracture criterion with assumed value of failure strain. HSE (2001) presented pioneering study results regarding temperature dependency of material strain hardening at the various level of temperatures, but did not show strain rate hardening at intermediate or hight strain rate ranges. Nemat-Nasser and Guo (2003) carried out fully coupled tests for DH-36 steel: strain hardening, strain rate hardening, and temperature hardening and softening at multiple steps of strain rates and temperatures. Main pillars of this paper are to provide theoretical backgrounds of strain and strain rate hardening. In addition, the procedure and methodology to derive material constants for static hardening constitutive equations of Ludwik, Hollomon, Swift, and Ramberg-Osgood and for dynamic hardening constitutive equations of power, Cowper-Symonds and Johnson-Cook.
조선 해양 구조물용 강재 파단 변형률에 관한 실험적 연구
정준모(Joonmo Choung),심천식(Chun-Sik Shim),김경수(Kyung Su Kim) 대한조선학회 2011 대한조선학회 학술대회자료집 Vol.2011 No.6
This is the third of several companion papers dealing with derivation of material constants for ductile failure criterion under hydrostatic stress. It is observed that ultimate engineering stresses and elongations at fracture from tensile tests for round specimens with various notch radii tend to increase and decrease, respectively, due to stress triaxiality. The engineering stress curves from tests are compared with numerical simulation results, and it is proved that curves from two approaches are very closely coincide each other. Failure strains are obtained from equivalent plastic strain histories from numerical simulations at the time when the experimental engineering stress falls down suddenly. After introducing a new concept of average stress triaxiality and accumulated average strain energy, material constants of Johnson-Cook failure criterion for critical energies of 100%, 50%, and 15% are presented. Experimental results conducted for EH-36 steel are relatively good agreement with 100% critical energy whereas literature states that aluminum fits with 15% critical energy. Therefore it is expected that a unified failure criterion, available for most kinds of ductile materials, of critical energy according to the used materials can be provided.
정준모(Joonmo Choung),임성우(Sung-Woo Im) 대한조선학회 2011 대한조선학회 학술대회자료집 Vol.2011 No.11
This is the fifth of serial companion papers dealing with dynamic hardening properties of various marine structural steels at intermediate strain rates. Five steps of strain rate levels of 0.001, 1, 10, 100, 200/s and three steps of temperature levels of LT(-40℃), RT, and HT(200℃) are taken into account for the dynamic tensile tests of three types of marine structural steels of API 2W50 and Classification EH36 and DH36. The number of specimens is totally 180 pieces. It is witnessed that effects of dynamic hardening become clearer at LT than at RT. Dynamic strain aging accompanying serrated flow stress curves is also observed from high temperature tests for all kinds of steels. Dynamic hardening factors (DHFs) at two temperature levels of LT and RT are derived at the three plastic strain levels of 0.05, 0.10, 0.15 from dynamic tensile tests meanwhile any DHF is not assessed for the high temperature tests since slight negative strain rate dependency due to dynamic strain aging has occurred. A new formulation to determine material constant D in Cowper-Symonds constitutive equation is provided as function of plastic strain rate as well as plastic strain level. The proposed formula is verified by comparing with test flow stress curves not only at intermediate strain rate ranges but also at high strain rate ranges.