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24th International Conference on Port and Ocean engineering under Arctic Conditions, POAC 2017

作者： Kim, Hyoil Im, Namkyun Sawamura, Junji Department of Naval Architecture and Ocean Engineering Osaka University Japan Division of Marine Transportation System Mokpo Maritime University Jeonnam Korea Republic of

Ship-ice interaction in pack ice is important issue for safe ship operation in ice-covered water. This paper presents an investigation of ship-ice interaction when an ice-going ship turns and moves straight in pack ice. Free-running model tests were conducted to elucidate ship-ice interaction in pack ice. A 1/100 scale ship model and disk-shaped synthetic ice floes were used in a free-running model test. The model ship, propelled with a constant engine RPM at full loading condition, had a GPS and a motion sensor installed onboard to measure the ship's trajectory and motion. Ice removal was measured using a vision inspection technique. In free-running tests, the model ship passed through pack ice of three ice concentrations (10%, 20%, and 30%) with no rudder action. In turning circle tests, the model ship passed through pack ice with 7.2% ice concentration. The authors proposed a numerical model to calculate ice loads and ship motions in pack ice based on Discrete Element Method. To validate the numerical model, ship motions and ice removal in the model tests were compared with the simulations. Numerical results showed good agreement with experimental test results. The effects of ice concentration on ship-ice interactions were investigated experimentally and numerically.

关键词： Numerical methods

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Determination of the optimal operating condition of the dual mixed refrigerant cycle at the pre-FEED stage of the LNG FPSO topside liquefaction process

Determination of the optimal operating condition of the dual...

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作者： Lee, Kyu-Yeul Cha, Ju-Hwan Lee, Joon-Chae Roh, Myung-Il Hwang, Ji-Hyun Department of Naval Architecture and Ocean Engineering Seoul National University Seoul Korea Republic of Department of Ocean System Engineering Mokpo National University Mokpo Korea Republic of School of Naval Architecture and Ocean Engineering University of Ulsan Seoul Korea Republic of

ISBN: (纸本)9781880653968

The dual mixed refrigerant (DMR) cycle, which pre-cools natural gas with the mixed refrigerants and then liquefies the natural gas with another set of mixed refrigerants, is well known for having the highest efficiency among the liquefaction cycles. Its possible application to LNG FPSO is also extensively investigated. In this study, the optimal operating conditions, such as the equipment's flow rate, pressure, temperature, and refrigerant composition per flow of the DMR cycle, were determined in consideration of power efficiency. To determine the optimal operating conditions, a mathematical model was formulated based on the mathematical model of the single mixed refrigerant (SMR) cycle with additional consideration of tees, phase separators, and common headers. In the mathematical model, the 227 operating conditions were defined as unknowns and 196 equality constraints related to the thermodynamics for the equipment were formulated. Further, the 15 given variables related to the natural gas, compressor efficiency and seawater coolers were used. This mathematical model can be regarded as the optimization problem, in which the number of unknowns is larger than the total number of equality constraints and given variables. To obtain the optimal operating conditions, the minimization of the required power for the compressors at the cycle was defined as an objective function. Moreover, set as design variables were the 16 operating conditions, such as flow rate, pressure, temperature and composition of the main and precooling refrigerant, natural gas temperature after precooling, and flow rate ratio for the tee. In addition, the temperature conditions for the equipment's operation were used as inequality constraints. The optimal operating conditions were then obtained by using a hybrid optimization method that consists of the genetic algorithm (GA) and sequential quadratic programming (SQP). The calculation results show that the required power at the obtained conditions w

关键词： Refrigerants

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Global analysis of flexible riser with internal and external pressure load effects 28

Global analysis of flexible riser with internal and external...

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28th International Ocean and Polar engineering Conference, ISOPE 2018

作者： Kim, Jeong Du Jang, Beom-Seon Yoon, Lan Hee DePartment of Naval Architecture and Ocean Engineering Seoul National University Seoul Korea Republic of Research Institute of Marine System Engineering Seoul National University Korea Republic of

ISBN: (纸本)9781880653876

This paper aims to suggest more accurate global time domain analysis of flexible risers and to investigate the effect of nonlinear bending model on global analysis results. The suggested global time domain analysis procedure, unlike to the previous studies, preliminarily estimate the bending hysteresis curve of each riser segment with different pressure loads. Then, the calculated curves are implemented in the global time domain analysis to reflect the nonlinear bending behavior of flexible riser. During the analysis, the resultant stress in a tensile wire is calculated through the theoretically derived stress model. Throughout the 6 different model, a comparative study is conducted to investigate the effect of nonlinear bending model. As a result, significant differences in both the structural responses and stress time history are observed when implementing a more detailed bending model in global time domain analysis. Copyright © 2018 by the International Society of Offshore and Polar Engineers (ISOPE)

关键词： Time domain analysis

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Structural impact under accidental LNG release on the LNG bunkering ship: Implementation of advanced cryogenic risk analysis

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Process Safety and Environmental Protection 2024年 186卷 329-347页

作者： Nubli, Haris Jung, Dongho Kim, Sang Jin Sohn, Jung Min Department of Naval Architecture and Marine System Engineering Pukyong National University Korea Republic of Department of Offshore Platform Research Division Korea Reseacrch Institute of Ships and Ocean Engineering Korea Republic of Department of Marine Environment and Engineering National Sun Yat-sen University Kaohsiung Taiwan Department of Marine Design Convergence Engineering Pukyong National University Korea Republic of

The potential risk associated with the accidental release of Liquefied Natural Gas (LNG) is a notable concern during the design phase of gas-handling facilities. One of the risk is an excessive cryogenic exposure to structures or equipment, leading to hazardous situations. This study aims to introduce a novel method that implements Advanced Cryogenic Risk Analysis (ACRA) to enhance the safety of LNG bunkering ship structure in case of cryogenic flow leakage. The method involves evaluating thermal loads based on the preceding simulated LNG release scenarios using Computational Fluid Dynamics (CFD). These thermal parameters are then employed in structural analysis through the Finite Element (FE) approach. The integration of thermal data from CFD simulations into the FE model was achieved using the Random Forest algorithm. The LNG bunkering structure is represented using DH36-grade steel material. Furthermore, to accurately capture the mechanical properties of DH36 steel, cryogenic tensile tests were conducted across a temperature range from 298.15 K to 113.15 K. The resulting stress-strain data from these tests were utilized to establish a reliable material model for conducting FE analysis. This paper comprehensively presents a novel ACRA procedure by utilizing physical parameter of the gas release cosnequence such as the steel temperature profile to identify the brittle failure under the accidental gas release on the LNG bunkering ship. In addition, quantitative risk analysis (QRA) was also presented regarding the cryogenic spill hazard, to link the probability and consequence aspects of the LNG bunkering risk, particularly the results of steel temperature, stress, and strain experienced by the ship's structure. Furthermore, the individual risk was also estimated. The implications of the findings are discussed in detail regarding the cryogenic risk, cryogenic tensile test and numerical analyses. © 2024 The Institution of Chemical Engineers

关键词： Hazardous materials spills

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Autonomous planning framework for distributed multiagent robotic systems

Autonomous planning framework for distributed multiagent rob...

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作者： Švaco, Marko Šekoranja, Bojan Jerbić, Bojan University of Zagreb Faculty of Mechanical Engineering and Naval Architecture Department of Robotics and Production System Automation Ivana Lučića 5 10000 Zagreb Croatia

ISBN: (纸本)9783642191695

In this paper a creative action planning algorithm (CAPA) is presented for solving multiagent planning problems and task allocation. The distributed multiagent system taken in consideration is a system of m autonomous agents. Agents workspace contains simplified blocks which form different space structures. By employing the planning algorithm and through interaction agents allocate tasks which they execute in order to assemble the required space structure. The planning algorithm is based on an inductive engine. From a given set of objects which can differ from the initial set agents need to reach a solution in the anticipated search space. A multiagent framework for autonomous planning is developed and implemented on an actual robotic system consisting of three 6 DOF industrial robots. © 2011 IFIP International Federation for Information Processing.

关键词： Multi agent systems

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Robust non-integer predictive control for wind turbine pitch angle regulation in full load regions using deep on-policy learning

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engineering Applications of Artificial Intelligence 2025年 156卷

作者： Mai The Vu Van-Truong Nguyen Quang Thang Do Wonkeun Youn Tuan Hai Nguyen Department of Artificial Intelligence and Robotics Sejong University Seoul 05006 Republic of Korea Faculty of Mechatronics SMAE Hanoi University of Industry Hanoi 10000 Viet Nam Department of Naval Architecture and Ocean Engineering Nha Trang University 02 Nguyen Dinh Chieu Nha Trang 650000 Viet Nam Department of Autonomous Vehicle System Engineering Chungnam National University Daejeon Republic of Korea Faculty of Engineering Dong Nai Technology University Bien Hoa City Vietnam

The pitch angle regulation of wind turbine (WT) plants faces serious challenges due to the nonlinear behavior of these systems and remarkable moment of inertia, along with stochastic changes in wind speed. In this paper, an adaptive pitch angle control based on fractional order model predictive control (FOMPC) is developed for variable speed of WT under full load region to regulate the rotor speed and to limit the output power. In particular, the deep state-action-reward-state-action (SARSA) is utilized to tune critical parameters of FOMPC, which is useful to stabilize rotor speed by adapting to the changes of turbulent wind conditions. By defining a reward function based on the specific goals of WT systems, the deep neural networks (DNNs) of the SARSA agent learn an effective policy for stabilizing the wind turbine, adjusting the FOMPC-based pitch angle control in response to varying wind conditions to capture the maximum output. By utilizing the training capability of DNNs, the FOMPC controller can dynamically respond to the changes in the WT system. The deployment of deep SARSA makes the intelligent controller to automatically learn and implement optimal control strategies in complex, dynamic environments, enhancing overall system performance and resilience. For comparison purposes, three other pitch angle controllers including the basic model predictive control (MPC), gain scheduling proportional-integral (GSPI) controller, and proportional-integral (PI) controller were also designed for the case-study. The feasibility of designed pitch angle controllers for WT stabilization was verified under two different operation conditions: normal and extreme stochastic wind circumstances. Dynamic responses and numerical analysis confirmed the suggested FOMPC-based deep SARSA agent can provide superior transient behavior and a higher level of robustness than the MPC, GSPI, and PI controller when the WT system is working at full load region.

关键词： Predictive control systems

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Streamwise dynamics controlled jet spreading, mixing and physical source of the vortices

Streamwise dynamics controlled jet spreading, mixing and phy...

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作者： Sau, Amalendu Hwang, Robert R. Department of Mechanical and Aerospace Engineering Gyeongsang National University Gyeongnam Jinju Korea Republic of Department of System Engineering and Naval Architecture National Taiwan Ocean University Keelung Taiwan

Within the framework of the present investigation we perform Direct Numerical Simulations to study the role of streamwise dynamics in the jet spreading and mixing, and provide a clear understanding about the source of these important vortices in two-step rectangular sudden expansion flows. The present setup is designed to generate higher mass entrainment, and the system generated passive forcing provided the necessary impetus for the sustained growth/evolution of the streamwise vertices, which played the key role in the mixing enhancement. On the other hand, by suitably placing two tiny rectangular 'tabs' on the inlet channel walls, the nature of growth and the dynamics of the streamwise extended three-dimensional vortical rollers could be effectively controlled. These vortices through their inflow/outflow type dynamics are found to effectively control the downstream jet spreading;and the associated physical processes either lead to quick axis switching of the jet section, or stop axis switching altogether. In addition, an extensive pressure analysis, as presented here, suggests that the transverse pressure gradient skewing is probably the major source of streamwise vorticity generation for the flow.

关键词： Vortex flow

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Measurement of instantaneous pressure distribution from PIV experiments

Measurement of instantaneous pressure distribution from PIV ...

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作者： Jaw, S.Y. Chen, C.J. Hwang, R.R. Department of System Engineering and Naval Architecture National Taiwan Ocean University Taiwan Florida A and M University Florida State University College of Engineering United States

ISBN: (纸本)9781615676248

In this study, a pressure equation solver modified from the SIMPLER algorithm is proposed to measure the whole field, instantaneous pressure distribution using the velocity vectors obtained from PIV experiments. The momentum equations are discretized using the finite analytic method. The discretized momentum equations, and the corresponding velocity components, are expressed in terms of the pseudo velocities and pressure gradients. A pressure equation can be derived by substituting the velocity expressions into the continuity equation. The velocity vectors obtained from PIV experiments are used to calculate the discretization coefficients and the pseudo velocities. The pressure distribution of the flow field can then be solved. A uniform flow due to pressure gradient between two parallel plates and a simulated impinging jet flow are tested first, then the flow past double cylinders are analyzed using the proposed scheme. Satisfactory results are obtained.

关键词： Pressure gradient

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Guidelines for Determining the Extent of Toxic Areas for Ships Using Ammonia as a Fuel 34th

Guidelines for Determining the Extent of Toxic Areas for Shi...

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34th International Ocean and Polar engineering Conference, ISOPE 2024

作者： Nam, Hyunjoon Kim, Do Kyun Kim, Sunghee Shin, Dongkyu System Safety Research Department HD Korea Shipbuilding and offshore Engineering Co Ltd Gyeonggi-do Korea Republic of Department of Naval Architecture and Ocean Engineering Seoul National University Seoul Korea Republic of

ISBN: (纸本)9781880653784

Guidelines are proposed to determine the extent of toxic area for ships using ammonia as a fuel. The guidelines clearly define the purpose of Toxic Area Classification and suggest a specific reference toxic concentration for determining the extent of toxic areas. Included within the guidelines is a chart developed to estimate hazardous distances according to the volumetric characteristics of toxic releases. A case study conducted on a large ammonia-fueled container ship demonstrates the effectiveness and practicality of the guidelines. The proposed guidelines can serve as a valuable tool for determining and justifying the extent of toxic areas. © 2024 by the International Society of Offshore and Polar Engineers (ISOPE).

关键词： Ammonia

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Numerical study for waveform inversion as an internal solitary wave over permeable trapezoidal topography 25

Numerical study for waveform inversion as an internal solita...

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25th International Ocean and Polar engineering Conference, ISOPE 2015

作者： Hsieh, Chih-Min Cheng, Ming-Hung Hwang, Robert R. Yang, Wen-Chang Department of Maritime Information and Technology National Kaohsiung Marine University Kaohsiung Taiwan Department of System Engineering and Naval Architecture National Taiwan Ocean University Keelung Taiwan Kaohsiung Taiwan

ISBN: (纸本)9781880653890

A finite volume method based Cartesian grids is adopted to solve the Reynolds averaged Navier-Stokes equations using a k-Ε turbulence model and porous media model for the study of the porous effect on the flow evolution as a large depression internal solitary wave propagates over a porous trapezoidal obstacle. Numerical results reveal that as the porosity increases, the waveform inversion becomes unapparent and is not found in the porosity higher than 0.2. In addition, the magnitudes of vorticity and turbulent energy seriously decrease because of acute reduction of the production term, which is induced by percolation and wave-pore interaction. Copyright © 2015 by the International Society of Offshore and Polar Engineers (ISOPE).

关键词： Porosity

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