Study on Dynamic Positioning Capacity Analysis Method Considering Wind Shielding Effect of Offshore Structure

2021 ◽  
pp. 1-11
Author(s):  
Jinhui He ◽  
Haibin Zhang ◽  
Renchuan Zhu
Keyword(s):  
Time Domain ◽  
Offshore Structures ◽  
Wind Load ◽  
New Method ◽  
Shielding Effect ◽  
Capacity Analysis ◽  
Dynamic Positioning ◽  
Time Domain Simulation ◽  
Environmental Loads ◽  
Load Calculation

Offshore structures floating at sea should use their dynamic positioning (DP) system to maintain position and heading against environmental loads, including wave loads, current loads, and wind loads. It is difficult to calculate environmental loads accurately and quickly, especially for wind loads due to the shielding effect of different parts on offshore structures. To improve the accuracy of wind load calculation, a new method considering shielding effect is proposed. With the new method, calculated wind force becomes much closer to wind tunnel test than the traditional method. As input data of DP capacity analysis, the environmental loads have critical impact on the design of DP system. A static method and a time-domain simulation method of DP capacity are also proposed, and a case study of drillship is carried out. The results of both static analysis and time-domain simulation of DP capacity show that the new wind load calculation method has improved the accuracy of environmental load calculation and DP capacity analysis. Introduction As the offshore oil and gas exploitation is going further into deep sea, offshore structures are to be used in harsh marine environments, including strong wind, current, and waves. Especially for wind, it can make great effect on the dynamic positioning (DP) system of offshore structures, which is designed to maintain position and heading. Once the DP system is not able to keep the offshore structures’ position and heading, it will cause an accident such as oil leakage and oil pollution in the ocean. Because of the wind shielding effect among all parts on offshore structures, such as deckhouse, derricks, cranes, pipe racks, the wind load is difficult to calculate accurately and quickly.

Time Domain Simulation of a Dynamic Positioning Deepwater Semisubmersible Drilling Platform

2014 ◽  
Author(s):  
Xu Yang ◽  
Liping Sun ◽  
Shuhong Chai
Keyword(s):  
Time Domain ◽  
Numerical Study ◽  
Angular Speed ◽  
Dynamic Positioning ◽  
Positioning System ◽  
Time Domain Simulation ◽  
Proportional Integral Derivative ◽  
Floating Structures ◽  
Environmental Loads ◽  
Dynamic Positioning System

DPS (dynamic positioning system) has been widely used in floating structures, especially in deepwater area. Time domain simulation of platforms with dynamic positioning system has great significance to DP capability and riser system. Motion response of a deepwater semi-submersible platform with DPS on time domain was presented in this paper. PID (proportional, integral, derivative) controller and thruster allocation method were applied in numerical simulations of DPS. Wind, current and wave environmental loads were analyzed and limited angular speed was considered as well. Thruster failure analyses were covered and discussed also. Experiments of DPS in deep-water basin of Harbin Engineering University (HEU) were presented and compared with numerical study.

scholarly journals Study on submerging operation design for heavy-lift barges based on a real case analysis

2017 ◽  
Vol 233 (1) ◽  
pp. 363-371
Author(s):  
Xin Wang ◽  
Wei Jun Ko
Keyword(s):  
High Risk ◽  
Time Domain ◽  
Case Analysis ◽  
Offshore Structures ◽  
Time Domain Simulation ◽  
Ballast Tank ◽  
Sea Trial ◽  
Heavy Lift ◽  
Simulation Results

Semi-submersible heavy-lift barges are widely used for transporting large offshore structures over long distances. The float-on and float-off operations of such vessels are considered as high-risk tasks even today. Improper flooding sequence may lead to accidents including loss of vessels and human lives. The main objective of this study is to provide valuable findings and guidelines for the design of submerging operations based on the case study of an unsuccessful submerging sea trial. A quasi-static time-domain simulation was conducted to investigate the unsuccessful trial and design a new flooding sequence. Based on the simulation results, the causes of the unsuccessful trial have been identified. Moreover, a new flooding sequence is proposed after examining various options. Since the vessel’s dimensions and ballast tank layout are typical and similar to many other heavy-lift barges, general conclusions for the design of submerging operations are summarized.

scholarly journals Fuel-Optimal Thrust-Allocation Algorithm Using Penalty Optimization Programing for Dynamic-Positioning-Controlled Offshore Platforms

Energies ◽  
2018 ◽  
Vol 11 (8) ◽  
pp. 2128 ◽  
Author(s):  
Se Kim ◽  
Moo Kim
Keyword(s):  
Quadratic Programming ◽  
Time Domain ◽  
Dynamic Positioning ◽  
Positioning System ◽  
Time Domain Simulation ◽  
Allocation Algorithm ◽  
Dynamic Positioning System ◽  
Fully Coupled ◽  
Pseudo Inverse ◽  
Thrust Allocation

This research, a new thrust-allocation algorithm based on penalty programming is developed to minimize the fuel consumption of offshore vessels/platforms with dynamic positioning system. The role of thrust allocation is to produce thruster commands satisfying required forces and moments for position-keeping, while fulfilling mechanical constraints of the control system. The developed thrust-allocation algorithm is mathematically formulated as an optimization problem for the given objects and constraints of a dynamic positioning system. Penalty programming can solve the optimization problems that have nonlinear object functions and constraints. The developed penalty-programming thrust-allocation method is implemented in the fully-coupled vessel–riser–mooring time-domain simulation code with dynamic positioning control. Its position-keeping and fuel-saving performance is evaluated by comparing with other conventional methods, such as pseudo-inverse, quadratic-programming, and genetic-algorithm methods. In this regard, the fully-coupled time-domain simulation method is applied to a turret-moored dynamic positioning assisted FPSO (floating production storage offloading). The optimal performance of the penalty programming in minimizing fuel consumption in both 100-year and 1-year storm conditions is demonstrated compared to pseudo-inverse and quadratic-programming methods.

scholarly journals Convolution-based time-domain simulation for fluidelastic instability in tube arrays

2021 ◽  
Author(s):  
Mingjie Zhang ◽  
Ole Øiseth
Keyword(s):  
Impulse Response ◽  
Response Function ◽  
Time Domain ◽  
Impulse Response Function ◽  
Time Domain Simulation ◽  
Unit Step ◽  
Tube Arrays ◽  
Unit Impulse ◽  
The Time Domain ◽  
Unit Impulse Response

AbstractA convolution-based numerical algorithm is presented for the time-domain analysis of fluidelastic instability in tube arrays, emphasizing in detail some key numerical issues involved in the time-domain simulation. The unit-step and unit-impulse response functions, as two elementary building blocks for the time-domain analysis, are interpreted systematically. An amplitude-dependent unit-step or unit-impulse response function is introduced to capture the main features of the nonlinear fluidelastic (FE) forces. Connections of these elementary functions with conventional frequency-domain unsteady FE force coefficients are discussed to facilitate the identification of model parameters. Due to the lack of a reliable method to directly identify the unit-step or unit-impulse response function, the response function is indirectly identified based on the unsteady FE force coefficients. However, the transient feature captured by the indirectly identified response function may not be consistent with the physical fluid-memory effects. A recursive function is derived for FE force simulation to reduce the computational cost of the convolution operation. Numerical examples of two tube arrays, containing both a single flexible tube and multiple flexible tubes, are provided to validate the fidelity of the time-domain simulation. It is proven that the present time-domain simulation can achieve the same level of accuracy as the frequency-domain simulation based on the unsteady FE force coefficients. The convolution-based time-domain simulation can be used to more accurately evaluate the integrity of tube arrays by considering various nonlinear effects and non-uniform flow conditions. However, the indirectly identified unit-step or unit-impulse response function may fail to capture the underlying discontinuity in the stability curve due to the prespecified expression for fluid-memory effects.

Study of HVDC System and Subsynchronous Oscillation

2015 ◽  
Vol 1092-1093 ◽  
pp. 356-361
Author(s):  
Peng Fei Zhang ◽  
Lian Guang Liu
Keyword(s):  
Power Plant ◽  
Time Domain ◽  
Simulation Method ◽  
Time Domain Simulation ◽  
Stable Convergence ◽  
Turbine Generator ◽  
Plant Model ◽  
Subsynchronous Oscillation ◽  
Hvdc System ◽  
Simulation Results

With the application and development of Power Electronics, HVDC is applied more widely China. However, HVDC system has the possibilities to cause subsynchronous torsional vibration interaction with turbine generator shaft mechanical system. This paper simply introduces the mechanism, analytical methods and suppression measures of subsynchronous oscillation. Then it establishes a power plant model in islanding model using PSCAD, and analyzes the effects of the number and output of generators to SSO, and verifies the effect of SEDC and SSDC using time-domain simulation method. Simulation results show that the more number and output of generators is detrimental to the stable convergence of subsynchronous oscillation, and SEDC、SSDC can restrain unstable SSO, avoid divergence of SSO, ensure the generators and system operate safely and stably

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