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Optimum Design and Global Analysis of Flexible Jumper for An Innovative Subsurface Production System in Ultra-Deep Water

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China Ocean Engineering 2014年第2期28卷 239-247页

作者：黄一甄兴伟张崎王文华 School of Naval Architecture and Ocean Engineering Dalian University of Technology Deepwater Engineering Research Center Dalian University of Technology State Key Laboratory of Structural Analysis for Industrial Equipment Dalian University of Technology

The study focuses on the flexible jumper issue of Subsurface Tension Leg Production （STLP） system concept, which is considered as a competing alternative system to support well completion devices and rigid risers in ultra-deep water for offshore petroleum production. The paper presents analytical and numerical approaches for the optimum design and global analysis of the flexible jumper. Criteria using catenary concept are developed to define the critical length for optimum design. Based on the criteria, detailed hydrodynamic analyses including quasi-static analysis, modal analysis, and dynamic analysis are performed. Modal analysis with respect to the quasi-static analysis shows that the existence of resonant modes requires special consideration. The results of dynamic analysis confirm the effectiveness of the de-coupled effect from the jumper on STLP system. The approaches developed in the study also have wide application prospect in reference to the optimum design and analysis of any Hybrid Riser （HR） concept.

关键词： subsurface production system flexible jumper dynamic analysis ultra-deep water

Longshore Currents over Barred Beach with Mild Slope

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China Ocean Engineering 2016年第2期30卷 193-204页

作者：王彦邹志利 State Key Laboratory of Coastal and Offshore Engineering Dalian University of Technology

The laboratory experiment and numerical simulations of wave-driven longshore currents by random waves on barred beaches with slopes of 1：100 and 1：40 were conducted to investigate the bimodal feature of mean longshore currents,with emphasis on the location and ratio of two peaks of longshore *** location and ratio of two peaks are controlled by the sand *** influences of wave heights and beach slopes on the longshore currents are *** simulations were also performed to compute the measured velocity profile,with the emphasis on the effect of lateral mixing,bottom friction and surface rollers on numerical results.

关键词： barred beach bimodal feature second peak modeling

Numerical Simulation of Dynamic Response of A Net Cage for Flatfish in Waves

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China Ocean Engineering 2014年第1期28卷 43-56页

作者：桂福坤赵云鹏许条建关长涛 National Engineering Research Center for Marine Aquaculture Zhejiang Ocean University State Key Laboratory of Coastal and Offshore Engineering Dalian University of Technology Yellow Sea Fisheries Research Institute

A numerical model of flatfish cage is built based on the lumped mass method and the principle of rigid body kinematics. To validate the numerical model, a series of physical model tests are conducted in the wave flume. The numerical results correspond well with the data sets from physical model test. The effect of weight of bottom frame, height of fish net and net shape on motion responses of fish cage and tension force on mooring lines is then analyzed. The results indicate that the vertical displacements of float collar and bottom frame decrease with the increase in the weight of bottom frame; the maximum tension force on mooring lines increases with the increasing weight of bottom frame. The inclination angles of float collar and bottom frame decrease with the increasing net height; the maximum tension force increases obviously with the increase of net height.

关键词： flatfish cage motion response numerical simulation physical model test

Hydrodynamic Analysis of Elastic Floating Collars in Random Waves

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China Ocean Engineering 2015年第3期29卷 341-356页

作者：白晓东赵云鹏董国海李玉成 State Key Laboratory of Coastal and Offshore Engineering Dalian University of Technology

As the main load-bearing component of fish cages, the floating collar supports the whole cage and undergoes large deformations. In this paper, a mathematical method is developed to study the motions and elastic deformations of elastic floating collars in random waves. The irregular wave is simulated by the random phase method and the statistical approach and Fourier transfer are applied to analyze the elastic response in both time and frequency domains. The governing equations of motions are established by Newton＇s second law, and the governing equations of deformations are obtained based on curved beam theory and modal superposition method. In order to validate the numerical model of the floating collar attacked by random waves, a series of physical model tests are conducted. Good relationship between numerical simulation and experimental observations is obtained. The numerical results indicate that the transfer function of out-of-plane and in-plane deformations increase with the increasing of wave frequency. In the frequency range between 0.6 Hz and 1.1 Hz, a linear relationship exists between the wave elevations and the deformations. The average phase difference between the wave elevation and out-of-plane deformation is 60° with waves leading and the phase between the wave elevation and in-plane deformation is 10° with waves lagging. In addition, the effect of fish net on the elastic response is analyzed. The results suggest that the deformation of the floating collar with fish net is a little larger than that without net.

关键词： floating collars random waves hydrodynamic characteristics in-plane and out-of-plane deformation net effect

Numerical Study on the Hydrodynamic Characteristics of Biofouled Full-Scale Net Cage

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China Ocean Engineering 2015年第3期29卷 401-414页

作者：毕春伟赵云鹏董国海 State Key Laboratory of Coastal and Offshore Engineering Dalian University of Technology

The effect of biofouling on the hydrodynamic characteristics of the net cage is of particular interest as biofouled nettings can significantly reduce flow of well-oxygenated water reaching the stocked fish. For computational efficiency, the porous-media fluid model is proposed to simulate flow through the biofouled plane net and full-scale net cage. The porous coefficients of the porous-media fluid model can be determined from the quadratic-function relationship between the hydrodynamic forces on a plane net and the flow velocity using the least squares method. In this study, drag forces on and flow fields around five plane nets with different levels of biofouling are calculated by use of the proposed model. The numerical results are compared with the experimental data of Swift et al.（2006） and the effectiveness of the numerical model is presented. On that basis, flow through full-scale net cages with the same level of biofouling as the tested plane nets are modeled. The flow fields inside and around biofouled net cages are analyzed and the drag force acting on a net cage is estimated by a control volume analysis method. According to the numerical results, empirical formulas of reduction in flow velocity and load on a net cage are derived as function of drag coefficient of the corresponding biofouled netting.

关键词： net cage biofouling drag force flow field numerical simulation

An Improved Coupling of Numerical and Physical Models for Simulating Wave Propagation

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China Ocean Engineering 2014年第1期28卷 1-16页

作者：阳志文柳淑学李金宣 State Key Laboratory of Coastal and Offshore Engineering Dalian University of Technology Department of Mechanical Engineering Technical University of Denmark

An improved coupling of numerical and physical models for simulating 2D wave propagation is developed in this paper. In the proposed model, an unstructured finite element model （FEM） based Boussinesq equations is applied for the numerical wave simulation, and a 2D piston-type wavemaker is used for the physical wave generation. An innovative scheme combining fourth-order Lagrange interpolation and Runge-Kutta scheme is described for solving the coupling equation. A Transfer function modulation method is presented to minimize the errors induced from the hydrodynamic invalidity of the coupling model and/or the mechanical capability of the wavemaker in area where nonlinearities or dispersion predominate. The overall performance and applicability of the coupling model has been experimentally validated by accounting for both regular and irregular waves and varying bathymetry. Experimental results show that the proposed numerical scheme and transfer function modulation method are efficient for the data transfer from the numerical model to the physical model up to a deterministic level.

关键词： coupling numerical model physical model wave propagation transfer function modulation

Experimental investigation of motion responses of tunnel element immerging by moored barge

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Journal of Hydrodynamics 2015年第6期27卷 857-864页

作者：左卫广王永学 State Key Laboratory of Coastal and Offshore Engineering Dalian University of Technology

In this paper, the barge effect on the motion responses of the ttmnel element immerging by the moored barge under waves is investigated experimentally. Both the motion responses of the tunnel element and the moored barge in the experiment are simultaneously acquired by the Untouched 6-D Measurement System. The results show that the sway motion responses of the tunnel element immerging by the moored barge are different from those without the barge. For the system of the tunnel element and the moored barge, the moored barge has two motion components in the sway direction. The high frequency motion of the moored barge has little effect on the high frequency motion of the tunnel element with moored barge. However, the low frequency motion of the moored barge has a significant effect on the sway motion of the tunnel element. The motion responses of the tunnel element and the barge in the heave and roll directions are mainly the high frequency motion.

关键词： tunnel element moored barge motion responses low frequency motion maximum offset

Focused Wave Properties Based on A High Order Spectral Method with A Non-Periodic Boundary

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China Ocean Engineering 2015年第1期29卷 1-16页

作者：李金宣柳淑学 State Key Laboratory of Coastal and Offshore Engineering Dalian University of Technology

In this paper, a numerical model is developed based on the High Order Spectral （HOS） method with a non-periodic boundary. A wave maker boundary condition is introduced to simulate wave generation at the incident boundary in the HOS method. Based on the numerical model, the effects of wave parameters, such as the assumed focused amplitude, the central frequency, the frequency bandwidth, the wave amplitude distribution and the directional spreading on the surface elevation of the focused wave, the maximum generated wave crest, and the shifting of the focusing point, are numerically investigated. Especially, the effects of the wave directionality on the focused wave properties are emphasized. The numerical results show that the shifting of the focusing point and the maximum crest of the wave group are dependent on the amplitude of the focused wave, the central frequency, and the wave amplitude distribution type. The wave directionality has a definite effect on multidirectional focused waves. Generally, it can even out the difference between the simulated wave amplitude and the amplitude expected from theory and reduce the shifting of the focusing points, implying that the higher order interaction has an influence on wave focusing, especially for 2D wave. In 3D wave groups, a broader directional spreading weakens the higher nonlinear interactions.

关键词： focused wave high order spectral method numerical model

Comparative Study of Two Approaches to Model the Offshore Fish Cages

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China Ocean Engineering 2015年第3期29卷 459-472页

作者：赵云鹏王欣欣 Jud DECEW Igor TSUKROV 白晓东毕春伟 State Key Laboratory of Coastal and Offshore Engineering Dalian University of Technology Center for Ocean Engineering and Mechanical Engineering Department University of New Hampshire Laboratory of Fisheries Engineering Fisheries College Ocean University of China

The goal of this paper is to provide a comparative analysis of two commonly used approaches to discretize offshore fish cages： the lumped-mass approach and the finite element technique. Two case studies are chosen to compare predictions of the LMA（lumped-mass approach） and FEA（finite element analysis） based numerical modeling techniques. In both case studies, we consider several loading conditions consisting of different uniform currents and monochromatic waves. We investigate motion of the cage, its deformation, and the resultant tension in the mooring lines. Both model predictions are sufficient close to the experimental data, but for the first experiment, the DUT-Flex Sim predictions are slightly more accurate than the ones provided by Aqua-FETM. According to the comparisons, both models can be successfully utilized to the design and analysis of the offshore fish cages provided that an appropriate safety factor is chosen.

关键词： hydrodynamics net cage lumped-mass approach truss and consistent net element