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Experimental and Numerical Examinations of Gap Resonance between Twin Oppositely Leaning Floating Barges in Proximity
Teng, Bin (Dalian University of Technology) | Li, Shu (Dalian University of Technology) | Tang, Junjun (Dalian University of Technology) | Zhao, Yifan (Dalian University of Technology)
Abstract Two-dimensional gap resonance between oppositely leaning floating twin barges in proximity subjected to normal incident waves is investigated by both model test and numerical simulation. The experimental data and numerical results of the gap resonance between twin oppositely leaning barges are in good agreement generally, and both of which show the resonant frequency of the fluid oscillation in the narrow gap decreases with the increase of the leaning angle relative to the vertical and the resonant wave height in the narrow gap decreases with the increase of the leaning angle. Introduction Side-by-side arrangement of floating structures in proximity is often applied in marine field operations, for example, the offloading from an FPSO (Floating Production Storage and Offloading) to an oil tank or LNG (Liquid Natural Gas) ship. As the incident wave frequency is close to the natural frequency of the confined fluid bulk between floating structures, large amplitudes of fluid oscillation in the narrow gap can be observed. With a two-dimension assumption, the wave-induced gap resonance between fixed floating barges has been extensively studied by theoretical analysis, laboratory test and numerical simulation. Miao et al. (2000 and 2001) studied the wave interaction with two floating caissons with a small gap between them and examined the resonant phenomenon of the oscillation inside the gap theoretically. Saitoh et al. (2006) and Iwata et al. (2007) conducted two-dimensional experiment to investigate the gap resonance between two and three fixed boxes, respectively. Their experimental results indicated that the maximal amplitude of resonant wave motion excited in the narrow gap can approach up to about five times of the incident wave amplitude. As for the numerical simulation employed for the gap resonance, there are two main numerical models. One is the potential flow model and the other is the viscous flow model. Based on the potential flow theory, various numerical codes (Zhu et al., 2005; Li et al., 2005; Teng et al., 2006; He et al., 2006; Zhu et al., 2008; Sun et al., 2010) have been developed. The potential models can predict the resonance frequency at the gap between boxes accurately, and run very fast. It is widely used to find the resonant frequencies at the gaps of various floating bodies in practices. However, for predicting the wave amplitude in the narrow gap accurately, a viscous model must be used, as the physical energy dissipation due to fluid viscosity, vortex shedding and even turbulence plays a dominate role for the amplitude of resonant oscillation. Employing the viscous flow theory, Computational Fluid Dynamics (CFD) methods have also been utilized to investigate the fluid resonance in the narrow gaps between fixed bodies due to incident waves (Lu et al., 2008; Lu et al., 2010a; Lu et al, 2010b; Lu et al., 2011). The CFD models have a good performance in predicting both resonant frequency and wave height in the narrow gap. Though the fluid viscosity and vortex shedding are considered in those models, the application for the interaction between the incident waves and the moving floating barges are rarely seen due to the complex in meshing for moving and inclined bodies.
- Asia > China (0.47)
- North America > United States > Illinois > Madison County (0.24)
- Reservoir Description and Dynamics > Fluid Characterization > Fluid modeling, equations of state (1.00)
- Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems > Floating production systems (1.00)
Abstract In the study, the results of a statistical modeling of global ice loads from drifting ice features on the "Molikpaq" (PA-A) ice-class platform for "Sakhalin-II" Project are investigated. The authors made a comparative analysis of ice loads on wide structure in the ice conditions of the Sea of Okhotsk according to the procedures and guidelines from different Codes. The cumulative distribution function and design ice loads on this platform is received, recommendations for future estimation of ice loads on Sakhalin offshore platforms are discussed.
- North America (1.00)
- Asia > Russia > Far Eastern Federal District > Sakhalin Oblast (0.47)
- Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems (0.49)
- Reservoir Description and Dynamics > Reservoir Characterization (0.34)
Numerical Simulation of Hydrodynamic Behaviors of Gravity Cage In Current And Waves
Zhao, Yun-Peng (State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology Dalian, China) | Li, Yu-Cheng (State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology Dalian, China) | Dong, Guo-Hai (State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology Dalian, China) | Teng, Bin (State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology Dalian, China) | Gui, Fu-Kun (Marine Science and Technology School, Zhejiang Ocean University, Zhoushan, China)
Knowledge of the hydrodynamic behavior of a net cage under the action of waves and currents is the basis of the design and management of net cages in the open sea. Techniques used to investigate the net cage have typically included the use of scaled physical and numerical models, and, where possible, field measurements. Comparing model tests and field measurements, the numerical simulation method is low in cost, easy to manage and a time-saver. In this paper, a numerical model has been developed by rigid body kinematics and the lumped mass method to investigate the dynamic response of the gravity cage in current and waves. Using the numerical model, the motion, net deformation and mooring line forces of the gravity cage were calculated under current only, waves only and combined wave and current flow, respectively. A series of physical experiments was carried out to evaluate the validity of the numerical model. The results of our numerical simulation are all in close agreement with the experimental data. This study shows that our model is valid for the simulation of the net cage in current and waves. INTRODUCTION Exposed net cages in the open sea are subjected to wave and current action. From an engineering perspective, net cage systems need to be designed to cost-effectively withstand extreme conditions while providing a suitable growing environment. Thus, knowledge of their hydrodynamic behavior under the action of waves and currents is important for the design and management of net cages in the open sea. The main methods used to investigate the net cage have typically included the scaled physical tests, numerical simulation and, where possible, field measurements. Many research studies have been conducted to better predict the dynamic performance and reliability of the net cage while subjected to wave and current forces.
- Research Report > Experimental Study (0.86)
- Research Report > New Finding (0.68)
- Reservoir Description and Dynamics > Reservoir Simulation (1.00)
- Data Science & Engineering Analytics > Information Management and Systems (1.00)
- Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems > Mooring systems (0.37)
ABSTRACT The paper presents the calculation of wave run-up on a floating body in current by a higher order boundary element method. The method is based on the perturbation expansion of velocity potential and Green's function in terms. of current velocity. Novel integral equation are employed, which improve the calculation of some of the Cauchy principal value integrations. In order to save computer time and storage, the numerical scheme has been designed to accept two, one or no planes of symmetry of the body geometry. INTRODUCTION Many researchers have developed efficient algorithms to evaluate the action on structure by waves and current individually. However, at as a common phenomenon in nature that waves and current co-exist, or bodies move in waves. When a current and waves coexist, the free surface boundary condition wall be changed. Accordingly, the diffraction and the radiation of waves from a body will be changed, and wave forces and wave run-up on structures will also be modified. The wave run-up is a dominant factor in the determination of the deck elevation of an offshore platform. An under-estimated elevation will not assure the safe normal operation of the platform, and an overestimated elevation will increase the cost and decrease the stability of the platform. In the calculation of wave diffraction and radiation around bodies, the integral equation method is widely used. For the wave and current problem, by using a Green's function (Wehausen and Laitone 1960) which satisfies the free water surface and far field conditions, the integration domain can be limited to the body surface and a small area on the free water surface. Unfortunately, the calculation of the Green's function is time consuming, so efficiency of this method is greatly reduced as compared with the case without a current.
- Asia > Japan (0.29)
- Europe > United Kingdom (0.28)
- Reservoir Description and Dynamics > Reservoir Characterization (0.68)
- Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems (0.48)
ABSTRACT A high order panel method has been developed for the calculation of wave diffraction and radiation by a moving body with a small steady forward speed. This has been used to compute results for a series of truncated cylinders with the same radius and draft but different comer radii. The results show that the most important hydrodynamic forces and amplitudes of body motion do not change significantly when the radius of the comer approaches zero. This suggests that even though in theory the potential flow solution is singular when the radius of the comer approaches zero, it is still possible to describe the body surface by a sharp comer in practical calculations, and to use the same method as for smooth bodies. INTRODUCTION Many moored and compliant offshore systems in deep water have low natural frequencies in their horizontal modes, which can be excited in random waves. As the low frequency response is a resonant phenomenon, it may only be predicted if adequate knowledge is available concerning low frequency damping. During low frequency excitation, wave drift forces are varying with the change of speed of the floating body, and this variation of the mean drift force can be considered as causing a form of damping. At any instant the action between the body and the fluid can be approximated as the problem of the body moving with a steady forward speed. Wichers defined the rate of change of the mean wave drift force with forward speed as the wave drift damping. Research has shown that the drift damping plays a role similar to that of viscous damping in the low frequency behaviour of a floating body. The prediction of wave drift damping depends on accurate calculation of velocity potentials diffracted and radiated by advancing bodies. In this respect, significant progress has recently been made. For the calculation of the potential flow problem around floating bodies with steady forward speeds, the integral equation method is widely used. Using a Green function which satisfies the free surface and the far field conditions, the integration domain can be limited to the body surface and a small area on the free surface. Recently a higher order method has been applied to this Problem. Higher order methods can provide accurate descriptions of body surfaces, and it is believed that they can also give accurate and continuous results along a discretised body surface. The difficulty in applying higher order panel methods lies in having to specify the solid angle of the body surface, and calculation of some singular integrals which exist only in a Cauchy principal value (CPV) sense. For the zero speed problem this can be avoided by indirect methods; for example, Noblesse and Chau and Eatock Taylor used another companion boundary integral equation inside the body, combined with the original integral equation, to cancel the solid angle and CPV integrals. For the radiation problem of a moving floating body with steady forward speed there are however other CPV integrals in the boundary integral.
- Reservoir Description and Dynamics (0.46)
- Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems (0.46)