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ABSTRACT This paper presents results of a berthing analysis and their significance to the design of berthing facilities in unique conditions where traditional methods may not apply. The analysis was conducted with a RANS based simulation model coupled with a six-degree-of-freedom motion code. This hybrid model treats the pier, ships, and harbor basin as a coupled system. The simulation used real design parameters of a conceptual floating pier in an extremely shallow basin to emphasize fluid effects. Results indicate that the flow induced by a large ship berthing in shallow water has crucial impacts on all aspects of a ship berth. This flow essentially dictates the berthing energy and hence the fender forces. Ship induced hydrodynamic forces could be multiple times of ship inertia. The flow further complicates couplings among floating pier and ships at berth. Fluid influences should hence be accentuated in the design of coupling structures for floating piers. Traditional methods for berthing energy assessment should be used with extra care when one or more of these situations exist: shallow water, large ship, and floating pier. INTRODUCTION Marine fenders are crucial to a ship berth. They provide cushion at berth to stop a docking ship in order without incurring damage to the ship or berth. A proper fender design should effectively absorb or dissipate the kinetic energy carried by a docking ship and thus mitigate the impact force to a sustainable level. Besides, it should protect ship and berth from incurable damages in the case of heavy weather or accident. Fender design normally involves extensive trade-offs depending on the type, purpose, site, function, and operation concept of a berthing facility. Berthing energy is nevertheless the common factor any feasible approach must address. This procedure can be found in any text book or design manuals.
ABSTRACT A chimera Reynolds-Averaged Navier-Stokes (RANS) method was coupled with a propeller analysis program to provide accurate resolution of the propeller-ship interactions. Calculations were performed for a Series-60 ship with the MAU propeller under various operating conditions. In the present interactive coupling approach, the propeller thrust and torque were represented by body-forces and added to the source functions of the RANS code to account for the propeller-induced effects. The propeller analysis program was then used to determine the new propeller blade loading distributions with the propeller inflow provided by the RANS solution. Several interactive coupling between the RANS and propeller analysis programs were performed to capture the propeller-ship interactions under various propeller operations including ahead, backing, crash-astern, and turning conditions. INTRODUCTION The potential flow methods based on the assumptions of inviscid fluid and irrotational motion are widely used in propeller flow analysis (Kerwin and Lee, 1978; Greeley and Kerwin, 1982). However, some off-design propeller flow phenomena are dominated by viscous effects and cannot be accurately predicted by the potential flow methods. Off-design conditions include all four quadrants as defined by the ship velocity Vs and the propeller angular velocity ω. The four modes of propeller operation are defined as ahead or forward (+Vs, +ω), backing or astern (−Vs, −ω), crash-ahead or reverse breaking (−Vs, +ω) and crashback or crash-astern (−Vs, +ω). During crash-astern and crash-ahead operations, the reversal of propeller rotation creates a relatively large angle of attack, causing the flow to separate at the leading edge of the blade. Jiang et al. (1991) extended the inviscid- flow propeller design methods for the simulation of backing and crash-astern conditions. They adopted a simplified approach in propeller flow analysis program PSF (Propeller Steady Force) with three-dimensional correction factors to account for the leading-edge separation under crash-astern conditions.
- North America > United States > Texas (0.28)
- North America > United States > California (0.28)
Flow Analysis of Rolling Rectangular Barge In Beam Sea Condition
Jung, Kwang Hyo (Ocean Engineering Program, Department of Civil Engineering, Texas A&M University) | Chang, Kuang-An (Ocean Engineering Program, Department of Civil Engineering, Texas A&M University) | Chen, Hamn-Ching (Ocean Engineering Program, Department of Civil Engineering, Texas A&M University) | Huang, Erick T. (Naval Facilities Engineering Service Center, Amphibious System Division)
ABSTRACT This paper presents laboratory observations of vortex generation and evolution process as regular waves passing a rectangular barge in a two dimensional wave tank. The test barge was mounted at the center of gravity by the hinge that allows the barge to roll only. Two regular waves with periods of 1.0 and 2.0 seconds, respectively, were selected for this study. Neither waves resulted in overtopping on deck. Spatial velocity field in water surrounding the barge and the roll responses of the barge were captured in PIV images for further process. The mean velocity field and its associated turbulence properties were reduced by averaging over sample PIV images recorded from repeated test runs based on phase averaging concept. The test results confirm that the vortex generation and evolution process can be clearly captured by the present technique. It is interesting to note that the size and trajectory of the vortices produced by waves of different period are remarkably different. The flow pattern and kinematic properties observed lead to a better understanding of the mechanism of eddy making and decay. This finding helps clarify near filed pressure distribution around a flat bottomed vessel and provide guideline to roll damping simulations. INTRODUCTION Viscous effect is known to heavily influence roll motion of a blunt shaped floating structure. Potential flow theories, although reproduce heave and pitch motion very well, are much less effective in predicting roll motion due to their negligence of fluid viscosity. This shortfall is normally compensated by introducing a viscous roll damping coefficient. However, a proper damping coefficient is rather difficult to come by owing to its highly nonlinear nature. Current practice often turns to empirical formulas, which require extensive calibrations with laboratory or field measurements. Nevertheless, these tests are time consuming and cost intensive, and results are case dependent.
- North America > United States > Texas (0.29)
- Asia > Middle East > Israel > Mediterranean Sea (0.24)
- Research Report > New Finding (0.34)
- Research Report > Experimental Study (0.34)