Reciprocal Form of the Wave Drift Force and Moment Acting on Floating Body

2008 ◽  
Author(s):  
Takashi Tsubogo
Keyword(s):  
Body Surface ◽  
Near Field ◽  
Floating Body ◽  
Far Field ◽  
Regular Waves ◽  
Momentum Theory ◽  
Wave Drift ◽  
Drift Force

This paper provides the reciprocal form on wave drift force and moment from the momentum theory. The author in Japan has transformed from the pressure integration on the wetted body surface oscillating in regular waves into the reciprocal form at the near field, then transformed into the form at the far field owing to Green’s second identity, and transformed into Maruo’s and Newman’s formulas. But in this paper the start point is the momentum theory and the goal is the reciprocal form. The obtained reciprocal form at the far field can be transformed into the integration over the wetted floating body surface owing to Green’s second identity.

scholarly journals Viscous-flow-based investigation of Cloaking phenomenon among multi-floating bodies and experimental verification

2019 ◽  
Vol 272 ◽  
pp. 01016
Author(s):  
Z K Wang ◽  
G H He ◽  
Z G Zhang ◽  
Y H Meng
Keyword(s):  
Experimental Research ◽  
Scattered Wave ◽  
Floating Body ◽  
Offshore Platforms ◽  
Floating Bodies ◽  
Cfd Simulations ◽  
Wave Drift ◽  
Real Coded Genetic Algorithm ◽  
Drift Force ◽  
Interaction Problem

The safety of mooring systems on offshore platforms seems more and more significant with the utilization of offshore space and resources, so the reduction of wave drift force is the key issue in this wave-body interaction problem. The wave drift force acting on the inner floating body surrounded by multiple small floating bodies can be reduced obviously with the occurrence of a phenomenon, which is called the Cloaking phenomenon. The Cloaking phenomenon refers to the reduction or complete elimination in amplitude of the scattered waves. In this paper, a real-coded genetic algorithm was used to optimize the parameters of outer floating bodies to minimize the scattered wave energy, and then the wave drift force acting on the inner body can be reduced. Furthermore, associated CFD simulations and experimental research were conducted with the above optimized parameters to investigate and verify the Cloaking phenomenon more systemically. It is shown that the wave drift force acting on the inner floating body in the Cloaking configuration can be reduced obviously both in numerical and experimental research, and the reduction of the wave drift force is closely related to the change of wave field around the structure.

Study on Dynamic Responses of a TLP in Waves

1987 ◽  
Vol 109 (1) ◽  
pp. 61-66 ◽  
Author(s):  
M. Kobayashi ◽  
K. Shimada ◽  
T. Fujihira
Keyword(s):  
Three Dimensional ◽  
Time History ◽  
Dynamic Responses ◽  
Irregular Waves ◽  
Fluid Viscosity ◽  
Regular Waves ◽  
Distribution Method ◽  
Wave Drift ◽  
Drift Force ◽  
Singularity Distribution

The dynamic responses of a TLP (Tension Leg Platform) in regular and irregular waves were investigated by model tests and calculations in both frequency and time domain. Hydrodynamic forces in regular waves were calculated by the three-dimensional singularity distribution method. Furthermore, a contribution of the fluid viscosity to wave drift force was discussed. Usefulness of the time history simulation was confirmed in the comparison between experimental and calculated time traces.

An Experimental Study of Negative Drift Force Acting on a Floating OWC “Backward Bent Duct Buoy”

2008 ◽  
Author(s):  
Yasutaka Imai ◽  
Kazutaka Toyota ◽  
Shuichi Nagata ◽  
Toshiaki Setoguchi ◽  
Junko Oda ◽  
...  
Keyword(s):  
Wave Energy ◽  
Fluid Velocity ◽  
Wave Energy Converter ◽  
Wave Direction ◽  
Regular Waves ◽  
Energy Converter ◽  
Negative Wave ◽  
Wave Drift ◽  
Negative Drift ◽  
Drift Force

The utilization of renewable energy is required immediately since emissions of carbon dioxide are being restricted. To this end, we are investigating the ocean wave energy converter, especially the floating OWC “Backward Bent Duct Buoy” (BBDB). The BBDB, proposed by Masuda in 1986, is a wave energy converter of the ‘moored floating oscillating water column’ type that is composed of an air chamber, an L-shaped bent duct, a buoyancy chamber, and a turbine. The BBDB has certain positive characteristics. Firstly, the primary conversion performance of the BBDB is better than other floating OWCs. Secondly, the length of the BBDB is shorter than other floating OWCs. Thirdly, as the BBDB advances in the incident wave direction with slow speed waves because of the negative wave drift force, the mooring cost can be reduced. In this research, experiments under a various wave periods were carried out to clarify the characteristics and cause of the generation of negative drift force acting on a BBDB in regular waves with a two-dimensional wave tank at Saga University. The length of the BBDB model is 85cm. To measure the wave drift force, the model is moored with horizontal wire-springs. The motions of the BBDB, such as surge, heave, and pitch, are measured by remotely using image processing. The fluid velocity around the BBDB is measured by using particle image velocimetry (PIV). Motion tests of the BBDB without mooring are also carried out to measure the horizontal velocity of the BBDB in waves. From the experimental results, the characteristics and causes of the generation of negative drift force acting on the BBDB in regular waves are discussed.

Numerical Evaluation of Ship Maneuvering Performance in Waves

2018 ◽  
Author(s):  
Min-Guk Seo ◽  
Bo Woo Nam ◽  
Yeon-gyu Kim
Keyword(s):  
Irregular Waves ◽  
Time Signal ◽  
Regular Waves ◽  
Ship Maneuvering ◽  
Wave Drift ◽  
Mmg Model ◽  
Free Running ◽  
Drift Force ◽  
Wave Drift Forces ◽  
Drift Forces

This paper considers a numerical computation of ship maneuvering performance in waves. For this purpose, modular-type maneuvering model (MMG model) is adopted and wave drift forces and moments are included in maneuvering equation of motion. Wave drift forces ware calculated using a seakeeping program based on higher-order Rankine panel method. When calculating the wave drift force acting on a ship, the forward speed, wave heading, wave period and drift angle of the ship are considered as key parameters. It means that ship’s lateral speed is also included to calculate wave drift force. Numerical simulations are carried out in regular waves using S175 containership and computation results are validated by comparing them with results of free-running model test. Using the developed program, numerical simulation in irregular waves are, also, conducted and discussion is made on the sensitivities of time signal of wave elevation on turning performance.

Study on Influence of Geometrical Dimensions of Floating Bodies on Cloaking Phenomenon

2016 ◽  
Author(s):  
Zhigang Zhang ◽  
Guanghua He ◽  
Xiaoqun Ju ◽  
Dong Yu
Keyword(s):  
Wave Interaction ◽  
Floating Body ◽  
Geometrical Parameters ◽  
Offshore Platforms ◽  
Ocean Engineering ◽  
Floating Bodies ◽  
Floating Structures ◽  
Wave Drift ◽  
Drift Force ◽  
Geometrical Dimensions

Mooring offshore floating structures such as offshore platforms in large waves and winds, against the drift force and rotational moments are challenging in offshore engineering and ocean engineering. To investigate these kind of problems named positioning problems accurately, not only in hydrodynamic forces of first order but also in time-averaged steady forces of second order named wave drift force need to be taken into account. That arranging of several small cylinders regularly on a circle concentric with a fixed floating body is considered to reduce the wave drift force. Fortunately, a Cloaking phenomenon occurs at certain conditions with proper geometrical dimensions of floating bodies, which can reduce the wave drift force acting on bodies, perfectly even to zero. In this paper, with a combination of higher-order boundary element method (HOBEM) and wave-interaction theory, the influences of geometrical parameters of outer surrounding cylinders on the wave drift force of floating bodies are systematically investigated and discussed.

Magnetic Tag Antenna for UHF Near-field and Far-Field RFID Applications

2015 ◽  
Vol 5 (2) ◽  
pp. 119
Author(s):  
Mondher Dhaouadi ◽  
M. Mabrouk ◽  
T. Vuong ◽  
A. Ghazel
Keyword(s):  
Near Field ◽  
Far Field ◽  
Rfid Applications

Far field modeling of the Mamala Bay outfalls

1998 ◽  
Vol 38 (10) ◽  
pp. 323-330
Author(s):  
Philip J. W. Roberts
Keyword(s):  
Field Model ◽  
Near Field ◽  
Far Field ◽  
Field Modeling ◽  
Visitation Frequency ◽  
Statistical Variation ◽  
Long Time ◽  
Harmonic Average ◽  
Ocean Outfall ◽  
Acoustic Doppler Current Profilers

The results of far field modeling of the wastefield formed by the Sand Island, Honolulu, ocean outfall are presented. A far field model, FRFIELD, was coupled to a near field model, NRFIELD. The input data for the models were long time series of oceanographic observations over the whole water column including currents measured by Acoustic Doppler Current Profilers and density stratification measured by thermistor strings. Thousands of simulations were made to predict the statistical variation of wastefield properties around the diffuser. It was shown that the visitation frequency of the wastefield decreases rapidly with distance from the diffuser. The spatial variation of minimum and harmonic average dilutions was also predicted. Average dilution increases rapidly with distance. It is concluded that any impact of the discharge will be confined to a relatively small area around the diffuser and beach impacts are not likely to be significant.

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