scholarly journals Far-field representation for the vertical force on a floating structure

2012 ◽  
Vol 712 ◽  
pp. 661-670 ◽  
Author(s):  
M. McIver
Keyword(s):  
Velocity Potential ◽  
Three Dimensional ◽  
Low Frequency ◽  
Exciting Force ◽  
Far Field ◽  
Vertical Force ◽  
Floating Structure ◽  
Field Representation ◽  
Reciprocity Relations ◽  
Scattering Potential

AbstractEquations are derived that relate the vertical hydrodynamic force on two- and three-dimensional structures that are floating in a fluid of infinite depth to the far-field dipole coefficient in the velocity potential. By an application of Green’s theorem to the radiation or scattering potential and a suitable test potential, the heave added mass, the heave damping and the vertical exciting force are shown to be expressible in terms of the dipole coefficient in the relevant potential. The results add to the known reciprocity relations, which relate quantities such as the damping and the exciting force to the amplitude of the far-field radiated wave. The expressions are valid at all frequencies, and their high- and low-frequency asymptotics are investigated.

scholarly journals Global relationships between two-dimensional water wave potentials

1996 ◽  
Vol 312 ◽  
pp. 299-309 ◽  
Author(s):  
M. McIver
Keyword(s):  
Water Wave ◽  
Small Amplitude ◽  
Velocity Potential ◽  
Two Dimensional ◽  
Reciprocity Relations ◽  
Moving Body ◽  
Calm Water ◽  
Exciting Forces ◽  
Scattering Potential ◽  
Scattering And Radiation

When a body interacts with small-amplitude surface waves in an ideal fluid, the resulting velocity potential may be split into a part due to the scattering of waves by the fixed body and a part due to the radiation of waves by the moving body into otherwise calm water. A formula is derived which expresses the two-dimensional scattering potential in terms of the heave and sway radiation potentials at all points in the fluid. This result generalizes known reciprocity relations which express quantities such as the exciting forces in terms of the amplitudes of the radiated waves. To illustrate the use of this formula beyond the reciprocity relations, equations are derived which relate higher-order scattering and radiation forces. In addition, an expression for the scattering potential due to a wave incident from one infinity in terms of the scattering potential due to a wave from the other infinity is obtained.

RESEARCH ON THE DISTRIBUTION OF PRESSURE FIELD ON THE BASILAR MEMBRANE IN THE PASSIVE SPIRAL COCHLEA

2014 ◽  
Vol 14 (04) ◽  
pp. 1450061 ◽  
Author(s):  
JIANWEI MA ◽  
WENJUAN YAO
Keyword(s):  
Velocity Potential ◽  
Pressure Field ◽  
Basilar Membrane ◽  
Separation Of Variables ◽  
Three Dimensional ◽  
Low Frequency ◽  
Helical Structure ◽  
Hearing Ability ◽  
Leading Role ◽  
First Case

The cochlea is the important auditory organ of the inner ear. It is responsible for transforming the acoustic signals into neural impulses that travel along the auditory nerve to the brain. The role of, perhaps, the most characteristic feature of the cochlea, its three-dimensional (3D) helical structure, has remained elusive. To address this problem, the present paper develops a 3D spiral cochlea mathematical model using orthogonal coordinate system. Based on the method of separation of variables and conformal transformation, equations of three cases for the velocity potential are derived to solve the steady flow problem of lymph in the cochlea. Then, the distribution of pressure field on the basilar membrane (BM) is obtained. By comparing the analytical results with FE analyses results, the derived formulas are demonstrated to be accurate and reliable. The conclusion can be drawn that the spiral shape and physical dimension of the cochlea have a significant influence on the distribution of pressure field. Interestingly, near the helicotrema, the velocity potential of the first case plays a leading role in pressure distribution on the BM. Therefore, it may enhance the vibration of BM and improve hearing ability in the low-frequency parts of human ears. The proposed model could provide an approach for further investigation of fluid-structure interaction problem in the cochlea.

NUMERICAL SOLUTION OF THE ACOUSTIC WAVE EQUATION AT THE LIMIT BETWEEN NEAR AND FAR FIELD PROPAGATION

2001 ◽  
Vol 12 (10) ◽  
pp. 1497-1507 ◽  
Author(s):  
ERICH STOLL ◽  
STEFAN DANGEL
Keyword(s):  
Wave Equation ◽  
Acoustic Wave ◽  
Seismic Waves ◽  
Near Field ◽  
Three Dimensional ◽  
Low Frequency ◽  
Far Field ◽  
Acoustic Wave Equation ◽  
Sound Sources ◽  
Continuous Waves

The acoustic wave equation is solved numerically for two and three-dimensional systems at the limit between near and far field propagation. Our results show that for large sound velocities, corresponding to wavelengths larger than the system, near field properties are dominant. When the near field conditions are no longer satisfied, standing waves close to the sound emitters and interference patterns between the near field and far field solutions appear. Our procedure is applied to sound sources, which broadcast coherent and continuous waves as well as to sources emitting bursts of incoherent and uncorrelated waves. Both cases can be used to simulate the spreading of low frequency seismic waves observed close to volcanoes and hydrocarbon reservoirs.

scholarly journals REEF3D Wave Generation Interface for Commercial CFD Codes

2020 ◽  
pp. 1-12
Author(s):  
Csaba Pakozdi ◽  
Hans Bihs ◽  
Arun Kamath
Keyword(s):  
Cfd Simulation ◽  
Velocity Potential ◽  
Three Dimensional ◽  
Wave Theory ◽  
Far Field ◽  
New Approach ◽  
Cfd Models ◽  
Numerical Wave ◽  
The One ◽  
General Interface

Abstract In recent years CFD developments have shown a trend to combine RANS CFD simulation with other methods such as wave theories or velocity potential based numerical wave tanks, in order to reduce to computation costs. This is however not a new approach, and there exists a large amount of literature about domain decomposition techniques describing a two way coupling between the RANS CFD models and other methods. One can also observe an increasing popularity in the use of a less sophisticated technique where different fluid solvers are combined with one-way coupling. In these methods a predefined solution is provided in the far-field, while a three-dimensional (3D) CFD simulation is applied in a limited zone near the structure. The predefined solution is used to specify the background far-field solution. The published solutions use wave theory or a numerical wave tank where the predefined solution is calculated parallel to the RANS solver. In this way it is possible to reduce the interpolation inaccuracy and the amount of transferred data to the CFD simulation. The disadvantage of this technique is that the far field solver has to be prepared in order to run in parallel with the CFD solver. Due to the one way coupling it is possible to predefine this information in tables before the CFD simulation. This technique makes it possible to define a general interface between difference solvers without modifying existing codes. This paper presents such a technique where the predefined solution is stored into files.

Motion Responses of a Catenary-Taut-Hybrid Moored Single Module of a Semisubmersible Very Large Floating Structure in Multisloped Seabed

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Yiting Wang ◽  
Xuefeng Wang ◽  
Shengwen Xu ◽  
Lei Wang
Keyword(s):  
Shallow Water ◽  
Time Domain ◽  
Large Scale ◽  
Bottom Topography ◽  
Three Dimensional ◽  
Low Frequency ◽  
Mooring System ◽  
Floating Structure ◽  
Mooring Lines ◽  
Motion Responses

Motion responses of moored very large floating structures (VLFSs) in coastal regions are remarkably influenced by shallow water, seabed topography, and mooring system, which were given particular focus in this paper. A three-dimensional (3D) numerical model of a moored semisubmersible single module (SMOD) was described, and time domain simulated and experimentally validated. A catenary-taut-hybrid mooring system was adopted considering coastal space limitations. Large-scale catenary mooring lines were deployed on the deep water side, while taut chains were used on the shore side to decrease the anchor radius. Although the mooring system may induce a stiffness difference between the two sides, the effectiveness of the mooring system was demonstrated by time-domain simulation and model tests. The moored semisubmersible SMOD in shallow water exhibits significant low frequency characteristics. Water depth, asymmetric stiffness, and bottom topography effects were investigated by a series of sensitivity studies. The results show that these factors play an important role in motion responses of the moored SMOD, which can further conduce to better understandings on the hydrodynamic of the semisubmersible-type VLFSs.

Mathematical Model Investigation of Far-Field Transport of Ocean-Dumped Sewage Sludge Related to Remote Sensing

1982 ◽  
Vol 14 (3) ◽  
pp. 33-39
Author(s):  
C Y Kuo
Keyword(s):  
New York ◽  
Sewage Sludge ◽  
Laboratory Data ◽  
Three Dimensional ◽  
Approximate Model ◽  
Transport Processes ◽  
Far Field ◽  
New York Bight ◽  
Mean Current

An existing, three-dimensional, Eulerian-Lagrangian finite-difference model was modified and used to examine the far-field transport processes of dumped sewage sludge in the New York Bight. Both in situ and laboratory data were utilized in an attempt to approximate model inputs such as mean current speed, vertical and horizontal diffusion coefficients, particle size distributions, and specific gravities. Concentrations of the sludge near the sea surface predicted from the computer model were compared qualitatively with those remotely sensed.

Contracting ducts of finite length

1951 ◽  
Vol 2 (4) ◽  
pp. 254-271 ◽  
Author(s):  
L. G. Whitehead ◽  
L. Y. Wu ◽  
M. H. L. Waters
Keyword(s):  
Stream Function ◽  
Finite Length ◽  
Velocity Potential ◽  
Three Dimensional ◽  
Relaxation Method ◽  
Two Dimensional ◽  
Dimensional Flow ◽  
Hodograph Plane ◽  
Two Dimensional Flow ◽  
Working Section

SummmaryA method of design is given for wind tunnel contractions for two-dimensional flow and for flow with axial symmetry. The two-dimensional designs are based on a boundary chosen in the hodograph plane for which the flow is found by the method of images. The three-dimensional method uses the velocity potential and the stream function of the two-dimensional flow as independent variables and the equation for the three-dimensional stream function is solved approximately. The accuracy of the approximate method is checked by comparison with a solution obtained by Southwell's relaxation method.In both the two and the three-dimensional designs the curved wall is of finite length with parallel sections upstream and downstream. The effects of the parallel parts of the channel on the rise of pressure near the wall at the start of the contraction and on the velocity distribution across the working section can therefore be estimated.

scholarly journals Evolution of a narrow-band spectrum of random surface gravity waves

2003 ◽  
Vol 478 ◽  
pp. 1-10 ◽  
Author(s):  
KRISTIAN B. DYSTHE ◽  
KARSTEN TRULSEN ◽  
HARALD E. KROGSTAD ◽  
HERVÉ SOCQUET-JUGLARD
Keyword(s):  
Three Dimensional ◽  
Low Frequency ◽  
Three Dimensions ◽  
Band Spectrum ◽  
Nls Equation ◽  
Random Surface ◽  
Narrow Bandwidth ◽  
Quasi Stationary State ◽  
The Stability ◽  
Three Dimensional Simulations

Numerical simulations of the evolution of gravity wave spectra of fairly narrow bandwidth have been performed both for two and three dimensions. Simulations using the nonlinear Schrödinger (NLS) equation approximately verify the stability criteria of Alber (1978) in the two-dimensional but not in the three-dimensional case. Using a modified NLS equation (Trulsen et al. 2000) the spectra ‘relax’ towards a quasi-stationary state on a timescale (ε2ω0)−1. In this state the low-frequency face is steepened and the spectral peak is downshifted. The three-dimensional simulations show a power-law behaviour ω−4 on the high-frequency side of the (angularly integrated) spectrum.

Prediction of Surge Motion Response of Floating Structure Using Kalman Smoother Adaptive Filters Based Time-Domain Volterra Model

2014 ◽  
Vol 660 ◽  
pp. 799-803
Author(s):  
Edwar Yazid ◽  
M.S. Liew ◽  
Setyamartana Parman ◽  
V.J. Kurian ◽  
C.Y. Ng
Keyword(s):  
Time Series ◽  
Transfer Function ◽  
Time Domain ◽  
Adaptive Filters ◽  
Low Frequency ◽  
Volterra Model ◽  
Floating Structure ◽  
Frequency Responses ◽  
Kalman Smoother ◽  
System Output

This work presents an approachto predict the low frequency and wave frequency responses (LFR and WFR) of afloating structure using Kalman smoother adaptive filters based time domain Volterramodel. This method utilized time series of a measured wave height as systeminput and surge motion as system output and used to generate the linear andnonlinear transfer function (TFs). Based on those TFs, predictions of surgemotion in terms of LFR and WFR were carried out in certain frequency ranges ofwave heights. The applicability of the proposed method is then applied in ascaled 1:100 model of a semisubmersible prototype.

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