scholarly journals Local Enhancements of the Mean Drift Wave Force on a Vertical Column Shielded by an Exterior Thin Porous Shell

2020 ◽  
Vol 8 (5) ◽  
pp. 349 ◽  
Author(s):  
Peiwen Cong ◽  
Yingyi Liu
Keyword(s):  
Near Field ◽  
Wave Interaction ◽  
Wave Force ◽  
Momentum Conservation ◽  
Far Field ◽  
Vertical Column ◽  
Porous Shell ◽  
Drift Wave ◽  
Direct Pressure ◽  
The Mean

The wave interaction with a vertical column shielded by an exterior porous shell is studied within the framework of potential flow theory. The structures are fixed rigidly at the sea bottom. The interior cylinder is impermeable, and the exterior shell is slightly porous and thin. Additionally, the exterior shell is assumed to have fine pores, and a linear pressure drop is adopted at the porous geometry. The mean drift wave force on the system is thereby formulated by two alternative ways, based respectively on the direct pressure integration, i.e., the near-field formulation, and the application of the momentum conservation theorem in the fluid domain, i.e., the far-field formulation. The consistency of the two formulations in calculating the mean drift wave force is assessed for the present problem. Numerical results illustrate that the existence of the porous shell can substantially reduce the mean drift wave force on the interior column. It also appears that the far-field formulation consists of a conventional part as well as an additional part caused by the energy dissipation through the porous geometry. The mean drift wave force on the system is dominated by the first part, which resembles that on an impermeable body. Local enhancements of the mean drift wave force are found at some specific wave frequencies at which certain propagation modes of the fluid satisfy a no-flow condition at the porous shell.

Near Field Expression of Ship Wave Resistance by Green’s Theorem

2016 ◽  
Author(s):  
Takashi Tsubogo
Keyword(s):  
Integral Equation ◽  
Near Field ◽  
Field Method ◽  
Momentum Conservation ◽  
Wave Resistance ◽  
Boundary Integral ◽  
Far Field ◽  
Ship Wave ◽  
Direct Pressure ◽  
Run Up

The ship wave resistance can be estimated by two alternative methods after solving the boundary integral equation. One is the far field method e.g. Havelock’s formula based on momentum conservation in fluid domain, and another is the near field method based on direct pressure integration over the wetted body surface. Nakos and Sclavounos (1994) had shown a new near field expression of ship wave resistance from the momentum conservation law in the fluid domain with linearized free surface condition. Their new expression differs slightly from the traditional near field form. This problem of near field expression is reconsidered in terms of Green’s second identity. After linearization of the free suface condition and some transformation of equations, the present paper will agree with the Nakos and Sclavounos’ near field expression for the ship wave resistance. Some numerical calculations of wave resistance from the far field method and from the near field method are shown using the classical Kelvin sources distributed on the centerplane of thin ship but solving the different boundary integral equation. Numerical results suggest that the problematic run-up square integration along the waterline is to be omitted as a higher order small quantity. If this run-up term is omitted in each method except for far field, the traditional direct pressure integrtaion is equal to the Nakos and Sclavounos’ near field expression.

The development of a partially mixed region in a stratified shear flow

1975 ◽  
Vol 71 (2) ◽  
pp. 407-415 ◽  
Author(s):  
R. J. Hartman
Keyword(s):  
Shear Strength ◽  
Wave Packet ◽  
Richardson Number ◽  
Near Field ◽  
Far Field ◽  
Uniform Shear ◽  
Stratified Shear Flow ◽  
The Mean ◽  
Kinematic Distortion ◽  
Qualitative Discussion

The influence of a mean uniform shear on the development of a partially mixed region in an unbounded stratified fluid is considered. Results are given for the very near field and the far field in the large-J (Richardson number) limit. A qualitative discussion for J [gsim ] 1 is also included. The near-field motion is modified on a time scale given by Rτ ∼ J−¼, where R = dU/dz is the mean shear strength. This modification is shown to be a consequence of the kinematic distortion of the wake profile by the mean shear. The radiation field is largely anticipated by the wave-packet discussion of an earlier paper.

Near Field Expression of Ship Wave Resistance by Yeung’s Method

2017 ◽  
Author(s):  
Takashi Tsubogo
Keyword(s):  
Green Function ◽  
Boundary Value Problem ◽  
Water Pressure ◽  
Near Field ◽  
Field Method ◽  
Wave Resistance ◽  
Alternative Methods ◽  
Far Field ◽  
Ship Wave ◽  
Direct Pressure

The ship wave resistance can be evaluated by two alternative methods after solving the boundary value problem. One is the far field method e.g. Havelock’s formula, and another is the near field method based on direct pressure integration over the wetted hull surface. As is well known, there exist considerable discrepancies between wave resistance results by far field method and by near field method. This paper presents a Lagally expression in consistency with Havelock’s formula. In order to derive the Lagally expression, the symmetry of Havelock’s Green function is used in the same manner as Yeung et al (2004). Another expression to examine the relation with water pressure integrations or to ensure physical consistency is also derived by slightly deforming that expression. Some numerical comparisons of wave resistance of Wigley, KCS and KVLCC2 models among by Havelock’s formula, some direct pressure integration methods and present two new near field expressions, are shown to demonstrate consistency numerically.

scholarly journals A COUPLING METHODOLOGY TO MODEL NEAR AND FAR FIELD EFFECTS OF STRUCTURES AND ENERGY DEVICES DUE TO WAVE INTERACTION

2018 ◽  
pp. 47
Author(s):  
Vasiliki Stratigaki ◽  
Peter Troch ◽  
David Forehand
Keyword(s):  
Wave Energy ◽  
Hydrodynamic Interaction ◽  
Near Field ◽  
Wave Interaction ◽  
Far Field ◽  
Wave Fields ◽  
Energy Devices ◽  
Field Effects ◽  
Wave Energy Converters ◽  
Coastal Defense

This study focuses on the numerical modeling of wave fields around structures due to their interaction with waves, with the intention to simulate both the resulting near and far field effects. Examples from the wave energy world are employed such as Wave Energy Converters (WECs), fixed or oscillating devices usually arranged in farms, that interact with the incoming waves and extract wave energy from them. As a result of the hydrodynamic interaction between the devices within a farm (so-called near-field effects), the power absorption of the farm is affected. Moreover, wave dissipation has been observed numerically (e.g. Troch et al., 2010) and in scale tests (e.g. Stratigaki et al., 2014; 2015) between the WEC farm location and e.g. the shoreline (so called far-field effects). These wave field changes can affect neighboring sea activities, coastal eco-systems, the coastline and even coastal defense conditions/parameters.

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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