Evaluation Of Low-Frequency Wave Damping

Hearn, Grant E.; Tong, K.C.

doi:10.4043/5176-ms

Cited by 3 publications

(3 citation statements)

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“…In earlier papers (3,4) the theoretical development of 2D based and different full 3D based wave drift damping calculation procedures has been dR w I au u-o ' " [ aR w • aWe JI aWe au u=o predicted and measured values, but the location of peaks is also quite different.…”

Section: Wave Dkift Dahpdigmentioning

confidence: 97%

“…The 3D theoretical wave' drift damping is based upon the near field Added Resistance Gradient (ARG) method developed by Hearn and"Tong (3,19) The 3D simplified theoretical wave drift damping is calculated from the frequency gradient of the wave drift forces, as described by Standing et a1 (5) and further investigated by Hearn and Tong (7).…”

Section: Abalysis Of a K)()jle]) Taber Aim A Kxmed Bakgementioning

confidence: 99%

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Wave Drift Damping Influences Upon The Time Domain Simulations Of Moored Structures

Hearn

Lau

Tong

1988

Offshore Technology Conference

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This paper is concerned with the effects of wave drift damping upon the motions of a moored tanker and a moored offshore barge. The assignment of wave drift damping coefficients, whether predicted or measured. has a significant effect upon the excursions of the moored structure and hence upon the associated line tensions experienced by the mooring system.Procedures for simulating the random sea and determining the Quadratic Transfer Functions of second order wave effects are discussed in the context of including such effects in the time domain simulation of a moored vessel.

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Section: Wave Dkift Dahpdigmentioning

confidence: 97%

Section: Abalysis Of a K)()jle]) Taber Aim A Kxmed Bakgementioning

confidence: 99%

Wave Drift Damping Influences Upon The Time Domain Simulations Of Moored Structures

Hearn

Lau

Tong

1988

Offshore Technology Conference

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“…The mean second order forces and moments are then evaluated using the modified near-field pressure integration formula of Hearn et al (1,2). The mean second order forces and moments are then evaluated using the modified near-field pressure integration formula of Hearn et al (1,2).…”

Section: Situations Analysedmentioning

confidence: 99%

The Influence of Tank Walls and Bottom Upon Low-Frequency Damping

Hearn

Liou

1990

All Days

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Open-water and in-tank theoretical predictions of the low frequency damping of four distinct structures are presented to demonstrate the sensitivity of the damping coefficients to tank wall influences and/or finite water depth effects. To include these effects, and to solve the open-water situation, an eigenfunction expansion matching technique is used to predict the required first order velocity potentials. Added resistance force predictions are performed using the near-field pressure integration analysis. The added resistance gradient (ARC) method is then used to predict the low frequency damping coefficients of the structures in open-water and in in-tank situations. The results presented are discussed in some detail. NOMENCLATURE Alj complex expansion coefficients D hemisphere and cylinder diameter Hl Hankel function of the first kind H Vertical distance from sea-bed / tank bottom to lowest underside point of structure h water depth J highest evanescent mode KI modified Bessel function of the second kind k superscript, k=1,2,.., 6 denoting surge, sway, heave, roll, pitch & yaw L highest harmonic propagating mode, or barge waterline or semi-submersible pontoon length mo real root of the dispersion equation mj imaginary roots of the dispersion equation _n inward normal vector on mean surface S Nk direction cosine in kth direction associated with _n p, q field point, source point R radius of matching(radiation) boundary r hemisphere and cylinder radius, or distance between generic points p and q Sb sea-bed surface Se side wall surface of wave tank Sf free-surface Sr matching boundary between inner and outer domain Sw wetted surface of structure T draught of barge U forward speed of structure W width of wave tank ?k complex amplitude of first order displacement in kth direction ? wavelength of incident wave ?I, ?O inner, outer fluid domains ? wave frequency ?e encounter wave frequency ?I, ?D incident, diffraction wave velocity potential ?k, ?k first order radiation velocity potentials INTRODUCTION Previously (1,2,3)* the surge related low frequency or wave drift damping coefficients have been calculated assuming infinite water depth and open-water conditions. Therefore, when comparing the theoretical predictions with the experimentally measured values it has been implicitly assumed that model scale and tank dimensions were such that tank influences were not important. Kaplan et al (4) suggested, in the presentation of the paper, that the difference between their predictions and Wichers' (5)experimental measurements of the low frequency damping of a 200,000 dwt tanker, was due to finite water depth effects at the lower frequencies. Alternatively, it is possible to attribute the differences to the use of the far-field radiation energy analysis approach to calculating the second order forces used to predict the low frequency damping. Certainly the apparent shift of the whole predicted low frequency damping transfer function to the right in Figure 2 of reference 4, which effectively attributes calculated damping values to higher frequencies, is consistent with our own experiences(2) of using a full 3D far-field based method.

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A numerical investigation of second-order difference-frequency forces and motions of a moored ship in shallow water

You

Faltinsen

2015

J. Ocean Eng. Mar. Energy

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Evaluation Of Low-Frequency Wave Damping

Cited by 3 publications

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Wave Drift Damping Influences Upon The Time Domain Simulations Of Moored Structures

Wave Drift Damping Influences Upon The Time Domain Simulations Of Moored Structures

The Influence of Tank Walls and Bottom Upon Low-Frequency Damping

A numerical investigation of second-order difference-frequency forces and motions of a moored ship in shallow water

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