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

Hearn, Grant E.; Lau, Siew Ming; Tong, K.C.

doi:10.4043/5632-ms

Cited by 3 publications

(4 citation statements)

References 6 publications

(13 reference statements)

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“…Each body 1 to has its own local Cartesian reference system as indicated in Figure 2. Each element centroid is located at its geometric centre except for the ship which has its centre in the ship water plane as indicated in assumption (8).…”

Section: Two Dimensional Simplified Physical Model Of Retardation Systemmentioning

confidence: 99%

“…When examining the behaviour of moored offshore structures it is usually the practice to ramp up the applied forces from a small percentage to fully calculated values over a significant earlier portion of the simulation. This approach is to prevent numerical shocks leading to excessive unrealistic motions (Hearn et al 1988). Here there are no real environmental influences other than the reactions to the presence of water.…”

Section: Validation Of Kane Based Predictionsmentioning

confidence: 99%

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Analysis of dynamic response of a restraining system for a powerless advancing ship based on the Kane method

et al. 2017

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Following general explanations of the working principles of different existing retardation systems to restrain an advancing powerless ship the principles of a new overhead retardation system are presented. A two dimensional simplified model of the activated overhead system is formulated based on Huston's interpretation of the Kane methodology. Reduced Kane equations are used in the actual simulation, once initial conditions and mechanical analysis of constituent elements have been formulated. Having presented the computational process the various velocity, motion and joint constraint force characteristics of the anchor, the ship and the other elements are monitored in the time domain for the duration of the retardation process. Validation of the Kane based method is established utilising the conservation law and the Lagrangian based formulation of the retardation system within the ADAMS software. The results indicate that a peak value of constraint will occur because of the sudden movement of anchor and this peak is affected significantly by initial ship speed. Variation in anchor chain, overall cable length and its horizontal projected length has little influence upon retardation system performance, whilst the changes of sea bed friction, anchor mass, water depth, initial ship velocity and ship mass will make retardation behaviour different.

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Section: Two Dimensional Simplified Physical Model Of Retardation Systemmentioning

confidence: 99%

Section: Validation Of Kane Based Predictionsmentioning

confidence: 99%

Analysis of dynamic response of a restraining system for a powerless advancing ship based on the Kane method

et al. 2017

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“…Assuming an inviscid and incompressible fluid, subject to irrotational flow, the composite unsteady velocity potential <P is expressible in the form 6 -k <P = [<PI + <PD + 2::…”

Section: Problem Formulation and Solutionmentioning

confidence: 99%

“…The 'forward speed corrected' velocity potentials are determined from the 'speed uncorrected' velocity potentials, provided by solving the proposed formulation, using standard strip-theory relationships (2,6). The 'forward speed corrected' velocity potentials are determined from the 'speed uncorrected' velocity potentials, provided by solving the proposed formulation, using standard strip-theory relationships (2,6).…”

Section: Problem Formulation and Solutionmentioning

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 New Design Of Cold Water Pipe For Use With Floating Otec Platforms

Brown¹,

Hearn²,

Langley³

Proceedings OCEANS

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

Cited by 3 publications

References 6 publications

Analysis of dynamic response of a restraining system for a powerless advancing ship based on the Kane method

Analysis of dynamic response of a restraining system for a powerless advancing ship based on the Kane method

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

A New Design Of Cold Water Pipe For Use With Floating Otec Platforms

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