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- Abolfazl, Shiri, 1975, et al.
(author)
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Hydrodynamics of a Displacement Air Cavity Ship
- 2012
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In: 29th Symposium on Naval Hydrodynamics, Gothenburg, Sweden, Aug. 2012.
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Conference paper (peer-reviewed)abstract
- To study the resistance reduction of an air cavity for adisplacement vessel, a simplified model of a single cavityis tested in a cavitation tunnel. The drag force actingon the cavity and the aft plate were measured andthe water-air interface was monitored in different conditions.Behavioural changes to the free surface wereobserved by changing the geometry and flow characteristicslike air pressure, air flow rate and water flow speed.Computational model for different cases with the samegeometry and conditions were simulated using computationalfluid dynamics(CFD).The length of the cavity was designed to include approximately2.5 times the expected wavelength of thewater-air interface with Froude number based on theship length of 0.19 which approximately represents adisplacement ship with multi-wave air cavity at its cruisingspeed.Parameters like cavity pressure play an important rolefor the wave’s shape and the stability of the free surfaceinside the cavity. Both computation and experimentshow that the amplitude of the wave is sensitive to the airpressure in the cavity and the re-attachment of the waterto the rear end of the cavity has a close correlationto the inlet air pressure and water velocity. The ultimategoal of this investigation is to minimize effective powerincluding air supply while reducing resistance in/aroundthe cavity, but equally important is it to gain amore basicunderstanding of the air-cavity’s behaviour and possibleadditional resistance components.
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| 2. |
- Allenström, Björn, et al.
(author)
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Amplification of ship generated wake wash due to coastal effects
- 2003
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In: Transactions - Society of Naval Architects and Marine Engineers. - 0081-1661. ; 111, s. 61-77
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Other publication (other academic/artistic)abstract
- This paper discusses the results from extensive wake wash measurements carried out with a model of a ROPAX ship passing a bay. The tests were carried out in SSPA 's sea-keeping and maneuvering basin. This model had been subjected to wash wave measurements in open water in previous tests, which gave possibilities for comparisons between restricted and unrestricted waters'. Six wave gauges were placed inside and outside the bay, and a significant drawdown was noticed in addition to amplifications of the Kelvin waves. The drawdown and the Kelvin waves that occurred in the bay are difficult to explain, but this paper makes an attempt to analyze the phenomena that occur. The different wave theories that can be used in this case are presented The methods that are used for analyzing the measured signals are described One conclusion that can be made is that drawdown caused by the Bernoulli wave can probably be considered a worse problem than ordinary wash waves (Kelvin waves) in restricted and especially shallow waters when looking at large displacement ships.
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| 4. |
- Andersson, Jennie, 1986, et al.
(author)
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Review and comparison of methods to model ship hull roughness
- 2020
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In: Applied Ocean Research. - : Elsevier Ltd. - 0141-1187 .- 1879-1549. ; 99
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Journal article (peer-reviewed)abstract
- There is a large body of research available focusing on how ship hull conditions, including various hull coatings, coating defects, and biofouling, influence the boundary layer, and hence resistance and wake field of a ship. Despite this there seems to be little consensus or established best practice within the ship design community on how to model hull roughness for ship-scale CFD. This study reviews and compares proposed methods to model hull roughness, to support its use in the ship design community. The impact of various types of roughness on additional resistance and wake fields are computed and presented for the well-established test case KVLCC2. The surfaces included in the review are divided into three groups: 1) high quality, newly painted surfaces, 2) surfaces with different extent of poor paint application and/or hull coating damages; and 3) surfaces covered with light slime layers. The review shows the use of a variety of roughness functions, both Colebrook-type and inflectional with three distinct flow regimes, as well as a variety of strategies to obtain the roughness length scales. We do not observe any convergence within the research community towards specific roughness functions or methods to obtain the roughness length scales. The comparison using KVLCC2 clearly illustrates that disparities in surface texture cause large differences in additional resistance, and consequently no strong correlation to a single parameter, e.g. AHR (Average Hull Roughness). This implies that, to be able to select a suitable hull roughness model for a CFD-setup, more details of the surface characteristics are required, such as hydrodynamic characterization of hull coating and expected fouling. © 2020 The Authors
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| 6. |
- Janson, Carl-Erik, 1957, et al.
(author)
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Calculation of deep-water wash waves using a combined Rankine/Kelvin source method
- 2003
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In: Journal of Ship Research. - 0022-4502 .- 1542-0604. ; 47:4, s. 313-326
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Journal article (peer-reviewed)abstract
- This paper presents a method for computation of far-field wash waves in deep water. The method combines a nonlinear Rankine source method in an inner domain with a Kelvin source method for the far-field waves in an outer domain. Kelvin sources are distributed on a vertical matching wall, positioned at the outer edge of the inner domain. These sources are used to specify a boundary condition for the disturbance velocity potential on the matching wall. The boundary condition is used in the Rankine source solution of the inner domain. The size of the inner domain can be reduced in the transverse direction compared to a method using Rankine sources only, as the wave reflections at the edge of the inner domain are eliminated. Further, the far-field waves can be computed using the solution on the matching wall together with the Kelvin source distribution. The verification of the present method includes a comparison for a single Kelvin point source and a comparison to a Rankine source method at intermediate distances for the Wigley hull and for a catamaran. A grid dependence study for the position, size, and panel density on the matching wall is included for the Wigley hull. Computed and measured longitudinal wave cuts are compared for a catamaran both in the inner and the outer domain. Good agreement is obtained.
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