| 1. |
- Abolfazl, Shiri, 1975, et al.
(författare)
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Hydrodynamics of a Displacement Air Cavity Ship
- 2012
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Ingår i: 29th Symposium on Naval Hydrodynamics, Gothenburg, Sweden, Aug. 2012.
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Konferensbidrag (refereegranskat)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.
(författare)
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Amplification of ship generated wake wash due to coastal effects
- 2003
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Ingår i: Transactions - Society of Naval Architects and Marine Engineers. - 0081-1661. ; 111, s. 61-77
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Annan publikation (övrigt vetenskapligt/konstnärligt)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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| 3. |
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| 4. |
- Andersson, Jennie, 1986, et al.
(författare)
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Review and comparison of methods to model ship hull roughness
- 2020
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Ingår i: Applied Ocean Research. - : Elsevier Ltd. - 0141-1187 .- 1879-1549. ; 99
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Tidskriftsartikel (refereegranskat)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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| 5. |
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| 6. |
- Janson, Carl-Erik, 1957, et al.
(författare)
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Calculation of deep-water wash waves using a combined Rankine/Kelvin source method
- 2003
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Ingår i: Journal of Ship Research. - 0022-4502 .- 1542-0604. ; 47:4, s. 313-326
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Tidskriftsartikel (refereegranskat)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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| 7. |
- Kim, Keunjae, et al.
(författare)
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A STUDY ON THE EFFECT OF HULL SURFACE TREATMENTS on SHIP PERFORMANCES
- 2021
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents a numerical analysis on the induced relation between hull surface roughness and ship performance and discuss how to maintain hull-surface with cost and environmental impact in mind. The analysis is based on CFD simulation of the ship performance due to change of hull surface roughness condition before/after dry-docking and in-water hull cleaning. A typical tanker ship, KVLCC2 is investigated for 14 different partial cleaning cases. The attainable reduction of propulsive power by hull surface treatment is estimated as an index, Cleaning Efficiency Index (CEI). A clear understanding is obtained how hull geometry has profound implication for the effect of roughness on the change of power. Partial hull cleaning of fore-end and stern-aft part of the hull was found to give higher relative CEI than entire hull cleaning. The present study provides guidelines which part of the hull to treat during dry-docking and hull cleaning process with better quality or higher priority if necessary
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| 8. |
- Kim, Keunjae, et al.
(författare)
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Hydrodynamic Design of Propulsion Devices taking into ac-count Full Scale Roughness Effects
- 2020
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper addresses the effects of hull roughness on pro-pulsion performance of ships and demonstrates the importance of taking full scale roughness effects into account when designing propulsion devices. The investigation of the hull roughness effect was performed numerically using SHIPFLOW with the built in roughness model based on the assumption that hull surface roughness is uniformly distributed and can be characterized by the equivalent sand roughness. The ship investigated is a SSPA VLCC with three typical energy saving devices (ESDs), which include a duct, a standard pre-swirl stator (PSS) and two SSPA generic ESDs (GKDM and GKDF). As an initial validation study, numerical simulation and model tests were carried out for the bare hull with two surface conditions: smooth and rough surface. The results from numerical simulation were validated against towing tank tests and clearly indicates a gradual change of flow characteristics/propulsion performances with hull roughness growth: thickening of boundary layer, increase of resistance and propulsion properties (T, Q and RPM). Following the model scale study, full scale simulations have been performed. The results from full scale simulations confirm the trend in increase of EHP and DHP as roughness grows, but even much faster in full scale compared to model scale. This paper will further focus on combined hull roughness and scale effects in the design of propeller/ESD and prediction of the performance of a ship. A quite interesting finding is that the roughness is not always affecting in negative direction. The propeller can be operating in more favorable conditions with higher angle of attack due to the thickening of the boundary layer with the increase of hull roughness. This can directly lead to the improvement of propulsive efficiency and in turn result in further power reduction with the use of ESDs. This paper will discuss additional steps needed to take into account of hull roughness in design optimization process of propeller and ESDs and present design methodology for the successful development of propellers and ESDs performing well in actual operational conditions.
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| 9. |
- Kim, Keunjae, et al.
(författare)
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Hydrodynamic optimization of pre-swirl stator by CFD and model testing
- 2013
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Ingår i: International Shipbuilding Progress. - 0020-868X .- 1566-2829. ; 60:1-4, s. 233-276
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Tidskriftsartikel (refereegranskat)abstract
- With environmental concerns becoming one of the most important issues facing the shipping/ship-building industry today, SSPA has witnessed strong demand for the development of energy saving devices (ESD). SSPA anticipates that the demand will be greater to respond to new requirements set by the IMO regulation on energy efficient design index (EEDI). SSPA has been involved in many joint research projects in developing energy saving solutions. Daewoo Shipbuilding and Marine Engineering Co. Ltd. (DSME) has developed several ESDs in cooperation with SSPA, where SSPA has tested most of the ESDs designed by DSME over the last 10 years. The pre-swirl stator (PSS) is a device mounted on the stern boss just upstream of the propeller (see Fig. 6 or Fig. 33). It is designed to generate pre-swirl flow to the propeller in order to gain a favorable interaction with the propeller that improves the propulsive efficiency and results in a power reduction. This paper is a full description of one of the developments of PSS from the early design stage, optimization phase, and confirmation by model tests to validation through sea trial tests.
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| 10. |
- Kim, Keunjae, et al.
(författare)
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Roughness Effects on Ship Design and Operation
- 2021
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Ingår i: Part of the Lecture Notes in Civil Engineering book series (LNCE, volume 63). - Singapore : Springer Science and Business Media Deutschland GmbH. - 9789811546235 ; , s. 186-204
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Konferensbidrag (refereegranskat)abstract
- Hull surface condition plays an important role for ships performances for new-built ships as well as ships in operation since the drag penalties due to hull roughness are substantial. It is a standard practice that ship design is based on performance evaluation by model testing of ship models with hydrodynamically smooth surface and the increase of resistance for new build condition is added by roughness correlation allowance based on empirical formula. Surface roughness effects beyond the new build condition are seldom considered in the design process. The question is whether hull roughness affects the flow characteristics to such extend that it influence with the resulting design. This is especially important for propellers or energy saving devices which are operating around the stern of the ship where the roughness effects on flow characteristics are most pronounced. This paper will discuss some practical questions related to the effect of hull roughness, both in terms flow characteristics, power increase and impact on ship design and operational practice.
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| 11. |
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| 12. |
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| 13. |
- Leer-Andersen, Michael, 1969
(författare)
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Two studies of ship flows
- 1999
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)
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| 14. |
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