| 1. |
- Alexandersson, Martin, et al.
(författare)
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Prediction of roll motion using fully nonlinear potential flow and ikeda’s method
- 2021
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Ingår i: Proceedings of the International Offshore and Polar Engineering Conference. - : International Society of Offshore and Polar Engineers. - 1098-6189 .- 1555-1792. - 9781880653821 ; , s. 1670-1679
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Konferensbidrag (refereegranskat)abstract
- Getting the best possible accuracy with the lowest possible computational cost is an important factor in the early design stage of ships. Potential flow-based analysis presents such a solution for seakeeping analyses. The accuracy of roll motion in potential flow is however not so good, due to the large influence from vicsous roll damping, which is missing in these calculations. This paper proposes a hybrid method, as a solution to this problem, where the viscous roll damping from Ikeda’s semi-empirical method is injected into an existing 3D unsteady fully nonlinear potential flow (FNPF) method. The hybrid method is investigated using roll decay tests with the KVLCC2 test case. This investigation shows that the accuracy of simulated roll motions is significantly improved and also shows good agreement with the corresponding roll decay model tests.
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| 2. |
- Calcagni, Danilo, et al.
(författare)
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Comparative analysis of the hydrodynamic performance of untwisted and twisted rudders using a hybrid RANSE/BEM model
- 2014
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Ingår i: Proceedings of the International Offshore and Polar Engineering Conference. - 1098-6189 .- 1555-1792. - 9781880653913 ; , s. 674-682
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Konferensbidrag (refereegranskat)abstract
- Results of a computational study on the hydrodynamic perfor- mance of twisted and untwisted rudders for a single screw vessel are presented. Ship flow simulations are performed by using a hybrid RANSE/BEM model. Numerical predictions by RANSE and BEM solvers are validated through comparisons against ex- perimental data for the ship considered in the study. The com- parative analysis of untwisted and twisted rudders is carried out by fully–appended ship flow simulations at uniform ship speed and rudder angles between 0 and 20 degrees. Numerical results predict comparable manoeuvring capabilities for the alternative layouts, whereas the twisted design allows to mitigate negative pressure peaks observed on the untwisted rudder surface over a range of helm angles.
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| 3. |
- Daiyong, Zhang, 1991, et al.
(författare)
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Sensitive analysis of voyage optimization algorithms for ship voyage planning
- 2021
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Ingår i: Proceedings of the International Offshore and Polar Engineering Conference. - 1098-6189 .- 1555-1792. ; , s. 2772-2779
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Konferensbidrag (refereegranskat)abstract
- Voyage optimization systems search for a ship's potential sailing area by estimating ETA, fuel consumption, fatigue, etc., along sailing area. However, the reliability of a voyage optimization system may be affected by different uncertainties, such as weather forecast input, ship performance models, and parameter settings in optimization algorithms. This study investigates voyage planning uncertainties associated with parameter setting of four optimization algorithms. Half years’ full-scale measurement of a containership sailing in the North Atlantic is used to study the sensitivities of voyage optimization due to parameter settings of the algorithms. Important parameter settings are summarized from the sensitivity analysis.
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| 4. |
- Engsig-Karup, Allan P., et al.
(författare)
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Unstructured Spectral Element Model for Dispersive and Nonlinear Wave Propagation
- 2016
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Ingår i: Proceedings of the International Offshore and Polar Engineering Conference. - 1098-6189 .- 1555-1792. - 9781880653883 ; 2016-January
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Konferensbidrag (refereegranskat)abstract
- We introduce a new stabilized high-order and unstructured numericalmodel for modeling fully nonlinear and dispersive water waves. Themodel is based on a nodal spectral element method of arbitrary order inspace and a σ-transformed formulation due to Cai, Langtangen, Nielsenand Tveito (1998). In the present paper we use a single layer ofquadratic (in 2D) and prismatic (in 3D) elements. The model has beenstabilized through a combination of over-integration of the Galerkinprojections and a mild modal filter. We present numerical tests ofnonlinear waves serving as a proof-of-concept validation for this newhigh-order model. The model is shown to exhibit exponentialconvergence even for very steep waves and there is a good agreementto analytic and experimental data.
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| 5. |
- Gharraee, Behrad, 1984, et al.
(författare)
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Numerical Simulation of Cavitation on a Horizontal Axis Tidal Turbine
- 2016
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Ingår i: Proceedings of the International Offshore and Polar Engineering Conference. - 1098-6189 .- 1555-1792. ; 2016-January
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Konferensbidrag (refereegranskat)abstract
- For tidal turbines mounted on floating structures the possibility ofcavitation occurring on the blades is higher than for seabed mountedtidal turbines. In this study we present Reynolds-Averaged Navier-Stokes (RANS) solutions of the well-studied Southampton three bladedhorizontal axis tidal turbine (HATT). The numerical simulations werecarried out using the ReFRESCO viscous flow solver using three typesof simulations: (i) steady wetted flow; (ii) unsteady wetted flow and(iii) unsteady cavitating flow. The wetted flow simulations gave overallgood prediction of thrust and power coefficients over the entireexperimental range of tip speed ratios (TSRs), with the unsteadysolution providing the better result. Low numerical uncertainties wereobtained for medium to high TSRs and larger for low TSR values,where the flow is transitional and highly separated. The dynamiccavitation simulation was carried out for the case of a cavitationnumber of 0.63 at a TSR of 7.5. The simulations showed a goodagreement of the extent of the sheet cavity. However, the dynamics ofthe sheet cavities have not been fully captured and the power and thrustcoefficients are under predicted compared to the experiments. This ismost likely due to lack of mesh resolution outside the wetted flowboundary layer where the cavity dynamics occur, and due to highnumerical and experimental uncertainties for such a complex flow case.The simulations showed that existing methodology used for computingcavitation on marine propellers could be applied to HATTs, yieldingreliable results. Importantly, simulation of cavitation on HATTs couldbe used as input for noise and erosion predictions.
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| 6. |
- Han, Jiru, et al.
(författare)
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An Artificial Potential Field Model for the Risk Assessment of Icebreaker Escort Operations
- 2022
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Ingår i: Proceedings of the International Offshore and Polar Engineering Conference. - 1098-6189 .- 1555-1792. ; , s. 1295-1302
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Konferensbidrag (refereegranskat)abstract
- The icebreaker escort operations are typical navigation models in Arctic shipping. The current studies mainly focus on analyzing and quantifying the ship navigation risk for icebreaker escort operations concerning ship-to-ship collision avoidance. However, scenarios of ship stuck in sea ice are also interested and lacking study. To this end, we proposed a risk assessment model based on the artificial potential field theory, including two parts: a) the icebreaker risk field and b) the sea ice risk field. The icebreaker risk field describes the ship-to-ship collision risk, while the sea ice risk field describes the risk of ships stuck in sea ice. The proposed model can determine fleet members’ minimum and maximum safety distances to enhance the safety of Arctic fleet shipping.
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| 7. |
- Hildeman, Anders, 1984, et al.
(författare)
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An evaluation of conditional spatial predictions of significant wave height based on the nonstationary spde model
- 2020
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Ingår i: Proceedings of the International Offshore and Polar Engineering Conference. - 1098-6189 .- 1555-1792. ; 2020-October, s. 2176-2183
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Konferensbidrag (refereegranskat)abstract
- The sea state plays an important role in offshore-and marine operations. It affects both direct costs as well as risks for human and/or material loss. A better understanding of the present-, near-future-, and far-future sea states will increase efficiency and safety in shipping since it allow a ship to reroute to a safer and/or more cost effective route. In the offshore industry it allows for minimizing downtime and aids in planning the construction of new offshore sites. Due to the complex nature of the sea state, its spatial distribution over a large region of ocean should be modeled using a probabilistic model. In this way, uncertainties due to lack of information and/or computing power can be quantified and decisions can be taken based on both what is known and what is not known. We analyze such a spatial probabilistic model in order to assess its ability to predict the significant wave height in the whole north Atlantic based only on measurements on a small line path, i.e., conditional prediction. This work is relevant for several applications, for instance data assimilation, oceanographic forecasting, and routing of ships.
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| 8. |
- Lang, Xiao, 1992, et al.
(författare)
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A Machine Learning Ship's Speed Prediction Model and Sailing Time Control Strategy
- 2022
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Ingår i: Proceedings of the International Offshore and Polar Engineering Conference. - 1098-6189 .- 1555-1792. ; , s. 3598-3605
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Konferensbidrag (refereegranskat)abstract
- This paper proposes a machine learning based ship speed over ground prediction model, driven by the eXtreme Gradient Boosting (XGBoost) algorithm. The dataset is acquired from a world-sailing chemical tanker with five years of full-scale measurements. The model is trained using encountered metocean environments and ship operation profiles in two scenarios, i.e., through RPM or propulsion power. This model is further combined with the particle swarm optimization (PSO) algorithm to integrate a sailing time control method. It optimizes constant RPM or power operation strategy to meet the requirements of fixed ETA.
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| 9. |
- Lang, Xiao, 1992, et al.
(författare)
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A Simplified Ship Wave Induced Added Resistance Calculation Method and Full-scale Measurements Validation in Head Sea
- 2020
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Ingår i: Proceedings of the International Offshore and Polar Engineering Conference. - 1098-6189 .- 1555-1792. ; 2020-October, s. 3394-3402
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Konferensbidrag (refereegranskat)abstract
- In this paper, we introduce a semi-empirical head wave added resistance calculation formula. The formula considers the ship hull forms as well as the main particulars and was verified by the available experimental data in the regular wave. One PCTC full-scale measurements were carried out to perform the added resistance validation in the irregular sea, with a newly proposed wave height correction factor. The encountered weather conditions were extracted from the reanalysis metocean data. The result indicated that the proposed formula has achieved reasonable accuracy with fast calculation, and was discussed with regards to uncertainties and prediction capacity.
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| 10. |
- Lang, Xiao, 1992, et al.
(författare)
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Comparison between Full-scale Measurements and Theoretical Fuel Consumption Model in a Real Arctic Ship Navigation
- 2019
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Ingår i: Proceedings of the International Offshore and Polar Engineering Conference. - 1098-6189 .- 1555-1792. - 9781880653852 ; 1, s. 886-892
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Konferensbidrag (refereegranskat)abstract
- Due to the global warming and the continuous decline of Arctic sea ice, maritime transport in the Arctic region has been increased dramatically. While operating in the Arctic area, ships face regular environment loads and ice loads synchronously, the consideration of ice resistance is essential for the fuel consumption estimation in the ice-covered water voyage. In this paper, a theoretical fuel consumption model is proposed based on empirical method for ship sailing through the Arctic route. The results are compared with the full-scale measurements in a real Arctic ship navigation, and discussed with regards to uncertainties and the prediction capacity of the fuel consumption model. The encountered sea states and ice thickness are constructed by hindcast reanalysis data and climate model projections.
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