| 1. |
- Alves Lopes, Rui Miguel, 1992, et al.
(författare)
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A numerical study on the influence of crossflow transition on a marine propeller in open water
- 2024
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Ingår i: Ocean Engineering. - 0029-8018. ; 310
-
Tidskriftsartikel (refereegranskat)abstract
- This work studies the influence of crossflow transition modelling on the performance and flow field of a controllable pitch propeller. The simulations are performed for two different crossflow terms, and baseline simulations without crossflow transition are performed as well. The results show that in the absence of a crossflow term, the flow over the propeller blades is almost fully laminar. When a crossflow term is included, a significant part of the flow becomes turbulent, thus causing a decrease in the thrust and torque coefficients. The change in the propeller performance is also due to the absence of laminar flow separation near the trailing edge, which is prevented when transition occurs upstream of that location due to crossflow. The comparison between the two crossflow terms shows that one always leads to a larger extent of turbulent flow and earlier transition than the other, although this not always translates in lower thrust and torque, depending on the considered advance coefficient. This illustrates the delicate balance in the effects taking place on the pressure and suction side of the propeller blades, and the importance of correctly including crossflow effects in simulations of model-scale propellers.
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| 2. |
- Alves Lopes, Rui Miguel, 1992, et al.
(författare)
-
Numerical assessment of surface roughness on a full scale propeller
- 2024
-
Ingår i: Proceedings of the 8th International Symposium on Marine Propulsors.
-
Konferensbidrag (refereegranskat)abstract
- This work addresses the performance of a full scale propeller in an open water setup for varying roughness heights, obtained with a RANS solver and the k-omega SST turbulence model. The application of roughness is done with wall functions and by resolving the boundary-layer. Two cases are considered for the same propeller geometry, one with and another without the anti-singing edge on the propeller blades. Baseline simulations without roughness are performed as well, and grid refinement studies are carried out to estimate the numerical uncertainty. The results showed that the influence of roughness is weak if wall functions are not used, whereas a significant decrease in thrust and torque is obtained if roughness is applied in conjunction with wall functions. The inclusion of the anti-singing edge leads to an increase in thrust and torque, but decrease in efficiency for low advance coefficients. The region of separated flow near the trailing edge of the propeller caused by the anti-singing edge is influenced by the roughness height, and is absent in the geometry without the anti-singing edge.
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| 3. |
- Andersson, Jennie, 1986, et al.
(författare)
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CFD Simulations of the Japan Bulk Carrier Test Case
- 2015
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Ingår i: NUMERICAL TOWING TANK SYMPOSIUM. 18TH 2015. (NUTTS 2015). - 9781510815858
-
Konferensbidrag (refereegranskat)abstract
- This computational fluid dynamics (CFD) validation study is performed as a foundation for further studies with focus on the interaction effects between propulsor and hull. To be able to study the interaction effects, an appropriate CFD methodology need to be established and validated for a bare hull, for the propulsion unit and for the combined system, a self-propelled hull. The work to validate a CFD model is initiated through the use of the JBC, Japan Bulk Carrier, open test case. The JBC test case is developed for the 2015 workshop on CFD in Ship Hydrodynamics. The tested JBC only exists in model scale with scale factor 1:40 (LPP = 7 m). Model ship speed is 1.179 m/s, corresponding to Fn = 0.142 and 14.5 kn, only calm water conditions are tested. There are two variants of the hull, with and without an energy saving device, within this study the one without is used. Test data used for validation of the CFD results are from towing tank experiments at NMRI. The aim of further studies is to study propulsor hull interaction in full scale, but since detailed test data in full scale is limited, all computations will be performed in model scale. The commercial CFD package STAR-CCM+, a finite volume method solver, is employed for all studies. STAR-CCM+ is a general purpose CFD code used for a wide variety of applications. It solves the conservation equations for momentum and mass, turbulence quantities and volume fraction of water using a segregated solver based on the SIMPLE-algorithm. A 2nd order upwind discretization scheme in space is used. It is of interest to study how a general purpose code can perform for detailed ship hydrodynamic analyses and which limitations that could be identified.
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| 4. |
- Andersson, Jennie, 1986, et al.
(författare)
-
Energy balance analysis of a propeller in open water
- 2018
-
Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 158, s. 162-170
-
Tidskriftsartikel (refereegranskat)abstract
- This paper proposes a methodology based on control volume analysis of energy, applied on Computational Fluid Dynamics (CFD) results, for analyzing ship propulsion interaction effects as a complement to the well-established terminology, including thrust deduction, wake fraction and propulsive efficiency. The method, titled Energy Balance Analysis, is demonstrated on a propeller operating in open water. Through consideration of a complete energy balance, including kinetic energy flux, turbulent kinetic energy flux, internal energy flux (originating from dissipation) and pressure work, all possible hydrodynamic losses are included in the analysis, implying that it should be possible to avoid sub-optimized solutions. The results for different control volumes and grid refinements are compared. The deviation of the power obtained from the proposed energy balance analysis relative to the power based on integrated forces on the propeller is less than 1%. The method is considered promising for analyzing and understanding propulsor hull interaction for conventional, as well as novel propulsion configurations. The energy balance analysis is conducted as a post-processing step and could be used in automated optimization procedures.
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| 5. |
- Andersson, Jennie, 1986, et al.
(författare)
-
Energy balance analysis of model-scale vessel with open and ducted propeller configuration
- 2018
-
Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 167, s. 369-379
-
Tidskriftsartikel (refereegranskat)abstract
- This paper focuses on performance analysis of a model scale vessel equipped with an open versus a ducted propeller in self-propulsion using a control volume analysis of energy, applied on Computational Fluid Dynamics (CFD) results. An energy balance analysis decompose the delivered power for each system into internal and turbulent kinetic energy fluxes, i.e. viscous losses, transverse kinetic energy losses, and pressure work and axial kinetic energy fluxes. Such a decomposition can facilitate understanding of system performance and pinpoint enhancement possibilities. For this specific case it is shown that the much higher required power for the ducted propeller configuration to the largest extent is due to higher viscous losses, caused by mainly propeller duct and different rudder configuration. The energy balance analysis is a post-processing tool with the only additional requirement of solving the energy equation, which can be employed with any CFD-code based on commonly available variables.
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| 6. |
- Andersson, Jennie, 1986, et al.
(författare)
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On the Selection of Optimal Propeller Diameter for a 120-m Cargo Vessel
- 2021
-
Ingår i: Journal of Ship Research. - 1542-0604 .- 0022-4502. ; 65:2, s. 153-166
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Tidskriftsartikel (refereegranskat)abstract
- In the preliminary design of a propulsion unit, the selection of propeller diameter is most commonly based on open water tests of systematic propeller series. The optimum diameter obtained from the propeller series data is, however, not considered to be representative for the operating conditions behind the ship, instead a slightly smaller diameter is often selected. We have used computational fluid dynamics to study a 120-m cargo vessel with an integrated rudder bulb–propeller hubcap system and a four-bladed propeller series, to increase our understanding of the hydrodynamic effects influencing the optimum. The results indicate that a 3–4% smaller diameter is optimal in behind conditions in relation to open water conditions at the same scale factor. The reason is that smaller, higher loaded propellers perform better together with a rudder system. This requires that the gain in transverse kinetic energy losses thanks to the rudder overcomes the increase in viscous losses in the complete propulsion system.
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| 7. |
- Andersson, Jennie, 1986, et al.
(författare)
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On the Selection of Optimal Propeller Diameter for a 120m Cargo Vessel
- 2018
-
Ingår i: SNAME 15th Propeller and Shafting Symposium, PSS 2018.
-
Konferensbidrag (refereegranskat)abstract
- In the preliminary design of a propulsion unit the selection of propeller diameter is most commonly based on open water tests of systematic propeller series. The optimum diameter obtained from the propeller series data is however not considered to be representative for the operating conditions behind the ship, instead a slightly smaller diameter is often selected. We have used computational fluid dynamics (CFD) to study a 120m cargo vessel with an integrated rudder bulb-propeller hubcap system and a 4-bladed propeller series, to increase our understanding of the hydrodynamic effects influencing the optimum. The results indicate that a 3-4 % smaller diameter is optimal in behind conditions in relation to open water conditions at the same scale factor. The reason is that smaller, higher loaded propellers perform better together with a rudder system. This requires that the gain in transverse kinetic energy losses thanks to the rudder overcomes the increase in viscous losses in the complete propulsion system
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| 8. |
- Arabnejad Khanouki, Mohammad Hossein, 1988, et al.
(författare)
-
Scale resolving simulations of the non-cavitating and cavitating flows in an axial water jet pump
- 2020
-
Ingår i: 33rd Symposium on Naval Hydrodynamics.
-
Konferensbidrag (refereegranskat)abstract
- In this paper, the non-cavitating and cavitating flows in the AxWJ-2 axial water jet pump of Johns Hopkins University are simulated using a Large Eddy Simulation(LES) approach. The non-cavitating simulations are performed on grids with different mesh resolutions and the effect of mesh resolution on predicting the performance and capturing the structure of Tip Leakage Vortex (TLV) is investigated. Based on this investigation, it can be concluded that the main feature of the non-cavitating TLV can be well captured compared with the experiment provided that a refinement region with at least 40 cells in the tip gap is used. The cavitating simulation using the same grid refinement also shows that the cavitating structures described in the experiment are predicted by the simulation. Furthermore, the structure of non-cavitating and cavitating TLVs are compared and the effects of cavitation on the structure of TLV are analyzed using the simulation results.
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| 9. |
- Eslamdoost, Arash, 1982, et al.
(författare)
-
A body-force model for waterjet pump simulation
- 2019
-
Ingår i: Applied Ocean Research. - : Elsevier BV. - 0141-1187. ; 90
-
Tidskriftsartikel (refereegranskat)abstract
- The role of waterjet pump is to generate thrust by increasing the flow head. Details of the flow inside waterjet pump are important when pump performance is of the main interest. However, in waterjet self-propulsion, pump induced effects are of the main interest rather than the details of the flow inside the pump. This permits sim- plification of pump models when using numerical methods for simulating the flow. In order to find a robust and yet accurate pump model suitable for Computational Fluid Dynamics based methods, models of different so- phistication level are studied in this paper. First, a Sliding Mesh approach, which is capable of capturing the flow details, is validated against a set of cavitation tunnel measurements. Then a series of simpler models, i.e. Moving Reference Frame technique and three different body-force models, are studied and their results are compared to the ones obtained from the Sliding Mesh approach. The results indicate that one of the body-force models which takes the guide vanes as well as the impeller induced flow swirl into account has the best compromise between the robustness and accuracy among the investigated pump models.
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| 10. |
- Eslamdoost, Arash, 1982, et al.
(författare)
-
A device for reducing the resistance of transom stern hulls
- 2021
-
Ingår i: Ocean Engineering. - : Elsevier Ltd. - 0029-8018 .- 1873-5258. ; 235
-
Tidskriftsartikel (refereegranskat)abstract
- A novel idea to reduce the resistance of a transom stern hull in displacement and semi-planing modes is investigated. By placing a spoon-shaped device in the recirculating zone behind the transom, the momentum of the forward-moving water will be absorbed, and a pushing force generated on the device. Numerical and experimental techniques are applied on a transom stern hull to optimize the shape and position of the device and to explore in detail the physics behind the gain. For the towed hull at a Froude number of 0.4, the maximum measured resistance reduction is 11%, while the computed maximum reduction is 17%. In self-propulsion with one propeller, the measured power reduction is 15%. The power cannot be computed with the applied propeller model, which is an axial body-force distribution in the propeller disk, but the reduction in thrust using the device is 11%. More significant gains are possible at smaller Froude numbers, while the effect is reduced at higher Froude numbers. Larger gains are achieved by splitting the thrust on two propellers. © 2021 The Authors
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| 11. |
- Eslamdoost, Arash, 1982, et al.
(författare)
-
A device for reducing the resistance of water surface vessels
- 2020
-
Patent (övrigt vetenskapligt/konstnärligt)abstract
- An object of the invention is to decrease the hull resistance of a water surface vessel. This object is reached with a water surface vessel extending in a longitudinal direction parallel to an intended direction of straight travel, the vessel presenting a transom, wherein the vessel is arranged to travel in a recirculating zone speed interval in which water is moving towards the transom in a recirculating zone behind the transom, wherein the vessel comprises a pushing device presenting a pushing surface located in relation to the intended direction of straight travel of the vessel behind the transom, at least a portion of the pushing surface facing at least partly backwards in relation to the intended direction of straight travel of the vessel, which pushing surface is arranged to be at least partly submerged into the recirculating zone when the vessel is travelling in the recirculation zone speed interval.
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| 12. |
- Eslamdoost, Arash, 1982, et al.
(författare)
-
A pressure jump method for modeling waterjet/hull interaction
- 2014
-
Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 88, s. 120-130
-
Tidskriftsartikel (refereegranskat)abstract
- A fast and robust method for the simulation of waterjet hull interaction is presented. Balancing the thrust force of the waterjet unit with the hull resistance, a method is developed for the prediction of the flow rate through the unit. The method is called the Pressure Jump Method and may be used in combination with both potential flow/boundary layer methods and more advanced viscous flow methods, for instance of the RANS type. In the present work the potential flow/boundary layer approach has been used. Validation of the method is accomplished through comparison of predicted results with measured data. The inlet velocity ratio, nozzle velocity ratio, gross thrust and thrust deduction are all within the experimental scatter. For the case studied the force and moment created by the waterjet unit cause the hull to sink deeper and attain a bow down trim compared to the bare hull case. The thrust deduction fraction is positive both in the computations and the measurements.
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| 13. |
- Eslamdoost, Arash, 1982, et al.
(författare)
-
Analysis of Propeller-Hull Interaction Phenomena on a Self-Propelled Axisymmetric Body
- 2017
-
Ingår i: 5th Int. Symposium on Marine Propulsor.
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Konferensbidrag (refereegranskat)abstract
- The Reynolds Transport theorem for energy is used to study propeller-hull interaction effects by analyzing different components of energy flux through a control volume around a self-propelled vessel. These components are the axial kinetic energy, the transversal kinetic energy, the turbulent kinetic energy, the internal energy and the pressure work. This energy balance approach is here used to study the influence of propeller diameter on the propulsive power. To this end, propellers of different diameters have been studied in behind condition. In order to keep the incoming wake into the propellers as simple as possible, an axi-symmetric hull shape is employed. The energy fluxes are calculated employing a RANS approach to solve the momentum transport and continuity equations together with the energy equation (the heat transfer equation in fluid). The latter equation is solved to compute the internal energy. The results show a minor difference on interaction effects. However, analyzing the energy flux components and their contribution to the total energy provides an extra tool for better understanding of the interaction effects.
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| 14. |
- Eslamdoost, Arash, 1982, et al.
(författare)
-
Analysis of the thrust deduction in waterjet propulsion – The Froude number dependence
- 2018
-
Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 152, s. 100-112
-
Tidskriftsartikel (refereegranskat)abstract
- The definition of thrust deduction in waterjet propulsion is different from that of a propeller driven hull and cannot be interpreted in the same way. A particularly interesting feature of the waterjet thrust deduction is the large variation with Froude number. This is well known from experience, but has never been fully explained. The objective of this paper is to use CFD to address the reasons for these large variations. To this end, the thrust deduction fraction is split into resistance increment fraction and jet thrust deduction fraction. The former is due to the self-propelled hull resistance change in comparison with the bare hull resistance and the latter is due to the difference between gross and net thrust. This split reveals that the main reason for the thrust deduction variation is the hull resistance change. Analysis of the resistance increment in different speed ranges is performed by studying the hydrostatic and hydrodynamic pressure changes on the hull as well as the friction change due to the waterjet system. Despite the negative thrust deduction fraction in the intermediate speed range there is no indication of a resistance reduction compared to that of the bare hull at these speeds.
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| 15. |
- Eslamdoost, Arash, 1982, et al.
(författare)
-
Application of Control Volume Energy Balance for Analysing Propeller-Hull Interaction in Presence of Free-surface
- 2019
-
Ingår i: Sixth International Symposium on Marine Propulsors.
-
Konferensbidrag (refereegranskat)abstract
- Reynolds-Transport Theorem can be employed for analysing the conservation of energy equation over a control volume. Through this approach we can decompose the propeller delivered power into mechanical and thermal energy components. This approach not only enables us to qualitatively describe the flow but also makes it possible to quantify different energy flux components and understand the energy loss mechanisms within the studied system. Employing this method, the effect of free-surface on propeller-hull interaction is studied for an axisymmetric body in the vicinity of free-surface relative to a deeply submerged body. The required flow quantities for the control volume analysis are obtained from a Reynolds- Averaged Navier-Stokes approach together with a Volume-of-Fluid method for capturing the free-surface. The mechanical and thermal energy flux components have been computed for control volumes of different sizes, even including the free-surface. These results deviate less than 0.5% from the propeller delivered power which verifies the applicability of the method for further analysis of the interaction effects. The self-propelled hull is studied in two different depths and thus the propeller loadings and efficiencies are different. The analysis of energy flux components quantitatively explains the reasons for the differences.
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| 16. |
- Eslamdoost, Arash, 1982, et al.
(författare)
-
Contribution of different parameters to the thrust deduction of a waterjet propelled hull
- 2013
-
Ingår i: 12th International Conference on Fast Sea Transportation, FAST 2013; Amsterdam; Netherlands; 2 December 2013 through 5 December 2013.
-
Konferensbidrag (refereegranskat)abstract
- In order to model the waterjet-hull interaction a method, which is based on the potential flow assumption with non-linear free surface boundary conditions, is developed and validated. By means of this method the effect of the sinkage, trim and local flow variation on the resistance increment of a waterjet driven craft has been estimated. Besides, assuming that each of the aforementioned parameters independently influences the resistance change, the resistance increment of the hull is estimated through a linear expansion in a Taylor series, which is a function of the hull sinkage, trim and the flow rate through the waterjet unit. Knowing the magnitude of each single parameter separately helps to understand the physics behind the thrust deduction and may aid in the optimization of the hull/propulsor configuration. Also it sheds some light on the reason for the negative thrust deduction fractions sometimes found on waterjet driven hulls.
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| 17. |
- Eslamdoost, Arash, 1982, et al.
(författare)
-
Energy Balance Approach for Studying Waterjet-Hull Interaction Effects
- 2023
-
Ingår i: Progress in Marine Science and Technology. - 2543-0955. ; 7, s. 275-289
-
Konferensbidrag (refereegranskat)abstract
- Waterjet-hull interaction effects are usually studied by analyzing hull attitude in the presence of a waterjet unit as well as the counteracting resistance and thrust forces. Since the waterjet unit is integrated with a hull, net thrust cannot be accurately measured. Instead, it is suggested to use an alternative measurable thrust, gross thrust, to study the interaction effects. Gross thrust is the momentum flux change through the waterjet unit and is calculated by obtaining axial velocity distribution at the inlet to the waterjet unit and the nozzle outlet. However, this approach does not provide detailed information about system power consumption. In this paper, a more comprehensive method is suggested in addition to the momentum flux approach. The method is based on the investigation of energy flux through the waterjet system. This approach not only enables us to qualitatively describe the flow but also makes it possible to quantify different energy flux components and understand the energy loss mechanisms within a waterjet system. The required flow quantities for this analysis are obtained from a Reynolds-Averaged Navier-Stokes approach together with a Volume-of-Fluid method for capturing the free surface. The transport equation for energy is also solved for obtaining the viscous losses in the form of internal energy increase in the flow. The sum of mechanical and thermal energy components computed by analyzing energy flux through the waterjet system deviates less than 0.5% from the pump-delivered power. This confirms the capability of the proposed method for capturing the decomposition of different energy components in the flow. Further analysis of the decomposition of energy flux through the waterjet system is carried out to identify the loss components in the flow.
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| 18. |
- Eslamdoost, Arash, 1982
(författare)
-
Investigations of Waterjet/Hull Interaction Effects
- 2012
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A waterjet propulsor operates in a different way than a conventional propeller. This makes it hard to use the same concepts for studying the thrust and powering of these systems. The net thrust of the propeller can be obtained by measuring the force transmitted through its shaft, but since there is not just a single contact point between the waterjet unit and the hull, the net thrust measurement cannot be easily accomplished for the waterjet unit. Instead another thrust force, which is simpler to measure, is defined to express the magnitude of the waterjet unit thrust. The new thrust definition is called the gross thrust and is obtained by the measurement of the momentum flux change through the waterjet control volume. In this thesis, it has been tried to find out the links between these two thrust forces. The original work fulfilled in this thesis can be divided in to two main parts. The first part is an introduction to an iterative algorithm for modelling the effect of the waterjet on the hull. The algorithm is called the Pressure Jump Method. This method is based on the fact that the resistance forces are balanced with the thrust force created by the head increase through the waterjet pump. In this thesis, the Pressure Jump Method is coupled with a potential flow solver capable of non-linear free-surface modelling but there is not any limitation for the method to be used in combination with, e.g., RANS solvers. Validation and verification of the Pressure Jump Method is accomplished by comparing the computational results with experimental data available from a test case. The second part of the thesis is dedicated to investigate the individual contribution of different parameters that may influence the thrust deduction of a waterjet-propelled craft. In this part the results obtained from the Pressure Jump Method along with some extra calculations are employed to find out the dominant parameters, which contribute to the thrust deduction.
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| 19. |
- Eslamdoost, Arash, 1982, et al.
(författare)
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Net and Gross Thrust in Waterjet Propulsion
- 2016
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Ingår i: Journal of Ship Research. - 1542-0604 .- 0022-4502. ; 60:2, s. 78-91
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Tidskriftsartikel (refereegranskat)abstract
- The measurement of the net thrust of a waterjet unit is a cumbersome task and thus as an alternative, the thrust of the waterjet system is expressed based on the momen- tum flux change through the waterjet unit, called gross thrust. The relation between net thrust and gross thrust is not fully understood, and in the current paper this relation is investigated by employing numerical simulations of the flow around a planing waterjet- propelled hull. The validation of the bare hull and self-propelled hull simulations is carried out through comparison of the computed results with experimental data.
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| 20. |
- Eslamdoost, Arash, 1982, et al.
(författare)
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On transom clearance
- 2015
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Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 99, s. 55-62
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Tidskriftsartikel (refereegranskat)abstract
- This paper deals with transom stern flow phenomena around the Froude number where the transom clears the water. Experimental and numerical results for a high-speed hull exhibit a pronounced peak in the resistance coefficient at the clearance speed. This is associated with a maximum in the non- dimensional transom submergence, a minimum in the pressure coefficient at the transom edge and a maximum in the curvature of the flow leaving the edge. Just before clearance, the sum of the hydrodynamic and hydrostatic pressures on the transom yields a force pointing forwards, thereby reducing resistance. This pushing force diminishes abruptly as the transom becomes dry. The total pressure resistance of the rest of the hull increases rapidly just before clearance, mostly due to the increase in hydrostatic pressure resistance, caused by the sudden increase in aft draft. It is the rapid loss of the transom pushing force, together with the rapid increase in pressure resistance of the rest of the hull just before clearance that creates the peak in the total resistance coefficient.
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| 21. |
- Eslamdoost, Arash, 1982, et al.
(författare)
-
Pressure Jump Approach for Modeling Waterjet/Hull Interaction
- 2011
-
Ingår i: 14th Numerical Towing Tank Symposium (NuTTS'11).
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The aim of the current paper is to introduce a method, which is not dependent on the pressure distribution on the waterjet intake streamtube. First the conventional momentum flux method is going to be discussed and then another approach, which is independent of the intake streamtube properties, is going to be introduced. This method, which here in this paper is called pressure jump approach, is adapted to a potential flow solver in SHIPFLOW commercial code. The code comes with a linear/none-linear free surface model and is capable of obtaining equilibrium sinkage and trim angle of the hull iteratively. A sink disk along with a body force at its center is applied for modelling the pump system effect.
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| 22. |
- Eslamdoost, Arash, 1982
(författare)
-
The Hydrodynamics of Waterjet/Hull Interaction
- 2014
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The objective of the present investigation is to explore the physics behind the waterjet/hull interaction, and in particular the negative thrust deduction often reported in the semi-planing speed range. Another objective is to propose a validated numerical technique for computing the hydrodynamics of waterjet-driven hulls.The parameters that play a role in the waterjet/hull interaction are split into global effects (i.e. sinkage and trim variations) and local effects (other effects caused by the intake suction) and each are addressed individually in this thesis. Investigation of these parameters is carried out in two different ways. First, assuming the flow to be potential flow, an algorithm is developed for modelling the water/hull interaction. Then, in the second part of the thesis, a technique employing a Reynolds-Averaged Navier-Stokes (RANS) solver is employed for modelling the flow and understanding the interaction effects.The algorithm used in the first part is called the Pressure Jump Method in this thesis. This method is based on the equilibrium condition that the resistance forces are balanced by the thrust force created by the head increase through the waterjet pump. The Pressure Jump Method is coupled with a potential flow solver capable of non-linear free-surface modelling. Validation and verification of the method are accomplished by comparing the computational results with experimental data available from a test case. The resistance increment of the hull is also estimated using the Pressure Jump Method and the dominant parameters, which contribute to the thrust deduction, are determined. General sinkage and trim changes between the bare hull and the self-propelled hull are also estimated by approximating the waterjet- propelled hull as a flat plate with a rectangular hole representing the intake opening.In the second part of the thesis, a technique using a RANS solver with a Volume of Fluid (VOF) free-surface representation combined with a body force representation of the pump is developed and validated against measurements. Using the results of this technique, the thrust deduction fraction is studied in detail from very low to high speeds. It is revealed that, in the lower speed range, the transom clearance plays an important role in the behaviour of the thrust deduction fraction. Therefore, the transom clearance phenomenon is studied in detail. The reasons for the waterjet-driven hull resistance increment are identified through studying the hydrostatic and the hydrodynamic pressure resistance as well as the frictional resistance variations over the entire speed range. The difference between the net thrust and the gross thrust of the waterjet system, which has been a controversial issue, is also studied in this thesis and it is seen that this difference may well be the reason for the negative thrust deduction. Other issues investigated in the thesis are the shape of the capture area and the streamtube within which all water going into the intake is contained, the importance of the velocity profile at the intake and exit, the pressure distribution at the exit and the diameter and position of the vena-contracta.
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| 23. |
- Eslamdoost, Arash, 1982, et al.
(författare)
-
WATERJET HULL INTERACTION
- 2010
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Ingår i: 13th Numerical Towing Tank Symposium.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The main objective of this work is to render the parameters involved in the watejet-hull interaction and finally define the weight of each of these parameters on the thrust deduction fraction. This would help to know how to control the thrust deduction fraction and try to keep this factor below zero to gain more efficiency for the hull and waterjet assembly. Aiming this goal, current paper is going to discuss some strategies for modeling waterjet-hull interaction starting with very simplified assumptions. The applied solver in this work is a potential code including a linear/none-linear free surface model which is capable of handling 6DoF simulation for calculating sinkage of a hull and its’ trim angle.
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| 24. |
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| 25. |
- Eslamdoost, Arash, 1982, et al.
(författare)
-
Waterjet Propulsion and Negative Thrust Deduction
- 2015
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Ingår i: Fourth International Symposium on Marine Propulsors, SMP’15.
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Konferensbidrag (refereegranskat)abstract
- The thrust deduction fraction of waterjet-propelled hulls is often reported to be negative in the speed range close to the operating speeds. In this paper, employing a numerical method, the bare hull and the self-propelled hull flows are studied. The changes between the bare hull and self- propelled hull resistances are investigated for understanding whether it is the waterjet hull resistance decrease which contributes to the negative thrust deduction fraction or there are some other effects rather than the resistance increment.
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| 26. |
- Eslamdoost, Arash, 1982, et al.
(författare)
-
Waterjet Propulsion and Thrust Deduction
- 2014
-
Ingår i: Journal of Ship Research. - 1542-0604 .- 0022-4502. ; 58:4, s. 201-215
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Tidskriftsartikel (refereegranskat)abstract
- The goal of this article is to describe and investigate the parameters that play a role in the waterjet–hull interaction. In general, these parameters can be split into sinkage, trim, and local flow variation from the bare hull to the self-propelled hull. Each of these parameters has in turn been split into components, which are estimated in relative size. For this purpose, a newly developed method for modeling waterjet-driven ves- sels is used. Knowing the magnitude of each single parameter separately helps to understand the physics behind the thrust deduction and may aid in the optimization of the hull/propulsor configuration.
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| 27. |
- Eslamdoost, Arash, 1982, et al.
(författare)
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Waterjet Self-Propulsion Simulation: A Body-Force Approach for Modelling the Pump
- 2017
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Ingår i: 11th Symposium on High Speed Marine Vehicles (HSMV 2017).
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Konferensbidrag (refereegranskat)abstract
- The waterjet pump can be treated in different ways in a Reynolds Averaged Navier-Stokes based numerical simulation. The most accurate model is to resolve the complete pump geometry with rotating impeller (e.g. rigid body rotation). Alternatively, in order to reduce the computational cost, a frozen rotor approach or a body-force model can be employed. In this paper, different body-force models are utilized to simulate the waterjet pump in self-propulsion. Then the body-force models are evaluated through a quantitative comparison of the pump flow rate, head rise and the detailed flow at the nozzle exit with the results obtained from the more sophisticated rigid body rotation and frozen rotor techniques. This evaluation reveals that a body-force model for pump induces very similar effects on the flow in comparison to the more sophisticated methods and can reliably be used for modelling waterjet-hull interaction effects in self-propulsion.
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| 28. |
- Irannezhad, Mohsen, 1990, et al.
(författare)
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Comprehensive computational analysis of the impact of regular head waves on ship bare hull performance
- 2023
-
Ingår i: Ocean Engineering. - : Elsevier Ltd. - 0029-8018 .- 1873-5258. ; 288
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Tidskriftsartikel (refereegranskat)abstract
- This paper focuses on investigating the impact of waves on ship hydrodynamic performance, enhancing our understanding of seakeeping characteristics and contributing to advanced ship and propeller design. It examines the resistance, motions, and nominal wake of the KVLCC2 bare hull, which is free to surge, heave, and pitch, in both calm water and regular head waves using a RANS approach. The research reveals a substantial dependency of the wake on grid resolution, particularly in calm water and shorter waves, while motions and resistance display a weaker dependency. The computed nominal wake is compared against towing tank SPIV measurements. Utilizing Fourier analyses and reconstructed time series, the study examines correlations among various factors influencing the bare hull's performance in waves. The axial velocity component of the wake in waves demonstrates significant time variations, mainly driven by higher harmonic amplitudes. This dynamic wake is influenced by instantaneous propeller disk velocities due to hull motions, orbital wave velocities, boundary layer contraction/expansion, bilge vortex and shaft vortex dynamics. The wake distribution at the propeller plane not only differs significantly from the calm water wake in longer waves but also exhibits notably larger time-averaged values (up to 21%).
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| 29. |
- Irannezhad, Mohsen, 1990, et al.
(författare)
-
Experimental and numerical investigations of propeller open water characteristics in calm water and regular head waves
- 2024
-
Ingår i: Ocean Engineering. - : Elsevier Ltd. - 0029-8018 .- 1873-5258. ; 302
-
Tidskriftsartikel (refereegranskat)abstract
- Propeller Open Water (POW) performance of a non-ventilating and fully-submerged propeller in model-scale is investigated in calm water and regular head waves using experimental tests (EFD) and Computational Fluid Dynamics (CFD). Laminar flow dominance is observed in calm water, particularly at higher advance ratios. Nevertheless, the findings in waves suggest increased turbulence, stemming from both the wave orbital velocities and the presumably increased turbulence level produced by the wave maker in the towing tank. Analysis of the CFD results obtained from the incident flow field and single-blade force and moment leads to the speculation that the observed discrepancies are associated with the inevitable asymmetric conditions and mechanical interference in the experiments which were absent in CFD. These can potentially alter the flow over the blades resulting in a different flow transition, separation, and coherent turbulent structure formation and hence forces and moments. The altered propeller performance in waves in comparison to calm water underlines the significance of waves on the propulsive factors and propeller design.
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| 30. |
- Irannezhad, Mohsen, 1990, et al.
(författare)
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Impacts of regular head waves on thrust deduction at model self-propulsion point
- 2024
-
Ingår i: Ocean Engineering. - : Elsevier Ltd. - 0029-8018 .- 1873-5258. ; 309
-
Tidskriftsartikel (refereegranskat)abstract
- The results obtained from the self-propulsion simulations using Computational Fluid Dynamics (CFD) in the current study, for a ship free to heave, pitch and surge with the means of a weak spring system, are combined with the formerly executed CFD results of the bare hull and propeller open water simulations to investigate the impacts of regular head waves on the propeller-hull interactions in comparison to calm water, at the self-propulsion point of the model. Despite a rather significant dependency of the nominal wake on the wave conditions, the Taylor wake fraction remains almost unchanged in different studied waves which is around 12% lower than the calm water value. The thrust deduction factor in waves is reduced (12.8%–26.1%) in comparison to the calm water value. The change of thrust deduction factor is found to be associated with the boundary layer contraction/expansion and vortical structure dynamics, originating from the wave orbital velocities as well as the significant shaft vertical motions and accelerations that resulted in a modified propeller action, and consequently diminished suction effect on the aft ship. The altered thrust deduction factor and wake fraction in waves in comparison to calm water underlines the significance of waves on the propulsive factors and propeller design.
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| 31. |
- Irannezhad, Mohsen, 1990, et al.
(författare)
-
Investigation of ship responses in regular head waves through a Fully Nonlinear Potential Flow approach
- 2022
-
Ingår i: Ocean Engineering. - : Elsevier Ltd. - 0029-8018 .- 1873-5258. ; 246
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, the hydrodynamic performance of a ship in terms of motions and resistance responses in calm water and in regular head waves is investigated for two loading conditions using a Fully Nonlinear Potential Flow (FNPF) panel method. The main focus is understanding the ship responses in a broad range of operational conditions. Comprehensive analyses of the motions and their correlation with the wave making resistance including their harmonics in waves are presented and compared against experimental data. The predicted motions compare well with experimental data but the resistance prediction is not quite as good. The natural frequencies for heave and pitch are estimated from a set of free decay motion simulations in calm water to provide a better insight into the ship behavior near resonance conditions in waves. Interestingly, in addition to the well known peak in the added wave resistance coefficient around wave lengths close to one ship length, a secondary peak is detected in the vicinity of wave lengths with half the ship length. © 2022 The Authors
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| 32. |
- Irannezhad, Mohsen, 1990, et al.
(författare)
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Numerical Investigation of a General Cargo Vessel Wake in Waves
- 2019
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Ingår i: Proceedings of the 22nd Numerical Towing Tank Symposium, NuTTS 2019.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Since calm water is rather an exception at an actual sea, optimizing propulsive efficiency of ships operating in more realistic environmental conditions than calm water has been gaining more attention recently. The effects of waves on propeller performance have been investigated by different researchers such as Taskar et al. (2016) who studied different influencing factors in terms of cavitation, pressure pulses and efficiency on propeller performance of KVLCC2. Since excessive wake variation in waves may have a significant impact on the propeller performance, it is important to study dynamics of the wake field for ships operating in waves. Although the propeller designers consider experienced-based margins for propellers operating in waves and off-design conditions, the knowledge of the wake field at different wave conditions for each specific hull could be beneficial in designing more efficient propeller. In this study, a general cargo vessel incorporating a Large Diameter Propeller (LDP) with a very small tip clearance is considered. In an earlier investigation, the authors of the current paper have carried out a study, Irannezhad et. al. (2019), on the propeller emergence risk assessment of the LDP vessel employing a potential flow panel code, SHIPFLOW Motions, as well as a viscous flow solver, STAR-CCM+. The aim of this paper is to first validate the LDP vessel computed heave and pitch motions as well as its resistance due to regular head waves in model scale against the experimental data, then to analyze the time-varying wake field and compare it in different wave conditions in the viscous flow solver. The propeller is not modeled in the simulations.
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| 33. |
- Irannezhad, Mohsen, 1990, et al.
(författare)
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Numerical Investigation of a Large Diameter Propeller Emergence Risk for a Vessel in Waves
- 2019
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Ingår i: 8th International Conference on Computational Methods in Marine Engineering, MARINE 2019. ; , s. 634-645
-
Konferensbidrag (refereegranskat)abstract
- Although a Large Diameter Propeller (LDP) has a significant potential to improve a vessel propulsive efficiency, it may have a higher risk of propeller emergence and thus thrust reduction relative to a conventional propeller. The instantaneous propeller submergence can be considered as the main factor in the inception of the propeller emergence when the interaction between a running propeller and free-surface are disregarded. Therefore, accurate prediction of the ship motions and the hull wake in the vicinity of the propeller play a significant role in the propeller emergence risk assessment. In an earlier investigation, the authors of the current paper have carried out a comprehensive study on the seakeeping performance of the LDP vessel employing a Fully Non-linear Unsteady Potential Flow Panel Code in which a selected number of critical operating conditions with respect to the risk of propeller emergence have been identified. The objective of this paper is to further investigate the selected critical operating conditions by a higher fidelity approach which also takes the viscous effects into account. To this end, an Unsteady Reynolds-Averaged Navier-Stokes (URANS) solver is used for studying the seakeeping performance of the LDP vessel. The propeller is not modeled in the simulations. A good agreement is seen between the computed motions and resistance in regular head waves and the measurements data. Also, the results are compared to those from the potential flow simulations.
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| 34. |
- Irannezhad, Mohsen, 1990, et al.
(författare)
-
Propeller Open Water Characteristics in Waves
- 2022
-
Ingår i: Proceedings of the 24th Numerical Towing Tank Symposium, NuTTS 2022. ; , s. 36-41
-
Konferensbidrag (refereegranskat)abstract
- The propulsion factors for ships when operating in waves deviate from those in calm water (Gerritsma et al. (1961), Moor and Murdey (1970) and Nakamura and Naito (1975)). Propeller-hull interaction effects are also different in waves compared to calm water. In order to map the differences in an ongoing research, the performance of a tanker ship in calm water and in regular head waves is being studied through the following steps: 1. bare hull performance in terms of resistance, motions and nominal wake in a range of operational conditions, 2. isolated effects of waves on performance degradation of the open water propeller, 3. propeller-hull interaction effects in self-propulsion. The main objective of this paper is to study the propeller open water (POW) performance in waves and compare it with calm water condition, representing step 2. To this end, a series of POW model tests are carried out in a towing tank for a range of regular head wave conditions. The propeller submergence is chosen to avoid propeller ventilation, while still being affected by the encountered waves. The tests are carried out for a series of advance ratios and wave steepnesses. The desired advance ratios are obtained by keeping the carriage speed constant and adjusting the propeller rotational speed. Numerical computations are also carried out for the same conditions using a Reynolds-Averaged Navier-Stokes (RANS) solver and validated against the model tests. The propeller characteristics including its thrust, torque and efficiency are studied. This paper presents the progress of the research and may be subjected to significant revisions.
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| 35. |
- Irannezhad, Mohsen, 1990, et al.
(författare)
-
Towards Uncertainty Analysis of CFD Simulation of Ship Responses in Regular Head Waves
- 2021
-
Ingår i: Proceedings of the 23rd Numerical Towing Tank Symposium, NuTTS 2021.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Ship hydrodynamic performance prediction in waves is a common practice in the early stages of the ship design process as the interaction between the ship and waves may adversely affect the hydrodynamic responses of the ship in comparison to calm water. Various well-established numerical and experimental methods are often utilized for prediction of ship performance in waves. Although the model tests are expensive and time consuming, a high level of accuracy is often achieved in such experiments. On the other hand, with respect to the increased computational power, prediction of ship performance in waves by the numerical methods based on Computational Fluid Dynamics (CFD) techniques are gradually acquiring more popularity. However, the validity of the incorporated discretization schemes and modelling assumptions in these state-of-the-art CFD methods are often overlooked and the method accuracy is mainly assessed through the validation of the results based on the respective model test data. Validation as an engineering exercise aims to show that the right equations are solved, while verification (mathematical exercise) is required to demonstrate that equations are solved right [1]. The eventual objective of this research is to perform verification and validation exercises of a ship performance prediction in regular head waves using CFD, whereas in this paper, the working progress is presented which may be subjected to significant revisions. To this end, extensive attempts have been made to investigate numerical wave propagation without the presence of the hull. Ship responses in waves are significantly influenced by the wave excitation forces. Therefore, not only high level of accuracy is required for the simulation of the numerical waves, but also quantification of the numerical uncertainties are of a great importance. This becomes even more challenging when the ship hydrodynamic responses, such as motions and added resistance in waves, exhibit dependencies on wave steepness. In this paper, the main focus of such uncertainty analyses is on the systematic grid convergence study.
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| 36. |
- Marimon Giovannetti, Laura, et al.
(författare)
-
Fluid-Structure Interaction of a Foiling Craft
- 2022
-
Ingår i: Journal of Marine Science and Engineering. - : MDPI. - 2077-1312. ; 10:3
-
Tidskriftsartikel (refereegranskat)abstract
- Hydrofoils are a current hot topic in the marine industry both in high performance sailing and in new passenger transport systems in conjunction with electric propulsion. In the sailing community, the largest impact is seen from the America’s cup, where boats are sailed at more than 50 knots (over 100 km/h) with 100% “flying” time. Hydrofoils are also becoming popular in the Olympics, as in the 2024 Olympic games 5 gold medals will be decided on foiling boats/boards. The reason for the increasing popularity of hydrofoils and foiling boats is the recent advances in composite materials, especially in their strength to stiffness ratio. In general, hydrofoils have a very small wetted surface area compared to the wetted surface area of the hull. Therefore, after “take-off” speed, the wetted surface area of the hull, and consequently the resistance of the boat, is reduced considerably. The larger the weight of the boat and crew and the higher the speeds, the greater the loads on the hydrofoils will be. The current research investigates the interaction effects between the fluid and structure of the ZP00682 NACRA 17 Z-foil. The study is carried out both experimentally, in SSPA’s cavitation tunnel, and numerically using a fully coupled viscous solver with a structural analysis tool. The experimental methodology has been used to validate the numerical tools, which in turn are used to reverse engineer the material properties and the internal stiffness of the NACRA 17 foil. The experimental flow speed has been chosen to represent realistic foiling speeds found in the NACRA 17 class, namely 5, 7, and 9 m/s. The forces and the deflection of the Z-foil are investigated, showing a maximum deflection corresponding to 24% of the immersed span. Finally, the effects of leeway and rake angles on the bending properties of the Z-foil are investigated to assess the influence of different angles in sailing strategies, showing that a differential rake set-up might be preferred in search for minimum drag. © 2022 by the authors.
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| 37. |
- Nouri, N. M., et al.
(författare)
-
An iterative scheme for axisymmetric supercavitating flow
- 2009
-
Ingår i: Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science. - 2041-2983 .- 0954-4062. ; 223:8, s. 1869-1876
-
Tidskriftsartikel (refereegranskat)abstract
- This article presents a numerical investigation of axisymmetric supercavitating flow. It is assumed that such a flow field could be estimated by a potential flow that neglects the viscosity effects and rotational motion of the fluid and assumes the flow as an irrotational flow field. One of the most adequate methods for modelling potential fields is the boundary element method, which is employed in this article. A novel iterative scheme is used to capture the free surface of an axisymmetric supercavity. This numerical algorithm is based on updating an initial guess for the cavity's boundary; the convergence criterion is the pressure amount on the free surface of the cavity, which converges to a constant value. To obtain finite lengths for supercavities, a cavity closure model is applied. The results are in good agreement with similar analytical and numerical solutions as well as the existing experimental data for supercavities characteristic properties and the drag coefficient on cavitators. The present iterative numerical algorithm is reliable for predicting the characteristics of a supercavitating flow. Moreover, the feasibility of the cavity capturing in a flow field with low cavitation number is especially attractive.
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| 38. |
- Nouri, N. M., et al.
(författare)
-
An iterative scheme for two-dimensional supercavitating flow
- 2009
-
Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 36:9, s. 708-715
-
Tidskriftsartikel (refereegranskat)abstract
- In the present research, supercavitating potential flow is studied numerically by the boundary element method (BEM). Using the advantages of BEM, an iterative algorithm has been introduced to capture cavity boundary in two-dimensional symmetric flows. In this algorithm, the cavity length is known and used to find the related cavitation number and cavity profile. In order to obtain finite length cavities, a cusped cavity closure model has been employed. Applying this cavity closure model, it is possible to change the cavity closure profile and its specified length. By comparing the results of the present analysis with previous analytical and numerical solutions as well as the experimental data, it can be concluded that the present iterative numerical algorithm is reliable and can be applied with BEM or other numerical methods to predict the characteristics of a supercavitating flow. Moreover, the feasibility of the cavity capturing in a flow field with low cavitation number is especially attractive.
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| 39. |
- Nylund, Amanda, 1989, et al.
(författare)
-
Modellering av omblandning i fartygs kölvatten, för ökad förståelse av belastning på havsmiljön till följd av utsläpp från fartyg
- 2020
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Östersjön är ett av världens mest intensivt trafikerade områden och i vissa delar sker en fartygspassage i genomsnitt var tolfte minut. Fartygen kan betraktas som flytande industrier som släpper ut föroreningar, försurande och övergödande ämnen som produceras i olika ombordssystem, såsom svart-, grå-, ballast-, läns-, kyl- och skrubbervatten, giftiga båtbottenfärger och propellerhylsolja. De senaste årens ökade förståelse för att sjöfartens utsläpp inte är negligerbara för havsmiljön belyses i Miljömålsberedningens betänkande Havet och människan (2020), där det bland annat föreslås att Havs- och vattenmyndigheten bör få i uppdrag att integrera övervakning av sjöfartens påverkan på havsmiljön i sin verksamhet. För att kunna göra detta på ett effektivt sätt är det nödvändigt att förstå hur föroreningar som släpps ut från fartyg sprids vidare i havsmiljön. Med utgångspunkt från denna kunskap kan miljöövervakningsprogram utformas och i förlängningen åtgärder vidtas för att minska påverkan från sjöfart på havsmiljön, exempelvis genom förbud mot utsläpp eller omledning av farleder i känsliga områden. I befintliga modelleringar av utsläpp från fartyg görs antagandet att utsläppen sker i ytan, vilket får till följd att beräkningen av spridningen i miljön i stor utsträckning kommer att styras av rådande vind- och strömförhållanden i ytskiktet. Detta kan vara acceptabelt, exempelvis vid modellering av lättare oljeprodukter, men för andra ämnen är det nödvändigt att förstå hur omblandningen i kölvattnet sker för att mer korrekt kunna beräkna hur föroreningarna sprider sig i miljön; strömförhållanden kan variera avsevärt i både riktning och styrka på 5–10 m djup, jämfört med i ytan. Syftet med den här förstudien var att undersöka förutsättningarna att kombinera beräkningsströmningsdynamik (Computational Fluid Dynamics (CFD)) som vanligtvis används för att göra högupplösta 3D modelleringar av strömningen runt skrov och propeller på fartyg, med regionala oceanografiska modeller. Användningen av den högupplösta 3D Reynolds- Medelvärdesbildad Navier-Stokes (3D RANS) modellen är dock beräkningsintensiv och brukar endast användas för att modellera närvaken, upp till någon fartygslängd akter om fartyget. För att kunna brygga över skalorna i fjärrvaken (ca 0,8–3 km) akter om fartyget är det därför lämpligt att försöka förenkla beräkningarna, vilket kan göras genom semi-empirisk modellering och 2D modellering av ett tvärsnitt av vaken över tid, vilka i begränsad omfattning validerats mot 3D RANS resultaten. Vidare har in-situ mätningar med en Acoustic Doppler Current Profiler (ADCP) använts för att validera utbredningen av det turbulenta vakområdet. Resultaten av förstudien, både från modellering och fältmätningarna, visar tydligt att utsläpp i fartygsvaken kan spridas på olika djup och i olika riktning som en effekt av omblandningen som sker i vaken. Vidare är hydrografin viktig för hur och var spridningen i vaken sker och fältmätningarna indikerar att när det finns en stark skiktning kommer det omblandade vattnet i fartygsvaken att spridas i sidled, längs med skiktningen, istället för nedåt mot botten. Ur miljöövervakningsperspektiv är det därför viktigt att känna till skiktningen och djupet i relation till farledernas placering, då det får konsekvenser för spridningen av föroreningar från farleden och därmed även var provtagning bör ske. Slutsatsen från förstudien är att det föreslagna ramverket, kombinationen av olika teoretiska modeller och in-situ mätningar, har stor potential för att kunna leverera indata till regionala oceanografiska modeller, för att kunna modellera den storskaliga spridningen av föroreningar från fartyg och farleder. Denna information är också kritisk för utformning av övervakningsprogram, där det är avgörande att mätningar görs där föroreningar från fartyg kan förväntas att återfinnas.
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