Evgeni Milanov - Academia.edu (original) (raw)
Papers by Evgeni Milanov
Polish Maritime Research, Aug 31, 2023
During tight manoeuvres, twin-screw ships equipped with two rudders located in the propeller slip... more During tight manoeuvres, twin-screw ships equipped with two rudders located in the propeller slip stream experience a fairly large imbalance in the hydrodynamic loads on the propeller and rudders. To investigate the phenomenon of rudder asymmetric load in some depth, manoeuvring experiments based on a free-running model were set up in which the kinematics of the model, the forces on the rudder and the stock moment were recorded. In parallel, with the aim of obtaining an exact estimation of free-stream characteristics of the rudder blade, corresponding wind tunnel experiments were also performed. Based on the results of this investigation, an analysis of the interaction effects within the hull-propeller-rudder system was performed and some conclusions were drawn.
Journal of Engineering Thermophysics, Jul 1, 2020
Operating characteristics of aeronautic and marine vehicles, as well as hydraulic machines design... more Operating characteristics of aeronautic and marine vehicles, as well as hydraulic machines designed for various purposes are largely affected by flow separation. Therefore, control of separated flows is an extremely important problem for modern aviation and marine engineering. Based on dynamometric measurements of forces and torque acting on model hydrofoils and the ship rudder, jet control of flow separation in cavitation-free and cavitation regimes at low and high angles of attack is studied. It is shown that generation of a near-wall jet can ensure a separationless flow around test models at angles of attack greater than 30 degrees. In this case, the lift coefficient of the hydrofoil can increase approximately by two or three times. Pressure fluctuations near the body and in its wake vanish due to flow stabilization; as a result, oscillations of hydrodynamic loads on the body decrease.
Sustainable Development and Innovations in Marine Technologies, 2019
International shipbuilding progress, 2013
The present work focuses on the application of simulation-based design for the resistance optimiz... more The present work focuses on the application of simulation-based design for the resistance optimization of waterjet propelled Delft catamaran, using integrated computational and experimental fluid dynamics. A variable physics/variable fidelity approach was implemented wherein the objective function was evaluated using both low fidelity potential flow solvers with a simplified CFD waterjet model and high fidelity RANS solvers with discretized duct flow calculations. Both solvers were verified and validated with data for the original hull. The particle swarm optimizer was used for single speed optimization at Fr = 0.5, and genetic algorithms were used for multi speed optimization at Fr = 0.3, 0.5 and 0.7. The variable physics/variable fidelity approach was compared with high fidelity approach for the bare-hull shape optimization and it showed an overall CPU time reduction of 54% and converged to the same optimal design at Fr = 0.5. The multi-speed optimization showed design improvement at Fr = 0.5 and 0.7, but not at Fr = 0.3 since the design variables were obtained based on sensitivity analysis at Fr = 0.5. High fidelity simulation results for the optimized barehull geometry indicated 4% reduction in resistance and the optimized waterjet equipped geometry indicated 11% reduction in effective pump power required at self-propulsion. Verification was performed for the optimized hull form and its reduction in powering will be validated in forthcoming experimental campaign.
HAL (Le Centre pour la Communication Scientifique Directe), Jul 1, 2017
International shipbuilding progress, Feb 1, 1987
Results of the experimental investigation of the effects of finite water depth on the hydrodynami... more Results of the experimental investigation of the effects of finite water depth on the hydrodynamic forces and moments acting on ship model moving in the horizontal plane are presented. The structure of the mathematical model used is verified after the multiple hnear regression and dispersion analysis methods. Comparison between the fuh scale and predicted ship manoeuvrabhity characteristics are made. This work is carried out at BSHC, Varna, Bulgaria with the help of PMM. 2.1. Experimental equipment and ship model
CERN European Organization for Nuclear Research - Zenodo, Nov 22, 2018
The maneuverability of a ship in waves is strongly influenced by vessel's inherent course stabili... more The maneuverability of a ship in waves is strongly influenced by vessel's inherent course stability and particularly by existing rudder design. The International Maritime Organization (IMO) has published a series of regulations regarding ship maneuverability in adverse conditions at low speed in the range of 4-6 knots. These new higher standard of IMO require new approaches to improve the maneuvering characteristics in waves of the ship comparing with current criteria for calm water. In the paper, to achieve higher rudder efficiency two technical solutions have been studied-traditional, by increase of rudder area with 20% and innovative-applying the effect of substitution of the trailing edge of the increased rudder design with the wedge tail. The results of aerodynamic tests performed in BSHC-Varna wind tunnel show a high efficiency in both types than original item, independently of the increased drag. The effect of wedge tail are mostly highlight in the created torque of the rudder, almost double compared to the others. This gives preconditions to analyze the ship energy efficiency of the design point of view.
CERN European Organization for Nuclear Research - Zenodo, Jun 28, 2017
During tight maneuvers twin-screw ships equipped with two rudders located in propeller slip strea... more During tight maneuvers twin-screw ships equipped with two rudders located in propeller slip stream are indicating quite large imbalance in propeller and rudder hydrodynamic loads. To investigate deeply the phenomena of rudder asymmetric load the appropriate maneuvering experiments with free running model have been setup by which the model kinematics and rudder forces and stock moment have been recorded. In parallel, aiming for exact estimation about rudder's blade free-stream characteristics corresponding wind tunnel experiment also were performed. Based on obtained investigation results, in the present paper the analysis of interaction effects in the system "hull-propeller-rudder" has been performed and related conclusions were drawn.
Journal of Fluids Engineering, 2019
In this paper, capabilities of state-of-the-art computational fluid dynamics (CFD) tools in the p... more In this paper, capabilities of state-of-the-art computational fluid dynamics (CFD) tools in the prediction of the flow-field around a multihull catamaran advancing in straight ahead motion at nonzero drift angles are investigated. CFD estimations have been provided by three research institutes by using their in-house codes: CNR-INM using Xnavis, IIHR using CFDShip-Iowa, and CNRS/ECN using ISIS. These allowed an in-depth comparison between different methodologies, such as structured overlapping grids versus unstructured grid, different turbulence models and detached eddy simulations (DES) approaches, and level-set (LS) versus volume of fluid (VoF). The activities were pursued within the NATO AVT-183 group “reliable prediction of separated flow onset and progression for air and sea vehicles,” aimed at the assessment of CFD predictions of large three-dimensional separated flows. Comparison between estimations is provided for both integral and local quantities, and for wave-induced vort...
International Shipbuilding Progress
The present work focuses on the application of simulation-based design for the resistance optimiz... more The present work focuses on the application of simulation-based design for the resistance optimization of waterjet propelled Delft catamaran, using integrated computational and experimental fluid dynamics. A variable physics/variable fidelity approach was implemented wherein the objective function was evaluated using both low fidelity potential flow solvers with a simplified CFD waterjet model and high fidelity RANS solvers with discretized duct flow calculations. Both solvers were verified and validated with data for the original hull. The particle swarm optimizer was used for single speed optimization at Fr = 0.5, and genetic algorithms were used for multi speed optimization at Fr = 0.3, 0.5 and 0.7. The variable physics/variable fidelity approach was compared with high fidelity approach for the bare-hull shape optimization and it showed an overall CPU time reduction of 54% and converged to the same optimal design at Fr = 0.5. The multi-speed optimization showed design improvement at Fr = 0.5 and 0.7, but not at Fr = 0.3 since the design variables were obtained based on sensitivity analysis at Fr = 0.5. High fidelity simulation results for the optimized barehull geometry indicated 4% reduction in resistance and the optimized waterjet equipped geometry indicated 11% reduction in effective pump power required at self-propulsion. Verification was performed for the optimized hull form and its reduction in powering will be validated in forthcoming experimental campaign.
ABSTRACT The results of a series of 3-DOF model experiments for high speed water jet propelled De... more ABSTRACT The results of a series of 3-DOF model experiments for high speed water jet propelled Delft372 catamaran in deep and shallow water are described. The hydrodynamic derivatives are estimated from captive model test in shallow towing tank condition and used to predict the maneuverability and course stability of the vessel using 3-DOFsystem based simulations. Then the simulation results are validated by free running model tests. The both results are in relatively good compliance, but analysis shows necessity of simulation model refinement.
ABSTRACT The accurate prediction of waterjet propulsion using CFD is of interest in the standpoin... more ABSTRACT The accurate prediction of waterjet propulsion using CFD is of interest in the standpoint of performance analyses of existing waterjet designs as well as design optimization of new waterjet propulsion systems for high-speed marine vehicles. Currently, the design and analysis of waterjets follow the ITTC '05 recommended procedures and guidelines which was validated by a rigorous experimental campaign through standardized testing. The current study focuses on validation of detailed duct flow simulations on catamarans using the Delft catamaran as the model. The validation work is conducted as a pre-requisite for subsequent URANS based optimization. The Delft catamaran model was build at BSHC and a customized waterjet was designed for the model based on pre-existing stock waterjet designs. Data from the model testing using the ITTC '05 procedures include net jet thrust, thrust-deduction, water-jet volume flow-rate, sinkage, trim, and jet velocity surveys at nozzle exit. Simulations were performed over a speed range of 0.4<Fr<0.75 using URANS and an actuator disk body-force model. The computed net jet thrust, thrust deduction, sinkage and trim compare well with experiments indicating that the present approach is an efficient tool to predict the performance of waterjet propelled JHSS and paves way for future optimization work.
The results of a series of 3-DOF model experiments for high speed water jet propelled Delft372 ca... more The results of a series of 3-DOF model experiments for high speed water jet propelled Delft372 catamaran in deep and shallow water are described. The hydrodynamic derivatives are estimated from captive model test in shallow towing tank condition and used to predict the maneuverability and course stability of the vessel using 3-DOFsystem based simulations. Then the simulation results are validated by free running model tests. The both results are in relatively good compliance, but analysis shows necessity of simulation model refinement.
TransNav, the International Journal on Marine Navigation and Safety of Sea Transportation
Recently, the submarine missions are often evolving into operating to littoral areas, which requi... more Recently, the submarine missions are often evolving into operating to littoral areas, which require operating in shallow water. Such shallow water operations strongly contrast with the traditional ones due to the effect of a close to free water surface expressed mainly by surface suction force. This influence is particularly important for submarine maneuverability accounting for restricted area available. The prediction of submarine behavior in similar conditions requires adequate mathematical model and understanding of the additional hydrodynamic load generated near the surface region. The paper is aimed for better understanding of these issues and relating to development of a submarine simulation model, the experimental program of towing and PMM captive tests of DARPA Suboff submarine model were conducted at a towing tank. The influence of phenomenon such as effect of a close to free surface and Froude number at hydrodynamic forces and moments including control surfaces effectiveness were investigated and also was estimated directional stability of motion in horizontal plane.
Maritime Technology and Research
Since the Energy Efficiency Design Index EEDI was introduced by International Maritime Organizati... more Since the Energy Efficiency Design Index EEDI was introduced by International Maritime Organization IMO, an increasing attention to the ship's controllability in waves, in particular at low speed is observed. One of the main reasons for this is the fact that, in order to satisfy the EEDI requirements, there is a tendency to reduce the power consumption and the propellers RPM reduction while maintaining existing control means, which results in reduced ship steerability mainly at low speed. This study considers the effect of regular sea waves on ship’s initial turning parameters at the set of service conditions. By means of free running model tests the influence of low advance speed on course and maneuvering trajectory changes in transient turning motion were investigated. The effects of the wave encounter angle variations were examined during the tests, including application of different wave lengths. Using the experimental results, an attempt was made to normalize the ship's...
TransNav, the International Journal on Marine Navigation and Safety of Sea Transportation
Recently, the submarine missions are often evolving into operating to littoral areas, which requi... more Recently, the submarine missions are often evolving into operating to littoral areas, which require operating in shallow water. Such shallow water operations strongly contrast with the traditional ones due to the effect of a close to free water surface expressed mainly by surface suction force. This influence is particularly important for submarine maneuverability accounting for restricted area available. The prediction of submarine behavior in similar conditions requires adequate mathematical model and understanding of the additional hydrodynamic load generated near the surface region. The paper is aimed for better understanding of these issues and relating to development of a submarine simulation model, the experimental program of towing and PMM captive tests of DARPA Suboff submarine model were conducted at a towing tank. The influence of phenomenon such as effect of a close to free surface and Froude number at hydrodynamic forces and moments including control surfaces effectiveness were investigated and also was estimated directional stability of motion in horizontal plane.
This paper presents the results of system-based maneuvering predictions of the Delft372 design ca... more This paper presents the results of system-based maneuvering predictions of the Delft372 design catamaran model for a set of water depth ratios and Froude number values. The simulation results were compared with the data, experimentally obtained by means of a radio-controlled free running model. Based on the analysis of standard maneuvers the vessel maneuverability and directional stability in the above navigation conditions have been estimated.
The Danube waterway provides a vital link in the transportation of a wide range of cargos carried... more The Danube waterway provides a vital link in the transportation of a wide range of cargos carried out by push-trains. A part of pusher solo operations are performed in port areas as well in deep water. In this study the Danube pusher model was tested extensively in deep, medium shallow and in very shallow water conditions in Bulgarian Ship Hydrodynamic Centre (BSHC) shallow water tank facility aiming for development of four-quadrant simulation model. The tests were performed in captive mode creating possibility for identification of hydrodynamic terms in mathematical model of the vessel manoeuvrability. Accounting for the pusher full-range operation specifics the suitable manoeuvring model was developed and tested. Simulation output data benchmarking has been done making use of purposely performed freerunning manoeuvring tests in BSHC manoeuvring basin. Resulting pusher model has been incorporated in the inland simulator software. The work is a part of large study dedicated to problems of Danube push-trains hydrodynamics and related to the further development of flexible model of convoy configurations simulation software.
Traditionally, the dominant part of merchant ship maneuvering investigations is related to the 3D... more Traditionally, the dominant part of merchant ship maneuvering investigations is related to the 3DOF motion in horizontal plane while the roll motions during maneuvers are neglected. Nowadays, many ships like container carriers with high deck load or ferry vessels with well developed superstructures have relatively small value of transverse metacentric height. This design peculiarity reflects into large roll angles when ship is turning. If maneuver is performed in shallow water, besides the changes in ship stability of motion, the effective ship draft to water depth ratio is reduced eroding safety UKC clearance. In the frame of ITTC workshop SIMMAN'2008 cooperative program a container vessel model KCS was tested at BSHC in free-sailing mode. In the paper, the results of additional extensive experimental investigations of shallow water effect as well as of variation in GM value on KCS standard maneuver parameters are presented. Included is an analysis of combined contribution of both effects in ship course stability and safety.
Polish Maritime Research, Aug 31, 2023
During tight manoeuvres, twin-screw ships equipped with two rudders located in the propeller slip... more During tight manoeuvres, twin-screw ships equipped with two rudders located in the propeller slip stream experience a fairly large imbalance in the hydrodynamic loads on the propeller and rudders. To investigate the phenomenon of rudder asymmetric load in some depth, manoeuvring experiments based on a free-running model were set up in which the kinematics of the model, the forces on the rudder and the stock moment were recorded. In parallel, with the aim of obtaining an exact estimation of free-stream characteristics of the rudder blade, corresponding wind tunnel experiments were also performed. Based on the results of this investigation, an analysis of the interaction effects within the hull-propeller-rudder system was performed and some conclusions were drawn.
Journal of Engineering Thermophysics, Jul 1, 2020
Operating characteristics of aeronautic and marine vehicles, as well as hydraulic machines design... more Operating characteristics of aeronautic and marine vehicles, as well as hydraulic machines designed for various purposes are largely affected by flow separation. Therefore, control of separated flows is an extremely important problem for modern aviation and marine engineering. Based on dynamometric measurements of forces and torque acting on model hydrofoils and the ship rudder, jet control of flow separation in cavitation-free and cavitation regimes at low and high angles of attack is studied. It is shown that generation of a near-wall jet can ensure a separationless flow around test models at angles of attack greater than 30 degrees. In this case, the lift coefficient of the hydrofoil can increase approximately by two or three times. Pressure fluctuations near the body and in its wake vanish due to flow stabilization; as a result, oscillations of hydrodynamic loads on the body decrease.
Sustainable Development and Innovations in Marine Technologies, 2019
International shipbuilding progress, 2013
The present work focuses on the application of simulation-based design for the resistance optimiz... more The present work focuses on the application of simulation-based design for the resistance optimization of waterjet propelled Delft catamaran, using integrated computational and experimental fluid dynamics. A variable physics/variable fidelity approach was implemented wherein the objective function was evaluated using both low fidelity potential flow solvers with a simplified CFD waterjet model and high fidelity RANS solvers with discretized duct flow calculations. Both solvers were verified and validated with data for the original hull. The particle swarm optimizer was used for single speed optimization at Fr = 0.5, and genetic algorithms were used for multi speed optimization at Fr = 0.3, 0.5 and 0.7. The variable physics/variable fidelity approach was compared with high fidelity approach for the bare-hull shape optimization and it showed an overall CPU time reduction of 54% and converged to the same optimal design at Fr = 0.5. The multi-speed optimization showed design improvement at Fr = 0.5 and 0.7, but not at Fr = 0.3 since the design variables were obtained based on sensitivity analysis at Fr = 0.5. High fidelity simulation results for the optimized barehull geometry indicated 4% reduction in resistance and the optimized waterjet equipped geometry indicated 11% reduction in effective pump power required at self-propulsion. Verification was performed for the optimized hull form and its reduction in powering will be validated in forthcoming experimental campaign.
HAL (Le Centre pour la Communication Scientifique Directe), Jul 1, 2017
International shipbuilding progress, Feb 1, 1987
Results of the experimental investigation of the effects of finite water depth on the hydrodynami... more Results of the experimental investigation of the effects of finite water depth on the hydrodynamic forces and moments acting on ship model moving in the horizontal plane are presented. The structure of the mathematical model used is verified after the multiple hnear regression and dispersion analysis methods. Comparison between the fuh scale and predicted ship manoeuvrabhity characteristics are made. This work is carried out at BSHC, Varna, Bulgaria with the help of PMM. 2.1. Experimental equipment and ship model
CERN European Organization for Nuclear Research - Zenodo, Nov 22, 2018
The maneuverability of a ship in waves is strongly influenced by vessel's inherent course stabili... more The maneuverability of a ship in waves is strongly influenced by vessel's inherent course stability and particularly by existing rudder design. The International Maritime Organization (IMO) has published a series of regulations regarding ship maneuverability in adverse conditions at low speed in the range of 4-6 knots. These new higher standard of IMO require new approaches to improve the maneuvering characteristics in waves of the ship comparing with current criteria for calm water. In the paper, to achieve higher rudder efficiency two technical solutions have been studied-traditional, by increase of rudder area with 20% and innovative-applying the effect of substitution of the trailing edge of the increased rudder design with the wedge tail. The results of aerodynamic tests performed in BSHC-Varna wind tunnel show a high efficiency in both types than original item, independently of the increased drag. The effect of wedge tail are mostly highlight in the created torque of the rudder, almost double compared to the others. This gives preconditions to analyze the ship energy efficiency of the design point of view.
CERN European Organization for Nuclear Research - Zenodo, Jun 28, 2017
During tight maneuvers twin-screw ships equipped with two rudders located in propeller slip strea... more During tight maneuvers twin-screw ships equipped with two rudders located in propeller slip stream are indicating quite large imbalance in propeller and rudder hydrodynamic loads. To investigate deeply the phenomena of rudder asymmetric load the appropriate maneuvering experiments with free running model have been setup by which the model kinematics and rudder forces and stock moment have been recorded. In parallel, aiming for exact estimation about rudder's blade free-stream characteristics corresponding wind tunnel experiment also were performed. Based on obtained investigation results, in the present paper the analysis of interaction effects in the system "hull-propeller-rudder" has been performed and related conclusions were drawn.
Journal of Fluids Engineering, 2019
In this paper, capabilities of state-of-the-art computational fluid dynamics (CFD) tools in the p... more In this paper, capabilities of state-of-the-art computational fluid dynamics (CFD) tools in the prediction of the flow-field around a multihull catamaran advancing in straight ahead motion at nonzero drift angles are investigated. CFD estimations have been provided by three research institutes by using their in-house codes: CNR-INM using Xnavis, IIHR using CFDShip-Iowa, and CNRS/ECN using ISIS. These allowed an in-depth comparison between different methodologies, such as structured overlapping grids versus unstructured grid, different turbulence models and detached eddy simulations (DES) approaches, and level-set (LS) versus volume of fluid (VoF). The activities were pursued within the NATO AVT-183 group “reliable prediction of separated flow onset and progression for air and sea vehicles,” aimed at the assessment of CFD predictions of large three-dimensional separated flows. Comparison between estimations is provided for both integral and local quantities, and for wave-induced vort...
International Shipbuilding Progress
The present work focuses on the application of simulation-based design for the resistance optimiz... more The present work focuses on the application of simulation-based design for the resistance optimization of waterjet propelled Delft catamaran, using integrated computational and experimental fluid dynamics. A variable physics/variable fidelity approach was implemented wherein the objective function was evaluated using both low fidelity potential flow solvers with a simplified CFD waterjet model and high fidelity RANS solvers with discretized duct flow calculations. Both solvers were verified and validated with data for the original hull. The particle swarm optimizer was used for single speed optimization at Fr = 0.5, and genetic algorithms were used for multi speed optimization at Fr = 0.3, 0.5 and 0.7. The variable physics/variable fidelity approach was compared with high fidelity approach for the bare-hull shape optimization and it showed an overall CPU time reduction of 54% and converged to the same optimal design at Fr = 0.5. The multi-speed optimization showed design improvement at Fr = 0.5 and 0.7, but not at Fr = 0.3 since the design variables were obtained based on sensitivity analysis at Fr = 0.5. High fidelity simulation results for the optimized barehull geometry indicated 4% reduction in resistance and the optimized waterjet equipped geometry indicated 11% reduction in effective pump power required at self-propulsion. Verification was performed for the optimized hull form and its reduction in powering will be validated in forthcoming experimental campaign.
ABSTRACT The results of a series of 3-DOF model experiments for high speed water jet propelled De... more ABSTRACT The results of a series of 3-DOF model experiments for high speed water jet propelled Delft372 catamaran in deep and shallow water are described. The hydrodynamic derivatives are estimated from captive model test in shallow towing tank condition and used to predict the maneuverability and course stability of the vessel using 3-DOFsystem based simulations. Then the simulation results are validated by free running model tests. The both results are in relatively good compliance, but analysis shows necessity of simulation model refinement.
ABSTRACT The accurate prediction of waterjet propulsion using CFD is of interest in the standpoin... more ABSTRACT The accurate prediction of waterjet propulsion using CFD is of interest in the standpoint of performance analyses of existing waterjet designs as well as design optimization of new waterjet propulsion systems for high-speed marine vehicles. Currently, the design and analysis of waterjets follow the ITTC '05 recommended procedures and guidelines which was validated by a rigorous experimental campaign through standardized testing. The current study focuses on validation of detailed duct flow simulations on catamarans using the Delft catamaran as the model. The validation work is conducted as a pre-requisite for subsequent URANS based optimization. The Delft catamaran model was build at BSHC and a customized waterjet was designed for the model based on pre-existing stock waterjet designs. Data from the model testing using the ITTC '05 procedures include net jet thrust, thrust-deduction, water-jet volume flow-rate, sinkage, trim, and jet velocity surveys at nozzle exit. Simulations were performed over a speed range of 0.4<Fr<0.75 using URANS and an actuator disk body-force model. The computed net jet thrust, thrust deduction, sinkage and trim compare well with experiments indicating that the present approach is an efficient tool to predict the performance of waterjet propelled JHSS and paves way for future optimization work.
The results of a series of 3-DOF model experiments for high speed water jet propelled Delft372 ca... more The results of a series of 3-DOF model experiments for high speed water jet propelled Delft372 catamaran in deep and shallow water are described. The hydrodynamic derivatives are estimated from captive model test in shallow towing tank condition and used to predict the maneuverability and course stability of the vessel using 3-DOFsystem based simulations. Then the simulation results are validated by free running model tests. The both results are in relatively good compliance, but analysis shows necessity of simulation model refinement.
TransNav, the International Journal on Marine Navigation and Safety of Sea Transportation
Recently, the submarine missions are often evolving into operating to littoral areas, which requi... more Recently, the submarine missions are often evolving into operating to littoral areas, which require operating in shallow water. Such shallow water operations strongly contrast with the traditional ones due to the effect of a close to free water surface expressed mainly by surface suction force. This influence is particularly important for submarine maneuverability accounting for restricted area available. The prediction of submarine behavior in similar conditions requires adequate mathematical model and understanding of the additional hydrodynamic load generated near the surface region. The paper is aimed for better understanding of these issues and relating to development of a submarine simulation model, the experimental program of towing and PMM captive tests of DARPA Suboff submarine model were conducted at a towing tank. The influence of phenomenon such as effect of a close to free surface and Froude number at hydrodynamic forces and moments including control surfaces effectiveness were investigated and also was estimated directional stability of motion in horizontal plane.
Maritime Technology and Research
Since the Energy Efficiency Design Index EEDI was introduced by International Maritime Organizati... more Since the Energy Efficiency Design Index EEDI was introduced by International Maritime Organization IMO, an increasing attention to the ship's controllability in waves, in particular at low speed is observed. One of the main reasons for this is the fact that, in order to satisfy the EEDI requirements, there is a tendency to reduce the power consumption and the propellers RPM reduction while maintaining existing control means, which results in reduced ship steerability mainly at low speed. This study considers the effect of regular sea waves on ship’s initial turning parameters at the set of service conditions. By means of free running model tests the influence of low advance speed on course and maneuvering trajectory changes in transient turning motion were investigated. The effects of the wave encounter angle variations were examined during the tests, including application of different wave lengths. Using the experimental results, an attempt was made to normalize the ship's...
TransNav, the International Journal on Marine Navigation and Safety of Sea Transportation
Recently, the submarine missions are often evolving into operating to littoral areas, which requi... more Recently, the submarine missions are often evolving into operating to littoral areas, which require operating in shallow water. Such shallow water operations strongly contrast with the traditional ones due to the effect of a close to free water surface expressed mainly by surface suction force. This influence is particularly important for submarine maneuverability accounting for restricted area available. The prediction of submarine behavior in similar conditions requires adequate mathematical model and understanding of the additional hydrodynamic load generated near the surface region. The paper is aimed for better understanding of these issues and relating to development of a submarine simulation model, the experimental program of towing and PMM captive tests of DARPA Suboff submarine model were conducted at a towing tank. The influence of phenomenon such as effect of a close to free surface and Froude number at hydrodynamic forces and moments including control surfaces effectiveness were investigated and also was estimated directional stability of motion in horizontal plane.
This paper presents the results of system-based maneuvering predictions of the Delft372 design ca... more This paper presents the results of system-based maneuvering predictions of the Delft372 design catamaran model for a set of water depth ratios and Froude number values. The simulation results were compared with the data, experimentally obtained by means of a radio-controlled free running model. Based on the analysis of standard maneuvers the vessel maneuverability and directional stability in the above navigation conditions have been estimated.
The Danube waterway provides a vital link in the transportation of a wide range of cargos carried... more The Danube waterway provides a vital link in the transportation of a wide range of cargos carried out by push-trains. A part of pusher solo operations are performed in port areas as well in deep water. In this study the Danube pusher model was tested extensively in deep, medium shallow and in very shallow water conditions in Bulgarian Ship Hydrodynamic Centre (BSHC) shallow water tank facility aiming for development of four-quadrant simulation model. The tests were performed in captive mode creating possibility for identification of hydrodynamic terms in mathematical model of the vessel manoeuvrability. Accounting for the pusher full-range operation specifics the suitable manoeuvring model was developed and tested. Simulation output data benchmarking has been done making use of purposely performed freerunning manoeuvring tests in BSHC manoeuvring basin. Resulting pusher model has been incorporated in the inland simulator software. The work is a part of large study dedicated to problems of Danube push-trains hydrodynamics and related to the further development of flexible model of convoy configurations simulation software.
Traditionally, the dominant part of merchant ship maneuvering investigations is related to the 3D... more Traditionally, the dominant part of merchant ship maneuvering investigations is related to the 3DOF motion in horizontal plane while the roll motions during maneuvers are neglected. Nowadays, many ships like container carriers with high deck load or ferry vessels with well developed superstructures have relatively small value of transverse metacentric height. This design peculiarity reflects into large roll angles when ship is turning. If maneuver is performed in shallow water, besides the changes in ship stability of motion, the effective ship draft to water depth ratio is reduced eroding safety UKC clearance. In the frame of ITTC workshop SIMMAN'2008 cooperative program a container vessel model KCS was tested at BSHC in free-sailing mode. In the paper, the results of additional extensive experimental investigations of shallow water effect as well as of variation in GM value on KCS standard maneuver parameters are presented. Included is an analysis of combined contribution of both effects in ship course stability and safety.