In this work was reported the analysis of the flow in the stern region and the hull-propeller int... more In this work was reported the analysis of the flow in the stern region and the hull-propeller interactions of a (semi-) planing hull using the commercial URANS code Siemens PLM Star CCM+. In the present study was conducted the resistance and self-propulsion test simulations to get self-propulsion factors (the wake and thrust deduction factors), using the Computational Fluid Dynamics (CFD) techniques. The computational results were validated by comparing with the benchmark towing tank data. The simulation of self-propulsion test is a non-trivial task for the high speed craft, in particular defining the correct trim and so the correct wake field. The reliability of the results is strictly connected to the high quality of the resistance test simulation and to the propeller-discretization method. The purpose of the current studies is to provide reliable and fast results of self-propulsion test simulation for the Fast Displacement hulls. For this reason, starting from different propeller discretization methods (i.e. the Actuator Disk method and the Fully Discretized Propeller) the results were compared in terms of accuracy and of computational effort. To take into account the motion of the hull and motion of the Fully Discretize Propeller the overset mesh technique was employed in all simulations.
The concept of Flettner rotor, a rotating cylinder immersed in a fluid current, with a top-mounte... more The concept of Flettner rotor, a rotating cylinder immersed in a fluid current, with a top-mounted disk, has been analyzed by means of unsteady Reynolds averaged Navier-Stokes simulations, with the aim of creating a suitable tool for the preliminary design of the Flettner rotor as a ship's auxiliary propulsion system. The simulation has been executed to evaluate the performance sensitivity of the Flettner rotor with respect to systematic variations of several parameters, that is, the spin ratio, the rotor aspect ratio, the effect of the end plates, and their dimensions. The Flettner rotor device has been characterized in terms of lift and drag coefficients, and these data were compared with experimental trends available in literature. A verification study has been conducted in order to evaluate the accuracy of the simulation results and the main sources of numerical uncertainty. All the simulation results were used to achieve a surrogate model of lift and drag coefficients. This model is an effective mathematical tool for the preliminary design of Flettner rotor. Finally, an example of assessment of the Flettner rotor performance as an auxiliary propulsion device on a real tanker ship is reported.
In the context of marine application of computational fluid dynamic (CFD), it is well
known that ... more In the context of marine application of computational fluid dynamic (CFD), it is well known that the numerical simulations of planing craft are significantly less reliable than that of displacement ships. For this reason, it is important to perform a comprehensive approach to the verification and validation (V&V) methodology and procedures for simulating CFD planing craft. In the first part of this paper, an assessment of the accuracy and effectiveness of different simulation setups and techniques for planing craft is performed. In the second part, the results of the V&V study are reported for three different hull models at four Froude numbers (Fr). The Unsteady Reynolds-Averaged Navier-Stokes code results were validated using benchmark experimental data obtained for three hull models characterized by systematic variation of the length to beam ratio. Grid independence, iteration, and time-step convergence analysis for response variables (resistance coefficients, wetted surfaces, and dynamic trim angles) were conducted using the main error and uncertainty estimation methods available in the literature. The same procedures were followed for the profiles of the wave patterns. The results showed that there was improved reliability of the numerical simulation of the planing craft in terms of the errors and uncertainties, related to the predictions of resistance, running attitude, and wave pattern. The results of the V&V study highlighted the fact that modeling of the planing craft is a critical point to improve the reliability of the numerical simulation.
The Italian Navy has performed a feasibility study about a new OPV (Offshore Patrol Vessel), char... more The Italian Navy has performed a feasibility study about a new OPV (Offshore Patrol Vessel), characterized by very high maximum speeds and a large differences between cruise and full speed. In this study, an attempt has been developed to adequately identify hull forms and to determine the maximum effectiveness of interceptor device to be applied on the displacing hull. Simulations have been carried out by using the RANSE code CD-Adapco STAR CCM+ v. 9.06. To take into account the low reliability of numerical simulations to predict the interceptor’s effectiveness, the towing tank experiences, carried out by INSEAN-CNR Rome on the reference hull form, have been compared with the numerical simulations. Finally, different configurations of hulls have been analyzed to minimize resistance. In addition, for the same aim, different mesh sizes and turbulence models have been tested. In brief, this work is divided into the following parts: • towing tank test experiences; • choice of the more reliable numerical procedure (by validation with towing tank test); • optimization of the hull forms in relation to drag resistance evaluated for the two operational speeds; • identification of interceptor suitable size to be applied to the final hull form.
This work is strictly related with the paper " The Naples Warped Hard Chine Hulls Systematic Seri... more This work is strictly related with the paper " The Naples Warped Hard Chine Hulls Systematic Series – First Part: Resistance in Still Water" presented at this same Symposium. The aim of this work is to show the results of the numerical evaluation of the hull-propeller interactions obtained by the commercial RANSE Computational Fluid Dynamic software CD-ADAPCO Star CCM+. In literature there is a significant lack of experimental data on wake and thrust fraction magnitude especially regarding medium and high speed vessels. This is due to the high costs and to the reduced reliability of the tests carried out with small models whose dimensions are constrained by the high Froude numbers. In spite of the high model speed, the smallness of the models induces small Reynolds numbers and therefore not negligible scale effects on propellers dynamic (laminar flow) and on wake intensity. In this paper a numerical analysis has been performed on the parent hull of the series. In particular, three procedures, characterized by simulations with different degree of freedom and different relations with experimental data, have been applied. The simulations have been carried out in the speed range Fr = 0.5 ÷ 1.5. This way is submitted also as an alternative to towing tank experiments on big models if these tests are not feasible.
The International Journal of Small Craft Technology, 2007
ABSTRACT The aim of this study has been the evaluation of the effects of varying longitudinal sta... more ABSTRACT The aim of this study has been the evaluation of the effects of varying longitudinal stagger, transverse separation and displacement on the resistance of two symmetric hull forms suitable for catamaran configuration over a speed range corresponding to Fn < 0.5. To achieve this aim at the Dipartimento di Ingegneria Navale di Napoli (DIN) an intensive experimental investigation has been carried out on two models in three configurations: monohull, symmetric and staggered catamaran. In particular, for one model, 6 clearances in the symmetrical configuration and 4 longitudinal staggers have been tested; for the other one 3 clearances and 3 staggers have been tested. The influence of displacement on resistance has been evaluated by testing the models for three different displacements
A program research on resistance characteristics of trimarans is developing at the Dipartimento d... more A program research on resistance characteristics of trimarans is developing at the Dipartimento di Ingegneria Navale (DIN) of the Università di Napoli “Federico II”. The results of the experimental program and the preliminary design of a 1500 TEUs container ship, 40 knots, range 4000 miles, have been presented in a previous paper. This paper presents an investigation of specific features of multi-hull hydrodynamics: the mutual interference of the hulls and the wave making component in the total resistance. Because of the complexity of the flow around ship’s hull, model experiments are still the most reliable data source on ship resistance determination; nevertheless, numerical methods have strongly advanced in this field, so that a combined use of both model tests and CFD codes can be very useful for ship design and for understanding the ship hydrodynamics. Finally, the experimental array tests on trimaran ship model has been extended to other mutual locations of trimaran hulls and ...
The main purpose of our work has been to develop a numerical method able to preview ship stern an... more The main purpose of our work has been to develop a numerical method able to preview ship stern and wake flows, showing at the same time how useful is a preliminary numerical design of the hull in the naval project loop. Turbulent ship flows are computed using an algorithm which solves incompressible RANS equations in generalized three dimensional curvilinear coordinates. An explicit finite difference scheme on single or multiblock non-staggered structured grids is used. Time integration is obtained with explicit multistage Runge-Kutta scheme. For the pressure field a pressure Poisson equation is derived from the continuity equation in conjunction with the momentum equation. Spalart-Allmaras one equation turbulence model is employed. Residual averaging and multilevel approach are used to improve the convergence rate. In this paper will be shown the validation of our code by the well known case of flat plate in turbulent flow and real cases on some ship hulls too. All cases are consid...
Flettner Rotors (FR) are spinning cylinders, which produce fluid dynamic lift by using the Magnus... more Flettner Rotors (FR) are spinning cylinders, which produce fluid dynamic lift by using the Magnus Effect. The Magnus force can be much greater in magnitude than the wing lifting force, given the same projected area and dynamic air pressure. The FR was used for ship's propulsion system in the 1920's. Nowadays, the FR is being seriously examined due to the necessity of renewable resources use. Since several months, the Dipartimento di Ingegneria Industriale of the Università degli Studi di Napoli " Federico II " has started a research about preliminary analysis for marine application of FR through Unsteady Reynolds Average Navier Stokes (U-RANS) simulations for 3D flow past a full-scale rotating [1]. The aerodynamic forces, Lift (L), Drag (D) and Aerodynamic Efficiency (L/D) of a FR are the response variables and are influenced by the following control factors: Spin Ratio (SR), i.e. the ratio of circumferential-cylinder-velocity-to-free stream-velocity; Aspect Ra...
SOMMARIO Nel lavoro gli autori propongono un metodo basato sull'utilizzo della tecnica fotogr... more SOMMARIO Nel lavoro gli autori propongono un metodo basato sull'utilizzo della tecnica fotogrammetrica per il rilievo in navigazione di vele in vera grandezza. L'utilizzo di tecniche ottiche di Reverse Engineering per il rilievo della forma consente, infatti, la ricostruzione tridimensionale del modello dell'intera vela. Ciò rende anche possibile il controllo su qualunque sezione e non solo su quelle precedentemente individuate dalle strisce di forma, risolvendo il problema relativo alla descrizione della parte bassa. Inoltre, la geometria della vela, così ottenuta (descritta mediante superfici NURBS), può essere paragonata direttamente a quella di progetto, consentendo di effettuare interessanti analisi in ambiente CFD, FEA e VPP. ABSTRACT In the following work the authors propose a method based on the use of the photogrammetry technique for the acquisition of sails in real dimensions during navigation. Use of optical techniques of Reverse Engineering for the acquisitio...
... Digital Library logo Take a look at the new version of this page: [ beta version ]. Tell us w... more ... Digital Library logo Take a look at the new version of this page: [ beta version ]. Tell us what you think. Functions and Methods to Analyze and Construct Developable Hull Surfaces. ... Collaborative Colleagues: Salvatore Miranda: colleagues. Claudio Pensa: colleagues. ...
ABSTRACT Documentation of maritime heritage is essential for its protection, and for reference in... more ABSTRACT Documentation of maritime heritage is essential for its protection, and for reference in restoration and renovation processes. These functions become problematic in the case of historical ships and boats that lack lines drawings. The purpose of this paper is to describe a procedure for creation of lines drawings based on the shape analysis of surviving historical boats or their small-scale models with the help of reverse engineering (RE) techniques. The paper describes how digital photogrammetry and the iterative method were used to analyze the shape of three historical boats: Tomahawk, Refola and Nada. The application of the proposed procedure produced the lines drawings of the boats as its result. The accuracy of the 3D CAD model obtained with the photogrammetric technique was verified by comparing it against a more accurate 3D model produced with the help of a RE laser scanner. The examination of the resulting lines drawings proves that the digital photogrammetry process and the proposed iterative method are adequate tools for developing lines plans of boat models. The research offers the methodological basis for the creation of an archive of lines drawings of historical boats. Such an archive would provide reference for philologically correct restorations, and permit definition and classification of distinctive elements of various types of historical boats, particularly those produced in the Campania Region.
The paper presents Unsteady Reynolds Average Navier Stokes (U-RANS) simulations for 3D flow past ... more The paper presents Unsteady Reynolds Average Navier Stokes (U-RANS) simulations for 3D flow past a full-scale rotating cylinder, known as Flettner Rotor (FR). The U-RANS simulations are performed using the commercially available flow simulation software CD-Adapco STAR CCM+. A preliminary 2D study was conducted to set-up a numerical model using a moving mesh technique; this analysis was directed to define suitable domain shape and dimension, time-step and grid-resolution. The further 3D simulations were performed to evaluate in deep the influence of some of the main parameters on the effectiveness of the rotors; in particular the Spin Ratio, i.e. the ratio of circumferential-cylinder-velocity-to-free stream-velocity (SR) and the effect of the endplates (EP) also called Thom disk. The functioning characteristic of the device has been predicted by lift and drag coefficients for various rotation rates. The selected dimensions of the cylinder and the chosen range of design parameters are similar to those of a real installation on board, therefore the Rn obtained (1.3 - 5.0 E+06) are quite close to the real values and significantly higher than the ones used by other authors in literature. The high-Rn simulations presented here were onerous in terms of computing time but they have proven to be very helpful to evaluate the reliability of numerical studies of large- and small-scale models. Data obtained ware compared with experimental trends found in the literature. The final task of the research is the assessment of FR concept as an effective naval propeller, therefore the downstream flow field has been closely studied in order to obtain simple and reliable indications on the effective positioning of multiple cylinders on the ship. This study is based on several visualizations of the rotating cylinder wake and takes into account the trailing vortices extinction distance. Consistently with the point of evaluating the necessity and the feasibility of high Rn simulations, a cost-and-benefit analysis has been enabled showing the computational times of the simulations and numbers of CPUs used.
In this chapter the main research fields of the above mentioned
research group of the naval secti... more In this chapter the main research fields of the above mentioned research group of the naval section of the Department of Industrial Engineering performed by SCoPE Supercomputing Center are summarized.
In this work was reported the analysis of the flow in the stern region and the hull-propeller int... more In this work was reported the analysis of the flow in the stern region and the hull-propeller interactions of a (semi-) planing hull using the commercial URANS code Siemens PLM Star CCM+. In the present study was conducted the resistance and self-propulsion test simulations to get self-propulsion factors (the wake and thrust deduction factors), using the Computational Fluid Dynamics (CFD) techniques. The computational results were validated by comparing with the benchmark towing tank data. The simulation of self-propulsion test is a non-trivial task for the high speed craft, in particular defining the correct trim and so the correct wake field. The reliability of the results is strictly connected to the high quality of the resistance test simulation and to the propeller-discretization method. The purpose of the current studies is to provide reliable and fast results of self-propulsion test simulation for the Fast Displacement hulls. For this reason, starting from different propeller discretization methods (i.e. the Actuator Disk method and the Fully Discretized Propeller) the results were compared in terms of accuracy and of computational effort. To take into account the motion of the hull and motion of the Fully Discretize Propeller the overset mesh technique was employed in all simulations.
The concept of Flettner rotor, a rotating cylinder immersed in a fluid current, with a top-mounte... more The concept of Flettner rotor, a rotating cylinder immersed in a fluid current, with a top-mounted disk, has been analyzed by means of unsteady Reynolds averaged Navier-Stokes simulations, with the aim of creating a suitable tool for the preliminary design of the Flettner rotor as a ship's auxiliary propulsion system. The simulation has been executed to evaluate the performance sensitivity of the Flettner rotor with respect to systematic variations of several parameters, that is, the spin ratio, the rotor aspect ratio, the effect of the end plates, and their dimensions. The Flettner rotor device has been characterized in terms of lift and drag coefficients, and these data were compared with experimental trends available in literature. A verification study has been conducted in order to evaluate the accuracy of the simulation results and the main sources of numerical uncertainty. All the simulation results were used to achieve a surrogate model of lift and drag coefficients. This model is an effective mathematical tool for the preliminary design of Flettner rotor. Finally, an example of assessment of the Flettner rotor performance as an auxiliary propulsion device on a real tanker ship is reported.
In the context of marine application of computational fluid dynamic (CFD), it is well
known that ... more In the context of marine application of computational fluid dynamic (CFD), it is well known that the numerical simulations of planing craft are significantly less reliable than that of displacement ships. For this reason, it is important to perform a comprehensive approach to the verification and validation (V&V) methodology and procedures for simulating CFD planing craft. In the first part of this paper, an assessment of the accuracy and effectiveness of different simulation setups and techniques for planing craft is performed. In the second part, the results of the V&V study are reported for three different hull models at four Froude numbers (Fr). The Unsteady Reynolds-Averaged Navier-Stokes code results were validated using benchmark experimental data obtained for three hull models characterized by systematic variation of the length to beam ratio. Grid independence, iteration, and time-step convergence analysis for response variables (resistance coefficients, wetted surfaces, and dynamic trim angles) were conducted using the main error and uncertainty estimation methods available in the literature. The same procedures were followed for the profiles of the wave patterns. The results showed that there was improved reliability of the numerical simulation of the planing craft in terms of the errors and uncertainties, related to the predictions of resistance, running attitude, and wave pattern. The results of the V&V study highlighted the fact that modeling of the planing craft is a critical point to improve the reliability of the numerical simulation.
The Italian Navy has performed a feasibility study about a new OPV (Offshore Patrol Vessel), char... more The Italian Navy has performed a feasibility study about a new OPV (Offshore Patrol Vessel), characterized by very high maximum speeds and a large differences between cruise and full speed. In this study, an attempt has been developed to adequately identify hull forms and to determine the maximum effectiveness of interceptor device to be applied on the displacing hull. Simulations have been carried out by using the RANSE code CD-Adapco STAR CCM+ v. 9.06. To take into account the low reliability of numerical simulations to predict the interceptor’s effectiveness, the towing tank experiences, carried out by INSEAN-CNR Rome on the reference hull form, have been compared with the numerical simulations. Finally, different configurations of hulls have been analyzed to minimize resistance. In addition, for the same aim, different mesh sizes and turbulence models have been tested. In brief, this work is divided into the following parts: • towing tank test experiences; • choice of the more reliable numerical procedure (by validation with towing tank test); • optimization of the hull forms in relation to drag resistance evaluated for the two operational speeds; • identification of interceptor suitable size to be applied to the final hull form.
This work is strictly related with the paper " The Naples Warped Hard Chine Hulls Systematic Seri... more This work is strictly related with the paper " The Naples Warped Hard Chine Hulls Systematic Series – First Part: Resistance in Still Water" presented at this same Symposium. The aim of this work is to show the results of the numerical evaluation of the hull-propeller interactions obtained by the commercial RANSE Computational Fluid Dynamic software CD-ADAPCO Star CCM+. In literature there is a significant lack of experimental data on wake and thrust fraction magnitude especially regarding medium and high speed vessels. This is due to the high costs and to the reduced reliability of the tests carried out with small models whose dimensions are constrained by the high Froude numbers. In spite of the high model speed, the smallness of the models induces small Reynolds numbers and therefore not negligible scale effects on propellers dynamic (laminar flow) and on wake intensity. In this paper a numerical analysis has been performed on the parent hull of the series. In particular, three procedures, characterized by simulations with different degree of freedom and different relations with experimental data, have been applied. The simulations have been carried out in the speed range Fr = 0.5 ÷ 1.5. This way is submitted also as an alternative to towing tank experiments on big models if these tests are not feasible.
The International Journal of Small Craft Technology, 2007
ABSTRACT The aim of this study has been the evaluation of the effects of varying longitudinal sta... more ABSTRACT The aim of this study has been the evaluation of the effects of varying longitudinal stagger, transverse separation and displacement on the resistance of two symmetric hull forms suitable for catamaran configuration over a speed range corresponding to Fn < 0.5. To achieve this aim at the Dipartimento di Ingegneria Navale di Napoli (DIN) an intensive experimental investigation has been carried out on two models in three configurations: monohull, symmetric and staggered catamaran. In particular, for one model, 6 clearances in the symmetrical configuration and 4 longitudinal staggers have been tested; for the other one 3 clearances and 3 staggers have been tested. The influence of displacement on resistance has been evaluated by testing the models for three different displacements
A program research on resistance characteristics of trimarans is developing at the Dipartimento d... more A program research on resistance characteristics of trimarans is developing at the Dipartimento di Ingegneria Navale (DIN) of the Università di Napoli “Federico II”. The results of the experimental program and the preliminary design of a 1500 TEUs container ship, 40 knots, range 4000 miles, have been presented in a previous paper. This paper presents an investigation of specific features of multi-hull hydrodynamics: the mutual interference of the hulls and the wave making component in the total resistance. Because of the complexity of the flow around ship’s hull, model experiments are still the most reliable data source on ship resistance determination; nevertheless, numerical methods have strongly advanced in this field, so that a combined use of both model tests and CFD codes can be very useful for ship design and for understanding the ship hydrodynamics. Finally, the experimental array tests on trimaran ship model has been extended to other mutual locations of trimaran hulls and ...
The main purpose of our work has been to develop a numerical method able to preview ship stern an... more The main purpose of our work has been to develop a numerical method able to preview ship stern and wake flows, showing at the same time how useful is a preliminary numerical design of the hull in the naval project loop. Turbulent ship flows are computed using an algorithm which solves incompressible RANS equations in generalized three dimensional curvilinear coordinates. An explicit finite difference scheme on single or multiblock non-staggered structured grids is used. Time integration is obtained with explicit multistage Runge-Kutta scheme. For the pressure field a pressure Poisson equation is derived from the continuity equation in conjunction with the momentum equation. Spalart-Allmaras one equation turbulence model is employed. Residual averaging and multilevel approach are used to improve the convergence rate. In this paper will be shown the validation of our code by the well known case of flat plate in turbulent flow and real cases on some ship hulls too. All cases are consid...
Flettner Rotors (FR) are spinning cylinders, which produce fluid dynamic lift by using the Magnus... more Flettner Rotors (FR) are spinning cylinders, which produce fluid dynamic lift by using the Magnus Effect. The Magnus force can be much greater in magnitude than the wing lifting force, given the same projected area and dynamic air pressure. The FR was used for ship's propulsion system in the 1920's. Nowadays, the FR is being seriously examined due to the necessity of renewable resources use. Since several months, the Dipartimento di Ingegneria Industriale of the Università degli Studi di Napoli " Federico II " has started a research about preliminary analysis for marine application of FR through Unsteady Reynolds Average Navier Stokes (U-RANS) simulations for 3D flow past a full-scale rotating [1]. The aerodynamic forces, Lift (L), Drag (D) and Aerodynamic Efficiency (L/D) of a FR are the response variables and are influenced by the following control factors: Spin Ratio (SR), i.e. the ratio of circumferential-cylinder-velocity-to-free stream-velocity; Aspect Ra...
SOMMARIO Nel lavoro gli autori propongono un metodo basato sull'utilizzo della tecnica fotogr... more SOMMARIO Nel lavoro gli autori propongono un metodo basato sull'utilizzo della tecnica fotogrammetrica per il rilievo in navigazione di vele in vera grandezza. L'utilizzo di tecniche ottiche di Reverse Engineering per il rilievo della forma consente, infatti, la ricostruzione tridimensionale del modello dell'intera vela. Ciò rende anche possibile il controllo su qualunque sezione e non solo su quelle precedentemente individuate dalle strisce di forma, risolvendo il problema relativo alla descrizione della parte bassa. Inoltre, la geometria della vela, così ottenuta (descritta mediante superfici NURBS), può essere paragonata direttamente a quella di progetto, consentendo di effettuare interessanti analisi in ambiente CFD, FEA e VPP. ABSTRACT In the following work the authors propose a method based on the use of the photogrammetry technique for the acquisition of sails in real dimensions during navigation. Use of optical techniques of Reverse Engineering for the acquisitio...
... Digital Library logo Take a look at the new version of this page: [ beta version ]. Tell us w... more ... Digital Library logo Take a look at the new version of this page: [ beta version ]. Tell us what you think. Functions and Methods to Analyze and Construct Developable Hull Surfaces. ... Collaborative Colleagues: Salvatore Miranda: colleagues. Claudio Pensa: colleagues. ...
ABSTRACT Documentation of maritime heritage is essential for its protection, and for reference in... more ABSTRACT Documentation of maritime heritage is essential for its protection, and for reference in restoration and renovation processes. These functions become problematic in the case of historical ships and boats that lack lines drawings. The purpose of this paper is to describe a procedure for creation of lines drawings based on the shape analysis of surviving historical boats or their small-scale models with the help of reverse engineering (RE) techniques. The paper describes how digital photogrammetry and the iterative method were used to analyze the shape of three historical boats: Tomahawk, Refola and Nada. The application of the proposed procedure produced the lines drawings of the boats as its result. The accuracy of the 3D CAD model obtained with the photogrammetric technique was verified by comparing it against a more accurate 3D model produced with the help of a RE laser scanner. The examination of the resulting lines drawings proves that the digital photogrammetry process and the proposed iterative method are adequate tools for developing lines plans of boat models. The research offers the methodological basis for the creation of an archive of lines drawings of historical boats. Such an archive would provide reference for philologically correct restorations, and permit definition and classification of distinctive elements of various types of historical boats, particularly those produced in the Campania Region.
The paper presents Unsteady Reynolds Average Navier Stokes (U-RANS) simulations for 3D flow past ... more The paper presents Unsteady Reynolds Average Navier Stokes (U-RANS) simulations for 3D flow past a full-scale rotating cylinder, known as Flettner Rotor (FR). The U-RANS simulations are performed using the commercially available flow simulation software CD-Adapco STAR CCM+. A preliminary 2D study was conducted to set-up a numerical model using a moving mesh technique; this analysis was directed to define suitable domain shape and dimension, time-step and grid-resolution. The further 3D simulations were performed to evaluate in deep the influence of some of the main parameters on the effectiveness of the rotors; in particular the Spin Ratio, i.e. the ratio of circumferential-cylinder-velocity-to-free stream-velocity (SR) and the effect of the endplates (EP) also called Thom disk. The functioning characteristic of the device has been predicted by lift and drag coefficients for various rotation rates. The selected dimensions of the cylinder and the chosen range of design parameters are similar to those of a real installation on board, therefore the Rn obtained (1.3 - 5.0 E+06) are quite close to the real values and significantly higher than the ones used by other authors in literature. The high-Rn simulations presented here were onerous in terms of computing time but they have proven to be very helpful to evaluate the reliability of numerical studies of large- and small-scale models. Data obtained ware compared with experimental trends found in the literature. The final task of the research is the assessment of FR concept as an effective naval propeller, therefore the downstream flow field has been closely studied in order to obtain simple and reliable indications on the effective positioning of multiple cylinders on the ship. This study is based on several visualizations of the rotating cylinder wake and takes into account the trailing vortices extinction distance. Consistently with the point of evaluating the necessity and the feasibility of high Rn simulations, a cost-and-benefit analysis has been enabled showing the computational times of the simulations and numbers of CPUs used.
In this chapter the main research fields of the above mentioned
research group of the naval secti... more In this chapter the main research fields of the above mentioned research group of the naval section of the Department of Industrial Engineering performed by SCoPE Supercomputing Center are summarized.
Uploads
Papers
known that the numerical simulations of planing craft are significantly less reliable
than that of displacement ships. For this reason, it is important to perform a comprehensive
approach to the verification and validation (V&V) methodology and procedures
for simulating CFD planing craft. In the first part of this paper, an assessment
of the accuracy and effectiveness of different simulation setups and techniques for
planing craft is performed. In the second part, the results of the V&V study are
reported for three different hull models at four Froude numbers (Fr). The Unsteady
Reynolds-Averaged Navier-Stokes code results were validated using benchmark
experimental data obtained for three hull models characterized by systematic variation
of the length to beam ratio. Grid independence, iteration, and time-step convergence
analysis for response variables (resistance coefficients, wetted surfaces, and
dynamic trim angles) were conducted using the main error and uncertainty estimation
methods available in the literature. The same procedures were followed for the
profiles of the wave patterns. The results showed that there was improved reliability
of the numerical simulation of the planing craft in terms of the errors and uncertainties,
related to the predictions of resistance, running attitude, and wave pattern. The results
of the V&V study highlighted the fact that modeling of the planing craft is a critical
point to improve the reliability of the numerical simulation.
• towing tank test experiences;
• choice of the more reliable numerical procedure (by validation with towing tank test);
• optimization of the hull forms in relation to drag resistance evaluated for the two operational speeds;
• identification of interceptor suitable size to be applied to the final hull form.
The aim of this work is to show the results of the numerical evaluation of the hull-propeller interactions obtained by the commercial RANSE Computational Fluid Dynamic software CD-ADAPCO Star CCM+.
In literature there is a significant lack of experimental data on wake and thrust fraction magnitude especially regarding medium and high speed vessels. This is due to the high costs and to the reduced reliability of the tests carried out with small models whose dimensions are constrained by the high Froude numbers. In spite of the high model speed, the smallness of the models induces small Reynolds numbers and therefore not negligible scale effects on propellers dynamic (laminar flow) and on wake intensity.
In this paper a numerical analysis has been performed on the parent hull of the series. In particular, three procedures, characterized by simulations with different degree of freedom and different relations with experimental data, have been applied. The simulations have been carried out in the speed range Fr = 0.5 ÷ 1.5. This way is submitted also as an alternative to towing tank experiments on big models if these tests are not feasible.
The further 3D simulations were performed to evaluate in deep the influence of some of the main parameters on the effectiveness of the rotors; in particular the Spin Ratio, i.e. the ratio of circumferential-cylinder-velocity-to-free stream-velocity (SR) and the effect of the endplates (EP) also called Thom disk.
The functioning characteristic of the device has been predicted by lift and drag coefficients for various rotation rates.
The selected dimensions of the cylinder and the chosen range of design parameters are similar to those of a real installation on board, therefore the Rn obtained (1.3 - 5.0 E+06) are quite close to the real values and significantly higher than the ones used by other authors in literature. The high-Rn simulations presented here were onerous in terms of computing time but they have proven to be very helpful to evaluate the reliability of numerical studies of large- and small-scale models. Data obtained ware compared with experimental trends found in the literature.
The final task of the research is the assessment of FR concept as an effective naval propeller, therefore the downstream flow field has been closely studied in order to obtain simple and reliable indications on the effective positioning of multiple cylinders on the ship. This study is based on several visualizations of the rotating cylinder wake and takes into account the trailing vortices extinction distance.
Consistently with the point of evaluating the necessity and the feasibility of high Rn simulations, a cost-and-benefit analysis has been enabled showing the computational times of the simulations and numbers of CPUs used.
Books
research group of the naval section of the Department of Industrial
Engineering performed by SCoPE Supercomputing Center are
summarized.
known that the numerical simulations of planing craft are significantly less reliable
than that of displacement ships. For this reason, it is important to perform a comprehensive
approach to the verification and validation (V&V) methodology and procedures
for simulating CFD planing craft. In the first part of this paper, an assessment
of the accuracy and effectiveness of different simulation setups and techniques for
planing craft is performed. In the second part, the results of the V&V study are
reported for three different hull models at four Froude numbers (Fr). The Unsteady
Reynolds-Averaged Navier-Stokes code results were validated using benchmark
experimental data obtained for three hull models characterized by systematic variation
of the length to beam ratio. Grid independence, iteration, and time-step convergence
analysis for response variables (resistance coefficients, wetted surfaces, and
dynamic trim angles) were conducted using the main error and uncertainty estimation
methods available in the literature. The same procedures were followed for the
profiles of the wave patterns. The results showed that there was improved reliability
of the numerical simulation of the planing craft in terms of the errors and uncertainties,
related to the predictions of resistance, running attitude, and wave pattern. The results
of the V&V study highlighted the fact that modeling of the planing craft is a critical
point to improve the reliability of the numerical simulation.
• towing tank test experiences;
• choice of the more reliable numerical procedure (by validation with towing tank test);
• optimization of the hull forms in relation to drag resistance evaluated for the two operational speeds;
• identification of interceptor suitable size to be applied to the final hull form.
The aim of this work is to show the results of the numerical evaluation of the hull-propeller interactions obtained by the commercial RANSE Computational Fluid Dynamic software CD-ADAPCO Star CCM+.
In literature there is a significant lack of experimental data on wake and thrust fraction magnitude especially regarding medium and high speed vessels. This is due to the high costs and to the reduced reliability of the tests carried out with small models whose dimensions are constrained by the high Froude numbers. In spite of the high model speed, the smallness of the models induces small Reynolds numbers and therefore not negligible scale effects on propellers dynamic (laminar flow) and on wake intensity.
In this paper a numerical analysis has been performed on the parent hull of the series. In particular, three procedures, characterized by simulations with different degree of freedom and different relations with experimental data, have been applied. The simulations have been carried out in the speed range Fr = 0.5 ÷ 1.5. This way is submitted also as an alternative to towing tank experiments on big models if these tests are not feasible.
The further 3D simulations were performed to evaluate in deep the influence of some of the main parameters on the effectiveness of the rotors; in particular the Spin Ratio, i.e. the ratio of circumferential-cylinder-velocity-to-free stream-velocity (SR) and the effect of the endplates (EP) also called Thom disk.
The functioning characteristic of the device has been predicted by lift and drag coefficients for various rotation rates.
The selected dimensions of the cylinder and the chosen range of design parameters are similar to those of a real installation on board, therefore the Rn obtained (1.3 - 5.0 E+06) are quite close to the real values and significantly higher than the ones used by other authors in literature. The high-Rn simulations presented here were onerous in terms of computing time but they have proven to be very helpful to evaluate the reliability of numerical studies of large- and small-scale models. Data obtained ware compared with experimental trends found in the literature.
The final task of the research is the assessment of FR concept as an effective naval propeller, therefore the downstream flow field has been closely studied in order to obtain simple and reliable indications on the effective positioning of multiple cylinders on the ship. This study is based on several visualizations of the rotating cylinder wake and takes into account the trailing vortices extinction distance.
Consistently with the point of evaluating the necessity and the feasibility of high Rn simulations, a cost-and-benefit analysis has been enabled showing the computational times of the simulations and numbers of CPUs used.
research group of the naval section of the Department of Industrial
Engineering performed by SCoPE Supercomputing Center are
summarized.