Olivia D'Ubaldo, C. Rizzo, D. Dessì, F. Passacantilli
The present paper describes the design concept and specifications of a hydrofoil model to be actually tested for flutter experimental analysis at CNR-INM Institute of Marine Engineering towing tank in Rome. The design procedure is the result of concurrent application of numerical and analytical approaches: CAD models are used for geometrical modelling and mass properties calculations, FEM is employed to calculate model stiffness, natural frequencies and verify model strength, and Theodorsen analytical approach is implemented to predict flutter velocity. Theodorsen approach allows calculating the flutter condition as a function of physical parameters as geometries, mass and stiffness, assuming two-dimensional, incompressible aerodynamic coefficients and sinusoidal harmonic motion at flutter instability condition (zero damping condition). As first step, the authors built a broad literature review upon past flutter experimental experiences in both air and water flow focusing on the troubles linked to the increase of flow density and viscosity, the technical issues to be considered when designing the flutter model and setting up experimental campaigns. Most of the flutter experimental campaigns reported in the literature deal with high mass ratio models as aerofoils operating in light, low viscosity fluids; less common are experimental reports about low mass ratio models as light hydrofoils. The design a dynamical scale of a hydrofoil model, flutter-tested in 1971, chosen as main reference. The model is designed to encounter flutter at a speed compatible with the range of velocity imposed by the water tank facilities. The combination of design parameters is optimised to meet facilities speed range, construction issues and Theodorsen approach application field.
{"title":"Low mass ratio hydrofoil flutter experimental model design procedure","authors":"Olivia D'Ubaldo, C. Rizzo, D. Dessì, F. Passacantilli","doi":"10.2218/marine2021.6859","DOIUrl":"https://doi.org/10.2218/marine2021.6859","url":null,"abstract":"The present paper describes the design concept and specifications of a hydrofoil model to be actually tested for flutter experimental analysis at CNR-INM Institute of Marine Engineering towing tank in Rome. The design procedure is the result of concurrent application of numerical and analytical approaches: CAD models are used for geometrical modelling and mass properties calculations, FEM is employed to calculate model stiffness, natural frequencies and verify model strength, and Theodorsen analytical approach is implemented to predict flutter velocity. Theodorsen approach allows calculating the flutter condition as a function of physical parameters as geometries, mass and stiffness, assuming two-dimensional, incompressible aerodynamic coefficients and sinusoidal harmonic motion at flutter instability condition (zero damping condition). As first step, the authors built a broad literature review upon past flutter experimental experiences in both air and water flow focusing on the troubles linked to the increase of flow density and viscosity, the technical issues to be considered when designing the flutter model and setting up experimental campaigns. Most of the flutter experimental campaigns reported in the literature deal with high mass ratio models as aerofoils operating in light, low viscosity fluids; less common are experimental reports about low mass ratio models as light hydrofoils. The design a dynamical scale of a hydrofoil model, flutter-tested in 1971, chosen as main reference. The model is designed to encounter flutter at a speed compatible with the range of velocity imposed by the water tank facilities. The combination of design parameters is optimised to meet facilities speed range, construction issues and Theodorsen approach application field.","PeriodicalId":367395,"journal":{"name":"The 9th Conference on Computational Methods in Marine Engineering (Marine 2021)","volume":"22 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123937377","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Cross-flow turbines (CFTs) are arousing a growing interest to harvest both off-shore wind and tidal currents. A promising characteristic of CFTs could be a high power-density in case of multi-device clusters or farms, achievable by shortening the distance between arrays as allowed by the fast energy recovery observed inside the wakes. However just few studies, only concerning symmetrical airfoils/hydrofoils, are found in literature. By means of 3d-URANS simulations and the momentum budget approach we investigated the effects of blade profile and turbine solidity on blade tip vortex generation and then on the mixing mechanisms supporting the reintroduction of streamwise momentum into the wake. Results indicate that: (a) a pair of counter-rotating vortices occurs in the wake at the turbine top and bottom ends, which rotation verse depends on blade profile and it is such as to generate positive vertical advection for camber-out profiles, but negative vertical advection for camber-in profiles; (b) camber-out profiles are much more effective in supporting the wake energy recovery due to the massive vertical advection induced by tip vortices; (c) for camber-in profiles the tip vortices poorly contribute to the wake recovery, that appears delayed and promoted by turbulent transport; (d) higher solidity implies stronger tip vortices and higher turbulent transport, therefore a faster wake recovery.
{"title":"Fluid dynamic mechanisms for the wake energy recovery in cross-flow turbines: effects of hydrofoil shape and turbine solidity","authors":"S. Zanforlin, P. Lupi","doi":"10.2218/marine2021.6854","DOIUrl":"https://doi.org/10.2218/marine2021.6854","url":null,"abstract":"Cross-flow turbines (CFTs) are arousing a growing interest to harvest both off-shore wind and tidal currents. A promising characteristic of CFTs could be a high power-density in case of multi-device clusters or farms, achievable by shortening the distance between arrays as allowed by the fast energy recovery observed inside the wakes. However just few studies, only concerning symmetrical airfoils/hydrofoils, are found in literature. By means of 3d-URANS simulations and the momentum budget approach we investigated the effects of blade profile and turbine solidity on blade tip vortex generation and then on the mixing mechanisms supporting the reintroduction of streamwise momentum into the wake. Results indicate that: (a) a pair of counter-rotating vortices occurs in the wake at the turbine top and bottom ends, which rotation verse depends on blade profile and it is such as to generate positive vertical advection for camber-out profiles, but negative vertical advection for camber-in profiles; (b) camber-out profiles are much more effective in supporting the wake energy recovery due to the massive vertical advection induced by tip vortices; (c) for camber-in profiles the tip vortices poorly contribute to the wake recovery, that appears delayed and promoted by turbulent transport; (d) higher solidity implies stronger tip vortices and higher turbulent transport, therefore a faster wake recovery.","PeriodicalId":367395,"journal":{"name":"The 9th Conference on Computational Methods in Marine Engineering (Marine 2021)","volume":"32 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125679320","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This work investigates the working characteristics of a large amplitude semi-passive flapping-foil with a prescribed sinusoidal heave motion and a passive pitch motion. Different from the active flapping foil with two degrees of freedom, this self-pitching flapping foil ( SPFF ) constructs a single degree of freedom spring mass system in the direction around the pitching motion axis. Because of the torsion spring attached to the foil, this kind of foil is a flow-induced vibration system, and the torsional spring stiffness, the foil inertia and the hydrodynamic added inertia should affect the propulsive performance. Its working characteristics are affected by two non-dimensional coeffificients: the frequency ratio r and spring stiffness ratio k’ according to dimensional analysis. In this paper, the fluid-structure coupling method is used to analyze the working characteristics of the self-pitching flapping foil with different parameter settings. After the verification of the numerical method, the investigation first discusses the working characteristics of the self-pitching flapping foil when the system resonates and identifies that the resonance can make the self-pitching flapping foil deviate from the ideal angle of attack, and its fluctuation of short-term average thrust coefficient becomes irregular. That leads to the performance degradation of self-pitching flapping foil and even the loss of propulsion ability. Then the influence of frequency ratio on the propulsive performance is investigated. The numerical results confirm that the semi-active flapping foil performs efficiently when the frequency ratio r is small, and the maximum efficiency can reach as high as 86%; the more suitable frequency ratio is recommended to be less than 0.5. Finally, the effect of spring stiffness ratio is discussed under a small frequency ratio. The results imply that the peak efficiency of self-pitching flapping foil is not monotonic with different spring stiffness ratio, and there is a maximum value; but self-pitching flapping foil can maintain the peak efficiency over a wider range of spring stiffness ratio, the range is 0.1 ~ 1000 in this report; Through the analysis of the performance curves of the foil with different pitching center positions, it indicates that the influence trend of pitching center position is close to that of the spring stiffness ratio.
{"title":"Working characteristics of self-pitching flapping foil propulsor","authors":"Mei Lei, W. Yan, Junwei Zhou, D. Yu, Pengcheng Wu","doi":"10.2218/marine2021.6840","DOIUrl":"https://doi.org/10.2218/marine2021.6840","url":null,"abstract":"This work investigates the working characteristics of a large amplitude semi-passive flapping-foil with a prescribed sinusoidal heave motion and a passive pitch motion. Different from the active flapping foil with two degrees of freedom, this self-pitching flapping foil ( SPFF ) constructs a single degree of freedom spring mass system in the direction around the pitching motion axis. Because of the torsion spring attached to the foil, this kind of foil is a flow-induced vibration system, and the torsional spring stiffness, the foil inertia and the hydrodynamic added inertia should affect the propulsive performance. Its working characteristics are affected by two non-dimensional coeffificients: the frequency ratio r and spring stiffness ratio k’ according to dimensional analysis. In this paper, the fluid-structure coupling method is used to analyze the working characteristics of the self-pitching flapping foil with different parameter settings. After the verification of the numerical method, the investigation first discusses the working characteristics of the self-pitching flapping foil when the system resonates and identifies that the resonance can make the self-pitching flapping foil deviate from the ideal angle of attack, and its fluctuation of short-term average thrust coefficient becomes irregular. That leads to the performance degradation of self-pitching flapping foil and even the loss of propulsion ability. Then the influence of frequency ratio on the propulsive performance is investigated. The numerical results confirm that the semi-active flapping foil performs efficiently when the frequency ratio r is small, and the maximum efficiency can reach as high as 86%; the more suitable frequency ratio is recommended to be less than 0.5. Finally, the effect of spring stiffness ratio is discussed under a small frequency ratio. The results imply that the peak efficiency of self-pitching flapping foil is not monotonic with different spring stiffness ratio, and there is a maximum value; but self-pitching flapping foil can maintain the peak efficiency over a wider range of spring stiffness ratio, the range is 0.1 ~ 1000 in this report; Through the analysis of the performance curves of the foil with different pitching center positions, it indicates that the influence trend of pitching center position is close to that of the spring stiffness ratio.","PeriodicalId":367395,"journal":{"name":"The 9th Conference on Computational Methods in Marine Engineering (Marine 2021)","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129926159","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
. A fully consistent finite element model for fluid-structure interaction between incompressible viscous fluids and elastic structures considering large structural deformation is presented. The coupling approach is based on a segregated solution procedure for the Navier-Stokes equations for incompressible viscous fluid flow and the structural equation of motion for elastic structures. The fluid-structure interaction model is applied on the 2D example of a rigid and elastic, respectively, flag in the quasi-harmonic fluid wake flow behind a square rigid obstacle. Time-harmonic pattern of fluid flow and time-harmonic structural deformation are evaluated at different steps of oscillation. Transient evolution of acting coupling forces on the common fluid-structure interface is shown and pointed out. The fluid-structure interaction model is further applied on the 3D example of a rigid and elastic, respectively, mast and sail structure that is exposed to quasi-stationary fluid flow on its surface. Corresponding structural response is analyzed with respect to different stages of fluid-structure coupling that can be applied to finally arrive at the fully consistent stage of the fluid-structure interaction model. Characteristics of fluid flow pattern and deformation of mast and sail structure are pointed out. The concised version only shows evaluation of computational results.
{"title":"Finite element modeling of fluid-structure interaction of an elastic 2D flag in harmonic viscous fluid flow and an elastic 3D sail structure in stationary viscous fluid flow (concised version)","authors":"C. Corte","doi":"10.2218/marine2021.6836","DOIUrl":"https://doi.org/10.2218/marine2021.6836","url":null,"abstract":". A fully consistent finite element model for fluid-structure interaction between incompressible viscous fluids and elastic structures considering large structural deformation is presented. The coupling approach is based on a segregated solution procedure for the Navier-Stokes equations for incompressible viscous fluid flow and the structural equation of motion for elastic structures. The fluid-structure interaction model is applied on the 2D example of a rigid and elastic, respectively, flag in the quasi-harmonic fluid wake flow behind a square rigid obstacle. Time-harmonic pattern of fluid flow and time-harmonic structural deformation are evaluated at different steps of oscillation. Transient evolution of acting coupling forces on the common fluid-structure interface is shown and pointed out. The fluid-structure interaction model is further applied on the 3D example of a rigid and elastic, respectively, mast and sail structure that is exposed to quasi-stationary fluid flow on its surface. Corresponding structural response is analyzed with respect to different stages of fluid-structure coupling that can be applied to finally arrive at the fully consistent stage of the fluid-structure interaction model. Characteristics of fluid flow pattern and deformation of mast and sail structure are pointed out. The concised version only shows evaluation of computational results.","PeriodicalId":367395,"journal":{"name":"The 9th Conference on Computational Methods in Marine Engineering (Marine 2021)","volume":"44 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125997424","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
. Slug flow, being the mixture of oil, gas and water, can increase the dynamics and structural response of a riser in internal fluid transportation due to the variation of slug flow's force caused by the time-space varying density. This paper presents a high-fidelity model of a flexible deep-water riser based on the absolute nodal coordinate formulation with slug flow in the arbitrary Lagrangian-Eulerian description. In the current paper, the Lagrangian and Eulerian description is introduced to describe the slug flow moving along the riser. Besides, a material coordinate is added together with the position and position gradient as the state variables. The riser is discretized into two types of elements, the constant-length and variable-length elements. The variable-length element is where the slug flow locates whose velocity of the material coordinates is equal to the slug flow speed, and its movement along the riser is simulated by the moving mesh technology. Considering the fact that the enormous ratio of the length to the riser's diameter, the Euler-Bernoulli beam theory is adopted to model the riser. In this paper, the equations of motion (EOM) of the riser subjected to the slug-flow and environmental loads are derived based on the generalized D'Alembert principle. The implicit time integration method is applied to solve the derived differential-algebraic equations. First, the proposed model and the slug flow method are validated. Second, Parametric studies are performed to quantitatively identify the design conditions most affected by the slug flow.
{"title":"Novel Modeling Methodology of the Deep-water Flexible Riser with the Slug-flow","authors":"Hanze Yu, Y. Xie, G. Li, Lijun Wang","doi":"10.2218/marine2021.6804","DOIUrl":"https://doi.org/10.2218/marine2021.6804","url":null,"abstract":". Slug flow, being the mixture of oil, gas and water, can increase the dynamics and structural response of a riser in internal fluid transportation due to the variation of slug flow's force caused by the time-space varying density. This paper presents a high-fidelity model of a flexible deep-water riser based on the absolute nodal coordinate formulation with slug flow in the arbitrary Lagrangian-Eulerian description. In the current paper, the Lagrangian and Eulerian description is introduced to describe the slug flow moving along the riser. Besides, a material coordinate is added together with the position and position gradient as the state variables. The riser is discretized into two types of elements, the constant-length and variable-length elements. The variable-length element is where the slug flow locates whose velocity of the material coordinates is equal to the slug flow speed, and its movement along the riser is simulated by the moving mesh technology. Considering the fact that the enormous ratio of the length to the riser's diameter, the Euler-Bernoulli beam theory is adopted to model the riser. In this paper, the equations of motion (EOM) of the riser subjected to the slug-flow and environmental loads are derived based on the generalized D'Alembert principle. The implicit time integration method is applied to solve the derived differential-algebraic equations. First, the proposed model and the slug flow method are validated. Second, Parametric studies are performed to quantitatively identify the design conditions most affected by the slug flow.","PeriodicalId":367395,"journal":{"name":"The 9th Conference on Computational Methods in Marine Engineering (Marine 2021)","volume":"21 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123696342","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
. The design, construction and evaluation of a test platform to test the International Moth class in real world conditions was undertaken with the aim to investigate the effects of altering the value of the proportional control coefficient on flight modes to provide data for further numerical simulations. Through consultation with industry, technical experts and reviews of literature, a design was produced that allowed foils to be tested over a range of velocities, foil configurations and control systems that would be free to move in pitch and heave, however constrained in roll, yaw, sway and surge. The rig with the degrees of freedom can be seen below in Figure 1. Improvement of an existing electronic ride control system (ERCS) allowed the test moth to be able to fly at a range of depth to chord ratios along with the capability to change the respective flight modes with varying amplitudes. Ultimately, it was concluded that in a real-world environment the differences in drag between the range of values tested resulted in no serious measurable performance gains despite significant motion variations. However, it was apparent that small relationships formed and that it is essential for more research to be conducted in order to validate the data. The rig developed provides an easily accessible method for testing control algorithms in a real-world environment without the need for complex sailing configurations. The rig also allows cheap ways of tuning a system that is ripe for full on-water implementation.
{"title":"Development of a Full Scale Moth Hydrofoil Control System Test Rig","authors":"Sean Kebbell, J. Binns","doi":"10.2218/marine2021.6863","DOIUrl":"https://doi.org/10.2218/marine2021.6863","url":null,"abstract":". The design, construction and evaluation of a test platform to test the International Moth class in real world conditions was undertaken with the aim to investigate the effects of altering the value of the proportional control coefficient on flight modes to provide data for further numerical simulations. Through consultation with industry, technical experts and reviews of literature, a design was produced that allowed foils to be tested over a range of velocities, foil configurations and control systems that would be free to move in pitch and heave, however constrained in roll, yaw, sway and surge. The rig with the degrees of freedom can be seen below in Figure 1. Improvement of an existing electronic ride control system (ERCS) allowed the test moth to be able to fly at a range of depth to chord ratios along with the capability to change the respective flight modes with varying amplitudes. Ultimately, it was concluded that in a real-world environment the differences in drag between the range of values tested resulted in no serious measurable performance gains despite significant motion variations. However, it was apparent that small relationships formed and that it is essential for more research to be conducted in order to validate the data. The rig developed provides an easily accessible method for testing control algorithms in a real-world environment without the need for complex sailing configurations. The rig also allows cheap ways of tuning a system that is ripe for full on-water implementation.","PeriodicalId":367395,"journal":{"name":"The 9th Conference on Computational Methods in Marine Engineering (Marine 2021)","volume":"103 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116357702","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
. Numerical method to simulate the motions of the floating body coupled with the tank liquids inside of the floating body using the overset grids method is developed. An in-house structured CFD solver which is capable the moving grid technique and overset grids method is utilized. The governing equations are 3D Navier-Stokes equations for the incompressible flow. Artificial compressibility approach is used for the velocity-pressure coupling. Spatial discretization is based on a finite-volume method. An interface capturing method based on a single phase level set approach is employed to simulate the liquid surface. Lateral regular waves are generated in the regions inside of the computational domain. The motions of the floating body are introduced by solving the motion equations and the hydrodynamic forces of the tanks are treated as the external forces in the motion equations. The computational grids of the floating body and tanks deform with the motions using the moving grid technique. The weight values for the overset-grid interpolation are determined by an in-house system which is based on Ferguson spline interpolation. The present method is applied to the condition with the floating box which has the 4 tanks inside and the lateral incoming regular waves. The overset grids are composed by the grids of the floating box, 4 tanks and background rectangular grid which generates the lateral regular waves. The amplitudes of the motions of the floating box are compared with the measured data and the present results show the features changing with the wave length ratio which are strongly affected by the liquid fluids inside of the tanks. The free surfaces around the floating box and inside of the tanks are indicated, and the interactions between the floating box and the liquid fluids of the tanks are revealed.
{"title":"Numerical Simulation of Strongly Coupled Liquid Fluids in Tanks inside of Floating Body and its Motions with Incoming Lateral Regular Waves","authors":"K. Ohashi","doi":"10.2218/marine2021.6814","DOIUrl":"https://doi.org/10.2218/marine2021.6814","url":null,"abstract":". Numerical method to simulate the motions of the floating body coupled with the tank liquids inside of the floating body using the overset grids method is developed. An in-house structured CFD solver which is capable the moving grid technique and overset grids method is utilized. The governing equations are 3D Navier-Stokes equations for the incompressible flow. Artificial compressibility approach is used for the velocity-pressure coupling. Spatial discretization is based on a finite-volume method. An interface capturing method based on a single phase level set approach is employed to simulate the liquid surface. Lateral regular waves are generated in the regions inside of the computational domain. The motions of the floating body are introduced by solving the motion equations and the hydrodynamic forces of the tanks are treated as the external forces in the motion equations. The computational grids of the floating body and tanks deform with the motions using the moving grid technique. The weight values for the overset-grid interpolation are determined by an in-house system which is based on Ferguson spline interpolation. The present method is applied to the condition with the floating box which has the 4 tanks inside and the lateral incoming regular waves. The overset grids are composed by the grids of the floating box, 4 tanks and background rectangular grid which generates the lateral regular waves. The amplitudes of the motions of the floating box are compared with the measured data and the present results show the features changing with the wave length ratio which are strongly affected by the liquid fluids inside of the tanks. The free surfaces around the floating box and inside of the tanks are indicated, and the interactions between the floating box and the liquid fluids of the tanks are revealed.","PeriodicalId":367395,"journal":{"name":"The 9th Conference on Computational Methods in Marine Engineering (Marine 2021)","volume":"24 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115591873","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Flow and air-entrainment around a surface piercing circular cylinder has been investigated experimentally and numerically. In water tunnel experiments, high speed video observations were made for surface piercing flow around a circular cylinder of 150 mm in diameter. Surface pressure measurements were also carried out at nine points around the cylinder. Flow velocity was from 1.5 to 3.0 m/s. The high-speed video observations showed that a pair of air pocket was formed on the side of the cylinder, and bubbles entrained into the air-pockets are shed downstream. The depth of the air-pocket fluctuated in a frequency range lower than the typical Karman vortex frequency. For numerical study, unsteady motion of air-entrainment process was simulated by an MPS method with some corrections to pressure calculation. The MPS calculation reproduced the dynamics of the air-pockets on the side of the cylinder. The time-variation of the predicted air-pocked depth also showed low-frequency fluctuations as observed in the experiment.
{"title":"Observations and Particle-based Simulation of Air-entrainment around a Surface Piercing Cylinder","authors":"Junya Arai, T. Mori","doi":"10.2218/marine2021.6845","DOIUrl":"https://doi.org/10.2218/marine2021.6845","url":null,"abstract":"Flow and air-entrainment around a surface piercing circular cylinder has been investigated experimentally and numerically. In water tunnel experiments, high speed video observations were made for surface piercing flow around a circular cylinder of 150 mm in diameter. Surface pressure measurements were also carried out at nine points around the cylinder. Flow velocity was from 1.5 to 3.0 m/s. The high-speed video observations showed that a pair of air pocket was formed on the side of the cylinder, and bubbles entrained into the air-pockets are shed downstream. The depth of the air-pocket fluctuated in a frequency range lower than the typical Karman vortex frequency. For numerical study, unsteady motion of air-entrainment process was simulated by an MPS method with some corrections to pressure calculation. The MPS calculation reproduced the dynamics of the air-pockets on the side of the cylinder. The time-variation of the predicted air-pocked depth also showed low-frequency fluctuations as observed in the experiment.","PeriodicalId":367395,"journal":{"name":"The 9th Conference on Computational Methods in Marine Engineering (Marine 2021)","volume":"80 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133573566","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
D. Di Capua, J. García, R. Pacheco, O. Casals, H. Tuula, A. Tissari, A. Korkealaakso
This paper describes the research performed within the scope of H2020 project NICESHIP in the development of suitable thermo-mechanical framework to analyse composite structures under fire loads. The framework couples the thermo-mechanical model that is detailed in the paper with the Fire Dynamics Simulator (FDS) in order to obtain the adiabatic temperature needed as input for thermal model. The thermo-mechanical model uses the adiabatic temperature to estimate the temperature profile across the thickness of each quadrilateral shell element and also takes into account the pyrolysis effect. The composite constitutive model employed is the so-called Serial/Parallel Rule of Mixtures (SPROM) and has been modified to take into account the thermal expansion. Finally the thermo-mechanical model is validated against two literature tests and then the developed framework of fire collapse analysis is illustrated by a marine real application of a fire case scenario in the superstructure of a containership where steel and FRP divisions are analysed.
{"title":"Computational analysis of resisting marine FRP divisions exposed to fire. Application to the analysis of ship structures.","authors":"D. Di Capua, J. García, R. Pacheco, O. Casals, H. Tuula, A. Tissari, A. Korkealaakso","doi":"10.2218/marine2021.6789","DOIUrl":"https://doi.org/10.2218/marine2021.6789","url":null,"abstract":"This paper describes the research performed within the scope of H2020 project NICESHIP in the development of suitable thermo-mechanical framework to analyse composite structures under fire loads. The framework couples the thermo-mechanical model that is detailed in the paper with the Fire Dynamics Simulator (FDS) in order to obtain the adiabatic temperature needed as input for thermal model. The thermo-mechanical model uses the adiabatic temperature to estimate the temperature profile across the thickness of each quadrilateral shell element and also takes into account the pyrolysis effect. The composite constitutive model employed is the so-called Serial/Parallel Rule of Mixtures (SPROM) and has been modified to take into account the thermal expansion. Finally the thermo-mechanical model is validated against two literature tests and then the developed framework of fire collapse analysis is illustrated by a marine real application of a fire case scenario in the superstructure of a containership where steel and FRP divisions are analysed.","PeriodicalId":367395,"journal":{"name":"The 9th Conference on Computational Methods in Marine Engineering (Marine 2021)","volume":"39 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133458601","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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