A novel data-driven turbulence modeling framework is presented and applied to the problem of junction body flow. In particular, a symbolic regression approach is used to find nonlinear analytical expressions of the turbulent stress–strain coupling that are ready for implementation in computational fluid dynamics (CFD) solvers using Reynolds-averaged Navier–Stokes (RANS) closures. Results from baseline linear RANS closure calculations of a finite square-mounted cylinder with a Reynolds number of 11,000, based on diameter and freestream velocity, are shown to considerably overpredict the separated flow region downstream of the square cylinder, mainly because of the failure of the model to accurately represent the complex vortex structure generated by the junction flow. In the present study, a symbolic regression tool built on a gene expression programming technique is used to find a nonlinear constitutive stress–strain relationship. In short, the algorithm finds the most appropriate linear combination of basis functions and spatially varying coefficients that approximate the turbulent stress tensor from high-fidelity data. Here, the high-fidelity data, or the so-called training data, were obtained from a hybrid RANS/Large Eddy Simulation (LES) calculation also developed with symbolic regression that showed excellent agreement with direct numerical simulation data. The present study, therefore, also demonstrates that training data required for RANS closure development can be obtained using computationally more affordable approaches, such as hybrid RANS/LES. A procedure is presented to evaluate which of the individual basis functions that are available for model development are most likely to produce a successful nonlinear closure. A new model is built using those basis functions only. This new model is then tested, i.e., an actual CFD calculation is performed, on the well-known periodic hills case and produces significantly better results than the linear baseline model, despite this test case being fundamentally different from the training case. Finally, the new model is shown to also improve predictive accuracy for a surface-mounted cube placed in a channel at a cube height Reynolds number of 40,000 over traditional linear RANS closures.
{"title":"Improved Junction Body Flow Modeling Through Data-Driven Symbolic Regression","authors":"Jack Weatheritt, R. Sandberg","doi":"10.5957/JOSR.09180053","DOIUrl":"https://doi.org/10.5957/JOSR.09180053","url":null,"abstract":"A novel data-driven turbulence modeling framework is presented and applied to the problem of junction body flow. In particular, a symbolic regression approach is used to find nonlinear analytical expressions of the turbulent stress–strain coupling that are ready for implementation in computational fluid dynamics (CFD) solvers using Reynolds-averaged Navier–Stokes (RANS) closures. Results from baseline linear RANS closure calculations of a finite square-mounted cylinder with a Reynolds number of 11,000, based on diameter and freestream velocity, are shown to considerably overpredict the separated flow region downstream of the square cylinder, mainly because of the failure of the model to accurately represent the complex vortex structure generated by the junction flow. In the present study, a symbolic regression tool built on a gene expression programming technique is used to find a nonlinear constitutive stress–strain relationship. In short, the algorithm finds the most appropriate linear combination of basis functions and spatially varying coefficients that approximate the turbulent stress tensor from high-fidelity data. Here, the high-fidelity data, or the so-called training data, were obtained from a hybrid RANS/Large Eddy Simulation (LES) calculation also developed with symbolic regression that showed excellent agreement with direct numerical simulation data. The present study, therefore, also demonstrates that training data required for RANS closure development can be obtained using computationally more affordable approaches, such as hybrid RANS/LES. A procedure is presented to evaluate which of the individual basis functions that are available for model development are most likely to produce a successful nonlinear closure. A new model is built using those basis functions only. This new model is then tested, i.e., an actual CFD calculation is performed, on the well-known periodic hills case and produces significantly better results than the linear baseline model, despite this test case being fundamentally different from the training case. Finally, the new model is shown to also improve predictive accuracy for a surface-mounted cube placed in a channel at a cube height Reynolds number of 40,000 over traditional linear RANS closures.","PeriodicalId":50052,"journal":{"name":"Journal of Ship Research","volume":"63 1","pages":"283-293"},"PeriodicalIF":1.4,"publicationDate":"2019-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45702640","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Dongyoung Kim, Yagin Kim, Jiajia Li, Robert Wilson, J. E. Martin, P. Carrica
We describe the implementation of several recently developed boundary layer transition models into the overset computational fluid dynamics code, REX, developed at the University of Iowa, together with an evaluation of its capabilities and limitations for naval hydrodynamics applications. Models based on correlations and on amplification factor transport were implemented in one- and two-equation Reynolds-averaged Navier-Stokes turbulence models, including modifications to operate in crossflow. Extensive validation of the transition models implemented in REX is performed for several 2- and 3-dimensional geometries of naval relevance. Standard tests with extensive available experimental data include flat plates in zero pressure gradient, an airfoil, and sickle wing. More complex test cases include the propeller, P4119, with some experimental data available, and the generic submersible, Joubert BB2, with no relevant experimental data available, to validate the transition models. Simulations for these last two cases show that extensive regions of laminar flow can be present on the bodies at laboratory scale and field scale for small vessels, and the potential effects on resistance and propulsion can be significant. Progress for prediction of attached, fully turbulent flows for practical aerodynamic and hydrodynamic applications has reached a relatively mature plateau. However, according to a recent comprehensive review of pacing items (Slotnick et al. 2014), the single largest hurdle for incorporating computational fluid dynamics (CFD) into the design process in the near future is the ability to accurately predict turbulent flows with boundary layer transition and separation. Transition can impact skin friction, heat transfer, noise, propulsion efficiency, and maneuverability. This is especially true at model scale and for small craft such as unmanned or autonomous surface and underwater vehicles.
{"title":"Boundary Layer Transition Models for Naval Applications: Capabilities and Limitations","authors":"Dongyoung Kim, Yagin Kim, Jiajia Li, Robert Wilson, J. E. Martin, P. Carrica","doi":"10.5957/JOSR.09180066","DOIUrl":"https://doi.org/10.5957/JOSR.09180066","url":null,"abstract":"We describe the implementation of several recently developed boundary layer transition models into the overset computational fluid dynamics code, REX, developed at the University of Iowa, together with an evaluation of its capabilities and limitations for naval hydrodynamics applications. Models based on correlations and on amplification factor transport were implemented in one- and two-equation Reynolds-averaged Navier-Stokes turbulence models, including modifications to operate in crossflow. Extensive validation of the transition models implemented in REX is performed for several 2- and 3-dimensional geometries of naval relevance. Standard tests with extensive available experimental data include flat plates in zero pressure gradient, an airfoil, and sickle wing. More complex test cases include the propeller, P4119, with some experimental data available, and the generic submersible, Joubert BB2, with no relevant experimental data available, to validate the transition models. Simulations for these last two cases show that extensive regions of laminar flow can be present on the bodies at laboratory scale and field scale for small vessels, and the potential effects on resistance and propulsion can be significant.\u0000 \u0000 \u0000 Progress for prediction of attached, fully turbulent flows for practical aerodynamic and hydrodynamic applications has reached a relatively mature plateau. However, according to a recent comprehensive review of pacing items (Slotnick et al. 2014), the single largest hurdle for incorporating computational fluid dynamics (CFD) into the design process in the near future is the ability to accurately predict turbulent flows with boundary layer transition and separation. Transition can impact skin friction, heat transfer, noise, propulsion efficiency, and maneuverability. This is especially true at model scale and for small craft such as unmanned or autonomous surface and underwater vehicles.\u0000","PeriodicalId":50052,"journal":{"name":"Journal of Ship Research","volume":"63 1","pages":"294-307"},"PeriodicalIF":1.4,"publicationDate":"2019-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.5957/JOSR.09180066","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44149269","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Yonghwan Kim, Dong-Min Park, JaeHyeck Lee, Byung-soo Kim, Kyung-Kyu Yang, Semyun Oh, Dong-Yeon Lee
In this study, the added resistance of a liquefied natural gas carrier (LNGC) in the presence of waves is studied experimentally and numerically. The ship model is an LNGC designed by Samsung Heavy Industries (SHI). Experiments on ship motion responses and added resistance under head sea conditions were conducted at the Seoul National University and SHI. The influences of the experimental methods (captive and self-propulsion methods), incident wave amplitude, and regular and irregular wave conditions on the added resistance are evaluated using the same model ship set at different scales. In the numerical studies, the motion responses and added resistance are obtained using three methods—the strip method by adopting momentum conservation; Rankine panel method using pressure integration; and computational fluid dynamics method, using the difference in the resistances in waves and calm water. The experimental and numerical results under various conditions are compared, and the characteristics of the experimental and numerical results are discussed. Unlike the resistance in calm water, additional resistance occurs because of winds, waves, current, and for other reasons in a seaway. This aforementioned resistance, caused by environmental conditions, is called an added resistance. Among the various types, the added resistance caused by water waves is investigated in this study.
{"title":"Numerical Analysis and Experimental Validation of Added Resistance on Ship in Waves","authors":"Yonghwan Kim, Dong-Min Park, JaeHyeck Lee, Byung-soo Kim, Kyung-Kyu Yang, Semyun Oh, Dong-Yeon Lee","doi":"10.5957/JOSR.10180091","DOIUrl":"https://doi.org/10.5957/JOSR.10180091","url":null,"abstract":"In this study, the added resistance of a liquefied natural gas carrier (LNGC) in the presence of waves is studied experimentally and numerically. The ship model is an LNGC designed by Samsung Heavy Industries (SHI). Experiments on ship motion responses and added resistance under head sea conditions were conducted at the Seoul National University and SHI. The influences of the experimental methods (captive and self-propulsion methods), incident wave amplitude, and regular and irregular wave conditions on the added resistance are evaluated using the same model ship set at different scales. In the numerical studies, the motion responses and added resistance are obtained using three methods—the strip method by adopting momentum conservation; Rankine panel method using pressure integration; and computational fluid dynamics method, using the difference in the resistances in waves and calm water. The experimental and numerical results under various conditions are compared, and the characteristics of the experimental and numerical results are discussed.\u0000 \u0000 \u0000 Unlike the resistance in calm water, additional resistance occurs because of winds, waves, current, and for other reasons in a seaway. This aforementioned resistance, caused by environmental conditions, is called an added resistance. Among the various types, the added resistance caused by water waves is investigated in this study.\u0000","PeriodicalId":50052,"journal":{"name":"Journal of Ship Research","volume":"63 1","pages":"268-282"},"PeriodicalIF":1.4,"publicationDate":"2019-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43864467","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Zhongshu Ren, Javad Javaherian, Christine M. Gilbert
A deeper comprehension of hydrodynamic slamming can be achieved by revisiting the wedge water entry problem using flexible structures. In this work, two wedge models that are identical, with the exception of different bottom thicknesses, are vertically dropped into calm water. Pressure, full-field out-of-plane deflection, strain, vertical acceleration, and vertical position are measured. Full-field deflections and strains are measured using stereoscopic-digital image correlation (S-DIC) and strain gauges. A nondimensional number, R, quantifying the relative stiffness of the structure with respect to the fluid load is revisited. An experimental parametric study on the effect of R on the nondimensional hydrodynamic pressure and the maximum strain is presented. It was found there is a sharp change in the trend of pressure and strain when R passes through a critical value. It was also discovered that the structural deformation causes a delay in the peak pressure arrival time and a reduction in the peak pressure magnitude during the wedge water entry. When high-speed planing craft operating in waves becomes airborne and reenters the water surface, a substantial impact or “slam” between the vessel bottom and the water surface will occur (Faltinsen 2005; Lloyd 1989). The bottom slamming events occur frequently and may injure the passengers, compromise the equipment onboard, or even damage the structure. Slamming is a major cause of speed reduction in small craft where slamming loads are important. Current design criteria are primarily based on empirical measurements with little regard for the fluid–structure interaction (FSI) physics of the slamming phenomenon. This study offers a first step toward better understanding of FSI in slamming for optimal structural design in the future. Since the cross sections of most surface effect ships may be approximated by a V-shaped wedge, the slamming characteristics of these sections may be examined by dropping a wedge model into water (Faltinsen 2005; Lloyd 1989). Studying the wedge water entry problem is also helpful in shedding light on the wet deck slamming of catamaran, sloshing under the chamfered roof of a partially filled tank (Faltinsen 2000), seaplane landing (Wagner 1932), water landing of spacecraft and solid rocket boosters, water landing/ditching of aircraft (Abrate 2013), and animal diving behavior (Chang et al. 2016).
{"title":"Vertical Wedge Drop Experiments as a Model for Slamming","authors":"Zhongshu Ren, Javad Javaherian, Christine M. Gilbert","doi":"10.5957/josr.10200053","DOIUrl":"https://doi.org/10.5957/josr.10200053","url":null,"abstract":"A deeper comprehension of hydrodynamic slamming can be achieved by revisiting the wedge water entry problem using flexible structures. In this work, two wedge models that are identical, with the exception of different bottom thicknesses, are vertically dropped into calm water. Pressure, full-field out-of-plane deflection, strain, vertical acceleration, and vertical position are measured. Full-field deflections and strains are measured using stereoscopic-digital image correlation (S-DIC) and strain gauges. A nondimensional number, R, quantifying the relative stiffness of the structure with respect to the fluid load is revisited. An experimental parametric study on the effect of R on the nondimensional hydrodynamic pressure and the maximum strain is presented. It was found there is a sharp change in the trend of pressure and strain when R passes through a critical value. It was also discovered that the structural deformation causes a delay in the peak pressure arrival time and a reduction in the peak pressure magnitude during the wedge water entry.\u0000 \u0000 \u0000 When high-speed planing craft operating in waves becomes airborne and reenters the water surface, a substantial impact or “slam” between the vessel bottom and the water surface will occur (Faltinsen 2005; Lloyd 1989). The bottom slamming events occur frequently and may injure the passengers, compromise the equipment onboard, or even damage the structure. Slamming is a major cause of speed reduction in small craft where slamming loads are important. Current design criteria are primarily based on empirical measurements with little regard for the fluid–structure interaction (FSI) physics of the slamming phenomenon. This study offers a first step toward better understanding of FSI in slamming for optimal structural design in the future. Since the cross sections of most surface effect ships may be approximated by a V-shaped wedge, the slamming characteristics of these sections may be examined by dropping a wedge model into water (Faltinsen 2005; Lloyd 1989). Studying the wedge water entry problem is also helpful in shedding light on the wet deck slamming of catamaran, sloshing under the chamfered roof of a partially filled tank (Faltinsen 2000), seaplane landing (Wagner 1932), water landing of spacecraft and solid rocket boosters, water landing/ditching of aircraft (Abrate 2013), and animal diving behavior (Chang et al. 2016).\u0000","PeriodicalId":50052,"journal":{"name":"Journal of Ship Research","volume":" ","pages":""},"PeriodicalIF":1.4,"publicationDate":"2019-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48844353","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Hydrofoils made of metal alloys were broadly used on high-speed boats in the past. Nowadays, much lighter hydrofoils made of composite materials are finding increasingly more applications on sailing yachts and powerboats. However, these hydrofoils are usually rather flexible, and their design requires computationally demanding analysis, involving hydroelastic calculations. In this study, exploratory high-fidelity simulations have been carried out for surface-piercing hydrofoils in unsteady conditions with help of a computational fluid dynamics solver for fluid flow coupled with a finite element solver for the foil structure. To model unsteady foil deformations, the morphing mesh approach was utilized, and the volume-of-fluid method was applied for multiphase flow simulations. The computational setup, as well as verification and validation study, is described in this paper. Three hydrofoils of different stiffness, including a perfectly rigid foil, were simulated in both calm water conditions and regular head waves. Representative examples of foil deflections and wave patterns, as well as time-dependent structural and hydrodynamic characteristics, are presented. Hydrofoils are efficient lift-generating devices intended for application in water flows. Hydrofoils have streamlined shapes, and when operating at small incidence angles, they can produce high lift forces at relatively low drag, when moving in a certain speed range. Due to this ability, hydrofoils and their derivatives are commonly used as control and propulsive devices, e.g., as rudders, fins, and propeller sections. In the second half of the last century, hydrofoils found broad applications on fast boats, such as passenger ferries and military ships (McLeavy 1976; Matveev & Duncan 2005). These craft were able to achieve high speeds at lift–drag ratios (LDR) around 12–15, significantly higher than LDR of other hulls, such as planing boats. However, due to rather limited favorable operational conditions with regard to speed and payload, popularity of hydrofoils somewhat receded. One of drawbacks was that hydrofoils were usually made of metal alloys, thus being relatively heavy and difficult to service.
{"title":"Numerical Modeling of Surface-Piercing Flexible Hydrofoils in Waves","authors":"M. Wheeler, K. Matveev","doi":"10.5957/josr.07200046","DOIUrl":"https://doi.org/10.5957/josr.07200046","url":null,"abstract":"\u0000 \u0000 Hydrofoils made of metal alloys were broadly used on high-speed boats in the past. Nowadays, much lighter hydrofoils made of composite materials are finding increasingly more applications on sailing yachts and powerboats. However, these hydrofoils are usually rather flexible, and their design requires computationally demanding analysis, involving hydroelastic calculations. In this study, exploratory high-fidelity simulations have been carried out for surface-piercing hydrofoils in unsteady conditions with help of a computational fluid dynamics solver for fluid flow coupled with a finite element solver for the foil structure. To model unsteady foil deformations, the morphing mesh approach was utilized, and the volume-of-fluid method was applied for multiphase flow simulations. The computational setup, as well as verification and validation study, is described in this paper. Three hydrofoils of different stiffness, including a perfectly rigid foil, were simulated in both calm water conditions and regular head waves. Representative examples of foil deflections and wave patterns, as well as time-dependent structural and hydrodynamic characteristics, are presented.\u0000 \u0000 \u0000 \u0000 Hydrofoils are efficient lift-generating devices intended for application in water flows. Hydrofoils have streamlined shapes, and when operating at small incidence angles, they can produce high lift forces at relatively low drag, when moving in a certain speed range. Due to this ability, hydrofoils and their derivatives are commonly used as control and propulsive devices, e.g., as rudders, fins, and propeller sections.\u0000 In the second half of the last century, hydrofoils found broad applications on fast boats, such as passenger ferries and military ships (McLeavy 1976; Matveev & Duncan 2005). These craft were able to achieve high speeds at lift–drag ratios (LDR) around 12–15, significantly higher than LDR of other hulls, such as planing boats. However, due to rather limited favorable operational conditions with regard to speed and payload, popularity of hydrofoils somewhat receded. One of drawbacks was that hydrofoils were usually made of metal alloys, thus being relatively heavy and difficult to service.\u0000","PeriodicalId":50052,"journal":{"name":"Journal of Ship Research","volume":" ","pages":""},"PeriodicalIF":1.4,"publicationDate":"2019-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49130244","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Two models of underwater gliders were tested in a wind tunnel: one corresponding to a legacy shape commonly used in contemporary vehicles and the other a scaled down version of a new design. Performance of the two vehicles was characterized over a range of speeds and angles of attack. Particular attention was paid to the effect of sharp features along the hulls of the two vehicles and how they affect the observed flow regime. It has been shown that the new design, which uses a bow shape designed to encourage natural laminar flow, benefits from a 10% reduction of parasitic drag and 13% increase in lift-to-drag when the hull surface is smooth. The legacy glider, made up of a faired bow and a cylindrical hull, suffers from laminar separation and up to 100% increase in induced drag if the flow over its bow is prevented from transitioning to a turbulent state before encountering adverse pressure gradient at lower Reynolds numbers. This results in lowering of attainable speed at shallow glide path angles, whereas the associated parasitic drag reduction is demonstrated to increase the maximum velocity of the glider when moving at glide slopes greater than approximately 30°. Underwater gliders are autonomous underwater vehicles (AUVs) that rely on using a buoyancy engine to ascend or descend through the water column, and by adjusting their pitch, they can use this vertical motion to develop forward thrust from their hydrofoils. This propulsion method allows them to undertake long-endurance missions, often several months long (Eriksen 2003; Rudnick et al. 2004; Graver 2005). Hydrodynamic performance of an underwater glider is primarily governed by its lift-to-drag (L/D) ratio, which dictates the minimum glide path angle the vehicle may adopt, and drag coefficient, which affects the maximum forward speed the glider may achieve for a fixed amount of vertical force developed (Graver 2005). It is thus important to minimize the drag of the AUV to allow it to perform longer deployments and gather more science data without increasing the size of the engine. Because of the typical Reynolds numbers on the vehicle hulls being less than 106 and of the order of 104–5 on the appendages, laminar and transitional flow regions may occur. Correctly identifying these is critical to achieve a robust performance prediction.
{"title":"Characterizing Influence of Transition to Turbulence on the Propulsive Performance of Underwater Gliders","authors":"A. Lidtke, S. Turnock, J. Downes","doi":"10.5957/JOSR.09180050","DOIUrl":"https://doi.org/10.5957/JOSR.09180050","url":null,"abstract":"Two models of underwater gliders were tested in a wind tunnel: one corresponding to a legacy shape commonly used in contemporary vehicles and the other a scaled down version of a new design. Performance of the two vehicles was characterized over a range of speeds and angles of attack. Particular attention was paid to the effect of sharp features along the hulls of the two vehicles and how they affect the observed flow regime. It has been shown that the new design, which uses a bow shape designed to encourage natural laminar flow, benefits from a 10% reduction of parasitic drag and 13% increase in lift-to-drag when the hull surface is smooth. The legacy glider, made up of a faired bow and a cylindrical hull, suffers from laminar separation and up to 100% increase in induced drag if the flow over its bow is prevented from transitioning to a turbulent state before encountering adverse pressure gradient at lower Reynolds numbers. This results in lowering of attainable speed at shallow glide path angles, whereas the associated parasitic drag reduction is demonstrated to increase the maximum velocity of the glider when moving at glide slopes greater than approximately 30°.\u0000 \u0000 \u0000 Underwater gliders are autonomous underwater vehicles (AUVs) that rely on using a buoyancy engine to ascend or descend through the water column, and by adjusting their pitch, they can use this vertical motion to develop forward thrust from their hydrofoils. This propulsion method allows them to undertake long-endurance missions, often several months long (Eriksen 2003; Rudnick et al. 2004; Graver 2005).\u0000 Hydrodynamic performance of an underwater glider is primarily governed by its lift-to-drag (L/D) ratio, which dictates the minimum glide path angle the vehicle may adopt, and drag coefficient, which affects the maximum forward speed the glider may achieve for a fixed amount of vertical force developed (Graver 2005). It is thus important to minimize the drag of the AUV to allow it to perform longer deployments and gather more science data without increasing the size of the engine. Because of the typical Reynolds numbers on the vehicle hulls being less than 106 and of the order of 104–5 on the appendages, laminar and transitional flow regions may occur. Correctly identifying these is critical to achieve a robust performance prediction.\u0000","PeriodicalId":50052,"journal":{"name":"Journal of Ship Research","volume":" ","pages":""},"PeriodicalIF":1.4,"publicationDate":"2019-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45322767","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
High-speed ships often experience over larger ship motions in waves. Therefore, highspeed ships without motion control hardly have practical commercial values. Recent years saw wider adoptions of T-foils on high-speed ships, which greatly improve ship performances in waves. In this study, we designed a series of model tests to study the motion-reducing effects of T-foils in waves. Heaves, pitches, and bow accelerations are quantities to be measured in the experimental tests. The study shows that the reduction effects of T-foil-controlled longitudinal motions of a trimaran model are prominent. Comparing with naked model tests, it is found that active T-foil controls may reduce motions of trimaran ships in irregular waves by about 20–30%. In the most favorable case, the reduction is as high as 51%. This study shows that installation of T-foils may dramatically reduce the motions and, thus, provide an efficient control tool to mitigate ship motions in waves. The main aims of the present study were to provide an experimental setup for model testing of an active T-foil control system and determine the control equations. Although the control and actuation systems designed in this study are simple, they do produce the required effects. The model-tested control equations can be used for high-speed foil-type ship design directly if proper similarity ratios are used to project the model test results to real ships. Increasing the length-to-beam ratio is one of the most effective ways to reduce wave-making resistance so that high speed can be achieved (Ackers et al. 1998). High-speed ships with very slender hulls are, however, not stable. Placing two small side hulls on the port and starboard with displacements less than 10% of the total ship displacements improves the ship's stability greatly. This simple consideration led to the fast development of trimaran hull forms in recent years (Coppola & Mandarino 2001; Degiuli et al. 2003; Oh et al. 2005). Encouraged by the successful sea trials of the 127-m-long littoral combat ship Independence at the speed of 50 knots, researchers move forward to search for new technology to improve the motion performances of trimaran hull forms in waves (Li et al. 2002; Hebblewhite et al. 2007; Jia et al. 2009). This is because high-speed ships are faced with the big challenge of severe oscillations in waves. Too large motion responses in waves would counterbalance the high-speed benefits. Therefore, motion control is crucial for high-speed trimaran ships.
{"title":"Experimental Study of Active T-Foil Control of Longitudinal Motions of a Trimaran Hull in Irregular Waves","authors":"Z. Zong, Yifang Sun, Yichen Jiang","doi":"10.5957/JOSR.05180020","DOIUrl":"https://doi.org/10.5957/JOSR.05180020","url":null,"abstract":"High-speed ships often experience over larger ship motions in waves. Therefore, highspeed ships without motion control hardly have practical commercial values. Recent years saw wider adoptions of T-foils on high-speed ships, which greatly improve ship performances in waves. In this study, we designed a series of model tests to study the motion-reducing effects of T-foils in waves. Heaves, pitches, and bow accelerations are quantities to be measured in the experimental tests. The study shows that the reduction effects of T-foil-controlled longitudinal motions of a trimaran model are prominent. Comparing with naked model tests, it is found that active T-foil controls may reduce motions of trimaran ships in irregular waves by about 20–30%. In the most favorable case, the reduction is as high as 51%. This study shows that installation of T-foils may dramatically reduce the motions and, thus, provide an efficient control tool to mitigate ship motions in waves. The main aims of the present study were to provide an experimental setup for model testing of an active T-foil control system and determine the control equations. Although the control and actuation systems designed in this study are simple, they do produce the required effects. The model-tested control equations can be used for high-speed foil-type ship design directly if proper similarity ratios are used to project the model test results to real ships.\u0000 \u0000 \u0000 Increasing the length-to-beam ratio is one of the most effective ways to reduce wave-making resistance so that high speed can be achieved (Ackers et al. 1998). High-speed ships with very slender hulls are, however, not stable. Placing two small side hulls on the port and starboard with displacements less than 10% of the total ship displacements improves the ship's stability greatly. This simple consideration led to the fast development of trimaran hull forms in recent years (Coppola & Mandarino 2001; Degiuli et al. 2003; Oh et al. 2005). Encouraged by the successful sea trials of the 127-m-long littoral combat ship Independence at the speed of 50 knots, researchers move forward to search for new technology to improve the motion performances of trimaran hull forms in waves (Li et al. 2002; Hebblewhite et al. 2007; Jia et al. 2009). This is because high-speed ships are faced with the big challenge of severe oscillations in waves. Too large motion responses in waves would counterbalance the high-speed benefits. Therefore, motion control is crucial for high-speed trimaran ships.\u0000","PeriodicalId":50052,"journal":{"name":"Journal of Ship Research","volume":" ","pages":""},"PeriodicalIF":1.4,"publicationDate":"2019-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42318964","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
E. L. Castro-Feliciano, Jing Sun, A. Troesch, M. Collette
This case study presents a novel insight into the design of a codesigned planing craft with an active control system (ACS), along with its potential advantages and disadvantages when compared with a traditionally designed vessel (i.e., a vessel whose geometry is first selected, and then its ACS is implemented). This work has three purposes:present tools a designer can use to codesign a planing craft with its ACS,use these tools to expand the design space and further explore the potential of codesign, andinvestigate the feasibility of having a planing craft with ACS designed to the codesign results found in 2) and compare it with a traditionally designed vessel. The vessel particulars that are numerically optimized are the beam, dead rise, longitudinal center of gravity (lcg), and two tuning parameters for the ACS's linear quadratic regulator. In the case study, the codesigned vessel had 4% lower drag at the design speed and Sea State (SS) 3, but on lower SS's it had drag savings of 10% and seakeeping improvements of around 40% for the investigated seakeeping metric. The case study suggests that although the codesigned vessel is technically feasible, it would require unconventional hull/deck design—a result which emphasizes the importance of considering the coupling between a planing craft and its ACS early in the concept design. In search for a better performing planing craft, a naval architect could consider using an active control system (ACS) on their designs. Although they will encounter published research confirming performance improvements when an ACS is used (Wang 1985; Savitsky 2003; Xi & Sun 2006; Kays et al. 2009; Engle et al. 2011; Hughes & Weems 2011; Rijkens et al. 2011; Shimozono & Kays 2011; Rijkens 2013), literature addressing the concept design process of a planing craft that will have an ACS is, to the best of the authors' knowledge, limited only to the previous work by the authors (Castro-Feliciano et al. 2016, 2018). The work by Castro-Feliciano et al. (2016, 2018) suggests that the benefit from codesigning (as opposed to sequentially designing the vessel geometry and later adding an ACS) can be significant and should be the design methodology followed when designing a planing craft that will have an ACS.
{"title":"Codesign Case Study of a Planing Craft with Active Control Systems","authors":"E. L. Castro-Feliciano, Jing Sun, A. Troesch, M. Collette","doi":"10.5957/JOSR.05170028","DOIUrl":"https://doi.org/10.5957/JOSR.05170028","url":null,"abstract":"This case study presents a novel insight into the design of a codesigned planing craft with an active control system (ACS), along with its potential advantages and disadvantages when compared with a traditionally designed vessel (i.e., a vessel whose geometry is first selected, and then its ACS is implemented). This work has three purposes:present tools a designer can use to codesign a planing craft with its ACS,use these tools to expand the design space and further explore the potential of codesign, andinvestigate the feasibility of having a planing craft with ACS designed to the codesign results found in 2) and compare it with a traditionally designed vessel.\u0000 The vessel particulars that are numerically optimized are the beam, dead rise, longitudinal center of gravity (lcg), and two tuning parameters for the ACS's linear quadratic regulator. In the case study, the codesigned vessel had 4% lower drag at the design speed and Sea State (SS) 3, but on lower SS's it had drag savings of 10% and seakeeping improvements of around 40% for the investigated seakeeping metric. The case study suggests that although the codesigned vessel is technically feasible, it would require unconventional hull/deck design—a result which emphasizes the importance of considering the coupling between a planing craft and its ACS early in the concept design.\u0000 \u0000 \u0000 In search for a better performing planing craft, a naval architect could consider using an active control system (ACS) on their designs. Although they will encounter published research confirming performance improvements when an ACS is used (Wang 1985; Savitsky 2003; Xi & Sun 2006; Kays et al. 2009; Engle et al. 2011; Hughes & Weems 2011; Rijkens et al. 2011; Shimozono & Kays 2011; Rijkens 2013), literature addressing the concept design process of a planing craft that will have an ACS is, to the best of the authors' knowledge, limited only to the previous work by the authors (Castro-Feliciano et al. 2016, 2018). The work by Castro-Feliciano et al. (2016, 2018) suggests that the benefit from codesigning (as opposed to sequentially designing the vessel geometry and later adding an ACS) can be significant and should be the design methodology followed when designing a planing craft that will have an ACS.\u0000","PeriodicalId":50052,"journal":{"name":"Journal of Ship Research","volume":" ","pages":""},"PeriodicalIF":1.4,"publicationDate":"2019-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48198792","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The sloshing phenomenon in a partially loaded oil tanker or liquid natural gas ship is a typical fluid-structure interaction problem involving multi-physics, violent free-surface flow, and nonlinear structural response. In the past decades, the complex phenomenon has been commonly investigated without consideration of the hydro-elastic behaviors of the bulkheads. In our previous work, the liquid sloshing phenomenon in a two-dimensional (2-D) elastic tank was numerically studied. However, the bulkheads of the tank will deform within the three-dimensional (3-D) space in reality. So, it is necessary to study the 3-D sloshing problem in an elastic tank. In this article, a hybrid approach is developed within the Lagrangian system. The moving particle semiimplicit (MPS) method is used to simulate the evolution of 3-D flow with a violent free surface, and the finite element method (FEM) is used for the numerical analysis of structural response due to the impact loads of the sloshing flow. To couple the MPS method and the FEM method, an interpolation scheme based on the kernel function of the particle method is proposed for the communication on the isomerous interface between the fluid and structure domains. The reliability of force and deformation interpolation modules is validated by two tests. Then, the sloshing phenomenon in a 3-D elastic tank is numerically investigated and compared against the previous published 2-D results. By varying the Young's modulus of the tank walls, characteristics regarding the evolutions of free surface, variation of impact pressures, and dynamic responses of the structures are presented. To support the transportation demands of natural resources, more and more vessels, such as the very large crude carriers and the liquid natural gas carriers, are manufactured. For these huge structures, risks such as local deformation or even damage of cargo-containment systems resulting from sloshing phenomena subsequently increase. Therefore, it is necessary to take the elasticity of the tank walls into account in the research of sloshing phenomena (Dias & Ghidaglia 2018). However, the phenomena involving the vibrations of the tank walls are complex. In the process of sloshing wave interacting with elastic bulkheads, the fragmentation, splash, and fusion of water are observed. Meanwhile, the structures vibrate nonlinearly under the impact loads resulting from the sloshing wave. These phenomena are hard to simulate realistically by the traditional mesh-based methods.
{"title":"Numerical Study of 3-D Liquid Sloshing in an Elastic Tank by MPS-FEM Coupled Method","authors":"Xiang Chen, You-lin Zhang, D. Wan","doi":"10.5957/JOSR.09180082","DOIUrl":"https://doi.org/10.5957/JOSR.09180082","url":null,"abstract":"The sloshing phenomenon in a partially loaded oil tanker or liquid natural gas ship is a typical fluid-structure interaction problem involving multi-physics, violent free-surface flow, and nonlinear structural response. In the past decades, the complex phenomenon has been commonly investigated without consideration of the hydro-elastic behaviors of the bulkheads. In our previous work, the liquid sloshing phenomenon in a two-dimensional (2-D) elastic tank was numerically studied. However, the bulkheads of the tank will deform within the three-dimensional (3-D) space in reality. So, it is necessary to study the 3-D sloshing problem in an elastic tank. In this article, a hybrid approach is developed within the Lagrangian system. The moving particle semiimplicit (MPS) method is used to simulate the evolution of 3-D flow with a violent free surface, and the finite element method (FEM) is used for the numerical analysis of structural response due to the impact loads of the sloshing flow. To couple the MPS method and the FEM method, an interpolation scheme based on the kernel function of the particle method is proposed for the communication on the isomerous interface between the fluid and structure domains. The reliability of force and deformation interpolation modules is validated by two tests. Then, the sloshing phenomenon in a 3-D elastic tank is numerically investigated and compared against the previous published 2-D results. By varying the Young's modulus of the tank walls, characteristics regarding the evolutions of free surface, variation of impact pressures, and dynamic responses of the structures are presented.\u0000 \u0000 \u0000 To support the transportation demands of natural resources, more and more vessels, such as the very large crude carriers and the liquid natural gas carriers, are manufactured. For these huge structures, risks such as local deformation or even damage of cargo-containment systems resulting from sloshing phenomena subsequently increase. Therefore, it is necessary to take the elasticity of the tank walls into account in the research of sloshing phenomena (Dias & Ghidaglia 2018). However, the phenomena involving the vibrations of the tank walls are complex. In the process of sloshing wave interacting with elastic bulkheads, the fragmentation, splash, and fusion of water are observed. Meanwhile, the structures vibrate nonlinearly under the impact loads resulting from the sloshing wave. These phenomena are hard to simulate realistically by the traditional mesh-based methods.\u0000","PeriodicalId":50052,"journal":{"name":"Journal of Ship Research","volume":" ","pages":""},"PeriodicalIF":1.4,"publicationDate":"2019-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43576388","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
An Wang, Hyun-Tae Kim, Kit Pan Wong, Miao Yu, K. Kiger, J. Duncan
The oblique impact of a flexible and a nearly rigid plate on a quiescent water surface is studied experimentally. Both plates are 122 cm long by 38 cm wide and are mounted with a 5° upward pitch angle and a 10° lateral roll angle. The plates are attached to a dual-axis instrument carriage. The horizontal and vertical components of the carriage (plate) motion are driven by servo motors and controlled by a single computer-based feedback system, which is set with a single trajectory that is traversed for all impact speeds. The transient strain at multiple locations on the upper surface of the plate is measured with optical fiber Bragg grating sensors and the out-of-plane deformation is measured with a photographic method. A cinematic laser-induced fluorescence technique is used to measure the water spray generated during the impact. Two types of spray are observed and several aspects of the spray behavior are found to be noticeably affected by the deformation of the plate. The maximum deflection along the plate's upper long edge is found to increase almost linearly with impact velocity. In rough seas, planing boats moving at high speed frequently slam into the water surface. The slamming process involves large highly transient pressures and forces on the hull, rapid accelerations of the boat and the water, the generation of water spray, and significant structural responses. This phenomenon is difficult to study numerically and experimentally because of the large motions of the hull and the violent motions of the water free surface, including the formation of spray sheets and the structural responses coupled with the flow dynamics. The problem of slamming (water entry) has received significant attention in the past. Many of the previous studies on this subject examine fundamental problems, such as the impact of a wedge or a flat plate on water surface. Some early theoretical studies on the water entry of a rigid wedge include, e.g., Von Karman (1929) and Wagner (1932). Wagner's model considers the water rising adjacent to the surface of a vertically moving wedge with small deadrise angle. This model was later extended to higher order (e.g., Oliver 2007) and other geometries (e.g., Howison et al. 1991). Based on Wagner's theory, Dobrovol'Skaya (1969) derived a similarity solution to the water entry of a wedge and the solution at small deadrise angles (down to 4°) was computed numerically by Zhao and Faltinsen (1993) using a nonlinear boundary element method. De Divitiis and de Socio (2002) studied the water entry of symmetric and asymmetric wedges. In their method, the flow field is represented by potential flow singularities whose intensities are determined as part of the solution. Moore et al. (2012) did a numerical study of normal and oblique water entry of a threedimensional rigid body with its bottom surface nearly parallel to the water surface.
{"title":"Spray Formation and Structural Deformation During the Oblique Impact of a Flexible Plate on a Quiescent Water Surface","authors":"An Wang, Hyun-Tae Kim, Kit Pan Wong, Miao Yu, K. Kiger, J. Duncan","doi":"10.5957/JOSR.10180093","DOIUrl":"https://doi.org/10.5957/JOSR.10180093","url":null,"abstract":"The oblique impact of a flexible and a nearly rigid plate on a quiescent water surface is studied experimentally. Both plates are 122 cm long by 38 cm wide and are mounted with a 5° upward pitch angle and a 10° lateral roll angle. The plates are attached to a dual-axis instrument carriage. The horizontal and vertical components of the carriage (plate) motion are driven by servo motors and controlled by a single computer-based feedback system, which is set with a single trajectory that is traversed for all impact speeds. The transient strain at multiple locations on the upper surface of the plate is measured with optical fiber Bragg grating sensors and the out-of-plane deformation is measured with a photographic method. A cinematic laser-induced fluorescence technique is used to measure the water spray generated during the impact. Two types of spray are observed and several aspects of the spray behavior are found to be noticeably affected by the deformation of the plate. The maximum deflection along the plate's upper long edge is found to increase almost linearly with impact velocity.\u0000 \u0000 \u0000 In rough seas, planing boats moving at high speed frequently slam into the water surface. The slamming process involves large highly transient pressures and forces on the hull, rapid accelerations of the boat and the water, the generation of water spray, and significant structural responses. This phenomenon is difficult to study numerically and experimentally because of the large motions of the hull and the violent motions of the water free surface, including the formation of spray sheets and the structural responses coupled with the flow dynamics.\u0000 The problem of slamming (water entry) has received significant attention in the past. Many of the previous studies on this subject examine fundamental problems, such as the impact of a wedge or a flat plate on water surface. Some early theoretical studies on the water entry of a rigid wedge include, e.g., Von Karman (1929) and Wagner (1932). Wagner's model considers the water rising adjacent to the surface of a vertically moving wedge with small deadrise angle. This model was later extended to higher order (e.g., Oliver 2007) and other geometries (e.g., Howison et al. 1991). Based on Wagner's theory, Dobrovol'Skaya (1969) derived a similarity solution to the water entry of a wedge and the solution at small deadrise angles (down to 4°) was computed numerically by Zhao and Faltinsen (1993) using a nonlinear boundary element method. De Divitiis and de Socio (2002) studied the water entry of symmetric and asymmetric wedges. In their method, the flow field is represented by potential flow singularities whose intensities are determined as part of the solution. Moore et al. (2012) did a numerical study of normal and oblique water entry of a threedimensional rigid body with its bottom surface nearly parallel to the water surface.\u0000","PeriodicalId":50052,"journal":{"name":"Journal of Ship Research","volume":" ","pages":""},"PeriodicalIF":1.4,"publicationDate":"2019-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49220330","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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