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We propose and validate a novel experimental technique to measure two-point statistics of turbulent flows. It consists of spreading rigid fibers in the flow and tracking their position and orientation in time and is therefore named “fiber tracking velocimetry.” By choosing different fiber lengths, i.e., within the inertial or dissipative range of scales, the statistics of turbulence fluctuations at the selected length scale can be probed accurately by simply measuring the fiber velocity at its two ends and projecting it along the transverse-to-fiber direction. By means of fully resolved direct numerical simulations and experiments, we show that these fiber-based transverse velocity increments are statistically equivalent to the (unperturbed) flow transverse velocity increments. Moreover, we show that the turbulent energy-dissipation rate can be accurately measured exploiting sufficiently short fibers. The technique is tested against standard particle tracking velocimetry (PTV) of flow tracers with excellent agreement. Our technique overcomes the well-known problem of PTV to probe two-point statistics reliably because of the fast relative diffusion in turbulence that prevents the mutual distance between particles to remain constant at the length scale of interest. This problem, making it difficult to obtain converged statistics for a fixed separation distance, is even more dramatic for natural flows in open domains. A prominent example is oceanic currents, where drifters (i.e., the tracer-particle counterpart used in field measurements) disperse quickly, but at the same time their number has to be limited to save costs. Inspired by our laboratory experiments, we propose pairs of connected drifters as a viable option to solve the issue., source:https://journals.aps.org/prx/abstract/10.1103/PhysRevX.11.031060

Thesis: Nav. E., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017., Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017., Cataloged from PDF version of thesis., Includes bibliographical references (pages 49-50)., The fluid-dynamic design of hydrofoils to support marine crafts at high speeds has received growing interest in recent years. Physics involved in the design of high-speed surface-piercing hydrofoils is complex involving three different fluid phases (air, water and vapor) and complex fluid dynamic mechanisms like unsteady cavitation and ventilation and their interaction. For speeds considerably higher than the incipient cavitation speed, the hydrofoil sections need to be adapted and design to exploit cavitation instead of avoiding it. This is particularly true for surface piercing hydrofoils that in addition to cavitation are affected by ventilation from the free surface. This thesis presents main results of an investigation into the relative formation of ventilation and cavitation regions of surface piercing super cavitating hydrofoils (SPSCHs), with special attention to the effects of cavitation number. A series of 3D multi-phase Reynold Averaged Navier-Stokes Equation (RANSE) simulations of varying cavitation number reveal the dependence of the ventilation and cavitation regions on the cavitation number, angle of attack, and distance from the free surface. The RANSE simulations are validated against an analytical estimate based on an appropriate lifting line method at near zero cavitation numbers, and against empirical results obtained through tow tank testing at higher cavitation numbers. The analytical and empirical validation bound the range of cavitation numbers considered in this study from [sigma]= 0.05 to [sigma]= 2.37., by Timothy Spaulding Dutton., Nav. E., S.M.

Thesis: Nav. E., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017., Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017., Cataloged from PDF version of thesis., Includes bibliographical references (pages 95-98)., Traditional propellers operate fully submerged, with cavitation limited as much as possible in order to minimize its disruptive and damaging consequences. Conversely, supercavitating propellers operate in an encompassing vapor cavity, thereby averting these negative effects while substantially reducing drag on the blades. Surface-piercing propellers, operating under a similar concept as supercavitation, often achieve even greater efficiency by drawing in an air cavity from the free surface. Existing small craft have demonstrated the ability of such propellers to yield extremely high speeds (110+ knots); nevertheless, the full potential of these propellers has yet to be explored. In particular, designs often neglect low-speed performance, focusing solely on high-speed operation. This research therefore developed a new surface-piercing propeller concept designed instead to maximize performance across the spectrum of operating speeds. Applying established theory for supercavitating hydrofoils, the new blades were shaped based on theoretical maximally-efficient two-dimensional profile sections. Furthermore, in order to affect the low-speed performance enhancement, the trailing edge of each profile was appended with a unique "tail" form that allows the blade to resemble a traditional propeller when operating at subcavitating speeds without sacrificing supercavitating performance. The design used an existing racing propeller as a baseline for comparison, matching certain characteristics (rotational speed, advance speed, number of blades, hub size) in order to ensure equivalent operating conditions. Computational fluid dynamics (CFD) of the 2D profiles informed changes to the profile shapes until lift-to-drag (L/D) was maximized while ensuring a fully-encompassing vapor cavity. The complete propeller was drafted from these optimized radial sections for full 3D CFD analysis. Results from both the 2D and 3D CFD simulations revealed promising benefits to propulsive efficiency, by Justin Richard Parker., Nav. E., S.M.

Thesis: Nav. E., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017., Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017., Cataloged from PDF version of thesis., Includes bibliographical references (pages 95-98)., Traditional propellers operate fully submerged, with cavitation limited as much as possible in order to minimize its disruptive and damaging consequences. Conversely, supercavitating propellers operate in an encompassing vapor cavity, thereby averting these negative effects while substantially reducing drag on the blades. Surface-piercing propellers, operating under a similar concept as supercavitation, often achieve even greater efficiency by drawing in an air cavity from the free surface. Existing small craft have demonstrated the ability of such propellers to yield extremely high speeds (110+ knots); nevertheless, the full potential of these propellers has yet to be explored. In particular, designs often neglect low-speed performance, focusing solely on high-speed operation. This research therefore developed a new surface-piercing propeller concept designed instead to maximize performance across the spectrum of operating speeds. Applying established theory for supercavitating hydrofoils, the new blades were shaped based on theoretical maximally-efficient two-dimensional profile sections. Furthermore, in order to affect the low-speed performance enhancement, the trailing edge of each profile was appended with a unique "tail" form that allows the blade to resemble a traditional propeller when operating at subcavitating speeds without sacrificing supercavitating performance. The design used an existing racing propeller as a baseline for comparison, matching certain characteristics (rotational speed, advance speed, number of blades, hub size) in order to ensure equivalent operating conditions. Computational fluid dynamics (CFD) of the 2D profiles informed changes to the profile shapes until lift-to-drag (L/D) was maximized while ensuring a fully-encompassing vapor cavity. The complete propeller was drafted from these optimized radial sections for full 3D CFD analysis. Results from both the 2D and 3D CFD simulations revealed promising benefits to propulsive efficiency, by Justin Richard Parker., Nav. E., S.M.

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017., Cataloged from PDF version of thesis., Includes bibliographical references (pages 111-115)., Efficient design of energy converters heavily depends on the capacity of the designer to accurately predict the device's dynamic, which ultimately leads to the power extraction. This is specially true for wave energy converters (WEC), which usually present a high cost per kWh generated. In this thesis a particular WEC which uses a rotating mass for power extraction is studied. A numerical model for the prediction of its motion and power extraction is presented. The nonlinear dynamic model consists of a time-domain three dimensional Rankine panel method coupled, in the time integration, with a MATLAB algorithm which solves for the equations of the gyroscope and Power Take-Off (PTO). The former acts as a force block, calculating the forces due to the waves on the hull, which is then sent to the latter through TCP/IP, which couples the external dynamics and performs the time-integration using a 4th order Runge-Kutta method. With the proposed code, two case studies are examined. The first consists of two gyroscopes, rotating in opposite directions, to negate undesirable yaw effects on the WEC's hull. The device's optimum PTO damping value and flywheel spin are then shown, which change for different sea states. The second is a comparison against results from experimental testing of a 1:50 model at the Davidson Laboratory during the Wave Energy Prize., by João Seixas de Medeiros., S.M.

Thesis: S.M. in Mechanical Engineering, Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015., Thesis: S.M. in Naval Architecture and Marine Engineering, Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015., Cataloged from PDF version of thesis., Includes bibliographical references (pages 73-74)., With emerging applications for high speed boats in commercial, military and off shore industries, there is a focus in the naval architecture community to improve the efficiency and performance characteristics of planing hulls. In the 1960's, Eugene Clement showed that considerable reductions in resistance at high speeds can be obtained by converting a conventional planing hull to a Dynaplane stepped planing hull. A Dynaplane stepped planing hull refers to a hull configuration where the majority of lift is provided by a swept back cambered surface, while the remainder of the lift is provided by an aft lifting surface that also provides trim control and stability. The afterbody is fully ventilated by use of a V-shaped step positioned at the trailing edge of the cambered surface. Clement's semi-empirical conversion method was based off tests performed at the David Taylor Model Basin and is limited to boats with a deadrise of less than 15°. Since the publication of his paper, advancements in CFD programs have made it possible to conduct accurate simulations of planing hulls with complex geometry, allowing for further development of Clement's method. This thesis expands Clement's method to high deadrise by applying it to a notional version of the Mark V Special Operations Craft used by the United States Navy with a design speed of 55kts. CFD simulations with fixed trim were run in order to refine the cambered surface, design the step and afterbody, to position the hydrofoil and to test the low speed performance of the interceptor. Once the hull design was finalized, simulations with two degrees of freedom were run to assess the dynamic stability of the hull. Through simulations, it was found that the configuration is dynamically stable and is able to reduce hull resistance at design speed by as much as 54% when compared with that of the original hull., by Calley Dawn Gray., S.M. in Mechanical Engineering, S.M. in Naval Architecture and Marine Engineering

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017., Cataloged from PDF version of thesis., Includes bibliographical references (pages 80-82)., The hybrid hydrofoil/SWATH, designed and patented by Stefano Brizzolara, is a novel vehicle design that is optimized to operate in both a high speed foilborne mode and a displacement mode. The retractable hydrofoils on the vehicle take on a unique four surface piercing anhedral foil configuration. This foilborne design is previously unassessed for stability and maneuvering characteristics. A six degree of freedom model of the foilborne vehicle dynamics is introduced as a framework to study vehicle stability and maneuvering. Linearized models of the vehicle dynamics are compared to the six degree of freedom results in both the vertical and horizontal planes. Foil configuration design criteria are derived for pitch equilibrium as well as pitch and directional stability. A method for turning the vehicle by rotationally actuating the foil dihedral angles is introduced, and the vehicle state in the unsteady and steady portion of the turn is simulated., by Samuel E. Williams., S.M.

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017., Cataloged from PDF version of thesis., Includes bibliographical references (pages 111-115)., Efficient design of energy converters heavily depends on the capacity of the designer to accurately predict the device's dynamic, which ultimately leads to the power extraction. This is specially true for wave energy converters (WEC), which usually present a high cost per kWh generated. In this thesis a particular WEC which uses a rotating mass for power extraction is studied. A numerical model for the prediction of its motion and power extraction is presented. The nonlinear dynamic model consists of a time-domain three dimensional Rankine panel method coupled, in the time integration, with a MATLAB algorithm which solves for the equations of the gyroscope and Power Take-Off (PTO). The former acts as a force block, calculating the forces due to the waves on the hull, which is then sent to the latter through TCP/IP, which couples the external dynamics and performs the time-integration using a 4th order Runge-Kutta method. With the proposed code, two case studies are examined. The first consists of two gyroscopes, rotating in opposite directions, to negate undesirable yaw effects on the WEC's hull. The device's optimum PTO damping value and flywheel spin are then shown, which change for different sea states. The second is a comparison against results from experimental testing of a 1:50 model at the Davidson Laboratory during the Wave Energy Prize., by João Seixas de Medeiros., S.M.

Thesis: S.M. in Mechanical Engineering, Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015., Thesis: S.M. in Naval Architecture and Marine Engineering, Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015., Cataloged from PDF version of thesis., Includes bibliographical references (pages 73-74)., With emerging applications for high speed boats in commercial, military and off shore industries, there is a focus in the naval architecture community to improve the efficiency and performance characteristics of planing hulls. In the 1960's, Eugene Clement showed that considerable reductions in resistance at high speeds can be obtained by converting a conventional planing hull to a Dynaplane stepped planing hull. A Dynaplane stepped planing hull refers to a hull configuration where the majority of lift is provided by a swept back cambered surface, while the remainder of the lift is provided by an aft lifting surface that also provides trim control and stability. The afterbody is fully ventilated by use of a V-shaped step positioned at the trailing edge of the cambered surface. Clement's semi-empirical conversion method was based off tests performed at the David Taylor Model Basin and is limited to boats with a deadrise of less than 15°. Since the publication of his paper, advancements in CFD programs have made it possible to conduct accurate simulations of planing hulls with complex geometry, allowing for further development of Clement's method. This thesis expands Clement's method to high deadrise by applying it to a notional version of the Mark V Special Operations Craft used by the United States Navy with a design speed of 55kts. CFD simulations with fixed trim were run in order to refine the cambered surface, design the step and afterbody, to position the hydrofoil and to test the low speed performance of the interceptor. Once the hull design was finalized, simulations with two degrees of freedom were run to assess the dynamic stability of the hull. Through simulations, it was found that the configuration is dynamically stable and is able to reduce hull resistance at design speed by as much as 54% when compared with that of the original hull., by Calley Dawn Gray., S.M. in Mechanical Engineering, S.M. in Naval Architecture and Marine Engineering

Thesis: Nav. E., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015., Thesis: S.M. in System Design and Management, Massachusetts Institute of Technology, Engineering Systems Division, System Design and Management Program, 2015., Cataloged from PDF version of thesis., Includes bibliographical references (pages 157-158)., As part of a 2014 thesis, the MIT Innovative Ship Laboratory (iShip) designed a high-speed planing hull form that was based on the Model Variant 5631 developed at the US Navy's David Taylor Model Basin [7] [3] [5]. This model was a variant of the parent hull 5628. The 5631 variant was a model of the 47 foot Motor Lifeboat of the US Coast Guard, which was a hard chine, deep-vee vessel. Model 5631 had no step, with a 20 degree dead rise angle. The Clement method [4] was used in order to design a cambered planing surface that would generate dynamic lift and support most of the weight of the vessel. A second cambered step was designed using an in-house lifting surface program. The step was designed such that, at top speed, the entire hull aft of the step would be ventilated. To accommodate this effect, the aft underbody design departed from the conventional dead-rise. Directional stability of the model in the pre-planing regime was increased by incorporating three vertices at the design dead-rise angle. A set of super-cavitating, surface-piercing hydrofoils were designed to be attached aft of the vessel transom in order to provide support and prevent re-wetting of the afterbody. The constructed hydrofoils were positioned in a vee configuration, differing from the anhedral design in the Faison thesis. A support manual control system for the hydrofoils was designed as part of this thesis. Known as Model 5631D, this dynaplane model underwent a series of tests at the 380 foot towing tank at the United States Naval Academy in Annapolis, Maryland, over the course of several days. Several parameters were varied during the tests: the cambered step (via the wedge insert), the carriage speed, and the model longitudinal center of gravity (LCG). In this thesis, data from the series of tests of Model 5631D will be compared to that of the tests of Model 5631 by combining methods from Savitsky [15] and Faltinsen [8] for data scaling of planing vessels. Both models were scaled to the s, by Matthew Joseph Williams., Nav. E., S.M. in System Design and Management

Thesis: Nav. E., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015., Thesis: S.M. in System Design and Management, Massachusetts Institute of Technology, Engineering Systems Division, System Design and Management Program, 2015., Cataloged from PDF version of thesis., Includes bibliographical references (pages 157-158)., As part of a 2014 thesis, the MIT Innovative Ship Laboratory (iShip) designed a high-speed planing hull form that was based on the Model Variant 5631 developed at the US Navy's David Taylor Model Basin [7] [3] [5]. This model was a variant of the parent hull 5628. The 5631 variant was a model of the 47 foot Motor Lifeboat of the US Coast Guard, which was a hard chine, deep-vee vessel. Model 5631 had no step, with a 20 degree dead rise angle. The Clement method [4] was used in order to design a cambered planing surface that would generate dynamic lift and support most of the weight of the vessel. A second cambered step was designed using an in-house lifting surface program. The step was designed such that, at top speed, the entire hull aft of the step would be ventilated. To accommodate this effect, the aft underbody design departed from the conventional dead-rise. Directional stability of the model in the pre-planing regime was increased by incorporating three vertices at the design dead-rise angle. A set of super-cavitating, surface-piercing hydrofoils were designed to be attached aft of the vessel transom in order to provide support and prevent re-wetting of the afterbody. The constructed hydrofoils were positioned in a vee configuration, differing from the anhedral design in the Faison thesis. A support manual control system for the hydrofoils was designed as part of this thesis. Known as Model 5631D, this dynaplane model underwent a series of tests at the 380 foot towing tank at the United States Naval Academy in Annapolis, Maryland, over the course of several days. Several parameters were varied during the tests: the cambered step (via the wedge insert), the carriage speed, and the model longitudinal center of gravity (LCG). In this thesis, data from the series of tests of Model 5631D will be compared to that of the tests of Model 5631 by combining methods from Savitsky [15] and Faltinsen [8] for data scaling of planing vessels. Both models were scaled to the s, by Matthew Joseph Williams., Nav. E., S.M. in System Design and Management

Thesis: Nav. E., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015., Thesis: S.M. in System Design and Management, Massachusetts Institute of Technology, Engineering Systems Division, System Design and Management Program, 2015., Cataloged from PDF version of thesis., Includes bibliographical references (pages 157-158)., As part of a 2014 thesis, the MIT Innovative Ship Laboratory (iShip) designed a high-speed planing hull form that was based on the Model Variant 5631 developed at the US Navy's David Taylor Model Basin [7] [3] [5]. This model was a variant of the parent hull 5628. The 5631 variant was a model of the 47 foot Motor Lifeboat of the US Coast Guard, which was a hard chine, deep-vee vessel. Model 5631 had no step, with a 20 degree dead rise angle. The Clement method [4] was used in order to design a cambered planing surface that would generate dynamic lift and support most of the weight of the vessel. A second cambered step was designed using an in-house lifting surface program. The step was designed such that, at top speed, the entire hull aft of the step would be ventilated. To accommodate this effect, the aft underbody design departed from the conventional dead-rise. Directional stability of the model in the pre-planing regime was increased by incorporating three vertices at the design dead-rise angle. A set of super-cavitating, surface-piercing hydrofoils were designed to be attached aft of the vessel transom in order to provide support and prevent re-wetting of the afterbody. The constructed hydrofoils were positioned in a vee configuration, differing from the anhedral design in the Faison thesis. A support manual control system for the hydrofoils was designed as part of this thesis. Known as Model 5631D, this dynaplane model underwent a series of tests at the 380 foot towing tank at the United States Naval Academy in Annapolis, Maryland, over the course of several days. Several parameters were varied during the tests: the cambered step (via the wedge insert), the carriage speed, and the model longitudinal center of gravity (LCG). In this thesis, data from the series of tests of Model 5631D will be compared to that of the tests of Model 5631 by combining methods from Savitsky [15] and Faltinsen [8] for data scaling of planing vessels. Both models were scaled to the s, by Matthew Joseph Williams., Nav. E., S.M. in System Design and Management

Thesis: S.M. in Naval Architecture and Marine Engineering, Massachusetts Institute of Technology. Department of Mechanical Engineering, 2015., Cataloged from PDF version of thesis., Includes bibliographical references (pages 85-86)., This thesis aims to give a contribution to the design of heavily loaded marine propellers by numerical methods. In this work, a wake-adapted, fully numerical, lifting line model is used to obtain the optimum circulation distribution along the propeller's blade via variational method, presented by Coney [9]. In this context, two approaches to the representation of the wake field are compared: the first approach utilizes Betz's condition for moderately loaded propellers, in which the wake is aligned with the hydrodynamic pitch angle. The second approach, in which the wake is aligned with the local velocities, utilizes Kutta's Law to create a zero-lift wake surface. A thorough comparison of the influence of the effect of tip vortex roll-up is done. A lifting surface method with fully aligned wake is developed and used to correct the optimum distribution of pitch and camber obtained by the new lifting line method. The resulting geometries, operating under heavily-loaded conditions, are submitted to a preliminary analysis in a boundary element-based potential flow code to verify the consistency of the results. This analysis confirms the better results obtained with the fully numerical lifting line model and the variations between the approaches in terms of circulation and pitch angle observed in the lifting line results are verified. Finally, the performance of propeller geometries generated with the approaches studied in this work are compared by high fidelity RANSE analysis. The CFD simulations confirm the higher accuracy of the method in which the wake geometry is aligned with the local velocities in terms of fulfillment of thrust requirement., by Giovani Diniz., S.M. in Naval Architecture and Marine Engineering

Thesis: Nav. E., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015., Thesis: S.M. in Ocean Engineering, Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015., This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections., Title as it appears in MIT Commencement Exercises program, June 5, 2015: Numerical and experimental investigation of non-linear seakeeping effect for inverted bow shapes. Cataloged from student-submitted PDF version of thesis., Includes bibliographical references (pages 147-148)., In this paper we investigate the resistance and seakeeping effects of an inverted bow by comparing the motions of an existing combatant hull, the Oliver Hazard Perry class frigate (FFG-7), with a modified version of the same hull with an inverted bow. The bow of the FFG-7 was redesigned by developing a set of basic curves that define the parametric surface of the new shape. Two 1/80th scale models were built, one of the original and one of the inverted bow frigate, with the same material, machining and finishing standards. Model tests were conducted in the United States Naval Academy Hydromechanics Laboratory for resistance in calm water and seakeeping in both regular waves and irregular head seas. The differences between the FFG-7 and the inverted bow responses are characterized in terms of pitch, heave, and vertical accelerations. A numerical verification and experimental validation of the seakeeping code Aegir was conducted using the inverted bow., by Jeffrey Kensett White., Nav. E., S.M. in Ocean Engineering

Thesis: Nav. E., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015., Thesis: S.M. in System Design and Management, Massachusetts Institute of Technology, Engineering Systems Division, System Design and Management Program, 2015., Cataloged from PDF version of thesis., Includes bibliographical references (pages 157-158)., As part of a 2014 thesis, the MIT Innovative Ship Laboratory (iShip) designed a high-speed planing hull form that was based on the Model Variant 5631 developed at the US Navy's David Taylor Model Basin [7] [3] [5]. This model was a variant of the parent hull 5628. The 5631 variant was a model of the 47 foot Motor Lifeboat of the US Coast Guard, which was a hard chine, deep-vee vessel. Model 5631 had no step, with a 20 degree dead rise angle. The Clement method [4] was used in order to design a cambered planing surface that would generate dynamic lift and support most of the weight of the vessel. A second cambered step was designed using an in-house lifting surface program. The step was designed such that, at top speed, the entire hull aft of the step would be ventilated. To accommodate this effect, the aft underbody design departed from the conventional dead-rise. Directional stability of the model in the pre-planing regime was increased by incorporating three vertices at the design dead-rise angle. A set of super-cavitating, surface-piercing hydrofoils were designed to be attached aft of the vessel transom in order to provide support and prevent re-wetting of the afterbody. The constructed hydrofoils were positioned in a vee configuration, differing from the anhedral design in the Faison thesis. A support manual control system for the hydrofoils was designed as part of this thesis. Known as Model 5631D, this dynaplane model underwent a series of tests at the 380 foot towing tank at the United States Naval Academy in Annapolis, Maryland, over the course of several days. Several parameters were varied during the tests: the cambered step (via the wedge insert), the carriage speed, and the model longitudinal center of gravity (LCG). In this thesis, data from the series of tests of Model 5631D will be compared to that of the tests of Model 5631 by combining methods from Savitsky [15] and Faltinsen [8] for data scaling of planing vessels. Both models were scaled to the s, by Matthew Joseph Williams., Nav. E., S.M. in System Design and Management

Thesis: S.B. in Mechanical Engineering and Ocean Engineering, Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015., Cataloged from PDF version of thesis., Includes bibliographical references (page 15)., The vertical structure of swash-zone flows and turbulence, which is critical to sediment transport and flooding due to over-topping of dunes, will be examined using a Smoothed Particle Hydrodynamics model (DualSPHysics) evaluated with field observations obtained near La Jolla, CA in fall 2003. The mesh-free model is based on the Lagrangian description of fluid particle motion, and is capable of tracking free surfaces with discontinuities, moving boundaries, and large deformations; such as those in plunging waves and hydraulic jumps that occur when a swash backwash collides with the following uprush. The model is initialized with a flat sea surface and the measured beach profile and is forced at the offshore boundary with waves observed in 5 m water depth. The model is used to simulate the cross-shore and vertical structure of wave orbital motions, turbulence, and time-mean flows across the surf zone to the swash zone over 10 min periods. Model simulations are compared with field observations of waves and mean flows collected near the bed in 2.5, 1.5, and 1.0 m water depths and at 5 locations in the swash zone. Offshore significant waves heights ranged from 0.5 m to 1.5 m and cross-shore velocities in the surf and swash were up to 0.8 in/s. Model-data comparisons will be presented, the dependence of simulations on free parameters such as smoothing length, distance between particles, and artificial viscosity will be described, and the simulated flows and turbulence will be discussed., by Mary Munro., S.B. in Mechanical Engineering and Ocean Engineering

Thesis: Nav. E., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015., Thesis: S.M. in System Design and Management, Massachusetts Institute of Technology, Engineering Systems Division, System Design and Management Program, 2015., Cataloged from PDF version of thesis., Includes bibliographical references (pages 157-158)., As part of a 2014 thesis, the MIT Innovative Ship Laboratory (iShip) designed a high-speed planing hull form that was based on the Model Variant 5631 developed at the US Navy's David Taylor Model Basin [7] [3] [5]. This model was a variant of the parent hull 5628. The 5631 variant was a model of the 47 foot Motor Lifeboat of the US Coast Guard, which was a hard chine, deep-vee vessel. Model 5631 had no step, with a 20 degree dead rise angle. The Clement method [4] was used in order to design a cambered planing surface that would generate dynamic lift and support most of the weight of the vessel. A second cambered step was designed using an in-house lifting surface program. The step was designed such that, at top speed, the entire hull aft of the step would be ventilated. To accommodate this effect, the aft underbody design departed from the conventional dead-rise. Directional stability of the model in the pre-planing regime was increased by incorporating three vertices at the design dead-rise angle. A set of super-cavitating, surface-piercing hydrofoils were designed to be attached aft of the vessel transom in order to provide support and prevent re-wetting of the afterbody. The constructed hydrofoils were positioned in a vee configuration, differing from the anhedral design in the Faison thesis. A support manual control system for the hydrofoils was designed as part of this thesis. Known as Model 5631D, this dynaplane model underwent a series of tests at the 380 foot towing tank at the United States Naval Academy in Annapolis, Maryland, over the course of several days. Several parameters were varied during the tests: the cambered step (via the wedge insert), the carriage speed, and the model longitudinal center of gravity (LCG). In this thesis, data from the series of tests of Model 5631D will be compared to that of the tests of Model 5631 by combining methods from Savitsky [15] and Faltinsen [8] for data scaling of planing vessels. Both models were scaled to the s, by Matthew Joseph Williams., Nav. E., S.M. in System Design and Management

Thesis: S.B. in Mechanical Engineering and Ocean Engineering, Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015., Cataloged from PDF version of thesis., Includes bibliographical references (page 15)., The vertical structure of swash-zone flows and turbulence, which is critical to sediment transport and flooding due to over-topping of dunes, will be examined using a Smoothed Particle Hydrodynamics model (DualSPHysics) evaluated with field observations obtained near La Jolla, CA in fall 2003. The mesh-free model is based on the Lagrangian description of fluid particle motion, and is capable of tracking free surfaces with discontinuities, moving boundaries, and large deformations; such as those in plunging waves and hydraulic jumps that occur when a swash backwash collides with the following uprush. The model is initialized with a flat sea surface and the measured beach profile and is forced at the offshore boundary with waves observed in 5 m water depth. The model is used to simulate the cross-shore and vertical structure of wave orbital motions, turbulence, and time-mean flows across the surf zone to the swash zone over 10 min periods. Model simulations are compared with field observations of waves and mean flows collected near the bed in 2.5, 1.5, and 1.0 m water depths and at 5 locations in the swash zone. Offshore significant waves heights ranged from 0.5 m to 1.5 m and cross-shore velocities in the surf and swash were up to 0.8 in/s. Model-data comparisons will be presented, the dependence of simulations on free parameters such as smoothing length, distance between particles, and artificial viscosity will be described, and the simulated flows and turbulence will be discussed., by Mary Munro., S.B. in Mechanical Engineering and Ocean Engineering

Thesis: S.M. in Naval Architecture and Marine Engineering; and S.M. in Mechanical Engineering , Massachusetts Institute of Technology, Department of Mechanical Engineering 2015, Cataloged from PDF version of thesis., Includes bibliographical references (pages 111-112)., Research on turbulence modeling in naval architecture has extensively increased in importance over the years and it is now considered one of the most important ways to accurately compute high Reynolds number flows with Reynolds Averaged Navier-Stokes Equations (RANSE) solvers. In naval architecture, turbulence models are necessary to solve typical hydrodynamic problems both in model scale, where Re=O(106), and in full scale, typically Re=O(108), since direct numerical simulations are not possible in these cases. This thesis aims to study the performance of different turbulence models to predict the laminar-turbulent transitional flow in the boundary layer of streamlined bodies. Starting with a systematic study on a flat plate and arriving to transitional flow airfoils like the NACA 651-213 a=0.5. The RANSE solver is built on the libraries of OpenFOAM(Open Field Operation and Manipulation) which is a free, open source CFD program which enables a large group of users to solve broad range of problems. Turbulence models considered range from one equation models such Spalart-Allmaras, two-equation models such as k-epsilon, k-omegaSST, three-equation model kkl-omega as RANS solvers, LES solvers and DES Solvers. The validation of OpenFoam based solver and the different turbulence models is made on the prediction of the friction and pressure drag components as well as lift predictions. In particular, the capability of the turbulent models to capture the transition between laminar and turbulent regime plays a vital role in engineering applications. Four different turbulence models are used in this scope: k-epsilon, k-omegaSST, Spalart- Allmaras and kkl-omega in conjunction with different wall functions. The flat plate case was simulated with all of these turbulence models by using the pimpleFoam transient solver and the hydrofoil case was tested with the kkl-omega and kOmegaSST models by using simpleFoam steady-state solver. The kkl-omega t.m. is one of the newest transition, by Mert Gokdepe., S.M.

Thesis: S.M. in Naval Architecture and Marine Engineering, Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015., Cataloged from PDF version of thesis., Includes bibliographical references (pages 121-123)., In ship design projects, it is of utmost importance to investigate a wide range of options during the concept design phase in order to determine which one best suits to the requirements. Although, keeping the concept design phase shorter in order to be competitive in the market is as important. The chances for a shipyard to win a contract would surely increase with a proposed design whose performances are demonstrated through a systematic evaluation of alternative solutions. However, the number of the design alternatives is inversely proportional to the time span of concept design for each alternative. The detailed evaluations at this stage can only be performed with CFD (Computational Fluid Dynamics) and FE (Finite Element) tools, and both require a complete representation of the ship hull geometry. So, only having a faster hull form generation tool would enable the designer to evaluate more options. It is possible to achieve rapid geometry generation through fully parametric modeling. Fully parametric hull modeling is the practice of creating the entire hull shape definition only from form parameters, without the need for offset data or predefined lines plan. In this thesis a fully parametric modeling tool, PHull, is developed using Java programming language for rapid geometry generation of high speed displacement monohulls, in order to be used in hydrodynamic optimization process. The results from the validation cases, FFG-7 and ATHENA Model 5365, are presented., Mert Timur., S.M. in Naval Architecture and Marine Engineering

Thesis (S.B. in Mechanical and Ocean Engineering)--Massachusetts Institute of Technology, Department of Mechanical Engineering, 2013., Cataloged from PDF version of thesis. Vita., Includes bibliographical references (page 26)., This paper describes the techniques used to fabricate a one meter long, 1/6 scale model of a Small Waterplane Area, Twin Hull (SWATH) Unmanned Surface Vehicle (USV) that will be used primarily for dynamic seakeeping testing in the MIT Tow Tank. The model represents a design conceived by Stefano Brizzolara, which will be used for launching, recovering, and servicing Unmanned Underwater Vehicles (UUV) at sea. Construction methods included a number of rapid prototyping methods rarely used for this kind of project, including 3D printing, lasercutting, and spraypainting. The benefits and disadvantages of each of these processes will be discussed. Although there was insufficient time to conduct any tow tank tests, several data-recording techniques are reviewed which may be used by future students continuing the research of this vessel., by John Robert DiMino., S.B.in Mechanical and Ocean Engineering

Thesis: S.M. in Naval Architecture and Marine Engineering, Massachusetts Institute of Technology, Department of Mechanical Engineering, 2013., Cataloged from PDF version of thesis., Includes bibliographical references (pages 75-76)., Before the detailed design of a new vessel a designer would like to explore the design space to identify an appropriate starting point for the concept design. The base design needs to be done at the preliminary design level with codes that execute fast to completely explore the design space. The intent of this thesis is to produce a preliminary design tool that will allow the designer to predict the total resistance and propeller wake for use in an optimization program, having total propulsive efficiency as an objective function. There exist design tools to predict the total resistance and propeller wake, but none that provide adequate computational times for the preliminary design stage. The tool developed uses a potential flow solution coupled with an integral boundary layer solver to predict the viscous resistance and propeller wake. The wave drag is calculated using a modified linear theory, thus eliminating the need to run fully three-dimensional free surface CFD codes. The tool developed is validated against published Series 60 test data., by Brian Johnson., S.M. in Naval Architecture and Marine Engineering