The ability to tailor the properties of structures made from composite materials gives designers ... more The ability to tailor the properties of structures made from composite materials gives designers new ways to improve their functionality. For example, the layup of a composite can be designed in such a way that elastic (e.g. bendtwist) couplings advantageously control how the shape and vibration characteristics of the structure changes under load. This ability to tailor composite materials is increasingly being used in marine propeller applications to improve their performance and control their vibration characteristics. However, designers face additional challenges when using these materials. The density of composites approaches that of water so fluid inertial effects become equal to or even greater than solid inertial effects. Moreover, the increased compliance of adaptive composite structures means that they can no longer be considered as approximately rigid, and flow-induced vibrations may develop. This means that load-dependent fluid-structure interaction effects must be unders...
A three-dimensional boundary element method is used for the numerical modeling of supercavitating... more A three-dimensional boundary element method is used for the numerical modeling of supercavitating propellers subjected to nonaxisymmetric in†ow. The method has been developed in the past for the prediction of unsteady sheet cavitation for conventional propellers. To allow for the treatment of supercavitating propellers, the method is extended to model the separated flow behind trailing edges with nonzero thickness. The convergence of the method is studied. Results from numerical validation, as well as comparisons of predictions with experimental measurements, are provided.
A three-dimensional low-order boundary element method is presented for the performance prediction... more A three-dimensional low-order boundary element method is presented for the performance prediction of surface-piercing propellers. The negative image method is used to account for free surface effects. Detachment locations of ventilated cavities are searched for iteratively using a modified smooth detachment condition. Results from parametric studies and validations with experimental measurements are shown.
In this work, a numerical method is presented for the hydrodynamic and hydroelastic analysis of N... more In this work, a numerical method is presented for the hydrodynamic and hydroelastic analysis of Newton-Rader (NR) propellers (Newton & Rader 1961). The NR propellers are a well-known series of three-bladed propellers specifically designed, extensively tested, and well documented for high-speed crafts. The tests were conducted at the Vosper Cavitation Tunnel, and the propellers exhibit both face and back cavitation patterns (Newton & Rader 1961). The predicted fully wetted and cavitating performance agreed well with experimental measurements. The results indicate that the NR propellers can achieve high efficiency in both the fully wetted and cavitating regimes if the blades exhibit only back cavitation. However, significant reduction in efficiency was observed in all cases when face cavitation develops. The effects of varying blade area ratio on the hydrodynamic and structural performance are discussed. The importance of hydroelastic effects for both model-scale and full-scale NR pro...
This paper investigates the novel concept of augmenting the maneuverability of underwater vehicle... more This paper investigates the novel concept of augmenting the maneuverability of underwater vehicles with cycloidal propellers. Cycloidal propellers have the potential of providing agile manoeuvring capabilities to an underwater vehicle such as enabling pure heave motion and spot turns. They will also enable the vehicle to surge in forward and backward directions with equal ease. Such manoeuvres are not possible with the more conventional screw propeller and control fin combinations. Moreover, cycloidal propellers can enable precise dynamic positioning in low speed applications like station-keeping, underwater surveying and maintenance, minesweeping and teaming activities. In this paper, manoeuvring capabilities of an underwater vehicle with conventional screw propeller and control fins only are compared with one augmented with cycloidal propellers. The cases considered include a turning circle manoeuvre, a low speed 180o turn and a low speed heave manoeuvre. A six degrees-of-freedom ...
The load dependent deformation responses and complex failure mechanisms of self-adaptive composit... more The load dependent deformation responses and complex failure mechanisms of self-adaptive composite propeller blades make the design, analysis, and scaling of these structures nontrivial. The objective of this work is to investigate and verify the dynamic similarity relationships for the hydroelastic response and potential failure mechanisms of self-adaptive composite marine propellers. A fully coupled, three-dimensional boundary element method-finite element method is used to compare the model and full-scale responses of a self-adaptive composite propeller. The effects of spatially varying inflow, transient sheet cavitation, and load-dependent blade deformation are considered. Three types of scaling are discussed: Reynolds scale, Froude scale, and Mach scale. The results show that Mach scaling, which requires the model inflow speed to be the same as the full scale, will lead to discrepancies in the spatial load distributions at low speeds due to differences in Froude number, but the...
ABSTRACT This work explores the idea of harvesting energy from ambient flows using flexible piezo... more ABSTRACT This work explores the idea of harvesting energy from ambient flows using flexible piezoelectric beams. Beams lose their stability and flutter above a critical length or flow speed or below a critical stiffness. During flutter, beams oscillate in increasing amplitude until they enter a self-sustained limit cycle oscillation, which could be exploited to harvest energy. The objectives of this study are to: (i) identify the flutter boundary of a flexible beam in viscous flow; (ii) explore the energy harvesting potential; and (iii) identify critical non-dimensional parameters and parametric relations that govern the response and stability of thin composite beams vibrating in a viscous fluid. Two-dimensional Navier-Stokes equations are solved with a nonlinear beam model coupled with a linear piezoelectric material constitutive model. The harvested energy potential for various solid/fluid combinations is investigated by varying the critical non-dimensional parameters, which are defined in terms of beam length, density, thickness, and stiffness; fluid speed and density; and piezoelectric material properties.
Journal of Offshore Mechanics and Arctic Engineering, Feb 1, 2010
The objective of this work is to develop and validate a coupled boundary element method-finite el... more The objective of this work is to develop and validate a coupled boundary element method-finite element method to simulate the transient fluid-structure interaction response of tidal turbines subject to spatially varying inflow. The focus is on tidal turbines, although the methodology is also applicable for the analysis and design of wind turbines. An overview of the formulation for both the fluid and solid domains, and the fluid-structure interaction algorithms, is presented. The model is validated by comparing the predicted thrust and power measurements, as well as cavitation patterns, with experimental measurements and observations for an 800 mm marine current turbine presented in the work of Bahaj et al. (2007, “Power and Thrust Measurements of Marine Current Turbines Under Various Hydrodynamic Flow Conditions in a Cavitation Tunnel and a Towing Tank,” Renewable Energy, 32, pp. 407–426). Additional numerical results are shown for the same turbine, but scaled up to 20 m in diameter, operating in a tidal boundary layer flow with a water depth of 30 m. The results show that transient cavitation will develop near the blade tip when the blades are near the free surface at highly-loaded off-design conditions, and the blades will undergo excessive deformation because of the high fluid loading and slender blade profile. The results also show that the natural frequencies of the blades are significantly reduced when operating in water, as compared with when operating in air, because of added-mass effects. In addition to demonstrating the need for proper consideration for fluid cavitation and structural response, current design challenges for both wind and tidal turbines are discussed.
The ability to tailor the properties of structures made from composite materials gives designers ... more The ability to tailor the properties of structures made from composite materials gives designers new ways to improve their functionality. For example, the layup of a composite can be designed in such a way that elastic (e.g. bendtwist) couplings advantageously control how the shape and vibration characteristics of the structure changes under load. This ability to tailor composite materials is increasingly being used in marine propeller applications to improve their performance and control their vibration characteristics. However, designers face additional challenges when using these materials. The density of composites approaches that of water so fluid inertial effects become equal to or even greater than solid inertial effects. Moreover, the increased compliance of adaptive composite structures means that they can no longer be considered as approximately rigid, and flow-induced vibrations may develop. This means that load-dependent fluid-structure interaction effects must be unders...
A three-dimensional boundary element method is used for the numerical modeling of supercavitating... more A three-dimensional boundary element method is used for the numerical modeling of supercavitating propellers subjected to nonaxisymmetric in†ow. The method has been developed in the past for the prediction of unsteady sheet cavitation for conventional propellers. To allow for the treatment of supercavitating propellers, the method is extended to model the separated flow behind trailing edges with nonzero thickness. The convergence of the method is studied. Results from numerical validation, as well as comparisons of predictions with experimental measurements, are provided.
A three-dimensional low-order boundary element method is presented for the performance prediction... more A three-dimensional low-order boundary element method is presented for the performance prediction of surface-piercing propellers. The negative image method is used to account for free surface effects. Detachment locations of ventilated cavities are searched for iteratively using a modified smooth detachment condition. Results from parametric studies and validations with experimental measurements are shown.
In this work, a numerical method is presented for the hydrodynamic and hydroelastic analysis of N... more In this work, a numerical method is presented for the hydrodynamic and hydroelastic analysis of Newton-Rader (NR) propellers (Newton & Rader 1961). The NR propellers are a well-known series of three-bladed propellers specifically designed, extensively tested, and well documented for high-speed crafts. The tests were conducted at the Vosper Cavitation Tunnel, and the propellers exhibit both face and back cavitation patterns (Newton & Rader 1961). The predicted fully wetted and cavitating performance agreed well with experimental measurements. The results indicate that the NR propellers can achieve high efficiency in both the fully wetted and cavitating regimes if the blades exhibit only back cavitation. However, significant reduction in efficiency was observed in all cases when face cavitation develops. The effects of varying blade area ratio on the hydrodynamic and structural performance are discussed. The importance of hydroelastic effects for both model-scale and full-scale NR pro...
This paper investigates the novel concept of augmenting the maneuverability of underwater vehicle... more This paper investigates the novel concept of augmenting the maneuverability of underwater vehicles with cycloidal propellers. Cycloidal propellers have the potential of providing agile manoeuvring capabilities to an underwater vehicle such as enabling pure heave motion and spot turns. They will also enable the vehicle to surge in forward and backward directions with equal ease. Such manoeuvres are not possible with the more conventional screw propeller and control fin combinations. Moreover, cycloidal propellers can enable precise dynamic positioning in low speed applications like station-keeping, underwater surveying and maintenance, minesweeping and teaming activities. In this paper, manoeuvring capabilities of an underwater vehicle with conventional screw propeller and control fins only are compared with one augmented with cycloidal propellers. The cases considered include a turning circle manoeuvre, a low speed 180o turn and a low speed heave manoeuvre. A six degrees-of-freedom ...
The load dependent deformation responses and complex failure mechanisms of self-adaptive composit... more The load dependent deformation responses and complex failure mechanisms of self-adaptive composite propeller blades make the design, analysis, and scaling of these structures nontrivial. The objective of this work is to investigate and verify the dynamic similarity relationships for the hydroelastic response and potential failure mechanisms of self-adaptive composite marine propellers. A fully coupled, three-dimensional boundary element method-finite element method is used to compare the model and full-scale responses of a self-adaptive composite propeller. The effects of spatially varying inflow, transient sheet cavitation, and load-dependent blade deformation are considered. Three types of scaling are discussed: Reynolds scale, Froude scale, and Mach scale. The results show that Mach scaling, which requires the model inflow speed to be the same as the full scale, will lead to discrepancies in the spatial load distributions at low speeds due to differences in Froude number, but the...
ABSTRACT This work explores the idea of harvesting energy from ambient flows using flexible piezo... more ABSTRACT This work explores the idea of harvesting energy from ambient flows using flexible piezoelectric beams. Beams lose their stability and flutter above a critical length or flow speed or below a critical stiffness. During flutter, beams oscillate in increasing amplitude until they enter a self-sustained limit cycle oscillation, which could be exploited to harvest energy. The objectives of this study are to: (i) identify the flutter boundary of a flexible beam in viscous flow; (ii) explore the energy harvesting potential; and (iii) identify critical non-dimensional parameters and parametric relations that govern the response and stability of thin composite beams vibrating in a viscous fluid. Two-dimensional Navier-Stokes equations are solved with a nonlinear beam model coupled with a linear piezoelectric material constitutive model. The harvested energy potential for various solid/fluid combinations is investigated by varying the critical non-dimensional parameters, which are defined in terms of beam length, density, thickness, and stiffness; fluid speed and density; and piezoelectric material properties.
Journal of Offshore Mechanics and Arctic Engineering, Feb 1, 2010
The objective of this work is to develop and validate a coupled boundary element method-finite el... more The objective of this work is to develop and validate a coupled boundary element method-finite element method to simulate the transient fluid-structure interaction response of tidal turbines subject to spatially varying inflow. The focus is on tidal turbines, although the methodology is also applicable for the analysis and design of wind turbines. An overview of the formulation for both the fluid and solid domains, and the fluid-structure interaction algorithms, is presented. The model is validated by comparing the predicted thrust and power measurements, as well as cavitation patterns, with experimental measurements and observations for an 800 mm marine current turbine presented in the work of Bahaj et al. (2007, “Power and Thrust Measurements of Marine Current Turbines Under Various Hydrodynamic Flow Conditions in a Cavitation Tunnel and a Towing Tank,” Renewable Energy, 32, pp. 407–426). Additional numerical results are shown for the same turbine, but scaled up to 20 m in diameter, operating in a tidal boundary layer flow with a water depth of 30 m. The results show that transient cavitation will develop near the blade tip when the blades are near the free surface at highly-loaded off-design conditions, and the blades will undergo excessive deformation because of the high fluid loading and slender blade profile. The results also show that the natural frequencies of the blades are significantly reduced when operating in water, as compared with when operating in air, because of added-mass effects. In addition to demonstrating the need for proper consideration for fluid cavitation and structural response, current design challenges for both wind and tidal turbines are discussed.
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