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Numerical models to simulate underwater turbine noise levels
Title
Numerical models to simulate underwater turbine noise levels.
Creator
Lippert, Renee'., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
This work incorporates previous work done by Guerra and the application of fluid dynamics. The structure attached to the turbine will cause unsteady fluctuations in the flow, and ultimately affect the acoustic pressure. The work of Guerra is based on a lot of assumptions and simplifications to the geometry of the turbine and structure. This work takes the geometry of the actual turbine, and uses computational fluid dynamic software to numerically model the flow around the turbine structure....
Show moreThis work incorporates previous work done by Guerra and the application of fluid dynamics. The structure attached to the turbine will cause unsteady fluctuations in the flow, and ultimately affect the acoustic pressure. The work of Guerra is based on a lot of assumptions and simplifications to the geometry of the turbine and structure. This work takes the geometry of the actual turbine, and uses computational fluid dynamic software to numerically model the flow around the turbine structure. Varying the angle of the attack altered the results, and as the angle increased the noise levels along with the sound pulse, and unsteady loading increased. Increasing the number of blades and reducing the chord length both reduced the unsteady loading.
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Date Issued
2012
PURL
http://purl.flvc.org/FAU/3355622
Subject Headings
Underwater acoustics, Mathematical models, Turbines, Vibration, Mathematical models, Fluid dynamics
Format
Document (PDF)
Detection, localization, and identification of bearings with raceway defect for a dynamometer using high frequency modal analysis of vibration across an array of accelerometers
Title
Detection, localization, and identification of bearings with raceway defect for a dynamometer using high frequency modal analysis of vibration across an array of accelerometers.
Creator
Waters, Nicholas., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
This thesis describes a method to detect, localize and identify a faulty bearing in a rotating machine using narrow band envelope analysis across an array of accelerometers. This technique is developed as part of the machine monitoring system of an ocean turbine. A rudimentary mathematical model is introduced to provide an understanding of the physics governing the vibrations caused by a bearing with a raceway defect. This method is then used to detect a faulty bearing in two setups : on a...
Show moreThis thesis describes a method to detect, localize and identify a faulty bearing in a rotating machine using narrow band envelope analysis across an array of accelerometers. This technique is developed as part of the machine monitoring system of an ocean turbine. A rudimentary mathematical model is introduced to provide an understanding of the physics governing the vibrations caused by a bearing with a raceway defect. This method is then used to detect a faulty bearing in two setups : on a lathe and in a dynamometer.
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Date Issued
2012
PURL
http://purl.flvc.org/FAU/3359156
Subject Headings
Marine turbines, Mathematical models, Vibration, Measurement, Fluid dynamics, Dynamic testing
Format
Document (PDF)
GALLOPING OF AN ELASTICALLY SUPPORTED BLUFF BODY IN TURBULENT FLOW
Title
GALLOPING OF AN ELASTICALLY SUPPORTED BLUFF BODY IN TURBULENT FLOW.
Creator
Li, Qiang, Florida Atlantic University, Lin, Y. K., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
The phenomenon of flow-induced vibration is found in many engineering systems. The fluid flow generates forces on the structure that cause motion of the structure. In turn, the structural motion changes the angle of attack between the flow and the structure, hence the forces on the structure. Furthermore, turbulence generally exists in a natural fluid flow; namely, the fluid velocity contains a random part. Thus, the problem is formulated as a nonlinear system under random excitations. This...
Show moreThe phenomenon of flow-induced vibration is found in many engineering systems. The fluid flow generates forces on the structure that cause motion of the structure. In turn, the structural motion changes the angle of attack between the flow and the structure, hence the forces on the structure. Furthermore, turbulence generally exists in a natural fluid flow; namely, the fluid velocity contains a random part. Thus, the problem is formulated as a nonlinear system under random excitations. This thesis is focused on one type of motion known as galloping. A mathematical model for the motion of an elastically supported square cylinder in turbulent flow is developed. The physical nonlinear equation is converted to ideal stochastic differential equations of the Ito type using the stochastic averaging method. The probability density for the motion amplitude and the values for the most probable amplitudes are obtained for various mean flow velocities and turbulence levels.
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Date Issued
1987
PURL
http://purl.flvc.org/fcla/dt/14361
Subject Headings
Random vibration--Mathematical models, Turbulence, Fluid dynamics
Format
Document (PDF)
Convex identification and nonlinear random vibration analysis of elastic and viscoelastic structures
Title
Convex identification and nonlinear random vibration analysis of elastic and viscoelastic structures.
Creator
Fang, Jianjie, Florida Atlantic University, Elishakoff, Isaac, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
This dissertation deals with the identification of boundary conditions of elastic structures, and nonlinear random vibration analysis of elastic and viscoelastic structures through a new energy-based equivalent linearization technique. In the part of convex identification, convex models are utilized to represent the degree of uncertainty in the boundary condition modification. This means that the identification is actually the identification of the convex model to which the actual boundary...
Show moreThis dissertation deals with the identification of boundary conditions of elastic structures, and nonlinear random vibration analysis of elastic and viscoelastic structures through a new energy-based equivalent linearization technique. In the part of convex identification, convex models are utilized to represent the degree of uncertainty in the boundary condition modification. This means that the identification is actually the identification of the convex model to which the actual boundary stiffness profile belongs. Two examples are presented to illustrate the application of the method. For the beam example the finite element analysis is performed to evaluate the frequencies of a beam with any specific boundary conditions. For the plate example, the Bolotin's dynamic edge effect method, generalized by Elishakoff, is employed to determine the approximate natural frequencies and normal modes of elastically supported isotropic, uniform rectangular plates. In the part of nonlinear random analysis, first a systematic finite element analysis procedure, based on the element's energy formulation, through conventional stochastic linearization technique, is proposed. The procedure is applicable to a wide range of nonlinear random vibration problem as long as element's energy formulations are presented. Secondly, the new energy-based stochastic linearization method in finite element analysis setting is developed to improve the conventional stochastic linearization technique. The entire formulation is produced in detail for the first time. The theory is applied to beam problem subjected to space-wise and time-wise white noise excitations. Finally, the new energy-based stochastic linearization technique is applied to treat nonlinear vibration problems of viscoelastic beams.
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Date Issued
1996
PURL
http://purl.flvc.org/fcla/dt/12467
Subject Headings
Elasticity, Viscoelasticity, Structural dynamics--Mathematical models, Vibration--Mathematical models
Format
Document (PDF)
Analysis of ship hull and plate vibrations caused by wave forces
Title
Analysis of ship hull and plate vibrations caused by wave forces.
Creator
Lakitosh, Fnu, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
In the present dissertation, the hydrodynamic and hydro-elastic characteristics of ship hull and plate vibrations are analyzed using theoretical and numerical methods. The wave forces are determined using a suite of methods which include the Froude-Krylov method for incident wave forces, Wagner's method and ABS rules for the slamming wave force, and numerical methods for nonlinear wave radiation forces. Finite difference methods are developed to determine the wave forced vibrations of ship...
Show moreIn the present dissertation, the hydrodynamic and hydro-elastic characteristics of ship hull and plate vibrations are analyzed using theoretical and numerical methods. The wave forces are determined using a suite of methods which include the Froude-Krylov method for incident wave forces, Wagner's method and ABS rules for the slamming wave force, and numerical methods for nonlinear wave radiation forces. Finite difference methods are developed to determine the wave forced vibrations of ship hull plates which are modeled using a range of plate theories including nonlinear plate theory with and without material damping and orthotropic plate theory for stiffened hull plates. For small amplitude deformation of thin plates, a semi-theoretical superposition method is used to determine the free and forced vibrations. The transient ship hull vibration due to whipping is also analyzed using the finite difference method. Results, in the form of deformations and stress distributions, are obtained for a range of scantling and wave parameters to identify key parameters to consider in ship structural design.
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Date Issued
2012
PURL
http://purl.flvc.org/FAU/3342196
Subject Headings
Vibration (Marine engineering), Hulls (Naval architecture), Ships, Hydraulic impact, Ocean waves, Mathematical models, Fluid dynamics, Mathematical models
Format
Document (PDF)
Dissipation and eddy mixing associated with flow past an underwater turbine
Title
Dissipation and eddy mixing associated with flow past an underwater turbine.
Creator
Reza, Zaqie, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
The objective of this thesis is to analyze the flow past an ocean current turbine using a finite volume Navier-Stokes CFD solver. A full 3-D RANS approach in a moving reference frame is used to model the flow. By employing periodic boundary conditions, one-third of the flow-field is analyzed and the output is replicated to other sectors. Following validation of the computation with an experimental study, the flow fields and particle paths for the case of uniform and sheared incoming flows...
Show moreThe objective of this thesis is to analyze the flow past an ocean current turbine using a finite volume Navier-Stokes CFD solver. A full 3-D RANS approach in a moving reference frame is used to model the flow. By employing periodic boundary conditions, one-third of the flow-field is analyzed and the output is replicated to other sectors. Following validation of the computation with an experimental study, the flow fields and particle paths for the case of uniform and sheared incoming flows past a generic turbine with various blade pitch angles are evaluated and analyzed. Flow field and wake expansion are visualized. Eddy viscosity effects and its dependence on flow field conditions are investigated.
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Date Issued
2010
PURL
http://purl.flvc.org/FAU/2683537
Subject Headings
Vibration (Aerodynamics), Fine element method, Marine turbines, Mathematical models, Water currents, Forecasting, Computational fluid dynamics
Format
Document (PDF)
Vibration analysis for ocean turbine reliability models
Title
Vibration analysis for ocean turbine reliability models.
Creator
Wald, Randall David., College of Engineering and Computer Science, Department of Computer and Electrical Engineering and Computer Science
Abstract/Description
Submerged turbines which harvest energy from ocean currents are an important potential energy resource, but their harsh and remote environment demands an automated system for machine condition monitoring and prognostic health monitoring (MCM/PHM). For building MCM/PHM models, vibration sensor data is among the most useful (because it can show abnormal behavior which has yet to cause damage) and the most challenging (because due to its waveform nature, frequency bands must be extracted from...
Show moreSubmerged turbines which harvest energy from ocean currents are an important potential energy resource, but their harsh and remote environment demands an automated system for machine condition monitoring and prognostic health monitoring (MCM/PHM). For building MCM/PHM models, vibration sensor data is among the most useful (because it can show abnormal behavior which has yet to cause damage) and the most challenging (because due to its waveform nature, frequency bands must be extracted from the signal). To perform the necessary analysis of the vibration signals, which may arrive rapidly in the form of data streams, we develop three new wavelet-based transforms (the Streaming Wavelet Transform, Short-Time Wavelet Packet Decomposition, and Streaming Wavelet Packet Decomposition) and propose modifications to the existing Short-TIme Wavelet Transform. ... The proposed algorithms also create and select frequency-band features which focus on the areas of the signal most important to MCM/PHM, producing only the information necessary for building models (or removing all unnecessary information) so models can run on less powerful hardware. Finally, we demonstrate models which can work in multiple environmental conditions. ... Our results show that many of the transforms give similar results in terms of performance, but their different properties as to time complexity, ability to operate in a fully streaming fashion, and number of generated features may make some more appropriate than others in particular applications, such as when streaming data or hardware limitations are extremely important (e.g., ocean turbine MCM/PHM).
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Date Issued
2012
PURL
http://purl.flvc.org/FAU/3359158
Subject Headings
Marine turbines, Mathematical models, Fluid dynamics, Structural dynamics, Vibration, Measurement, Stochastic processes
Format
Document (PDF)
Vibration, buckling and impact of carbon nanotubes
Title
Vibration, buckling and impact of carbon nanotubes.
Creator
Pentaras, Demetris., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
Natural frequencies of the double and triple-walled carbon nanotubes are determined exactly and approximately for both types. Approximate solutions are found by using Bubnov-Galerkin and Petrov-Galerkin methods. For the first time explicit expressions are obtained for the natural frequencies of double and triple-walled carbon nanotubes for different combinations of boundary conditions. Comparison of the results with recent studies shows that the above methods constitute quick and effective...
Show moreNatural frequencies of the double and triple-walled carbon nanotubes are determined exactly and approximately for both types. Approximate solutions are found by using Bubnov-Galerkin and Petrov-Galerkin methods. For the first time explicit expressions are obtained for the natural frequencies of double and triple-walled carbon nanotubes for different combinations of boundary conditions. Comparison of the results with recent studies shows that the above methods constitute quick and effective alternative techniques to exact solution for studying the vibration properties of carbon nanotubes. The natural frequencies of the clamped-clamped double-walled carbon nanotubes are obtained; exact solution is provided and compared with the solution reported in the literature. In contrast to earlier investigation, an analytical criterion is derived to establish the behavior of the roots of the characteristic equation. Approximate Bubnov-Galerkin solution is also obtained to compare natural frequencies at the lower end of the spectrum. Simplified version of the Bresse-Timoshenko theory that incorporates the shear deformation and the rotary inertia is proposed for free vibration study of double-walled carbon nanotubes. It is demonstrated that the suggested set yields extremely accurate results for the lower spectrum of double-walled carbon nanotube. The natural frequencies of double-walled carbon nanotubes based on simplified versions of Donnell shell theory are also obtained. The buckling behavior of the double-walled carbon nanotubes under various boundary conditions is studied. First, the case of the simply supported double-walled carbon nanotubes at both ends is considered which is amenable to exact solution., Then, approximate methods of Bubnov-Galerkin and Petrov-Galerkin are utilized to check the efficacy of these approximations for the simply supported double-walled carbon nanotubes. Once the extreme accuracy is demonstrated for simply supported conditions, the approximate techniques are applied to two other cases of the boundary conditions, namely to clamped-clamped and simply supported-clamped double-walled carbon nanotubes. For the first time in the literature approximate expression for the buckling loads are reported for these boundary conditions. The dynamic deflection of a single-walled carbon nanotube under impact loading is analyzed by following a recently study reported on the energy absorption capacity of carbon nanotubes under ballistic impact.
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Date Issued
2009
PURL
http://purl.flvc.org/FAU/186764
Subject Headings
Nanostructured materials, Buckling (Mechanics), Plates (Engineering), Vibration, Mathematical models, Structural analysis
Format
Document (PDF)
Vibration tailoring of inhomogeneous beams and circular plates
Title
Vibration tailoring of inhomogeneous beams and circular plates.
Creator
Pentaras, Demetris., Florida Atlantic University, Elishakoff, Isaac, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
The vibrational behavior of inhomogeneous beams and circular plates is studied, utilizing the semi-inverse method developed by I. Elishakoff and extensively discussed in his recent monograph (2005). The main thread of his methodology is that the knowledge of the mode shape is postulated. The candidate mode shapes can be adopted from relevant static, dynamic or buckling problems. In this study, the exact mode shapes are sought as polynomial functions, in the context of vibration tailoring, i.e...
Show moreThe vibrational behavior of inhomogeneous beams and circular plates is studied, utilizing the semi-inverse method developed by I. Elishakoff and extensively discussed in his recent monograph (2005). The main thread of his methodology is that the knowledge of the mode shape is postulated. The candidate mode shapes can be adopted from relevant static, dynamic or buckling problems. In this study, the exact mode shapes are sought as polynomial functions, in the context of vibration tailoring, i.e. designing the structure that possesses the pre-specified value. Apparently for the first time in the literature, several closed-form solutions for vibration tailoring have been derived for vibrating inhomogeneous beams and circular plates. Twelve new closed-form solutions for vibration tailoring have been derived for an inhomogeneous polar orthotropic plate that is either clamped or simply supported around its circumference. Also, the vibration tailoring of a polar orthotropic circular plate with translational spring is analyzed. There is considerable potential of utilizing the developed method for design of functionally graded materials.
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Date Issued
2006
PURL
http://purl.flvc.org/fcla/dt/13344
Subject Headings
Acoustical engineering, Plates (Engineering)--Vibration--Mathematical models, Buckling (Mechanics), Structural analysis
Format
Document (PDF)
Rain-wind-induced cable vibrations in cable-stayed bridges
Title
Rain-wind-induced cable vibrations in cable-stayed bridges.
Creator
Calle, Oscar F., Reddy, Dronnadula V., Florida Atlantic University, College of Engineering and Computer Science, Department of Civil, Environmental and Geomatics Engineering
Abstract/Description
This research is aimed at investigating and analyzing the rain-windinduced cable vibration phenomena experienced in cables of cable-stayed bridges and also the countermeasures employed by engineers to mitigate the large-amplitude vibration problem reported by various researchers around the world. In order to investigate the problem of the water rivulet creation at the top of the cable surface, a single-degree-of-freedom (SDOF) analytical model was developed and analyzed. This thesis studies...
Show moreThis research is aimed at investigating and analyzing the rain-windinduced cable vibration phenomena experienced in cables of cable-stayed bridges and also the countermeasures employed by engineers to mitigate the large-amplitude vibration problem reported by various researchers around the world. In order to investigate the problem of the water rivulet creation at the top of the cable surface, a single-degree-of-freedom (SDOF) analytical model was developed and analyzed. This thesis studies the aerodynamic instability of cables in cable-stayed bridges by doing literature review of a typical in-situ test, developing a single degree-of-freedom (SDOF) analytical model, and an ANSYS finite element model. Furthermore, a linear viscous damper that acts as a countermeasure to the large amplitudes of vibration is reported and analyzed. The suppression characteristics and damper effectiveness of such countermeasure are summarized.
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Date Issued
2014
PURL
http://purl.flvc.org/fau/fd/FA00004271, http://purl.flvc.org/fau/fd/FA00004271
Subject Headings
Bridges -- Aerodynamics, Bridges -- Vibration -- Prevention, Cable stayed bridges -- Maintenance and repair, Damping (Mechanics), Structural dynamics, Vibration -- Mathematical models, Wind resistant design
Format
Document (PDF)