Current Search: Vibration  Mathematical models (x)
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 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.
Show less  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)
 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.
Show less  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)
 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 flowinduced 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 flowinduced 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.
Show less  Date Issued
 1987
 PURL
 http://purl.flvc.org/fcla/dt/14361
 Subject Headings
 Random vibrationMathematical models, Turbulence, Fluid dynamics
 Format
 Document (PDF)
 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 energybased 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 energybased 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 energybased 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 spacewise and timewise white noise excitations. Finally, the new energybased stochastic linearization technique is applied to treat nonlinear vibration problems of viscoelastic beams.
Show less  Date Issued
 1996
 PURL
 http://purl.flvc.org/fcla/dt/12467
 Subject Headings
 Elasticity, Viscoelasticity, Structural dynamicsMathematical models, VibrationMathematical models
 Format
 Document (PDF)
 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 hydroelastic 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 FroudeKrylov 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 hydroelastic 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 FroudeKrylov 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 semitheoretical 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.
Show less  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)
 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 NavierStokes CFD solver. A full 3D RANS approach in a moving reference frame is used to model the flow. By employing periodic boundary conditions, onethird of the flowfield 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 NavierStokes CFD solver. A full 3D RANS approach in a moving reference frame is used to model the flow. By employing periodic boundary conditions, onethird of the flowfield 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.
Show less  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)
 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 waveletbased transforms (the Streaming Wavelet Transform, ShortTime Wavelet Packet Decomposition, and Streaming Wavelet Packet Decomposition) and propose modifications to the existing ShortTIme Wavelet Transform. ... The proposed algorithms also create and select frequencyband 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).
Show less  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)
 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 triplewalled carbon nanotubes are determined exactly and approximately for both types. Approximate solutions are found by using BubnovGalerkin and PetrovGalerkin methods. For the first time explicit expressions are obtained for the natural frequencies of double and triplewalled 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 triplewalled carbon nanotubes are determined exactly and approximately for both types. Approximate solutions are found by using BubnovGalerkin and PetrovGalerkin methods. For the first time explicit expressions are obtained for the natural frequencies of double and triplewalled 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 clampedclamped doublewalled 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 BubnovGalerkin solution is also obtained to compare natural frequencies at the lower end of the spectrum. Simplified version of the BresseTimoshenko theory that incorporates the shear deformation and the rotary inertia is proposed for free vibration study of doublewalled carbon nanotubes. It is demonstrated that the suggested set yields extremely accurate results for the lower spectrum of doublewalled carbon nanotube. The natural frequencies of doublewalled carbon nanotubes based on simplified versions of Donnell shell theory are also obtained. The buckling behavior of the doublewalled carbon nanotubes under various boundary conditions is studied. First, the case of the simply supported doublewalled carbon nanotubes at both ends is considered which is amenable to exact solution., Then, approximate methods of BubnovGalerkin and PetrovGalerkin are utilized to check the efficacy of these approximations for the simply supported doublewalled 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 clampedclamped and simply supportedclamped doublewalled 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 singlewalled carbon nanotube under impact loading is analyzed by following a recently study reported on the energy absorption capacity of carbon nanotubes under ballistic impact.
Show less  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)
 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 semiinverse 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 semiinverse 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 prespecified value. Apparently for the first time in the literature, several closedform solutions for vibration tailoring have been derived for vibrating inhomogeneous beams and circular plates. Twelve new closedform 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.
Show less  Date Issued
 2006
 PURL
 http://purl.flvc.org/fcla/dt/13344
 Subject Headings
 Acoustical engineering, Plates (Engineering)VibrationMathematical models, Buckling (Mechanics), Structural analysis
 Format
 Document (PDF)
 Title
 Rainwindinduced cable vibrations in cablestayed 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 rainwindinduced cable vibration phenomena experienced in cables of cablestayed bridges and also the countermeasures employed by engineers to mitigate the largeamplitude 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 singledegreeoffreedom (SDOF) analytical model was developed and analyzed. This thesis studies...
Show moreThis research is aimed at investigating and analyzing the rainwindinduced cable vibration phenomena experienced in cables of cablestayed bridges and also the countermeasures employed by engineers to mitigate the largeamplitude 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 singledegreeoffreedom (SDOF) analytical model was developed and analyzed. This thesis studies the aerodynamic instability of cables in cablestayed bridges by doing literature review of a typical insitu test, developing a single degreeoffreedom (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.
Show less  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)