Current Search: Vibration (x)
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Title

VIBRATION ANALYSIS OF RECTANGULAR PLATES WITH COMPLETE AND PARTIAL CONSTRAINEDLAYER DAMPING TREATMENTS.

Creator

HSU, HONGYUAN., Florida Atlantic University, Stevens, Karl K.

Abstract/Description

A theoretical analysis for predicting the system loss factors and natural frequencies of rectangular plates with complete and partial constrainedlayer damping treatments has been presented. This analysis is based upon an energy approach to the free vibration of plates. Results predicted were compared with those from experiments. Satisfactory agreement has been reached. Both the theoretical and the experimental results presented in this thesis indicate clearly that partial constrainedlayer...
Show moreA theoretical analysis for predicting the system loss factors and natural frequencies of rectangular plates with complete and partial constrainedlayer damping treatments has been presented. This analysis is based upon an energy approach to the free vibration of plates. Results predicted were compared with those from experiments. Satisfactory agreement has been reached. Both the theoretical and the experimental results presented in this thesis indicate clearly that partial constrainedlayer damping treatments can provide effective, or even superior, amounts of damping, and that their use can lead to significant savings in material costs and weight.
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Date Issued

1983

PURL

http://purl.flvc.org/fcla/dt/14160

Subject Headings

Damping (Mechanics), Vibration, Plates (Engineering)Vibration

Format

Document (PDF)


Title

Vibration of nonlocal carbon nanotubes and graphene nanoplates.

Creator

Hache, Florian, Elishakoff, Isaac, Challamel, Noël, Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering

Abstract/Description

This thesis deals with the analytical study of vibration of carbon nanotubes and graphene plates. First, a brief overview of the traditional BresseTimoshenko models for thick beams and UflyandMindlin models for thick plates will be conducted. It has been shown in the literature that the conventionally utilized mechanical models overcorrect the shear effect and that of rotary inertia. To improve the situation, two alternative versions of theories of beams and plates are proposed. The first...
Show moreThis thesis deals with the analytical study of vibration of carbon nanotubes and graphene plates. First, a brief overview of the traditional BresseTimoshenko models for thick beams and UflyandMindlin models for thick plates will be conducted. It has been shown in the literature that the conventionally utilized mechanical models overcorrect the shear effect and that of rotary inertia. To improve the situation, two alternative versions of theories of beams and plates are proposed. The first one is derived through the use of equilibrium equations and leads to a truncated governing differential equation in displacement. It is shown, by considering a power series expansion of the displacement, that this is asymptotically consistent at the second order. The second theory is based on slope inertia and results in the truncated equation with an additional sixth order derivative term. Then, these theories will be extended in order to take into account some scale effects such as interatomic interactions that cannot be neglected for nanomaterials. Thus, different approaches will be considered: phenomenological, asymptotic and continualized. The basic principle of continualized models is to build continuous equations starting from discrete equations and by using Taylor series expansions or Padé approximants. For each of the different models derived in this study, the natural frequencies will be determined, analytically when the closedform solution is available, numerically when the solution is given through a characteristic equation. The objective of this work is to compare the models and to establish the eventual superiority of a model on others.
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Date Issued

2018

PURL

http://purl.flvc.org/fau/fd/FA00013019

Subject Headings

Carbon nanotubes, Graphene, Vibration

Format

Document (PDF)


Title

Effects of an internal flow on the vibration of thin cylindrical shells.

Creator

Leyrat, Gilles F., Florida Atlantic University, Cuschieri, Joseph M., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering

Abstract/Description

The response and the dynamic stability of thin cylindrical shells excited by a point force with an internal heavy medium (water) moving with a constant mean flow velocity are investigated. Two sets of analysis are discussed, one for infinitely long shells and one for shells of finite length. The infinite condition applies to shells which are sufficiently long to be considered infinite. In this case, the solution is obtained by means of a spatial Fourier transform in the axial direction and a...
Show moreThe response and the dynamic stability of thin cylindrical shells excited by a point force with an internal heavy medium (water) moving with a constant mean flow velocity are investigated. Two sets of analysis are discussed, one for infinitely long shells and one for shells of finite length. The infinite condition applies to shells which are sufficiently long to be considered infinite. In this case, the solution is obtained by means of a spatial Fourier transform in the axial direction and a modal decomposition in the circumferential direction. Using this solution, input and transfer accelerances are determined. The results of this part of this analysis show that input accelerances are globally preserved as the mean flow velocity changes. For the transfer accelerances, broadband peaks appear which are caused by the phase matching between propagating waves of different mode numbers. These broadband peaks are shifted and modified by the mean flow velocity. For shells of finite length, simply supported boundary conditions are assumed. In this case, the response is obtained by using a normal mode expansion of the in vacuo shell and the KirchhofHelmholtz equation derived for a fluid moving at constant flow velocity and bounded by a perfectly rigid cylinder. For finite shells, the main effect of the flow on the response is to decrease the natural frequencies of the shell. The extent of the change in frequency depends on the circumferential and axial mode numbers. Experimental results are also presented for a pipe shell of radius 0.025m and wall thickness 1.5mm. These results are compared with the analytical results for similar shell and flow condition and the agreement is very good. Using the analysis developed for the response, results are presented on the instabilities that can be induced by the flow. It is found that these instabilities are not restricted to finite pipes, but can also exist for cylindrical shells of infinite extent.
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Date Issued

1990

PURL

http://purl.flvc.org/fcla/dt/12249

Subject Headings

Shells (Engineering)Vibration

Format

Document (PDF)


Title

A STUDY OF FRICTION DAMPING AS APPLIED TO VIBRATING STRUCTURES.

Creator

DESAI, VIJAY R., Florida Atlantic University, Cuschieri, Joseph M.

Abstract/Description

Of the many methods of introducing damping in vibrating structures, the dissipation of energy due to interfacial slip can significantly increase the damping loss factor. However, because of the lack of understanding and other phenomena such as fretting corrosion and loss of structural rigidity, friction damping is rarely used. A study was thus undertaken to investigate this complex phenomenon, with emphasis on trying to gain a better understanding of friction damping with certain parameters...
Show moreOf the many methods of introducing damping in vibrating structures, the dissipation of energy due to interfacial slip can significantly increase the damping loss factor. However, because of the lack of understanding and other phenomena such as fretting corrosion and loss of structural rigidity, friction damping is rarely used. A study was thus undertaken to investigate this complex phenomenon, with emphasis on trying to gain a better understanding of friction damping with certain parameters such as clamping pressure, frequency, magnitude of excitation and surface finish. Although the nonlinearities associated with friction makes this mechanism difficult to model mathematically, finite element (FE) analysis shows some promise. Although the results obtained using an FE model were not exactly comparable to the experimental results, these analytical results did show the same general trends as observed in the experiments.
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Date Issued

1987

PURL

http://purl.flvc.org/fcla/dt/14369

Subject Headings

Damping (Mechanics), Vibration

Format

Document (PDF)


Title

VIBRATION ANALYSIS OF RECTANGULAR PLATES UNDER FLUID LOADING.

Creator

LEE, TZER CHIA., Florida Atlantic University, Dunn, Stanley E., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering

Abstract/Description

An energy method is presented for predicting the natural frequencies, radiation loss factor and system loss factor of simply supported rectangular plates under fluid loading. Both bare plates and plates with complete damping treatments are considered. Results obtained using the method developed are compared with two other theories. The agreement is generally good. The study points out the need for detailed analyses of plate vibration patterns and their associated radiation output under...
Show moreAn energy method is presented for predicting the natural frequencies, radiation loss factor and system loss factor of simply supported rectangular plates under fluid loading. Both bare plates and plates with complete damping treatments are considered. Results obtained using the method developed are compared with two other theories. The agreement is generally good. The study points out the need for detailed analyses of plate vibration patterns and their associated radiation output under various plate boundary conditions. There also exists a need for carefully conducted experimental work to verify the applicability of the current theory.
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Date Issued

1981

PURL

http://purl.flvc.org/fcla/dt/14086

Subject Headings

Plates (Engineering)Vibration

Format

Document (PDF)


Title

An application of perturbation techniques to the vibration analysis of structures with viscoelastic coating modifications.

Creator

Kelly, William Joseph, Jr., Florida Atlantic University, Stevens, Karl K., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering

Abstract/Description

Proper application of matrix perturbation theory to the structural modification of vibrating systems yields accurate results without resolving the eigenvalue problem. For this reason it seems that the method may require less computer time and cost in performing iterative type design work. This thesis investigates the application of firstorder perturbation techniques to a torsional shaft system subject to viscoelastic damping treatment modifications. The modifications are of general form in...
Show moreProper application of matrix perturbation theory to the structural modification of vibrating systems yields accurate results without resolving the eigenvalue problem. For this reason it seems that the method may require less computer time and cost in performing iterative type design work. This thesis investigates the application of firstorder perturbation techniques to a torsional shaft system subject to viscoelastic damping treatment modifications. The modifications are of general form in that the coating length and thickness are not restricted. Large modifications are built up by a series of small firstorder perturbations. In addition to developing a better understanding of the usefulness of this application of perturbation theory, the goal of this paper is also to understand the nonproportional damping effects of partial viscoelastic coatings.
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Date Issued

1988

PURL

http://purl.flvc.org/fcla/dt/14455

Subject Headings

Vibration, Perturbation (Mathematics)

Format

Document (PDF)


Title

Vibrational power flow in thick connected plates.

Creator

McCollum, Michele D., Florida Atlantic University, Cuschieri, Joseph M., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering

Abstract/Description

The total vibrational power flow in connected plate structures is investigated using an analytical "Power Flow" approach. The effects of shear and rotary inertia on the flexural wave transmission and the influence of inplane wave generation at structural discontinuities are included in the analytical model. In formulating a Power Flow model, the structure is divided into substructures whose responses may be determined analytically to obtain expressions for the input and transfer mobilities...
Show moreThe total vibrational power flow in connected plate structures is investigated using an analytical "Power Flow" approach. The effects of shear and rotary inertia on the flexural wave transmission and the influence of inplane wave generation at structural discontinuities are included in the analytical model. In formulating a Power Flow model, the structure is divided into substructures whose responses may be determined analytically to obtain expressions for the input and transfer mobilities of the substructures. For the case of platetype structures joined along a line, the mobilities are functions of both frequency and space. The power transmission between the individual plate substructures is then written as a function of these mobility expressions. The structure of concern in this dissertation consists of two plates connected in an Lconfiguration. In obtaining the expressions for the mobilities, the vibrational response of the individual plates is determined by solving the appropriate equations of motion. In this study the antisymmetric (flexural) motion is described using Mindlin's (1951) thick plate approximation to the threedimensional equations of motion. The applicability of this thick plate formulation is limited to frequencies below the frequency of the first antisymmetric mode of thicknessshear vibration of the plate. The symmetric (inplane) motion of the plates is described using the generalized theory of plane stress which neglects the direct coupling of the inplane motion with the thickness vibration modes, and is therefore valid only for frequencies which are lower than the frequency of the first mode of pure thickness vibration of the plate. The results for the power transmission in the Lplate obtained using the Power Flow formulation are verified at high frequencies by comparison with the results obtained using the Statistical Energy Analysis (SEA) technique. The SEA formulation for the Lplate is based on Mindlin's equations for flexural motion and the theory of generalized plane stress for inplane vibration. The results of the Power Flow formulation are verified at low frequencies by the results obtained using a Finite Element model of the Lshaped plate.
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Date Issued

1988

PURL

http://purl.flvc.org/fcla/dt/11929

Subject Headings

Plates (Engineering)Vibration

Format

Document (PDF)


Title

VIBRATION ANALYSIS OF RECTANGULAR PLATES WITH COMPLETE CONSTRAINEDLAYER DAMPING TREATMENTS.

Creator

CO, CHIMIN., Florida Atlantic University, Stevens, Karl K.

Abstract/Description

An energy method for predicting the natural frequencies and loss factors of Rectangular Plates with Complete ConstrainedLayer Damping Treatments has been presented. Results obtained using the method developed were compared with those of two former theories. The agreement between the current theory and these two theories was generally good. There is a serious need for carefully conducted experimental work to verify the applicability of the current theory and of the various other laminated...
Show moreAn energy method for predicting the natural frequencies and loss factors of Rectangular Plates with Complete ConstrainedLayer Damping Treatments has been presented. Results obtained using the method developed were compared with those of two former theories. The agreement between the current theory and these two theories was generally good. There is a serious need for carefully conducted experimental work to verify the applicability of the current theory and of the various other laminated plate theories in existence. It is believed that the method of analysis presented can be extended to handle plates with partial constrainedlayer damping treatments.
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Date Issued

1981

PURL

http://purl.flvc.org/fcla/dt/14085

Subject Headings

Plates (Engineering)Vibration

Format

Document (PDF)


Title

FLIGHT TESTS OF AN OPEN LOOP HIGHER HARMONIC CONTROL SYSTEM ON AN S76A HELICOPTER.

Creator

WALSH, DAVID M., Florida Atlantic University, Goankar, Gopal, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering

Abstract/Description

Flight tests of an open loop higher harmonic vibration control system were conducted on an S76A helicopter during the early part of 1985. This paper discusses the design, conduct and results of those tests. The flight tests included evaluations of Higher Harmonic Control (HHC) inputs in the longitudinal, lateral and collective axes at varying amplitudes and phases. These flight tests have demonstrated the feasibility of HHC on a medium size, high speed helicopter. Significant vibration...
Show moreFlight tests of an open loop higher harmonic vibration control system were conducted on an S76A helicopter during the early part of 1985. This paper discusses the design, conduct and results of those tests. The flight tests included evaluations of Higher Harmonic Control (HHC) inputs in the longitudinal, lateral and collective axes at varying amplitudes and phases. These flight tests have demonstrated the feasibility of HHC on a medium size, high speed helicopter. Significant vibration reductions throughout the aircraft were demonstrated at forward speeds up to 150 knots. The capability of HHC to reduce vibrations was also demonstrated at varying rotor speeds and during maneuvers. Structural data obtained during testing, showed a general increase in control system loads during HHC operation. However, no loads were above structural limits and it appears that a control system could be designed with sufficient strength to accept all HHC loads.
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Date Issued

1986

PURL

http://purl.flvc.org/fcla/dt/14341

Subject Headings

Vibration (Aeronautics), Helicopters

Format

Document (PDF)


Title

Mobility power flow analysis of connected thick plates with a step discontinuity.

Creator

Faivre d'Arcier, Eric., Florida Atlantic University, Cuschieri, Joseph M.

Abstract/Description

In this thesis the flow of vibration power between two coupled, finite plates of arbitrary thicknesses is considered using a Mobility Power Flow (MPF) approach. The plate structure is divided into substructures and mobility functions are determined for the independent substructures. Power flow expressions are derived based on continuity of forces and displacements. The solution presented here considers the effects of both inplane waves and outofplane waves. The solution is applicable to...
Show moreIn this thesis the flow of vibration power between two coupled, finite plates of arbitrary thicknesses is considered using a Mobility Power Flow (MPF) approach. The plate structure is divided into substructures and mobility functions are determined for the independent substructures. Power flow expressions are derived based on continuity of forces and displacements. The solution presented here considers the effects of both inplane waves and outofplane waves. The solution is applicable to frequencies below the first mode of thicknessshear vibration. The results obtained show that at low frequencies, the outofplane waves dominate in the transmission of vibrational power. However, at high frequencies or for thick plates, the inplane waves play a significant role in the power transmission through the plate.
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Date Issued

1991

PURL

http://purl.flvc.org/fcla/dt/14705

Subject Headings

VibrationMeasurement

Format

Document (PDF)


Title

ANALYSIS OF FREE VIBRATIONS OF BEAMS WITH VARYING DEGREES OF UNCONSTRAINED VISCOELASTIC DAMPING LAYER COVERAGE.

Creator

DE AGUIAR, JOAO BATISTA., Florida Atlantic University, Dunn, Stanley E.

Abstract/Description

A method of analysis addressing the problem of predicting the performance of beams with viscoelastic damping layer coating of varying degrees of coverage undergoing free vibrations is presented. Results based on this analysis and using mechanical properties of selected materials are generated for five different boundary conditions. The analytical results are verified experimentally for the case of a clampedfree beam. Also the main hypotheses employed in the theoretical approach are verified....
Show moreA method of analysis addressing the problem of predicting the performance of beams with viscoelastic damping layer coating of varying degrees of coverage undergoing free vibrations is presented. Results based on this analysis and using mechanical properties of selected materials are generated for five different boundary conditions. The analytical results are verified experimentally for the case of a clampedfree beam. Also the main hypotheses employed in the theoretical approach are verified. Finally, an analysis of the results leads to a discussion of the dynamic properties of coated beams.
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Date Issued

1982

PURL

http://purl.flvc.org/fcla/dt/14097

Subject Headings

Viscoelasticity, GirdersVibration

Format

Document (PDF)


Title

The measurement of structural power flow in thin plate structures.

Creator

Padiyar, Satish., Florida Atlantic University, Cuschieri, Joseph M., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering

Abstract/Description

An analytical and experimental investigation of the flow of vibrational power in a thin, Lshaped, finite plate structure subjected to mechanical and acoustic excitation is presented. In the analytical approach, mobility functions are used to determine the structural intensity vectors at various locations on the plate structure. Simulation results of intensity vectors estimated using three different measurement schemes are compared. The experimentally measured intensity vectors, for the case...
Show moreAn analytical and experimental investigation of the flow of vibrational power in a thin, Lshaped, finite plate structure subjected to mechanical and acoustic excitation is presented. In the analytical approach, mobility functions are used to determine the structural intensity vectors at various locations on the plate structure. Simulation results of intensity vectors estimated using three different measurement schemes are compared. The experimentally measured intensity vectors, for the case of mechanical excitation, using a four accelerometer array, are presented. They are found to match well with the results from the corresponding simulation. Similar results are obtained for the case of acoustic excitation of the Lshaped plate. The general pattern of the structural intensity vectors is found to be in agreement with the expected results.
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Date Issued

1990

PURL

http://purl.flvc.org/fcla/dt/14678

Subject Headings

Plates (Engineering)Vibration

Format

Document (PDF)


Title

Structural intensity measurements in thick structures.

Creator

Vallory, Joelle., Florida Atlantic University, Cuschieri, Joseph M., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering

Abstract/Description

Structural intensity is propagated through a thick structure by both inplane and outofplane (transverse) waves. These waves propagate at different phase speeds and therefore it is important to distinguish the components of the structural intensity associated with each wave type. To show the presence of these different wave components, experimental results are performed on a thick beam. Using a frequencywavenumber analysis, the different waves and contributions to the structural intensity...
Show moreStructural intensity is propagated through a thick structure by both inplane and outofplane (transverse) waves. These waves propagate at different phase speeds and therefore it is important to distinguish the components of the structural intensity associated with each wave type. To show the presence of these different wave components, experimental results are performed on a thick beam. Using a frequencywavenumber analysis, the different waves and contributions to the structural intensity are identified. The significance of the contributions to the structural intensity are a function of both frequency and thickness of the structure. Using simulated measurements on a thick Lshaped plate, the relative importance between the inplane and outofplane contributions to structural intensity as a function of frequency and thickness is demonstrated. It is shown that inplane wave contributions increase in importance as frequency or thickness increases.
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Date Issued

1991

PURL

http://purl.flvc.org/fcla/dt/14697

Subject Headings

Structural dynamics, Noise, Vibration

Format

Document (PDF)


Title

Transmission of vibrational power in joined structures.

Creator

Gibert, Thierry M., Florida Atlantic University, Cuschieri, Joseph M.

Abstract/Description

The objective of this thesis is the investigation of the transmission of vibrational power between beamlike and platelike structures with joints using Statistical Energy Analysis (SEA) and an experimental approach. In the case of the Lshaped plate the influence of different structure parameters is investigated to determine possible ways to reduce both the transmitted power and the noise radiated by the receiver structure. The total transmitted power is measured and compared to theoretical...
Show moreThe objective of this thesis is the investigation of the transmission of vibrational power between beamlike and platelike structures with joints using Statistical Energy Analysis (SEA) and an experimental approach. In the case of the Lshaped plate the influence of different structure parameters is investigated to determine possible ways to reduce both the transmitted power and the noise radiated by the receiver structure. The total transmitted power is measured and compared to theoretical predictions. Also power maps are generated which show the transmission of vibrational power from the source beam to the receiver beam. In the power flow measurements three different techniques are implemented with similar results which all match the analytical results.
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Date Issued

1988

PURL

http://purl.flvc.org/fcla/dt/14436

Subject Headings

Vibration, Power transmission

Format

Document (PDF)


Title

EXPERIMENTAL MODAL ANALYSIS OF A DISCMILL FIBERIZER DISC (VIBRATION, PLATES, RESONANCES).

Creator

FREEZE, WILLIAM PRESTON., Florida Atlantic University, Stevens, Karl K.

Abstract/Description

Modal analysis testing techniques were used to determine the modal parameters and mode shapes for flexural vibration of a Fiberizer Discmill disc to help define a safe operating speed range. The modal parameters and mode shapes were determined for the first six diametral modes, the first concentric mode, and the first rigid body shaft mode. The disc consisted of a circular aluminum plate with eight equally and symmetrically spaced radial cutters on one face of the disc and eight equally...
Show moreModal analysis testing techniques were used to determine the modal parameters and mode shapes for flexural vibration of a Fiberizer Discmill disc to help define a safe operating speed range. The modal parameters and mode shapes were determined for the first six diametral modes, the first concentric mode, and the first rigid body shaft mode. The disc consisted of a circular aluminum plate with eight equally and symmetrically spaced radial cutters on one face of the disc and eight equally spaced peripheral cutters located on the rim of the disc midway between the angular locations of the radial cutters. All cutters were of tool steel. The safe area of operation is determined to be between 3000 rpm and 3600 rpm. The experimental setup and procedure Is described in detail with particular emphasis on validation of assumptions required for the analytical approaches used in calculating the modal data.
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Date Issued

1986

PURL

http://purl.flvc.org/fcla/dt/14329

Subject Headings

Milling machinery, VibrationMeasurement

Format

Document (PDF)


Title

Concurrent engineering design of a miniature piezotransducervibrator.

Creator

Hedayatnia, Mostafa., Florida Atlantic University, Mazouz, Abdel Kader, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering

Abstract/Description

A stateoftheart PiezoTransducerVibrator suitable for a wristwatch has been developed based on a "Customer Comprehension" program: To look at the product from the customer point of view and try to satisfy those needs simultaneously using computer simulation leading to a reliable design in a shorter cycle time. This device is a miniature integrated compact form of both audio and silent alerts which uses less than 8 mA current; desirable to be used in equipments with very small power...
Show moreA stateoftheart PiezoTransducerVibrator suitable for a wristwatch has been developed based on a "Customer Comprehension" program: To look at the product from the customer point of view and try to satisfy those needs simultaneously using computer simulation leading to a reliable design in a shorter cycle time. This device is a miniature integrated compact form of both audio and silent alerts which uses less than 8 mA current; desirable to be used in equipments with very small power sources. A new ergonomic study was conducted in comprehending the minimum acceptable shake and frequency on human wrist. The complete Piezobender structure, its driving format, and its vibration has been modeled accurately to obtain an optimum geometry design for the best possible shake, satisfying all constraints.
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Date Issued

1994

PURL

http://purl.flvc.org/fcla/dt/12358

Subject Headings

Piezoelectric transducers, Wrist watches, Vibrators

Format

Document (PDF)


Title

Mobility power flow analysis of an infinite cylindrical shell with an enclosed plate discontinuity.

Creator

Buchmann, Patrick Pierre., Florida Atlantic University, Cuschieri, Joseph M.

Abstract/Description

A mobility power flow approach is used to study the response of an infinitelylong cylindrical shell with an internal plate discontinuity. The shell is excited by either a ring radial force or by a plane acoustic wave. The junction between the shell and the internal plate is assumed to be radially pinned such that inplane waves of the plate can be neglected. The junction forces are expressed in terms of the mobility functions of the plate and the shell. From knowledge of the junction forces...
Show moreA mobility power flow approach is used to study the response of an infinitelylong cylindrical shell with an internal plate discontinuity. The shell is excited by either a ring radial force or by a plane acoustic wave. The junction between the shell and the internal plate is assumed to be radially pinned such that inplane waves of the plate can be neglected. The junction forces are expressed in terms of the mobility functions of the plate and the shell. From knowledge of the junction forces and velocities, the power input, the power flow from the shell to the plate, the shell response and the radiated farfield scattered pressure are determined for the circumferential mode n = 0. The results show how the energy propagates from one structure to the other, and present a very clear picture of the characteristics of the scattering pattern from the junction forces.
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Date Issued

1994

PURL

http://purl.flvc.org/fcla/dt/15113

Subject Headings

Shells (Engineering)Vibration, Plates (Engineering)Vibration, Structural dynamics, Vibration

Format

Document (PDF)


Title

Estimates of water turbine noise levels.

Creator

Guerra, Julian., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering

Abstract/Description

This work seeks to understand water turbine noise generation and to make preliminary estimations of the noise levels. Any structure attached to a turbine upstream its blades will generate unsteady fluctuating loads on the blade's surface, which are proportional to the radiated acoustic pressure. The noise levels of a simplified turbine based on existing designs surpass the ambient noise levels of the ocean at low frequencies ( 30 Hz).
Show moreThis work seeks to understand water turbine noise generation and to make preliminary estimations of the noise levels. Any structure attached to a turbine upstream its blades will generate unsteady fluctuating loads on the blade's surface, which are proportional to the radiated acoustic pressure. The noise levels of a simplified turbine based on existing designs surpass the ambient noise levels of the ocean at low frequencies (< 20 Hz) by approximately 50 dB ref 1 μPa and stay under the ambient noise levels at higher frequencies for a bladepassing frequency of 0.83 Hz and point of observation (100 m, 45 degrees, 45 degrees) from the hub. Streamlining the crosssection of the upstream structure as well as reducing its width decrease the noise levels by approximately 40 dB ref 1 μPa, at low frequencies and moderately increase them at higher frequencies. Increasing the structurerotor distance decreases the noise levels with increasing frequencies (> 30 Hz).
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Date Issued

2011

PURL

http://purl.flvc.org/FAU/3170958

Subject Headings

Turbines, Vibration, Testing, Underwater acoustics, Fluid dynamics

Format

Document (PDF)


Title

ANALYSIS OF DAMPING LAYER TREATMENTS FOR PLATES USING EXPERIMENTALLY DETERMINED MODE SHAPES.

Creator

JAISING, VINOD R., Florida Atlantic University, Stevens, Karl K.

Abstract/Description

A method of analysis is presented to determine the natural frequencies and loss factors of a plate covered with viscoelastic coating, using experimentally obtained mode shapes. The mode shapes for a square plate clamped on all edges are determined using an HP 5423 A Structural Dynamics Analyzer. A computer program, based on the method of analysis, is developed to determine the natural frequencies and loss factors of a rectangular plate covered with viscoelastic material, and clamped on all...
Show moreA method of analysis is presented to determine the natural frequencies and loss factors of a plate covered with viscoelastic coating, using experimentally obtained mode shapes. The mode shapes for a square plate clamped on all edges are determined using an HP 5423 A Structural Dynamics Analyzer. A computer program, based on the method of analysis, is developed to determine the natural frequencies and loss factors of a rectangular plate covered with viscoelastic material, and clamped on all edges. It was found that, for a fully coated plate, and for a mesh with twentyfive mesh points, the error in the fundamental frequency was approximately 5 percent. A comparison between the mode shapes for the bare plate and for the fully coated plate revealed no significant difference. It was also found that increasing the number of measurement points would not significantly improve the results.
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Date Issued

1981

PURL

http://purl.flvc.org/fcla/dt/14050

Subject Headings

Plates (Engineering)Vibration, Damping (Mechanics)

Format

Document (PDF)


Title

Adaptive control of vibration in flexible smart structures.

Creator

Gopinathan, Murali., Florida Atlantic University, Pajunen, Grazyna, College of Engineering and Computer Science, Department of Computer and Electrical Engineering and Computer Science

Abstract/Description

This dissertation is concerned with the relevant research in developing finite dimensional indirect adaptive schemes to control vibrations in flexible smart structures based on the finite element approximation of the infinite dimensional system. The advantage of this type of modeling is that the dominant modes of vibrations wherein the total energy is concentrated are accommodated thereby avoiding the socalled "spillover" phenomenon. Further, the mass, stiffness and damping coefficients...
Show moreThis dissertation is concerned with the relevant research in developing finite dimensional indirect adaptive schemes to control vibrations in flexible smart structures based on the finite element approximation of the infinite dimensional system. The advantage of this type of modeling is that the dominant modes of vibrations wherein the total energy is concentrated are accommodated thereby avoiding the socalled "spillover" phenomenon. Further, the mass, stiffness and damping coefficients associated with each element appear explicitly in the model facilitating the derivation of the ARMA parametric representation which is suitable for online estimation of the structural parameters. The statespace representation of the finite dimensional model is used to design an indirect linear quadratic self tuning regulator algorithm using the parameter estimation, indicated above. Further, a method to choose the control and state weighting matrices (required to design the controller) to yield a stable closedloop system, is presented. Simulation results demonstrating the performance of the adaptive control system are presented. Another algorithm based on the model reference technique is also developed by considering the discrete time approximation of the finite dimensional model. This control algorithm in conjunction with the parameter estimation constitute an indirect model reference adaptive control system. Simulation results are presented to demonstrate the effect of the reference model parameters, which may impose certain constraints on the force requirements causing actuator saturation and thereby affecting the stability of the closedloop system. In order to overcome the problem of using bulky and expensive sensors to measure transverse displacement and velocity, a new spatial recursive technique to estimate these variables alternatively by using a distributed set of (measured) strain data, is developed. Relevant algorithm enables the use of smart materials to sense the strain developed at various locations along the length of the structure leading to the development of flexible smart structures. Experimental results on the personal computer based control of vibrations in an aluminum beam using patches of polyvinyldene fluoride (PVDF), and lead zirconate titanate (PZT) as sensors and control actuators respectively, are furnished to demonstrate the feasibility of realtime implementation of the above mentioned control algorithms.
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Date Issued

1995

PURL

http://purl.flvc.org/fcla/dt/12418

Subject Headings

Adaptive control systems, Smart structures, Vibration

Format

Document (PDF)
Pages