Current Search:  Shells Engineering (x)

View All Items

  • CSV Spreadsheet
(1 - 6 of 6)
Effects of an internal flow on the vibration of thin cylindrical shells
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 Kirchhof-Helmholtz 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.
Show less
Date Issued
1990
PURL
http://purl.flvc.org/fcla/dt/12249
Subject Headings
Shells (Engineering)--Vibration
Format
Document (PDF)
Free and random vibrations of shells of revolution with interior supports
Title
Free and random vibrations of shells of revolution with interior supports.
Creator
Xia, Zhiyong., Florida Atlantic University, Yong, Yan, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
A new analytical method based on the wave propagation scheme has been developed for the dynamic analysis of axially symmetric shells with arbitrary boundary conditions and interior supports. In this approach, a shell structure is considered as a waveguide and the response to external excitations is treated as a superposition of wave motions. To segregate the effect of the interior supports, the waveguide is first divided into several sub-waveguides. Upon analyzing these sub-waveguides...
Show moreA new analytical method based on the wave propagation scheme has been developed for the dynamic analysis of axially symmetric shells with arbitrary boundary conditions and interior supports. In this approach, a shell structure is considered as a waveguide and the response to external excitations is treated as a superposition of wave motions. To segregate the effect of the interior supports, the waveguide is first divided into several sub-waveguides. Upon analyzing these sub-waveguides separately, a composition scheme is adopted to relate them by connecting the wave components according to the continuity conditions for the state variables at each interior supports. Closed form solutions for free and random vibration are derived. The proposed method is presented in a general fashion and numerical examples are given to illustrate the application of the theory.
Show less
Date Issued
1990
PURL
http://purl.flvc.org/fcla/dt/14659
Subject Headings
Shells (Engineering)--Vibration, Wave guides
Format
Document (PDF)
Interlaminar crack propagation in thick composite shells
Title
Interlaminar crack propagation in thick composite shells.
Creator
Ozdil, Feridun., Florida Atlantic University, Carlsson, Leif A., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
Delamination growth has been investigated as a potential failure mechanism for filament-wound composite cylinders used for offshore and underwater structures. Analysis and experiments on DCB, ENF, and MMB beam fracture specimens machined from angle-ply laminate panels and filament-wound composite cylinders are presented. Bending analysis of beam fracture specimens machined from flat panels and composite cylinders was derived from first order shear deformation theory and one-dimensional...
Show moreDelamination growth has been investigated as a potential failure mechanism for filament-wound composite cylinders used for offshore and underwater structures. Analysis and experiments on DCB, ENF, and MMB beam fracture specimens machined from angle-ply laminate panels and filament-wound composite cylinders are presented. Bending analysis of beam fracture specimens machined from flat panels and composite cylinders was derived from first order shear deformation theory and one-dimensional expressions obtained from laminated plate and shell theories. For the DCB specimens, elastic foundation effects were modeled. Experiments on flat, glass/polyester laminate beam specimens considered [0]6, [+/-30]5 and [+/-45] 5 lay-ups with mid-plane delaminations. Experiments on beam specimens machined from composite cylinders were conducted on [+/- q ]6 and [+/- q ]12 lay-ups with mid-surface delaminations where q = 30 degrees, 55 degrees and 85 degrees. For all lay-ups and specimen configurations, beam model predictions of compliance were in good agreement with experimental data over the range of laminate thicknesses, ply angles, and crack lengths examined. Fracture toughness for delamination propagation was examined for flat glass/polyester panels and glass/epoxy cylinders. The initiation value of mode II fracture toughness, GIIc, was much larger than the initiation value of mode I fracture toughness GIc. The initiation value of mixed mode fracture toughness, Gc, increased with decreased ratio GI/GII and increased ply angle q . Debonding of transversely oriented fiber bundles was observed as a major crack arrest and fracture resistance mechanism for the flat, glass/polyester angle-ply laminates. Bridging by interlaced fiber bundles and crack jumping to another interface contributed to crack arrest and limited the growth in the curved, glass/epoxy angle-ply laminates. For all lay-ups, the crack propagated in a non-uniform manner across the width of the specimen as explained by elastic coupling effects in the laminate beams of the cracked region.
Show less
Date Issued
1999
PURL
http://purl.flvc.org/fcla/dt/12588
Subject Headings
Laminated materials, Shells (Engineering), Composite materials
Format
Document (PDF)
Buckling of composite cylindrical shells with geometric, thickness and material imperfections
Title
Buckling of composite cylindrical shells with geometric, thickness and material imperfections.
Creator
Li, Yiwei., Florida Atlantic University, Elishakoff, Isaac, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
This dissertation deals with the determination of buckling loads of composite cylindrical shell structures which involve uncertainty either in geometry, namely thickness variation, or in material properties. Systematic research has been carried out, which evolves from the simple isotropic cases to anisotropic cases. Since the initial geometric imperfection has a dominant role in the reduction of those imperfection-sensitive structures such as cylindrical shells, the combined effect of...
Show moreThis dissertation deals with the determination of buckling loads of composite cylindrical shell structures which involve uncertainty either in geometry, namely thickness variation, or in material properties. Systematic research has been carried out, which evolves from the simple isotropic cases to anisotropic cases. Since the initial geometric imperfection has a dominant role in the reduction of those imperfection-sensitive structures such as cylindrical shells, the combined effect of thickness variation and initial imperfection is also investigated in depth. Both analytic and numerical methods are used to derive the solutions to the problems and asymptotic formulas relating the buckling load to the geometric (thickness variation and/or initial imperfection) parameter are established. It is shown that the axisymmetric thickness variation has the most detrimental effect on the buckling load when the modal number of thickness variation is twice as much as that of the classical buckling mode. For the composite shells with uncertainty in material properties, the convex modelling is employed to evaluate the variability of buckling load. Based on the experimental data for the elastic moduli of the composite laminates, the upper and lower bounds of the buckling load are derived, which are numerically substantiated by the results from nonlinear programming. These bounds will be useful in practice and can provide engineers with a better view of the real load-carrying capacity of the composite structure. Finally, the elastic modulus is modeled as a function of coordinates to complete the study on variability of material property so that the result can be obtained to account for the situation where the elastic modulus is different from one place to another in the structure.
Show less
Date Issued
1996
PURL
http://purl.flvc.org/fcla/dt/12444
Subject Headings
Composite materials, Buckling (Mechanics), Shells (Engineering), Structural dynamics
Format
Document (PDF)
Mobility power flow analysis of an infinite cylindrical shell with an enclosed plate discontinuity
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 infinitely-long 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 in-plane 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 infinitely-long 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 in-plane 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 far-field 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.
Show less
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)
Mobility power flow (MPF) approach applied to fluid-loaded shells with ring discontinuities
Title
Mobility power flow (MPF) approach applied to fluid-loaded shells with ring discontinuities.
Creator
McCain, Thomas Scott., Florida Atlantic University, Cuschieri, Joseph M., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
The vibrational and acoustic characteristics of fluid-loaded, cylindrical shells with single or multiple, aperiodically-spaced ring discontinuities are studied using an approach based on the mobility power flow (MPF) method and a hybrid numerical/analytical method for the evaluation of the velocity Green's function of the shell. The discontinuities are associated with internal structures coupled to the shell via ring junctions. The approach is a framework allowing alternative shell and/or...
Show moreThe vibrational and acoustic characteristics of fluid-loaded, cylindrical shells with single or multiple, aperiodically-spaced ring discontinuities are studied using an approach based on the mobility power flow (MPF) method and a hybrid numerical/analytical method for the evaluation of the velocity Green's function of the shell. The discontinuities are associated with internal structures coupled to the shell via ring junctions. The approach is a framework allowing alternative shell and/or internal structure models to be used. The solution consists of the net vibrational power flow between the shell and internal structure(s) at the junction(s), the shell's velocity Green's function, and the far-field acoustic pressure. Use of the MPF method is advantageous because the net power flow solution can be used as a diagnostic tool in ascertaining the proper coupling between the shell and internal structure(s) at the junction(s). Results are presented for two canonical problems: an infinite, thin cylindrical shell, externally fluid-loaded by a heavy fluid, coupled internally to: (1) a single damped circular plate bulkhead, and (2) a double bulkhead consisting of two identical damped circular plates spaced a shell diameter apart. Two excitation mechanisms are considered for each model: (1) insonification of the shell by an obliquely-incident, acoustic plane wave, and (2) a radial ring load applied to the shell away from the junction(s). The shell's radial velocity Green's function and far-field acoustic pressure results are presented and analyzed to study the behavior of each model. In addition, a comparison of these results accentuates the qualitative difference in the behavior between the single and multiple junction models. When multiple internal structures are present, the results are strongly influenced by inter-junction coupling communicated through the shell and the fluid. Results are presented for circumferential modes n = 0 & 2. The qualitative differences in the results for modes n = 0 and n = 2 (indicative of all modes n > 0ified in the far-field acoustic pressure and velocity Green's function response with the characteristics of the shell and internal plate bulkhead. The results for the single junction model demonstrate the significance of the shell's membrane waves on the reradiation of acoustic energy from the shell; however, when multiple junctions are present, inter-junction coupling results in a significant broad acoustic scattering pattern. Using the results and analysis presented here, a better understanding can be obtained of fluid-loaded shells, which can be used to reduce the strength of the acoustic pressure field produced by the shell.
Show less
Date Issued
1996
PURL
http://purl.flvc.org/fcla/dt/12490
Subject Headings
Shells (Engineering)--Vibration, Cylinders--Vibration, Fluid dynamics, Sound--Transmission
Format
Document (PDF)