Showing papers on "Shell (structure) published in 1989"
596 citations
TL;DR: In this article, a discrete canonical, singularity-free mapping between the five and the six degree of freedom formulation is constructed by exploiting the geometric connection between the orthogonal group (SO(3)) and the unit sphere (S2).
Abstract: Computational aspects of a linear stress resultant (classical) shell theory, obtained by systematic linearization of the geometrically exact nonlinear theory, considered in Part I of this work, are examined in detail. In particular, finite element interpolations for the reference director field and the linearized rotation field are constructed such that the underlying geometric structure of the continuum theory is preserved exactly by the discrete approximation. A discrete canonical, singularity-free mapping between the five and the six degree of freedom formulation is constructed by exploiting the geometric connection between the orthogonal group (SO(3)) and the unit sphere (S2). The proposed numerical treatment of the membrane and bending fields, based on a mixed Hellinger-Reissner formulation,provides excellent results for the 4-node bilinear isoparametric element. As an example, convergent results are obtained for rather coarse meshes in fairly demanding, singularity-dominated, problems such as the classical rhombic plate test. The proposed theory and finite element implementation are evaluated through an extensive set of benchmark problems. The results obtained with the present approach exactly match previous solutions obtained with state-of-the-art implementations based on the so-called degenerated solid approach.
450 citations
TL;DR: In this article, the optical phase conjugation is enhanced from each nonlinear region because the optical field can be concentrated in both the interior and the exterior neighborhoods of the particle and magnified at the surface-mediated plasmon resonance.
Abstract: Calculations of the nonlinear-optical behavior are developed for model composites of nanospheres with a metallic core and nonlinear shell or with a nonlinear core and metallic shell suspended in a nonlinear medium. Optical phase conjugation is shown to be enhanced from each nonlinear region because the optical field can be concentrated in both the interior and the exterior neighborhoods of the particle and magnified at the surface-mediated plasmon resonance. For the model composite with a metallic core, a limited range of resonance tunability can be achieved by adjustment of shell thickness; the frequency range is dependent on the dielectric dispersion of the metal. For the composite with a metallic shell instead of a metallic core, this restriction is reduced so that tunability from ultraviolet to infrared can be attained. Enhancement of the phase-conjugate signal is calculated for the electrostrictive mechanism dominant in the microsecond time scale and for the electronic mechanism dominant in the picosecond time scale. Calculations based on the dielectric functions for gold and for aluminum indicate that phase-conjugate reflectivity enhancements of 108 can be achieved. The imaginary components of the composite dielectric functions are shown to limit the magnitude of the field enhancement at the surface-plasmon resonance and determine the absorption and figure of merit of the composite.
410 citations
TL;DR: Ojakangas et al. as mentioned in this paper considered a model of Europa consisting of an ice shell that is decoupled from a silicate core by a layer of liquid water, and calculated the thickness of the shell as a function of colatitude and longitude.
340 citations
TL;DR: In this paper, a multi-layered thin shell coupled with an active distributed vibration actuator was proposed and evaluated, where the dynamics and control of distributed mechanical systems were derived based on Love's theory and Hamilton's principle.
281 citations
TL;DR: In this article, the authors examined the elastic buckling strength of thin cylindrical shells under axial compression, with imperfections arising at circumferential welded joints, and the effects of the welded joint depression amplitude, the shell radius-to-thickness ratio, a change of shell plate thickness at the weld, and internal pressurization are all examined.
Abstract: Metal silos and tanks are subject to axial compressive stresses in their cylindrical shell walls. The buckling strength is very sensitive to geometric imperfections in the wall. The most regular and well‐defined imperfection is the local depression adjacent to a circumferential weld, caused by the plate rolling process and shrinkage of the weld.This paper examines the elastic buckling strengths of thin cylindrical shells under axial compression, with imperfections arising at circumferential welded joints. The effects of the welded joint depression amplitude, the shell radius‐to‐thickness ratio, a change of shell plate thickness at the weld, and internal pressurization are all examined. The study is confined to cylinders with a radius‐to‐thickness ratio in excess of 100, as thicker shells are rare for these structures. It is shown that a welded joint depression is one of the most deleterious practical imperfection forms currently known.
172 citations
156 citations
TL;DR: In this paper, the authors proposed replacing the thick shell with an intelligent shell which provides active flux freezing on much longer time scales, but only for times shorter than the shell's resistive diffusion time.
Abstract: Reversed field pinches are conventionally stabilized by surrounding the plasma with a thick metallic shell. This suppresses flux penetration but only for times shorter than the shell's resistive diffusion time. To improve on this the author proposes replacing the thick shell with an intelligent shell which provides active flux freezing on much longer time scales.
152 citations
TL;DR: In this article, the microstructure and mechanical properties of abalone shells were studied and it was found that fracture strength, αf, is 180 MPa, and fracture toughness, KIC, is 7 ± 3 MPa-m1/2; these values are comparable with or better than most “high technology” ceramic materials.
Abstract: The microstructure and mechanical properties of abalone shell were studied. It was found that fracture strength, αf, is 180 MPa, and fracture toughness, KIC, is 7 ± 3 MPa-m1/2; these values are comparable with or better than most “high technology” ceramic materials. The microarchitecture of the nacre section of the red abalone shell is similar to a “brick and mortar” structure, where CaCO3 is the brick and organic matter is the mortar, constituting 95% and 5% of the microstructure by volume, respectively. This impressive combination of af and KIc values is attributed to the laminated structure of the shell with hard and thick (0.25±0.5 μm) CaCO3 and superplastic and thin (20–30 nm) organic components. Although there are several toughening mechanisms operating in the shell, fractographic studies identified sliding of CaCO3 layers and bridging by the organic layers to be the most effective ones. These phases also have a strong interface. The results of our experiments are discussed in the context of using abalone shell as a model for the design of synthetic laminates such as cermet (ceramic-metal) and cerpoly (ceramic-polymer) composites.
123 citations
123 citations
TL;DR: In this article, nonlinear convective solutions for a shell with properties characteristic of the earth's whole mantle for Rayleigh numbers up to 70,000 were presented, and two distinct convective patterns (cubic and tetrahedral) were identified which are closely related to the geometric planforms predicted by the analytical theories of slightly supercritical spherical convection.
Abstract: Nonlinear convective solutions are presented for a shell with properties characteristic of the earth's whole mantle for Rayleigh numbers up to 70,000. The solutions are validated numerically, and two distinct convective patterns (cubic and tetrahedral) are identified which are closely related to the geometric planforms predicted by the analytical theories of slightly supercritical spherical convection. A quantitative analysis of the horizontal and vertical structures of the velocity and temperature fields of the solutions is presented, and their heat transport properties are examined, including the total heat flow and the spatial distribution of the heat flux at the shell boundaries.
TL;DR: Theoretically predicted thin shell modes, phase locked to the wall, are prominent experimentally as mentioned in this paper, and current pulses of 3-5 ms are obtained, compared with the shell time constant for vertical field penetration of 0.5 ms.
Abstract: Results are presented from thin (resistive) shell experiments on HBTX and compared with theoretical (linear and non-linear) studies of the plasma stability. Current pulses of 3-5 ms are obtained, compared with the shell time constant for vertical field penetration of 0.5 ms. Theoretically predicted thin shell modes, phase locked to the wall, are prominent experimentally.
01 Jan 1989
TL;DR: In this article, a bending theory for thin shells undergoing finite rotations is presented, and its associated finite element model is described The kinematic assumption is based on a Reissner-Mindlin theory, and the starting point for the derivation of the strain measures is the polar decomposition of the material deformation gradient.
Abstract: A bending theory for thin shells undergoing finite rotations is presented, and its associated finite element model is described The kinematic assumption is based on a Reissner-Mindlin theory The starting point for the derivation of the strain measures is the polar decomposition of the material deformation gradient The work-conjugate stress resultants and stress couples are integrals of the Biot stress tensor This tensor is invariant with respect to rigid body motions and therefore appropriate for the formulation of constitutive equations The rotations are described by using Eulerian angles The finite element discretization of arbitrary shells is performed using isoparametric elements The advantage of the proposed shell formulation and its numerical model is shown by application to different non-linear plate and shell problems Finite rotations can be calculated within one load increment Thus the step size of the load increment is only imited by the local convergence behaviour of Newton's method or the appearance of stability phenomena
Patent•
10 Mar 1989
TL;DR: An improved golf ball is defined as a hollow, spherical shell of a deformable polymeric material which is filled with either a liquid or a unitary, non-cellular core of a material which, at the time of introduction into the shell, is a liquid.
Abstract: An improved golf ball having a coefficient of restitution of at least 0.700 and comprising a hollow, spherical shell of a deformable polymeric material which is filled with either a liquid or a unitary, non-cellular core of a material which, at the time of introduction into the shell, is a liquid. The spherical shell may be solid or cellular. The core material may be added through a hole in the shell as a liquid, a gel or a melt. In the preferred embodiment, the spherical shell is formed from two half shells which are bonded to each other. The mating edges of the half shells may have surface configurations which maximize their contact area.
TL;DR: A critical assessment of the 4-node assumed strain element as proposed by Dvorkin and Bathe is made in this paper, where the element performed excellently in all investigated shell problems which sometimes caused difficulties for other assumed strain techniques.
Abstract: A critical assessment of the 4‐node assumed strain element as proposed by Dvorkin and Bathe is made. The element performed excellently in all investigated shell problems which sometimes caused difficulties for other assumed strain techniques. For efficient computation in the non‐linear range, linearization of the virtual work equation is done to yield the consistent tangent stiffness. The shell formulation is done for stress and strain tensors based on local element coordinates. To demonstrate the effectiveness and rapid convergence of the non‐linear formulation, three examples are tested for large displacements.
TL;DR: In this paper, a moving reference frame is introduced for the analysis of accretionary shell growth, where the aperture becomes the focus of the analysis, mathematically and conceptually, in conformity with biological reality.
Abstract: A moving reference frame is introduced for the analysis of accretionary shell growth. Simple principles of motion and stepwise growth define the model. At each growth step, the aperture migrates from its present position to a new position, according to locally defined rules. The aperture becomes the focus of the analysis, mathematically and conceptually, in conformity with biological reality. Kinematic principles provide the analytical framework for describing the aperture's trajectory (kinematics is the study of motion). The aperture “translates,” “rotates,” and “dilates.” The model offers exceptional flexibility in the analysis of accretionary growth forms and is particularly well-suited to analysis of conical and loosely coiled shell geometries. Computer simulations illustrate the principles of a moving reference model. The inverse problem of finding the aperture motions from actual shell data is rigorously specified, for both planispiralled and helicospiralled shell forms.
TL;DR: A modal analysis of acoustic radiation by a finite cylindrical shell immersed in light of heavy fluid is presented in this paper, where the authors focused on the explanation of radiation phenomena in both fluids.
TL;DR: Ojakangas et al. as mentioned in this paper developed equations describing the variations in the inertia tensor of a body when second harmonic degree topography is added to the base of the crust.
Patent•
25 Jan 1989
TL;DR: In this article, a net layer is used to define the shell of a building and a hardening layer is applied to fix the shape of the net layer and establish wall, roof, and floor.
Abstract: A net layer ( 32 ) defines the shell ( 40 ) of a building, carried by any necessary supports. A hardening layer ( 34 ) is applied to fix the shape of the net layer ( 32 ) and to establish wall, roof, and floor. Optionally the shell is of sufficient strength to receive application of further layers in order to define an exoskeleton. Structures of roof sections include parallel-sided segments and converging-sided segments, with troughed or domed section shapes. Structures of walls include opposed shell sides ( 35 ), ( 78 ) and central filler layers ( 70 ), together defining an exoskeleton. Posts ( 72 ) can add additional structural capacities for supporting walls, roof and floor and can be formed integrally of net ( 32 ) and hardener ( 34 ).
Patent•
13 Jul 1989
TL;DR: In this paper, a hemispherical shell is used to uniformly irradiate an area of a surface which accurately defines the area under irradiation and collects lights reflected from the area and scatters it back towards the surface.
Abstract: A device for uniformly irradiating an area of a surface which accurately defines the area under irradiation and collects lights reflected from the area and scatters it back towards the surface. The device comprises a hemispherical shell (3) whose inside surface is coated with a diffuse reflector and a light source (11) mounted in the shell. The light source may be a diffusing device connected to a laser remote from the shell (3) via an optical fibre (7). In use the shell (3) is placed against the surface under illumination so that the edges of the shell (3) define the area under illumination and the use of the diffusely reflecting surface of the shell prevents any escape of light. A deformable sheet of partly reflective and partly transmissive material may be placed across the open mouth of the hemisphere to cover the target area to increase the uniformity of illumination when the device is used on uneven surfaces. The device is particularly useful in photodynamic therapy.
TL;DR: In this paper, a limiting shell thickness is found at which a kinematic collapse mechanism develops, and the role of hoop stress in permitting the construction of such a shell without centering.
Abstract: Renaissance ogival domes of unreinforced stone masonry can be analyzed as structures of rigid material with no tensile strength. Solutions can be obtained for the static equilibrium of the structure; the results represent an extension or variant to membrane shell theory. A limiting shell thickness is found at which a kinematic collapse mechanism develops. The limit state analysis also identifies the role of hoop stress in permitting the construction of such a shell without centering. The analysis has its counterpart in a study published in 1742, that being the first modern structural analysis. The analysis procedure shows the clear relation between geometry (shell shape) and internal forces.
Patent•
31 Jan 1989
TL;DR: In this article, an acetabulum is prepared with an inner surface having a spherical configuration complementary to the second spherical surface portion of the shell component, the radius of the first spherical surface part being slightly greater than the radius radius of second spherical surfaces.
Abstract: An acetabular cup has a shell component with an outer surface including a first spherical surface portion and a second spherical surface portion, and an acetabulum is prepared with an inner surface having a spherical configuration complementary to the second spherical surface portion of the shell component, the radius of the first spherical surface portion being slightly greater than the radius of the second spherical surface portion such that upon nesting of the second spherical surface portion of the shell component in contiguous relationship with the inner surface of the acetabulum, the first spherical surface portion engages the inner surface of the acetabulum in an interference fit to secure the shell component within the prepared acetabulum.
Patent•
17 Feb 1989TL;DR: In this article, a double shell filter consisting of an inner shell of bounded 80 to 400 U.S. mesh screen particles and an outer shell of bonded 20 to 80 mesh screen carbon particles was described, where the inner and outer particles were bonded internally to each other and the two shells were bonded together by an ultra high molecular weight polymer binder having a melt index of less than about 1 gram per ten minutes.
Abstract: The specification discloses a double shell filter comprising an inner shell of bounded 80 to 400 U.S. mesh screen carbon particles and an outer shell of bonded 20 to 80 mesh screen carbon particles wherein the inner and outer particles are bonded internally to each other and the two shells are bonded together preferably by an ultra high molecular weight polymer binder having a melt index of less than about 1 gram per ten minutes as determined by ASTM D1238 at 190 degrees C. and 15 kilograms load.
Patent•
16 Mar 1989
TL;DR: A small tank or vessel for the containment of pressurized fluids is formed by joining the outer edges of the arms of integral upright and inverted double-Y sections arranged side by side.
Abstract: A small tank or vessel for the containment of pressurized fluids is formed by joining the outer edges of the arms of integral upright and inverted double-Y sections arranged side by side The arms are part cylinders terminating in the vertical centerline of a cylinder so that a septum between adjacent cylindrical lobes is formed by the vertical legs of the double-Y A semi-cylindrical shell may be attached to the outer arms of each outside double-Y form
TL;DR: In this article, the authors applied the finite element method to study the effect of moisture and temperature on the stability of a general orthotropic cylindrical composite shell panel subjected to axial or in-plane shear loading.
TL;DR: In this paper, a substructure synthesis method based on state space mathematics is proposed for the eigensolution of axisymmetric joined/hermetic thin shell structures, which is validated by applying it to structural elements such as a cylinder, a cone, a sphere, and a toroidal segment.
TL;DR: In this paper, a nine node finite element model was developed for analysis of geometrically non-linear composite shells based on the degenerate solid shell concept and utilizes a set of assumed strain fields as well as assumed displacement two different local orthogonal coordinate systems were used to maintain invariance of the element stiffness matrix.
Abstract: A nine node finite element model has been developed for analysis of geometrically non-linear laminated composite shells. The formulation is based on the degenerate solid shell concept and utilizes a set of assumed strain fields as well as assumed displacement Two different local orthogonal co-ordinate systems were used to maintain invariance of the element stiffness matrix. The formulation assumes strain and the determinant of the Jacobian matrix to be linear in the thickness direction. This allows analytical integration in the thickness direction regardless of ply layups. The formulation also allows the reference plane to be different from the shell midsurface. The results of numerical tests demonstrate the validity and the effectiveness of the present approach.
Patent•
3M1
TL;DR: In this article, the authors propose a closure for use in providing an environmental seal about a wire junction, which comprises a closable shell defining, when closed, an internal wire junction receiving chamber having first and second opposite open ends, for receiving of wires there through.
Abstract: A closure for use in providing an environmental seal about a wire junction. The closure comprises a closable shell defining, when closed, an internal wire junction receiving chamber having first and second opposite open ends, for receipt of wires therethrough. The shell comprises first and second shell sections, and an interference fit locking arrangement oriented between the shell sections. In one embodiment, the shell sections are unitary, i.e. they are joined along a hinge line. In an alternate embodiment, the shell sections are independent of one another, but engageable in a nesting manner. The interference locking mechanism preferably comprises a plurality of elongate, continuous, interengageable rachet teeth. In use, sealant material is positioned within the shell sections, and a junction to be sealed is enclosed therein.
TL;DR: In this paper, a new finite element formulation for elastic-plastic large deflection analysis of shells of revolution is presented, which contains most of the best features of nonlinear finite element analyses currently available in the literature, together with some new numerical schemes to improve the capability, accuracy and speed of the computation.
TL;DR: In this paper, a single pass girth butt welding of a carbon-manganese pipe is studied numerically using the finite element codes ADINAT/ADINA, and a rotationally symmetric finite element model is employed in both the thermal and mechanical analysis.
Abstract: Single‐pass girth butt welding of a carbon‐manganese pipe is studied numerically using the finite element codes ADINAT/ADINA. A rotationally symmetric finite element model is employed in both the thermal and mechanical analysis. This model is used to investigate the influence on the residual stress state of pipe geometry, mesh density and material modelling. The results from the present study are compared with previous results from two different FE analyses and an experimental investigation. One of the FE analyses was fully three dimensional and the other employed shell elements. The calculated residual stresses were found to differ significantly only when different material models were employed. The thermal strain seemed to be the material parameter with the largest influence on the residual stress state. Especially the changes in thermal strain during phase transformations seemed to have a great influence. This means that the temperature field should be determined accurately enough to predict when and where the different phase transformations occur. Almost the same residual stresses were obtained for two pipes with different pipe geometries and weld parameters.