Proximal Shell Research Articles

Response of an underwater cylindrical composite shell to a proximal implosion

An experimental investigation is conducted to study the dynamic underwater response of a cylindrical composite shell under near critical hydrostatic pressure, to the implosion of another shell in proximity. A primary cylindrical composite shell is imploded in proximity to a secondary shell which is similar in all respects except for the secondary shell having a smaller length. Length differences of 10% and 20% are chosen to simulate variations in collapse pressures occurring in shells from real life manufacturing defects and/or degradation during operational use. The response of the secondary shell is investigated to understand if and how its collapse occurs in addition to studying the Fluid-Structure Interaction (FSI) phenomenon. The pair of shells are subjected to underwater hydrostatic loading using a large pressure vessel suitable for high-speed photography in conjunction with 3D Digital Image Correlation (DIC). 3D-DIC is employed to obtain full-field displacement measurements of both the shells, and local dynamic pressure histories are also simultaneously recorded. The primary shell always imploded first, causing a dynamic loading on the secondary shell. In cases of implosion of the secondary shell, although the transient radial deformations occurred in mode 2, the failure itself occurred with a localized failure of the shell walls. It is observed that there exists an inner critical stand-off distance for the secondary shell to fail catastrophically upon the implosion of the primary shell, and an outer critical stand-off distance beyond which the secondary shell does not implode. A critical stand-off distance is found to exist only in the case of the 10% smaller secondary shell length. If the secondary shell stand-off distance is more than the outer critical distance or when length of the secondary shell is 20% smaller, the secondary shell responds with bending and breathing modes and no visible damage is recorded. When the stand-off distance is in between the inner and the outer critical distances, the relative orientation of the incipient modal shapes of the two shells is the factor governing the collapse of the secondary shell. A method is also developed to decouple full-field 3D-DIC measurements into bending and breathing deformation measurements.

Scattering from fluid loaded targets in proximity to a sediment interface: Numerical results

A null-field T-matrix formalism developed for plane-wave scattering from a fluid-loaded elastic spherical shell in proximity to a rough fluid elastic interface [J. Acoust. Soc. Am. 101, 767–788 (1997)] is extended to include scattering from sound-hard and -soft spherical targets and a sound-hard finite cylinder with hemispherical end caps and, for a planar interface, sound-hard, sound-soft, and fluid-saturated poroelastic sediments. A variety of numerical results are obtained that demonstrate some of the effects of target and sediment parameters on target–boundary acoustic coupling and target strength. Then, for small amplitude surface roughness, a perturbation formalism is used to indicate some of the effects of interface roughness.

Scattering from a fluid loaded elastic spherical shell in proximity to a rough interface: Numerical results.

A null field T‐matrix formalism is developed and used to calculate plane‐wave scattering from a fluid loaded elastic spherical shell in proximity to sound hard, sound soft, fluid–fluid, and fluid–elastic interfaces with periodic surface roughness. For each type of interface, the Helmholtz–Kirchhoff integral representation of the various scattered pressure and displacement fields are constructed; the surface fields are required to satisfy the appropriate boundary conditions and the scattered fields are required to satisfy the extended boundary condition. Spherical basis functions are used to construct a free field T‐matrix for the elastic shell and rectangular vector basis functions are used to construct a representation of the free field T‐matrix for the rough interface. The free field T‐matrices are introduced into the Helmholtz–Kirchhoff equations for the scattered fields and the null field equations for the shell‐interface system and an ‘‘exact’’ analytical solution is obtained. Numerical results are obtained that demonstrate the effects of boundary type, elastic parameters, roughness geometry, amplitude, and slope on the scattered pressure field and on the ability to ‘‘see’’ the scatter from the elastic shell.

Scattering from a fluid‐loaded elastic spherical shell in proximity to a rough fluid–elastic interface: Numerical results

A null field T‐matrix formalism is developed and used to calculate scattering of a pressure wave from a fluid‐loaded elastic spherical shell in proximity to a rough fluid–elastic interface. The Helmholtz–Kirchhoff integral representations of the various scattered pressure and displacement fields are constructed. The surface fields are required to satisfy the elastic boundary conditions and the scattered fields are required to satisfy the extended boundary condition. The free‐field T matrices for the elastic shell and the rough fluid–elastic interface are constructed and used in the Helmholtz–Kirchhoff and the null field equations for the shell‐interface system. It is shown that the T matrix for the system is simply related to the free‐field T matrices for the shell and the rough fluid–elastic interface. A perturbative solution is obtained for scattering from arbitrary roughness, and an ‘‘exact’’ solution is obtained for scattering from periodic roughness. The ‘‘exact’’ solution is used to obtain a variety of numerical results that show some of the effects of the acoustic coupling that occurs between the rough interface and the elastic spherical shell.

Developmental changes in the cell columns and trophoblastic shell of the macaque placenta: an immunohistochemical study localizing type IV collagen, laminin, fibronectin and cytokeratins.

Developmental changes in the organization of cells and extracellular matrix in the cell columns and trophoblastic shell of macaque placentas have been examined between 37 days of gestation and term. Between 37 and 53 days a thickened basement membrane developed between the trophoblast cells of the proximal cell columns and the mesenchymal cores of contiguous anchoring villi. This layer stained strongly for type IV collagen and laminin, but weakly for fibronectin. Large "lakes" of extracellular matrix immunoreactive for all 3 of these antigens were present in the distal columns, while smaller amounts were distributed between cells of the proximal columns. During this period the trophoblast cells in the proximal shell reorganized, forming strands of cells that were separated by bands of matrix immunoreactive for type IV collagen, laminin, and fibronectin. Staining for these antigens decreased abruptly at the junction between fetal and maternal tissues. Between 66 and 104 days the thick basement membrane of the proximal columns persisted, but stained only weakly for each of the 3 extracellular matrix antigens. The large lakes of matrix in the distal columns characteristic of earlier stages gradually disappeared. The cell columns became progressively shorter and the tips of the anchoring villi became embedded in the trophoblastic shell. The matrix of the shell decreased in immunostaining intensity except for narrow rims around the trophoblast cells. Gestational ages later than 104 days showed few additional changes in the distribution of the matrix antigens or cell organization of the columns and shell. The thick basement membrane-like layer persisted to term although it continued to stain weakly for the 3 matrix antigens. The distal ends of most anchoring villi were embedded in the trophoblastic shell. The developmental changes in the organization of the columns and shell may be related to changes in placental growth rate.