| 1. |
- Sunnersjö, Staffan, 1948, et al.
(författare)
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Hydrodynamic inertia and damping of ship hull vibrations
- 1988
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Ingår i: Transactions of the Royal Institute of Naval Architects. - 0035-8967. ; 130, s. 107-117
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Tidskriftsartikel (refereegranskat)abstract
- The entrained water plays an important role in ship hull vibrations. The classic Lewis method for calculation of hydrodynamic added mass has some inherent shortcomings that can result in insufficient accuracy, particularly for higher order modes. This is essentially due to the fact that the Lewis method uses a diagonal mass matrix that is dependent on the mode of vibration, while the physical reality is more accurately represented by a mode-independent, full mass matrix. Such full mass matrices can be calculated with Finite Volume or Source- Sink methods, which, however, require extensive computer calculations with detailed input data. A method is presented with which the Lewis transform can be used to determine a full mass matrix and gives very good agreement with Finite Volume calculations for a test case on a small ship. The Finite Volume calculations have also been used to study damping …
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| 2. |
- Bergdahl, Lars, 1943
(författare)
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Vågor och vågkrafter
- 1984
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Kompendium i Kursen Vågor och vågkrafter. Speciellt borr- och produktionsplattformar för offshoreindustrin
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| 3. |
- Boström, Anders E, 1951, et al.
(författare)
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Elastic wave scattering by a three-dimensional inhomogeneity in an elastic half space
- 1980
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Ingår i: Wave Motion. - 0165-2125. ; 2, s. 335-353
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we will consider scattering of elastic waves in a half space. The half space is an isotropic, linear and homogeneous medium except for a finite inhomogeneity. The T-matrix method (also called the "extended boundary condition method" or "null field approach") is extended to derive expressions for the elastic field inside the half space and the surface field on the interface. The assumptions on the source that excites the half space are fairly weak. In the numerical applications found in this paper we assume a Rayleigh surface wave to be the incoming field, and we only compute the surface displacements. We make illustrations on some simple type of scatterers (spheres and spheroids; the latter ones can be arbitrarily oriented).
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| 4. |
- Boström, Anders E, 1951
(författare)
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Multiple scattering of elastic waves by bounded obstacles
- 1980
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Ingår i: Journal of the Acoustical Society of America. - 1520-8524 .- 0001-4966. ; 67, s. 399-413
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Tidskriftsartikel (refereegranskat)abstract
- The transition matrix method for stationary elastic waves is extended to a great class of obstacles characterized by piecewise constant properties. First, the translation properties of the basis functions is used to treat two and, then, then several homogeneous obstacles, and thereafter an obstacle with consecutively enclosing layers is considered. It is then indicated how these two basic methods of combination can be applied tp treat more complex cases, including an obstacle consisting of several nonenclosing parts. Finally, we give some numrecal applications of configurations of spherical and nonspherical obstacles in and below the resonance region.
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| 5. |
- Boström, Anders E, 1951
(författare)
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Scattering by a smooth elastic obstacle
- 1980
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Ingår i: Journal of the Acoustical Society of America. - 1520-8524 .- 0001-4966. ; 67, s. 1904-1913
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Tidskriftsartikel (refereegranskat)abstract
- In the present paper we adapt the transition matrix method to the case of a smooth elastic obstacle. The boundary conditions employed are discussed in some detail and are seen to be responsible for the fact that the rather complicated formal solution in many respects resembles that of an elastic obstacle in a fluid. Comparisons are made between the smooth and the usually employed welded obstacles, and for spheres approximate expressions are given for the transition matrices in the long wavelength limit. Numerical results (cross sections and surface stresses) are given for spheres and spheroids, and it is then seen that often the smooth and welded obstacles, at least qualitatively, show similar features.
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| 6. |
- Boström, Anders E, 1951, et al.
(författare)
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Scattering of a pulsed Rayleigh wave by a spherical cavity in an elastic half space
- 1983
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Ingår i: Wave Motion. - 0165-2125. ; 5, s. 137-143
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Tidskriftsartikel (refereegranskat)abstract
- The time-dependant scattering by a spherical cavity in an elastic half space is considered. The incoming wave is a pulsed Rayleigh wave. The stationary part of the problem is solved by the T-matrix method, and an integration in frequency is perforemd with a modified gaussian weight function. The displcsement components at some points on the surface of the half space are computed and shown in a number of plots.
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| 7. |
- Boström, Anders E, 1951
(författare)
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Scattering of acoustic waves by a layered elastic obstacle in a fluid - an improved null field appraoch
- 1984
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Ingår i: Journal of the Acoustical Society of America. - 1520-8524 .- 0001-4966. ; 76, s. 588-593
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Tidskriftsartikel (refereegranskat)abstract
- Scattering by a layered elastic obstacle submerged in a fluid is considered. The null field approach (T-matrix method) is used, but the method is modified so that all surface fields can be expanded in spherical harmonics. The resulting method is then compared with the conventional null field approach (which uses expansions in regular wavefunctions), and it is concluded that the present method is better in general. It is, however, doubtful if the null field approach is applicable to cases where there is no sphere that circumscribes the core and inscribes the outer surface. Some numerical results are given for a layered spheroid and superspheroid.
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| 8. |
- Boström, Anders E, 1951
(författare)
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Scattering of stationary acoustic waves by an elastic obstacle immersed in a fluid
- 1980
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Ingår i: Journal of the Acoustical Society of America. - 1520-8524 .- 0001-4966. ; 67, s. 390-398
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Tidskriftsartikel (refereegranskat)abstract
- The scattering of stationary acoustic waves by a bounded elastic obstacle in an inviscid fluid is considered. The developed formalism is an extension of the transition matrix method, which has been given by Waterman for acoustic, electromagnetic, and elastic scattering. In fact the problem at hand is more complex than the elastic case, something which is apparent in the solution. It is possible to obtain some different forms for the transition matrix, depending upon whether the Rayleigh hypothesis enters or not. It is worthy of notice that the more general formalism, i.e., the one not assuming the Rayleigh hypothesis, is also the more efficient numerically. Numerical results are given for spheroids and an object resembling the number "8".
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| 9. |
- Boström, Anders E, 1951
(författare)
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Transmission and reflection of acoustic waves by an obstacle in a waveguide
- 1980
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Ingår i: Wave Motion. - 0165-2125. ; 2, s. 167-184
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Tidskriftsartikel (refereegranskat)abstract
- By an extension of the null field approach introduced by Waterman the transmission and reflection of acoustic waves by an obstacle in a waveguide are considered. The waveguide is assumed to have a constant cross section but otherwise the geometry is left arbitrary. The scattered field is obtained as a complicated mode sum containing the transition matrix of the obstacle, the reflection matrix of the waveguide wall, and the transformation relations between the cylindrical and spherical basis functions. For a circular cross section of the waveguide relatively explicit expressions are given for the transmission and reflection coefficients, and numerical results are shown for spherical and spheroidal obstacles in rotaionally symmetric configurations. Several natural extensions of the present results are finally recognized.
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| 10. |
- Boström, Anders E, 1951, et al.
(författare)
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Propagation of elastic surface waves along a cylindrical cavity and their excitation by a point force
- 1982
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Ingår i: Journal of the Acoustical Society of America. - 1520-8524 .- 0001-4966. ; 72, s. 998-1004
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Tidskriftsartikel (refereegranskat)abstract
- The existence of surface wave modes, propagating along on infinite cylindrical cavity in an elastic medium, is established for every integer m, where m is the azimuthal mode number. These waves are analogous to the Rayleigh wave on a half-space, being confined to the immediate vicinity of the cavity. The modes exhibit dispersion and have a cutoff frequency that increases with m, except for the flexural (m=1) mode which exists at all frequencies. At cutoff the phase velocity is equal to that of the shear waves and decreases, with increasing frequency, to that of the Rayleigh wave. We present results for the group velocities and displacement and stress fields of the modes and also exhibit the effect of various point forces acting near the cavity. In the vicinity of the cavity, not too near the point force, the surface wave contribution dominates the total displacement field.
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