| 1. |
- Bergdahl, Lars, 1943, et al.
(författare)
-
Time simulation of the motion of a tension leg platform
- 1988
-
Ingår i: BOSS'88 Proceedings of the international conference on behaviour of offshore structures. - 8251908558 ; 2, s. 875-890
-
Konferensbidrag (refereegranskat)abstract
- The time-domain motion of a Tension Leg Platform is studied. The used method is based on a convolution technique in which the hydrodynamic reaction force from the frequency-domain solution is Fourier transformed to the time domain. Such a method allows one to consider arbitrary time varying external forces as for example non-linear reaction forces from tendons as well as transient loads.In the developed model time series of first-order wave forces and second-orde slowly varying wave forces are calculated for irregular plane and short-crested waves. Exciting forces due to wind and current are calculated using drag coefficients from model tests. The equations of motion in the time domain are solved for a tension-leg platform performing rigid body motion and results in time series of the motions as well as of the tension in the tendons.Numerical simulations have been carried out and the results are discussed. A comparison is made between calculations and model tests for a tension-leg platform in irregular long-crested waves.
|
|
| 2. |
- Danielsson, Per-Erik
(författare)
-
Implementations of the Convolution Operation
- 1982
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The first part of this article surveys a large number of implementations of the convolution operation (which is also known as the sum-of-products, the inner product) based on a systematic exploration of index permutations. First we assume a limited amount of parallelism in the form of an adder. Next, multipliers and RAM:s are utilized. The so called distributed arithmetic follows naturally from this approach.The second part brings in the concept of pipelining on the bitlevel to obtain high throughput convolvers adapted for VLSI-design (systolic arrays). The serial/parallel multiplier is analyzed in a way that unravels a vast amount new variations. Even more interesting, all these new variations can be carried over to serial/parallel convolvers. These novel devices can be implemented as linear structures of identical cells where the multipliers are embedded at equidistant intervals.
|
|
| 3. |
- Sunnersjö, Staffan, 1948, et al.
(författare)
-
Hydrodynamic inertia and damping of ship hull vibrations
- 1988
-
Ingår i: Transactions of the Royal Institute of Naval Architects. - 0035-8967. ; 130, s. 107-117
-
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 …
|
|
| 4. |
- Berbyuk, Viktor, 1953, et al.
(författare)
-
Mathematical design of gantry robots for automating assembly processes
- 1989
-
Ingår i: Soviet journal of computer and systems sciences. - 0882-4002. ; 27:2, s. 1-8
-
Tidskriftsartikel (refereegranskat)abstract
- A methodology for an automatic selection of the structural schema and the parameters of an assembly robot based on an optimization procedure is described. A finite collection of so-called test positions for the operating element which are determined by the robot purpose and by its characteristic movements is specified. The dynamic, strength, etc. characteristics are computed at these test positions for each structural schema and the constraints for the optimization problem are formulated. The procedure for selecting the structural schema of the robot and its technical parameters consists of minimizing some functional for the indicated constraints. An example of computing the parameters of a gantry robot is given.
|
|
| 5. |
|
|
| 6. |
- Berbyuk, Viktor, 1953, et al.
(författare)
-
Problems of optimizing of structures and laws of control of the motion of electromechanical manipulators
- 1987
-
Ingår i: Soviet journal of computer and systems sciences. - 0882-4002. ; 25:6, s. 103-112
-
Tidskriftsartikel (refereegranskat)abstract
- A number of problems of optimizing the structural parameters and control laws aimed at minimizing the manipulator mass, the energy expenditures, and the maximum power of the electric motors, are formulated and solved within the framework of a mathematical model of an electromechanical manipulator that takes into account the distributed elasticity of an extended link. A formalization method is developed and an algorithm for solving the problem of the mathematical design of an optimal manipulator is proposed. The effect of the values of the moment of the electromagnetic forces at the initial and final instants of the control process on the kinematic and dynamic characteristics of the controlled motions of an elastic electromechanical manipulator is investigated.
|
|
| 7. |
- Bergdahl, Lars, 1943
(författare)
-
Vågor och vågkrafter
- 1984
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Kompendium i Kursen Vågor och vågkrafter. Speciellt borr- och produktionsplattformar för offshoreindustrin
|
|
| 8. |
- Boström, Anders E, 1951, et al.
(författare)
-
Elastic wave scattering by a three-dimensional inhomogeneity in an elastic half space
- 1980
-
Ingår i: Wave Motion. - 0165-2125. ; 2, s. 335-353
-
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).
|
|
| 9. |
- Boström, Anders E, 1951
(författare)
-
Multiple scattering of elastic waves by bounded obstacles
- 1980
-
Ingår i: Journal of the Acoustical Society of America. - 1520-8524 .- 0001-4966. ; 67, s. 399-413
-
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.
|
|
| 10. |
- Boström, Anders E, 1951
(författare)
-
Scattering by a smooth elastic obstacle
- 1980
-
Ingår i: Journal of the Acoustical Society of America. - 1520-8524 .- 0001-4966. ; 67, s. 1904-1913
-
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.
|
|
