| 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. |
- 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 …
|
|
| 3. |
|
|
| 4. |
- Isaksson, Ove
(författare)
-
Numerical analysis of elastohydrodynamic contacts using power-law lubricant with special reference to water-based hydraulic fluids
- 1987
-
Ingår i: ASLE transactions. - : Informa UK Limited. - 0569-8197. ; 30:4, s. 501-507
-
Tidskriftsartikel (refereegranskat)abstract
- A numerical solution of the elastohydrodynamic lubrication problem for pure rolling with non-Newtonian lubricants is outlined. The non-Newtonian rheological model used is a modified power-law tau equals K multiplied by (times) gamma **n. At low shear rate gamma less than gamma //b, the lubricant is Newtonian, but when gamma greater than gamma //b the lubricant becomes non-Newtonian, tau equals K multiplied by (times) gamma **n. At high shear rate ( gamma yields infinity ) the lubricant becomes Newtonian again with the same viscosity as the base lubricant. By using this rheological model a modified Reynolds' equation is derived. The influence of the n-value and gamma //b on the film thickness has been investigated. Plots of the pressure distribution and film thickness within the contact for fluids with G-values in the range 169-986 is presented. These G-values are typical for water-based hydraulic fluids. For fluids with low n-values (n less than 0. 5) the pressure profile approaches the Hertzian pressure distribution and the minimum film thickness is that given by the base fluid viscosity.
|
|
| 5. |
|
|
| 6. |
- Isaksson, Ove
(författare)
-
Rheology for water-based hydraulic fluids
- 1987
-
Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 115:1-2, s. 3-17
-
Tidskriftsartikel (refereegranskat)abstract
- High water-based hydraulic fluids with slightly higher viscosities than water, for instance 95-5 emulsions and micro-emulsions, do not show any significant deviation from a Newtonian fluid. Adding polymeric viscosity improvers for the purpose of increasing the viscosity will be successful as long as the shear rate is low. However, as the shear rate is increased, higher than about 10**3 s** minus **1, the viscosity will decrease and the advantage of the improver will vanish. The shear rate available was too low to break down the viscosity improvers. This is shown by the fact that the shear stress curve is reversible. Non-Newtonian fluids approach a more Newtonian behavior when the temperature is increased. The viscosity increase with pressure is much lower for water-based fluids than for a mineral oil. The pressure coefficient is about 10 times higher for mineral oils. The pressure coefficient increases if the water content of a water-based fluid is reduced.
|
|
| 7. |
|
|
| 8. |
- Isaksson, Ove
(författare)
-
Rheology of jet fuel contaminated hydraulic fluid
- 1988
-
Konferensbidrag (refereegranskat)abstract
- The viscosity at different pressures, temperatures and shear rates has been investigated. Furthermore, traction measurements between a steel ball and steel plate have been carried out. The results are compared with theoretical predictions. A decrease in oil film thickness due to viscosity loss has been established for fluids containing jet fuel. The pressure-viscosity-coefficient, the viscosity increase with pressure, is not effected by adding jet fuel to the hydraulic fluid.
|
|
| 9. |
- Isaksson, Ove
(författare)
-
Water-based hydraulic fluids : rheology and elastohydrodynamic lubrication
- 1986
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Experiments have been carried out to measure traction, antiwear and rheological properties of water-based hydraulic fluids. Four types of fluids have been examined, emulsions, micro-emulsions, synthetic solutions and water-glycols. A numerical solution of the elastohydrodynamic lubrication problem for pure rolling with non-Newtonian lubricants is also outlined. The non-Newtonian rheological model used is a power-law, ... Non-Newtonian behaviour has been established for fluids with polymeric viscosity improvers. These non-Newtonian effects are less pronounced at high temperatures. The surface charge for emulsion droplets increases the viscosity considerably but on the other hand ionic contaminations decrease the viscosity. The viscosity increase with pressure is much lower for water-based fluids than for mineral oils. For fluids with low n-values (n < 0.5) the pressure profile in elastohydrodynamic contacts approaches the Hertzian pressure distribution and the minimum film thickness will be that given by the base fluid viscosity. The wear-rate is lowest for those fluids having the highest pressureviscosity coefficient along with a Newtonian behaviour. The water-glycols give low traction coefficients but will not prevent wear at high loads. There is a decrease in both wear rate and traction for emulsions having a less pronounced droplet stability. The same improvement is reached using micro-emulsions, with smaller droplets.
|
|
| 10. |
|
|
