| 1. |
|
|
| 2. |
- Field, J.E., et al.
(författare)
-
Studies of two-dimensional liquid-wedge impact and their relevance to liquid-drop impact problems
- 1985
-
Ingår i: Proceedings of The Royal Society of London. Series A, Mathematical and physical sciences. - : The Royal Society. - 0080-4630. ; 401:1821, s. 225-249
-
Tidskriftsartikel (refereegranskat)abstract
- In the initial stage of liquid-drop impact, the contact region expands faster than the wave speed in the liquid. This causes compressible behaviour in the liquid, and high transient pressures. High-velocity jetting results when the wave motion in the liquid overtakes the expanding contact edge and moves up the free surface of the drop. The detailed pressure fields in this early time history of impact have been calculated by Lesser (Proc. R. Soc. Lond. 377, 289 (1981)) for both two and three-dimensional liquid masses and for targets of finite admittance. An important result is that the edge pressures exceed the central ‘water-hammer’ pressure 3ρ0CUi and at the time of shock-detachment approach ca. 3ρ0CUi. At this stage the edge pressures, for both spherical drops and two-dimensional liquid wedges, depend only on the impact velocity and the instantaneous angle between the liquid and solid surfaces. This suggests that the essential features of the early stage of liquid impact can be usefully studied by producing impacts with two-dimensional liquid wedges, and predicted data for pressures, shock angles and velocities are presented. Experiments are described for producing impacts with preformed shapes by using water-gelatine mixtures and observing the impact events with high-speed photography. The results confirm the main features of the model and give information on edge pressures, jetting, cavitation in the liquid and the effect of the admittance of the solid. The relevance of the results to the damage and erosion of materials subjected to liquid impact is discussed. In particular, it is possible to explain the apparently low damage-threshold of some materials, the form of damage and its development with repeated impact. The study highlights the importance of the detailed surface geometry in the region of contact.
|
|
| 3. |
|
|
| 4. |
|
|
| 5. |
- Field, J.E., et al.
(författare)
-
High-speed photographic study of laser damage and ablation
- 2015
-
Ingår i: Imaging Science Journal. - 1368-2199 .- 1743-131X. ; 63:3, s. 119-136
-
Tidskriftsartikel (refereegranskat)abstract
- This paper reviews earlier work and describes a photographic investigation of damage produced in glasses, polymers and crystals by Q-switched and non-Q-switched laser pulses. The cameras used in the study include a Wollensak Fastax WF3 camera, a Beckman & Whitley (model 189) rotating mirror camera, and a Beckman & Whitley (model 501) image converter camera. The formation of internal disc-type cracks with the non-Q-switched pulse was studied in detail. The use of these cracks for fracture energy studies is demonstrated. Photographic sequences show the production of micro-plasmas associated with damage, and stress waves formed during irradiation in both solids and liquids. A recent development is that of digital holography which adds phase and intensity information to the more conventional photographic techniques. This technique is used here to study laser ablation and wave propagation in water. The photographic data shows the processes taking place in the laser interaction with a wide range of materials and should be of interest to modellers.
|
|
| 6. |
- Field, J.E., et al.
(författare)
-
On the mechanics of high speed liquid jets
- 1977
-
Ingår i: Proceedings of The Royal Society of London. Series A, Mathematical and physical sciences. - : The Royal Society. - 0080-4630. ; 357:1689, s. 143-162
-
Tidskriftsartikel (refereegranskat)abstract
- Both experimental and theoretical methods are used to investigate the mechanics of the emergence and flight of a liquid jet travelling at speeds supersonic relative to the sound speed of the liquid. The experimental work uses an Imacon image converter camera to follow the mechanical events at micro-second framing intervals. The theoretical investigation employs similarity arguments and the Tschaplygin transformation to investigate the role of liquid overcompression in the process of the jet emergence. In addition, simple theoretical arguments are used to examine the effects of Stokes drag on the small liquid particle shroud surrounding the jet and Taylor instability effects in the late time history of the jet’s flight. An evacuated chamber is used to verify the theoretical prediction that subsonic (relative to the liquid sound speed) jets will not undergo the violent decompression process predicted for supersonic jets. The experimental and theoretical evidence are synthesized into an overall picture of the jet’s history from initial decompression of an overdense supersonic jet to the breakup of the resulting liquid slugs by deceleration and Taylor instability.
|
|
| 7. |
|
|
| 8. |
- Lesser, Martin B., et al.
(författare)
-
The impact of compressible liquids
- 1983
-
Ingår i: Annual Review of Fluid Mechanics. - : Annual Reviews. - 0066-4189 .- 1545-4479. ; 15, s. 97-122
-
Tidskriftsartikel (refereegranskat)abstract
- Consideration is given to liquid impact in the supersonic regime in order to characterize pressure loading and other mechanisms which could damage a solid target such as a jet in flight. The liquid mass is treated as having a free surface, while the solid is assumed linear elastic. During contact, the fluid is maintained as a continuum and the solid becomes a homogeneous and isotropic elastic material. The processes have been described analytically and numerically by incompressible models, by water entry models, and with two-dimensional calculations. Experimentation has been performed with single and multiple impact techniques, with attention given to jetting, the jetting angle, impact pressures, and impacts on a wetted surface. High edge pressures have been observed, as has cavitation in the liquid and detachment of the edge shock. The presence of a liquid film on the surface of the object has been found to significantly affect the extent of erosion.
|
|
