The influence of air and scale on wave impact pressures
TL;DR: In this article, a relationship between the level of aeration and the violence of the impact is derived, which enables the reduction in impact pressure caused by aeration to be estimated and provides a better means of predicting impact pressures in laboratory seawater wave tests from freshwater tests than either the Froude or Cauchy laws.
About: This article is published in Coastal Engineering.The article was published on 2001-04-01. It has received 150 citations till now. The article focuses on the topics: Aeration & Poison control.
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TL;DR: In this paper, the authors focus on the results of theoretical work, making particular note of the value of considering pressure impulse, and highlight the aspects that are poorly understood, including the role of entrained and trapped air in wave impacts.
Abstract: ▪ Abstract The more violent impacts of water waves on walls create velocities and pressures having magnitudes much larger than those associated with the propagation of ordinary waves under gravity. Insight into these effects has been gained by irrotational-flow computations and by investigating the role of entrained and trapped air in wave impacts. This review focuses on the results of theoretical work, making particular note of the value of considering pressure impulse, and highlights the aspects that are poorly understood.
344 citations
TL;DR: In this paper, the effects of entrained and entrapped air on wave impacts are investigated and the characteristics of the impacts depend on the breaker conditions and four different types of impact are identified and discussed.
265 citations
TL;DR: In this article, the effect of formation of entrapped air pockets on the wave forces is studied by including air pressure relief openings on the deck of the model and the role of girders on the forces.
159 citations
TL;DR: In this article, Denny et al. measured the maximum hydrodynamic forces imposed on organism-sized benthic objects and related these forces to nearshore significant wave heights.
Abstract: Hydrodynamic forces from breaking waves are among the most important sources of mortality in the rocky intertidal zone. Information about the forces imposed by breaking waves is therefore critical if we are to interpret the mechanical design and physiological performance of wave-swept organisms in an ecologically and evolutionarily relevant context. Wave theory and engineering experiments predict that the process of wave breaking sets a limit on the maximum force to which organisms can be subjected. Unfortunately, the magnitude of this limit has not been determined on rocky shores. To this end, at a moderately exposed shore in central California, we measured the maximum hydrodynamic forces imposed on organism-sized benthic objects and related these forces to nearshore significant wave heights. At 146 of 221 microsites, there was a significant and substantial positive correlation between force and wave height, and at 130 of these microsites, force increased nonlinearly toward a statistically defined limit. The magnitude of this limit varied among sites, from 19 to 730 newtons (N). At 37 other sites, there was no significant correlation between surf zone force and wave height, indicating that increased wave height did not translate into increased force at these sites either. At only 16 sites did force increase in proportion to wave height without an apparent upper bound. These results suggest that for most microsites there is indeed a limiting wave height beyond which force is independent of wave height. The magnitude of the limit varies substantially among microsites, and an index of local topography was found to predict little of this variation. Thus, caution must be exercised in any attempt to relate observed variations in ocean ‘‘waviness’’ to the corresponding rates of microsite disturbance in intertidal communities. Rocky intertidal invertebrates and algae live in a world of extreme environmental severity, and the risk of damage or dislodgment from wave-generated forces is thought to be among the most important determinants of survival in this habitat (e.g., Dayton 1971; Levin and Paine 1974; Koehl 1979; Paine 1979; Paine and Levin 1981; Sousa 1984; Denny 1987, 1988; Carrington 1990, 2002; Bertness et al. 1991; Hunt and Scheibling 1996; Blanchette 1997). Quantifying the hydrodynamic forces acting on organisms, and how they vary in space and in time, is therefore key to understanding the evolutionary and ecological consequences of morphological design and the subsequent effects of wave-driven forces on the dynamics of intertidal ecosystems (Denny 1988; Koehl 1996; Denny and Wethey 2001; Carrington 2002).
106 citations
Cites background from "The influence of air and scale on w..."
...Engineers have long been interested in the forces that waves can exert, but their measurements have focused on the pressures imposed as water strikes a breakwater or cylindrical support member (e.g., Chan et al. 1995; Kobayashi and Demerbilek 1995; Bird et al. 1998; Kobayashi 1999; Bullock et al. 2001)....
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...…have long been interested in the forces that waves can exert, but their measurements have focused on the pressures imposed as water strikes a breakwater or cylindrical support member (e.g., Chan et al. 1995; Kobayashi and Demerbilek 1995; Bird et al. 1998; Kobayashi 1999; Bullock et al. 2001)....
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TL;DR: In this paper, an exact Riemann solver is developed to permit a finite-volume solution to the flow model with smallest possible local error. And the subsequent impact is modelled with a novel compressible-flow model for a homogeneous mixture of incompressible liquid and ideal gas.
Abstract: When an ocean wave breaks against a steep-fronted breakwater, sea wall or a similar marine structure, its impact on the structure can be very violent. This paper describes the theoretical studies that, together with field and laboratory investigations, have been carried out in order to gain a better understanding of the processes involved. The wave's approach towards a structure is modelled with classical irrotational flow to obtain the different types of impact profiles that may or may not lead to air entrapment. The subsequent impact is modelled with a novel compressible-flow model for a homogeneous mixture of incompressible liquid and ideal gas. This enables a numerical description of both trapped air pockets and the propagation of pressure shock waves through the aerated water. An exact Riemann solver is developed to permit a finite-volume solution to the flow model with smallest possible local error.The high pressures measured during wave impacts on a breakwater are reproduced and it is shown that trapped air can be compressed to a pressure of several atmospheres. Pressure shock waves, reflected off nearby surfaces such as the seabed, can lead to pressures comparable with those of the impact. Typical examples of pressure-time histories, force and impulse are presented and discussed in terms of their practical implications. The numerical model proposed is relevant for a variety of flows where air effects are important. Further applications, including extended studies of wave impacts, are discussed.
106 citations
Cites background or methods or result from "The influence of air and scale on w..."
...Further details of the variability found in the laboratory may be found in Bullock et al. (2007)....
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...Bullock et al. (2007) used their experimental measurements of sub-atmospheric and oscillatory pressures in the impact zone, similar to those described above, to help identify high-aeration wave impacts where air entrapment was suspected....
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...Even at small scale, the resultant difference in aeration level between seawater breakers and freshwater breakers of the same size results in a tendency for the former to generate impacts of longer duration and lower peak pressure in comparison with the latter (Bullock et al. 2001)....
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...This is largely due to the fact that the high-pressure region increases with the size of the air pocket and lends support to the observation of Bullock et al. (2007) that, even when the pressures during a high-aeration impact are lower, the fact that the impact is generally less spatially localized than a low-aeration impact reduces the chance of the resultant force being lower....
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...This is in agreement with Wood, Peregrine & Bruce (2000), who showed that the presence of trapped air can act to increase the pressure impulse for wave impacts, and Bullock et al. (2007), who concluded that the impulse due to a high-aeration impact could well be higher than that due to a low-aeration impact....
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References
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Book•
01 Jan 1873
TL;DR: The most influential nineteenth-century scientist for twentieth-century physics, James Clerk Maxwell (1831-1879) demonstrated that electricity, magnetism and light are all manifestations of the same phenomenon: the electromagnetic field as discussed by the authors.
Abstract: Arguably the most influential nineteenth-century scientist for twentieth-century physics, James Clerk Maxwell (1831–1879) demonstrated that electricity, magnetism and light are all manifestations of the same phenomenon: the electromagnetic field. A fellow of Trinity College Cambridge, Maxwell became, in 1871, the first Cavendish Professor of Physics at Cambridge. His famous equations - a set of four partial differential equations that relate the electric and magnetic fields to their sources, charge density and current density - first appeared in fully developed form in his 1873 Treatise on Electricity and Magnetism. This two-volume textbook brought together all the experimental and theoretical advances in the field of electricity and magnetism known at the time, and provided a methodical and graduated introduction to electromagnetic theory. Volume 2 covers magnetism and electromagnetism, including the electromagnetic theory of light, the theory of magnetic action on light, and the electric theory of magnetism.
9,565 citations
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16 Nov 2012
TL;DR: In this article, the authors present a bibliographie (a la fin de chaque chapitre), and index reference record created on 2004-09-07, modified on 2016-08-08
Abstract: Note: + bibliographie (a la fin de chaque chapitre), + index Reference Record created on 2004-09-07, modified on 2016-08-08
2,580 citations
TL;DR: In this article, the authors studied the physics and characteristics of impact pressure due to collisions of breaking waves against a vertical wall and found that when a small amount of air is entrapped between the breaking wave and the wall at the collision, the impact pressure increases considerably.
236 citations
TL;DR: The results suggest that the present design approaches cannot explain most of the failure modes reported, and that the stability of vertical breakwaters is an integrated and complex problem which can satisfactorily be solved only by dynamic analysis and probabilistic design approaches.
224 citations