· · · Repository Hydraulic Engineering Reports

This paper has two main objectives: (1) to describe the experimental work carried out in order to verify the theoretical method from Martin (1995) for the calculation of wave forces on crown walls and (2) to show some results from field and lab measurements and compare these data to calculations from several analytical methods. The Principe de Asturias Breakwater at Port of Gijon has been taken as the reference structure in this study. The experimental work (prototype and scale models) has been carried out over the same cross section, corresponding to this breakwater. Three scales have been used here: scale 1:1 (prototype measurements), scale 1:18..4 (tests done at Laboratorio de Ingenieria Maritima, UPC, Barcelona) and scale 1 :90 (tests done at Laboratorio de Ingenierfa Oceanogratica, Universidad de Cantabria). Therefore, data from the same phenomena in three different scales are available, which will provide the basis to analyse scale effects in the lab. The main part of the experimental work was carried out from 1995 to 1998 .. Due to the large costs of such a long experimental project, several organisations (referred in the acknowledgements section) were asked for financial support to the study. This is a good example of long-term project which was possible by the joint effort of, several institutions (public and private) within the European Research Framework. In the paper, forces from the tests are compared to calculations done from the method proposed by Martin (1995). The comparison shows good agreement between the calculations and the measurements from the lab, and not-so-good agreement to prototype data. From these results, it can be stated that the method is working well as it was developed from lab data From this study, it can be stated that differences to prototype forces are due to scale effects between lab and prototype measurements.

Afmeerkrachten bij centrisch en excentrisch botsen van een schip tegen fenderpalen en bij aanvaren van een verend remmingwerk; invloed traagheid van het water op afmeerkrachten, aanvullende beschouwing betreffende botsen van schepen tegen remmingwerken (rekenen in tijddomein)

A multitude of conceptual models of floating breakwaters have been proposed without extensive or complete evaluation of most of these concepts. The technical literature regarding floating breakwater applicability and design procedures is fragmentary and sometimes confusing. Clear, concise guidance does not always exist for those responsible for planning and developing wave protection measures which utilize floating breakwaters. This study reviewed and evaluated the existing technical literature (theoretical, field, and laboratory) on floating breakwater concepts. While floating breakwaters provide a lesser assurable degree of protection than a permanently fixed breakwater, they are in general less expensive and can be moved from one location to another. The cost of a floating system is only slightly dependent on ,.,rater depth and foundation conditions. Adequate wave reduction or energy attenuation can be attained by a floating breakwater only if the incident wave is of a relatively low height. A reasonable magnitude appears to be an incident wave height not exceeding 4 feet, with a corresponding wave period not exceeding 4 seconds. Floating breakwaters can attenuate waves with these incident characteristics to a magnitude tolerable in a small-craft mooring area (wave heights up to 1.5 feet). Open-ocean applications of a distinctly different concept can be formulated to withstand substantial increases in the incident wave characteristics. A group of prismatic structures contains the simplest forms of floating breakwaters. This group offers the best possibilities for multiple use as walkways, storage, boat moorings, and fishing piers. In addition to mass, the radius of gyration and the depth of submergence appear to significantly influence the attenuation characteristics. As the ratio of breakwater width-to wavelength increases to values greater than 0.5, the wave attenuation features of the structure not only improve markedly, but the net result of the forces on the mooring and anchoring system becomes substantially less. This occurs because the wave dynamics are exerting forces on a part of the structure in a direction opposite to those forces on other parts of the breakwater.

Shock pressures of high intensity and short duration may occur during breaking of waves on coastal structures, slamming of ships, landing of seaplanes, and water entry of naval projectiles with flat nose. The phenomenon of shock pressures resulting from the impact between a solid and a liquid can better be described as a water hammer phenomenon wherein the elasticity of the solid and the compressibility of the liquid are the governing factors. The water hammer theory predicts the extreme values of shock pressures since it neglects the effect of air that might be entrapped between the solid an the liquid at the moment of impact. Analytical formulations of shock pressures as a water hammer phenomenon and as the compression of a thin layer of air entrapped between the solid and the liquid at the moment of impact are presented in this report. Tests were conducted by dropping a steel, aluminum or plastic plate whose edge was hinged at the water surface into a 3- by 3- by 6-ft steel tank that was partially filled with water. The shock pressures were measured at two locations by means of strain gage and piezoelectric type pressure cells mounted in the plate with special adapters. The ratio between the recorded and theoretical pressures when treated statistically was found to fit the Poisson distribution well. Correlation between the recorded pressures and the shape of the surface of contact between the solid and the liquid at the moment of impact indicated that although shock pressures have a great intensity, they have a short duration and occur only at some spots on the surface of the solid. Therefore (a) they should not be applied as static pressure for checking the stability of the coastal structure as a whole, (b) they may be absorbed by flexible structures, (c) they may cause cracks in rigid structures such as steel caissons filled with rock, and (d) they may affect the stability of structures that have natural frequencies within the range of duration of shock pressures. Equations and diagrams for the prediction of the magnitude and duration of shock pressures resulting from the impact between a solid and a liquid are presented herein.

Research on rubble mound breakwaters when confronted with waves. The rapport covers the flow characteristics and mound stability under regular waves and under oblique wave attack. The authors find a formula for rough, permeable slopes, flow characteristics under the action of a regular wave train by a function of the type. Furthermore they conclude that the distribution of flow characteristics in sea state can be obtained on the basis of interaction curves and joint probability density function of wave heights and periods. The conclusions on the mound stability of breakwaters are: -Stability conditions of an undefined, rough, permeable slope are governed by the stability function. -The stability function depends only on Iribarren's number. -Randomness can be accounted for by using confidence bands for the stability function. -For each type of armour unit, an optimum slope of maximum stability exists. The greater the interlocking among armour units the steeper the optimum slope and the more peaked the stability maximum. -Given a rubble mound breakwater a minimum sea state exists which produces a significant failure probability. If a sea state is presented which is the same or higher than this minimum, failure of the structure is only a question of the duration of the sea state. Conclusions on the characteristics and stability of rubble mound breakwaters under oblique wave attack: -There is a dangerous lack of experimental data on the subject. -Run-up and run-down under small oblique incidence of waves (angle lower than 45 degrees) are function of Ir.cos(theta). For higher incidence angles the hypothesis is unreliable. -The stability of steep slopes under oblique wave attack is not worse than under perpendicular wave incidence. For milder slopes the opposite may be true. -The failure of probability of a rubble mound breakwater under a sea state with oblique incidence, can be calculated by taking into account the breaking limit, the interaction curve and a joint distribution of wave heights and periods.

Experimental research to the influence of the air pressure on the impact pressure cause by breaking waves. The research shows that there are three factors which load the structure during the breaking of waves: the water layer over the structure, the shock due to the impact of the water jet from breaking and the air pocket entrapped in the water mass. The influence of all of the factors is determined.