Francisco Martin

Experimental study of wave-induced flow in a porous structure

Abstract The kinematics and dynamics of oscillatory flow in porous media are experimentally studied in an idealized porous structure. The concept of seepage velocity, extensively used in literature for the study of porous media, is analyzed. Spatial and temporal fluctuations due to irregularities in the porous structure are evaluated; it is shown that, quantitatively, spatial fluctuations are always more important. Measurements of the velocity, pressure field and wave height inside the structure reveal that the flow behaviour changes, resulting in two characteristic regions: transition and transmission regions. The relative width of the structure, B/L, associated with the formation of a standing wave and resonant conditions inside the structure, was found to be an important parameter to establish the location of the two regions. The transition region is characterized by very irregular records with secondary peaks, little or no dissipation and important higher harmonics in the velocity spectra. Dissipation is the most important factor in the transmission region where the flow tends to become more regular. The porous structure works as a filter, filtering out the higher frequencies as the oscillation propagates towards the leeside of the structure.

Wave loads on rubble mound breakwater crown walls

Abstract Crown walls are primarily built to reduce wave overtopping of mound breakwaters. Several methods have been proposed to calculate wave loads on the crown wall, e.g., Iribarren and Nogales [Iribarren, R., Nogales, C., 1964. Obras Maritimas. Dossat (Ed.), Madrid, 376 pp.], Jensen [Jensen, O.J., 1984. A Monograph on Rubble Mound Breakwaters. Danish Hydraulic Institute] and Gunbak and Gokce [Gunbak, A.R., Gokce, T., 1984. Wave screen stability of rubble-mound breakwaters. International Symposium of Maritime Structures in the Mediterranean Sea. Athens, Greece, pp. 2.99–2.112]. In this paper, a new method based on those previous results, and on further experimental work, using monochromatic waves, is presented. The application of the new method requires waves breaking on the armour layer; i.e., only broken waves will reach the crown wall. The method is extended to irregular waves via the hypothesis of equivalence introduced by Saville [Saville, T., 1962. An approximation of the wave run-up frequency distribution. Proc. 8th International Conference on Coastal Engineering, Mexico City] and is applied to the crown walls of Gijon and Bilbao breakwaters in Spain. The comparison of the probability force distributions obtained by the present method to that measured by Burcharth et al. [Burcharth, H.F., Frigaard, P., Berenguer, J.M., Gonzalez, B., Uzcanga, J., Villanueva, J., 1995. Design of the Ciervana breakwater, Bilbao. In: T. Telford (Ed.), Proc. 4th Coastal Structures and Breakwaters, Chap. 3. Institution of Civil Engineers] and Jensen (1984) is relatively good.

PROTOTYPE ANALYSIS OF STABILITY OF RUBBLE MOUND PROTECTIONS FOR SUBMARINE OUTFALLS

This paper presents the construction, surveying and results of a prototype experiment on stability of rubble mound protection for submarine outfalls. Taking advantage of the Santander outfall construction, financial support from the European Community was obtained to carry out the experiment that consisted of covering the outer layer of the outfall’s protection with two extra layers of rubble with a stone weight smaller than that of the project. Three stone weights were tested in three different stretches of the outfall. The experiment lasted two years, during which waves and stone movements were surveyed. Damage and wave data were analyzed and the damage parameter is presented here as a function of the mobility parameter. To take into account the random characteristics of waves in the sea states, a Montecarlo simulation is used here to calculate the mobility parameters corresponding to all the waves of all the sea states that reached the experimental sections. The use of the average of the 50 biggest mobility parameters that reached the test sections at the survey date is proposed here to represent damage results against the mobility parameter. Using this mobility parameter, prototype results compare well with laboratory experiments carried out with regular waves. INTRODUCTION Submarine outfalls for wastewater are economical alternatives in coastal areas to wastewater treatment plants. In coastal areas of high wave energy like the northwest of Spain and in those sites were the bottom characteristics do not allow the burial of the pipe, the outfalls are protected by several layers of rubble. 1 Associate Professor, University of Cantabria, Avda. de los Castros, s/n 39005 Santander, Spain. vidalc@unican.es 2 Assoc. Researcher, University of Cantabria, Avda. de los Castros, s/n 39005 Santander, Spain. lomonacop@unican.es 3 Associate Professor, University of Cantabria, Avda. de los Castros, s/n 39005 Santander, Spain. martinfl@unican.es Vidal, Lomonaco, and Martin 1 The existing methods for the assessment of the armor layer stability against wave action are based on extrapolations of formulas developed for submerged breakwaters or for the determination of sediment transport on horizontal bottoms. The existing uncertainty about their applicability to the deep outfall protections may result in conservative, oversized designs. During the 1990’s, the application in Spain of the European Union regulations for wastewater emissions generated a high number of outfall projects for coastal cities in the North Atlantic waters of Spain. Most of these outfalls were designed with rubble protections. The application of the existing formulas showed great differences among the prescribed weights of the stones required in those sections of the outfall where the water was deep enough to prevent the rubble from the direct action of the breaking waves. To cover this lack of stability formulations, the Ocean & Coastal Research Group (hereafter GIOC) of the University of Cantabria started in 1997 several R&D Projects founded by the Spanish Commission for Science and Technology (CICYT) and by the European Founds for Regional Development (FEDER). After extensive experimental work in wave tank, a methodology for the assessment of the stability of near bed rubble protections, based on the mobility parameter, was presented in Vidal et al. (1999). In 1999, the GIOC obtained FEDER founding to carry out the construction and survey of several prototype test sections over the outfall of Santander that was being built at that time. The outfall’s building company, Dragados y Construcciones, S.A, collaborated in the Project, building these test sections after the main protection was completed. The prototype experiments started in September 1999 and ended in August 2001. The objective of the test was to measure the stone movement due to wave action. This paper presents the prototype experiment and their results. SITE DESCRIPTION AND WORK PLAN The prototype experiment was designed to take place over the outfall of Santander that extends 2 Km into the Cantabrian sea from the cliffs of La Virgen del Mar (6 Km to the northwest o the city) up to 40 m water depth, were the diffusion section is located, see figure 1. The pipe is buried in the rocky bottom at a 15-m water depth. Deeper than this, the pipe lays over the bottom, protected by a core of 5 cm gravel, a filter of two layers of 200-300 Kg of quarry stones, and an armor of two layers of 3,000 Kg quarry stones, see figure 2. Vidal, Lomonaco, and Martin 2 ATLANTIC OCEAN PENAS EMOD Diffusion section REMRO Test section Santander Figure 1: Location of test section and wave buoys. The prototype experiment was planned to start just after the protection of the pipe was completed. Test sections were built using the same equipment and type of rock used by the building company.

STABILITY OF NEAR-BED RUBBLE-MOUND STRUCTURES

Detailed studies have been undertaken to assist in the design of major extensions to the port of Haifa. Both numerical and physical model studies were done to optimise the mooring conditions vis a vis the harbour approach and entrance layout. The adopted layout deviates from the normal straight approach to the harbour entrance. This layout, together with suitable aids to navigation, was found to be nautically acceptable, and generally better with regard to mooring conditions, on the basis of extensive nautical design studies.Hwa-Lian Harbour is located at the north-eastern coast of Taiwan, where is relatively exposed to the threat of typhoon waves from the Pacific Ocean. In the summer season, harbour resonance caused by typhoon waves which generated at the eastern ocean of the Philippine. In order to obtain a better understanding of the existing problem and find out a feasible solution to improve harbour instability. Typhoon waves measurement, wave characteristics analysis, down-time evaluation for harbour operation, hydraulic model tests are carried out in this program. Under the action of typhoon waves, the wave spectra show that inside the harbors short period energy component has been damped by breakwater, but the long period energy increased by resonance hundred times. The hydraulic model test can reproduce the prototype phenomena successfully. The result of model tests indicate that by constructing a jetty at the harbour entrance or building a short groin at the corner of terminal #25, the long period wave height amplification agitated by typhoon waves can be eliminated about 50%. The width of harbour basin 800m is about one half of wave length in the basin for period 140sec which occurs the maximum wave amplification.Two-stage methodology of shoreline prediction for long coastal segments is presented in the study. About 30-km stretch of seaward coast of the Hel Peninsula was selected for the analysis. In 1st stage the shoreline evolution was assessed ignoring local effects of man-made structures. Those calculations allowed the identification of potentially eroding spots and the explanation of causes of erosion. In 2nd stage a 2-km eroding sub-segment of the Peninsula in the vicinity of existing harbour was thoroughly examined including local man-induced effects. The computations properly reproduced the shoreline evolution along this sub-segment over a long period between 1934 and 1997.In connection with the dredging and reclamation works at the Oresund Link Project between Denmark and Sweden carried out by the Contractor, Oresund Marine Joint Venture (OMJV), an intensive spill monitoring campaign has been performed in order to fulfil the environmental requirements set by the Danish and Swedish Authorities. Spill in this context is defined as the overall amount of suspended sediment originating from dredging and reclamation activities leaving the working zone. The maximum spill limit is set to 5% of the dredged material, which has to be monitored, analysed and calculated within 25% accuracy. Velocity data are measured by means of a broad band ADCP and turbidity data by four OBS probes (output in FTU). The FTUs are converted into sediment content in mg/1 by water samples. The analyses carried out, results in high acceptance levels for the conversion to be implemented as a linear relation which can be forced through the origin. Furthermore analyses verifies that the applied setup with a 4-point turbidity profile is a reasonable approximation to the true turbidity profile. Finally the maximum turbidity is on average located at a distance 30-40% from the seabed.

Measurement of Armor Damage on Rubble Mound Structures: Comparison between Different Methodologies

This paper describes how the assessment of armor damage on rubble mound structures can be carried out with different methodologies that need to be properly calibrated in order to guarantee the reliability of the results. A comparison of the different methods used and the steps required to measure the armor damage are presented in detail.

A STATISTICAL TOOL FOR BREAKWATER DESIGN

Detailed studies have been undertaken to assist in the design of major extensions to the port of Haifa. Both numerical and physical model studies were done to optimise the mooring conditions vis a vis the harbour approach and entrance layout. The adopted layout deviates from the normal straight approach to the harbour entrance. This layout, together with suitable aids to navigation, was found to be nautically acceptable, and generally better with regard to mooring conditions, on the basis of extensive nautical design studies.Hwa-Lian Harbour is located at the north-eastern coast of Taiwan, where is relatively exposed to the threat of typhoon waves from the Pacific Ocean. In the summer season, harbour resonance caused by typhoon waves which generated at the eastern ocean of the Philippine. In order to obtain a better understanding of the existing problem and find out a feasible solution to improve harbour instability. Typhoon waves measurement, wave characteristics analysis, down-time evaluation for harbour operation, hydraulic model tests are carried out in this program. Under the action of typhoon waves, the wave spectra show that inside the harbors short period energy component has been damped by breakwater, but the long period energy increased by resonance hundred times. The hydraulic model test can reproduce the prototype phenomena successfully. The result of model tests indicate that by constructing a jetty at the harbour entrance or building a short groin at the corner of terminal #25, the long period wave height amplification agitated by typhoon waves can be eliminated about 50%. The width of harbour basin 800m is about one half of wave length in the basin for period 140sec which occurs the maximum wave amplification.Two-stage methodology of shoreline prediction for long coastal segments is presented in the study. About 30-km stretch of seaward coast of the Hel Peninsula was selected for the analysis. In 1st stage the shoreline evolution was assessed ignoring local effects of man-made structures. Those calculations allowed the identification of potentially eroding spots and the explanation of causes of erosion. In 2nd stage a 2-km eroding sub-segment of the Peninsula in the vicinity of existing harbour was thoroughly examined including local man-induced effects. The computations properly reproduced the shoreline evolution along this sub-segment over a long period between 1934 and 1997.In connection with the dredging and reclamation works at the Oresund Link Project between Denmark and Sweden carried out by the Contractor, Oresund Marine Joint Venture (OMJV), an intensive spill monitoring campaign has been performed in order to fulfil the environmental requirements set by the Danish and Swedish Authorities. Spill in this context is defined as the overall amount of suspended sediment originating from dredging and reclamation activities leaving the working zone. The maximum spill limit is set to 5% of the dredged material, which has to be monitored, analysed and calculated within 25% accuracy. Velocity data are measured by means of a broad band ADCP and turbidity data by four OBS probes (output in FTU). The FTUs are converted into sediment content in mg/1 by water samples. The analyses carried out, results in high acceptance levels for the conversion to be implemented as a linear relation which can be forced through the origin. Furthermore analyses verifies that the applied setup with a 4-point turbidity profile is a reasonable approximation to the true turbidity profile. Finally the maximum turbidity is on average located at a distance 30-40% from the seabed.