Modification of Airflow Structure Due to Wave Breaking on a Submerged Topography

Experimental results from a combined wind–wave tank are presented. Wind profiles and resulting wind–wave spectra are described, and an investigation of the airflow above breaking waves is presented. Monochromatic waves created by the wave maker are directed towards a submerged topography. This causes the waves to break at a predictable location, facilitating particle-image-velocimetry measurements of the airflow above steep breaking and non-breaking waves. We analyze how the breaking state modifies the airflow structure, and in particular the extent of the sheltered area on the leeward side of the waves. Results illustrate that while the geometrical properties of the waves greatly influence the airflow structure on the leeward side of the waves, the state of breaking (i.e., whether the waves are currently in a state of active breaking) is not observed to have a clear effect on the extent of the separated flow region, or on the velocity distribution within the sheltered region.

Contribution of Infragravity Waves to Run-up and Overwash in the Pertuis Breton Embayment (France)

Wave run-up and dune overwash are typically assessed using empirical models developed for a specific range of often-simplistic conditions. Field experiments are essential in extending these formulae; yet obtaining comprehensive field data under extreme conditions is often challenging. Here, we use XBeach Surfbeat (XB-SB)—a shortwave-averaged but wave-group resolving numerical model—to complement a field campaign, with two main objectives: i) to assess the contribution of infragravity (IG) waves to washover development in a partially-sheltered area, with a highly complex bathymetry; and ii) to evaluate the unconventional nested-modeling approach that was applied. The analysis shows that gravity waves rapidly decrease across the embayment while IG waves are enhanced. Despite its exclusion of gravity-band swash, XB-SB is able to accurately reproduce both the large-scale hydrodynamics—wave heights and mean water levels across the 30 × 10 km embayment; and the local morphodynamics—steep post-storm dune profile and washover deposit. These findings show that the contribution of IG waves to dune overwash along the bay is significant and highlight the need for any method or model to consider IG waves when applied to similar environments. As many phase-averaged numerical models that are typically used for large-scale coastal applications exclude IG waves, XB-SB may prove to be a suitable alternative.

Can Marina Qualify as a Place of Refuge?

This paper deals with marinas as potential places of refuge. A place of refuge is a port, a part of a port, a sheltered wharf or anchorage, or another sheltered area where temporary accommodation of vessels and marine facilities is possible in order to render assistance or avoid potential threats to humans, ships and the environment. Marinas, as the most important type of nautical port, are suitable for smaller vessels. In countries like the Republic of Croatia, where the development of nautical tourism is of great importance, the obligation of marinas to provide assistance or grant access to ships in distress needs to be established. Thereby, it is essential to take into account all marina characteristics and compare them with those of other types of ports. In Croatian legislation, places of refuge are regulated by the Ordinance on Places of Refuge compliant with IMO Guidelines A.949 (23) and A.950 (23) and European Directives (2002/59 / EC). The paper analyses the suitability of the marinas as places of refuge for vessels, primarily vessels for nautical tourism.

ANALYSIS OF LONG-CIRCUIT TYPE CAISSONS FOR ATTENUATION OF LONG-PERIOD WAVES

Breakwaters provide convenient shelter for short-period waves, thus limiting the amount of energy entering the harbor. This wave energy in the port basins may be amplified, due to the wave reflection, disturbing port operations. Anti-reflective Jarlan-type (ARJ) structures (see Jarlan, 1961) have been proposed in the literature, along with other structures, to alleviate wave disturbance within port basins. ARJ anti-reflective mechanism is based on the destructive interference of waves. An anti-reflective zone width, B, must be almost a quarter of the wavelength for maximum efficiency. Longer waves easily enter the port-sheltered area where resonance phenomena could magnify its energy under certain conditions. This low-frequency energy is much more difficult to dissipate. Port resonance is the phenomenon of energy amplification that takes place in a harbor or port basin if the incident waves have frequencies close to those of the natural oscillation of the mass of water in the port basin. These infragravity long waves are frequently reported as causing trouble in cargo handling areas of many ports (see Rabinovich, 2009), even causing breakages of mooring lines and other relevant damage (see Thotagamuwage and Pattiaratchi, 2014).

Research on modeling and simulation in overshadowing influence of coastal building on vessel traffic service radar

The reflection characteristics of radar waves in coastal high-rise buildings form a certain shielding area, which makes it difficult for vessel traffic service to control the ship dynamic situation in sheltered waters. To study the overshadowing influence of coastal buildings on the vessel traffic service radar, an expression model of shielding area is established based on the structure characteristics of buildings and the relative height of radar. Then, the coordinate system is established, and the range and height of the shelter area are calculated, according to the geometric relation. Based on the theory of radar electromagnetic wave diffraction, the target height is calculated. Finally, taking the prince’s Bay Cruise Terminal Building on the radar Shekou radar as an example, the shielding area and height are calculated and visualized by the numerical calculation model and verified by real vessel test and observation. The building with a height of 60 m has covered 973,090 m2 of sheltered area for Shekou radar. The results can be used not only to analyze the influence of buildings on existing vessel traffic service radar stations but also to provide an important reference for site selection of vessel traffic service radar stations.

Composition And Characteristic Of The Surficial Sediments In The Southern Corniche Of Jeddah, Red Sea Coast

This work discusses the composition and characteristic of the surficial sediments in the southern corniche of Jeddah, Saudi Red Sea coast, in an attempt to infer the surficial distribution pattern of minerals and provenance of sediments. Twenty-six superficial sediments samples were collected from backreef and forereef areas and were analyzed for grain size, CaCO3 content, and mineralogy. The textural of grain size range from gravel to mud fraction. The mud-dominated substrates (<63 µm) occur generally in the back-reef area near the shoreline (sheltered area) and in the lagoon. Gravel rich-sediments are mostly found in forereef regions. The highest content of aragonite and Mg-calcite occur in the forereef area, probably because to suitability the forereef region for chemical and biochemical precipitation of these minerals. High Mg-calcite and Dolomite are low in both the regions. The pyrite occurs in lagoon; this indicates the reductive conditions in this part. However, on the contrary the percentage of carbonate minerals were low in the backreef-flat area, which could be attributed to the supply of non-carbonate terrigenous materials. The terrigenous material contains quartz, k-feldspar, plagioclase and amphibole minerals and are dominant in backreef-flat area with averages of 12.7%, 7.13%, 2.93% and 0.65%, respectively. Their abundance could be attributed to the supply of terrigenous materials by Aeolian deposits and intermittent Wadis.

Effect of Corrugation on the Performance of Porous Baffles Used as Weather Shelters on Oil and Gas Platforms

Porous baffles are usually used for weather protection on onshore and offshore oil installations in order to provide a sheltered area for personnel to operate. Corrugated fences are more favourable than flat fences in large installations, due to their increased stiffness; however, the performance of those fences is expected to differ from flat fences due to changes in porosity and flow structure. In this work, the experimental and numerical studies of the influence of corrugated fence on the flow characteristics are presented. The tri-dimensional effect imposed by the angle of corrugation and the depth of the fence influences the windward and leeward flow characteristics with respect to the fence. Velocity coefficient is used as one important parameter for measuring the performance of porous fences. It was found that, under similar conditions, the total obstruction produced by the corrugated fence varies significantly from that of the flat fence. Hence, velocity reduction for a corrugated fence system is expected to be smaller. A complete description of the physics of the fluid mechanics around the fence is given. Furthermore, the behaviour of the stream lines close to the fences in both cases; corrugated and non-corrugated, were studied using CFD techniques. Through observation of local pressure distribution, it was possible to reveal how velocity variations were concentrated around the inclined sections of the corrugated fence. In performing the numerical simulations, a two dimensional approach was initially implemented to capture the flow behaviour in the vicinity of the inclined sections. Subsequently, a tri-dimensional simulation on a section of the fence was undertaken and compared with experimental data. The results of the simulations were in good agreement with experimental data obtained from wind tunnel tests.

Wave Absorption Improvements Inside the Moonpool of a Monocolumn Platform With an Internal Dock

Monocolumn platforms are usually considered an alternative concept for drilling and offshore production unit designs. This concept could provide high stability, small motions and also storage capacity. More recently, it was considered for a logistic hub platform design. The use of this concept with an opening for boat docking seems to provide a feasible solution for the people transfer in harsh environments, especially in areas like pre-salt Brazilian offshore fields, which are also very far from the coast. Although the helicopter technology has been improved in recent years to attend transport requirements from shore to the platforms, the use of a hub platform at sea still shows some economical and operational advantages, related to the conventional operations. Although the sheltered area provided by the interior of the monocolumn platform seems to solve the transfer problem in harsh environments, the hydrodynamic behavior of the moonpool became a problem to be solved during the feasibility studies of the concept, since the moonpool water column elevations tends to be resonant in special cases. To deal with this problem, some attempts were done to absorb the wave energy inside the moonpool and eliminate its resonance, achieving the desired level of absorption. This work shows the attempts and the results obtained, which has proven the feasibility of the concept.

Hydrodynamic Moonpool Behavior in a Monocolumn Hub Platform With an Internal Dock

One of the possible uses of a Mono Column Platform is its application as a Hub Platform for people transportation to very far offshore production platforms. Considering a trip from shore to the Hub by a High Speed Vessel (HSV) and by helicopter from the hub to the production platforms, the use of this kind of unit can provide small motions for helicopter operations and a sheltered area for people landing. The use of the moonpool area as an internal dock for the HSV docking was studied in this paper considering an opening in the Mono Column hull to allow the access of the HSV to the moonpool area. The hydrodynamics aspects of the moonpool behavior were assessed considering both experimental and numerical tools and a comparison between these approaches had been also performed.