Effects of waves and currents on gravity-type cages in the open sea

2008 ◽  
Vol 38 (2) ◽  
pp. 105-116 ◽  
Author(s):  
Chai-Cheng Huang ◽  
Hung-Jie Tang ◽  
Jin-Yuan Liu
Keyword(s):  
Open Sea ◽  
Author(s):  
Lin Li ◽  
Zhiyu Jiang ◽  
Jungao Wang ◽  
Muk Chen Ong

A vessel-shaped fish farm concept for open sea applications has been proposed recently. The whole system consists of a vessel-shaped floater, fish cages positioned longitudinally along the floater, and a single-point mooring system. The whole system weathervanes; this feature increases the spread area for the fish waste. However, the downstream cages may experience reduced water exchange when the vessel is parallel to the currents. This situation may jeopardize the fish health. A dynamic positioning (DP) system may be necessary to improve the flow conditions. This paper investigates the misalignment angle between the heading of the vessel-shaped fish farm and the currents under combined wave and current conditions. The misalignment angle is critical for the estimation of the DP system consumption. A numerical model of the fish farm system with flexible nets is developed. Current reduction factors are included to account for the flow velocity reductions between the net panels. The heading of the system is obtained by finding the equilibrium condition of the whole system under each combined wave and current condition. An integrated method using metamodels is proposed and applied for the prediction of the misalignment angle for a reference site. The probability distribution of the misalignment angle between the vessel heading and the currents is calculated using the Kriging metamodel for the reference site. Based on the prediction, the requirement for the DP system to improve the flow condition in the fish cages is discussed.


Author(s):  
Marcelo Anunciação Jaculli ◽  
José Ricardo Pelaquim Mendes ◽  
Kazuo Miura ◽  
Márcio Yamamoto

The construction of subsea wells under deep water depths brought the necessity to understand the behavior of columns on such conditions. These columns can be risers, drill strings or casing strings, which are either being installed by lowering them until they reach the sea bottom and/or inside the well, or they are already connected and fully operational. Since these columns are exposed to the open sea, environmental loads such as waves and currents will affect them. Depending on how harsh these environmental conditions are, drilling operations may be suspended. Therefore, understanding how such loads interact with such columns are of the utmost importance if one wants to ensure operational safety. In this paper, we discuss about the problem of emergency disconnections of risers. The concern of doing an emergency disconnection is fundamental for ensuring operational safety because the well will lose a safety barrier, as the level of the drilling fluid inside the well can no longer be controlled after the riser is disconnected, and thus the fluid cannot maintain its downhole pressure anymore. This work focuses on a finite elements modeling of riser dynamics, with the appropriate applied loads, to verify under which sea conditions the riser must be disconnected. The result of such analysis is called an “operational map”, which displays the maximum values of stress along the riser as a function of different sea conditions. Using the riser material properties, this map can then be divided in two regions — failure and admissible — and thus one can see for which sea conditions the riser must be disconnected to avoid its failure. The contribution of the present study is proposing a methodology to elaborate an operational map for a given riser scenario, from which both failure and admissible regions can be seen for emergency disconnection operations.


1997 ◽  
Vol 13 ◽  
pp. 741-746
Author(s):  
Shigeo Takahashi ◽  
Kojiro Suzuki ◽  
Tomomitsu Okamura ◽  
Hironobu Miura ◽  
Syunji Sakamoto ◽  
...  

Author(s):  
Óscar Ibáñez ◽  
Juan Ramón Rabuñal Dopico

During the past several decades, a number of attempts have been made to contain oil slicks (or any surface contaminants) in the open sea by means of a floating barrier. Many of those attempts were not very successful especially in the presence of waves and currents. The relative capabilities of these booms have not been properly quantified for lack of standard analysis or testing procedure (Hudon, 1992). In this regard, more analysis and experimental programs to identify important boom effectiveness parameters are needed. To achieve the desirable performance of floating booms in the open sea, it is necessary to investigate the static and dynamic responses of individual boom sections under the action of waves; this kind of test is usually carried out in a wave flume, where open sea conditions can be reproduced at a scale. Traditional methods use capacitance or conductivity gauges (Hughes, 1993) to measure the waves. One of these gauges only provides the measurement at one point; further, it isn’t able to detect the interphase between two or more fluids, such as water and a hydrocarbon. An additional drawback of conventional wave gauges is their cost. Other experiments such as velocity measurements, sand concentration measurements, bed level measurements, breakwater’s behaviour, etc… and the set of traditional methods or instruments used in those experiments which goes from EMF, ADV for velocity measurements to pressure sensors, capacity wires, acoustic sensors, echo soundings for measuring wave height and sand concentration, are common used in wave flume experiments. All instruments have an associate error (Van Rijn, Grasmeijer & Ruessink, 2000), and an associate cost (most of them are too expensive for a lot of laboratories that can not afford pay those amount of money), certain limitations and some of them need a large term of calibration. This paper presents another possibility for wave flume experiments, computer vision, which used a cheap and affordable technology (common video cameras and pc’s), it is calibrated automatically (once we have developed the calibration task), is a non-intrusive technology and its potential uses could takes up all kind experiments developed in wave flumes. Are artificial vision’s programmers who can give computer vision systems all possibilities inside the visual field of a video camera. Most experiments conducted in wave flumes and new ones can be carried out programming computer vision systems. In fact, in this paper, a new kind of wave flume experiment is presented, a kind of experiment that without artificial vision technology it couldn’t be done.


Author(s):  
Nobuhiro Matsunaga ◽  
Misao Hashida ◽  
Hiroshi Kawakami

Author(s):  
J. Manning
Keyword(s):  

Author(s):  
Mateusz Lisak

The issue of discovery of a sea route to India is one of the most important questions about Indo-Roman trade relations and it has yet to be resolved. Historians tend to focus on who and when made the first open-sea journey, and whether it was a sudden change or a process. Conditions essential for discovery of a new route are not considered (not clear – are not considered here, in this paper?), nor are the circumstances that would have made this journey possible. Another issue (of what?) is the case of the Arabia Eudaimon port. The 1st-century AD Periplus Maris Erythraei states that the port had been ransacked and there was no direct connection between India and Egypt, but that all ships were forced to stop there. Thus the resumption of active trade with India necessitated the lifting of the tentative blockade of Arabia Eudaimon and discovering the trans-oceanic route. The nautical guide, however, does not describe the new repute in the context of the troubles in Bab el-Mandeb, but can we be really sure that these two events were not related? What were the circumstances and conditions that had to be met for it to be possible to discover a new route?


Author(s):  
Irina Mesenzeva ◽  
Irina Mesenzeva ◽  
Elena Sovga ◽  
Elena Sovga ◽  
Tatyana Khmara ◽  
...  

The ability of a bay and gulf ecosystems to self-purification was estimated and the current ecological state of the Sevastopol Bay in whole and the separated parts of the bay was given as an example. A zoning by type of anthropogenic impact subject to the water exchange with the open sea and an influence of the Chernaya River run-off were taken into account. A comparative analysis of assimilation capacity of the most environmentally disadvantaged part of the Sevastopol Bay (the Southern Bay) and the clean water area, bordering on the open sea, was carried out. The hydrodynamic regime of the Sevastopol Bay was described using numerical modelling. The prospect, opportunity and examples of the methodology for assessing the assimilation capacity of marine ecosystems are demonstrated.


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