The paper considers the technologies of the perspective marine industrial complex of aquaculture with energy supply from renewable sources. Technological schemes of structures and devices of the onshore plant for the cultivation of hydrobionts, a marine underwater farm and a supply vessel for working with marine plantations are presented. A universal autonomous mobile wave device is presented as a variant of using the energy of waves of the open ocean.
Currently, self-contained, civilian, volatile devices for navigational equipment of the seas, research submarine and surface autonomous devices, mainly receive power from batteries. The number of these facilities is more than one million and the priority task is to prevent adverse ecological consequences of energy supply for the world ocean, regardless of costs. For these purposes, separate developments are used for solar energy, wind energy, waves, currents, temperature differences and salinity of sea water. The optimal result will be the transfer of production and processing ships to hydrogen technologies. A more complex factor threatening the Earth's ecology is due to the rapid growth of industrial coastal marine aquaculture enterprises.
PERSPECTIVE COMPLEX OF MARICULTURE
A comprehensive program for the development of marine aquaculture technologies is required, taking into account the need for clean energy and the future creation of marine underwater plantations, while preserving the coastal environment and local aquatic organisms.Modular plant for breeding hydrobionts
The future network complex developed by Loshchenkov, Knyazhev (2014) for the coasts of the Far East of Russia can serve as a contribution to the development of the Program. The complex contains a coastal enterprise for the cultivation of hydrobionts, bottom plantations in the natural environment and underwater plantations in the water column in the shelf zone.
Coastal breeding plant, due to placement in remote, inaccessible ecologically clean areas of the coast, with valuable local species, is semi-automatic, in a modular design. The plant is located, after studying local geological, meteorological, hydrological and hydrobiological parameters in the places of maximum energy flows, Pool modules and energy modules are manufactured depending on the type of hydrobiont and local natural renewable energy sources. The scheme of the plant for the cultivation of hydrobionts on island of Popov of the Peter the Great Gulf developed for the mariculture enterprise is shown in Fig. 1.
In this paper, the power capture performance of a Pelamis-like wave energy converter (WEC) is studied. The Pelamis-like WEC is simplified as three floating cylindrical pontoons which are hinged together. And the relative motion is converted into electricity by the power take off (PTO) system which is simplified as a linear damper. Frequency domain method which is based on linear potential theory is used to establish the equations of motion of the floating system. Considering the displacement constraints between pontoons, the dynamic response of the Pelamis-like WEC can be analyzed in regular waves. Based on the calculated results, the effects of wave frequencies, wave directions, the damping coefficient of the PTO system, as well as the geometric quantities on the power capture performance of the Pelamis-like WEC are studied in detail. It is found that for a given Pelamis-like WEC, there exists an optimum combination of damping coefficient, wave direction, wave frequency, hinge axis inclination to make the maximum power capture.
In recent years, wave energy utilization has been a hot topic of ocean energy development. In order to capture wave energy, various types of wave energy device have been proposed and studied, such as oscillating water column (OWC), floating structure wave energy converter (WEC) and overtopping WEC, etc. The Pelamis-like WEC, as a kind of floating WEC, consists of several floating-body modules which are hinged together. And the relative angular motion between adjacent floating elements is converted into electricity by the power take off (PTO) system. In spite of a lot of researches focusing on Pelamis-like WEC, only a few of them are concerned with hydrodynamics. Dalton (2010) has investigated on the performance and economic viability of the Pelamis-like WEC over a 20-year project time period using 2007 wave energy data from various global locations: Ireland, Portugal, USA and Canada. Palha (2010) described the study of the impact of energy absorption by wave farms on the near shore wave climate and, in special, the influence of the incident wave conditions and the number and position of the wave farms, on the near shore wave characteristics is studied and discussed; Henderson (2006) described the hydraulic power take-off system employed in the Pelamis wave energy converter. He presented the process of the system’s development, including simulation and laboratory tests at 1/7th and full-scale, as well as results of efficiency measurements. O’Connor (2013) presented the results of a case study comparing the performance of two wave energy devices at various scaled power ratings deployed at several European wave energy locations. Yemm (2012) introduced the Pelamis-like WEC in detail, and pointed out that pitch axis and yaw axis were not designed horizontal and vertical but with a certain offset angle. Thiam (2010) studied the power generation efficiency of the Pelamis systematically. He focuses on a simplified model of the Pelamis wave energy converter, with the model consisting of a modified Euler-Bernoulli beam oriented head-on to incoming ocean waves and with energy conversion accounted for by a damping term, where the additional bending moment is proportional to the time derivative of the beam curvature. But no literature exists to study the efficiency of power generation from the aspect of the hydrodynamic model. Multi-body floating model is supposed to be a more accurate method to analyze this problem. He (2013) utilized the AQWA hydrodynamic software to calculated swing angles, hydrodynamic coefficients, and wave exciting forces, but he didn’t mention the efficiency of power generation. Gou (2004, 2014) studied the hydrodynamic interaction effects between wave and two connected floating structures by the boundary integral method. This method is used to study the performance of a Pelamis-like WEC.
In this paper, a series of experiments are conducted to investigate the motion characteristics of the coupled tunnel-pontoons system in beam irregular waves during element ballasting. The 6-DOF motions of both the tunnel and pontoon were measured synchronously and presented quantitatively under wave actions of various wave periods and wave heights. The motion of the pontoon and tunnel are compared with negative buoyancy η=0.0% and 1.5%. For η=0.0%, the maximum downward displacement of the tunnel is significantly larger than that of the pontoon, while after ballasting their upward displacement gap is considerable.
Immersed tube tunnels composed of prefabricated elements have been proven to be an economical and preferable construction of any type of underwater tunnel crossing nowadays (Ingerslev 2012). The concrete tunnel elements are always completed in shipyards and attached with immersion rigs. Once the weather and sea condition are suitable, the elements can be dragged and moored over the dredged trench. And then the elements are suspended from the immersion rigs through connecting cables and immerged by ballasting to provide sufficient buoyancy resistance (Granz 2001). During the critical immersion stage, the motions of the coupled tunnel-rigs system under wave actions will directly affect the landing position of tunnel element and the security of the suspending and mooring lines, which is one of the most critical issue in the installation of element immersion.
Until now, several researches have been carried out on the analysis of the motion responses of the tunnel and dynamic loadings of the suspension lines exposed to currents and waves. Zhou et al. (2001), Zhan et al. (2001), and Xiao et al. (2010) conducted experimental studies on the tensions of the mooring lines and suspension lines for the towing, standby and immersion of the tunnel element across rivers under a few regular wave and current conditions. Chen et al. (2009a, b) applied potential theory to study the motions of the immersed tunnel element with a fixed twin barge under various immersion depths, neglecting the influence of the floating pontoons. Chakrabarti (2008) and Cozijn (2009) carried out both model tests and time-domain simulation to investigate the motions and dynamic responses of the tunnel element at different immersion depths. Their results indicated that the two pontoons with the tunnel element are more sensitive to longer period waves. However, there were limited data presented in proving the conclusion. Nagel (2011) conducted 2D frequency domain analysis on the influence of swell and wind waves on the dynamic behaviors of the tunnel element when immersed 1 meter below water surface. It was concluded that some natural frequencies of the tunnel-pontoon system were close to the frequency of in-situ swell waves in which large motions of the element and high suspension tensions occurred. Zuo et al. (2015) and Yang et al. (2017) investigated the motion characteristics of the immersed tunnel element suspended from a twin-barge under random wave conditions using experimental tests and numerical model. In their study, three different immersion depths are considered varying from 10m to 20m, but the responses of the element immersed near water surface was not mentioned. Song et al. (2014,2015) and Huang et al. (2015) performed experimental investigations on the motions of the tunnel the dynamic responses of the hoist ropes subjected to irregular waves. And the freeboard elimination stage during ballasting was verified to be the critical scenario considering its most drastic dynamic loadings and concomitantly frequent slack occurrence on the connecting suspension lines. Unfortunately, these investigations haven't measured the synchronous motion of the tunnel element and floating pontoon under waves. Hence, the coupled effect of pontoon motion on the tunnel during ballasting have not been addressed thus far.
Meng, Xun (Ocean University of China, Shandong Provincial Key Laboratory of Ocean Engineering) | Liu, Meng (Ocean University of China) | Huang, Weiping (Ocean University of China, Shandong Provincial Key Laboratory of Ocean Engineering) | Fu, Qiang (Ocean University of China, CIMC Offshore Engineering Institute Company Limited)
This paper studies on the typical design load cases that dominate the characteristics of structural stress distributions. The OC4-DeepCwind conceptual semi-submersible substructure with the 5.0MW floating offshore wind turbine (FOWT) is adopted as the target structure. Parametric finite element method (FEM) is employed for idealized numerical modelling. Different environmental load cases controlled by random variable parameters such as wave directions, phases, heights and periods are imported into static probabilistic design system (PDS) as samples. Core areas with localized stress concentration based on probability statistics and corresponding typical design load cases are summarized. This study presents a method of effectively simplifying the complicated dynamic strength analysis procedures and would serve as a reference of reasonable optimization of main dimensions of the semi-submersible FOWTs.
Due to the depletion reserves and negative environmental influences of fossil fuels, human beings have been forced to seeking for alternative energy sources. According to the report of Intergovernmental Panel on Climate Change (IPCC), nearly 80 percent of the world’s energy supply could be provided by renewable energy resources in 2050, and wind energy would make up one of the largest contributions to the energy system by then (Sun, Huang and Wu, 2012). Nowadays wind energy industry has moved its interest offshore. Reference shows that offshore wind power will cover 14% of European electricity demand by 2030 (Athanasia, Anne-Bénédicte, and Jacopo, 2012). In the first half of 2017, developers have totally installed about 6.1GW of capacity, including 1.3GW in Europe. The activity in the offshore market is 2.6 times higher than for the first half of 2016 (WindEurope, 2017).
Most offshore wind farms so far are installed and operating in shallow waters (<30m), where bottom-fixed foundations with simplified structure concepts such as monopile and gravity concrete caisson are widely used (Failla and Arena, 2015). At water depths between 30m and 60m, multi-foot foundations such as tripod or jacket support are considered (Lozano-Mjinguez, Kolios and Brennan, 2011). For the benefits of relatively unrestricted space, lower social impacts and rich wind resources, wind farms are pushed into deeper waters. For cost-effective solutions, floating offshore wind turbines (FOWTs) become feasible options to extract energy (Meng, Lou and Shi, 2014).
Zhao, Xuanlie (Dalian University of Technology) | Ning, Dezhi (Dalian University of Technology) | Johanning, Lars (Dalian University of Technology, University of Exeter) | Teng, Bin (Dalian University of Technology)
High construction-cost is one of the barriers that limited the developments of wave energy utilization. Integrating wave energy converters (WECs) into other marine structures may reduce the construction cost of WECs effectively. In this paper, an integrated system with a medium array (11 devices) of heaving point absorber WECs (PAWECs) arranged at the weather side of a fixed pontoon-type structure is proposed. The hydrodynamics of the PAWECs are investigated numerically by using higher-order boundary element method (HOBEM) code package (i.e., WAFDUT), which is developed based on linear potential flow theory. The hydrodynamic performance (including interaction factor, wave exciting force and heave response) of the WEC array with the rear pontoon is investigated with focus on the influence of the spacing between the WEC array and the pontoon (WEC-pontoon spacing). For sake of comparisons, the results corresponding to the isolated WEC array, i.e., without the pontoon, are presented. Results show that the performance of the pontoon-integrated WEC array performs better than that without the pontoon.
One obstacle that limits the wave energy utilization is the high construction cost. Integrations of wave energy converters (WECs) and other marine structures (such as breakwaters, offshore wind turbine, offshore platforms, etc.) have attracted much attention for its advantage of cost-sharing (Mustapa et al., 2017; Astariz and Iglesias, 2015; Favaretto et al., 2017). The cost reduction of WECs caused by the integration scheme may enhance the competitiveness of the wave energy converters. Pontoon-type structures are very common in offshore engineering, such as breakwaters, floating docks, ships, etc. In addition to the sharing of the infrastructures of both aspects, the WEC devices can provide power to the offshore operation in a convenient way.
It is understood that, for the pontoon-type structures, the wave conditions at the weather side can be described as the superposition of the incident waves and the reflected waves caused by the pontoon. Thus, it is expected that the energy conversion efficiency of the WECs can be improved. There are some cutting edge studies on improving the efficiency of WECs (mainly including oscillating water column WECs and heaving point absorber WECs) by using the reflection of costal structures. The detailed investigations can be found in Howe and Nader (2017), McIver and Evans (1988), Mavrakos et al. (2004), Schay et al. (2013) and Zhao et al. (2017).
Liu, Xiaolei (Shanghai Jiao Tong University) | Wang, Xuefeng (Shanghai Jiao Tong University) | Xu, Shengwen (Shanghai Jiao Tong University) | Ding, Aibing (Shanghai Jiao Tong University) | Kou, Yufeng (Shanghai Jiao Tong University)
This article is mainly concerned with yield and fatigue strength of a single module (SMOD) of a VLFS to be served near Xisha Islands of South China Sea under survival and long term environmental conditions, respectively. Bending moments, torsion moments, split forces and transverse forces between pontoons and accelerations of deck mass are selected as characteristic responses. Global structural stresses obtained with the design wave method were examined according to the rules. The spectral-based fatigue assessment method was adopted to predict global fatigue lives based on an S-N curve fatigue approach, thereby accumulating partial damages weighted over sea states and wave directions. Key regions that have high stresses or low fatigue lives are determined by the calculation results. The proposed method and aforementioned key regions may be helpful for designing and checking the strength of a VLFS when encountering various sea states.
Very Large Floating Structures (VLFSs) can be used as artificial floating landing spaces on the sea, where the sea states are often quite severe and complicated. Like other marine structures, stresses of VLFS structures are changeable due to the varing wave loads in harsh marine environment. Wave induced stresses are the main cause of structural damages. It is necessary to forecast the residual yield strength and fatigue lives of the structures so as to ensure that the VLFS is safe enough to resist the wave loads in such hazardous conditions.
Most of the reports on stresses on a VLFS are focused on the its hydroelastic responses (e.g., Fujikubo et al, 2002; Inoue et al, 2002; Hong et al, 2004; Seto et al, 2005; Iijima and Fujikubo, 2018). While only a few studies (Li et al, 2015; Qi et al, 2018) are concerned with its structural strength and fatigue analysis which are among the most significant techniques for design, construction and operation of a VLFS. The single module (SMOD) of a VLFS in the present work employs a structural form of semi-submersible type whose upper hull is raised above the sea level using columns to minimize the effects of waves.
Steel Catenary Riser (SCR) is the most cost effective option for numerous deep water field developments. Despite its structural simplicity, the design and analysis of SCR's can be complex especially due to the hydrodynamic forces. This paper selects three of the unexplained observations in SCR analyses, solves the mysteries analytically, and provides recommendations accordingly for improving riser design.
The three selected observations that are not well understood occur at three distinct locations along the SCR: the hang-off, the middle section, and the Touch Down Zone (TDZ). The riser maximum stress at the hang-off can be lower when the wave particle motion is considered in the dynamic simulation compared with using vessel motion time trace only. The TDZ fatigue damage is observed to be lower when background current is applied along riser in the motion fatigue analysis, even if the current direction is perpendicular to the riser motion direction. Finally, the motion fatigue response is observed to be better with a shorter strake length compared with that of the configuration wherein the strake coverage is extended to the seabed.
The first two phenomena are generally explained by the "damping" effect, however, how the damping works was never clearly demonstrated. The third observation is actually contradictive to the damping effect as less strake length results in smaller drag forces and thus less damping. All of the above phenomena are related to the hydrodynamic forces that are exerted onto the riser by the surrounding sea water. Those forces are calculated by Morison's equation which includes drag force and inertia forces. In this paper, a detailed analytical study using Morison's equation illustrates how the drag force or inertia forces will affect the riser motion, and which force is the dominating one, for each of the three observations aforementioned.
The understanding of these riser hydrodynamic behaviors leads to improved riser design. The applications of wave hydrodynamics and background currents present more realistic riser responses and reduce conservatism and thus cost. A riser with shorter strake length but more fatigue life will result in reduced cost too provided that adequate VIV fatigue life is preserved.
A semi-submersible is a field proven solution that allows for hydrocarbon production through steel catenary risers for locations subjected to very intense hurricane / cyclonic / typhoon conditions. The semi-submersible can be made applicable to a broader range of offshore fields if it is able to export a dry gas. The produced liquids – condensate – may be stored onboard the semi-submersible and be off-loaded via a shuttle tanker.
While at first sight a typical semi-submersible has ample room for storage of condensate, the storage and off-loading requirements introduce a whole new set of functional, regulatory and safety requirements to the system. Operator requirements and operator preferred practices impose additional requirements. In a sense, the semi-submersible with storage fulfills several of the functions also found on an FPSO, though volumetric quantities are much smaller, a range of 100,000 bbls to 150,000 bbls of storage is considered.
Regulatory requirements, such as set forth in IMO, MODU, MARPOL, Flag State and Class, are typically intended for oil tanker / FPSO application, and their applicability to semi-submersible can be ambiguous. Regulatory requirements to consider include double-hull requirement, whether unsegregated storage is allowed and the definition of Classified Spaces and confined spaces, whether hydrocarbon storage during (hurricane) abandonment is allowed, etc.
Whether to store the hydrocarbons separately or unsegregated is one of the most important decisions that affect the layout, geometry and thus cost of the semi-submersible. Also the off-load frequency, the off-load parcel size, and whether to allow for a varying draft or to maintain draft and compensate for the varying condensate payload, have a significant impact on the overall concept. The storage compartments inside the hull will have to be compatible with the hull framing and equipment already located inside the hull.
Producing wet gas into a dry gas and condensate is proven technology on a semi-submersible and FPSO. Analogous to the FPSO, the produced condensate is first kept in storage tanks and is then transferred to an off-loading vessel. The location of the offloading equipment and tank cleaning, as performed on an FPSO, are additional operational aspects be addressed. Above all, the marine crew on the semi-submersible will now have to be much more familiar with marine operations than what they are today.
This paper identifies and discusses the additional requirements that are the result of storing condensate (hydrocarbons) in the hull of a semi-submersible. Many of these requirements have a large impact on the design and operation of the semi-submersible. The paper indicates that a semi-submersible with condensate storage of 125,000 bbls is practical and a layout is provided at concept level.
Pontoon boats have grown to have a significant presence in the pleasure boat market. They feature a wide normally stable platform and are most usually utilized on rivers and lakes where waves are smaller and occur less frequently. Likely as a result of their popularity and features, they have also been utilized in coastal waters where when in waves there have been reported instances of these vessels pitch poling in head seas as well as overturning or capsizing in beam seas or in a broach. There have been accidents with loss of life, Figure 1 and 2. A typical pontoon boat is a twin hull or catamaran essentially consisting of a wide flat deck atop twin outboard cylindrical hulls running the length of the boat and at the outboard extremities of the deck, (Figure 1). Variations include shaped bows and trimaran, or three hull, versions as well, Figure 1. They provide a large deck area for their size as the deck beam is normally the same from bow to stern. They are very stable in calm water as a result of the wide separation of the pontoons as is typical for multi-hull vessels. These types of boats are of a different nature than the catamaran shown in Figure 1 which has more freeboard, sheer and bow height, as well as shaped hulls.
Loading into or unloading of oil and gas from very large crude carrier (VLCC) normally happens in the open sea, since water depth of about 18 to 22 m are needed for such vessels, and ports to accommodate such vessels are not available everywhere. For example, in Kuwait, oil loading terminal is located at a distance of 12 km from the coast at a mean water depth of 20 m. The waves at this location are predominantly approaching the mooring vessels from northwest and southwest and are moderate most of time, with wave heights less than 1.0 m for more than 85% of the time in a year. Wave height exceeds more than 2.0 m for up to 15 days in a year. During such wave climate, oil loading operation is risky. Stopping one day of oil loading operation means revenue loss of about 100 million US $ to the country. Hence it is required to reduce the wave climate around the loading terminal. Construction of any fixed wave barrier like offshore rubble mound breakwater will be out of question for few reasons. It will be prohibitively expensive (for example, each m run of the offshore breakwater will consume more than 1000 m3 of stones, which will cost about 20,000 KD/m run and hence for say 1000 m length of an offshore rubble mound breakwater, it will cost about 20 million KD); presence of such fixed structure is a navigational hazard; reorientation is not possible when the incident wave direction changes significantly from one season to another season. Kuwait Institute for Scientific Research has carried out studies on Floating breakwaters (FBW). The wave transmission and mooring forces were measured for a wide range of wave conditions. Studies were carried out on conventional pontoon breakwaters and then on FBWs with different number of skirt walls fixed at the keel of the pontoon FBWs. Wave transmission is found to be reduced significantly (to the order of 25% to 60%) by adding three or five skirt walls.
However, mooring forces are increasing to an extent of 20% to 30%. A basic design and cost analysis is carried out for the floating breakwater and is compared with the rubble mound offshore breakwater. For the floating breakwater with skirt walls, the volume of material required is less than 10% of the material for rubble mound breakwater and cost saving to the tune of 50% to 70% is possible. The cost for construction and installation of such floating breakwater for 1 km length will be about 3 million KD, which is about 10% of the earnings/day of export operation. The results of this study can be used for cost effective design of floating wave barriers and loading of crude oil can be done for the whole year with less risk induced by the wave actions.