Deepwater Deployment Research Articles

Development of a nature-based solution for mitigation of Pacific oyster summer mortality: use of the intertidal zone to improve resilience to environmental stressors

In recent years, Pacific oyster growers in British Columbia (BC), Canada have experienced devastating losses due to summer mortality syndrome. While anecdotal evidence suggests that intertidally-grown oysters may fare better during mass mortality events than deep-water counterparts, there remains a lack of research examining how different culture conditions may influence severity. To address this, we compared growth, condition, histopathology, reproductive status, and survival between intertidally- and deep-water-cultured oysters over 2 years at three oyster farms in Baynes Sound (BC). A reciprocal transplant was carried out after 1 year to test the use of the intertidal as a mechanism for promotion of physiological resilience prior to deep-water deployment. Field trial results showed significantly higher final survival in oysters transferred from the intertidal to deep water (83.5%) compared to those maintained in deep water (63.6%), but only at one farm, likely as a consequence of varying physical and/or biological characteristics associated with particular farm locations. Histopathology showed little role of disease with regards to varying survival among treatments, though higher occurrence of Viral Gametocytic Hypertrophy was observed in Year 1 oysters under deep-water (62.2%) versus intertidal (37.8%) conditions. Additionally, after 2 years, there was no significant difference in oyster size nor condition index between oysters transplanted from the intertidal to deep water and those solely cultured in deep water. A laboratory-challenge experiment determined significantly different survival curves of Year 1 intertidally- and deep-water-cultured oysters under immersion/emersion and warming conditions, with final survival of 88% and 64%, respectively, under conditions of high temperature (25°C) and immersion. Likewise, Year 2 (i.e. post-transfer) intertidally- and deep-water-cultured oysters showed significantly different survival curves under laboratory-based Vibrio challenge conditions (16°C) with final survival of 63% and 34%, respectively. Results suggest that partial culture in the intertidal at some farms may be an effective method for conferring resilience to summer mortality in Pacific oysters.

Survey on Low-Cost Underwater Sensor Networks: From Niche Applications to Everyday Use

Traditionally, underwater acoustic modems and positioning systems were developed for military and Oil & Gas industries, that require deep water deployments and extremely reliable systems, focusing on high power expensive systems and leaving the use of low-cost devices only attractive for academic studies. Conversely, recent developments of low-cost unmanned vehicles, such as remotely operated vehicles (ROVs) and autonomous underwater vehicles (AUVs), suitable for shallow water coastal missions, and the need of sensors network deployments for measuring water quality and studying the effect of climate change in coastal areas, called to the need of low-cost and low-power acoustic modems and positioning systems that are gaining more and more momentum to date. The use of these devices can enable a wide set of applications, often based on low-cost AUV swarm formations, where an acoustic link between the vehicles is required to coordinate the mission, perform the maneuvers, and maintain the formation along the time. Moreover, they can make environmental wireless sensor deployment cost effective by substituting wired systems. Underwater positioning systems, usually used in large-scale operations, can be finally applied to small-scale application thanks to the reduction in costs, at the price of a lower transmission and positioning range and precision. While in open-sea application this performance reduction is a huge limitation, in river, lagoon, port and lake deployments this is not an issue, given that the extremely shallow water and the presence of many obstacles would deteriorate the acoustic signal anyway, not allowing long range transmissions even with expensive and sophisticated acoustic devices. In this paper, we review the recent developments of low-cost and low-power acoustic communication and positioning systems, both analyzing University prototypes and new commercial devices available in the market, identifying advantages and limitations of these devices, and we describe potential new applications that can be enabled by these systems.

Improved empirical formulation for seabed trench and its influence on fatigue performance of steel catenary risers under directional waves and currents

Steel catenary riser (SCR) offers a cost-effective solution to deep water deployments. Hanging from a floater, an SCR is usually subjected to large tensions at hang-off location and large bending moments at touchdown zone (TDZ) which leads to fatigue damage. Field observations showed that a trench gradually formed in seabed with the depth might reach to five times of SCR’s diameter. However, flat seabed was often assumed for the modeling of SCRs to avoid the time-consumingly dynamic simulation of trench development. Few studies have been conducted to evaluate the influence of trench on SCR fatigue performance, and led to contradictory conclusions, i.e., some studies suggested that fatigue damages of SCRs at TDZ were reduced, while, others proved that they were increased, if considering the presence of trench. This contradiction may be explained by factors including inappropriate trench model and different sea states assumed by different researchers. An iterative procedure initially developed by Wang and Low and further improved in the present work was used to estimate the position and the length of a trench and, then, an improved empirical formulation was generated to predefine the trench model for the finite element analysis of SCR. Additionally, dynamic simulations were conducted to study the influence of trench on fatigue performance of SCRs encountering directional waves, currents and floater offset. Results showed that presence of trench always reduced fatigue damages of SCR at TDZ compared with the flat seabed.

Dual-flap Floating Oscillating Surge Wave Energy Converter: Modelling and Experiment Evaluation

Bottom-hinged oscillating surge wave energy converters have been proposed in literature to extract energy from the surge wave motions. This study investigates a dual-flap out-of-phase floating oscillating surge wave energy converter (FOSWEC) for deep water deployment where the wave power density is larger and the WECs are less visible. The proposed FOSWEC consists of a floating platform and two pivoting flaps. The distance between the two flaps is around half of the wavelength in order to achieve out-of-phase motion, decrease the motion of the frame and reduce mooring load. Numerical modelling and dynamic analysis are formulated using the WEC-Sim. Numerical simulation results of the average power and optimal PTO damping with different viscous drag coefficients and PTO rotatory inertias are presented. Simulation results show the proposed dual-flap design can significantly mitigate the platform's horizontal motion so that the mooring load can be reduced. To experimentally evaluate the system performance, a 1:10 scaled prototype was designed, fabricated and tested in the wave tank based on the Froude scaling law. Experimental results were verified with modeling results and revealed the out-of-phase phenomenon as desired.

Design Optimization and Coupled Dynamics Analysis of an Offshore Wind Turbine with a Single Swivel Connected Tether

The increased interest in renewable wind energy has stimulated many offshore wind turbine concepts. This paper presents a design optimization and a coupled dynamics analysis of a platform with a single tether anchored to the seabed supported for a 5 MW baseline wind turbine. The design is based on a concept named SWAY. We conduct a parametric optimization process that accounts for important design considerations in the static and dynamic view, such as the stability, natural frequency, performance requirements, and cost feasibility. Through these optimization processes, we obtain and present the optimized model. We then establish the fully coupled aero-hydro-servo-elastic model by the time-domain simulation tool FAST (Fatigue, Aerodynamics, Structures, and Turbulence) with the hydrodynamic coefficients from an indoor program HydroGen. We conduct extensive time-domain simulations with various wind and wave conditions to explore the effects of wind speed and wave significant height on the dynamic performance of the optimized SWAY model in various water depths. The swivel connection between the platform and tether is the most special design for the SWAY model. Thus, we compare the performance of models with different tether connection designs, based on the platform motions, nacelle velocity, nacelle accelerations, resonant behaviors, and the damping of the coupled systems. The results of these comparisons demonstrate the advantage of the optimized SWAY model with the swivel connection. From these analyses, we prove that the optimized SWAY model is a good candidate for deep water deployment.

A finite element based study on lowering operation of subsea massive structure

Subsea production system has been increasingly used in recent South China Sea offshore developments. With deepwater applications, constituent parts of subsea systems become more complicated and enlarged. Increases on the weight and geometry of each component bring challenges to installations. A recent accomplished deployment on a subsea massive jumper shows the weight and length have been up to 120 tons and 90 m, respectively with sophisticated geometry. It is considerably difficult to install heavy and large subsea structures, especially in South China Sea where severe environmental conditions are common. In addition, deepwater deployment may alter natural frequency of the hoisting system and the altered frequency may be close to possible environmental conditions. To deal with the above two issues, traditionally, engineers need to carry out series of complicated numerical analyses which are on case basis and significantly time-consuming. Existing studies focus on the optimization on analysis techniques by conducting laboratory testing and numerical simulations. However, easy-to-use guidance on massive subsea structure installation are somewhat limited. The studies presented in this paper aim to achieve a simplified guidance which can briefly screen the cases subject to axial resonance and provide visible correlations between hoisting system integrity and key installation parameters.

Numerical simulation of deepwater deployment for offshore structures with deploying cables

Deepwater deployment of offshore structures in different sea states was investigated. The whole deployment system was modeled as a lumped mass model, and discretization scheme for cable geometry and methodology for calculating the internal and external force acting on deploying cable were presented. The deployment model suitable for the time-varying length of deploying cable was specified. The free-surface flow fields together with the ship motions were used to calculate dynamic tension in the deploying cable during deployment of the structure. The deployment of deep sea mining system which was a typical subsea working system was employed. Based on lumped mass analysis model and parameters of deep sea mining system, numerical simulations were performed, and dynamic load and dynamic amplification factor (DAF) with different cable parameters, deploying velocities and sea states were obtained. It is shown that cable parameters and amplitudes of ocean waves can significantly influence the dynamic load and DAF, and the time-varying natural period of deploying system is a dominant factor, while the effect of deploying velocity is not obvious.

Solar-Macro-Algae Based Biogas Hybrid System for Future Offshore Installation

Marine algae biomass energy source is increasing getting approval from policy maker and community. Beside production of seaweed for biomass energyhas potential economic benefits in Malaysia. Prototype plantations have been deployed in coastal areas and therefore are competing for limited space with other shoreside activities such as recreation and industry. If seaweed can be cultivated in relatively deeper waters away from populated areas, production may be expanded using larger areas not presently exploited for other purposes. Prototype systems aquaculture plantations have so far relied on ad hoc, field developed mooring systems, rather than engineering design principles. Such systems may not be sufficiently reliable for deepwater deployments, where repairs are more costly and resources are scarce. Considerable experience and hands-on knowledge has been obtained, the design concepts can be used as a basis for further improvements. The paper describe integrative approach to ocean energy by combining capability of solar and biogas.

Acoustic detection of ultra-high-energy neutrinos

At ultra-high energies (>1018eV) the Earth is opaque to neutrinos and detection techniques other than the optical Cherenkov technique must be pursued. Here the possibility of detecting neutrinos via their acoustic signature is discussed. The paper presents an overview of current worldwide activities in the acoustic detection field which includes recent results from test experimental set-ups, simulation work, sensitivity calculations and results from data taken at deep-water deployments.

Offshore Wind Electricity: A Viable Energy Option for the Coastal United States

U.S. offshore wind energy resources are abundant, indigenous, and broadly dispersed among the most expensive and highly constrained electricity load centers. Economic capacity expansion models developed at the National Renewable Energy Laboratory show that offshore wind energy can compete in future U.S. electric energy markets without major changes in the market variables or revolutionary technological breakthroughs. However, significant research, development, and deployment will be needed to bring the current technology through a course of cost reductions. To maximize the resource potential, these reductions need to be made along parallel technology paths that will expand the available resource by allowing wind turbines to be installed in deep water. Analysis shows that incremental technology improvements leading to moderate cost reductions, and reasonable increases in the cost of conventional energy will help offshore wind achieve cost competitiveness by 2030 and become a major contributor to the energy supply of the United States. This paper describes a wide range of technical research and development that can reduce costs and improve technology for deep water deployment.

Assessment of hydrodynamic properties of bodies with complex shapes

For the purpose of simulation of the offshore deployment of industrial modules in very deep water, two methods for assessing the inertial properties of bodies with complex geometries are proposed in this work. The first method is referred to as the frequency limit method and is a theoretical procedure using the widespread availability of seakeeping codes and the respective limits established therein to find the added mass, including the rotational inertia. The only prerequisite is that the body must have one plane of symmetry. Sets of results are published for the first time in graph and table format that will prove useful for designers. The second method is referred to here as the constant acceleration method and is an experimental method that calls for a well-controlled dynamometric car. Once constant acceleration has been applied to a towed body, this paper shows how to get the added mass for consistency in multiple runs. Both methods are applicable for deep-water deployment of a manifold, and the coherence between the two distinct methods is shown.

The Acoustic Detection of Ultra-High Energy Neutrinos - a Status Report

An overview is presented of current worldwide activities in the field of the acoustic detection of ultra-high energy neutrinos. Emphasis is placed on recent results from test experimental setups, simulation work, sensitivity calculations and on data taken at deep-water deployments.