Ocean Energy

The people in the offshore oil and gas industry have an expectation that they can work each day with zero harm to their safety or the environment. The Ocean Energy Safety Institute and the Research Partnership to Secure Energy for America have teamed up to create a roadmap to reach this goal. The Research Partnership to Secure Energy for America (RPSEA) has released its Technology Roadmap, a plan that outlines the challenges and research needs of the US onshore and offshore oil and gas industry for the coming decade.

The development of new technologies for clean, reliable renewable energy is a key challenge for modern society. Tidal energy is an important renewable energy source with significant advantages over competing sources, including predictability and repeatability (Uihlein and Magagna, 2016). This paper is concerned with establishing the optimum operating performance of a range of novel vertical axis tidal turbines for micro-hydro power through analytical modelling. The development of wind turbine technology is significantly more progressed in this area, leading to potential technology transfer opportunities for tidal turbine developers. Roberts et al. (2016) have recently assessed a number of state-of-the-art tidal turbines and identified key challenges faced by these emerging technologies.

Disk-shaped oceanographic buoys are commonly deployed with instrumentation to monitor and store localized environmental conditions for later transmission to passing oceanographic vessels or orbiting satellites for analysis and interpretation. The instrumentation and beacons are powered by battery packs and may utilize solar panels for recharging. Unfortunately, both the solar panels and instrumentation are too often vandalized. This research study investigates a SEAREV buoy design concept that features a pendulum wave energy conversion system inside an enclosure beneath the standard buoy hull. In this research study, a Lagrange formulation is used to develop equations of motion that are coupled with a hydraulic power take-off system. An in-house simulation model was selected to predict the buoy surge and pitch motions needed to estimate the electrical energy generated from a design seas. An iterative computational scheme was developed that utilizes an equivalent damping model of the power take-off system. The illustrative examples consider two four-meter disk buoys modified with a SEAREV wave energy conversion device, and they are subjected to relatively benign sea conditions using field measurements obtained by the National Oceanic and Atmospheric Administration (NOAA) in the Gulf of Mexico. A scatter diagram of the data was developed and used as the basis to estimate the buoy surge and pitch response and the resulting power generated. Bounded power estimates are presented and based on a limited survey of disk buoy power requirements; the predicted results for the system without optimization can provide four to five watts of power, and the findings are quite promising.

Abstract

The mechanical properties of rock masses are significantly affected by the additional mechanical compliance that result from joints, fractures or faults. The effects of these features, generally referred to as joints, can be so influential in many problems of geology, geophysics, mining engineering and so on that it is important to assess its influence on the mechanical properties of rock masses. As one of important rock masses’ seismic properties, the stress wave energy attenuation in jointed rock mass is studied in the paper in the aspect of its relationship with rough joints. Thus, a series of uniaxial compression experiments were conducted on a split Hopkinson pressure bar systems (SHPB). And specimen is made of two cylindrical rocks extracted from a same granite. Where two rocks contact makes a joint. And artificial joints with different roughness are made by notching one surface of the joint to a different degree. Here, the joint matching coefficient are introduced to estimate joint roughness, which equals the ratio of contact area of two cylindrical rocks to cross-section area of them. In tests, the incident, reflected and transmitted waves across the joints were recorded from the strain gauges stuck on the input and output bars of SHPB. Then, the seismic quality factor Q_seismic can be calculated by the recorded data, which is adopted in the paper to describe the stress wave energy attenuation during travelling across jointed rock masses. Based on the experiment data, we can know how joints with different matching coefficient effect stress wave energy attenuation.

1. Introduction

The term rock joint is used to describe the mechanical discontinuities of geological origin, that intersect almost all near-surface rock masses (Barton and Choubey, 1977). And it is well known that the rock joints have a significant effect on the mechanical behavior of the rock masses, which is of great importance to evaluate the stability and the damage of rock structures under dynamic load, like earthquake, explosion and so on. As one of important rock seismic properties, the stress wave energy attenuation in jointed rock mass is worth to study.

In the past, lots of researches have been conducted on the mechanical properties of rock joints. To investigate the joint deformation, Bandis, Lumsden et al (Bandis et al., 1983) built static Bandis-Barton (B-B) model through a large number of static tests. The model described the hyperbolic relationship between stress and joint closure. Based on that, Zhao, Cai et al (Zhao et al., 2008) proposed the dynamic Bandis-Barton (B-B) model, which was applied to predict stress wave attenuation across factures, and it turned out that a fracture with higher values of dynamic fracture closure constant and dynamic fracture stiffness constant leads to lower attenuation.

The interest in developing new technologies to produce energy with low environmental impact by using renewable sources has grown all over the world in recent years. The economics of wave energy converters (WECs) is of particular interest. The key factors affecting the cost of energy of marine renewable devices include performance, capital costs, operating & maintenance costs and risks due to the offshore environment. The energy converted into electricity by a WEC is a function of the wave climate at the installation location. Assessments of efficiency open up a large number of questions. These include the theoretical maximum energy that the converter could be expected to capture, the intermediate efficiencies of its prime mover and individual power take-off system components, and the certainty to which the resource's energy content itself can be described. Furthermore, overall efficiency may be influenced by certain control and operating regimes that relate to other aspects of the design, including survivability. This paper presents a mathematical method to describe the economics of a wave energy converter based on performance, capital costs, operating & maintenance costs and risks. In the economic performance estimation, the wave energy converter investment and associated investment analysis is based on variables that are allocated to drivers for cost and efficiency.

ABSTRACT

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.

INTRODUCTION

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.

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.

ABSTRACT

The overtaking interaction of the double solitary waves over a plane slope is studied experimentally. The slope of the plane beach is 1:20. For the cases of the double solitary waves of different amplitude ratios and different relative wave crest distances, the time series of the surface elevation and waterline movement are measured by wave gauges and recorded by high speed cameras respectively. Three categories of overtaking solitary wave interactions are reproduced in the wave flume. It is found that the maximum runup amplification coefficient of the double solitary waves is dependent of the relative distance between two initial peaks of the double solitary waves. Breaking of solitary waves plays an important role in damping the wave energy and then changing the maximum runup of the double solitary waves.

INTRODUCTION

It has been a traditional subject to understand the runup of the long wave propagating over a constant depth region and then climbing up a sloping beach of constant slope because of importance of predicting tsunami runup on beaches. Based on the assumption that solitary waves can be used to model some characteristics of the propagation of tsunamis from offshore to beach, much work on physical and mathematical models of propagation and runup of a single solitary wave on the beach has been done, particularly at the W.M. Keck Lab of Hydraulic and Water Resources, California Institute of Technology. Hammack (1972) implemented experimentally the generation of tsunamis in a flume of uniform depth by an impulsively raised or lowered portion of the bottom. Goring (1978) proposed the solitary wave generation method for a wave flume with a piston type wavemaker and presented the experimental and numerical studies on the solitary wave propagating from a water layer of constant depth to the continental shelf. Synolakis (1987) proposed an analytical solution of the solitary wave propagation and runup to the shallow water equations and presented the characteristics of runup of breaking and non-breaking solitary waves. Li & Raichlen (2001) proposed a nonlinear solution to the nonlinear shallow water equations by using a hodograph transformation and reported an experimental study on runup of nonbreaking and breaking solitary wave. Madsen et al (2008) discussed, considering the effects of geophysical scales on wave propagations, the possibility of solitary wave generation in an ocean and presented the numerical results of disintegration of a long wave into an undular bore. Using the Boussinesq model, Baba et al.(2015) presented numerical simulations of the undular bore generation for 2011 Tohoku tsunami event, which shows that there are several solitary waves riding on a long leading wave front in Sendai shallow coastal region. Zhao et al (2016) studied numerically the generation of undular bores and soliton fission for the long waves propagating on the gentle continental shelves in both the East China Sea and the South China Sea.

ABSTRACT

In a wave energy generation system, MPPT (maximum power point tracking) control can maximize the output power of a WEG (wave energy generator) according to the change of the waves. Due to the irregular movement of the waves and the characteristics of the LMMHD (liquid metal magneto-hydrodynamic) generator, the output of the LMMHD WEG is characterized by low voltage, high current, and irregular variation. Therefore, to withstand the large current the PCS (power conversion system) needs to be designed in parallel with multiple modules, which needs to solve the problem of current sharing. On the other hand, a control system with fast response speed is needed for the MPPT to track wave changes quickly. In this paper, a system model of the LMMHD WEG is analyzed firstly, and an MPPT control strategy that can automatically identify the sea state and can automatically realize current sharing is proposed based on the output characteristics of LMMHD WEG. Then, a MPPT control system is designed for a given LMMHD WEG, and a simulation experiment with changing sea state is carried out in MATLAB/Simulink. The comparison between the experimental results and theoretical values verifies the validity of the proposed MPPT control method.

INTRODUCTION

With the increase of human activities at sea, the human demand for marine energy is also increasing. Wave energy has the characteristics of wide distribution, high energy density and large reserves, and it is one of the most promising marine energy. Wave energy generation is the main method of wave energy utilization. The WEGS (wave energy generation system) can provide continuous power supply for ocean power users such as UUV (Unmanned Underwater Vehicle) underwater charging platform, subsea scientific observation network, and ocean ranch, etc., which can solve the power problem of marine users. However, because of the characteristics of random variation of the waves, the wave energy captured by the WEG is also randomly changing. MPPT control can maximize the output power of a WEG according to the change of the waves. (Hugo and Martinez 2016; Chen, Yang and Yang 2017; Zheng, Yang, Lin, Huang and Duan 2107).

ABSTRACT

In the present paper, two types of wave energy converters (WECs) in uni-/multi-directional waves are investigated using a potential-flow model. The first example is a flap-type oscillating wave surge converter (OWSC) which is similar to the configurations of Oyster wave power device. The second case is an attenuator-type WEC which is based on the Pelamis P2 machine; the modelled WEC is simplified as 5 interconnected rigid modules. Both hydrodynamic interactions and mechanical connections have been considered in the present analyses. The emphases have been put on the effects of directional spreading on the performance of the WECs. Significant reductions of power output have been found in multi-directional seas.

INTRODUCTION

There have been many designs or concepts to harness wave power from the ocean. Wave energy converters (WECs) can be divided into different groups according to the method used to capture the wave power (http://www.emec.org.uk/marine-energy/wave-devices/), i.e. attenuator, point absorber, oscillating wave surge converters (OWSC), oscillating water column (OWC), overtopping/terminator device, submerged pressure differential, bulge wave, rotating mass, etc. Most wave energy devices convert kinetic energy into mechanical motions to generate electricity. They usually include moving components and complicated mechanical conversion systems (e.g. power take-off systems). So both hydrodynamic and dynamic interactions have to be considered in numerical investigations.

Numerical methods for hydrodynamic modelling fall into potential- or viscous-flow frames (Li and Yu, 2012). Linear or nonlinear wave theories can be used for potential-flow analyses. Linear wave theory is usually used for operational sea states and nonlinear wave theory is adopted for the analyses of strongly non-linear waves and extreme events (Coe and Neary, 2014). When viscous effects cannot be neglected, empirical viscous coefficients have been introduced to provide reasonable predictions. However, these coefficients are geometry dependent and limited to model scale. The difficulty of this approach has been highlighted by Pauw et al. (2007) and Sun et al. (2015). A good alternative is to use a computational fluid dynamic (CFD) model such as that presented by Wei et al. (2013).

ABSTRACT

Artificial sandbar, widely used in a lot of nourishment projects, is defined as the nearshore placement serving as an underwater berm for purpose of beach nourishment or stabilization. A series of experiments were conducted to investigate the wave-sandbar interactions under five irregular wave conditions of JOSWAP spectra. The wave surface elevations, velocity changes and turbidity were measured for analysis during the experiment. In general, the responses of a submerged artificial sandbar to irregular waves can be summarized as followings. The waves mainly broke on the crest of the sandbar in both spilling and plunging type and wave energy are redistributed under large waves. The turbidity grows when the incident wave height increases. The difference of turbulent kinetic energy between two ADVs augments with the increase of the incident wave height. The profile of sandbar has developed from a symmetrical shape to an asymmetrical shape with a steep landward slope and a mild seaward slope in large incident wave.

INTRODUCTION

Coastal erosion, generally described as recession of coastal line and erosion of beach, is a common problem throughout the world. Particularly, China is one of the worst-hit countries with the erosion taking about 70% of the sandy coast and nearly all open silty coast. As a consequence, land loss, destruction of coastal construction and environment degradation are threatening the human life and property. To protect beach against erosion, both hard structures and soft defense measures are attempted. The hard structures, such as groins, offshore breakwaters and seawalls onshore, turn out to cause erosion locally or downstream more or less. Unlike hard structures, beach nourishment, as a soft measure to recharge the eroded coast with sediment from somewhere else, is one of the most effective and eco-friendly methods (Dean, 2005). In a beach nourishment project, the location of sediment placement is a key parameter. The sediment is usually supplemented to the beach onshore or offshore and the latter practice often develops a submerged sandbar offshore.