Project

This project aims to suppress the oscillation motion of floating offshore wind turbines and to improve the structural safety margin of the turbines. The tension leg platform has good vertical stiffness, but insufficient horizontal stiffness and are prone to yawing motion. By establishing a vibration isolation system to resist and dissipate wave impact and wind load impact. The excitation and damage caused by external loads to the wind turbine can be effectively mitigated. The response of the wind turbine is analyzed based on the wave load spectrum and the response curve of the floating platform is calculated using numerical simulation as a basis for designing the hybrid vibration isolation system. A suitable control strategy is selected to first dissipate the waves by controlling the actuators and then dissipate the energy using hybrid vibration isolation. Simulations and experimental studies are used to select the appropriate dynamic parameters for the vibration isolation system to achieve the desired response of the wind turbine. The life state analysis of key components such as tension legs is carried out. The performance degradation characteristics and laws of wind turbines under low-frequency cyclic waves are studied to ensure their safe operation.

Mussels and other marine fouling settle on the part of offshore wind turbines and production platforms that is underwater.
The fouling worsens the load from the waves and reduces the load-bearing capacity of the structure by 25-65 percent. Today, the fouling is removed manually – typically using manually controlled underwater robots – which is a time-consuming and financially burdensome process.

The idea for the solution consists of three elements. 1. cleaning rings around the supporting structures that remove fouling when the water moves. 2. a robot that can move on the supporting structures and send a message about the size of the fouling. 3. A robot that can remove fouling by high-pressure washing underwater. The effect of the solution will be an extension of the service life of the structure, and an expected reduction in costs by 30-40 percent. In the North Sea alone, the industry currently spends a three-digit million amount annually on removing marine fouling.

A more and more widespread way to protect the coast against ongoing erosion is to build so-called Low Crested Structures (LCSs). Despite a large number of coast parallel LCSs exist, the structural performance of these structures are not fully clarified. The LCSs dealt with are coast parallel detached rubble mound structures, either emerging slightly above the water surface or somewhat submerged like a reef.

Initially results of a study of the geometry of existing LCSs are presented. The geometry and structural performance of existing LCSs form the basis of the limits for new design equations. New improved design formulas for calculation of static stability of LCSs are developed on the basis of new 2D and 3D laboratory experiments with scale models. The formulas are specially designed for breakwaters subject to shallow water waves and/or depth limited waves, as the majority of existing LCSs are exposed to such conditions. The formulas are validated against prototype experience. Ecological aspects in relation to structural stability are important, and design guidance on how to consider ecology in the design is therefore given. The new design guidance adds practical and helpful knowledge to the toolbox of the designing engineer.

The Danish wave energy sector consists of several large floating and loosely anchored wave power plants. These plants require specially designed anchoring systems, as “standard” solutions (largely coming from the offshore oil and gas industry) are not designed for the conditions and specifications applicable to wave power plants. For these wave power plants, it is necessary to reduce the resulting anchoring and structural loads, which can be done by making the anchoring solutions more compliant. This will reduce the costs of the anchoring solution and the structure of the plant and thereby the overall costs of the plant and its produced energy, while making the systems more reliable.

The four plants selected to be part of this project are all at a stage of development where they have either completed, or are about to complete, testing of the plants at sea. The four plants are Floating Power Plant, Wave Dragon, Weptos and Leancon. They all require comparable anchoring solutions, as the plants are large, floating, loosely anchored structures operating in water depths of around 30 – 100 m at full commercial scale. This project investigates and compares different anchoring solutions that are useful for these wave power plants. The anchoring solutions are assessed step by step, in order to carry out a systematic and thorough evaluation. The project is organised in the following work packages:

- WP 1: Design practices and tools.
- WP 2: Anchoring solutions.
- WP 3: Preliminary design.
- WP 4: Full analysis.
- WP 5: Cost evaluation.
- WP 6: Selection and results.
- WP 7: Dissemination and project management.

Throughout the project, reports will be produced presenting the results of the selected studies and milestones according to the project Gantt chart. Each of them is crucial for the next step of the analysis and will thus be of great importance. The final results of this project are numerous. It will provide experience and insight into the development of anchoring solutions for all project partners. Furthermore, it will provide the developers with detailed analyses of the various anchoring solutions, and evaluate their prices and practical applicability. Aalborg University will build up experience and know-how in the field, which will enable them, and/or a possible spin-off company, to offer design services in the field to companies in the future. It is also expected to be significant cost and reliability benefits, in addition to having an effective anchoring solution, for the partner plants.

The overarching objective of VALID (Verification through Accelerated testing Leading to Improved wave energy Designs) is to de-risk the whole WEC design process in terms of components reliability and survivability by developing an integrated and open platform for the testing of critical components and subsystems, proposing novel testing procedures going beyond current testing practices. As a consequence, it will facilitate developers to take sound design decisions at early stages of technology developments.

Wave power is one of the most reliable resources for renewable energy utilisation. However, the development of high-performance wave energy converters (WECs) is a complex challenge and requires a solid framework of evaluation tools. The EU-funded VALID project will focus on developing and validating a new test rig platform and methodology for accelerated hybrid testing that can be used across the wave energy sector. By improving the reliability and survivability of the components and subsystems that form WECs, the project aims to establish a standard for future use.

Moorings of floating oil and gas (O&G) structures present surprisingly large failure rates. A top solution is a redundancy in the design. However, marine renewables cannot afford such redundancy in the mooring design to obtain a competitive levelised cost of energy (LCOE). The EU-funded ISLINGTON project will reduce uncertainties in the estimated fatigue damage of mooring cables due to soil-cable interaction in the touch-down zone (TDZ) and the economic cost for marine renewables. ISLINGTON will improve the numerical modelling of the cable-soil interaction in the TDZ for mooring cables, generate experimental data for mooring line trenching and perform a numerical investigation of the effect of trenching on the fatigue of mooring cables.

In Europe, coastal areas are great zones of settlement and play a vital role in the wealth of many nations. Over the past 50 years, the population living in European coastal municipalities has more than doubled and in 2001, it reached 70 million inhabitants. The total value of economic assets located within 500 meters of the European coastline was estimated at between € 500 and 1,000 billion in 2000. [THESEUS, 2010]

This PhD stipend is affiliated with the 4 year research project THESEUS (“Innovative technologies for safer European coasts in a changing climate”) funded by the European Commission (6.5 million Euro). The objective of the project is to study the application of innovative combined coastal mitigation and adaptation technologies generally aiming at delivering a safe (or low-risk) coast for human use/development and healthy coastal habitats as sea levels rise and climate changes (and the European economy continues to grow). The general aim of this PhD project is to develop and evaluate innovative methods for mitigation of flooding and coastal erosion hazard in the context of increasing storminess and sea level rise.

The PhD project will be related mainly to experimental testing of various innovative methods for improving the safety of European coasts in a changing climate. These methods will among others be upgrade of existing defences (dikes, breakwaters etc.) and reduction of wave energy at the coasts by utilization of wave energy converters placed offshore. Concerning the use of wave energy converters for coastal protection, an additional numerical study will be performed, where the numerical model is calibrated and validated against the experimental test-data. Thereby, it is possible to apply the evaluated wave energy converters at any shoreline. Moreover, the consequence of overtopping waves on dikes will be investigated in oblique- and short-crested waves which can be used to more realistically evaluate the consequence of sea water level rise.

The general aim of the PhD project is to develop and evaluate innovative methods for mitigation of flooding and coastal erosion hazard in the context of increasing storminess and sea level rise. The PhD project will be related mainly to experimental testing of various innovative methods for improving the safety of European coasts in a changing climate. These methods will among others be upgrade of existing defenses (dikes, breakwaters etc.) and reduction of wave energy at the coasts by utilization of wave energy converters placed near-shore.

In connection with the construction of the Nysted (Rødsand) offshore wind farm, an experimental study of the erosion protection around the turbine foundations has been carried out. The project has determined comparative erosion depths around different foundation types placed on sand. In addition, tests have been carried out with the proposed erosion protection. The project has been carried out for SEAS Distribution, the Wind Power Department and Carl Bro Anlæg A/S. (Peter Frigaard, Morten Kramer, Tue Hald).

A strong Indonesian grid over a large geographic area is required in order to integrate wind, solar or other RES. HVDC links would allow transmitting carbon-neutral power from islands where its generation is more efficient and viable to those with high consumption. Consequently, the number of CFPP reduces, the percentage of electricity generated via RES increases and grid reliability improves by increasing the level of interconnection. Besides a strong contribution to reduce the Indonesian carbon footprint from electricity generation and improve the security of supply, other big prospects arise from having HVDC links:

Submarine cables between the main islands would lay in the vicinity of small islands, offshore oil platforms and offshore areas with high wind. The taping of these lower power areas to the main link would allow eliminating fossil generation at the small islands, as well as to ease the construction of offshore RES by reducing costs.
A modular approach through the years is possible, allowing a higher adaptability and a better business case from a step-by-step expansion
Boost economy growth outside Java, via RES power-plants, new/enhanced infrastructures, which lead to new local business opportunities
The results can be replicated not only for other island areas (e.g. Philippines), but also onshore in regions with high RES potential and weak grids, as Africa;
To have HVDC-VSC technology in Indonesia is a crucial backbone for a S.E. Asia electrical grid. The project will not address this, but its outcome is key for further development of electrical interconnection between S.E. Asia countries and/or to interface Indonesia with the Australia-ASEAN Power Link.