Large-Scale Model Investigation for Monopile Decommissioning of Offshore Wind Turbines: Overpressure and Vibratory Pile

2021 ◽  
Author(s):  
Nils Hinzmann ◽  
Patrick Lehn ◽  
Jörg Gattermann
Keyword(s):  
Large Scale ◽  
Planning Process ◽  
Complete Removal ◽  
Offshore Wind ◽  
Scale Model ◽  
Offshore Wind Turbines ◽  
Large Scale Model ◽  
First Results ◽  
Set Up ◽  
Large Scale Tests

Abstract As of now, only a small number of offshore foundations, related to offshore wind energy, were decommissioned in Europe. With a diameter up to nine meter, an embedment of about 40 meter and a set up effect over 25 years, the necessary force to pull the pile out of the seabed can be assumed, if at all determinable, to be enormous. The piles that were decommissioned were cut beneath the mud line, which leaves approximately one third of the foundation permanently in the seabed. Different methods and techniques for a complete removal of offshore pile foundation are currently investigated within the project DeCoMP. Vibratory extraction aims for a reduction of the pile skin friction by creating a layer of less density between the pile shaft and pending soil. During the design and planning process for vibratory installation or extraction a drivability prediction is a key element. In order to identify and characterize soil parameter for the numerical simulation of a drivability prediction, large-scale tests are performed by the Institute of Geomechanics and Geotechnics of the Technische Universität Braunschweig (IGG-TUBS) [1]. In this paper first results of pilot tests with two vibrators are presented and key elements such as crane uplift, frequency and acceleration displayed.

Large-Scale Tests With Hydraulic and Pneumatic Overpressure for Monopile Decommissioning of Offshore Wind Turbines

2020 ◽  
Author(s):  
Nils Hinzmann ◽  
Jörg Gattermann ◽  
Patrick Lehn
Keyword(s):  
Large Scale ◽  
Wind Farm ◽  
Complete Removal ◽  
Offshore Wind ◽  
Lateral Loads ◽  
Offshore Wind Turbines ◽  
Measurement Concept ◽  
Set Up ◽  
The One ◽  
Large Scale Tests

Abstract The complete decommissioning of an offshore wind farm can be considered as a highly complex and hazardous approach. An unknown number of variables and unforeseen circumstances are involved in the decommissioning process. On the one hand the decommissioning of the top structure, such as blades, turbine and mast, can be handled relatively risk free by reversing the installation steps. More focus needs to be given to the recycling method and logistic. The foundation decommissioning on the other hand is a much more challenging procedure. Originally designed for high axial and lateral loads, the foundations are generally oversized concerning the loading capacity. With a diameter up to nine meter, an embedment of about 40 meter and a set up effect over 25 years, the necessary force to pull the pile out of the seabed can be assumed, if at all determinable, to be enormous. Different methods and techniques for a complete removal of offshore pile foundation are currently investigated within the project DeCoMP. Vibratory extraction and jet drilling aim for a reduction of the pile skin friction by creating a layer of less density between the pile shaft and pending soil. In a different approach the seabed is used as an abutment and a pressing force is applied by creating an overpressure inside the pile. The results of pilot test, presented in this paper, show the capability of overpressure pile decommissioning. On this basis scaled test with an extensive measurement concept will be carried out in 2020.

Development of 3MW Tidal Energy Platform

2013 ◽  
Author(s):  
Erik ter Brake ◽  
Mike Todman ◽  
John Armstrong
Keyword(s):  
Large Scale ◽  
Tidal Energy ◽  
Model Testing ◽  
Offshore Wind ◽  
Scale Model ◽  
Easy Access ◽  
Main Body ◽  
Sudden Increase ◽  
Large Scale Model ◽  
The Cost

The Triton-3 platform is a novel tidal energy harvester capable of producing 3MW from tidal flow. The platform is a floating structure moored to the seabed by a single-point fully articulated anchorage, and carries three power trains and a number of marine auxiliaries. The driver for the design as developed by TidalStream Ltd is to reduce the cost of energy production in order to compete with the current cost of offshore wind. Independently audited cost modelling shows that tidal stream energy can become competitive with offshore wind, achieving a generating cost as low as 10p/kWh at the best sites. This generating cost is estimated to be less than half that which could be achieved at a similar site from a single seabed-located turbine. The driving aspects for the competitive cost are maximising the capacity per mooring point, reducing installation costs by float-out solutions and by providing easy access to the tidal equipment. Access is achieved by allowing the platform to come to the surface by means of de-ballasting. By doing so, there is no need for large workboats and/or diver activities to perform regular inspection and maintenance on the tidal equipment, reducing the cost significantly. The technical aspects that arise when developing the tidal turbine platform for a typical offshore location are investigated by Houlder Ltd and discussed in this paper. A number of technical challenges have been addressed where the rotational stability in both roll and pitch are of interest. The roll of the platform is heavily affected by the performance of the turbines; sudden increase or reduction in thrust will induce significant rolling moments that must not impair the integrity of the platform. Pitching of the platform allows it to reach the surface when de-ballasted for maintenance and inspection. During normal operations, the platform remains aligned with the current and in doing so maximises the performance of the turbines. The paper illustrates how these aspects have been achieved by means of passive solutions. By means of positioning and shaping the main body of the platform, a working configuration has been developed where the rotations of the platform remain within a limited window maximising the potential power production. The concept has been tested by TidalStream during a large-scale model testing campaign where the unit was subject to different current speeds and different turbine configurations and fault cases. This publication compares the results of the large scale model testing with numerical models developed in OrcaFlex and shows the effectiveness of the passive solutions.

New Approach for Offshore Pile Decommissioning With Hydraulic Presses and Floating Panels

2020 ◽  
Author(s):  
Patrick Lehn ◽  
Nils Hinzmann ◽  
Jörg Gattermann
Keyword(s):  
Large Scale ◽  
Competent Authority ◽  
Wind Farms ◽  
Renewable Energies ◽  
Offshore Wind ◽  
Offshore Wind Farms ◽  
Pullout Resistance ◽  
Offshore Wind Turbines ◽  
Technical Solutions ◽  
Large Scale Tests

Abstract Renewable Energies become more and more important in industries and society all over the world. In Germany, offshore wind farms generated 49 % of the renewable energies in 2018. Monopiles are the preferred system for the foundation of offshore wind turbines in water depths up to 40 m. They are authorized by the competent authority for 25 years. When reaching the end of lifetime, the structure inclusive the foundation must be decommissioned. The decommissioning of monopiles will be challenging in the future and can lead to unexpected costs and risks for the owners. Removing the monopiles in it’s entirely ensures the opportunity to reuse the space for new offshore wind farms. The Institute of Geomechanics and Geotechnics of the Technische Universität Braunschweig (IGG-TUBS) obtained the funding for the research program on technical solutions with large-scale tests for decommissioning of offshore monopiles named DeCoMP. Several decommissioning methods such as vibratory extraction, internal dredging, external jet drilling, decommissioning with overpressure and the use of buoyancy force are investigated. The proposed paper will present technical opportunities and issues for extracting the pile with hydraulic presses in combination with a steel framework. Hydraulic presses brace the steel framework with the monopile. Further hydraulic presses, positioned at a certain distance to the pile on the framework, use the seabed as abutments to push out the monopile. In addition, results of a feasibility study to remove monopiles with floatation panels are presented in this paper. This method is based on floating panels, which are attached to the monopile above the mud line. These panels are inflated with air pressure to reach the required amount of buoyancy to overcome the pullout resistance. The decommissioning solutions are compared to point out possible combinations.

Installation and lateral loading tests of suction caissons in silt

2011 ◽  
Vol 48 (7) ◽  
pp. 1070-1084 ◽  
Author(s):  
Bin Zhu ◽  
De-qiong Kong ◽  
Ren-peng Chen ◽  
Ling-gang Kong ◽  
Yun-min Chen
Keyword(s):  
Wind Turbines ◽  
Large Scale ◽  
Lateral Loading ◽  
Offshore Wind ◽  
Scale Model ◽  
Moment Capacity ◽  
Offshore Wind Turbines ◽  
Rotation Center ◽  
Cone Penetration Tests ◽  
Caisson Foundations

A number of potential offshore wind turbines in China will be constructed in sandy silt seabeds, and the mono-caisson foundation is an important choice for these offshore wind turbines. A program of large-scale model tests on suction installation and lateral loading of caisson foundations in saturated silt were carried out in a large soil tank at Zhejiang University. Test results of installation resistance during suction installation show that the seepage effect is limited in silt, and the suction required to penetrate the caisson can be well predicted based on the sleeve friction and cone resistance of cone penetration tests. The deformation mechanism and soil-structure interaction of a caisson subjected to lateral loads were investigated. The instantaneous rotation center of the model caisson at failure was at the depth of about four-fifths of the skirt length, almost directly below the lid center. Based on the assumption of a common position of the instantaneous rotation center and dominating resistance forces on the caisson, an analytical expression for the ultimate moment capacity was presented.

Experimental Study on Installation of Composite Bucket Foundations for Offshore Wind Turbines in Silty Sand

2016 ◽  
Vol 138 (6) ◽  
Author(s):  
Puyang Zhang ◽  
Zhi Zhang ◽  
Yonggang Liu ◽  
Hongyan Ding
Keyword(s):  
Wind Turbines ◽  
Large Scale ◽  
Silty Sand ◽  
Offshore Wind ◽  
Scale Model ◽  
Positive Pressure ◽  
Adjustment Process ◽  
Outer Diameter ◽  
Bucket Foundation ◽  
Offshore Wind Turbines

The composite bucket foundation (CBF) is a cost-competitive foundation for offshore wind turbines, which can be adapted to the loading characteristics and development needs of offshore wind farms due to its special structural form. There are seven sections divided inside the CBF by steel bulkheads, which are arranged in a honeycomb structure. The six peripheral sections with the skirt have the same proportions while the middle orthohexagonal one is a little larger. With the seven-section structure, the CBF has reasonable motion characteristics and towing reliability during the wet-tow construction process. Moreover, the pressure inside the compartments can control the levelness of the CBF during suction installation. Several large-scale model tests on suction installation of CBF have been performed in order to explore the feasibility of the tilt adjusting technique in saturated silty sand off the coast of Jiangsu in China. The composite bucket foundation in the tests has an outer diameter of 3.5 m and a clear wall height of 0.9 m. During the suction-assisted penetration process, the pressures in all the compartments were controlled to level the foundation in a timely operation. A convenient method is to improve the CBF inclination by controlling the inside differential pressure among the compartments. It can be commonly carried out by applying suction/positive pressure with intermittent pumping among the seven compartments. Another adjusting technique for a big tilt with deeper penetration is operated with decreasing the penetration depth achieved by suction-assisted lowering the relatively high compartments and positive pressures raising the relatively low compartments. Test results show that the reciprocating adjustment process can be repeated until the CBF is completely penetrated into a designed depth.

Large-Scale Experiments of Wave-Overtopping Loads on Walls: Layer Thicknesses and Velocities

2018 ◽  
Author(s):  
Lorenzo Cappietti ◽  
Irene Simonetti ◽  
Andrea Esposito ◽  
Maximilian Streicher ◽  
Andreas Kortenhaus ◽  
...  
Keyword(s):  
Large Scale ◽  
Scale Validation ◽  
Irregular Waves ◽  
Scale Model ◽  
Small Scale ◽  
Wave Loads ◽  
Wave Overtopping ◽  
Large Scale Model ◽  
Vertical Walls ◽  
Set Up

Wave-Overtopping loads on vertical walls, such as those located on top of a dike, have been investigated in several small-scale experiments in the past. A large-scale validation for a mild foreshore situation is still missing. Hence the WALOWA (WAve LOads on WAlls) experimental campaign was carried out to address this topic. This paper, first presents a description of the large-scale model, the measurement set-up and the experimental methodologies, then it focuses on the layer thicknesses and velocities of the flows created on the promenade by the wave overtopping. A set of resistive wave gauges, ultrasonic distance sensors and velocimeters have been used to conduct these measurements. Preliminary data analysis and results, related to a 1000 irregular waves long test, are discussed. The momentum flux of these flows is studied and its implications, for the wave-overtopping loads acting on the vertical walls, are highlighted.

scholarly journals EXTERNAL AND INTERNAL WAVE SET-UP AT POROUS PBA REVETMENTS ON A SAND FOUNDATION

2012 ◽  
Vol 1 (33) ◽  
pp. 27
Author(s):  
Gisa Foyer ◽  
Hocine Oumeraci
Keyword(s):  
Large Scale ◽  
Wave Length ◽  
Irregular Waves ◽  
Scale Model ◽  
Large Scale Model ◽  
Internal Set ◽  
Deep Water Wave ◽  
Set Up ◽  
The Stability ◽  
Almost All

Wave set-up is generally considered for the stability analysis of beaches, but not or not explicitly for the design of revetments. Based on large-scale model results with regular and irregular waves, it is shown in this paper that this is not justified. For this purpose, the wave set-up on a porous bonded revetment and the related internal set-up in the sand foundation below the revetment are analysed for different breaker types. The results particularly show that (i) considerable set-up values are obtained for almost all breaker types, (ii) a good correlation exists with the deep water wave length for both external and internal set-up and (iii) the internal set-up is significantly affected by the wave set-up on the slope. Empirical formulae for the prediction of the external and internal set-up are also proposed for both regular and irregular waves.

Large-Scale Investigations of Geotextile Sandcontainers Used for Scour Protection of Offshore Monopiles Supporting Wind Energy Turbines

2006 ◽  
Author(s):  
Joachim Gru¨ne ◽  
Uwe Sparboom ◽  
Reinold Schmidt-Koppenhagen ◽  
Zeya Wang ◽  
Hocine Oumeraci
Keyword(s):  
Large Scale ◽  
Research Programme ◽  
Scale Model ◽  
Research Centre ◽  
Large Wave ◽  
Wave Channel ◽  
Large Scale Model ◽  
First Results ◽  
The Stability ◽  
Scour Protection

An innovative scour protection for monopile structures was proposed by using geotextile sand containers in a research programme started recently. Large-scale model tests on the stability of such alternative scour protection are being performed in the Large Wave Channel (GWK) of the Coastal Research Centre (FZK). First results are reported from basic test series performed with single geotextile sand containers and container groups with different container weights, varied in sizes and percentages of filling. Further an empirical approach on the stability of sand containers is estimated as a first approximation from the results.

RANCANG BANGUN PERANGKAT EKSPERIMENTASI PROSES PIROLISIS BIOMASA GELOMBANG MIKRO

2013 ◽  
Vol 14 (2) ◽  
Author(s):  
Noor Fachrizal
Keyword(s):  
Large Scale ◽  
Continuous Model ◽  
Biomass Energy ◽  
Scale Model ◽  
Small Scale ◽  
Laboratory Apparatus ◽  
Liquid Form ◽  
Large Scale Model ◽  
Bio Oil ◽  
Pyrolysis Of Biomass

Biomass such as agriculture waste and urban waste are enormous potency as energy resources instead of enviromental problem. organic waste can be converted into energy in the form of liquid fuel, solid, and syngas by using of pyrolysis technique. Pyrolysis process can yield higher liquid form when the process can be drifted into fast and flash response. It can be solved by using microwave heating method. This research is started from developing an experimentation laboratory apparatus of microwave-assisted pyrolysis of biomass energy conversion system, and conducting preliminary experiments for gaining the proof that this method can be established for driving the process properly and safely. Modifying commercial oven into laboratory apparatus has been done, it works safely, and initial experiments have been carried out, process yields bio-oil and charcoal shortly, several parameters are achieved. Some further experiments are still needed for more detail parameters. Theresults may be used to design small-scale continuous model of productionsystem, which then can be developed into large-scale model that applicable for comercial use.

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