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Chen, Mingsheng (Key Laboratory of High Performance Ship Technology, Wuhan University of Technology), Ministry of Education / School of Naval Architecture, Ocean and Energy Power Engineering, Wuhan University of Technology) | Zhou, Hao (Key Laboratory of High Performance Ship Technology, Wuhan University of Technology), Ministry of Education / School of Naval Architecture, Ocean and Energy Power Engineering, Wuhan University of Technology) | Li, Chun Bao (Key Laboratory of High Performance Ship Technology, Wuhan University of Technology), Ministry of Education / School of Naval Architecture, Ocean and Energy Power Engineering, Wuhan University of Technology)
ABSTRACT Floating wind turbine technology has become mature in recent years, it tends to be large-scale and deep-water deployment. Nowadays floating wind turbines are mainly semi-submersible platforms that are sensitive to the change of water depth and are mostly designed in deep water over 100 meters. However, the water depth in the South China Sea tends to be shallower than the North-sea in Europe, which should result in different mooring and platform dynamic response characteristics. So, the adaptability of a large floating wind turbine to the middle and shallow waters of the South China Sea has attracted much attention in China. In this paper, the DTU10MW wind turbine designed by the Technical University of Denmark and the OO-STAR platform proposed by the University of Stuttgart are taken as the research objects. The hydrodynamic model is established by AQWA. Based on the potential flow theory, the hydrodynamic coefficients of the OO-STAR platform in three different water depths are compared and further imported into OPENFAST for fully coupled time-domain simulation. Firstly, mooring schemes of different water depths are designed based on the bottom anchor uplift. Then various natural periods of OO-STAR are evaluated (mainly including platform motion and pitch vibration of the tower), Finally, based on the power spectral density method, the tower-base fore-aft bending moments, platform motion, and mooring response characteristics are analyzed under the low-frequency excitation load of turbulence wind and different water depth, and the excitation action of the 1P effect to the structural response is also considered. It provides a reference for the design of super large floating wind turbines in a medium and shallow seas in China. 1. INTRODUCTION Over decades of development in renewable industry, offshore wind energy has become renewable energy indispensably. The total global installed base of the floating offshore wind turbines (FOWT) is 35.3GW until 2020 (GWEC 2021). China ranks second in the world with 9.88GW offshore installed. Without a doubt that FOWT will flourish in China. The world has entered the operational stage of 5MW FOWT with the completion of the world's first floating wind farm (H. R. 2015). At the same time, the Kincardine offshore wind farm under construction marks the exploration of the 10MW level of floating wind turbines. The large-scale FOWT has deepened its deployment depth. However, The South China Sea has a vast sea area as the depth of 50 meters (Hsiao et al., 2016). The bottom-fixed substructure can no longer be used at deeper water depths(>50m) due to the high cost (Han et al., 2017), Therefore, it is of great significance to study the mooring and platform dynamic characteristics of ultra-large floating wind turbines in different water depths.
Abstract The steel structures of offshore wind turbine foundations have so far only been protected cathodically (galvanic anodes/impressed current systems) in the underwater area. More recent German regulations recommend an additional coating in order to reduce the required anode masses (1). In most cases, organic top coatings are used for this purpose, which significantly reduces the necessary protective current requirement. However, organic top coatings lose their barrier protection effect due to damage, defects and ageing, which increases the protective current requirement again. Mechanical loads already during transport and installation ("pile driving"), as well as (hydro-)abrasion by sand near the seabed during the period of use, make it useful to consider the tribological properties. Introduction Metallic coatings as a protective coating are characterized by excellent corrosion protection behavior and show extreme resistance to mechanical loads as well. Pure metallic coatings or duplex systems are already being used successfully in other areas of offshore structures. For example, areas in the tidal water zone, such as boat landings, usually receive a duplex system consisting of thermal spayed coating and a fitting topcoat. Add-on parts are often protected exclusively by a metallic zinc coating. A thermal spray coating in the submerged zone thus represents a logical alternative to the organic topcoat system. Thermal Spraying Zinc-Aluminum in Submerged Zone Thermal spraying has also been used in the offshore wind energy sector for a long time. Components such as the boot landings (Fig 1) on the offshore towers and other components in the area of the water exchange zone are specified as duplex coating, consisting of a zinc-aluminum spray coating (TSZA) and a subsequent multi-layer paint coating. This design is a proven system. In field tests carried out over many years by the MPA Stuttgart (Federal Materials Testing Institute of the State of Baden Württemberg) (3) together with the Grillo company, the corrosive resistance of thermally sprayed zinc coatings and in particular of zinc alloy coatings with up to 22 wt.% Al without subsequent color coating could be proven (Fig 2). Up to these alloy contents of aluminum in the zinc alloy, the cathodic corrosion protection remains completely intact.
ABSTRACT In the new Stuttgart 21 rail construction project, injections to seal anhydrite-bearing rock had to be carried out in the 3,200 m long twin-tube Feuerbach Tunnel. This article explains the further development of the equipment and technology and the implementation of digitalisation of the grouting works. INTRODUCTION The Feuerbach tunnel is an approximately 3,200-metre long twin railway tunnel and part of the Stuttgart 21 rail project. It connects the existing regional and intercity railway line in the north of Stuttgart to the city's new main station. It is currently under construction. The tunnel runs through strata of the Gypsum Keuper. If water comes into contact with the anhydrite-bearing Gypsum Keuper, a swelling can arise. Consequently, the conventional tunneling is done without using water in these sections. Despite this, water can get through the excavation-disturbed zone to the dry, unleached Gypsum Keuper underneath it. If there is anhydrite-bearing rock in these areas, it can swell. Due to this, many tunnels incurred damage in the past, for example in the form of heaves, which can reach the surface of the ground even of deep-lying tunnels.
Borisade, Friedemann (University of Stuttgart) | Koch, Christian (University of Stuttgart) | Lemmer, Frank (University of Stuttgart) | Cheng, Po Wen (University of Stuttgart) | Campagnolo, Filippo (Technical University of Munich) | Matha, Denis (Ramboll Wind)
The subject of this study is the verification and the validation of existing numerical codes for floating offshore wind turbine structures using wave tank model tests as part of the INNWIND.EU project. A model of the OC4-DeepCwind semisubmersible platform, together with a Froude-scaled rotor model, is tested in a combined wind-and-wave basin. The simulation environment comprises a multibody approach with hydrodynamic and aerodynamic loads and mooring line forces. The focus of this paper is the validation of the hydrodynamics of a modified model hull shape, which compensates for the excess mass of the nacelle. The results show that the simulation model agrees well with the experiment. Introduction At offshore sites with higher water depths, the use of floating structures is more reasonable than the use of large fixed-bottom structures such as monopiles, tripods, and jackets as described by James and Costa Ros (2015) and Beiter et al. (2016). A floating wind turbine experiences many different loading conditions. Floater motion with six degrees of freedom (6DOF) as well as aerodynamic and hydrodynamic loads have to be considered. At this point, few floating wind turbine prototypes have been built, e.g., the Fukushima FORWARD project, which was started in 2013. To increase the reliability of wind turbines for floating applications, validated simulation codes are needed to predict the forces on the system structure and their dynamic responses for combined stochastic wave and wind loadings (Müller et al., 2016). Although several verification tests have been done by Robertson et al. (2013), Huijs et al. (2014), and Müller et al. (2014), for example, the validation of coupled simulation of floating wind turbines is still part of current research. This work is associated with task 4.2 of the INNWIND.EU project as part of its model test campaign at LHEEA, École Centrale de Nantes (ECN), France, in 2014. INNWIND.EU, with its 27 European partners, aims to improve the design of beyond-state-of-the-art 10–20 MW offshore wind turbines, including hardware demonstration. A scaled 10 MW model of the OC4-DeepCwind semisubmersible was built at the University of Stuttgart, together with a Froude-scaled wind turbine with low Reynolds rotor blades, developed by the Politecnico di Milano.
Abstract A numerical model was created to predict timing and location of salt precipitation near the well bore region of mature gas wells. The model provides quantitative insight into the relevant reservoir and well properties that govern salt precipitation and its remediation. The model is used to predict the well's gas production and improve mitigation strategies. The numerical model has been developed using Dumu, a simulator developed by the University of Stuttgart. The model has been extended to incorporate several additional features essential to model salt precipitation and dissolution. A sensitivity study has been conducted to evaluate the impact of varying parameters such as initial liquid saturation, permeability, salinity, well pressure and drawdown on the model. Production loss mitigation strategies used can differ depending on the location and timescales of precipitation. A study of the parameters controlling the productivity of wells plagued by salt precipitation shows scope for improving reservoir management strategies which can delay the onset of salt clogging thereby improving gas production.
Wittke, W. (Consulting Engineers for Tunneling and Geotechnical Engineering Ltd.) | Schmitt, D. (Consulting Engineers for Tunneling and Geotechnical Engineering Ltd.) | Wittke-Gattermann, P. (Consulting Engineers for Tunneling and Geotechnical Engineering Ltd.)
ABSTRACT: In the course of the design and construction of the Boβler tunnel it is investigated whether and how it is possible to extend the tunnel sections, which are excavated with a tunnel boring machine, in comparison with the lengths determined in the contract. In this connection, the tunnel section located in the formation Aalenium 2 (al2), for which squeezing conditions are expected, is of major importance. Therefore, a vertical exploration shaft and a horizontal exploration gallery have been excavated starting from an intermediate access, in order to explore the layers of the al2 formation. These works have been accompanied by an intensive monitoring program as well as by field and laboratory testing. The results of geotechnical investigations were evaluated with the aid of three-dimensional finite element analyses. On this basis, the rock mechanical parameters of the layers of al2 were reviewed and upgraded. On the basis of the results of corresponding stability analyses for the segmental lining of the tunnel, it can be expected that the tunnel section crossing Aalenium 2 can be driven with a tunnel boring machine, if the thickness of the segments is increased from 45 cm, as planned in other tunnel sections, to 65 cm. 1 SPECIFICATIONS IN TENDER DOCUMENTS The 8.800 m long Boβlertunnelis part of the new Railway Line from Stuttgart to Munich which is currently under construction. Starting from the portal Aichelberg the following strata are crossed: Aalenium 1, Aalenium 2 and Bajocium to Callovium of the Brown Jurassic formation as well as rocks of the Upper Jurassic formation. The maximum overburden of the tunnel amounts to ~280m. In the corresponding area the tunnel is located in the Aalenium 2 and 1 of the Brown Jurassic formation (Fig. 1). In the course of exploration for this project among other data the uniaxial strength of the different rock types was determined (WBI 2010). The corresponding characteristic values are given in Figure 1. If these values are divided by the unit weight of the rock, the height of overburden can be derived for which the vertical pressure equals the uniaxial strength. These heights are represented with red lines in Figure 1. It can be seen, that in the area in which the tunnel runs through the strata of Aalenium 2 the existing overburden of up to 280 m is much larger than the derived value of 120 m. Thus, squeezing rock conditions were expected in this tunnel section.
Huang, Fei (Uppsala University) | Juhlin, Christopher (Uppsala University) | Han, Li (CNOOC Research Institute) | Kempka, Thomas (GFZ German Research Centre for Geosciences) | Norden, Ben (GFZ German Research Centre for Geosciences) | Lüth, Stefan (GFZ German Research Centre for Geosciences) | Zhang, Fengjiao (Uppsala University)
Summary The seismic complex decomposition technique is a spectral decomposition method using inversion strategies to decompose a seismic trace into its constituent frequencies and corresponding complex coefficients. This method has high time-frequency resolution and it is not necessary to select a signal window in comparison to conventional spectral decomposition methods. The thickness of the reservoir at the Ketzin pilot site is relatively thin, making it difficult to resolve seismically due to the band-limited seismic spectrum. This study presents an application of seismic complex decomposition to the time-lapse 3D seismic datasets at the Ketzin pilot site for estimating the temporal thickness of the injected CO2 within the thin reservoir via frequency tuning. Quantitative analysis for CO2 thickness and mass is investigated. Comparison between the real recorded data and the estimates shows that our results are reliable in assessing the amount of the CO2 in the plume at the Ketzin pilot site. Introduction The Ketzin pilot site is located west of Berlin, Germany, as an in situ laboratory for monitoring the storage of carbon dioxide (CO2) in a saline aquifer. The project was initiated in 2004 with the aim to verify effective monitoring methods for mapping the injected CO2 plume and to provide operational field experience of CO2 geological storage (Martens et al., 2013; Martens et al., 2014). One injection/observation well (Ktzi 201) and two observation wells (Ktzi 200 and Ktzi 202) were drilled in 2007 prior to CO2 injection. Over a 5-year period, up to 67 kt of CO2 were injected into the target reservoir, the fluviatile and heterogeneous Upper Stuttgart Formation. It is characterized by alternating siltstones and mudstones with poor reservoir properties and sandstone channels with good reservoir properties. The main-reservoir sandstone unit is 9- 20 m thick in the three wells (Norden et al., 2010). The time-lapse 3D seismic method has proven to be a successful technique to monitor the growth of the CO2 plume at the Ketzin site. A 3D baseline seismic survey was acquired in autumn 2005 prior to CO2 injection (Juhlin et al., 2007). Two 3D repeat seismic surveys were acquired in autumn 2009 and autumn 2012, after about 22 kt and 61 kt of CO2 had been injected, respectively. Results from the time-lapse analysis (Figure 1) show conspicuous amplitude anomalies due to changes in the reservoir properties after CO2 injection and a preferred westward trend of CO2 migration, reflecting the internal heterogeneity of the reservoir.
Abstract In Stuttgart, the Rosenstein-Tunnel is currently under construction in combination with the third Leuze-Tunnel, which is also under work. This will improve the traffic conditions in the highly populated city areas, located north of downtown Stuttgart. The owner, the City of Stuttgart, had to face challenging conditions when setting up the project. This includes the impact of urban environment at both tunnel portals and within the open cut sections. Intensive actions were required concerning cable and pipe routing and various traffic phases with local detours, which have to manage the traffic and to enable the construction works at the same time. The ground conditions with the presence of mineral water have a major impact on the tunnel construction works. As the project is partly located in an area, in which dewatering of groundwater is not allowed, restrictions of the tunneling sequence and the provision of injections became necessary. 1 Introduction to the Project Stuttgart, as the capitol of the south German federal state of Baden-Württemberg, has an important meaning for economy and politics and has become one of the most prospering zones in southern Germany. The improvement of the traffic infrastructures for the major federal roads as well as for the German railway is the dominating actual topic in Stuttgart and this will continue at least for the next 5 years. At the south bank of the river Neckar in the district of Bad Cannstatt, the junction of the two federal main roads B 10 and B 14 shall be released by a new third tunnel near the thermal bath Leuze. Following the river downstream, the B 10 circumnavigates the Wilhelma zoo by a road "knee". This edge will be shortened by the new Rosenstein-Tunnel with a length of totally 1.3 km, from which approx. 750 m are realized by underground excavation of two separate tunnel tubes, which are connected by four cross-cuts. Additionally, in the center of the tunnel length there is a section with an extended cross-section for emergency stops, which is a major safety issue of the tunnel. Figure 1 displays the general project layout for the Rosenstein-Tunnel. The major urban challenges in this project area can be introduced such as follows:
Abstract An integrated hydro-mechanical assessment of the Ketzin pilot site for CO2 storage, Germany, has been carried out in the present study. For that purpose, history matched reservoir simulation models were coupled with regional-scale hydro-mechanical simulation models. Simulation results reveal maximum vertical displacements of about 6mm at the reservoir top and 4mm at the ground surface. Neither shear nor tensile failure is observed in the hydro-mechanical model at the end of the simulation time. Consequently, reservoir, caprock and fault integrity are maintained during the entire CO2 storage operation. 1. Introduction The Ketzin pilot site is located about 40 km west of Berlin in the State of Brandenburg (Germany) settled in a double-anticline system (Ketzin-Roskow) with a graben zone dominating the double-anticline top. CO2 injection at the Ketzin pilot site into the Stuttgart Formation (Keuper) is being carried out since June 2008, whereas about 67,270 t CO2 were injected until site abandonment started in September 2013 (Martens et al. 2013, 2012, Würdemann et al. 2010). The maximum pore pressure increase during five years of storage operation was about 1.6MPa, while the initial pore pressure at reservoir depth (about 640 m) in the injection well was 6.2MPa (Möller et al. 2012). A verification of mechanical caprock and fault integrity was undertaken in the scope of a risk assessment prior to the injection start. At that time, data on site behaviour resulting from CO2 injection was not available. New data from site operation, geological modelling (Norden & Frykman 2013, Kempka et al. 2013a) and history matched multi-phase flow simulations (Kempka &0 Kühn 2013, Kempka et al. 2010) were integrated into our 3D hydro-mechanical simulations based on a 40 km×40 km 3D structural geological model taking into account all 24 known major faults in that area. The main aim of the present study was to determine, if reservoir rock, caprock or fault integrity may be compromised by the CO2 storage operation in addition to a verification of vertical displacements at the ground surface for a later model validation against satellite-based Interferometric Synthetic Aperture Radar (InSAR) monitoring results.
ABSTRACT: A recent method for the estimation of maximum (SH) and minimum (Sh) horizontal stress magnitudes consists of using radial profiles of the three shear moduli obtained from the Stoneley and cross-dipole sonic data in a vertical wellbore. These shear moduli change as a function of formation stresses, which in turn change as a function of the radial position away from the wellbore. Two difference equations are constructed from the three far-field shear moduli and the other two are constructed from differences in the shear moduli at two radial positions with different stresses in the presence of near-wellbore stress concentrations. Outputs from this inversion algorithm include SH and Sh magnitudes, and an acoustoelastic parameter (AE) expressed in terms of two rock nonlinear constants referred to a local reference state. Additionally, the orientation of the SH direction is identified from that of the fast shear azimuth. Hence the principal horizontal stress state is fully determined. This technique has been used to obtain reservoir stresses in an on-going reservoir geomechanical study of seal integrity in a CO2 storage experiment conducted at the Ketzin site, Germany. The reservoir consists of a Stuttgart sandstone formation that extends from 630 to 701 m. We have analyzed borehole sonic data in a vertical injection wellbore (CO2 Ktzi 201/2007) from 175 to 755 m. Crossing dipole dispersions over a depth interval of 638 to 651 m imply that the horizontal stress-induced anisotropy is dominating the dipole shear slowness anisotropy. Processing of the cross-dipole data yields the mean fast-shear azimuth of 150+/-5 degrees East of North that identifies SH direction. Radial profiles of the three shear slownesses obtained from the Stoneley and cross-dipole data have been used to estimate the SH and Sh magnitudes at 8 depths distributed between 640 and 648 m.