| 1. |
- Mathern, Alexandre, 1986, et al.
(författare)
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Concrete Support Structures for Offshore Wind Turbines: Current Status, Challenges, and Future Trends
- 2021
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Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 14:7
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Forskningsöversikt (refereegranskat)abstract
- Today’s offshore wind turbine support structures market is largely dominated by steel structures, since steel monopiles account for the vast majority of installations in the last decade and new types of multi-leg steel structures have been developed in recent years. However, as wind turbines become bigger, and potential sites for offshore wind farms are located in ever deeper waters and ever further from the shore, the conditions for the design, transport, and installation of support structures are changing. In light of these facts, this paper identifies and categorizes the challenges and future trends related to the use of concrete for support structures of future offshore wind projects. To do so, recent advances and technologies still under development for both bottom-fixed and floating concrete support structures have been reviewed. It was found that these new developments meet the challenges associated with the use of concrete support structures, as they will allow the production costs to be lowered and transport and installation to be facilitated. New technologies for concrete support structures used at medium and great water depths are also being developed and are expected to become more common in future offshore wind installations. Therefore, the new developments identified in this paper show the likelihood of an increase in the use of concrete support structures in future offshore wind farms. These developments also indicate that the complexity of future support structures will increase due to the development of hybrid structures combining steel and concrete. These evolutions call for new knowledge and technical know-how in order to allow reliable structures to be built and risk-free offshore installation to be executed.
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| 2. |
- Bourne-Webb, Peter, et al.
(författare)
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Analysis and design methods for energy geostructures
- 2016
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Ingår i: Renewable and Sustainable Energy Reviews. - : Elsevier BV. - 1879-0690 .- 1364-0321. ; 65, s. 402-419
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Forskningsöversikt (refereegranskat)abstract
- Based on discussions at the international workshop on “Thermoactive geotechnical systems for near-surface geothermal energy”, hosted at École Polytechnique Fédérale de Lausanne (EPFL), Switzerland (http://www.olgun.cee.vt.edu/workshop/), this article attempts to provide a broad overview of the analysis methods used for evaluation of systems that use either boreholes or geo-structures for heat exchange. It identifies commonalities where knowledge transfer from the former to the latter can be made, and highlights where there are significant differences that may limit this cross-fertilisation. The article then focusses on recent developments and current understanding pertaining to the analysis of the thermo-mechanical interaction between a geostructure and the ground, and how this may be incorporated into the geotechnical design of energy geostructures.
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| 3. |
- Aderemi, Adetomiwa, et al.
(författare)
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Porosity and permeability calculations in a Biolithite using x-ray tomography images
- 2023
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Ingår i: SEG Technical Program Expanded Abstracts. - 1052-3812. ; 2023-August, s. 1700-1704
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Forskningsöversikt (refereegranskat)abstract
- Engineering energy storage/extraction for geoenergy applications (e.g., geothermal energy extraction, CO2 and/or Hydrogen storage) requires a very good knowledge of subsurface heterogeneities. One of the principal factors that influences the response of the underground system is the continuously evolving pore networks of the targeted rocks. This work aims to understand the pore network of a natural Biolithite (Figure 1), coming from a Greek outcrop, and to predict the permeability of lab-scale systems (due to diagenetic alterations and/or natural deformation) using x-ray computed tomography (CT) images (3D) and stochastic model reconstructions. We emphasize on the importance of a reproducible image analysis workflow (Figure 2) during reservoir description, as an input to extracting pore network models that have representative geometrical and topological characteristics at core-plug scale.
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| 4. |
- Al-Jabban, Wathiq, et al.
(författare)
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Briefing : Common laboratory procedures to prepare and cure stabilised soil specimens: a short review
- 2020
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Ingår i: Geotechnical Research. - UK : Institution of Civil Engineers (ICE). - 2052-6156. ; 7:1, s. 3-10
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Forskningsöversikt (refereegranskat)abstract
- Soil stabilisation is used extensively to improve the physical and mechanical properties of soils to achieve the desired strength and durability properties. During the design process, laboratory investigation is conducted firstly to obtain an enhancement in soil strength and stiffness, in addition to the type and amount of binder required. The methods of preparing and curing specimens of soil–binder mixtures directly influence the properties of the stabilised soils. The most common laboratory protocols used for preparing and curing the specimens of stabilised soil are presented in this short review. The review focuses on several aspects such as homogenisation of the natural soil, mixing type and duration, mould type, moulding techniques and curing time and condition. This review can assist various construction projects that deal with soil improvement to choose an appropriate method for preparing and curing a soil–binder mixture to simulate the field conditions as much as possible and obtain uniform soil–binder mixtures.
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| 5. |
- Jacks, Gunnar, et al.
(författare)
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Soil degradation caused by human water maagement
- 2008
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Ingår i: Water for Food: Formas-publikation. - Stockholm : Forskningsrådet Formas. - 1653-3003. ; , s. 113-118, s. 111-118
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Forskningsöversikt (övrigt vetenskapligt/konstnärligt)
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| 6. |
- Ronczka, Mathias, et al.
(författare)
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Electric resistivity and seismic refraction tomography : A challenging joint underwater survey at Äspö Hard Rock Laboratory
- 2017
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Ingår i: Solid Earth. - : Copernicus GmbH. - 1869-9510 .- 1869-9529. ; 8:3, s. 671-682
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Forskningsöversikt (refereegranskat)abstract
- Tunnelling below water passages is a challenging task in terms of planning, pre-investigation and construction. Fracture zones in the underlying bedrock lead to low rock quality and thus reduced stability. For natural reasons, they tend to be more frequent at water passages. Ground investigations that provide information on the subsurface are necessary prior to the construction phase, but these can be logistically difficult. Geophysics can help close the gaps between local point information by producing subsurface images. An approach that combines seismic refraction tomography and electrical resistivity tomography has been tested at the Äspö Hard Rock Laboratory (HRL). The aim was to detect fracture zones in a well-known but logistically challenging area from a measuring perspective. The presented surveys cover a water passage along part of a tunnel that connects surface facilities with an underground test laboratory. The tunnel is approximately 100ĝ€m below and 20ĝ€m east of the survey line and gives evidence for one major and several minor fracture zones. The geological and general test site conditions, e.g. with strong power line noise from the nearby nuclear power plant, are challenging for geophysical measurements. Co-located positions for seismic and ERT sensors and source positions are used on the 450ĝ€m underwater section of the 700ĝ€m profile. Because of a large transition zone that appeared in the ERT result and the missing coverage of the seismic data, fracture zones at the southern and northern parts of the underwater passage cannot be detected by separated inversion. Synthetic studies show that significant three-dimensional (3-D) artefacts occur in the ERT model that even exceed the positioning errors of underwater electrodes. The model coverage is closely connected to the resolution and can be used to display the model uncertainty by introducing thresholds to fade-out regions of medium and low resolution. A structural coupling cooperative inversion approach is able to image the northern fracture zone successfully. In addition, previously unknown sedimentary deposits with a significantly large thickness are detected in the otherwise unusually well-documented geological environment. The results significantly improve the imaging of some geologic features, which would have been undetected or misinterpreted otherwise, and combines the images by means of cluster analysis into a conceptual subsurface model.
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| 7. |
- Sandström, Rolf
(författare)
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Basic Analytical Modeling of Creep Strain Curves
- 2023
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Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 16:9
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Forskningsöversikt (refereegranskat)abstract
- Creep strain versus time curves (creep curves) have traditionally been described with the help of empirical models where a number of adjustable parameters are involved. These models are simple to use, but they cannot be applied for prediction. For understanding the general behavior of primary and tertiary creep, they are still useful. In fact, the phi model can represent primary creep, and the Omega model tertiary creep for a number of materials. However, in recent years, basic analytical models have been formulated that can predict and describe creep strain data without using fitting parameters. In the paper, a review of these models is given. A number of applications of the models are also given. It is demonstrated that the basic models can quantitatively predict observations. They also provide derivations of some empirical findings.
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| 8. |
- Sissakian, V. K., et al.
(författare)
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Geomorphology, Stratigraphy and Tectonics of the Mesopotamian Plain, Iraq : A Critical Review
- 2021
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Ingår i: Geotectonics. - : Springer. - 0016-8521 .- 1556-1976. ; 55:1, s. 135-160
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Forskningsöversikt (refereegranskat)abstract
- The Mesopotamian Plain is part of the Mesopotamia which extends for vast area bigger than the plain. The plain is almost flat and vast lowland, which has clearly defined physiographic boundaries with the other surrounding physiographic provinces. The plain is a huge accumulation geomorphologic unit, where the fluvial, lacustrine, and the Aeolian landforms prevail; the fluvial units being the abundant among others. However, estuarine and marine forms also are developed, but restricted to the extreme southeastern reaches of the plain. The Mesopotamian Plain is covered totally by Quaternary sediments among which the fluvial origin is the most prevailing and more specifically the flood plain sediments. The flood plain sediments are the Holocene in age, whereas the Pleistocene sediments are restricted to alluvial fan sediments and river terraces. The flood plain sediments cover majority of the Mesopotamian Plain, whereas the alluvial sediments are restricted to the northern-eastern, western and southern peripheral parts only. Different geomorphological features indicate the Neotectonic activity in the plain, such as migrations of rivers due to growing of subsurface anticlines. The extreme southeastern part is covered by the tidal flat and sabkha sediments. Marshes and shallow depressions are also covered by the Holocene sediments which are contaminated by the Aeolian sediments. Mesopotamian Plain is a part of the Mesopotamian Foredeep which is a part of the Zagros Foreland Basin including the Zagros Fold-Thrust Belt. It is large continuously subsiding basin since the Upper Miocene (11.62 Ma). The plain shows no structural features on the surface, except the main fault escarpment representing the part of Abu Jir Active Fault Zone. However, the rolling topography, in the northern parts of the plain indicates subsurface anticlines that are still growing up, such as Balad, Samarra, Tikrit and Baiji anticlines indicating the Neotectonic activity. Moreover, many buried subsurface anticlines are present in different parts of the plain. All of them are growing anticlines and have caused continuous shift to Tigris and Euphrates rivers and their distributaries indicating the Neotectonic activities. The minimum and maximum subsidence amounts in the plain since the Upper Miocene are zero and -2500 m, respectively.
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| 9. |
- Tao, Hai, et al.
(författare)
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Groundwater level prediction using machine learning models: A comprehensive review
- 2022
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Ingår i: Neurocomputing. - : Elsevier. - 0925-2312 .- 1872-8286. ; 489, s. 271-308
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Forskningsöversikt (refereegranskat)abstract
- Developing accurate soft computing methods for groundwater level (GWL) forecasting is essential for enhancing the planning and management of water resources. Over the past two decades, significant progress has been made in GWL prediction using machine learning (ML) models. Several review articles have been published, reporting the advances in this field up to 2018. However, the existing review articles do not cover several aspects of GWL simulations using ML, which are significant for scientists and practitioners working in hydrology and water resource management. The current review article aims to provide a clear understanding of the state-of-the-art ML models implemented for GWL modeling and the milestones achieved in this domain. The review includes all of the types of ML models employed for GWL modeling from 2008 to 2020 (138 articles) and summarizes the details of the reviewed papers, including the types of models, data span, time scale, input and output parameters, performance criteria used, and the best models identified. Furthermore, recommendations for possible future research directions to improve the accuracy of GWL prediction models and enhance the related knowledge are outlined.
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| 10. |
- Tenzer, Robert, et al.
(författare)
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Definition of Physical Height Systems for Telluric Planets and Moons
- 2018
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Ingår i: Surveys in geophysics. - : Springer Netherlands. - 0169-3298 .- 1573-0956. ; 39:3, s. 313-335
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Forskningsöversikt (refereegranskat)abstract
- In planetary sciences, the geodetic (geometric) heights defined with respect to the reference surface (the sphere or the ellipsoid) or with respect to the center of the planet/moon are typically used for mapping topographic surface, compilation of global topographic models, detailed mapping of potential landing sites, and other space science and engineering purposes. Nevertheless, certain applications, such as studies of gravity-driven mass movements, require the physical heights to be defined with respect to the equipotential surface. Taking the analogy with terrestrial height systems, the realization of height systems for telluric planets and moons could be done by means of defining the orthometric and geoidal heights. In this case, however, the definition of the orthometric heights in principle differs. Whereas the terrestrial geoid is described as an equipotential surface that best approximates the mean sea level, such a definition for planets/moons is irrelevant in the absence of (liquid) global oceans. A more natural choice for planets and moons is to adopt the geoidal equipotential surface that closely approximates the geometric reference surface (the sphere or the ellipsoid). In this study, we address these aspects by proposing a more accurate approach for defining the orthometric heights for telluric planets and moons from available topographic and gravity models, while adopting the average crustal density in the absence of reliable crustal density models. In particular, we discuss a proper treatment of topographic masses in the context of gravimetric geoid determination. In numerical studies, we investigate differences between the geodetic and orthometric heights, represented by the geoidal heights, on Mercury, Venus, Mars, and Moon. Our results reveal that these differences are significant. The geoidal heights on Mercury vary from − 132 to 166 m. On Venus, the geoidal heights are between − 51 and 137 m with maxima on this planet at Atla Regio and Beta Regio. The largest geoid undulations between − 747 and 1685 m were found on Mars, with the extreme positive geoidal heights under Olympus Mons in Tharsis region. Large variations in the geoidal geometry are also confirmed on the Moon, with the geoidal heights ranging from − 298 to 461 m. For comparison, the terrestrial geoid undulations are mostly within ± 100 m. We also demonstrate that a commonly used method for computing the geoidal heights that disregards the differences between the gravity field outside and inside topographic masses yields relatively large errors. According to our estimates, these errors are − 0.3/+ 3.4 m for Mercury, 0.0/+ 13.3 m for Venus, − 1.4/+ 125.6 m for Mars, and − 5.6/+ 45.2 m for the Moon.
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