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C. van Beek
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1
We present a development of capacitively coupled EM sensors integrated in non-corrosive casings for permanent CSEM monitoring in boreholes. Capacitive sensors are required to detect low-frequency (diffusive-field) signals where voltage measurements fail and ammeters need to be used. The permanent installation in boreholes necessitates surface placement of the electronic components to ensure their longevity and accessibility. An issue is that small current signals need to be transferred over a large distance via cables whose capacitances are larger than the ones from the sensors, so a circuit of a Zero-Resistance Ammeter with Integrator (ZRA-I) was developed for annihilating the cable-capacitance effect. Via modelling, lab and small-scale field testing, we were able to show that capacitive sensors with ZRA-I electronics worked well: although the desired signal is slightly decreased compared to the one from galvanically coupled sensors, the signal-to-noise ratios are comparable, for the frequencies used. So we show that capacitive sensors can successfully be integrated in composite casings and, with the proper sensor electronics, can well be used for permanent CSEM monitoring in boreholes.
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We present a development of capacitively coupled EM sensors integrated in non-corrosive casings for permanent CSEM monitoring in boreholes. Capacitive sensors are required to detect low-frequency (diffusive-field) signals where voltage measurements fail and ammeters need to be used. The permanent installation in boreholes necessitates surface placement of the electronic components to ensure their longevity and accessibility. An issue is that small current signals need to be transferred over a large distance via cables whose capacitances are larger than the ones from the sensors, so a circuit of a Zero-Resistance Ammeter with Integrator (ZRA-I) was developed for annihilating the cable-capacitance effect. Via modelling, lab and small-scale field testing, we were able to show that capacitive sensors with ZRA-I electronics worked well: although the desired signal is slightly decreased compared to the one from galvanically coupled sensors, the signal-to-noise ratios are comparable, for the frequencies used. So we show that capacitive sensors can successfully be integrated in composite casings and, with the proper sensor electronics, can well be used for permanent CSEM monitoring in boreholes.
The high-precision scrap sorting for effective metal recycling can bring substantial environmental and economic benefits. This article presents a magnetic image sensor that can help to identify the ferrous contaminants inside nonferrous scraps of large sizes. First, the concept and the theory for detecting ferrous contaminants are described. In particular, an inversion algorithm is proposed to characterize the size and position of ferrous contaminants inside the main scrap bodies. Then, based on computed and measured results, the feasibility of sensor design using either 1-D Hall arrays or 1-D pickup coils is demonstrated. Finally, methods are suggested to minimize disturbing signals from very large nonferrous pieces passing through the slightly uneven magnetic field. The obtained findings in this study may apply not only to nonferrous scraps but many other materials of which the mass ratio of the ferrous contaminant to the main material is small.
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The high-precision scrap sorting for effective metal recycling can bring substantial environmental and economic benefits. This article presents a magnetic image sensor that can help to identify the ferrous contaminants inside nonferrous scraps of large sizes. First, the concept and the theory for detecting ferrous contaminants are described. In particular, an inversion algorithm is proposed to characterize the size and position of ferrous contaminants inside the main scrap bodies. Then, based on computed and measured results, the feasibility of sensor design using either 1-D Hall arrays or 1-D pickup coils is demonstrated. Finally, methods are suggested to minimize disturbing signals from very large nonferrous pieces passing through the slightly uneven magnetic field. The obtained findings in this study may apply not only to nonferrous scraps but many other materials of which the mass ratio of the ferrous contaminant to the main material is small.
Conference paper
(2022)
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H. Hendrikse, T.C. Hammer, C.C. Owen, M.A. van den Berg, C. van Beek, Arttu Polojärvi, Otto Puolakka, Tom Willems
With the recent surge in development of offshore wind in the Baltic Sea, Bohai Sea and other ice-prone regions, a need has arisen for new basin tests to qualify the interaction between offshore wind turbines and sea ice. To this end, a series of model tests was performed at the Aalto ice basin as part of the SHIVER project. The tests were aimed at modeling the dynamic interaction between flexible, vertically-sided structures and ice failing in crushing. A real-time hybrid test setup was used which combines numerical and physical components to model the structure. This novel test setup enabled the testing of a wide range of structure types, including existing full-scale structures for which ice-induced vibrations have been documented, and a series of single-degree-of-freedom oscillators to obtain a better understanding of the fundamental processes during dynamic ice-structure interaction. The tests were primarily focused on the dynamic behavior of support structures for offshore wind turbines under ice crushing loads. First results of the campaign show that the combination of the use of cold model ice and not scaling time and deflection of the structure can yield representative ice-structure interaction in the basin. This is demonstrated with experiments during which a scaled model of the Norströmsgrund lighthouse and Molikpaq caisson were used. The offshore wind turbine tests resulted in multi-modal interaction which can be shown to be relevant for the design of the support structure. The dataset has been made publicly available for further analysis.
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With the recent surge in development of offshore wind in the Baltic Sea, Bohai Sea and other ice-prone regions, a need has arisen for new basin tests to qualify the interaction between offshore wind turbines and sea ice. To this end, a series of model tests was performed at the Aalto ice basin as part of the SHIVER project. The tests were aimed at modeling the dynamic interaction between flexible, vertically-sided structures and ice failing in crushing. A real-time hybrid test setup was used which combines numerical and physical components to model the structure. This novel test setup enabled the testing of a wide range of structure types, including existing full-scale structures for which ice-induced vibrations have been documented, and a series of single-degree-of-freedom oscillators to obtain a better understanding of the fundamental processes during dynamic ice-structure interaction. The tests were primarily focused on the dynamic behavior of support structures for offshore wind turbines under ice crushing loads. First results of the campaign show that the combination of the use of cold model ice and not scaling time and deflection of the structure can yield representative ice-structure interaction in the basin. This is demonstrated with experiments during which a scaled model of the Norströmsgrund lighthouse and Molikpaq caisson were used. The offshore wind turbine tests resulted in multi-modal interaction which can be shown to be relevant for the design of the support structure. The dataset has been made publicly available for further analysis.
Journal article
(2022)
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Hayo Hendrikse, Tim C. Hammer, Marnix van den Berg, Tom Willems, Cody C. Owen, Kees van Beek, Nick J.J. Ebben, Otto Puolakka, Arttu Polojärvi
Basin tests were performed at the Aalto Ice Tank to gather data on ice-structure action and interaction from ice failing against a vertically sided cylindrical pile. The tests were performed with a real-time hybrid test setup, which combined physical and numerical components to simulate a range of test structures in real-time. The dataset includes results from tests with offshore wind turbine structures, structural models representing a series of single- and multi-degree-of-freedom oscillators, and scaled dynamic models of the Norströmsgrund lighthouse and the Molikpaq caisson structure. In addition, forced vibration tests and rigid structure tests were performed. Ice loads and structural response were measured with accelerometers, displacement sensors, potentiometers, strain gauges and load cells and the ice-structure interaction process was filmed from three different camera angles. The resulting raw data have been categorized and stored as unfiltered time series. A total of 259 different tests are included in the dataset. The model ice formation procedure and the test temperature were aimed at creating model ice that mimics the material behavior of full-scale saline ice during crushing failure, with a specific focus on the transition from brittle to ductile behavior. The data can be used for validation of models for dynamic ice-structure interaction. The offshore wind turbine data can be used to study the effect of wind loading on the interaction with ice and the effect of the specific dynamic properties of wind turbine structures with monopile foundations on the ice-structure interaction process. The forced-oscillation data can be used to quantify the time and speed dependant aspects of ice loading. The Norströmsgrund lighthouse and the Molikpaq data can be used as a reference comparison to full-scale data on ice loads.
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Basin tests were performed at the Aalto Ice Tank to gather data on ice-structure action and interaction from ice failing against a vertically sided cylindrical pile. The tests were performed with a real-time hybrid test setup, which combined physical and numerical components to simulate a range of test structures in real-time. The dataset includes results from tests with offshore wind turbine structures, structural models representing a series of single- and multi-degree-of-freedom oscillators, and scaled dynamic models of the Norströmsgrund lighthouse and the Molikpaq caisson structure. In addition, forced vibration tests and rigid structure tests were performed. Ice loads and structural response were measured with accelerometers, displacement sensors, potentiometers, strain gauges and load cells and the ice-structure interaction process was filmed from three different camera angles. The resulting raw data have been categorized and stored as unfiltered time series. A total of 259 different tests are included in the dataset. The model ice formation procedure and the test temperature were aimed at creating model ice that mimics the material behavior of full-scale saline ice during crushing failure, with a specific focus on the transition from brittle to ductile behavior. The data can be used for validation of models for dynamic ice-structure interaction. The offshore wind turbine data can be used to study the effect of wind loading on the interaction with ice and the effect of the specific dynamic properties of wind turbine structures with monopile foundations on the ice-structure interaction process. The forced-oscillation data can be used to quantify the time and speed dependant aspects of ice loading. The Norströmsgrund lighthouse and the Molikpaq data can be used as a reference comparison to full-scale data on ice loads.
With the ongoing development of offshore wind in cold regions where the foundations are exposed to sea ice, there is a strong need for data to validate the numerically predicted dynamic interaction between ice and structure used for design. Full-scale data is non-existent and only a limited number of experimental campaigns in ice tanks have been conducted for this specific problem. When compared to traditional structures subjected to sea ice loading like lighthouses and oil and gas platforms, the motion of the turbines at the ice action point is both in line with the ice drift direction but also significantly across due to the interaction of the turbine with the wind. Furthermore, the structure being slender overall and having a large top mass results in a very particular set of modes of oscillation where at least both the first and second global bending mode are expected to interact with the ice. To capture this complexity, a real-time hybrid test setup has been designed for basin tests in the SHIVER project and is presented in this paper. The setup uses two integrated linear actuators to control the motion of a rigid pile in two dimensions. Loads at the ice-action point are measured and used in a numerical model where these are combined with virtual loads, for example wind loading, to determine the response of the structure which is then applied in the physical setup by the actuators. The system allows to test a wide range of combinations of structural stiffness, mass, and damping, including structural properties typically associated with the relevant modes of oscillation of offshore wind turbines.
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With the ongoing development of offshore wind in cold regions where the foundations are exposed to sea ice, there is a strong need for data to validate the numerically predicted dynamic interaction between ice and structure used for design. Full-scale data is non-existent and only a limited number of experimental campaigns in ice tanks have been conducted for this specific problem. When compared to traditional structures subjected to sea ice loading like lighthouses and oil and gas platforms, the motion of the turbines at the ice action point is both in line with the ice drift direction but also significantly across due to the interaction of the turbine with the wind. Furthermore, the structure being slender overall and having a large top mass results in a very particular set of modes of oscillation where at least both the first and second global bending mode are expected to interact with the ice. To capture this complexity, a real-time hybrid test setup has been designed for basin tests in the SHIVER project and is presented in this paper. The setup uses two integrated linear actuators to control the motion of a rigid pile in two dimensions. Loads at the ice-action point are measured and used in a numerical model where these are combined with virtual loads, for example wind loading, to determine the response of the structure which is then applied in the physical setup by the actuators. The system allows to test a wide range of combinations of structural stiffness, mass, and damping, including structural properties typically associated with the relevant modes of oscillation of offshore wind turbines.
Conference paper
(2020)
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Athanasios Tsetas, Sergio S. Gómez, Andrei V. Metrikine, Apostolos Tsouvalas, Kees van Beek, F. Sadeghi Tehrani, Evangelos Kementzetzidis, Federico Pisanò, Ahmed Elkadi, Maxim Segeren, Timo Molenkamp
A novel pile-driving technique, named Gentle Driving of Piles (GDP), that combines axial low-frequency and torsional high-frequency vibrations has been developed and tested recently. During the experimental campaign, several piles were installed onshore, making use of the GDP shaker. Besides those, a number of additional piles were installed using conventional pile-driving techniques, i.e. impact piling and axial vibratory driving. After the completion of the installation phase, the installed piles have been subjected to impact hammer tests with the following goals. First, the in-situ dynamic properties of the pile-soil system have been identified. Second, the post-installation soil state has been investigated, along with its evolution in time for each pile driving scenario. Preliminary analyses, of the data collected during the impact tests show dissimilar trends in the overall dynamic response between the piles installed with impact hammer and those installed with the axial and the GDP shakers.This observation suggests a difference in the post-installation dynamic behaviour of the pile-soil systems related to different pile-driving techniques. In this paper, a first attempt is made to identify the differences in the overall pile-soil dynamic behaviour of the piles installed by means of the three different pile-driving techniques.
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A novel pile-driving technique, named Gentle Driving of Piles (GDP), that combines axial low-frequency and torsional high-frequency vibrations has been developed and tested recently. During the experimental campaign, several piles were installed onshore, making use of the GDP shaker. Besides those, a number of additional piles were installed using conventional pile-driving techniques, i.e. impact piling and axial vibratory driving. After the completion of the installation phase, the installed piles have been subjected to impact hammer tests with the following goals. First, the in-situ dynamic properties of the pile-soil system have been identified. Second, the post-installation soil state has been investigated, along with its evolution in time for each pile driving scenario. Preliminary analyses, of the data collected during the impact tests show dissimilar trends in the overall dynamic response between the piles installed with impact hammer and those installed with the axial and the GDP shakers.This observation suggests a difference in the post-installation dynamic behaviour of the pile-soil systems related to different pile-driving techniques. In this paper, a first attempt is made to identify the differences in the overall pile-soil dynamic behaviour of the piles installed by means of the three different pile-driving techniques.
This work reports on the development of microstructural and mechanical properties of mortar cubes under the synergetic action of stray current and various environmental/curing conditions. The study refers to specimens cured for 24h only, followed by a 112 days period of partial or full submersion in water or alkaline medium. Additionally, equally prepared mortar specimens were tested in sealed conditions. The outcomes for submerged and saturated conditions were compared to sealed conditions. Three current density regimes were employed i.e. 1 A/m2, 100 mA/m2, and 10 mA/m2, simulating different levels of stray (DC) current environment. The highest level of 1A/m2 was also comparable to stray current densities, as measured in field conditions. The tests were designed in a way, so that the effects of diffu-sion-controlled transport (ions leaching due to concentration gradients), were distinguished from migration-controlled ones (ion/water transport in stray current conditions). Mechanical, microstructural and electrical properties were moni-tored throughout the test. For water-conditioned specimens, the stray current was found to accelerate degradation pro-cesses. This was reflected by decreased compressive strength, reduced electrical resistivity and increased porosity of the matrix. The results were attributed to leaching-out of alkali ions due to concentration gradients, where except diffusion, migration took place i.e. the leaching-out effect was accelerated by water and ions migration in conditions of stray cur-rent flow. In contrast, stray current flowing through mortar in sealed conditions (as well as through mortar in alkaline medium) resulted in increased compressive strength and electrical resistivity. These were accompanied by densification of the bulk matrix and reduced porosity. It can be concluded that for a cement-based material at early hydration age, both positive and negative effects of stray current flow can be expected. The level and direction of these effects are dependent on the external environment and the current density levels, where stray currents above 100 mA/m2 and in conditions of concentration gradients with the external medium, would lead to more pronounced negative effects on microstructural and micromechanical performance.
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This work reports on the development of microstructural and mechanical properties of mortar cubes under the synergetic action of stray current and various environmental/curing conditions. The study refers to specimens cured for 24h only, followed by a 112 days period of partial or full submersion in water or alkaline medium. Additionally, equally prepared mortar specimens were tested in sealed conditions. The outcomes for submerged and saturated conditions were compared to sealed conditions. Three current density regimes were employed i.e. 1 A/m2, 100 mA/m2, and 10 mA/m2, simulating different levels of stray (DC) current environment. The highest level of 1A/m2 was also comparable to stray current densities, as measured in field conditions. The tests were designed in a way, so that the effects of diffu-sion-controlled transport (ions leaching due to concentration gradients), were distinguished from migration-controlled ones (ion/water transport in stray current conditions). Mechanical, microstructural and electrical properties were moni-tored throughout the test. For water-conditioned specimens, the stray current was found to accelerate degradation pro-cesses. This was reflected by decreased compressive strength, reduced electrical resistivity and increased porosity of the matrix. The results were attributed to leaching-out of alkali ions due to concentration gradients, where except diffusion, migration took place i.e. the leaching-out effect was accelerated by water and ions migration in conditions of stray cur-rent flow. In contrast, stray current flowing through mortar in sealed conditions (as well as through mortar in alkaline medium) resulted in increased compressive strength and electrical resistivity. These were accompanied by densification of the bulk matrix and reduced porosity. It can be concluded that for a cement-based material at early hydration age, both positive and negative effects of stray current flow can be expected. The level and direction of these effects are dependent on the external environment and the current density levels, where stray currents above 100 mA/m2 and in conditions of concentration gradients with the external medium, would lead to more pronounced negative effects on microstructural and micromechanical performance.