@article{AlaladeReichertKoehnetal., author = {Alalade, Muyiwa and Reichert, Ina and K{\"o}hn, Daniel and Wuttke, Frank and Lahmer, Tom}, title = {A Cyclic Multi-Stage Implementation of the Full-Waveform Inversion for the Identification of Anomalies in Dams}, series = {Infrastructures}, volume = {2022}, journal = {Infrastructures}, number = {Volume 7, issue 12, article 161}, editor = {Qu, Chunxu and Gao, Chunxu and Zhang, Rui and Jia, Ziguang and Li, Jiaxiang}, publisher = {MDPI}, address = {Basel}, doi = {10.3390/infrastructures7120161}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20221201-48396}, pages = {19}, abstract = {For the safe and efficient operation of dams, frequent monitoring and maintenance are required. These are usually expensive, time consuming, and cumbersome. To alleviate these issues, we propose applying a wave-based scheme for the location and quantification of damages in dams. To obtain high-resolution "interpretable" images of the damaged regions, we drew inspiration from non-linear full-multigrid methods for inverse problems and applied a new cyclic multi-stage full-waveform inversion (FWI) scheme. Our approach is less susceptible to the stability issues faced by the standard FWI scheme when dealing with ill-posed problems. In this paper, we first selected an optimal acquisition setup and then applied synthetic data to demonstrate the capability of our approach in identifying a series of anomalies in dams by a mixture of reflection and transmission tomography. The results had sufficient robustness, showing the prospects of application in the field of non-destructive testing of dams.}, subject = {Damm}, language = {en} } @article{ChenSchwingKarlovšeketal., author = {Chen, Zhen and Schwing, Moritz and Karlovšek, Jurij and Wagner, Norman and Scheuermann, Alexander}, title = {Broadband Dielectric Measurement Methods for Soft Geomaterials: Coaxial Transmission Line Cell and Open-Ended Coaxial Probe}, series = {International Journal of Engineering and Technology}, volume = {2014}, journal = {International Journal of Engineering and Technology}, number = {volume 6, number 5}, doi = {10.7763/IJET.2014.V6.728}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20210408-43984}, pages = {373 -- 380}, abstract = {Broadband dielectric measurement methods based on vector network analyzer coupled with coaxial transmission line cell (CC) and open-ended coaxial probe (OC) are simply reviewed, by which the dielectric behaviors in the frequency range of 1 MHz to 3 GHz of two practical geomaterials are investigated. Kaolin after modified compaction with different water contents is measured by using CC. The results are consistent with previous study on standardized compacted kaolin and suggest that the dielectric properties at frequencies below 100 MHz are not only a function of water content but also functions of other soil state parameters including dry density. The hydration process of a commercial grout is monitored in real time by using OC. It is found that the time dependent dielectric properties can accurately reveal the different stages of the hydration process. These measurement results demonstrate the practicability of the introduced methods in determining dielectric properties of soft geomaterials.}, subject = {Impedanzspektroskopie}, language = {en} } @article{WagnerBoreRobinetetal., author = {Wagner, Norman and Bore, Thierry and Robinet, Jean-Charles and Coelho, Daniel and Taillade, Frederic and Delepine-Lesoille, Sylvie}, title = {Dielectric relaxation behavior of Callovo-Oxfordian clay rock: A hydraulic-mechanical-electromagnetic coupling approach}, series = {Journal of Geophysical Research: Solid Earth}, journal = {Journal of Geophysical Research: Solid Earth}, doi = {10.1002/jgrb.50343}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20170428-31681}, pages = {4729 -- 4744}, abstract = {Water content is a key parameter to monitor in nuclear waste repositories such as the planed underground repository in Bure, France, in the Callovo-Oxfordian (COx) clay formation. High-frequency electromagnetic (HF-EM) measurement techniques, i.e., time or frequency domain reflectometry, offer useful tools for quantitative estimation of water content in porous media. However, despite the efficiency of HF-EM methods, the relationship between water content and dielectric material properties needs to be characterized. Moreover, the high amount of swelling clay in the COx clay leads to dielectric relaxation effects which induce strong dispersion coupled with high absorption of EM waves. Against this background, the dielectric relaxation behavior of the clay rock was studied at frequencies from 1 MHz to 10 GHz with network analyzer technique in combination with coaxial transmission line cells. For this purpose, undisturbed and disturbed clay rock samples were conditioned to achieve a water saturation range from 0.16 to nearly saturation. The relaxation behavior was quantified based on a generalized fractional relaxation model under consideration of an apparent direct current conductivity assuming three relaxation processes: a high-frequency water process and two interface processes which are related to interactions between the aqueous pore solution and mineral particles (adsorbed/hydrated water relaxation, counter ion relaxation and Maxwell-Wagner effects). The frequency-dependent HF-EM properties were further modeled based on a novel hydraulic-mechanical-electromagnetic coupling approach developed for soils. The results show the potential of HF-EM techniques for quantitative monitoring of the hydraulic state in underground repositories in clay formations.}, subject = {Lehm}, language = {en} } @article{BoreWagnerLesoilleetal., author = {Bore, Thierry and Wagner, Norman and Lesoille, Sylvie Delepine and Taillade, Frederic and Six, Gonzague and Daout, Franck and Placko, Dominique}, title = {Error analysis of clay-rock water content estimation with broadband high-frequency electromagnetic sensors—air gap effect}, series = {Sensors}, journal = {Sensors}, doi = {10.3390/s16040554}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20170418-31248}, pages = {1 -- 14}, abstract = {Broadband electromagnetic frequency or time domain sensor techniques present high potential for quantitative water content monitoring in porous media. Prior to in situ application, the impact of the relationship between the broadband electromagnetic properties of the porous material (clay-rock) and the water content on the frequency or time domain sensor response is required. For this purpose, dielectric properties of intact clay rock samples experimental determined in the frequency range from 1 MHz to 10 GHz were used as input data in 3-D numerical frequency domain finite element field calculations to model the one port broadband frequency or time domain transfer function for a three rods based sensor embedded in the clay-rock. The sensor response in terms of the reflection factor was analyzed in time domain with classical travel time analysis in combination with an empirical model according to Topp equation, as well as the theoretical Lichtenecker and Rother model (LRM) to estimate the volumetric water content. The mixture equation considering the appropriate porosity of the investigated material provide a practical and efficient approach for water content estimation based on classical travel time analysis with the onset-method. The inflection method is not recommended for water content estimation in electrical dispersive and absorptive material. Moreover, the results clearly indicate that effects due to coupling of the sensor to the material cannot be neglected. Coupling problems caused by an air gap lead to dramatic effects on water content estimation, even for submillimeter gaps. Thus, the quantitative determination of the in situ water content requires careful sensor installation in order to reach a perfect probe clay rock coupling.}, subject = {Wassergehalt}, language = {en} } @article{BremerWollweberWeigandetal., author = {Bremer, K. and Wollweber, M. and Weigand, F. and Rahlves, M. and Kuhne, Michael and Helbig, R. and Roth, B.}, title = {Fibre Optic Sensors for the Structural Health Monitoring of Building Structures}, series = {Procedia Technology 26}, journal = {Procedia Technology 26}, doi = {10.1016/j.protcy.2016.08.065}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20170331-30912}, pages = {524 -- 529}, abstract = {In this work different fibre optic sensors for the structural health monitoring of civil engineering structures are reported. A fibre optic crack sensor and two different fibre optic moisture sensors have been designed to detect the moisture ingress in concrete based building structures. Moreover, the degeneration of the mechanical properties of optical glass fibre sensors and hence their long-term stability and reliability due to the mechanical and chemical impact of the concrete environment is discussed as well as the advantage of applying a fibre optic sensor system for the structural health monitoring of sewerage tunnels is demonstrated.}, subject = {Structural Health Monitoring}, language = {en} } @article{BumbergerMaiSchmidtetal., author = {Bumberger, Jan and Mai, Juliane and Schmidt, Felix and L{\"u}nenschloß, Peter and Wagner, Norman and T{\"o}pfer, Hannes}, title = {Spatial Retrieval of Broadband Dielectric Spectra}, series = {Sensors}, journal = {Sensors}, doi = {10.3390/s18092780}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20180906-37831}, pages = {1 -- 22}, abstract = {A broadband soil dielectric spectra retrieval approach ( 1 MHz- 2 GHz) has been implemented for a layered half space. The inversion kernel consists of a two-port transmission line forward model in the frequency domain and a constitutive material equation based on a power law soil mixture rule (Complex Refractive Index Model - CRIM). The spatially-distributed retrieval of broadband dielectric spectra was achieved with a global optimization approach based on a Shuffled Complex Evolution (SCE) algorithm using the full set of the scattering parameters. For each layer, the broadband dielectric spectra were retrieved with the corresponding parameters thickness, porosity, water saturation and electrical conductivity of the aqueous pore solution. For the validation of the approach, a coaxial transmission line cell measured with a network analyzer was used. The possibilities and limitations of the inverse parameter estimation were numerically analyzed in four scenarios. Expected and retrieved layer thicknesses, soil properties and broadband dielectric spectra in each scenario were in reasonable agreement. Hence, the model is suitable for an estimation of in-homogeneous material parameter distributions. Moreover, the proposed frequency domain approach allows an automatic adaptation of layer number and thickness or regular grids in time and/or space.}, subject = {Theoretische Elektrotechnik}, language = {en} } @article{ScheuermannHuebnerSchlaegeretal., author = {Scheuermann, Alexander and Huebner, Christof and Schlaeger, Stefan and Wagner, Norman and Becker, Rolf and Bieberstein, Andreas}, title = {Spatial time domain reflectometry and its application for the measurement of water content distributions along flat ribbon cables in a full-scale levee model}, series = {Water Resources Research}, journal = {Water Resources Research}, doi = {10.1029/2008WR007073}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20170425-31601}, abstract = {Spatial time domain reflectometry (spatial TDR) is a new measurement method for determining water content profiles along elongated probes (transmission lines). The method is based on the inverse modeling of TDR reflectograms using an optimization algorithm. By means of using flat ribbon cables it is possible to take two independent TDRmeasurements from both ends of the probe, which are used to improve the spatial information content of the optimization results and to consider effects caused by electrical conductivity. The method has been used for monitoring water content distributions on a full-scale levee model made of well-graded clean sand. Flood simulation tests, irrigation tests, and long-term observations were carried out on the model. The results show that spatial TDR is able to determine water content distributions with an accuracy of the spatial resolution of about ±3 cm compared to pore pressure measurements and an average deviation of ±2 vol \% compared to measurements made using another independent TDR measurement system.}, subject = {Damm}, language = {en} } @article{MosaviHosseiniImaniZalzaretal., author = {Mosavi, Amir and Hosseini Imani, Mahmood and Zalzar, Shaghayegh and Shamshirband, Shahaboddin}, title = {Strategic Behavior of Retailers for Risk Reduction and Profit Increment via Distributed Generators and Demand Response Programs}, series = {Energies}, volume = {2018}, journal = {Energies}, number = {11, 6}, publisher = {MDPI}, address = {Basel}, doi = {10.3390/en11061602}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20180628-37546}, pages = {24}, abstract = {Following restructuring of power industry, electricity supply to end-use customers has undergone fundamental changes. In the restructured power system, some of the responsibilities of the vertically integrated distribution companies have been assigned to network managers and retailers. Under the new situation, retailers are in charge of providing electrical energy to electricity consumers who have already signed contract with them. Retailers usually provide the required energy at a variable price, from wholesale electricity markets, forward contracts with energy producers, or distributed energy generators, and sell it at a fixed retail price to its clients. Different strategies are implemented by retailers to reduce the potential financial losses and risks associated with the uncertain nature of wholesale spot electricity market prices and electrical load of the consumers. In this paper, the strategic behavior of retailers in implementing forward contracts, distributed energy sources, and demand-response programs with the aim of increasing their profit and reducing their risk, while keeping their retail prices as low as possible, is investigated. For this purpose, risk management problem of the retailer companies collaborating with wholesale electricity markets, is modeled through bi-level programming approach and a comprehensive framework for retail electricity pricing, considering customers' constraints, is provided in this paper. In the first level of the proposed bi-level optimization problem, the retailer maximizes its expected profit for a given risk level of profit variability, while in the second level, the customers minimize their consumption costs. The proposed programming problem is modeled as Mixed Integer programming (MIP) problem and can be efficiently solved using available commercial solvers. The simulation results on a test case approve the effectiveness of the proposed demand-response program based on dynamic pricing approach on reducing the retailer's risk and increasing its profit. In this paper, the decision-making problem of the retailers under dynamic pricing approach for demand response integration have been investigated. The retailer was supposed to rely on forward contracts, DGs, and spot electricity market to supply the required active and reactive power of its customers. To verify the effectiveness of the proposed model, four schemes for retailer's scheduling problem are considered and the resulted profit under each scheme are analyzed and compared. The simulation results on a test case indicate that providing more options for the retailer to buy the required power of its customers and increase its flexibility in buying energy from spot electricity market reduces the retailers' risk and increases its profit. From the customers' perspective also the retailers'accesstodifferentpowersupplysourcesmayleadtoareductionintheretailelectricityprices. Since the retailer would be able to decrease its electricity selling price to the customers without losing its profitability, with the aim of attracting more customers. Inthiswork,theconditionalvalueatrisk(CVaR)measureisusedforconsideringandquantifying riskinthedecision-makingproblems. Amongallthepossibleoptioninfrontoftheretailertooptimize its profit and risk, demand response programs are the most beneficial option for both retailer and its customers. The simulation results on the case study prove that implementing dynamic pricing approach on retail electricity prices to integrate demand response programs can successfully provoke customers to shift their flexible demand from peak-load hours to mid-load and low-load hours. Comparing the simulation results of the third and fourth schemes evidences the impact of DRPs and customers' load shifting on the reduction of retailer's risk, as well as the reduction of retailer's payment to contract holders, DG owners, and spot electricity market. Furthermore, the numerical results imply on the potential of reducing average retail prices up to 8\%, under demand response activation. Consequently, it provides a win-win solution for both retailer and its customers.}, subject = {Risikomanagement}, language = {en} } @article{LorekWagner, author = {Lorek, Andreas and Wagner, Norman}, title = {Supercooled interfacial water in fine grained soils probed by dielectric spectroscopy}, series = {Cryosphere}, journal = {Cryosphere}, doi = {10.5194/tc-7-1839-2013}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20170516-31840}, pages = {1839 -- 1855}, abstract = {Water substantially affects nearly all physical, chemical and biological processes on the Earth. Recent Mars observations as well as laboratory investigations suggest that water is a key factor of current physical and chemical processes on the Martian surface, e.g. rheological phenomena. Therefore it is of particular interest to get information about the liquid-like state of water on Martian analogue soils for temperatures below 0 °C. To this end, a parallel plate capacitor has been developed to obtain isothermal dielectric spectra of fine-grained soils in the frequency range from 10 Hz to 1.1 MHz at Martian-like temperatures down to -70 °C. Two Martian analogue soils have been investigated: a Ca-bentonite (specific surface of 237 m2 g-1, up to 9.4\% w / w gravimetric water content) and JSC Mars 1, a volcanic ash (specific surface of 146 m2 g-1, up to 7.4\% w / w). Three soil-specific relaxation processes are observed in the investigated frequency-temperature range: two weak high-frequency processes (bound or hydrated water as well as ice) and a strong low-frequency process due to counter-ion relaxation and the Maxwell-Wagner effect. To characterize the dielectric relaxation behaviour, a generalized fractional dielectric relaxation model was applied assuming three active relaxation processes with relaxation time of the ith process modelled with an Eyring equation. The real part of effective complex soil permittivity at 350 kHz was used to determine ice and liquid-like water content by means of the Birchak or CRIM equation. There are evidence that bentonite down to -70 °C has a liquid-like water content of 1.17 monolayers and JSC Mars 1 a liquid-like water content of 1.96 monolayers.}, subject = {Grundwasser}, language = {en} } @article{LorekWagner, author = {Lorek, Andreas and Wagner, Norbert}, title = {Supercooled interfacial water in fine-grained soils probed by dielectric spectroscopy}, series = {Cryosphere}, journal = {Cryosphere}, doi = {10.25643/bauhaus-universitaet.3149}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20170425-31490}, pages = {1839 -- 1855}, abstract = {Water substantially affects nearly all physical, chemical and biological processes on the Earth. Recent Mars observations as well as laboratory investigations suggest that water is a key factor of current physical and chemical processes on the Martian surface, e.g. rheological phenomena. Therefore it is of particular interest to get information about the liquid-like state of water on Martian analogue soils for temperatures below 0 °C. To this end, a parallel plate capacitor has been developed to obtain isothermal dielectric spectra of fine-grained soils in the frequency range from 10 Hz to 1.1 MHz at Martian-like temperatures down to -70 °C. Two Martian analogue soils have been investigated: a Ca-bentonite (specific surface of 237 m2 g-1, up to 9.4\% w / w gravimetric water content) and JSC Mars 1, a volcanic ash (specific surface of 146 m2 g-1, up to 7.4\% w / w). Three soil-specific relaxation processes are observed in the investigated frequency-temperature range: two weak high-frequency processes (bound or hydrated water as well as ice) and a strong low-frequency process due to counter-ion relaxation and the Maxwell-Wagner effect. To characterize the dielectric relaxation behaviour, a generalized fractional dielectric relaxation model was applied assuming three active relaxation processes with relaxation time of the ith process modelled with an Eyring equation. The real part of effective complex soil permittivity at 350 kHz was used to determine ice and liquid-like water content by means of the Birchak or CRIM equation. There are evidence that bentonite down to -70 °C has a liquid-like water content of 1.17 monolayers and JSC Mars 1 a liquid-like water content of 1.96 monolayers.}, subject = {Wasser}, language = {en} }