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Zhebel, E. (author), Minisini, S. (author), Kononov, A. (author), Mulder, W.A. (author)The finitedifference method is widely used for timedomain modelling of the wave equation because of its ease of implementation of highorder spatial discretization schemes, parallelization and computational efficiency. However, finite elements on tetrahedral meshes are more accurate in complex geometries near sharp interfaces. We compared the...conference paper 2012
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Zhebel, E. (author), Minisini, S. (author), Mulder, W.A. (author)We solve the threedimensional acoustic wave equation, discretized on tetrahedral meshes. Two methods are considered: masslumped continuous finite elements and the symmetric interiorpenalty discontinuous Galerkin method (SIPDG). Combining the spatial discretization with the leapfrog timestepping scheme, which is secondorder accurate and...conference paper 2012
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Kazei, V.V. (author), Ponomarenko, A.V. (author), Troyan, V.N. (author), Kashtan, B.M. (author), Mulder, W.A. (author)Full waveform inversion suffers from local minima, due to a lack of low frequencies in the data. A reflector below the zone of interest may, however, help in recovering the longwavelength components of a velocity perturbation, as demonstrated in a paper by Mora. With the Born approximation for the perturbation in a reference model consisting of...conference paper 2012
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Kononov, A. (author), Minisini, S. (author), Zhebel, E. (author), Mulder, W.A. (author)Finiteelement modelling of seismic wave propagation on tetrahedra requires meshes that accurately follow interfaces between impedance contrasts or surface topography and have element sizes proportional to the local velocity. We explain a mesh generation approach by example. Starting from a finitedifference representation of the velocity model,...conference paper 2012
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Wirianto, M. (author), Mulder, W.A. (author), Slob, E.C. (author)In the application of controlled source electromagnetics for reservoir monitoring on land, the timelapse signal measured with a surfacetosurface acquisition can reveal the lateral extent on the surface of resistivity changes at depth in a hydrocarbon reservoir under production. However, a direct interpretation of the timelapse signal may...conference paper 2012
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Kavian, M. (author), Slob, E.C. (author), Mulder, W.A. (author)Macroscopic measurements of electrical resistivity require frequencydependent effective models that honor the microscopic effects observable in macroscopic measurements. Effective models based on microscopic physics exist alongside with empirical models. We adopted an empirical model approach to modify an existing physical model. This provided...journal article 2012
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Kavian, M. (author), Slob, E.C. (author), Mulder, W.A. (author)We measured the electric parameters for four different configurations of unconsolidated homogeneous and layered sands as a function of frequency, water saturation, and salinity under fluid flow conditions. Our objective is to determine if the effect of heterogeneities at scales much smaller than the skin depth can be captured by introducing...journal article 2011
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Wirianto, M. (author), Mulder, W.A. (author), Slob, E.C. (author)In the application of controlled source electromagnetics for reservoir monitoring on land, repeatability errors in the source will mask the timelapse signal due to hydrocarbon production when recording surface data close to the source. We demonstrate that at larger distances, the airwave will still provide sufficient illumination of the target....journal article 2011
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 Slob, E.C. (author), Hunziker, J.W. (author), Mulder, W.A. (author) journal article 2010
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 Wirianto, M. (author), Mulder, W.A. (author), Slob, E.C. (author) journal article 2010
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Hak, B. (author), Mulder, W.A. (author)Seismic data enable imaging of the Earth, not only of velocity and density but also of attenuation contrasts. Unfortunately, the Born approximation of the constantdensity viscoacoustic wave equation, which can serve as a forward modelling operator related to seismic migration, exhibits an ambiguity when attenuation is included. Different...journal article 2010
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Van Leeuwen, T. (author), Mulder, W.A. (author)Waveequation traveltime tomography tries to obtain a subsurface velocity model from seismic data, either passive or active, that explains their traveltimes. A key step is the extraction of traveltime differences, or relative phase shifts, between observed and modelled finitefrequency waveforms. A standard approach involves a correlation of the...journal article 2010
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Van Leeuwen, T. (author), Mulder, W.A. (author)In seismic imaging, one tries to infer the medium properties of the subsurface from seismic reflection data. These data are the result of an active source experiment, where an explosive source and an array of receivers are placed at the surface. Due to the absence of low frequencies in the data, the corresponding inverse problem is strongly non...journal article 2009
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 Mulder, W.A. (author), Hak, B. (author) journal article 2009
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Plessix, R.E. (author), Mulder, W.A. (author)We discuss some computational aspects of resistivity imaging by inversion of offshore controlledsource electromagnetic data. We adopt the classic approach to imaging by formulating it as an inverse problem. A weighted leastsquares functional measures the misfit between synthetic and observed data. Its minimization by a quasiNewton algorithm...journal article 2008
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Mulder, W.A. (author)The performance of a multigrid solver for timeharmonic electromagnetic problems in geophysical settings was investigated. With the low frequencies used in geophysical surveys for deeper targets, the lightspeed waves in the earth can be neglected. Diffusion of induced currents is the dominant physical effect. The governing equations were...journal article 2008
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Mulder, W.A. (author), Wirianto, M. (author), Slob, E.C. (author)We modeled timedomain EM measurements of induction currents for marine and land applications with a frequencydomain code. An analysis of the computational complexity of a number of numerical methods shows that frequencydomain modeling followed by a Fourier transform is an attractive choice if a sufficiently powerful solver is available. A...journal article 2007
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Jönsthövel, T.B. (author), Oosterlee, C.W. (author), Mulder, W.A. (author)We evaluated multigrid techniques for 3D diffusive electromagnetism. The Maxwell equations and Ohm's law were discretised on stretched grids, with stretching in all coordinate directions. We compared standard multigrid to alternative multigrid approaches with linewise smoothing and semicoarsening, both as a standalone solver and as a...conference paper 2006
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Jönsthövel, T.B. (author), Oosterlee, C.W. (author), Mulder, W.A. (author)We evaluated multigrid techniques for 3D diffusive electromagnetism. The Maxwell equations and Ohm's law were discretised on stretched grids, with stretching in all coordinate directions. We compared standard multigrid to alternative multigrid approaches with linewise smoothing and semicoarsening, both as a standalone solver and as a...conference paper 2006
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Riyanti, C.D. (author), Erlangga, Y.A. (author), Plessix, R.E. (author), Mulder, W.A. (author), Vuik, C. (author), Oosterlee, C. (author)The timeharmonic wave equation, also known as the Helmholtz equation, is obtained if the constantdensity acoustic wave equation is transformed from the time domain to the frequency domain. Its discretization results in a large, sparse, linear system of equations. In two dimensions, this system can be solved efficiently by a direct method. In...journal article 2006