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Harmankaya, U (author), Kaslilar, A. (author), Wapenaar, C.P.A. (author), Draganov, D.S. (author)Unexpected geological structures can cause safety and economic risks during underground excavation. Therefore, predicting possible geological threats while drilling a tunnel is important for operational safety and for preventing expensive standstills. Subsurface information for tunneling is provided by exploratory wells and by surface...journal article 2018
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Al-Djema, Rawsan (author)Sandy soils are characterized by negligible cohesion (compared to clay) and limited drainage capacity (compared to gravel), which makes these soils susceptible to excess pore (water) pressure accumulation induced by short term dynamic loading cycles. Pile driving subjects the soil to such type of dynamic loading. Accumulation of excess pore...master thesis 2018
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Zafar, Shanza (author)To solve the problem of optimal control for nonlinear system, Actor Critic Designs (ACD) can be utilized which use the concept of Reinforcement learning (RL) and function approximators such as Neural networks (NN). Traditional ACD methods require a model NN that needs to be trained offline. Recently, research focus has been shifted to model-free...master thesis 2018
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Oud, G.T. (author)This research entails the numerical simulation of physical flow instabilities that can occur in two-phase pipe flows with a new efficient algorithm. The fluids are assumed to be immiscible, and the flow is incompressible and isothermal in a straight circular pipe section with a certain inclination. The numerical algorithm that was developed...doctoral thesis 2017
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Sun, S. (author), Kooij, B.J. (author), Jin, T. (author), Yarovoy, Alexander (author)In this paper, we improved the performance of the contrast source inversion (CSI) method by incorporating a so-called cross-correlated cost functional, which interrelates the state error and the data error in the measurement domain. The proposed method is referred to as the cross-correlated CSI. It enables better robustness and higher inversion...journal article 2017
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Cedillo Galarza, J.S. (author)In order to propose a new sewer inspection method, a velocity/turbidity profiler (Ubertone, UB Flow F-315) has been tested in a laboratory. A 50 m glass flume has been adapted with several lateral connections (with a range of diameters, angles, intrusions, cracks), supplied by a 1 m3 tank. Placed just below the free surface on a rotating (to...master thesis 2016
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Oosting, R.M. (author)Ultrasound imaging is known to be non-invasive, fast, and cost-effective. However, a drawback is its reflection on bone. Therefore, an alternative acoustic wave propagating technique is being developed that eventually should be able to diagnose osteochondral defects (OCDs) that are now often missed with conventional imaging techniques. A novel...master thesis 2016
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Sarkalkan, N. (author), Loeve, A.J. (author), Van Dongen, K.W.A. (author), Tuijthof, G.J.M. (author), Zadpoor, A.A. (author)(Osteo)chondral defects (OCDs) in the ankle are currently diagnosed with modalities that are not convenient to use in long-term follow-ups. Ultrasound (US) imaging, which is a cost-effective and non-invasive alternative, has limited ability to discriminate OCDs. We aim to develop a new diagnostic technique based on US wave propagation through...journal article 2015
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Daryani, K.E. (author), Mohamad, H. (author)This paper studies the effect of soil spatial variability on bearing capacity of shallow foundations. The stochastic soil property is the undrained shear strength considered as a non-Gaussian random variable. The random variable is simulated using Local Average Subdivision Method. A Monte Carlo simulation approach is followed in combination with...conference paper 2015
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Knibbe, H.P. (author), Mulder, W.A. (author), Oosterlee, C.W. (author), Vuik, C. (author)Three-dimensional reverse-time migration with the constant-density acoustic wave equation requires an efficient numerical scheme for the computation of wavefields. An explicit finite-difference scheme in the time domain is a common choice. However, it requires a significant amount of disk space for the imaging condition. The frequency-domain...journal article 2014
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Zhebel, E. (author), Minisini, S. (author), Kononov, A. (author), Mulder, W.A. (author)With the rapid developments in parallel compute architectures, algorithms for seismic modeling and imaging need to be reconsidered in terms of parallelization. The aim of this paper is to compare scalability of seismic modeling algorithms: finite differences, continuous mass-lumped finite elements and discontinuous Galerkin finite elements. The...journal article 2013
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Caggiano, A. (author), Pepe, M. (author), Koenders, E.A.B. (author), Martinelli, E. (author), Etse, G.J. (author)Heat production induced by the hydration reaction and the resulting temperature evolution in the early phases of setting and hardening processes are critical phenomena, often leading to premature cracking of concrete members. However, the interest for simulating such phenomena is also related to the fundamental relationships between the nature...conference paper 2012
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Thorbecke, J.W. (author), Draganov, D. (author)In passive seismic interferometry, new reflection data can be retrieved by crosscorrelating recorded noise data. The quality of the retrieved reflection data is, among others, dependent on the duration and number of passive sources present during the recording time, the source distribution, and the source strength. To investigate these relations...journal article 2011
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Abubakar, A. (author), Hu, W. (author), Habashy, T.M. (author), Van den Berg, P.M. (author)We have applied the finite-difference contrast-source inversion (FDCSI) method to seismic full-waveform inversion problems. The FDCSI method is an iterative nonlinear inversion algorithm. However, unlike the nonlinear conjugate gradient method and the Gauss-Newton method, FDCSI does not solve any full forward problem explicitly in each iterative...journal article 2009
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El Yadari, N. (author), Ernst, F. (author), Mulder, W. (author)The effect of the near surface on seismic land data can be so severe that static corrections are insufficient. Full-waveform inversion followed by redatuming may be an alternative, but inversion will work only if the starting model is sufficiently close to the true model. As a first step toward determining a viscoelastic near-surface model, we...journal article 2008
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Caro, J. (author), Roeling, E.M. (author), Rong, B. (author), Nguyen, H.M. (author), Van der Drift, E.W.J.M. (author), Rogge, S. (author), Karouta, F. (author), Van der Heijden, R.W. (author), Salemink, H.W.M. (author)A high-contrast-ratio (30 dB) photonic band gap in the near-infrared transmission of hole-type GaN two-dimensional photonic crystals (PhCs) is reported. These crystals are deeply etched in a 650 nm thick GaN layer grown on sapphire. A comparison of the measured spectrum with finite difference time domain simulations gives quantitative agreement...journal article 2008
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Spetzler, J. (author), Sijacic, D. (author), Wolf, K.H.A.A. (author)Time-lapse seismic monitoring is the geophysical discipline whereby multiple data sets recorded at the same location but at different times are used to locate and quantify temporal changes in the elastic parameters of the subsurface. We validate a time-lapse monitoring method by crosswell tomography using two types of wavefield-modeling...journal article 2007
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Groenenberg, R.M. (author)The production potential of deep-water reservoirs is primarily determined by rock bulk volume, porosity and permeability. Quantification of the geometry and spatial distribution of reservoir sands in deep-water deposits can provide crucial information to assess sand body volume, connectivity and the distribution of permeability baffles. This...doctoral thesis 2007
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Kenjere, S. (author), Hanjali?, K. (author), Renaudier, S. (author), Stefani, F. (author), Gerbeth, G. (author), Gailitis, A. (author)Magnetic fields of planets, stars, and galaxies result from self-excitation in moving electroconducting fluids, also known as the dynamo effect. This phenomenon was recently experimentally confirmed in the Riga dynamo experiment [ A. Gailitis et al., Phys. Rev. Lett. 84, 4365 (2000) ; A. Gailitis et al., Physics of Plasmas 11, 2838 (2004) ],...journal article 2006
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Validation of first-order diffraction theory for the traveltimes and amplitudes of propagating wavesJocker, J. (author), Spetzler, J. (author), Smeulders, D.M.J. (author), Trampert, J. (author)Ultrasonic measurements of acoustic wavefields scattered by single spheres placed in a homogenous background medium (water) are presented. The dimensions of the spheres are comparable to the wavelength and the wavelength and represent both positive (rubber) and negative (teflon) velocity anomalies with respect to the background medium. The...journal article 2006