Immersive wave experimentation: linking physical laboratories and virtual simulations in real-time
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Date
2020
Publication Type
Doctoral Thesis
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Abstract
Seismic waves propagating through the interior of the Earth enable scientists to study its structure
across many scales. With the advent of digital computers, numerical simulations have almost entirely
replaced analogue models and physical laboratories to help interpret the observations and to
improve our understanding of complex wave phenomena. Nonetheless, laboratory studies remain
of key importance to bridge existing gaps between field observations and numerical simulations as
such laboratories allow to study realistic Earth materials in a controlled environment. However, even
the smallest seismic wavelengths used in field seismic surveys are considerably larger than the size
of physical laboratories, resulting in contamination of the signal of interest, particularly due to undesired
wavefield reflections from the laboratory boundaries. This issue is commonly overcome by
increasing the frequency of the probing signal, thereby isolating the signals of interest in time. As
wave propagation in many materials is significantly frequency-dependent, such upscaling approaches
can impede the comparability between laboratory and real-world observations.
This thesis presents a fundamentally different seismic wave propagation laboratory by physically
implementing the recent theory of immersive boundary conditions (IBCs) on the edge of the laboratory.
These boundary conditions link the wave propagation in the physical laboratory with that
in a virtual simulation surrounding the laboratory in real-time. Consequently, the laboratory is fully
immersed in the simulation, which allows waves to propagate seamlessly between the physical and
virtual realms, without sensing the physical boundary of the laboratory. Such immersive wave experiments
circumvent the aforementioned limitations of conventional laboratories, thus bridging the
frequency gap between laboratory studies and field observations, and literally connecting physical
and numerical wave propagation experiments. Wave propagation in a physical medium with either
unknown or accepted physical relations can be directly coupled to the propagation in a numerical
simulation with either hypothesized or accepted physical relations. This constitutes a new approach
for laboratory validation of existing wave theories and the possibility to explore and discover new
physical relations.
This study demonstrates immersive wave experimentation for the first time, using a subset of a 1600-
channel high-performance, low-latency control system. In the presented one- and two-dimensional
acoustic experiments, dense sensor surfaces inside the laboratories record the acoustic wavefields,
which are then extrapolated in real-time to the laboratory boundaries, where they are injected as the
signatures of closely-spaced secondary sources. The emitted secondary wavefields suppress broadband
reflections from the laboratory boundaries and correctly reproduce all wavefield interactions with surrounding virtual simulations. The experiments also demonstrate that immersive wave experimentation
does not require prior knowledge of the primary source wavefield nor of the medium
properties inside the recording surface. The high-performance, low-latency control system is also
introduced here, together with a discussion of practical requirements and limitations arising from a
physical implementation of IBCs, and possible solutions to correct for hardware imperfections violating
the IBC theory. These findings pave the way for fully immersive wave experimentation in three
dimensions using the full 1600-channel control system, for which the design and control hardware
are also presented here.
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published
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Examiner : Robertsson, Johan O.A.
Examiner : van Manen, Dirk-Jan
Examiner : Snieder, Roel
Examiner : Curtis, Andrew
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Publisher
ETH Zurich
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Subject
GEOPHYSICS; wave propagation; LABORATORY EXPERIMENTS (SCIENCE)
Organisational unit
03953 - Robertsson, Johan / Robertsson, Johan