Thin-sheet EM modelling of the Tasman Sea

1989 ◽  
Vol 20 (2) ◽  
pp. 177 ◽  
Author(s):  
G.S. Heinson ◽  
F.E.M. Lilley
Keyword(s):  
Large Scale ◽  
Salt Water ◽  
Thin Sheet ◽  
Three Dimensional ◽  
One Dimensional ◽  
The Earth ◽  
Tasman Sea ◽  
Modelling Techniques ◽  
Tectonic Features ◽  
The University

The Tasman Project of Seafloor Magnetotelluric Exploration (TPSME) took place between December 1983 and April 1984 (Filloux et al., 1985; Ferguson et al., 1985; Lilley etal., 1989). Seven magnetotelluric and two (additional) magnetometer sites spanned a range of tectonic features across the Tasman Sea. Initial analysis by Ferguson (1988) indicated large-scale three-dimensional induction effects to be present in the data. It was concluded that the most probable causes were the continental margin effect and changes in bathymetry.In the present paper, a method is presented of modelling the salt water of the Tasman Sea and adjoining oceans as a thin sheet of variable lateral conductance, which overlies a series of uniform layers representing the solid Earth. The theory and a suitable computer algorithm were developed in a group led by J. T. Weaver at the University of Victoria, B.C., Canada. Many of the features present in the TPSME data are reproduced by this method, and with a greater understanding of induction processes in the ocean which is thus obtained, it is possible to remove three-dimensional effects from observed data. The TPSME data are then solely a measure of the response of the Earth directly beneath the observing sites, and one-dimensional modelling techniques may be used to determine the conductivity structures.

scholarly journals Seismic performance analysis and assessment of a precast bridge computational model

DYNA ◽  
2020 ◽  
Vol 87 (212) ◽  
pp. 80-89
Author(s):  
José Benjumea ◽  
Mehdi Saiidi ◽  
Ahmad Itani
Keyword(s):  
Performance Analysis ◽  
Computational Model ◽  
Seismic Performance ◽  
Earthquake Engineering ◽  
Large Scale ◽  
Three Dimensional ◽  
Shake Table ◽  
Bridge Model ◽  
Precast Elements ◽  
The University

A large-scale, two-span bridge model constructed by assembling precast elements was tested under a series of bi-axial ground motionssimulated on a shake table at the Earthquake Engineering Laboratory at the University of Nevada, Reno. The response of the bridge wasestimated before the tests using a three-dimensional computational model developed in OpenSees software. After the tests, key measuredseismic responses were compared to those predicted by the computational model to assess the modeling assumptions. Relatively largeerrors for the displacements, base shears, and hysteretic response of the bridge were observed. The influence of the earthquake loading,materials, connectivity of the precast elements, and boundary conditions in the computational model on the errors are discussed in thispaper. Future modeling directions are proposed to reduce these errors.

Diffraction and Instability of Short-Crested Limited-Length One-Dimensional Coherent Wave Trains

2015 ◽  
Author(s):  
Alexander V. Babanin ◽  
Takuji Waseda
Keyword(s):  
Modulational Instability ◽  
Three Dimensional ◽  
Lateral Spread ◽  
Wave Tank ◽  
One Dimensional ◽  
Coherent Wave ◽  
Limited Length ◽  
Lateral Extent ◽  
Wave Trains ◽  
The University

Alternative representations of the wave field (as opposed to superposition of Fourier components) are possible. In this paper, behaviour of short-crested limited-length one-dimensional coherent wave trains is investigated. Experiments were conducted in the three-dimensional wave tank of the University of Tokyo. Description of the directional wave tank and its capacity to generate short-crested coherent wave trains, including those concurrent, superposed and directionally-superposed is provided. If the crest is shorter than the lateral extent of the wave tank, diffraction tends to redistribute the wave energy into clear surfaces, and thus energy of the wave trains is reduced and the modulational instability bandwidth changes correspondingly. Rates of such nonlinear lateral spread are estimated, and they are proportional to mean wave steepness. To avoid the diffraction, in further tests concurrent trains were mechanically generated, each of which occupied half of the lateral width of the wave tank and had the same energy as another half. The trains had the same frequency, and in order to keep them separate phase shift of 180 degrees was used. Sideband growth was significantly impaired by comparison with the long-crested evolution of the train with the same steepness.

The asymptotic response of three‐dimensional basin offsets to magnetotelluric fields at long periods: The effects of current channeling

Geophysics ◽  
1982 ◽  
Vol 47 (11) ◽  
pp. 1562-1573 ◽  
Author(s):  
John F. Hermance
Keyword(s):  
Thin Sheet ◽  
Three Dimensional ◽  
Sedimentary Basins ◽  
Transverse Magnetic ◽  
Clear Correlation ◽  
One Dimensional ◽  
Skewness Coefficient ◽  
Order Of Magnitude ◽  
D Model ◽  
Telluric Currents

A simple, inexpensive numerical algorithm is used to analyze the asymptotic long‐period behavior of magnetotelluric (MT) fields in the vicinity of lateral offsets in sedimentary basins. The model is based on the distortion or channeling of telluric currents in a horizontal thin sheet. Although a gross oversimplification of nature, the model represents a class of structures which, because of excessive computer costs, have been relatively unstudied previously. Within, and closely adjacent to, the region of the three‐dimensional (3-D) offset, significant distortion of the MT parameters occurs. Skewness coefficients vary from negligible values to over 0.7. Principal resistivities vary by an order of magnitude. On the other hand, there is not a clear correlation between the degree of distortion of the parameters usually evaluated during MT surveys and the magnitude of conventional 3-D indicators (e.g., the skewness coefficient). Calculations have simulated the technique of averaging resistivity parameters from a large number of field sites in order to arrive at a regionally representative one‐dimensional (1-D) model. The results indicate that unless care is taken in adapting the nature of the averaging algorithm to the class of distortions encountered, significant bias of the averaged parameters may result. Our results also suggest that for this class of structures grave problems may be associated with using the principal resistivity perpendicular to geologic strike, the so‐called transverse magnetic (TM) mode, to infer an equivalent two‐dimensional (2-D) model for the region. A 2-D model would likely show significant modulations in the physical character of the basement which are, in fact, an artifact of telluric distortion caused by current channeling in the surficial heterogeneity.

Low-frequency seismology and the three-dimensional structure of the Earth

1989 ◽  
Vol 328 (1599) ◽  
pp. 329-349 ◽  
Keyword(s):  
Large Scale ◽  
Inner Core ◽  
Three Dimensional ◽  
Low Frequency ◽  
Quantitative Agreement ◽  
Phase Behaviour ◽  
Dimensional Structure ◽  
Order Structure ◽  
Three Dimensional Structure ◽  
The Earth

We attempt to catalogue those features of the three-dimensional structure of the Earth that are well-constrained by low-frequency data (i.e. periods longer than about 125 seconds). The dominant signals in such data are the surface-wave equivalent modes whose phase characteristics are mainly affected by a large scale structure of harmonic degree two in the upper mantle. Available aspherical models predict this phase behaviour quite well, but do not give an accurate prediction of the observed waveforms and we must appeal to higher-order structure an d /o r coupling effects to give the observed complexity of the data. Strong splitting of modes which sample the cores of the Earth is also observed and, though we do not yet have a model of aspherical structure which gives quantitative agreement with these data, anisotropy or large-scale aspherical structure in the inner core appears to be required to model the observed signal.

Geometry and visual realism of ship models for digital ship bridge simulators

2016 ◽  
Vol 231 (1) ◽  
pp. 329-341
Author(s):  
Jose Miguel Varela ◽  
C. Guedes Soares
Keyword(s):  
Virtual Environments ◽  
Three Dimensional ◽  
Ocean Engineering ◽  
Modelling Techniques ◽  
Marine Technology ◽  
And Performance ◽  
Visual Realism ◽  
The University

This article addresses the main requirements and the process of creating the geometry of ship models that fulfil the highly demanding request for realism and performance of the virtual environments currently used in modern ship bridge simulators. It starts with a classification of the ships based on their role in the simulation and on the type of simulator used, and defines the main characteristics of the models. It also discusses the importance of a well-defined workflow and its impact on the modelling time and on the quality of the final product. The article provides contributions in the following areas: identification of the main requirements of polygonal models of ships for ship simulators; effective workflow for ship three-dimensional modelling and identification of most suitable modelling techniques for efficient creation of ship models. The study is supported by real examples of three-dimensional modelling of ships with different sizes and characteristics currently used by the ship manoeuvring simulator in the Centre for Marine Technology and Ocean Engineering of the University of Lisbon.

Unraveling Life's Building Blocks: Sculpture Inspired by Proteins

Leonardo ◽  
2013 ◽  
Vol 46 (1) ◽  
pp. 12-17 ◽  
Author(s):  
Julian Voss-Andreae
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Building Blocks ◽  
Holistic View ◽  
Algorithmic Approach ◽  
One Dimensional ◽  
Molecular Building Blocks ◽  
Geometric Elements ◽  
Point Of Departure

Inspired by proteins, the molecular building blocks of life, the author's presented work re-creates the first step of the emergence of three-dimensional bodies from one-dimensional DNA. Utilizing an algorithmic approach as his point of departure, the artist follows his vision freely, creating sculptures that bring life's isolated components emotionally back to life. In this sequel to an earlier Leonardo article on the inception of his protein-inspired sculptures, the author presents the unfolding of his vision: Large-scale works of increasing formal and conceptual complexity display the emergence of an organic aesthetic from geometric elements and inspire a more holistic view of nature than that provided by reductionist science alone.

scholarly journals On the dilatational stability of the Earth

1906 ◽  
Vol 77 (519) ◽  
pp. 486-499 ◽  
Keyword(s):  
Hydrostatic Pressure ◽  
Equilibrium Configuration ◽  
Three Dimensional ◽  
Point Of View ◽  
The Body ◽  
Elastic Solids ◽  
Ordinary Experience ◽  
One Dimensional ◽  
The Earth ◽  
Interesting Paper

The theory of elastic solids usually proceeds upon the assumption that the body is initially in a state of ease, free from stress and strain. Displacements from this condition, due to given forces, or vibrations about it, are then investigated, and they are subject to the limitation that Hooke’s law shall be applicable throughout and that the strain shall everywhere be small. When we come to the case of the earth, supposed to be displaced from a state of ease by the mutual gravitation of its parts, these limits are transgressed; and several writers who have adopted this point of view have indicated the obstacles which inevitably present themselves. In his interesting paper Professor Jeans, in order to attain mathematical definiteness, goes the length of introducing forces to counteract the self-gravitation: “That is to say, we must artificially annul gravitation in the equilibrium configuration, so that this equilibrium configuration may be completely unstressed, and each element of matter be in its normal state.” How wide a departure from actuality is here implied will be understood if we reflect that under such forces the interior of the earth would probably be as mobile as water. It appears to me that a satisfactory treatment of these problems must start from the condition of the earth as actually stressed by its self-gravitation, and that the difficulties to be faced in following such a course may not be so great as has been supposed. The stress, which is so enormous as to transcend all ordinary experience, is of the nature of a purely hydrostatic pressure, and as to this surely there can be no serious difficulty. After great compression the response to further compressing stress is admittedly less than at first, but there is no reason to doubt that the reaction is purely elastic and that the material preserves its integrity. At this point it may be well to remark, in passing, upon the confusion often met with in geological and engineering writings arising from the failure to distinguish between a one-dimensional and a three-dimensional, or hydrostatic, pressure. When rock or cast iron is said to be crushed by such and such a pressure, it is the former kind of pressure which is, or ought to be, meant. meant. There is no evidence of crushing under purely hydrostatic pressure, however great.

scholarly journals Tropical Transition of the 2001 Australian Duck

2010 ◽  
Vol 138 (6) ◽  
pp. 2038-2057 ◽  
Author(s):  
Luke Andrew Garde ◽  
Alexandre Bernardes Pezza ◽  
John Arthur Tristram Bye
Keyword(s):  
Potential Vorticity ◽  
Large Scale ◽  
Three Dimensional ◽  
Vertical Wind Shear ◽  
Heat Fluxes ◽  
Pressure System ◽  
Surface Heat Fluxes ◽  
Warm Core ◽  
Tasman Sea ◽  
Upper Level

Abstract In March 2001, a hybrid low pressure system, unofficially referred to as Donald (or the Duck), developed in the Tasman Sea under tropical–extratropical influence, making landfall on the southeastern Australian coast. Here, it is shown that atmospheric blocking in the Tasman Sea produced a split in the subtropical jet, allowing persistent weak vertical wind shear to manifest in the vicinity of the developing low. It is hypothesized that this occurred through sustained injections of potential vorticity originating from higher latitudes. Hours before landfall near Byron Bay, the system developed an eye with a short-lived warm core at 500 hPa. Cyclone tracking revealed an erratic track before the system decayed and produced heavy rains and flash flooding. A three-dimensional air parcel backward-trajectory scheme showed that the air parcels arriving in the vicinity of the mature cyclone originated from tropical sources at lower levels and from the far extratropics at higher levels, confirming the hybrid characteristics of this cyclone. A high-resolution (0.15°) nested simulation showed that recent improvements in the assimilation scheme used by the Australian models allowed for accurately simulating the system’s trajectory and landfall, which was not possible at the time of the event. Compared to the first South Atlantic hurricane of March 2004, the large-scale precursors were similar; however, the Duck was exposed to injections of upper-level potential vorticity and favorable surface heat fluxes for a shorter period of time, resulting in it achieving partial tropical transition only hours prior to landfall.

The electromagnetic response of thin sheets buried in a uniformly conducting half‐space

Geophysics ◽  
1987 ◽  
Vol 52 (1) ◽  
pp. 108-117 ◽  
Author(s):  
R. Clark Robertson
Keyword(s):  
Thin Layer ◽  
Half Space ◽  
Thin Sheet ◽  
Three Dimensional ◽  
Horizontal Layer ◽  
Thin Layers ◽  
Electromagnetic Response ◽  
Thin Sheets ◽  
Magnetotelluric Data ◽  
The Earth

The interpretation of magnetotelluric data is hampered by the effect of three‐dimensional (3-D) conductivity variations within the earth. In particular, the effects of deep structures are masked by heterogeneities near the surface. In order to understand the effects of 3-D anomalies on magnetotelluric investigations, the electromagnetic response of 3-D models of the earth must be investigated. One technique used to model a 3-D earth is the thin‐sheet approximation. This technique confines all lateral changes in conductivity to a horizontal layer in a laterally homogeneous earth; however, the thin‐sheet technique can be applied only to anomalies that are electrically thin at the frequency of investigation. The thin‐sheet technique can be extended to include a greater variety of models by stacking heterogeneous thin layers. As a first step, the thin‐sheet technique is extended to model a buried, heterogeneous thin layer. Extension of the method to account for buried thin sheets is theoretically and computationally more involved than for a surface thin sheet, but the buried thin sheet still has computational advantages over other 3-D models.

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