AN EXPERIMENTAL DEVICE FOR COMPUTING MAGNETIC AND GRAVITATIONAL ANOMALIES

Geophysics ◽  
1940 ◽  
Vol 5 (1) ◽  
pp. 22-30 ◽  
Author(s):  
J. W. Fisher
Keyword(s):  
Small Diameter ◽  
Gravity Anomalies ◽  
Magnetic Anomalies ◽  
Mutual Inductance ◽  
Search Coil ◽  
Anomalous Body ◽  
Magnetic Model ◽  
Electro Magnetic ◽  
Vertical Spacing ◽  
Made In

Based upon the fact that gravitational and magnetic anomalies are functions of the solid angle subtended at the point of measurement by the contours of the anomalous body, an electro‐magnetic model is described which permits direct measurement of the desired quantities in terms of mutual inductance. A model of the subsurface “structure” is made in the form of a coil in which the vertical spacing of the turns is kept constant and the shape of the helix conforms to the contours of the structure. A small search coil is then located at the point corresponding to that at which a gravimetric or magnetometric observation is desired. The mutual inductance between the search coil and the main coil is then measured and may be expressed in terms of the magnetic or gravity anomaly arising from the simulated structure. For magnetic anomalies the search coil is made as compact as possible whereas in the case of gravity anomalies the search coil is in the form of a long solenoid of small diameter, evenly wound along its length, in order to affect the integration necessary to measure the magnetic potential analogous to the desired gravitational quantity.

scholarly journals Measurements of vector magnetic anomalies on board the icebreaker Shirase and the magnetization of the ship

1999 ◽  
Vol 42 (2) ◽  
Author(s):  
Y. Nogi ◽  
K. Kaminuma
Keyword(s):  
Magnetic Field ◽  
Geomagnetic Field ◽  
Magnetic Anomalies ◽  
The Other ◽  
South Indian Ocean ◽  
Permanent Magnetic Field ◽  
South Indian ◽  
Antarctic Research ◽  
Permanent Magnetization ◽  
Made In

Vector measurements of the geomagnetic field have been made in the South Indian Ocean since 1988 when a Shipboard Three Component Magnetometer (STCM) was installed on board the icebreaker Shirase by the 30th Japanese Antarctic Research Expedition (JARE-30). Twelve constants related to the ship's induced and permanent magnetic field were determined by the data obtained from the JARE-30 to the JARE-35. The constants related to the ship's magnetic susceptibility distribution are almost stable throughout the cruise and mostly depend on the ship's shape. On the other hand, the constants related to the ship's permanent magnetization are variable. However, absolute values of total intensity geomagnetic field calculated from vector geomagnetic field is possible to use, if the constraints from total intensity geomagnetic field measured by the proton magnetometer and/or satellite derived magnetic anomalies are applied.

Analytical expressions for gravity anomalies due to homogeneous polyhedral bodies and translations into magnetic anomalies

Geophysics ◽  
1979 ◽  
Vol 44 (4) ◽  
pp. 730-741 ◽  
Author(s):  
M. Okabe
Keyword(s):  
Gravitational Potential ◽  
Computing Time ◽  
Gravity Anomalies ◽  
Magnetic Anomalies ◽  
Two Dimensions ◽  
First Derivative ◽  
Second Derivatives ◽  
Analytical Expressions ◽  
Derivatives Of ◽  
The Magnetic Field

Complete analytical expressions for the first and second derivatives of the gravitational potential in arbitrary directions due to a homogeneous polyhedral body composed of polygonal facets are developed, by applying the divergence theorem definitively. Not only finite but also infinite rectangular prisms then are treated. The gravity anomalies due to a uniform polygon are similarly described in two dimensions. The magnetic potential due to a uniformly magnetized body is directly derived from the first derivative of the gravitational potential in a given direction. The rule for translating the second derivative of the gravitational potential into the magnetic field component is also described. The necessary procedures for practical computer programming are discussed in detail, in order to avoid singularities and to save computing time.

Drill holes deflection determination for small diameter bits in wood-based materials

BioResources ◽  
2021 ◽  
Vol 16 (2) ◽  
pp. 3808-3814
Author(s):  
Patryk Maciej Król
Keyword(s):  
Computer Vision ◽  
Medium Density Fiberboard ◽  
Small Diameter ◽  
Automatic Measurement ◽  
Medium Density ◽  
Research Attention ◽  
High Class ◽  
Drill Holes ◽  
Made In

The growing interest in wood accessories has focused scientific research attention on wood cutting with small diameter tools. A problem that may arise when drilling wood is the phenomenon of wandering – when the hole is not made in the designed place. The difficulty in studying small diameter drill holes (0.5 mm to 0.9 mm) is due to the difficulty of automatic measurement. The development of an appropriate methodology may allow for the observation of this phenomenon without the need for high-class hardware and expensive software. This article presents the results of tests carried out on nearly 500 samples made of various wood-based materials (high-density fiberboard (HDF), medium-density fiberboard (MDF), chipboard, and plywood) in terms of the usefulness of the OpenCV computer vision library for the determination of wandering.

Comoros – New Evidence and Arguments for Continental Crust

2016 ◽  
Author(s):  
John Milsom ◽  
Phil Roach ◽  
Chris Toland ◽  
Don Riaroh ◽  
Chris Budden ◽  
...  
Keyword(s):  
Continental Crust ◽  
Fracture Zone ◽  
Seismic Data ◽  
Gravity Anomalies ◽  
Magnetic Anomalies ◽  
Magnetic Data ◽  
The West ◽  
Sea Floor ◽  
Inappropriate Use ◽  
Sea Floor Spreading

ABSTRACT As part of an ongoing exploration effort, approximately 4000 line-km of seismic data have recently been acquired and interpreted within the Comoros Exclusive Economic Zone (EEZ). Magnetic and gravity values were recorded along the seismic lines and have been integrated with pre-existing regional data. The combined data sets provide new constraints on the nature of the crust beneath the West Somali Basin (WSB), which was created when Africa broke away from Gondwanaland and began to move north. Despite the absence of clear sea-floor spreading magnetic anomalies or gravity anomalies defining a fracture zone pattern, the crust beneath the WSB has been generally assumed to be oceanic, based largely on regional reconstructions. However, inappropriate use of regional magnetic data has led to conclusions being drawn that are not supported by evidence. The identification of the exact location of the continent-ocean boundary (COB) is less simple than would at first sight appear and, in particular, recent studies have cast doubt on a direct correlation between the COB and the Davie Fracture Zone (DFZ). The new high-quality reflection seismic data have imaged fault patterns east of the DFZ more consistent with extended continental crust, and the accompanying gravity and magnetic surveys have shown that the crust in this area is considerably thicker than normal oceanic and that linear magnetic anomalies typical of sea-floor spreading are absent. Rifting in the basin was probably initiated in Karoo times but the generation of new oceanic crust may have been delayed until about 154 Ma, when there was a switch in extension direction from NW-SE to N-S. From then until about 120 Ma relative movement between Africa and Madagascar was accommodated by extension in the West Somali and Mozambique basins and transform motion along the DFZ that linked them. A new understanding of the WSB can be achieved by taking note of newly-emerging concepts and new data from adjacent areas. The better-studied Mozambique Basin, where comprehensive recent surveys have revealed an unexpectedly complex spreading history, may provide important analogues for some stages in WSB evolution. At the same time the importance of wide continent-ocean transition zones marked by the presence of hyper-extended continental crust has become widely recognised. We make use of these new insights in explaining the anomalous results from the southern WSB and in assessing the prospectivity of the Comoros EEZ.

scholarly journals Gravity Measurements on the Athabaska Glacier, Alberta, Canada

1963 ◽  
Vol 4 (35) ◽  
pp. 617-631
Author(s):  
E. R. Kanasewich
Keyword(s):  
Cross Section ◽  
Three Dimensional ◽  
Gravity Anomalies ◽  
Independent Data ◽  
Surface Slope ◽  
Average Shear Stress ◽  
Glacier Valley ◽  
Gravity Measurements ◽  
Average Shear ◽  
Made In

AbstractThe thickness of the Athabaska Glacier has been obtained along eight transverse profiles by an investigation of gravity anomalies. Three-dimensional computations with a low-speed digital computer were made in this study to acquire more precise results than previously obtained. The thickness of the glacier varies front 326 m. on a line below the lower ice fall to 49 m. near the terminus. The accuracy of the results is discussed and compared with independent data from bore holes and a seismic program. The cross-section of the glacier valley was found to approximate a parabola on several lines. From a knowledge of the thickness. shape and surface slope of the glacier, the average shear stress exerted by the bed on the ice was found to be 1.0 bar.

Reduction to the pole of the North American magnetic anomalies

Geophysics ◽  
1990 ◽  
Vol 55 (2) ◽  
pp. 218-225 ◽  
Author(s):  
J. Arkani‐Hamed ◽  
W. E. S. Urquhart
Keyword(s):  
North America ◽  
Gravity Anomalies ◽  
Magnetic Anomalies ◽  
Gravity Gradient ◽  
Plate Boundaries ◽  
Gravity Gradients ◽  
The North ◽  
Vertical Gravity Gradient ◽  
Regional Tectonic ◽  
Vertical Gravity

Magnetic anomalies of North America are reduced to the pole using a generalized technique which takes into account the variations in the directions of the core field and the magnetization of the crust over North America. The reduced‐to‐the‐pole magnetic anomalies show good correlations with a number of regional tectonic features, such as the Mid‐Continental rift and the collision zones along plate boundaries, which are also apparent in the vertical gravity gradient map of North America. The magnetic anomalies do not, however, show consistent correlation with the vertical gravity gradients, suggesting that magnetic and gravity anomalies do not necessarily arise from common sources.

Non-uniform air gap modeling and electromagnetic characteristics of a new six-phase doubly salient electro-magnetic generator

2020 ◽  
Vol 64 (1-4) ◽  
pp. 1325-1335
Author(s):  
Xiaoyu Zhou ◽  
Liwei Shi ◽  
Junhao An ◽  
Fukang Ding
Keyword(s):  
Finite Element ◽  
Linear Structure ◽  
Mutual Inductance ◽  
Air Gap ◽  
Electromagnetic Properties ◽  
Element Analysis ◽  
Doubly Salient ◽  
Electro Magnetic ◽  
Magnetic Generator ◽  
Gap Structure

The voltage harmonics of the six-phase doubly salient electro-magnetic generator (DSEG) are large, and the electromagnetic isolation is poor due to the mutual inductance of the armature winding. An optimization scheme for the stator non-uniform air gap structure is proposed. By establishing a non-uniform air gap angle function model, the analytical expression of the induced electromotive force in the non-uniform air gap structure is derived. Using finite element and mathematical model to verify that the stator tip is changed from circular arc to linear structure can increase power and reduce voltage high harmonics, improve the power quality of the generator. Based on the equivalent magnetic circuit, the influence of the winding method of the excitation winding on the mutual inductance of the armature winding is studied. When the field winding is wound interval every two stator poles, the mutual inductance is small. The electromagnetic properties of the new six-phase electric excitation double salient pole are analyzed by two-dimensional finite element analysis. The rationality of the proposed motor structure is verified by experiments.

scholarly journals Gravity Measurements on the Athabaska Glacier, Alberta, Canada

1963 ◽  
Vol 4 (35) ◽  
pp. 617-631 ◽  
Author(s):  
E. R. Kanasewich
Keyword(s):  
Cross Section ◽  
Three Dimensional ◽  
Gravity Anomalies ◽  
Independent Data ◽  
Surface Slope ◽  
Average Shear Stress ◽  
Glacier Valley ◽  
Gravity Measurements ◽  
Average Shear ◽  
Made In

AbstractThe thickness of the Athabaska Glacier has been obtained along eight transverse profiles by an investigation of gravity anomalies. Three-dimensional computations with a low-speed digital computer were made in this study to acquire more precise results than previously obtained. The thickness of the glacier varies front 326 m. on a line below the lower ice fall to 49 m. near the terminus. The accuracy of the results is discussed and compared with independent data from bore holes and a seismic program. The cross-section of the glacier valley was found to approximate a parabola on several lines. From a knowledge of the thickness. shape and surface slope of the glacier, the average shear stress exerted by the bed on the ice was found to be 1.0 bar.

The Plane Parallel Flow of a Binary Mixture of Fluids

1981 ◽  
Vol 48 (4) ◽  
pp. 707-716
Author(s):  
L. M. Srivastava ◽  
V. P. Srivastava
Keyword(s):  
Binary Mixture ◽  
Particle Deposition ◽  
Numerical Study ◽  
Infinite Plate ◽  
Small Diameter ◽  
Hankel Transform ◽  
Physical Importance ◽  
Strong Motivation ◽  
Insight Into ◽  
Made In

The flow of a binary mixture of chemically inert incompressible, Newtonian fluids over an infinite plate, set into motion in its plane by impulse and by oscillation, is studied. The binary mixture consists of (i) two different viscous density nonstratified fluids, and (ii) two different viscous density stratified fluids. The exact solutions are obtained using two methods, (i) Laplace transform and (ii) Hankel transform. To further study the velocities and the wall shear stress, asymptotic expansion are found for small and large times. Some other results of physical importance such as results for noninteracting fluids, strongly interacting fluids, and extremely different fluids are also derived and compared analytically with other results. Finally, to gain an insight into the patterns of the flow, numerical study of the results has been made in detail using digital computer. A strong motivation of the present analysis has been the hope that such a theory of fluids is useful in providing some insight in rheological properties of complex fluids as polymers, liquid crystals and, in particular, blood in the vessels of small diameter. Also the theory of fluids might provide an improved understanding of such diverse subjects as diffusion of proteins, swimming of micro-organism and particle deposition in respiratory tract.

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