scholarly journals “Global Dynamics” of a Temperate Valley Glacier, Mer De Glace, and Past Velocities Deduced from Forbes’ Bands

1981 ◽  
Vol 27 (96) ◽  
pp. 207-226 ◽  
Author(s):  
Louis Lliboutry ◽  
Louis Reynaud
Keyword(s):  
Atmospheric Pressure ◽  
State Energy ◽  
The Body ◽  
Global Dynamics ◽  
Perturbation Equation ◽  
Sliding Velocity ◽  
Velocity Fluctuations ◽  
Valley Glacier ◽  
New Perturbation ◽  
Solid Type

AbstractTransverse profiles and velocities which have been measured on the ablation zone of Mer de Glace more or less continuously since 1891 contradict the Weertman–Nye theory of glacier kinematic waves. Faint broad waves, which undoubtedly result from fluctuations in the balance, travel down the glacier faster than this theory predicts. (This theory having first been completed by taking changes in width with time and with distance down the glacier into account.) On the other hand, velocity fluctuations are synchronous and more or less the same over the entire length studied (6 km).These discrepancies result from bottom friction being of the solid type, i.e. independent of sliding velocity. Friction should also be almost insensitive to discharge in subglacial waterways, since in the steady state energy for keeping them open, not entirely flooded, and at atmospheric pressure, is superabundant. The sliding velocities at all cross-profiles are thus controlled by some areas where the body of the glacier suffers strong deformation because the valley shape is far from cylindrical. One such controlling zone exists on Mer de Glace owing to the existence of a subglacial transverse shoulder. A new perturbation equation and a new rough expression for wave velocity are given.Intervals between Forbes’ bands were plotted on seven aerial surveys between 1939 and 1979. Progressive tilting of the slices of blue, dusty ice from the position from which these dark bands proceed and progressive lowering of their exposed edge must be taken into account. This analysis confirms the validity of our simple model for velocity fluctuations and allows us to estimate the entire series since the year 1888.

scholarly journals “Global Dynamics” of a Temperate Valley Glacier, Mer De Glace, and Past Velocities Deduced from Forbes’ Bands

1981 ◽  
Vol 27 (96) ◽  
pp. 207-226 ◽  
Author(s):  
Louis Lliboutry ◽  
Louis Reynaud
Keyword(s):  
Atmospheric Pressure ◽  
State Energy ◽  
The Body ◽  
Global Dynamics ◽  
Perturbation Equation ◽  
Sliding Velocity ◽  
Velocity Fluctuations ◽  
Valley Glacier ◽  
New Perturbation ◽  
Solid Type

AbstractTransverse profiles and velocities which have been measured on the ablation zone of Mer de Glace more or less continuously since 1891 contradict the Weertman–Nye theory of glacier kinematic waves. Faint broad waves, which undoubtedly result from fluctuations in the balance, travel down the glacier faster than this theory predicts. (This theory having first been completed by taking changes in width with time and with distance down the glacier into account.) On the other hand, velocity fluctuations are synchronous and more or less the same over the entire length studied (6 km).These discrepancies result from bottom friction being of the solid type, i.e. independent of sliding velocity. Friction should also be almost insensitive to discharge in subglacial waterways, since in the steady state energy for keeping them open, not entirely flooded, and at atmospheric pressure, is superabundant. The sliding velocities at all cross-profiles are thus controlled by some areas where the body of the glacier suffers strong deformation because the valley shape is far from cylindrical. One such controlling zone exists on Mer de Glace owing to the existence of a subglacial transverse shoulder. A new perturbation equation and a new rough expression for wave velocity are given.Intervals between Forbes’ bands were plotted on seven aerial surveys between 1939 and 1979. Progressive tilting of the slices of blue, dusty ice from the position from which these dark bands proceed and progressive lowering of their exposed edge must be taken into account. This analysis confirms the validity of our simple model for velocity fluctuations and allows us to estimate the entire series since the year 1888.

On planar oscillations of a body with a variable mass distribution in an elliptic orbit

2011 ◽  
Vol 225 (10) ◽  
pp. 2288-2295 ◽  
Author(s):  
A Burov ◽  
I Kosenko
Keyword(s):  
Mass Distribution ◽  
Large Scale ◽  
Variable Mass ◽  
Relative Equilibria ◽  
The Body ◽  
Global Dynamics ◽  
Central Field ◽  
Attitude Dynamics ◽  
Orbital Eccentricity ◽  
Space Elevators

Planar motion of an orbiting body having a variable mass distribution in a central field of gravity is under analysis. Within the so-called ‘satellite approximation’ planar attitude dynamics is reduced to the 3/2-degrees of freedom description by one ODE of second order. The law of the mass distribution variations implying an existence of the special relative equilibria, such that the body is oriented pointing to the attracting centre by the same axis for any value of the orbit eccentricity is indicated. For particular example of an orbiting dumb-bell equipped by a massive cabin, wandering between the ends of the dumb-bell. For this example stability of the equilibria such that the dumb-bell ‘points to’ the attracting centre by one of its ends is studied. The chaoticity of global dynamics is investigated. Two important examples of a vibrating dumb-bell and of a dumb-bell equipped by a cabin wandering between its endpoints are considered. The dynamics of space objects, including moving elements, has been investigated by many authors. These studies usually have been connected with the necessity to estimate the influence of relative motions of moving parts, for example, crew motions [ 1 , 2 ], circulation of liquids [ 3 ], etc. on the attitude dynamics of a spacecraft. The development of projects of large-scale space systems with mobile elements, in particular, of satellite systems with tethered elements and space elevators, has posed problems related to their dynamics. Various aspects of the role of mass distribution even for the simplest orbiting systems, like dumb-bell systems are known since the publications [ 4 – 7 ], etc. The possibility of the sudden loss of stability because of the mass redistribution has been pointed out in reference [ 8 ] (see also references [ 9 – 13 ]). The considered system belongs to the mentioned class of systems and represents by itself one of the simplest systems allowing both analytical and numerical treatment, without supplementary simplifying assumptions such as smallness of the orbital eccentricity. Another set of applied problems is related to orientation keeping of the system for deployment and retrieval of tethered subsatellites as well as for relative cabin motions of space elevators. In particular, the problem of the stabilization/destabilization possibility for the given state of motion due to rapid oscillations of the cabin exists. This could be the subject of another additional investigation.

scholarly journals General Theory of Subglacial Cavitation and Sliding of Temperate Glaciers

1968 ◽  
Vol 7 (49) ◽  
pp. 21-58 ◽  
Author(s):  
L. Lliboutry
Keyword(s):  
Frictional Force ◽  
Atmospheric Pressure ◽  
Hydraulic System ◽  
Water Pressure ◽  
Realistic Model ◽  
Point Of View ◽  
Small Scale ◽  
Sliding Velocity ◽  
Surface Slope ◽  
Geometrical Progression

AbstractEarlier theories of Weertman and the present author are reviewed and compared; both are insufficient to account for the facts observed at the tongue of the Allalingletscher.A calculation of the stresses and heat flow at the bed of a glacier with a sinusoidal profile is given which takes account of any degree of subglacial cavitation. The sliding due to plasticity and that due to pressure melting are related to this degree of cavitation and it is shown that these two terms are additive. There results an expression for the frictionfωin terms of the total sliding velocityuand the height of the bumpsa. For a given and large enough value ofu,fω(a) exhibits two maxima which are equal and independent ofu.The paper then considers a more realistic model of the bed consisting of a superposition of sine waves all having the same roughnessr, andadecreasing in a geometrical progression. The biggestamay be inferred from the overall profile of the bedrock; the resulting frictional force can be regarded either as part of the total frictional forcefin an overall view for whichf=ρghsinαholds, or else as a correction to such a value on the small scale (the best point of view for crevasse studies). To a first approximation Coulomb’s law of friction holds provided one takes account of the interstitial water pressure at the ice-rock interface.This interstitial pressurepis next related to the thickness of the glacierh. If the subglacial hydraulic system is at atmospheric pressure,pis proportional toh. Next, if the sliding velocity is not too large, the surface slope approaches 1.6r≈ 0.12 and kinematic waves (which move four times as fast as the ice) disappear rapidly. If the hydraulic system is not at atmospheric pressure the surface slope is smaller and flow instabilities can occur.

CHANGES IN THYROID ACTIVITY AT LOW ATMOSPHERIC PRESSURES AND AT HIGH ALTITUDES, AS TESTED WITH 131I

1952 ◽  
Vol 8 (4) ◽  
pp. 308-320 ◽  
Author(s):  
F. VERZÁR ◽  
E. SAILER ◽  
V. VIDOVIC
Keyword(s):  
Atmospheric Pressure ◽  
Atmospheric Oxygen ◽  
The Body ◽  
Normal Velocity ◽  
High Altitudes ◽  
Low Oxygen ◽  
Thyroid Activity ◽  
Natural Conditions ◽  
Adrenocortical Activity ◽  
Low Atmospheric Pressure

The activity of the thyroid gland of rats was observed by measuring the uptake of 131I in the living animal over a period of several days. The method is described in detail, and the importance of iodine contained in the diet or applied to the skin, in affecting the results, is stressed. Reduction of the atmospheric pressure to 250 and 380 mm Hg decreases the uptake of 131I. The lower the pressure, the less iodine is concentrated in the thyroid. Under natural conditions a small decrease of thyroid activity at an altitude of 3450 m (490 mm Hg) can be noticed, but not at 2010 m altitude (592 mm Hg). The depression of the thyroid is temporary; after some days 131I is taken up again with normal velocity. At low atmospheric pressure (below 480 mm Hg) the body temperature decreases, but this, too, is restored to normal in 3–4 days. The adaptation of thyroid activity to low atmospheric (oxygen) pressure may play an important part during acclimatization to high altitudes. The mechanism underlying the alteration in thyroid function and, in particular, the relation between the thyroid and adrenocortical activity is discussed. It is suggested that the increased adrenocortical activity and the decrease of thyroid activity observed at low oxygen or atmospheric pressure may be inter-connected.

On the instability of ventilated cavities

1966 ◽  
Vol 26 (3) ◽  
pp. 437-457 ◽  
Author(s):  
L. C. Woods
Keyword(s):  
Pressure Fluctuations ◽  
Unsteady Motion ◽  
Cavitation Number ◽  
The Body ◽  
Supply Rate ◽  
Velocity Fluctuations ◽  
Air Supply ◽  
Resonance Frequencies ◽  
Axis Of Symmetry ◽  
The Mathematical Model

It has been found that ventilated cavities extending behind hydrofoils, plates, and other two-dimensional bodies, oscillate when the air supply rate is sufficient to reduce the cavitation number to about one-fifth of its natural value. As the rate increases further, higher modes of oscillation occur in which the cavity–water interface supports several waves that are convected downstream towards the wake, which, owing to a pinching-off action replacing the usual entrainment sink, consists of a sequence of large bubbles drifting downstream. A theory of such flows that allows both for the convected velocity fluctuations in the cavity, and for the transport of bubble volume down the wake, is given in this paper. Coupled with a rather simple phenomenological relation between the pressure fluctuations within the cavity and the departure of the pinched-off rear portion of the cavity—explained in terms of the action of the re-entrant jet—this theory successfully predicts the resonance frequencies obtained in experiments by Silberman & Song.The theory also provides a solution of the more general problem of determining the fluctuations in the pressure distribution over the whole surface of the body, when it is in a prescribed unsteady motion along its axis of symmetry (the theory is confined to symmetrical bodies and flows). Thus the growth in drag due to a sudden increment in the upstream velocity can be predicted, and also the damping forces acting on the body when it is forced to oscillate at a given frequency. It is shown that in all cases the body is unstable.One important feature of the mathematical model chosen is that it completely avoids the presence of a time-dependent sink at infinity—with its associated infinite pressures—by conserving total volume of wake and cavity in just the same way as vorticity is conserved in unsteady aerofoil theory.

scholarly journals Spin-up in a tank induced by a rotating bluff body

1999 ◽  
Vol 388 ◽  
pp. 49-68 ◽  
Author(s):  
D. MAYNES ◽  
J. KLEWICKI ◽  
P. McMURTRY
Keyword(s):  
Steady State ◽  
Turbulent Diffusion ◽  
Bluff Body ◽  
Fluid Velocity ◽  
Tangential Velocity ◽  
The Body ◽  
Mean Flow ◽  
Velocity Fluctuations ◽  
Acceleration Rate ◽  
Time Required

Spin-up of a turbulent flow in a cylindrical tank caused by a rotating bluff body has been investigated using flow visualization, fluid velocity measurements, and hydrodynamic torque measurements. During the spin-up process three distinct temporal regimes exist. These regimes are: (i) a build-up regime where the torque and the tangential velocity fluctuations in the close proximity of the body remain constant; (ii) a decay regime where these quantities decay with power-law relations; and (iii) a mean flow steady state where these values remain relatively constant. Experiments were conducted in two tanks differing in volume by a factor of 80 and with a large range of bluff body sizes. A non-dimensional time scale, τ, based upon turbulent diffusion is determined and the tangential velocity fluctuations and torque coefficient start to decay at a fixed value of τ. Likewise, steady state is attained at a larger fixed value of τ. This time scaling is physically based upon the time required for momentum to be transferred over the entire tank volume due to turbulent diffusion, and is general for any body size, tank size, rotation rate, and acceleration rate.

Nonlinear traveltime inversion scheme for crosshole seismic tomography in tilted transversely isotropic media

Geophysics ◽  
2008 ◽  
Vol 73 (4) ◽  
pp. D17-D33 ◽  
Author(s):  
Bing Zhou ◽  
Stewart Greenhalgh ◽  
Alan Green
Keyword(s):  
Seismic Tomography ◽  
Velocity Structure ◽  
Body Wave ◽  
Transversely Isotropic ◽  
The Body ◽  
Body Waves ◽  
Inversion Method ◽  
Perturbation Equation ◽  
Transversely Isotropic Media ◽  
Isotropic Media

Crosshole seismic tomography often is applied to image the velocity structure of an interwell medium. If the rocks are anisotropic, the tomographic technique must be adapted to the complex situation; otherwise, it leads to a false interpretation. We propose a nonlinear kinematic inversion method for crosshole seismic tomography in composite transversely isotropic media with known dipping symmetry axes. This method is based on a new version of the first-order traveltime perturbation equation. It directly uses the derivative of the phase velocity rather than the eigenvectors of the body-wave modes to overcome the singularity problem for application to the two quasi-shear waves. We applied an iterative nonlinear solver incorporating our kinematic ray-tracing scheme and directly compute the Jacobian matrix in an arbitrary reference medium. This reconstructs the five elastic moduli or Thomsen parameters from the first-arrival traveltimes of the three seismic body waves (qP, qSV, qSH) in strongly and weakly anisotropic media. We conducted three synthetic experiments that involve determining anisotropic parameters for a homogeneous rock, reconstructing a fault embedded in a strongly anisotropic background, and imaging a complicated four-layer model containing a small channel and a buried dipping interface. We compared results of our nonlinear inversion method with isotropic tomography and the traditional linear anisotropic inversion scheme, which showed the capability and superiority of the new scheme for crosshole tomographic imaging.

scholarly journals CONSUMPTION AND USE OF OXYGEN BY THE BODY OF PERSONS WITH CARDIOVASCULAR PATHOLOGY WITH CHANGES IN GEOMAGNETIC ACTIVITY

2021 ◽  
Vol 3 (1) ◽  
pp. 323-330
Author(s):  
Gennady A. Usenko ◽  
Dmitry V. Vasendin
Keyword(s):  
Solar Activity ◽  
Radio Emission ◽  
Arterial Hypertension ◽  
Air Temperature ◽  
Atmospheric Pressure ◽  
The Body ◽  
Emission Flux ◽  
Oxygen Utilization ◽  
Gamma Background ◽  
The One

The aim of the study was to identify and evaluate the relationship between the indicators of solar activity, the content of magnesium in the blood and the level of oxygen utilization by tissues in men with different temperaments and anxiety, suffering from arterial hypertension. During the period of the study from 1995 to 2015, sick and healthy men were divided into equal groups with a predominance of choleric, sanguine, phlegmatic and melancholic temperament with high and low anxiety. The average annual values of the Wolf numbers, the radio emission of the Sun at a wavelength of 10,7 cm, atmospheric pressure, gamma background and air temperature were taken into account, and the content of magnesium and hemoglobin in the blood serum was determined. The oxygen concentration was determined by the calculated method. A statistically significant direct correlation has been established between the increase in solar activity (Wolf numbers, radio emission flux at a wavelength of 10.7 cm), on the one hand, and atmospheric pressure, air temperature, and the gamma background of the environment, on the other. Under the same environmental conditions, the content of magnesium in the blood and the level of oxygen utilization by the body tissues of patients with arterial hypertension decreased in the temperamental range from high- and low-anxiety sympathotonics (choleric and sanguine) to parasympathotonics (high- and low-anxiety phlegmatic and melancholic). During the study period, a statistically significant relationship was established between an increase in solar activity (Wolf numbers, radio emission flux), atmospheric pressure, air temperature, and gamma background, on the one hand, and a decrease in the content of magnesium in the blood, as well as the level of oxygen utilization by tissues in healthy high- and low-anxiety individuals and patients with arterial hypertension, regardless of temperament.

scholarly journals Load of gondola with floor decking at handling operations

2015 ◽  
Vol 2015 (4) ◽  
pp. 45-49
Author(s):  
Владимир Кобищанов ◽  
Vladimir Kobishchanov ◽  
Кирилл Герасимов ◽  
Kirill Gerasimov ◽  
Дмитрий Расин ◽  
...  
Keyword(s):  
Maximum Stress ◽  
The Body ◽  
Dynamic Loads ◽  
Normal Stresses ◽  
Test Results ◽  
Load Drop ◽  
Small Areas ◽  
Car Body ◽  
Deflected Mode ◽  
Solid Type

A gondola with a body of solid type – an eco-nomically effective unit of a rollingstock. Most of the damages of gondola bodies is caused at handling operations with the failure of requirements observance established. In the paper the assessment of deflected mode body in the body at the lump load drop with the mass of 500 kg is carried out. Normal stresses and travels arising at the blow of load in the sections of joints of frame beams between each other, side and end walls are analyzed. The values of stresses three times higher than the foreseen ones with “Standards…” are adopted as reference valuations. It is substantiated by test results and the comparison of material characteristics at deadweight and dynamic loads. As a result of car body multichoice computations on basis of the detailed MCE there was established the following: the closer the place of a lump blow to a supporting longitudinal to the car body end is, the stresses are higher in it. Stresses arising in the supporting longitudinal situated between an end girder and a body bolster beam reach 998 H/mm, at the same time in the middle of the car body of a gondola they do not exceed 450 H⁄mm². If a load lump falls down on the joint of cross-beams and longitudinal ones, then stresses in their sections 10-15 times less, than if the fall were to a strengthening beam. In the main the maximum stress distribution is limited by small areas located between two neighboring crossbeams. The research results have shown, it is necessary that additional bearing elements absorbing a blow should be introduced in a frame.

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