scholarly journals Subtidal circulation in a microtidal Mediterranean bay

2019 ◽  
Vol 82 (4) ◽  
pp. 231 ◽  
Author(s):  
Pablo Cerralbo ◽  
Manuel Espino ◽  
Manel Grifoll ◽  
Arnoldo Valle-Levinson
Keyword(s):  
Vertical Structure ◽  
Function Analysis ◽  
Low Frequency ◽  
Wind Speeds ◽  
Subtidal Circulation ◽  
Nw Mediterranean ◽  
The Rich ◽  
Set Up ◽  
Freshwater Inputs ◽  
Mean Circulation

We examine the role of different forcings on the subtidal circulation in a microtidal bay with freshwater inputs in the NW Mediterranean Sea: Alfacs Bay. Observations of subtidal flow in summer 2013 and winter 2014 reveal a two-layered, vertically sheared circulation. During the summer, there is a significant positive correlation between surface currents and winds along the main axis of the bay, while a negative correlation is observed between wind and the bottom layers. During the winter, the cross-shore response is correlated with the most energetic winds, showing a two-layered vertical structure inside the bay and a nearly depth-independent water motion caused by high wind speeds at the bay mouth. The vertical structure of the velocities, as determined through empirical orthogonal function analysis, confirms that surface layers are affected by winds and bottom currents correlated negatively with winds as a response of the wind set-up. Seasonal mean circulation reveals gravitational exchange at the bay mouth during the summer. However, mean circulation is unclear in the inner bay and close to the drainage channels. Observed flow patterns are supported by modelling results that confirm the persistence of averaged current in the low-frequency dynamics. Re-circulation areas in the inner bay indicate the rich spatial variability in flow at low-frequency time scales.

M. V. Nadkarni. Farmer's Movements in India. New Delhi: Allied Publishers Pvt. Ltd., 1987.237 pp.,Price: (hardbound edition) Rupees (Indian) 100.00.

1988 ◽  
Vol 27 (3) ◽  
pp. 333-335
Author(s):  
Khwaja Sarmad
Keyword(s):  
Tamil Nadu ◽  
Rural Poverty ◽  
Price Policy ◽  
New Delhi ◽  
Root Cause ◽  
The Subject ◽  
The Rich ◽  
Land Holdings ◽  
Set Up ◽  
Agricultural Price

This book is a comprehensive analysis of farmers' movements in India with a focus on the movements in Tamil Nadu, Maharashtra, Punjab and Karnatka. It examines the economic, social and political aspects of the farmers' struggle for a better deal within regional and national perspectives and evaluates the potential impact of these struggles on economic development in general, and on rural development, in particular. In a most competent way the author has presented the current state of the debate on the subject. He deals exhaustively with the subject of agricultural price policy and argues against the proposition that favourable price-setting for farm products is adequate to alleviate rural poverty. A better way to tackle this problem is to improve the per capita output in the rural sector, since the root cause of the problem is not unfavourable terms of trade but the increasing proportion of land holdings, which are economically not viable. Agricultural price policy is analyzed within the context of class relations, which enables to establish a link between the economic and political demands of the farmers. This analysis leads the author to conclude, that in contrast with the peasants' movements in India, which helped to break up the feudal agrarian set-up, the recent farmers' movements, with a few exceptions, have little revolutionary content. Their leadership has been appropriated by the rich landowners, who have transformed the movements into a lobby for advancing their own interests, within the existing power structure, to the neglect of the poorer peasantry.

Simulation Study on Dynamic Reactive Power Compensation of Grid-Connected Wind Farms

2013 ◽  
Vol 756-759 ◽  
pp. 4171-4174 ◽  
Author(s):  
Xiao Ming Wang ◽  
Xing Xing Mu
Keyword(s):  
Voltage Stability ◽  
Wind Farm ◽  
Reactive Power ◽  
Wind Farms ◽  
Reactive Power Compensation ◽  
Wind Speeds ◽  
Wind Generators ◽  
Reactive Compensation ◽  
Farm Model ◽  
Set Up

With the Asynchronous wind generators as research object, this paper analyzes the problems of the voltage stability and the generation mechanism of the reactive power compensation during the wind farms connected operation. For paralleling capacitor bank has shown obvious defects, therefore this paper employs dynamic reactive power compensation to improve reactive characteristics of grid-connected wind farms. With the influences of different wind disturbances and grid faults on wind farms, wind farm model is set up and dynamic reactive power compensation system and wind speeds are built in the Matlab/Simulink software, The simulation result shows that they can provide reactive power compensation to ensure the voltage stability of the wind farms. But STATCOM needs less reactive compensation capacity to make sure the voltage and active power approaching steady state before the faults more quickly, Therefore STATCOM is more suitable for wind farms connected dynamic reactive power compensation.

scholarly journals Meteorological conditions over Antarctic blue-ice areas and their influence on the local surface mass balance

2001 ◽  
Vol 47 (156) ◽  
pp. 37-50 ◽  
Author(s):  
Richard Bintanja ◽  
Carleen H. Reijmer
Keyword(s):  
Mass Balance ◽  
Low Frequency ◽  
Meteorological Conditions ◽  
Surface Mass Balance ◽  
Surface Mass ◽  
Wind Speeds ◽  
Dry Conditions ◽  
The Difference ◽  
Sublimation Rates ◽  
Different Characteristics

AbstractThis paper addresses the causes of the prevailing meteorological conditions observed over an Antarctic blue-ice area and their effect on the surface mass balance. Over blue-ice areas, net accumulation is zero and ablation occurs mainly through sublimation. Sublimation rates are much higher than over adjacent snowfields. The meteorological conditions favourable for high sublimation rates (warm, dry and gusty) are due to the specific orographic setting of this blue-ice area, with usually a steep upwind mountainous slope causing strong adiabatic heating. Diabatic warming due to radiation, and entrainment of warm air from aloft into the boundary layer augment the warming. The prevailing warm, dry conditions explain roughly 50% of the difference in sublimation, and the different characteristics of blue ice (mainly its lower albedo) the other 50%. Most of the annual sublimation (∼70%) takes place during the short summer (mainly in daytime), with winter ablation being restricted to occasional warm, dry föhn-like events. The additional moisture is effectively removed by entrainment and horizontal advection, which are maximum over the blue-ice area. Low-frequency turbulent motions induced by the upwind mountains enhance the vertical turbulent transports. Strong gusts and high peak wind speeds over blue-ice areas cause high potential snowdrift transports, which can easily remove the total precipitation, thereby maintaining zero accumulation.

scholarly journals FIELD MEASUREMENTS AND MODELLING OF NEARSHORE CURRENTS AT A HIGH-ENERGY GEOLOGICALLY-CONSTRAINED BEACH

2020 ◽  
pp. 18
Author(s):  
Arthur Mouragues ◽  
Philippe Bonneton ◽  
Bruno Castelle ◽  
Vincent Marieu
Keyword(s):  
Surf Zone ◽  
Low Frequency ◽  
Field Measurements ◽  
High Energy ◽  
Oblique Wave ◽  
Wave Forcing ◽  
Circulation Patterns ◽  
Wave Conditions ◽  
Nearshore Currents ◽  
Set Up

We present field measurements of nearshore currents at a high-energy mesotidal beach with the presence of a 500-m headland and a submerged reef. Small changes in wave forcing and tide elevation were found to largely impact circulation patterns. In particular, under 4-m oblique wave conditions, our measurements indicate the presence of an intense low-frequency fluctuating deflection rip flowing against the headland and extending well beyond the surf zone. An XBeach model is further set up to hindcast such flow patterns.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/EiqnjBIkWJE

Research on Vibration Isolation System Based on Disturbance Observer PID Control Algorithm

2017 ◽  
Vol 865 ◽  
pp. 480-485
Author(s):  
Jian Liang Li ◽  
Xiao Xi Liu ◽  
Shu Qing Li ◽  
Zhi Fei Tao ◽  
Lei Ma
Keyword(s):  
Pid Control ◽  
Disturbance Observer ◽  
Control Algorithm ◽  
Vibration Isolation ◽  
Low Frequency ◽  
Isolation System ◽  
Vibration Isolation System ◽  
Virtual Test ◽  
Set Up ◽  
And Control

The research mainly focuses on the performance of the controllable hypocenter in the low frequency band. The hybrid vibration isolation method based on the disturbance observer PID control algorithm is used to improve the excitation signal quality. Based on the analysis of the structure and working principle of vibration isolator, the physical model and mathematical model are established, and the simulation test of ZK-5VIC virtual test vibration and control system is carried out. The experimental platform of hybrid vibration isolation system with low frequency interference is set up. The experiment of excitation and acquisition of low frequency signal is carried out, which provides the theoretical basis and guarantee for the vibration isolation technology in the low frequency range below 3Hz.

Dynamic modulation of cerebrovascular resistance as an index of autoregulation under tilt and controlled Pet CO2

2002 ◽  
Vol 283 (3) ◽  
pp. R653-R662 ◽  
Author(s):  
Michael R. Edwards ◽  
J. Kevin Shoemaker ◽  
Richard L. Hughson
Keyword(s):  
Transfer Function ◽  
Function Analysis ◽  
Low Frequency ◽  
Mean Flow ◽  
Low Frequencies ◽  
Cerebrovascular Autoregulation ◽  
Cerebrovascular Resistance ◽  
Arterial Blood ◽  
Transfer Function Analysis ◽  
Frequency Changes

Transfer function analysis of the arterial blood pressure (BP)-mean flow velocity (MFV) relationship describes an aspect of cerebrovascular autoregulation. We hypothesized that the transfer function relating BP to cerebrovascular resistance (CVRi) would be sensitive to low-frequency changes in autoregulation induced by head-up tilt (HUT) and altered arterial Pco 2. Nine subjects were studied in supine and HUT positions with end-tidal Pco 2(Pet CO2 ) kept constant at normal levels: +5 and −5 mmHg. The BP-MFV relationship had low coherence at low frequencies, and there were significant effects of HUT on gain only at high frequencies and of Pco 2 on phase only at low frequencies. BP → CVRi had coherence >0.5 from very low to low frequencies. There was a significant reduction of gain with increased Pco 2 in the very low and low frequencies and with HUT at the low frequency. Phase was affected by Pco 2 in the very low frequencies. Transfer function analysis of BP → CVRi provides direct evidence of altered cerebrovascular autoregulation under HUT and higher levels of Pco 2.

Low-frequency laboratory measurements of the elastic properties of sandstone flooded with supercritical CO2

2013 ◽  
Vol 53 (2) ◽  
pp. 484
Author(s):  
Vassili Mikhaltsevitch ◽  
Maxim Lebedev ◽  
Boris Gurevich
Keyword(s):  
Supercritical Co2 ◽  
Low Frequency ◽  
Bedding Plane ◽  
Residual Water ◽  
Laboratory Measurements ◽  
Elastic Parameters ◽  
Sandstone Sample ◽  
Confining Pressures ◽  
The Difference ◽  
Set Up

This extended abstract presents the results of the first low-frequency experiments conducted on a sandstone sample (Donnybrook, WA) flooded with supercritical CO2 (scCO2). The experiments investigated the effects of scCO2 injection on the elastic and anelastic properties of the rock. The sandstone sample (porosity—11.4%, permeability—0.28 mD) was cut in the direction orthogonal to a formation-bedding plane and tested in a Hoek's triaxial pressure cell equipped with the means for independent control of pore and confining pressures. The pore and confining pressures were set up at 10 and 31 MPa correspondingly. The low-frequency system and the pump comprising of scCO2 were held at a temperature of 42°C. Supercritical CO2 was injected into the sample preliminary saturated with distilled water. The amount of the residual water in the sample after the scCO2 injection was about 40% of pore volume. The elastic parameters obtained for the sample with scCO2 at frequencies from 0.1–100 Hz are very close to those for the dry sample. Some discrepancy in calculated acoustic velocities are caused by the difference in water and scCO2 densities. The measured extensional attenuation is larger when the sample is saturated with scCO2. The applicability of Gassmann's fluid substitution theory for the interpretation of obtained results was also tested during the experiments.

SOME RECENT ADVANCES IN OFFSHORE REGIONAL RECONNAISSANCE GEOPHYSICAL SURVEY METHODS

1967 ◽  
Vol 7 (1) ◽  
pp. 40
Author(s):  
K. R. Vale
Keyword(s):  
Phase Measurement ◽  
Survey Methods ◽  
Geophysical Methods ◽  
Low Frequency ◽  
Mineral Resources ◽  
Simultaneous Recording ◽  
Navigation Systems ◽  
Local Networks ◽  
Set Up ◽  
Geophysical Survey Methods

Traditional geophysical methods in use offshore include the airborne magnetometer, underwater gravity meter, and seismic reflection with 24-channel recording and large explosive energy source. Navigation is by range-range and hyperbolic phase-comparison radio systems set up as local networks. Other methods now being used include towed magnetometer, surface gravity meter, and automatic continuous seismic profilers, and all three methods can be used for simultaneous recording from a single recording boat. Navigation systems not requiring local networks include satellite radio doppler, very low frequency phase measurement and sonar doppler devices. These may be used word-wide and 24 hours per day. A single recording boat may thus be virtually self-sufficient. The Bureau of Mineral Resources plans a survey for 1967 that will use a number of these geophysical methods and navigation aids.

Effect on Water Leak of Tiled Roofs by Wind Flow Over Japanese Residence

2010 ◽  
Author(s):  
Satoru Okamoto
Keyword(s):  
Wind Tunnel ◽  
Low Frequency ◽  
Video Camera ◽  
Wind Flow ◽  
Leak Test ◽  
Low Velocity ◽  
Artificial Rainfall ◽  
Water Leak ◽  
Series Of Experiments ◽  
Set Up

This paper describes a water leak test of roof tiles. The 100 roof tiles were set up on 10 lines and 10 rows on the pitched roof in the downstream of the flow from the wind tunnel. The flow velocity was increased gradually from the low velocity to the high velocity, and the effects of the wind on the roof tiles were investigated by the water leak test. The situation of the water leak test was filmed by video camera. Two accelerometers were simultaneously used. The roof tiles which showed significant vibration at any velocity were found in a series of experiments and the accelerometers were attached to the two neighboring roof tiles on the model roof. The water leak phenomena in the experiment by using the artificial rainfall apparatus are discussed in this paper. Some mechanisms with relatively large amplitudes at low-frequency vibrations, which caused water leak phenomena were made clear.

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