Recording Current Meter

At the Kap Arkona position (KA in Fig. 6.1), the BSH was running a waverider buoy for several years. The position with a water depth of 40 m is situated at the southern border of the Arkona basin about 10 miles east of northern Riigen. Two current meter moorings were deployed at this position During fall 2003, a RCMS recorded the current at 10 m depth for 75 days (Table 6.15). The averaged vector speed was very weak and the stability factor amounted to 8% only. During the observation period, the local winds were mostly from westerly directions. They were interrupted by northerly winds and more often by southeasterly winds. 

Surface sediment samples were collected from Loch Sunart, a sea loch (fjord) on the NW coast of Scotland, during cruises aboard the R. V. Clupea (April 1999) and the R. V. Envoy (July 2001 and June 2002). Bottom water temperature and salinity measurements were recorded using a STD Plus 646 conductivity, temperature and depth (CTD) probe at each sample site (Table 1). No data were collected on pH and carbonate ion concentration. Two stationary Anderaa RCM-7 current meters complete with temperature and conductivity sensors and a data logger were deployed in the inner basin (56.6842°N, -5.6211°W) between 21 June 2001 and the 18 June 2002, and the main... 

Fig. iO. Velocity vectors recorded for successive 20-min time intervals by a current meter 2 m above the bottom near the geometrical center of Long Island Sound. The rotary character of the tide and the net drift of bottom water due to the estuarine circulation are shown. 

Fig. I. Map of Long Island and Block Island Sounds showing the locationsof tide gauges,anemometers,and current meters. The tide gauges were at New London (NL), New Haven (NH), Bridgeport (Bpt), Port Jefferson (PJ), New Rochelle (NR), Montauk (M), and Sandy Hook (SH). Newport (Np) is 67 km east of NL and not shown on the map. Current meters were operated at locations J, D, S, X, and Y a water level recorder was also operated at J. Stratford Point is St. Anemometer locations are shown by open circles. Power calculations are done for the section between A and B. 

The power-crossing section A-B during the storm can be evaluated from the current meter records from locations D and S and tide gauge data, but the quality of the data is not as high as that shown in Fig. 2 for two reasons. First, mechanical clocks were used in the current meters and interpolated corrections for their rates are required. Second, the available water level data are from a tide gauge within New Haven Harbor (rather than one at a current meter site), and a correction for the phase and amplitude difference of the tide between this location and that of the current meters is required. The tide height was corrected by a factor of... 

Certain additional measurements are clearly needed in the Sound. An array of current meters and water level recorders should be operated on a cross section so that the lateral variation of the power flux can be reliably determined. Longer data runs for h and v are needed to adequately define the mean tidal dissipation. Simultaneous measurements of sediment resuspension and transport and of the tidal dissipation could be used to test the hypothesized interrelation between these quantities. 

Currents in the Sound are due to the tidal stream, to the estuarine circulation, and to wind stress acting on the water surface. Systematic surveys of the currents in the Sound have been made from time to time by the U.S. National Ocean Survey. Current meters have been placed in grid-pattern arrays for time intervals sufficiently long to reveal the principal tidal constituents of the current. Data obtained this way were used by G. A. Riley (1952, 1956) to describe the estuarine circulation of the Sound. The utility of these meter records in the study of sediment transport is limited because the observations were all made during the... 

We have previously reported that, although most storms do not alter the bottom-water resultant flow vectors, the probability of large water speeds over the bottom is increased (Bokuniewicz et ai, 1975b) when the wind stress is high. We now present further evidence on this effect. A periodogram calculated for a current meter record obtained in the western end of Long Island Sound is presented in Fig. 6. Three tidal peaks are... 

Fig 6. Periodogram calculated from a current meter record made in western Long Island Sound (7.4 km north of Eatons Neck) showing the dominant semidiurnal tide and two shallow water constituents (CPH, cycles/hr). 

In an early study of oceanic bottom water flow within the C-C F.Z., Johnson (1972) deployed free-fall bottom current meters in an area north of the Clipperton Fracture Zone where substantial sediment erosion was known to occur. The limited data showed that the bottom currents were generally slow (<10 cm see ) but fluctuated markedly due to a strong semi-diurnal tidal component. It was also established that the currents flowed mainly to the east with minor variations due to topographic effects. In addition, data from a 14-day record of bottom current measurements taken at 210 m above the sea floor revealed an averge bottom water flow of 2.0 cm sec in an ENE direction with peak velocities of up to 16.5 cm sec at semidiurnal periods. These data showed that peak velocities of bottom water transport were strong enough to erode and transport sediment in the area (Amos et al. 1977). 

Fio. 2. Experimental arrangement for measuring/< in semi-insulating materials. The sample is located in a Dewar between the magnet poles. E, vibrating reed electrometer R, recorder and digital data processor F, feedback-driven shields P, potential probes M, current meter. 

Ellis, G.H. (1920). Car for current-meter gaging stations. Engineering News-Record 84(2) 80. Ellis, G.H. (1920). Hydraulics of the intake to a pipe drop. Engineering News-Record 85(12) 565. 

Fortier, S., Hoff, E.J. (1920). Defects in current meters and a new design. Engineering News-Record 5 20y. 923-924. 

Current meters are hydrodynamic instruments with rotating vanes or buckets. The speed of their rotation is proportional to the flow velocity. The forerunners of current meters were the paddle wheels developed in the early 18 century. These were applied by Francesco Domenico Michelotti (1710-1777) in 1767, or by Pierre-Louis Du Buat (1734-1809) in 1786. There are two principal types of current meters, namely the screw and the cup types. The first was conceived by the famous British engineer Robert Hooke in 1783 to measure wind velocity with four vanes similar to a windmill. This type was developed by Reinhard Woltman (1757-1837) in 1790, Andre Baumgarten (1808-1859), Albert Ott (1847-1895), Alphonse Fteley (1837-1903) and Haskell, among many others. The other type meter has several cups on spokes rotating around an axis oriented transverse to the current. These anemometers were first applied around 1850 to measure wind velocities, and then were developed by Theodore Gunville Ellis (1829-1883), or William G. Price (1853-1928) to record flow velocity in rivers. 

Anonymous (1921). Dean Haskell s retirement. Cornell Civil Engineer 29(6) 109. P Anonymous (1924). Dean E.E. Haskell. Engineering News-Record 93(24) 847. P Anonymous (1925). Haskell, Eugene Elwin. Who s who in America 13 1488. Marquis Chicago. Haskell, E.E. (1902). Current meter and weir discharges. Trans. ASCE 47 387-389. 

Figures 3.2 and 3.3. It is essential that a high-input-impedance voltmeter, such as an electronic instrument with 11 Mfi input impedance, be used. If a low-input-impedance instrument is used, part of the recorded current will be that drawn by the voltmeter and not the cell current. Depending upon the cell configuration, either a milliammeter or microammeter is used to measure current These meters have high internal resistances, and this produces a voltage drop across the meter when current exists. This is the reason it is necessary to monitor the voltage directly across the cell.

A current meter and camera were placed at 710 m depth on the bottom of the eastern Florida Straits to record interaction of sea-floor sediment with overlying current flow... 

Linear polarization instruments provide an instantaneous corrosion-rate data, by utilizing polarization phenomena. These instruments are commercially available as two-electrode Corrater and three electrode Pairmeter (Figure 4-472). The instruments are portable, with probes that can be utilized at several locations in the drilling fluid circulatory systems. In both Corrater and Pairmeter, the technique involves monitoring electrical potential of one of the electrodes with respect to one of the other electrodes as a small electrical current is applied. The amount of applied current necessary to change potential (no more than 10 to 20 mV) is proportional to corrosion intensity. The electronic meter converts the amount of current to read out a number that represents the corrosion rate in mpy. Before recording the data, sufficient time should be allowed for the electrodes to reach equilibrium with the environment. The corrosion-rate reading obtained by these instruments is due to corrosion of the probe element at that instant [184]. 

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