Performance test results for the EG&amp;amp;G vector measuring current meter (VMCM)

Mero, T.

doi:10.1109/ccm.1982.1158439

Cited by 8 publications

(8 citation statements)

References 2 publications

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“…By that time a commerical source of self-contained 316 stainless steel bearings had been found, and these bearings were fitted to the hub assemblies of the EG&G VMCMs deployed in CODE 2 with only minor modification to the hub cap design. Tow tank tests conducted by Mero [1982] show that the steady flow calibration curves for the EG&G VMCM sensor sets (incorporating the CODE 1 design) were identical within experimental error to those reported by Weller and Davis [1980]. Since the new hub design does not change the external shape of the hub, we expect that the flow response of the SIO and EG&G propeller sensors in CODE I and CODE 2 should be identical.…”

Section: Vmcmmentioning

confidence: 59%

“…Steady tow tank experiments conducted by R. A. Weller (personal communication, 1985) and Mero [1982] confirm that the SIO and EG&G VMCMs have essentially identical steady flow characteristics and horizontal and vertical cosine responses. The primary deviations of both instruments from a perfect cosine response are due to flow distortion caused by the instrument support rods and electronics housing.…”

Section: In a Second Class Of Unsteady Laboratory Experiments Conductmentioning

confidence: 76%

“…The primary deviations of both instruments from a perfect cosine response are due to flow distortion caused by the instrument support rods and electronics housing. In a steady horizontal flow of magnitude 42 cm/s, Mero [1982] found that the wake of the leading support rod caused a 4% to 6% reduction of the measured velocity: this effect is less noticeable in a slower flow of 21 cm/s. For comparison, McCullough [1975] found that the support rods in the VACM in steady flows typically cause about a 5% variation in the rotor speed.…”

Section: In a Second Class Of Unsteady Laboratory Experiments Conductmentioning

confidence: 89%

“…The VACM has six support rods, so the measured speed is less sensitive to flow orientation. Mero [1982] also tested the EG&G VMCM in unsteady flows to study the response of the VMCM in simple wave conditions. The entire current meter was mounted on a mechanical device designed by Kalvaitis [1975] to produce simple harmonic circular motion in the vertical plane while towed at a steady velocity along the David Taylor Naval Ship Research and Development Center tow basin.…”

Section: In a Second Class Of Unsteady Laboratory Experiments Conductmentioning

confidence: 99%

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A comparison of the vector‐averaging current meter and new Edgerton, Germeshausen, and Grier, Inc., vector‐measuring current meter on a surface mooring in Coastal Ocean Dynamics Experiment 1

Beardsley¹

1987

J. Geophys. Res.

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An intercomparison experiment was conducted between a near-surface vector-averaging current meter (VACM) and an Edgei'ton, Germeshausen, and Grier, Inc., vector-measuring current meter (VMCM) at a midshelf mooring site (38ø32.8'N, 123ø22.6'W) located in 90 m of water off northern California between April and July 1981. The VACM and VMCM were deployed at 9 and 11 m, respectively, beneath a 1.5-m spherical surface buoy on a slack mooring. The VACM and VMCM 1-hr vector-averaged velocities were highly correlated with a complex correlation coefficient amplitude of 0.991, indicating the relative effectiveness of the internal vector-averaging sampling scheme of the VACM and the flow sensors of the VMCM to filter much of the wave-induced high-frequency currents and mooring motion. The vectoraveraged VACM speeds S a generally exceeded the VMCM speeds S,,, with a mean and maximum speed difference of 4 and 14 cm/s, respectively. Since the observed difference in vector-averaged speeds, AS -Sa -S,, was larger on average than an independent estimate of the true shear by a factor of 4 to 5, most of the difference in the observed VACM and VMCM vector-averaged speeds has been attributed to instrumental error. The surface wave climate was measured nearby over the shelf during part of the experiment, and a significant correlation was found between estimates of the rms horizontal velocity and rms difference vertical velocity on the basis of the observed wave data and a VACM-derived rms wave speed W, defined as (R 2 --Sa2) 1/2, where R is the hourly averaged VACM rotor speed. This result allows the fractional vector-averaged speed difference AS/S m to be determined experimentally from the field data as a function of S,W, a signal-to-noise parameter expressing the ratio of the observed VMCM vectoraveraged speed to the VACM-derived rms wave speed W. Although significant scatter occurs between simultaneous 1-hr vector-averaged VACM and VMCM speeds, the average fractional speed difference AS/Sm decreases from about 0.57 ___ 0.10 (at 95% confidence) at Sr,/W = 0.15 to about 0.20 at S,v/W = 1 and remains approximately constant at 0.16 ___ 0.02 for S,v/W between about 1.5 and 2.0. Thus the fractional speed difference observed in the field is a relatively well-defined function of the relative magnitudes of the mean horizontal and wave-associated flow components. Comparison of these field measurements with published laboratory data on the performance of the VACM and VMCM in unsteady flow suggests that the field and laboratory measurements are consistent and can be used to estimate the absolute fractional speed error of each current meter as a function of u/w, where u is the true mean horizontal vector speed and w the amplitude of the rms wave-induced oscillatory velocity. The combined laboratory and Coastal Ocean Dynamics Experiment 1 field data thus indicate that in an absolute sense the VACM overresponds by about 18-20% at u/w = 0.5 to about 10-11% at u/w = 2.0, while the VMCM underresponds by about -5 to -6% for u/w between 0.5 to 2.0. The...

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Section: Vmcmmentioning

confidence: 59%

Section: In a Second Class Of Unsteady Laboratory Experiments Conductmentioning

confidence: 76%

Section: In a Second Class Of Unsteady Laboratory Experiments Conductmentioning

confidence: 89%

Section: In a Second Class Of Unsteady Laboratory Experiments Conductmentioning

confidence: 99%

See 2 more Smart Citations

A comparison of the vector‐averaging current meter and new Edgerton, Germeshausen, and Grier, Inc., vector‐measuring current meter on a surface mooring in Coastal Ocean Dynamics Experiment 1

Beardsley¹

1987

J. Geophys. Res.

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“…The VACM is specifically designed to measure currents even when oscillatory currents from large surface waves are present. A detailed description of the design and measurement characteristics is provided by McCullough, 1975, Mero, 1982and Beardsleyetal., 1987. The meter measured the average current direction and speed every 15 minutes.…”

Section: Instrumentationmentioning

confidence: 99%

The Monterey Submarine Canyon, California moored array data report

Kinoshita¹,

Noble²

1995

Open-File Report

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Observations of small eddies in the Beaufort Sea

D’Asaro¹

1988

J. Geophys. Res.

133

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The horizontal and vertical variations of velocity, temperature, density, and turbulent kinetic energy dissipation in the central Beaufort Sea were measured with helicopter‐borne expendable current profilers and conductivity‐temperature‐depth units. Almost all velocity differences larger than 0.05 m s−1 could be consistently interpreted as being due to nearly circular eddies with a diameter of 10–20km, a thickness of 50–500 m, peak velocities of 0.07–0.3 m s−1, and little expression at the top of the ocean. Four such eddies were found. Two anticyclones were found and accurately sampled. Two cyclones were found but were only poorly sampled; both were beneath and close to one of the anticyclones. Relative vorticity could be computed for two anticyclones and one cyclone. Within experimental error, the two anticyclones, and all historical Beaufort Sea anticyclones, had a relative vorticity of −ƒ and thus zero potential vorticity at the center. The cyclone had a central relative vorticity of about 0.5ƒ and thus a different value of potential vorticity than the surrounding fluid. One anticyclonic eddy (B) was sampled seven times over a period of 23 days. Its measured velocity and density fields were in approximate gradient wind balance. Its central core contained values of temperature, nitrate, and silicate that were different from those outside the core at the same density. It moved eastward at about 0.02 m s−1 through the surrounding fluid. Measurements of turbulent kinetic energy dissipation were almost always less than the noise level of the instrument (about 10−9 W kg−1), corresponding to a mean dissipation much less than this and a minimum decay time due to turbulence much longer than 0.3 year. The nondimensional strength (Rossby number) and shape (Burger number) of anticylcone B are very similar to those of other Beaufort Sea anticyclones and similar to those of small mid‐latitude eddies. Each of the eddies observed here was centered on a temperature maximum associated with one of the warm water masses that advect into the Arctic Ocean. The two anticyclones were centered on temperature maxima originating in the Pacific Ocean, whereas the two cyclones were centered on temperature maxima from the Atlantic Ocean. This is consistent with the hypothesis that the eddies are formed as these water masses enter the Arctic Ocean.

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Performance test results for the EG&G vector measuring current meter (VMCM)

Cited by 8 publications

References 2 publications

A comparison of the vector‐averaging current meter and new Edgerton, Germeshausen, and Grier, Inc., vector‐measuring current meter on a surface mooring in Coastal Ocean Dynamics Experiment 1

A comparison of the vector‐averaging current meter and new Edgerton, Germeshausen, and Grier, Inc., vector‐measuring current meter on a surface mooring in Coastal Ocean Dynamics Experiment 1

The Monterey Submarine Canyon, California moored array data report

Observations of small eddies in the Beaufort Sea

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