Shear Probes Research Articles

A Dynamic Flight Model for Slocum Gliders and Implications for Turbulence Microstructure Measurements

Abstract The turbulent dissipation rate ε is a key parameter to many oceanographic processes. Recently, gliders have been increasingly used as a carrier for microstructure sensors. Compared to conventional ship-based methods, glider-based microstructure observations allow for long-duration measurements under adverse weather conditions and at lower costs. The incident water velocity U is an input parameter for the calculation of the dissipation rate. Since U cannot be measured using the standard glider sensor setup, the parameter is normally computed from a steady-state glider flight model. As ε scales with U2 or U4, depending on whether it is computed from temperature or shear microstructure, respectively, flight model errors can introduce a significant bias. This study is the first to use measurements of in situ glider flight, obtained with a profiling Doppler velocity log and an electromagnetic current meter, to test and calibrate a flight model, extended to include inertial terms. Compared to a previously suggested flight model, the calibrated model removes a bias of approximately 1 cm s−1 in the incident water velocity, which translates to roughly a factor of 1.2 in estimates of the dissipation rate. The results further indicate that 90% of the estimates of the dissipation rate from the calibrated model are within a factor of 1.1 and 1.2 for measurements derived from microstructure temperature sensors and shear probes, respectively. We further outline the range of applicability of the flight model.

Subclavian artery, subclavian vein, anterior scalene muscle, middle scalene muscle, and first rib were separated using endoscopic graspers and a hook-type electrocautery probe (or ultrasonic shear probe) under the traction of the first rib

Subclavian artery, subclavian vein, anterior scalene muscle, middle scalene muscle, and first rib were separated using endoscopic graspers and a hook-type electrocautery probe (or ultrasonic shear probe) under the traction of the first rib

The parietal pleura of the first rib was opened using a 5-mm endoscopic grasper and either a hook-type electrocautery probe or an ultrasonic shear probe

The parietal pleura of the first rib was opened using a 5-mm endoscopic grasper and either a hook-type electrocautery probe or an ultrasonic shear probe

Effects of Lateral Deformation by Thermoresponsive Polymer Brushes on the Measured Friction Forces.

The nanotribological properties of hydrophilic polymer brushes are conveniently analyzed by lateral force microscopy (LFM). However, the measurement of friction for highly swollen and relatively thick polymer brushes can be strongly affected by the tendency of the compliant brush to be laterally deformed by the shearing probe. This phenomenon induces a "tilting" in the recorded friction loops, which is generated by the lateral bending and stretching of the grafts. In this study we highlight how the brush lateral deformation mainly affects the friction measurements of swollen PNIPAM brushes (below LCST) when relatively short scanning distances are applied. Under these conditions, the energy dissipation recorded by LFM is almost uniquely determined by stretching and bending of the compliant brush back and forth along the scanning direction, and it is not correlated to dynamic friction between two sliding surfaces. In contrast, when the scanning distance applied during LFM is relevantly longer than the brush lateral deformation, sliding of the probe on the brush interface becomes dominant, and a correct measurement of dynamic friction can be accomplished. By increasing the temperature above the LCST, the PNIPAM brushes undergo dehydration and assume a collapsed morphology, thereby hindering their lateral deformation by scanning probe. Hence, at 40 °C in water the recorded friction loops do not show any tilting and LFM accurately describes the dynamic friction between the probe and the polymer surface.

Inverse Sub-structuring Method for Multi-coordinate Rigidly Coupled Product Transport System based on a Novel Shearing Probe Technique

The inverse sub-structuring method can predict the component-level frequency response functions (FRFs) of product (critical component) for product transport system from only measured system-level FRFs, facilitating the cushioning packaging design. However, the FRFs of the coupling interface between product and vehicle are usually of extreme difficulty to be measured due to the limited accessible space. To overcome this difficulty, the authors suggested a so-called FRF probe technique method in the previous study, which may be more suitable for the single-coordinate coupled system. In practice, most of the product transport systems should be treated as multi-coordinate coupled system. The aim of this paper is to derive a new FRF-based inverse sub-structuring method for multi-coordinate rigidly coupled product transport system and develop a new shearing probe technique to obtain the difficult-to-monitor FRFs at the coupling interface, which will be validated by a lumped mass model and finite element models, respectively, showing perfect agreement. Finally, the experiment on a physical prototype of multi-coordinate rigidly coupled product transport system is performed to further check the feasibility of the application prospect of the shearing probe technique for inverse analysis of product transport system. The method proposed in this study will provide the packaging designers an alternative method to monitor the integrity of product transport system. Copyright © 2017 John Wiley & Sons, Ltd.

An Expendable Microstructure Profiler for Deep Ocean Measurements

AbstractMeasurements of turbulence in the deep ocean, particularly close to the bottom, are extremely sparse because of the difficulty and operational risk of obtaining deep profiles near the seafloor. A newly developed expendable instrument—the VMP-X (Vertical Microstructure Profiler–Expendable)—carries two microstructure shear probes to measure the fluctuations of vertical shear into the dissipation range and can profile down to a depth of 6000 m. Data from nine VMP-X profiles in the western Pacific Ocean near 11.6°N over rough topography display bottom-intensified turbulence with dissipation rates increasing by two factors of 10 to 4 W kg−1 within 200 m above the bottom. In contrast, over smooth topography in the southern South China Sea near 11°N, three profiles show that turbulence in the bottom boundary layer increases only slightly, with dissipation rates reaching 1 W kg−1. The eddy diffusivity over rough topography reached to 5 m2 s−1. The average diffusivity over all depths was 0.3 and 0.9 m2 s−1 for the tests in the southern South China Sea and in the western Pacific Ocean, respectively, and these values are much larger than previous estimates of less than ≈0.1 m2 s−1 for the main thermocline.

Spectral and Structure Function Estimates of Turbulence Dissipation Rates in a High-Flow Tidal Channel Using Broadband ADCPs

AbstractSpectral and structure function methods are implemented to compute the dissipation rate ε from broadband, diverging-beam acoustic Doppler current profiler (ADCP) data collected at four sites in a high-flow tidal channel. This paper shows that middepth estimates of ε obtained from spectral and second-order structure function (SF2) methods are both lognormally distributed with comparable means and variances. Speed bin–averaged ε values agree to within 16%, depending on the site and tidal phase (ebb/flood). The close agreement between the two independent methods provides further support for the argument put forward by McMillan et al.: that is, that the factor-of-2 difference between shear probe and (spectral) ADCP estimates of ε was likely caused by spatial differences in turbulence levels. The agreement between the spectral and both second- and third-order structure function methods also supports the use of for the SF2 universal constant. Notably, however, the SF3 method was less robust for these data. Two additional aspects of the SF2 approach are examined in some detail: 1) the differences from upstream- and downstream-facing beams are shown to arise from the Reynolds stress and 2) the inability of the ADCP to resolve small-scale motions does not affect the estimates of ε but yields apparent Doppler noise levels that—counterintuitively—decrease with increasing flow speed and increasing dissipation rate. A modified SF2 method that accounts for the variance associated with the unresolved scales removes the flow speed dependence and yields noise level estimates that agree with the spectral values.

Turbulence Estimation Using Fast-Response Thermistors Attached to a Free-Fall Vertical Microstructure Profiler

AbstractEstimation of turbulence intensity with a fast-response thermistor is examined by comparing the energy dissipation rate from a Fastip Probe, model 07 (FP07), thermistor with from a shear probe, both of which are attached to a free-fall microstructure profiler with the fall rate of 0.6–0.7 m s−1. Temperature gradient spectra corrected with previously introduced frequency response functions represented by a single-pole low-pass filter yields with a bias that strongly depends on turbulence intensity. Meanwhile, the correction with the form of a double-pole low-pass filter derives less bias than of single-pole low-pass filter. The rate is compatible with when the double-pole correction with the time constant of 3 × 10−3 s is applied, and 68% of data are within a factor of 2.8 of in the wide range of = 10−10–3 × 10−7 W kg−1. The rate is still compatible with even in the anisotropy range, where the buoyancy Reynolds number is 20–100. Turbulence estimation from the fast-response thermistor is thus confirmed to be valid in this range by applying the appropriate correction to temperature gradient spectra. Measurements with fast-response thermistors, which have not been common because of their poor frequency response, are less sensitive to the vibration of profilers than those with shear probes. Hence, measurements could be available when a fast-response thermistor is attached to a CTD frame or a float, which extends the possibility of obtaining much more turbulence data in deep and wide oceans.

Rates of Dissipation of Turbulent Kinetic Energy in a High Reynolds Number Tidal Channel

AbstractThe ability to estimate the rate of dissipation (ε) of turbulent kinetic energy at middepth in a high-speed tidal channel using broadband acoustic Doppler current profilers (ADCPs) is assessed by making comparisons to direct measurements of ε obtained using shear probes mounted on a streamlined underwater buoy. The investigation was carried out in Grand Passage, Nova Scotia, Canada, where the depth-averaged flow speed reached 2 m s−1 and the Reynolds number was 8 × 107. The speed bin–averaged dissipation rates estimated from the ADCP data agree with the shear probe data to within a factor of 2. Both the ADCP and the shear probe measurements indicate a linear dependence of ε on the cube of the flow speed during flood and much lower dissipation rates during ebb. The ebb–flood asymmetry and the small-scale intermittency in ε are also apparent in the lognormal distributions of the shear probe data. Possible sources of bias and error in the ε estimates are investigated, and the most likely causes of the discrepancy between the ADCP and shear probe estimates are the cross-channel separation of the instruments and the high degree of spatial variability that exists in the channel.

Characteristics of Microstructure Turbulence Measurements With a Moored Instrument in the South China Sea

AbstractA newly designed autonomous instrument was evaluated for long-term ocean turbulence measurements in the South China Sea from October 19, 2013, to February 10, 2014 at 21°09.90′N, 117°42.03′E. A shear velocity time series was collected continuously for 115 days at a single depth of 250 m using two orthogonal shear probes (PNS06). The mechanical design of wings is developed for an observation platform to achieve characteristics of stability and flexibility of current direction tracking. The depth and pitch in comparison with ambient current speed are analyzed, and the results indicate that the platform has satisfied stability requirements for turbulence measurement. The comparison between the instrument heading and current direction shows that the instrument flexibly responds to variations of ambient currents. Throughout the observation period, 62% of the data sets is of significant correlation with correlation coefficients above 0.5, and 4% is of strong correlation. The shear velocity spectra correspond well to the theoretical Nasmyth spectrum, and the magnitude of dissipation rates estimated from shear is approximately Ο(10−8) W kg−1. The moored instrument is functional as designed and provides a reliable observation platform for extended turbulent measurements.

Longitudinal spread of mechanical excitation through tectorial membrane traveling waves

The mammalian inner ear separates sounds by their frequency content, and this separation underlies important properties of human hearing, including our ability to understand speech in noisy environments. Studies of genetic disorders of hearing have demonstrated a link between frequency selectivity and wave properties of the tectorial membrane (TM). To understand these wave properties better, we developed chemical manipulations that systematically and reversibly alter TM stiffness and viscosity. Using microfabricated shear probes, we show that (i) reducing pH reduces TM stiffness with little change in TM viscosity and (ii) adding PEG increases TM viscosity with little change in TM stiffness. By applying these manipulations in measurements of TM waves, we show that TM wave speed is determined primarily by stiffness at low frequencies and by viscosity at high frequencies. Both TM viscosity and stiffness affect the longitudinal spread of mechanical excitation through the TM over a broad range of frequencies. Increasing TM viscosity or decreasing stiffness reduces longitudinal spread of mechanical excitation, thereby coupling a smaller range of best frequencies and sharpening tuning. In contrast, increasing viscous loss or decreasing stiffness would tend to broaden tuning in resonance-based TM models. Thus, TM wave and resonance mechanisms are fundamentally different in the way they control frequency selectivity.

Effect of Chemically Adsorbed Molecules on the Viscous Friction of Nanometer-Thick Liquid Lubricant Films Coated on a Diamond-Like Carbon Surface

Nanometer-thick liquid lubricant films are used for lubrication of miniaturized mechanical systems such as hard disk drives and microelectromechanical systems. In particular at the head–disk interface of hard disk drives, the lubricant thin film is coated on a diamond-like carbon surface, and the films are usually composed of both chemically and physically adsorbed lubricant molecules. The combination of these two types of molecules leads to high lubrication performance. However, the detailed mechanism is not fully understood. The aim of this study was to clarify the effect of chemically adsorbed lubricant molecules on the viscous friction of lubricant films. Two different samples were tested: One was the lubricant film composed of both chemically and physically adsorbed molecules, and the other was the lubricant film with only physically adsorbed molecules. We used a fiber wobbling method (FWM), which we developed in our previous study, to measure the viscous friction. The FWM uses a spherical-ended glass fiber as a shearing probe and enables friction forces in the order of 0.1 nN to be measured at precisely controlled nanometer-scale gap widths. For the fair comparison of friction forces between the samples with different compositions, the contact area between the probe tip and the lubricant film must be the same. To determine the contact area in the friction measurement, we improved the FWM system to enable simultaneous measurement of friction force and contact area. Experimental results showed the 1-nm-thick layer of chemically adsorbed molecules in the lubricant film effectively reduced the viscous friction.

Modeling of turbulent dissipation and its validation in periodically stratified region in the Liverpool Bay and in the North Sea

The present work explores the applicability of an alternative eddy viscosity formulation in numerical models dealing with the dynamics of the coastal ocean. The formulation is based on the Reynolds stress anisotropy–anisotropy being an important tool for capturing turbulent mixing. Initially idealized entrainment scenarios are evaluated that are typical for shelf seas viz. entrainment in linearly stratified and two-layer fluids caused by surface wind stress or barotropic pressure gradient-driven bottom stress. An attempt is made to simulate the realistic semi-diurnal cycle of turbulent dissipation in Liverpool Bay Region of Freshwater Inflow (ROFI) in the Irish Sea characterized by strong horizontal gradients and interactions with tidal flow. Turbulent dissipation cycles with a 25-h period using free-falling light yo-yo (FLY) dissipation profiler exhibits a strong asymmetry between ebb and flood. The above dynamics involving tidal straining during the ebb and mixing during the flood has been simulated using k– $$ \varepsilon $$ and the alternative formulated turbulence scheme in a one-dimensional (1-D) dynamic model. The model is forced with observed tidal flow and horizontal gradients of temperature and salinity. Simulated dissipation cycles show good agreement with observation. The present work also involves a comparison of dissipation rate measurements in northern North Sea using the abovementioned turbulence schemes—the measurements being taken using free-falling shear probes and CTD (conductivity, temperature, and depth) sensors. The main forcing provided for the upper and bottom boundary layers are atmospheric forcing and tides, respectively. To compare the observations and model results, quantitative error measurements have also been studied which reveal the applicability of the alternative turbulence scheme.

Observations of Turbulence Caused by a Combination of Tides and Mean Baroclinic Flow over a Fjord Sill

AbstractThis study investigates the dissipation rates and flow conditions at the Drøbak Sill in the Oslofjord. The area was transected 13 times with a free-falling microstructure shear probe during 4 days in June 2011. At the same time, an ADCP was deployed inside the sill. During most tidal cycles, internal hydraulic jumps with high dissipation rates were found on the downstream side of the sill. However, the internal response varied strongly between different tidal cycles with similar barotropic forcing. In the beginning of the observational period, ebb tides had no hydraulic jumps, and in the end one of the flood tides did not have a hydraulic jump. During the same period, the mean baroclinic exchange flow changed from inflow to outflow in the bottom layer. The authors conclude that the conditions at the sill are on the edge of forming hydraulic jumps and that the mean baroclinic exchange may push the flow above or below the limit of a hydraulic jump depending on the situation. This conclusion is supported by two-layer hydraulic theory. The volume-integrated dissipation rates within 500 m from the sill crest compare well with estimates of energy loss in the lower layer calculated from the Bernoulli drop under the assumption of no energy loss in the upper layer. Finally, the mean dissipation rate at the sill was compared with the radiation of internal tidal energy away from the sill, and it was found that about 60%–90% of the total energy loss was dissipated locally.

Structure Optimal Design and Performance Test of Airfoil Shear Probes

Airfoil shear probes are instruments used to measure the turbulent kinetic energy dissipation rate in the ocean. The cantilever beams and piezoelectric ceramics sheets are core components of shear probes. The former is the force transferring unit that amplifies the shear force acting on the probe tip. The latter is the piezoelectric transduction element that transforms force to electrical charges. As obbligato components for shear velocity measurement, both the cantilever beam and piezoelectric ceramics sheet have significant influence on the performances of the sensor. Optimizing the dimensions of the cantilever beam and the piezoelectric ceramics sheet could improve the measuring performance of the shear probe, such as sensitivity and resonance frequency. In this paper, multiobjective optimization algorithm is used to obtain the main design parameters of the shear probe with appropriate sensitivity and resonance frequency. Serial tests are conducted including the tap test and the calibration test to examine the resonance frequency in wet mode, and analyze the sensitivity of the probe, respectively. Soon afterward, the sea trials were carried out in the Western Pacific Ocean. The power spectrum from shear velocity data shows a good agreement with the Nasmyth spectrum. The experiments also testify the validity of the optimal design method of the shear probe.

The Air–Sea Interaction Profiler (ASIP): An Autonomous Upwardly Rising Profiler for Microstructure Measurements in the Upper Ocean

Abstract The upper few meters of the ocean form a critical layer for air–sea interaction, but because of observational challenges this region is undersampled. However, the physical processes controlling momentum transfer, gas exchange, and heat transfer are all concentrated in the uppermost region of the ocean. To study this region, the Air–Sea Interaction Profiler (ASIP) was developed. This is an autonomous microstructure vertical profiling instrument that provides data from a maximum depth of 100 m to the ocean surface and allows measurements to be performed in an undisturbed environment. The core sensor package on ASIP includes shear probes, microstructure and CTD-quality temperature and conductivity sensors, a photosynthetically active radiation (PAR) sensor, and an oxygen optode providing a repeated high-resolution dataset immediately below the air–sea interface. Autonomous profiling is accomplished with thrusters that submerge the positively buoyant instrument. Once the desired depth is reached, ASIP ascends through the water column acquiring data. At the surface, ASIP acquires its position and transmits this over the Iridium satellite network. ASIP is then placed in a low-power mode for a specified period, whereupon it repeats the profile cycle. Two-way communication over the Iridium network allows mission parameters to be changed in real time. ASIP has been used to study several scientific questions, such as the impact of diurnal warming on atmospheric processes, turbulence scaling in the upper ocean, parameterizing air–sea gas exchange, salinity gradients in the ocean surface boundary layer (OSBL), and consequences for remote sensing.

Measuring Turbulent Dissipation Using a Tethered ADCP

Abstract The structure function method for estimating the dissipation rate of turbulent kinetic energy, previously validated for measurements from seabed fixed mounts, is applied to data from 1.2-MHz acoustic Doppler current profiler (ADCP) instruments operating in pulse–pulse coherent mode and mounted in midwater below a tethered buoy. Movements of the buoy introduce additional relative velocity components, but it is hypothesized that these flow components should not seriously interfere with the turbulence information because (i) horizontal or vertical translation induces the same flow component in all cells of an ADCP beam and (ii) any rotation of the instrument about its center induces flow components that are normal to the beam direction, and thus neither affect the structure function. This hypothesis is tested by comparing a series of dissipation measurements from a moored ADCP with those from a free-falling Vertical Microstructure Profiler (VMP) shear probe deployed from a nearby research vessel. The results indicate generally good conformity in both mean and variability over almost two decades of dissipation rates. The noise level of the structure function estimates with the pulse–pulse coherent ADCP is close to that of the VMP at ~3 × 10−10 W kg−1. This approach offers the prospect of long time series measurements of dissipation rate from moorings, albeit with restricted vertical range of a few meters.

Dissipation measurements using temperature microstructure from an underwater glider

Microstructure measurements of temperature and current shear are made using an autonomous underwater glider. The glider is equipped with fast-response thermistors and airfoil shear probes, providing measurements of dissipation rate of temperature variance, χ, and of turbulent kinetic energy, ε, respectively. Furthermore, by fitting the temperature gradient variance spectra to a theoretical model, an independent measurement of ε is obtained. Both Batchelor (εB) and Kraichnan (εK) theoretical forms are used. Shear probe measurements are reported elsewhere; here, the thermistor-derived εB and εK are compared to the shear probe results, demonstrating the possibility of dissipation measurements using gliders equipped with thermistors only. A total of 152 dive and climb profiles are used, collected during a one-week mission in the Faroe Bank Channel, sampling the turbulent dense overflow plume and the ambient water above. Measurement of ε with thermistors using a glider requires careful consideration of data quality. Data are screened for glider flight properties, measurement noise, and the quality of fits to the theoretical models. Resulting dissipation rates from the two independent methods compare well for dissipation rates below 2×10−7 W kg−1. For more energetic turbulence, thermistors underestimate dissipation rates significantly, caused primarily by increased uncertainty in the time response correction. Batchelor and Kraichnan spectral models give very similar results. Concurrent measurements of ε and χ are used to compute the dissipation flux coefficient Γ (or so-called apparent mixing efficiency). A wide range of values is found, with a mode value of Γ≈0.14, in agreement with previous studies. Gliders prove to be suitable platforms for ocean microstructure measurements, complementary to existing methods.

Microstructure Measurements from an Underwater Glider in the Turbulent Faroe Bank Channel Overflow

AbstractMeasurements of ocean microstructure are made in the turbulent Faroe Bank Channel overflow using a turbulence instrument attached to an underwater glider. Dissipation rate of turbulent kinetic energy ε is measured using airfoil shear probes. A comparison is made between 152 profiles from dive and climb cycles of the glider during a 1-week mission in June 2012 and 90 profiles collected from the ship using a vertical microstructure profiler (VMP). Approximately one-half of the profiles are collocated. For 96% of the dataset, measurements are of high quality with no systematic differences between dives and climbs. The noise level is less than 5 × 10−11 W kg−1, comparable to the best microstructure profilers. The shear probe data are contaminated and unreliable at the turning depth of the glider and for U/ut < 20, where U is the flow past the sensor, ut = (ε/N)1/2 is an estimate of the turbulent velocity scale, and N is the buoyancy frequency. Averaged profiles of ε from the VMP and the glider agree to better than a factor of 2 in the turbulent bottom layer of the overflow plume, and beneath the stratified and sheared plume–ambient interface. The glider average values are approximately a factor of 3 and 9 times larger than the VMP values in the layers defined by the isotherms 3°–6° and 6°–9°C, respectively, corresponding to the upper part of the interface and above. The discrepancy is attributed to a different sampling scheme and the intermittency of turbulence. The glider offers a noise-free platform suitable for ocean microstructure measurements.

Turbulence structure in the upper ocean: a comparative study of observations and modeling

Observations of turbulent dissipation rates measured by two independent instruments are compared with numerical model runs to investigate the injection of turbulence generated by sea surface gravity waves. The near-surface observations are made by a moored autonomous instrument, fixed at approximately 8 m below the sea surface. The instrument is equipped with shear probes, a high-resolution pressure sensor, and an inertial motion package to measure time series of dissipation rate and nondirectional surface wave energy spectrum. A free-falling profiler is used additionally to collect vertical microstructure profiles in the upper ocean. For the model simulations, we use a one-dimensional mixed layer model based on a k–ε type second moment turbulence closure, which is modified to include the effects of wave breaking and Langmuir cells. The dissipation rates obtained using the modified k–ε model are elevated near the sea surface and in the upper water column, consistent with the measurements, mainly as a result of wave breaking at the surface, and energy drawn from wave field to the mean flow by Stokes drift. The agreement between observed and simulated turbulent quantities is fairly good, especially when the Stokes production is taken into account.