scholarly journals An ultra-thin boundary layer for high-accuracy simulations of light propagation

2020 ◽  
Author(s):  
Gerwin Osnabrugge ◽  
Maaike Benedictus ◽  
Ivo Vellekoop
Keyword(s):  
Boundary Layer ◽  
Light Propagation ◽  
High Accuracy ◽  
Thin Boundary Layer

Two months of measurements with an autonomous thermodynamic Raman lidar in Lindenberg

2021 ◽  
Author(s):  
Diego Lange Vega ◽  
Andreas Behrendt ◽  
Volker Wulfmeyer
Keyword(s):  
Boundary Layer ◽  
Water Vapor ◽  
Inversion Layer ◽  
Measurement Range ◽  
High Accuracy ◽  
Free Troposphere ◽  
Raman Lidar ◽  
Backscatter Coefficient ◽  
Geophysical Research ◽  
Turbulence Scale

<p>Between 15 July 2020 and 19 September 2021, the Atmospheric Raman Temperature and Humidity Sounder (ARTHUS) collected data at the Lindenberg Observatory of the Deutscher Wetterdienst (DWD), including temperature and water vapor mixing ratio with a high temporal and range resolution.</p> <p>During the operation period, very stable 24/7 operation was achieved, and ARTHUS demonstrated that is capable to observe the atmospheric boundary layer and lower free troposphere during both daytime and nighttime up to the turbulence scale, with high accuracy and precision, and very short latency. During nighttime, the measurement range increases even up to the tropopause and lower stratosphere.</p> <p>ARTHUS measurements resolve the strength of the inversion layer at the planetary boundary layer top, elevated lids in the free troposphere, and turbulent fluctuations in water vapor and temperature, simultaneously (Lange et al., 2019, Wulfmeyer et al., 2015). In addition to thermodynamic variables, ARTHUS provides also independent profiles of the particle backscatter coefficient and the particle extinction coefficient from the rotational Raman signals at 355 nm with much better resolution than a conventional vibrational Raman lidar.</p> <p>At the conference, highlights of the measurements will be presented. Furthermore, the statistics of more than 150 comparisons with local radiosondes will be presented which confirm the high accuracy of the temperature and moisture measurements of ARTHUS.</p> <p><strong><em>Acknowledgements</em></strong></p> <p>The development of ARTHUS was supported by the Helmholtz Association of German Research Centers within the project Modular Observation Solutions for Earth Systems (MOSES). The measurements in Lindenberg were funded by DWD.</p> <p><strong><em>References </em></strong></p> <p>Lange, D., Behrendt, A., and Wulfmeyer, V. (2019). Compact operational tropospheric water vapor and temperature Raman lidar with turbulence resolution. <em>Geophysical Research Letters</em>, 46. https://doi.org/10.1029/2019GL085774</p> <p>Wulfmeyer, V., R. M. Hardesty, D. D. Turner, A. Behrendt, M. P. Cadeddu, P. Di Girolamo, P. Schlüssel, J. Van Baelen, and F. Zus (2015), A review of the remote sensing of lower tropospheric thermodynamic profiles and its indispensable role for the understanding and the simulation of water and energy cycles, <em>Rev. Geophys.</em>, 53,819–895, doi:10.1002/2014RG000476</p>

scholarly journals Flow around a Circular Cone in a Thin Boundary Layer (Consideration on a Front Stagnation Point)

2008 ◽  
Vol 74 (740) ◽  
pp. 803-810 ◽  
Author(s):  
Takatsugu KAMEDA ◽  
Tetsuya SUMIDA ◽  
Shinsuke MOCHIZUKI ◽  
Hideo OSAKA
Keyword(s):  
Boundary Layer ◽  
Stagnation Point ◽  
Circular Cone ◽  
Thin Boundary Layer

Effect of Carbon Nanotube-Phosphinate Ionic Liquid Thin Boundary Layer on the Tribological Behavior of Aluminum Alloy in Steel-on-Aluminum Contact

2018 ◽  
Author(s):  
Miguel A. Gutierrez ◽  
Michael Gydesen ◽  
Caitlin Marcellus ◽  
Ivan Puchades ◽  
Brian Landi ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Ionic Liquid ◽  
Aluminum Alloy ◽  
Optical Microscopy ◽  
Coefficient Of Friction ◽  
Tribological Behavior ◽  
Sliding Contact ◽  
Wear Volume ◽  
Thin Boundary Layer ◽  
Boundary Film

In this study, the tribological behavior of the Trihexyl tetradecylphosphonium-bis(2,4,4-trimethylpentyl)phosphinate [THTDP][Phos] ionic liquid with and without single-wall carbon nanotubes (SWCNT) dispersion as a thin boundary layer was intended for investigation. However, the surface heat treatment process was not sufficient to form a thin film on the sample surfaces. Thus, in each test condition, the lubricating agents were used as external (liquid) lubricants. Specifically, [THTDP][Phos] and ([THTDP][Phos]+0.1 wt.% SWCNT) boundary film layers were applied on 6061-T6 aluminum alloy disk samples and tested under sliding contact with 1.5 mm diameter 420C stainless steel balls using a ball-on-flat linearly reciprocating tribometer. A commercially available Mobil Super 10W-40 engine oil (MS10W40) was also tested and used as this investigation’s datum. The tribological behavior of [THTDP][Phos] and ([THTDP][Phos]+SWCNT) boundary film layers was analyzed via wear volume calculations from optical microscopy measurements, as well as by observation of the transient coefficient of friction (COF) obtained through strain gauge measurements made directly from the reciprocating member of the tribometer. Results indicate the potential for reduction of wear volume and coefficient of friction in the IL lubricated steel-on-aluminum sliding contact through (SWCNT) dispersion in the ionic liquid. Wear results are based on measurements obtained using optical microscopy (OM). Results discussed display improved tribological performance for both [THTDP][Phos] and ([THTDP][Phos]+SWCNT) over baseline MS10W40 oil lubricant for both roughness values tested for the steel-on-aluminum contact. No measurable improvements were observed between [THTDP][Phos] and ([THTDP][Phos]+SWCNT) tests.

Tracking Control of Variable Structure Using Fuzzy Variable Boundary Layer

1999 ◽  
Vol 3 (4) ◽  
pp. 332-338
Author(s):  
Heejin Lee ◽  
◽  
Dong-Yon Kim ◽  
Taeck-Kie Lee ◽  
Sang-Hoon Kim ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Fuzzy Variable ◽  
Variable Structure ◽  
Thin Boundary Layer ◽  
Variable Boundary ◽  
Structure Control ◽  
Fuzzy Algorithms ◽  
Variable Structure System ◽  
Control Gain ◽  
Better Than

Control gain greatly affects variable structure system (VSS) performance as a system design parameter. The thin boundary layer used to eliminate chatter neighbors the sliding surface. Sliding control based on a variable boundary layer tracks better than a fixed layer. We propose variable structure control using fuzzy algorithms in control gain and the boundary layer to increase tracking efficiency, proving its feasibility in application to a simple nonlinear system.

Vortex Shedding From Two Surface-Mounted Prismatic Obstacles in Lock-in Regime

2003 ◽  
Author(s):  
Robert J. Martinuzzi ◽  
Brian Havel
Keyword(s):  
Boundary Layer ◽  
Vortex Shedding ◽  
Three Dimensional ◽  
Front Face ◽  
Thin Boundary Layer ◽  
Tandem Arrangement ◽  
Freestream Velocity ◽  
Square Cylinders ◽  
Shedding Frequency ◽  
Lock In

Periodic vortex shedding from two surface-mounted cubes, of height H, in tandem arrangement placed in a thin boundary layer is investigated for a spacing 2H using phase-averaged laser Doppler velocimetry measurements. Tests were conducted for a Reynolds number of 22000, based on H and the freestream velocity, and an approximately 0.07H thick laminar boundary layer. For this obstacle spacing, the shedding frequency scales linearly with the obstacle spacing. It is shown that in this lock-in regime, periodic shedding is triggered by the displacement of the vertical flow along the front face of the downstream obstacle and is thus different from that observed for two-dimensional cylinders in uniform streams. The existence of this three-dimensional effect is then used to explain why lock-in cannot be observed for square cylinders in tandem arrangement.

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