scholarly journals Design and Motion Performance Analysis of Turbulent AUV Measuring Platform

Sensors ◽  
2022 ◽  
Vol 22 (2) ◽  
pp. 460
Author(s):  
Yunli Nie ◽  
Dalei Song ◽  
Zhenyu Wang ◽  
Yan Huang ◽  
Hua Yang
Keyword(s):  
Autonomous Underwater Vehicle ◽  
Simulation Analysis ◽  
Northern South China Sea ◽  
Angle Of Attack ◽  
Horizontal Distance ◽  
Flow Distortion ◽  
High Quality ◽  
Maximum Angle ◽  
Motion Performance ◽  
Shear Probe

The use of a multi-functional autonomous underwater vehicle (AUV) as a platform for making turbulence measurements in the ocean is developed. The layout optimization of the turbulence package and platform motion performance are limitation problems in turbulent AUV design. In this study, the computational fluid dynamics (CFD) method has been used to determine the optimized layout position and distance of the shear probe integrated into an AUV. When placed 0.8 D ahead of the AUV nose along the axis, the shear probe is not influenced by flow distortion and can contact the water body first. To analyze the motion of the turbulence AUV, the dynamic model of turbulence AUV for planar flight is obtained. Then, the mathematical equations of speed and angle of attack under steady-state motion have also been obtained. By calculating the hydrodynamic coefficients of the turbulence AUV and given system parameters, the simulation analysis has been conducted. The simulation results demonstrated that the speed of turbulent AUV is 0.5–1 m/s, and the maximum angle of attack is less than 6.5°, which meets the observation requirements of the shear probe. In addition, turbulence AUV conducted a series of sea-trials in the northern South China Sea to illustrate the validity of the design and measurement. Two continuous profiles (1000 m) with a horizontal distance of 10 km were completed, and numerous high-quality spatiotemporal turbulence data were obtained. These profiles demonstrate the superior flight performance of turbulence AUV. Analysis shows that the measured data are of high quality, with the shear spectra being in very good agreement with the Nasmyth spectrum. Dissipation rates are consistent with background shear. When shear velocity is weak, the measurement of dissipation rate is 10−10 W Kg−1. All indications are that the turbulence AUV is suitable for long-term, contiguous ocean microstructure measurements, which will provide data needed to understand the temporal and spatial variability of the turbulent processes in the oceans.

scholarly journals Study on the Motion Stability of the Autonomous Underwater Helicopter

2022 ◽  
Vol 10 (1) ◽  
pp. 60
Author(s):  
Yuan Lin ◽  
Jin Guo ◽  
Haonan Li ◽  
Hai Zhu ◽  
Haocai Huang ◽  
...  
Keyword(s):  
Autonomous Underwater Vehicle ◽  
Angle Of Attack ◽  
Vertical Movement ◽  
Plane Motion ◽  
Hydrodynamic Performance ◽  
Scale Model ◽  
Motion Stability ◽  
Movement Stability ◽  
Stability Indexes ◽  
Drag Ratio

The hydrodynamic performance of a novel hovering autonomous underwater vehicle, the autonomous underwater helicopter (AUH), with an original disk-shaped hull (HG1) and an improved fore–aft asymmetric hull (HG3), is investigated by means of computational fluid dynamics with the adoption of overlapping mesh method. The hydrodynamic performance of the two hull shapes in surge motion with variation of the angle of attack is compared. The results show that HG3 has less resistance and higher motion stability compared to HG1. With the angle of attack reaching 10 degrees, both HG1 and HG3 achieve the maximum lift-to-drag ratio, which is higher for HG3 compared to HG1. Furthermore, based on the numerical simulation of the plane motion mechanism test (PMM) and according to Routh’s stability criterion, the horizontal movement and vertical movement stability indexes of HG1 and HG3 (GHHG1=1.0, GVHG1=49.7, GHHG2=1.0, GVHG3=2.1) are obtained, which further show that the AUH has better vertical movement stability than the torpedo-shaped AUV. Furthermore, the scale model tail velocity experiment indirectly shows that HG3 has better hydrodynamic performance than HG1.

Lip Separation and Inlet Flow Distortion Control in Ducted Fans Used in VTOL Systems

2014 ◽  
Author(s):  
Ali Akturk ◽  
Cengiz Camcı
Keyword(s):  
Angle Of Attack ◽  
Axial Flow ◽  
Vertical Force ◽  
High Angle ◽  
Flow Distortion ◽  
High Angle Of Attack ◽  
Inlet Flow ◽  
Flight Velocity ◽  
Ducted Fan ◽  
Inlet Flow Distortion

This paper describes a novel ducted fan inlet flow conditioning concept that will significantly improve the performance and controllability of ducted fan systems operating at high angle of attack. High angle of attack operation of ducted fans is very common in VTOL (vertical take off and landing) UAV systems. The new concept that will significantly reduce the inlet lip separation related performance penalties in the edgewise/forward flight zone is named DOUBLE DUCTED FAN (DDF). The current concept uses a secondary stationary duct system to control inlet lip separation related momentum deficit at the inlet of the fan rotor occurring at elevated edgewise flight velocities. The DDF is self-adjusting in a wide edgewise flight velocity range and its corrective aerodynamic effect becomes more pronounced with increasing flight velocity due to its inherent design properties. Most axial flow fans are designed for an axial inlet flow with zero or minimal inlet flow distortion. The DDF concept is proven to be an effective way of dealing with inlet flow distortions occurring near the lip section of any axial flow fan system, especially at high angle of attack. In this present paper, a conventional baseline duct without any lip separation control feature is compared to two different double ducted fans named DDF CASE-A and DDF CASE-B via 3D, viscous and turbulent flow computational analysis. Both hover and edgewise flight conditions are considered. Significant relative improvements from DDF CASE-A and DDF CASE-B are in the areas of vertical force (thrust) enhancement, nose-up pitching moment control and recovery of fan through-flow mass flow rate in a wide horizontal flight range.

Fan Aerodynamics With a Short Intake at High Angle of Attack

2020 ◽  
Author(s):  
Ben Mohankumar ◽  
Cesare A. Hall ◽  
Mark J. Wilson
Keyword(s):  
Pressure Ratio ◽  
Angle Of Attack ◽  
Radial Pressure ◽  
Separation Mechanism ◽  
Flow Distortion ◽  
Ratio Distribution ◽  
Rotor Design ◽  
Velocity Triangle ◽  
Tip Velocity ◽  
High Work

Abstract Future turbofan engines seek shorter intakes to reduce the cruise fuel burn of a low pressure ratio, large diameter fan. However, shorter intakes increase the level of flow distortion entering the rotor when the aircraft angle of attack (AOA) is high, reducing thrust when critically needed. This paper considers how the fan rotor radial pressure ratio distribution and tip velocity triangle can be designed to improve thrust at high AOA. Full annulus, unsteady CFD is performed on three rotor designs coupled to a short intake. We show that rotor design for high AOA should be guided by three flow mechanisms. Mechanism i) is caused by high Mach number flow over the bottom intake lip, which chokes the rotor leading to high loss. Mechanism ii) is the loss generation in the rotor tip as it passes through an intake separation. Mechanism iii) shows radial flows through the rotor change both the amount and the way work is imparted on the flow. Two comparable rotor design philosophies for high thrust are proposed; high work or low loss. Rotors designed to a mid-high radial pressure ratio distribution impart high work on streamlines that migrate radially towards the hub and exit the rotor at highly cambered sections. Meanwhile, tip-high designs reduce choking losses in the midspan when operating with a separated intake, particularly when the tip velocity triangle is designed to high axial velocity diffusion over high camber. However, such designs suffer with higher tip losses after exiting an intake separation.

Introduction of Circumferentially Nonuniform Variable Guide Vanes in the Inlet Plenum of a Centrifugal Compressor for Minimum Losses and Flow Distortion

2016 ◽  
Vol 138 (9) ◽  
Author(s):  
Ismail Sezal ◽  
Nan Chen ◽  
Christian Aalburg ◽  
Rajesh Kumar V. Gadamsetty ◽  
Wolfgang Erhard ◽  
...  
Keyword(s):  
Oil And Gas ◽  
Variable Speed ◽  
Flow Distortion ◽  
Flow Rates ◽  
Guide Vanes ◽  
Baseline Design ◽  
Pressure Losses ◽  
Operating Range ◽  
Maximum Angle ◽  
The Impact

In the oil and gas industry, large variations in flow rates are often encountered, which require compression trains with a wide operating range. If the stable operating range at constant speed is insufficient, variable speed drivers can be used to meet the requirements. Alternatively, variable inlet guide vanes (IGVs) can be introduced into the inlet plenum to provide pre- or counterswirl to the first-stage impeller, possibly eliminating the need for variable speed. This paper presents the development and validation of circumferentially nonuniform IGVs that were specifically designed to provide maximum angle variation at minimum losses and flow distortion for the downstream impeller. This includes the comparison of three concepts: a baseline design based on circumferentially uniform and symmetric profiles, two circumferentially nonuniform concepts based on uniquely cambered airfoils at each circumferential position, and a multi-airfoil configuration consisting of a uniquely cambered fixed part and a movable part. The idea behind the circumferentially nonuniform designs was to take into account nonsymmetric flow features inside the plenum and a bias toward large preswirl angles rather than counter-swirl during practical operation. The designs were carried out by computational fluid dynamics (CFD) and first tested in a steady, full-annulus cascade in order to quantify pressure losses and flow quality at the inlet to the impeller at different IGV setting angles (ranging from −20 deg to +60 deg) and flow rates. Subsequently, the designs were mounted in front of a typical oil and gas impeller on a high-speed rotating rig in order to determine the impact of flow distortion on the impeller performance. The results show that pressure losses in the inlet plenum could be reduced by up to 40% with the circumferentially nonuniform designs over the symmetric baseline configuration. Furthermore, a significant reduction in circumferential distortion could be achieved with the circumferentially nonuniform designs. The resulting improvement in impeller performance contributed approximately 40% to the overall efficiency gains for inlet plenum and impeller combined.

scholarly journals Feasibility Study Using UAV Aerial Photogrammetry for a Boundary Verification Survey of a Digitalized Cadastral Area in an Urban City of Taiwan

2020 ◽  
Vol 12 (10) ◽  
pp. 1682
Author(s):  
Shih-Hong Chio ◽  
Cheng-Chu Chiang
Keyword(s):  
Unmanned Aerial Vehicle ◽  
Focal Length ◽  
Horizontal Distance ◽  
Control Points ◽  
High Quality ◽  
Aerial Photogrammetry ◽  
Cadastral Maps ◽  
Urban City ◽  
Aerial Vehicle ◽  
Overlap Analysis

In conducting land boundary verification surveys in digitalized cadastral areas in Taiwan, possible parcel points must be surveyed. These points are employed in the overlap analysis and map registration of possible parcel points and digitalized cadastral maps to identify the coordinates of parcel points. Based on the computed horizontal distance and angle between control points and parcel points, parcels are staked out using ground surveys. Most studies survey possible parcel points using ground surveys with, for example, total stations. Compared with ground surveys, UAV (Unmanned Aerial Vehicle) aerial photogrammetry can provide more possible parcel points. Thus, an overlap analysis of digitalized cadastral maps, combined with the collection of possible parcel points, will be more comprehensive. In this study, a high-quality-medium format camera, with a 55 mm focal length, was carried on a rotary UAV to take images, with a 3 cm ground sampling distance (GSD), flying 300 m above the ground. The images were taken with an 80% end-lap and side-lap to increase the visibility of the terrain details for stereo-mapping. According to the test conducted in this study, UAV aerial photogrammetry can accurately provide supplementary control points and assist in the boundary verification of digitalized cadastral areas in Taiwan.

scholarly journals Technical note: Turbulence measurements from a Light Autonomous Underwater Vehicle

2021 ◽  
Author(s):  
Eivind Hugaas Kolås ◽  
Tore Mo-Bjørkelund ◽  
Ilker Fer
Keyword(s):  
Barents Sea ◽  
Autonomous Underwater Vehicle ◽  
Underwater Vehicle ◽  
Technical Note ◽  
Turbulence Measurements ◽  
Marine Systems ◽  
The Barents Sea ◽  
Accelerometer Signal ◽  
Shear Probe ◽  
Good Agreement

Abstract. A self-contained turbulence instrument from Rockland Scientific was installed on a Light Autonomous Underwater Vehicle (AUV) from OceanScan Marine Systems and Technology Lda. We report on the data quality and discuss limitations of dissipation estimated from two shear probes during a deployment in the Barents Sea in February 2021. The AUV mission lasted for 5 hours, operating at a typical horizontal speed of 1.2 m s−1. The AUV was programmed to find and cross the maximum along-path thermal gradient at 10, 20 and 30 m depths along 4 km transects. Although the AUV vibrations contaminate the shear probe records, the noise is mitigated by removing vibration-induced components from shear spectra using accelerometer signal measured in multiple directions. Dissipation rate estimates in the observed transects varied in the range 1 × 10−8 and 6 × 10−6 W kg−1, with the values from the two orthogonal probes typically in agreement to within a factor of 2. Dissipation estimates from the AUV show good agreement with nearby vertical microstructure profiles obtained from the ship during the transects, indicating that the turbulence measurements from the AUV are reliable for this relatively turbulent environment. However, the lowest reliable dissipation rates are limited to 5 × 10−8 W kg−1, making this setup unfit for use in quiescent environments.

Depositional Palaeoenvironment and Models of the Eocene Lacustrine Source Rocks in the Northern South China Sea

2021 ◽  
Author(s):  
Niubin Zhao
Keyword(s):  
Organic Matter ◽  
South China Sea ◽  
South China ◽  
Deep Water ◽  
Northern South China Sea ◽  
Volcanic Rocks ◽  
Source Rocks ◽  
High Quality ◽  
Reducing Conditions ◽  
Parent Rocks

<p>      Element geochemical analysis of 94 ditch cutting samples of the shale source rock from the Wenchang Formation in the Zhuyi sub-basin and the Liushagang Formation in the Weixinan sub-basin was conducted to determine their palaeoenvironment and main controlling factors and to further establish development models. The results indicate that freshwater and a warm and humid climate were characteristics of the depositional palaeoenvironment between Wenchang and Liushagang formations. During the deposition of Wenchang Formation, the parent rocks mainly consisted of felsic volcanic rocks, the water was characterized by a high palaeoproductivity, shallow-deep water depths, and weakly reducing conditions, whereas during the deposition of Liushagang Formation, the parent rocks mainly consisted of mafic volcanic rocks,<strong> </strong>and the palaeoproductivity, palaeowater depth, and reducing conditions of the water were better than during the deposition of<strong> </strong>Wenchang Formation. The formation of high-quality source rocks in the Liushagang Formation were mainly controlled by two factors: (1) the mafic igneous rock provenance and strong weathering provided macronutrients (e.g. P, Fe) for water; (2) high palaeoproductivity provided the source of organic matter, which played a much important role than preservation condition of organic matter. For Wenchang Formation, the good preservation of organic matter which was created by the reducing environment in deep water was also necessary. Accordingly, two models were briefly summarized: a productivity and preservation model for the Wenchang Formation source rocks and a productivity model for the Liushagang Formation source rocks, both of them can develop high-quality source rocks, but the source rock quality of the former were lower than of the latter, this was mainly attributed to the difference in the nutrients and palaeoproductivity. This study provides valuable guidance for oil and gas exploration in the northern South China Sea and the study of lacustrine source rocks in other areas.</p>

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

2014 ◽  
Vol 31 (5) ◽  
pp. 1128-1150 ◽  
Author(s):  
Ilker Fer ◽  
Algot K. Peterson ◽  
Jenny E. Ullgren
Keyword(s):  
Dissipation Rate ◽  
Bottom Layer ◽  
Buoyancy Frequency ◽  
Underwater Glider ◽  
High Quality ◽  
Velocity Scale ◽  
Microstructure Measurements ◽  
Shear Probe ◽  
Better Than ◽  
Made In

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.

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