FEATURES OF USING AN UNMANNED AIRCRAFT IN EMERGENCY SITUATIONS

The article identifies the conditions and factors that will affect the operation of unmanned aerial vehicles during its use in emergencies. The purpose of the study is to systematize the conditions and factors that will affect the functioning of specific technical means of surveillance installed on the unmanned aerial vehicle. The study of conditions and factors was carried out with a preliminary determination of the general indicators of efficiency of specific technical means of observation installed on the drone, which include: the probability of detection and recognition of the object by the operator (pilot-operator) on the display screen; the scale of the image on the display screen; viewing angle of the species technical means of observation; transverse capture of the area during aerial surveillance with the help of specific technical means; spectral range of operation of the species technical means of observation and the height of observation. According to the results of research, the conditions and factors include: unmanned aerial vehicle; set task for observation (monitoring); terrain features; control by the pilot (pilot-operator); weather conditions; gusts of wind; season; time of day; drone vibrations during flight; atmospheric turbulence; control of specific technical means of observation by the operator (pilot-operator); temperature regime; the presence of a library of signatures of the object of observation. It is concluded that the results of the study of conditions and factors that will affect the use of specific technical means of observation installed on an unmanned aerial vehicle are the basis for developing relevant requirements for specific technical means of observation of visible and infrared wavelengths of the electromagnetic spectrum. Further research should be carried out in the following areas: development or purchase of unmanned aerial vehicles for observation during the prevention and elimination of emergencies; development of libraries of signatures of objects of observation; research of possibilities of application of spectrozonal or multispectral species equipment for observation; creation of special training grounds for training and retraining of pilots and operators of unmanned aerial vehicles, etc.

Toward Industrial Applicability of DNB Predictions in CFD With Improved Wall Boiling Models

The design of Pressurized Water Reactor (PWR) fuel has to rely on costly prototypical experimental campaigns, due to the inherent limitations of legacy lumped-parameter thermal-hydraulics codes. By resolving the fine spatial scales, computational fluid dynamics (CFD) methods offer the opportunity of delivering improved fuel design, taking full advantage of three-dimensional mixing and turbulence control, but must extend their predictive capabilities to multiphase conditions up to DNB, where the maturity and accuracy of the methods is still developing. In this paper, the closures developed within the Eulerian-Eulerian two-fluid model framework are assembled and extended to a general boiling formulation to deliver prediction of DNB at reactor conditions. The classic heat flux partitioning approach is advanced through selection of optimal closures for interaction length scale, nucleation site density, and bubble departure diameter, and further extended though the addition of a consistent DNB detection criterion, to reflect the near wall two phase characteristics. Assessment is performed at 138 bar against the experimental dataset for vertical pipe, where the inlet subcooling ranges from 1 to 150 K and the mass flux varies from 600 kg/(m2.s) to 2650 kg/(m2.s). The presented closures demonstrate consistent agreement with the experimental data, in particular in light of the calibration free application, while further work is ongoing to close the remaining gap and support the introduction of further modeling improvements.

Numerical Simulation and Experiments of Flow-Induced Oscillations of Single-Cylinder With Large Passive Turbulence Control

Passive turbulence control (PTC) is being used in the Marine Renewable Energy Laboratory (MRELab) of the University of Michigan to enhance flow induced oscillations (FIO) of cylinders in the VIVACE (Vortex Induced Vibration for Aquatic Clean Energy) Converter. Large PTC triggers VIV and galloping at lower flow speeds for energy harvesting. Currently, FIO of cylinders with large PTC for high Re has received limited attention and, particularly, the effect of variable PTC height on FIO of cylinders. The vast majority of ocean currents, rivers, and tides are too slow for Marine Hydro Kinetic (MHK) energy technologies to harness it. In order to enhance FIO and to initiate galloping earlier, a circular cylinder is geometrically modified using straight strips placed on the cylinder surface symmetrically PTC strips on the cylinder effectively change the flow properties. In the present study, the FIO of a single-cylinder with large PTC, on end linear-springs, is modelled and simulated using a Fluid-Structure Interaction (FSI) code. Results are verified by corresponding experimental data. Results show that VIV onset occurs at lower Re for large-PTC cylinder in comparison with lower-PTC cylinder. Contrary to smooth cylinders for which the amplitude ratio is small in the transition region between VIV and galloping, application of large PTC leads to high amplitude response in the transition region. The mechanism behind this observation is the further departure of the geometry from the smooth circular cylinder. The latter does not exhibit galloping due to flow and geometric symmetry in all directions. Moreover, in the galloping region, the amplitude ratio increases with the height of PTC. Earlier onset of galloping and enhancement of geometric asymmetry support this observation as well.

Vortex-Induced Vibration Characteristics of a PTC Cylinder with a Free Surface Effect

The experimental study of vortex induced vibration needs to be carried out in water tunnel, but in previous associated simulation work, the water tunnel was treated as an infinite flow field in the depth direction with the effect of the free surface neglected. In the paper, the dynamic characteristics and physical mechanisms of a passive turbulence control (PTC) cylinder in a flow field with a free surface is studied, and the combined technique of a volume of fluid (VOF) method and vortex-induced vibration (VIV) was realized. In the range of Reynolds number studied in this paper (3.5 × 104 ≤ Re ≤ 7.0 × 104), the dynamic parameters (lift and drag coefficients), vortex structures, VIV response (amplitude and frequency ratios), and energy harvesting characteristics of a PTC cylinder under different flow conditions were obtained. The study found that: (1) the shear layer was made more unstable behind the cylinder by the free surface, which made it quicker to reach periodic stability, and the asymmetry shortened the initial stage of vibration of the oscillator, which made it easier to produce dynamic control of the motion of the oscillator; (2) the presence of the free surface only affected the positive amplitude ratio, but had almost no effect on the negative amplitude ratio; (3) the frequency ratio in the free surface flow was closer to the experimental data; (4) the presence of the free surface did not affect the detached vortex pattern in the flow around the stationary cylinder, but in the VIV, the lower the free surface height Z, the more vortices that were shed from the moving cylinder.

Study on turbulence drag reduction of riblet plate in hypersonic turbulent flows

This paper focuses on turbulence drag reduction of riblet plate in hypersonic turbulent flows. We use direct numerical simulation (DNS) and large eddy simulation (LES) to simulate three-dimensional spatially-developing boundary layer over the flat plate and riblet plate with a free-stream Mach number [Formula: see text]. The results reveal the influence of different riblet heights [Formula: see text] and riblet distances [Formula: see text] on drag reduction effect. The drag reduction effect increases with the increase of riblet height and the decrease of riblet distance within suitable range of parameter values. Through analysis, it can be seen that the riblet plate affects the turbulent contribution of the skin friction by suppressing or destroying the large-scale vortex structure. Combined with the actual engineering design requirements, we can use the riblet plate with appropriate parameters to achieve the purpose of turbulence control.