Components Of Velocity Vector Research Articles

A Wall-following Controller Design Method for Underactuated AUVs: An Adaptive Internal Model Approach

Abstract This paper addresses the problem of path-following control of an underactuated autonomous underwater vehicle (AUV) subjected to ocean current disturbances along a given spatial path with a certain speed profile. The control architecture is the classical inner-outer loop structure that includes an observer to estimate the ocean current. For disturbance rejection, we model the ocean current as output of an exosystem and then we design an adaptive internal model to estimate the current vector and deal with uncertainties on the frequencies of the current velocity vector components. To complement this controller, we next consider the wall-following problem using profiling mechanical sonar. In order to construct a desired path, we resort to a cubic B-spline fitting method, the control points of which are obtained by a best B-spline fit to the acquired profiling sonar data. We use the above path following controller to drive the vehicle to follow the constructed path. The results of the proposed controller design for the wall-following problem are demonstrated using numerical simulations. Finally, future direction and extension of the current work toward the automatic inspection of underwater structures will be provided in the last section.

On two thought experiments revealing two massive theoretical anomalies, proving both the contemporary “ray of light” paradigm to be flawed and the impossibility of a photon to inherit any velocity vector component from its source

The existence of two massive theoretical anomalies is demonstrated through two straightforward thought experiments. Those anomalies make it clear that photon’s trajectory models, based on contemporary light paradigms, become unacceptably inaccurate during fundamental research. Contemporary science still considers, as an accurate paradigm, “light” to travel in space as a “ray of light” (“beam of light”, “laser beam”). This simplistic and inaccurate model was used by Michelson and Morley in their world famous fundamental experiment, the latter still being considered as a prime contemporary paradigm. It is however a fact that any “light” signal consists of a vast collection of individual photons. At any specific moment in time, during its travel in space, each individual photon is located in its individual location in space. The modelling of the “trajectory” of a collection of photons, through an extremely simplistic “ray-of-light” concept then results in the two massive theoretical anomalies. The latter two thus fully falsify, as a Karl Popper’s type of strong “falsification by anomaly”, the “ray of light” paradigm. They also clearly prove that it is impossible for a photon to inherit any of the velocity vector components of its source. Consequently, they thus also falsify numerous other contemporary, light based, paradigms.

Reconciling different formulations of viscous water waves and their mass conservation

The viscosity of water induces a vorticity near the free surface boundary. The resulting rotational component of the fluid velocity vector greatly complicates the water wave system. Several approaches to close this system have been proposed. Our analysis compares three common sets of model equations. The first set has a rotational kinematic boundary condition at the surface. In the second set, a gauge choice for the velocity vector is made that cancels the rotational contribution in the kinematic boundary condition, at the cost of rotational velocity in the bulk and a rotational pressure. The third set circumvents the problem by introducing two domains: the irrotational bulk and the vortical boundary layer. This comparison puts forward the link between rotational pressure on the surface and vorticity in the boundary layer, addresses the existence of nonlinear vorticity terms, and shows where approximations have been used in the models. Furthermore, we examine the conservation of mass for the three systems, and how this can be compared to the irrotational case.

A Tethered Air Blimp (TAB) for observing the microclimate over a complex terrain

Abstract. This study presents the first environmental monitoring field campaign of a newly developed Tethered Air Blimp (TAB) system to investigate the microclimate over a complex terrain. The use of a tethered balloon in complex terrains such as mines and tailings ponds is novel and the focus of the present study. The TAB system was fully developed and launched at a mining facility in northern Canada in May 2018. This study describes the key design features, the sensor payload on board, calibration, and the observations made by the TAB system. The system measured meteorological conditions including components of wind velocity vector, temperature, relative humidity, and pressure over the first few tens of metres of the atmospheric boundary layer. The measurements were made at two primary locations in the facility: (i) near a tailings pond and (ii) in a mine pit. TAB measured the dynamics of the atmosphere at different diurnal times (e.g. day versus night) and locations (near a tailings pond versus inside the mine). Such dynamics include mean and turbulence statistics pertaining to flow momentum and energy, and they are crucial in the understanding of emission fluxes from the facility in future studies. In addition, TAB can provide boundary conditions and validation datasets to support mesoscale dispersion modelling or computational fluid dynamics simulations for various transport models.

Wind–Temperature Regime and Wind Turbulence in a Stable Boundary Layer of the Atmosphere: Case Study

The paper presents the results of probing the stable atmospheric boundary layer in the coastal zone of Lake Baikal with a coherent Doppler wind lidar and a microwave temperature profiler. Two-dimensional height–temporal distributions of the wind velocity vector components, temperature, and parameters characterizing atmospheric stability and wind turbulence were obtained. The parameters of the low-level jets and the atmospheric waves arising in the stable boundary layer were determined. It was shown that the stable atmospheric boundary layer has an inhomogeneous fine scale layered structure characterized by strong variations of the Richardson number Ri. Layers with large Richardson numbers alternate with layers where Ri is less than the critical value of the Richardson number Ricr = 0.25. The channels of decreased stability, where the conditions are close to neutral stratification 0 < Ri < 0.25, arise in the zone of the low-level jets. The wind turbulence in the central part of the observed jets, where Ri > Ricr, is weak, increases considerably to the periphery of jets, at heights where Ri < Ricr. The turbulence may intensify at the appearance of internal atmospheric waves.

Passive Acoustic Signal Processing at Low Frequency With a 3-D Acoustic Vector Sensor Hosted on a Buoyancy Glider

This article deals with the detection of low-frequency noise sources and the estimation of their direction of arrivals using an acoustic vector sensor hosted on a buoyancy Slocum glider. The sensor used is a 3-D directional hydrophone capable of acquiring both the acoustic pressure and the components of the particle velocity vector. This article presents experimental results with data collected at sea and describes the signal processing chain, including detection, direction of arrival, and clustering. The vehicle is equipped with a modem and is supported by an ultrashort baseline (USBL) located on a mother ship or gateway to achieve the navigational accuracy required for correct target localization. The surface vessel localizes the glider via the USBL and then transmits position fixes, which are used by the underwater vehicle to reset the drift error of its navigation filter. The results discussed in this article demonstrate two important achievements, i.e., an underwater glider can produce accurate bearing estimates on a target and the feasibility of the integration of an acoustic modem and a USBL positioning system on a glider. The results obtained open up the possibility of using multiple autonomous sensorized gliders integrated in intelligent surveillance robotic networks.

Coating deposition regularity depended on orientation difference in PS-PVD plasma jet

The YSZ coatings are prepared by the plasma spray-physical vapor deposition (PS-PVD) technology based on a specific experimental design. The structure, thickness and growth angle of YSZ coatings on the entire circumferential surface of the cylindrical sample are studied. The results indicated that the structure, thickness and deflection growth angle of YSZ coatings are related to the orientation of deposition location. The numerical simulation of the multiphase mixed fluid near the substrate is carried out and the deposition regularity and mechanism of YSZ coatings prepared by PS-PVD is deduced. The growth rate is related to the local characteristics of the plasma flow field, and is directly proportional to the field pressure and inversely proportional to the field velocity. The growth angle of the coating is generally affected by the flow direction of the plasma jet. Especially, the normal component of velocity vector, Vnorm, mainly affects the speed at which the coating grows vertically upwards. The tangential component of velocity vector, Vtan, determines the degree that the coating growth direction deviates from the vertical direction. When Vtan ≠ 0, the coating forms a fine column with a certain deflection angle and finally develops into an oblique columnar structure.

Coordination of the microwave module used in the Doppler meter of the velocity vector components

The article describes a method for coordinating the microwave path and verifying the microwave module of the DMVC. The method for coordinating and adjusting the microwave module helps measure and evaluate characteristics of the device to confirm compliance with the DMVC requirements.

ОПИСАНИЕ ПРОЦЕССА ИСТЕЧЕНИЯ ДВУХФАЗНОЙ СРЕДЫ ИЗ КАМЕРЫ ПОМОЛА ДЕЗИНТЕГРАТОРА В ПЛОСКОСТИ, ПЕРПЕНДИКУЛЯРНОЙ ОСИ ВРАЩЕНИЯ РОТОРОВ

Currently, disintegrators are equipment used for grinding and mixing various materials. The ad-vantages of disintegrators are the ability to control the rotation frequency of the rotors and change the geometric parameters to obtain a grinding product with the required grain composition, as well as the simplicity of the design. This article describes the flow of a two-phase medium from the grinding chamber to the outlet pipe, whose axis is shifted relative to the plane passing through the center of rotation of the rotors. A design scheme for the two-phase flow into the outlet pipe in a plane perpen-dicular to the axis of the cylindrical body is presented. It is assumed that the movement of the two-phase medium from the grinding chamber to the outlet pipe occurs at a constant modulus speed. The diagram of the two-phase flow is considered taking into account that the length of the outlet pipe sig-nificantly exceeds its width. The relations determining the change of the velocity vector components near the two-phase flow outlet to the outlet pipe are obtained. Based on the obtained expressions, the trajectory of the two-phase flow from the grinding chamber to the outlet pipe is determined. Thus, us-ing the results of this theoretical study, it is possible to provide a rational ratio of the main design pa-rameters of the disintegrator unloading unit.

Operating Parameters of a Slide Bearing with Parabolic-Shaped Slide Surfaces with Consideration of the Stochastic Changes in the Lubrication Gap Height

Abstract In this article, the authors present the equations of the hydrodynamic theory for a slide bearing with parabolic-shaped slide surfaces. The lubricating oil is characterized by non-Newtonian properties, i.e. an oil for which, apart from the classic oil viscosity dependence on pressure and temperature, also an effect of the shear rate is taken into account. The first order constitutive equation was adopted for considerations, where the apparent viscosity was described by the Cross equation. The analytical solution uses stochastic equations of the momentum conservation law, the stream continuity and the energy conservation law. The solution takes into account the expected values of the hydrodynamic pressure EX[p(ϕ,ζ)], of the temperature EX[T(ϕ,y,ζ)], of the velocity value of lubricating oil EX[vi(ϕ,y,ζ)], of the viscosity of lubricating oil EX[ηT(ϕ,y,ζ)] and of the lubrication gap height EX[εT(ϕ,ζ)]. It was assumed, that the oil is incompressible and the changes in its density and thermal conductivity were omitted. A flow of lubricating oil was laminar and non-isothermal. The research concerned the parabolic slide bearing of finite length, with a smooth sleeve surface, with a full wrap angle. The aim of this work is to derive the stochastic equations, that allow to determine the temperature distribution, hydrodynamic pressure distribution, velocity vector components, load carrying capacity, friction force and friction coefficient, in the parabolic sliding bearing, lubricated with non-Newton (Cross) oil, including the stochastic changes in the lubrication gap height. The paper presents the results of analytical and numerical calculation of flow and operating parameters in parabolic sliding bearings, taking into account the stochastic height of the lubrication gap. Numerical calculations were performed using the method of successive approximations and finite differences, with own calculation procedures and the Mathcad 15 software.

Eulerian conditional statistics of turbulent flow in a macroscale multi-inlet vortex chemical reactor

The conditional velocity time averages (⟨Ui|ξ⟩) and conditional mixture fraction time averages (⟨Φ|ωi⟩) were computed based on the Eulerian approach from the experimental data measured in a macroscale multi-inlet vortex chemical reactor. The conditioning events were determined by equally sized intervals of the sample space variable for the mixture fraction (ξ) and the velocity vector (ωi). The experimental data, which consisted of instantaneous velocities and concentration fields for two Reynolds numbers (Re = 3250 and 8125), were acquired using the simultaneous stereoscopic particle image velocimetry (stereo-PIV) and planar laser induced fluorescence techniques. Two mathematical models, the linear approximation and probability density function (PDF) gradient diffusion, were validated by experimental results. The results of the velocity conditioned on the mixture fraction demonstrated that the linear model works well in a low turbulence region away from the reactor center. Near the reactor center, high velocity gradients coupled with low concentration gradients reduce the accuracy of the linear model predictions. Nevertheless, an excellent agreement was found for the conditional events within ±2Φrms (mixture fraction root mean square). Due to lower concentration gradient in the tangential direction, the linear model better predicted the tangential velocity component for all locations investigated. The PDF model with an isotropic turbulent diffusivity performed inadequately for the tangential and axial velocity components. A modified version of the PDF model that considers the three components of the turbulent diffusivity produced a better agreement with the experimental data especially in the spiral arms regions of significant concentration gradients. Furthermore, the mixture fraction conditioned on the velocity vector components showed a more linear behavior near the reactor center, where the PDF of the mixture fraction is a Gaussian distribution. As the concentration gradients became prominent away from the reactor, ⟨Φ|ωi⟩ also deviated from the linear pattern. This was especially remarkable for the mixture fraction conditioned on the tangential velocity. The overall prediction of ⟨Φ|ωi⟩ improves at higher Reynolds number as the fluid mixing is enhanced.

A stochastic approach to the solution to the differential equation of heat transfer in the atmosphere

In this work, a model of heat transfer in the atmosphere is proposed. This model is based on a stochastic interpretation of the velocity vector components. Histograms of the wind speed distribution averaged over a relatively short time interval are obtained and analyzed. The proposed model is formulated based on empirical distributions. Explicit expressions for the first and the second-moment functions solving the heat transfer equation with random coefficients are presented. A function that estimates errors resulting from replacing a random coefficient in an equation with its mathematical expectation is also obtained. An example that demonstrates the effectiveness of the proposed approach in the case of a Gaussian distribution of the horizontal component of wind speed is presented. In this case, the first and second-moment functions in the frame of the proposed model are presented.

Interdaily Variations of Three Wind Velocity Components Retrieved from Long-Term Continuous Minisodar Measurements in the ABL

Statistical analysis of results of long-term continuous 8-day measurements of three components of wind velocity vector with a minisodar in the atmospheric boundary layer is presented for altitudes of 5–200 m and their interdaily variations are studied. The temporal dynamics of vertical profiles of the wind velocity components demonstrates that there are linear segments on the vertical velocity profiles for which the altitude behavior of the velocity components is well approximated by a linear dependence. The analysis of interdaily variations of three wind velocity components has allowed us to establish that all wind velocity components increase with sounding altitude. Attention is drawn to the synchronous character of occurrence of the maxima and minima of x- and y-components. For all components, the semidiurnal behavior (with the velocity decrease since midnight till noon and its subsequent increase since noon till midnight) is clearly traced that can be explained by morning warming and evening cooling of the underlying surface accompanied by the most intensive changes of wind velocity components.

Attitude recovery scheme of magnetically controlled satellite with constant thrust

When the constant thrust is acting directly on the bias momentum satellite, one component of the angular velocity vector would increment gradually to a larger one or even to infinite, which beyond the controllable region corresponding to B-dot algorithm. And in the following rate damping control process, the corresponding control effort would lead to attitude instability. In this study, under the constant thrust, the satellite's attitude evolution laws is researched and, under the control effort corresponding to B-dot damping algorithm, the satellite's tumbling mechanism is analyzed. Two critical angular velocities, respectively corresponding to the watershed value and the saddle point value, are determined according to the details of attitude control systems, including attitude control cycle and the corresponding time sequence. Theoretical analysis results show that, when the angular velocity is larger than the first critical angular velocity corresponding to the controllable region of B-dot algorithm, the B-dot damping algorithm would fail to de-tumble the satellite. On the contrary, the corresponding control effort would drive the angular velocity to another critical angular velocity, which is the saddle point for B-dot algorithm. Finally, a series of simulation examples are presented to verify the proposed conclusions.

Analytical Synthesis of a Modal Controller by Output Vector for Attitude Control of a Descent Module during Its Descent in the Earth’s Atmosphere

A new analytical algorithm of modal control is developed for the sixth-order control system that represents the problem of descent module attitude stabilization using the values of two angles measured by free gyroscope and three components of angular velocity vector with respect to the corresponding coordinate axes measured by the angular velocity sensor. This algorithm belongs to the category of dynamic object control algorithms by the output vector and it is based on synthesis of a state vector observer.

METHOD FOR PREDICTING PARAMETERS OF THE AEROIONIC MODE IN OPEN TERRAIN GROUND AREAS

Purpose. The scientific work is devoted to the development of a new method for forecasting aeroionic mode in working areas at industrial sites, taking into account ionizing sources and surrounding obstacles. Methodology. To find the concentration of positive aeroions, dust and negative aeroions, we use 3D mass transfer equations that take into account the rate of recombination of ions having different polarity and the rate of recombination of ions with dust particles. The numerical solution is based on the integration of the mass transfer equations using the finite-difference method, which turns out to be stable for any step in time. To determine the components of the air velocity vector, a three-dimensional model of the potential flow is used, where the Laplace equations for the velocity potential are the modeling equations. Findings. The mathematical method of numerical calculation of the concentration of positive, negative aeroions and dust has been developed. A feature of the method is the possibility of predicting the aeroionic mode, taking into account all physical factors that significantly affect the formation of concentration zones of aeroions in working areas at industrial sites. The method is not tied to a particular industrial site, it allows us to estimate the value of the concentration of aeroions both locally and in the entire calculated region. Originality. A method for prediction of aeroionic mode in working areas is developed based on 3D modeling of the propagation of negative, positive aeroions and dust under the influence of wind and diffusion, which allows to obtain results at each point of space or in a specific cross-section. Practical value. The proposed method of forecasting was used to solve the problem of estimating aeroionic mode in industrial zones in the open area of the industrial site of the Dnipro oil extraction plant in the presence of emission sources: positive aeroions during the operation of vehicles and respiration of workers; dust during the movement of workers and vehicles; negative aeroions of the ionizer installed in the working zone. The regularities of changes in the concentration of aeroions of various polarity and dust at a height of 1.7 m are determined, which corresponds to the position of the respiratory organs of workers. Quantitative results are needed in assessing the permissible working conditions in the workplaces of industrial sites of enterprises when creating new jobs and reengineering existing ones.

Flow Velocity and Field‐Aligned Current Associated With Field Line Resonance: SuperDARN Measurements

AbstractThis study presents observations of the two‐dimensional velocities and field‐aligned currents of magnetospheric field line resonances. Knowledge of the two‐dimensional plasma flows is essential for determining the field‐aligned current structure of the field line resonance and for understanding the role that field line resonances play in the generation of some auroral arc forms. In this work the full velocity vectors are determined from a high‐resolution fit to the Super Dual Auroral Radar Network (SuperDARN) line‐of‐sight data. Two discrete field line resonance events are presented, one at 4.0 mHz (4‐ to 5‐min period) and the other at 0.6 mHz (30‐min period). Band‐pass filtering the north‐south and east‐west components of the total convection velocity vectors reveals the two‐dimensional velocity field specific to an individual field line resonance. The field line resonance velocities exhibit periodic vorticity, which correspond to periodic poleward moving bands of enhanced field‐aligned current. Assuming a constant ionospheric Pedersen conductance of 10 S, peak field‐aligned current values are estimated to be 2–4 μA/m2. The field‐aligned currents alternate between upward and downward directed and peak in magnitude ~0.5–1° poleward and/or equatorward of the peak in field line resonance flow velocity. A Swarm satellite overpass occurs directly over the 0.6‐mHz field line resonance. The SuperDARN field‐aligned current profile along the Swarm trajectory is found to be similar in magnitude and structure to that determined from Swarm‐A and Swarm‐C in situ measurements.

Enhancing ambient noise correlation processing using vector sensors.

Ambient noise cross-correlations between separated sensors can yield estimates of the Green's function between them. Vector sensors (which record both pressure and acoustic velocity vector components) can leverage their directionality to reject ambient noise sources that do not contribute to the emergence of the Green's function, thus improving performance over standard omnidirectional hydrophones. To quantify this performance gain, a time-domain analytical expression for the correlation between each component of a vector sensor in the presence of an isotropic ambient noise field is derived. Improvement of the velocity channel correlations relative to pressure channel correlations is examined for varying bandwidth, sensor separation distance, and additive channel noise levels. Last, the experimentally measured reduction in variance for the velocity channels correlations vs pressure correlations, using drifting vector sensors deployed in the Long Island Sound, were found to be comparable to the theoretical prediction. Overall, both theoretical and experimental results indicate modest gains are obtained when extracting the Green's function from velocity correlations over using pressure correlations. Thus, vector sensors can be used to reduce the required averaging time for this noise correlation processing, which may be especially useful, for instance, in a fluctuating environment or for drifting sensors.

AN ANALYSIS OF HYDRODYNAMIC PRESSURE DISTRIBUTION AND LOAD CARRYING CAPACITY OF A CONICAL SLIDE BEARING LUBRICATED WITH NON -NEWTONIAN SECOND GRADE FLUI

In this paper, the authors present the equations of the hydrodynamic lubrication theory for conical slide bearings lubricated with the oil with properties described by the Rivlin-Ericksen model. It is assumed, that the considered lubricating oil shows non-Newtonian properties, i.e. it is an oil for which, apart from the classic dependence of oil viscosity on pressure, temperature and operating time, there is also a change in dynamic viscosity values caused by the changes of shear rate. The method of a small parameter was used to solve the conservation of momentum, stream continuity, and energy conservation equations. The small parameter method consists in presenting the sought functions (pressure, temperature, components of the velocity vector) in the form of a uniformly convergent series expansion in powers of a constant small parameter. These functions are substituted into the system of basic equations, and then the series are multiplied by the Cauchy method. By a comparison of the coefficients with the same powers of a small parameter, we obtain systems of partial differential equations, from which the subsequent approximations of unknowns of the sought functions are determined. The small parameter method separates the non-linear system of partial differential equations and creates several linear systems of equations. The aim of this work is to derive the equations describing and allowing the determination of the temperature distribution, hydrodynamic pressure distribution, velocity vector components, load carrying capacity, friction force and friction coefficient in the gap of conical slide bearing, lubricated with the oil of the properties described by the Rivlin-Ericksen model, taking into account its viscosity changes due to time of operation.

Investigation of the influence of combustion-induced thermal expansion on two-point turbulence statistics using conditioned structure functions

The second-order structure functions (SFs) of the velocity field, which characterize the velocity difference at two points, are widely used in research into non-reacting turbulent flows. In the present paper, the approach is extended in order to study the influence of combustion-induced thermal expansion on turbulent flow within a premixed flame brush. For this purpose, SFs conditioned to various combinations of mixture states at two different points (reactant–reactant, reactant–product, product–product, etc.) are introduced in the paper and a relevant exact transport equation is derived in the appendix. Subsequently, in order to demonstrate the capabilities of the newly developed approach for advancing the understanding of turbulent reacting flows, the conditioned SFs are extracted from three-dimensional (3-D) direct numerical simulation data obtained from two statistically 1-D planar, fully developed, weakly turbulent, premixed, single-step-chemistry flames characterized by significantly different (7.53 and 2.50) density ratios, with all other things being approximately equal. Obtained results show that the conditioned SFs differ significantly from standard mean SFs and convey a large amount of important information on various local phenomena that stem from the influence of combustion-induced thermal expansion on turbulent flow. In particular, the conditioned SFs not only (i) indicate a number of already known local phenomena discussed in the paper, but also (ii) reveal a less recognized phenomenon such as substantial influence of combustion-induced thermal expansion on turbulence in constant-density unburned reactants and even (iii) allow us to detect a new phenomenon such as the appearance of strong local velocity perturbations (shear layers) within flamelets. Moreover, SFs conditioned to heat-release zones indicate a highly anisotropic influence of combustion-induced thermal expansion on the evolution of small-scale two-point velocity differences within flamelets, with the effects being opposite (an increase or a decrease) for different components of the local velocity vector.