Simultaneous Velocity Research Articles

Risley-prism-based multi-beam scanning LiDAR for high-resolution three-dimensional imaging

Light detection and ranging (LiDAR) as a significant approach to three-dimensional perception has increasingly suffered from challenges for compact structure, high resolution and strong adaptability. This paper presents a versatile LiDAR system that incorporates multi-beam scanning using Risley prisms and coherent detection based on triangular frequency modulation. By combining Risley-prism-based multi-beam steering model with simultaneous distance and velocity measurements, the LiDAR architecture for three-dimensional imaging is theoretically demonstrated. A unified LiDAR point cloud processing framework is developed, where the multi-mode integrated filtering method is proposed for outlier removal using point cloud characteristics. The coarse-fine coupled strategy is also formulated to combine statistical modeling with iterative optimization for multi-channel point cloud registration. It is experimentally validated that our LiDAR can achieve high-resolution three-dimensional information acquisition against long range, and the proposed point cloud processing technique can fully reconstruct the spatial form of object while preserving sufficient details.

Multi-Functional Microwave Photonic Radar System for Simultaneous Distance and Velocity Measurement and High-Resolution Microwave Imaging

A photonic-assisted multi-functional radar system for simultaneous distance and velocity measurement and high-resolution microwave imaging is proposed and experimentally demonstrated by using a composite transmitted microwave signal of a single-chirped linearly frequency-modulated (LFM) signal and a single-tone microwave signal. In the system, the transmitted signal is generated via photonic frequency up-conversion based on a single integrated dual-polarization dual-parallel Mach-Zehnder modulator (DPol-DPMZM), while the echo signals scattered from the target are de-chirped to two low-frequency signals using a microwave photonic frequency mixer. By using the two low-frequency de-chirped signals, the real-time distance and radial velocity of the moving target can be measured accurately according to the round-trip time of the echo signal and its Doppler frequency shift. Compared with the previously reported distance and velocity measurement methods, where two LFM signals with opposite chirps are used, these parameters can be obtained using only a single-chirped LFM signal and a single-tone microwave signal. Meanwhile, high-resolution inverse synthetic aperture radar (ISAR) imaging can also be realized using ISAR imaging algorithm. An experiment is performed to verify the proposed multi-functional microwave photonic radar system. An up-chirped LFM signal from 8.5 to 12.5 GHz and an 8.0 GHz single-tone microwave signal are used as the transmitted signal. The results show that the absolute measurement errors of distance and radial velocity are less than 5.9 cm and 2.8 cm/s, respectively. ISAR imaging results are also demonstrated, which proves the high-resolution and real-time ISAR imaging ability of the proposed system.

Simultaneous velocity and concentration profiling of nuclear waste suspensions in pipe flow, using ultrasonic Doppler and backscatter analysis

Complex magnox ponds at Sellafield retain hydroxide-based sludge with unknown physicochemical properties. The sludge is a corroded form of magnesium-based fuel cladding used in first generation magnox reactors. Long term storage and open-air aqueous conditions are major contributors to corrosion. Waste needs to be transported to interim storage using engineered pipelines. Remote in situ characterisation of sludge was achieved using a non-invasive ultrasonic velocity profiler (UVP). The UVP uses raw velocity and echo amplitude to extract velocity and acoustic profiles. Profiles are used to understand effect of particle size and concentration on attenuation. Spherical glass particles with two size distributions of known acoustic behaviour were analysed to establish acoustic profiles. 4MHz frequency transducers were mounted in-line on engineered pipelines, 90 deg and 135 deg to flow. Data were extracted from in situ transducers for validation and non-contact probes were utilised to prove data could be collected safely without exposure. Flow rate was varied to ensure full developed flow before analysis. Profiles extracted from concentration arrays were analysed to understand particle segregation in horizontal pipe arrangements and attenuation. Remote in-line characterisation allows safe analysis, whilst in-line characterisation saves time and money. Moving forward, complex non-defined nuclear simulants will be analysed to investigate the UVP's limitations.

Combining simultaneous density and velocity measurements of rotor blade tip vortices under cyclic pitch conditions

An investigation into blade tip vortices of a sub-scale rotor under cyclic pitch conditions is carried out. Background oriented schlieren (BOS), particle image velocimetry (PIV), and computational fluid dynamics (CFD) are applied to the same test cases. This approach allows to combine the velocity data from PIV in a measurement plane, the density related data from BOS in a measurement volume, and the comprehensive set of flow variables provided by unsteady detached eddy simulations. Vortices up to an age of varPsi _{{text {v}}}= {70}^circ in case of PIV and CFD, and up to varPsi _{{text {v}}}= {200}^circ in case of BOS are considered. The vortex locations are obtained through all three techniques. The unsteadiness of the vortices was obtained by the experimental results, whereas CFD provides an average solution. An increased position scatter was observed during the downstroke of the pitch cycle with both experimental methods and was found to be in good agreement. In the second part, the PIV velocity data are compared to common vortex models. An approach to link the density distribution and the swirl velocity is applied to the measured data. Based on the CFD results, it is shown that the assumption of isothermal flow yields better agreement between velocity and density than isentropic flow.Graphic abstract

Simultaneous imaging of two-phase velocities in particle-laden flows by two-color optical phase discrimination.

In this Letter, we present a particle image/tracking velocimetry (PIV/PTV) technique for simultaneous velocity measurement of both fluid and particle phases, adopting newly developed optical phase discrimination methods and novel optical particles. Spherical acrylic (PMMA) particles of diameter ∼O(100µm) were used as the particle phase, while fine BAM:Eu2+ phosphors of diameter ∼O(1µm) were used as the fluid tracer. Under Nd:YAG 355 nm laser excitation, both the laser-induced fluorescence (LIF) from PMMA and laser-induced phosphorescence (LIP) from BAM:Eu2+ provided sufficiently strong signals for PIV imaging with two non-intensified cameras and were clearly separable for phase discrimination using spectral filters and temporal profiles. The advantages of the PIV/PTV method include the relatively low cost of BAM:Eu2+ phosphors, high sphericity and narrow size distribution of PMMA particles with LIF emission, and direct optical discrimination eliminating artifacts, while requiring much less computational capacity for PIV/PTV processing of complex particle-laden flows.

Random acceleration process on finite intervals under stochastic restarting

The escape of the randomly accelerated undamped particle from the finite interval under action of stochastic resetting is studied. The motion of such a particle is described by the full Langevin equation and the particle is characterized by the position and velocity. We compare three resetting protocols, which restarts velocity or position (partial resetting) and the whole motion (position and velocity—full resetting). Using the mean first passage time we assess efficiency of restarting protocols in facilitating or suppressing the escape kinetics. There are fundamental differences between partial resetting scenarios which restart velocity or position, as in the limit of very frequent resets only the position resetting (regardless of initial velocity) can trap the particle in the finite domain of motion. The velocity resetting or the simultaneous position and velocity restarting provide a possibility of facilitating the undamped escape kinetics.

Application of simultaneous time-resolved 3-D PTV and Two Colour LIF in Studying Rayleigh-Benard Convection

To study the flow topology and temperature distribution of Rayleigh-Benard convection in a highly slender cell, measurement of the simultaneous velocity and temperature in the 3-D domain is required. For this aim, implementing a simultaneous time-resolved 3-D PTV and two-colour PLIF is planned. As a part of this development, for both PTV and two-colour PLIF techniques, the experimental setup has been implemented separately to measure time-resolved 2-D velocity and temperature and is presented in this paper. For PTV, a scanning system is also utilized to scan the flow field to capture the planar velocity in different depths of the flow domain. Progress on calculation of the out-of-plane velocity component including the theory is discussed. Finally, results of the time-resolved 2-D PTV and PLIF systems are presented.

Simultaneous velocity and density measurements of fully developed Rayleigh-Taylor mixing

The dynamics of molecular mixing and the energy transfer process in the Rayleigh-Taylor instability (RTI) are studied through the collection of simultaneous velocity-density measurements using particle image velocimetry (PIV) and laser induced fluorescence (LIF). Statistically stationary experiments are performed in a convective-type gas tunnel facility which allows long experimental times and enables collection of statistically important turbulence data. The data and analyses presented in this paper are expected to help validate variable-density turbulence models and further our understanding of instability-driven flows.

Anisotropy of Magnetic Field and Velocity Fluctuations in the Solar Wind

Abstract We present a large statistical study of the fluctuation anisotropy in minimum variance (MV) frames of the magnetic field and solar wind velocity. We use 2, 10, 20, and 40 minute intervals of simultaneous magnetic field (the Wind spacecraft) and velocity (the Spektr-R spacecraft) observations. Our study confirms that magnetic turbulence is a composite of fluctuations varying along the mean magnetic field and those changing in the direction perpendicular to the mean field. Regardless of the length scale within the studied range of spacecraft-frame frequencies, ≈90% of the observed magnetic field fluctuations exhibit an MV direction aligned with the mean magnetic field, ≈10% of events have the MV direction perpendicular to the background field, and a negligible portion of fluctuations has no preferential direction. On the other hand, the MV direction of velocity fluctuations tends to be distributed more uniformly. An analysis of magnetic compressibility and density fluctuations suggests that the fluctuations resemble properties of Alfvénic fluctuations if the MV direction is aligned with background magnetic field whereas slow-mode-like fluctuations have the MV direction perpendicular to the background field. The proportion between Alfvénic and slow-mode-like fluctuations depends on plasma β and length scale: the dependence on the solar wind speed is weak. We present 3D numerical MHD simulations and show that the numerical results are compatible with our experimental results.

Observer-based saturated proportional derivative control of perturbed second-order systems: Prescribed input and velocity constraints

This study introduces a new methodology for controlling second-order nonlinear systems in point-to-point tasks with simultaneous input and velocity saturation constraints. The proposed approach utilizes a robust disturbance observer for compensating for the unknown dynamics and disturbances affecting the system. Then, the disturbance observer is combined with a saturated proportional derivative (PD) controller. The resulting control signal allows solving the regulation problem and generating input values and velocities with some prescribed bounds defined by the user. Based on the Lyapunov-theory, asymptotic stability of the origin of the closed-loop error dynamics is attained, which implies that the position regulation objective is achieved while keeping the input and velocity values within prescribed bounds defined by the user. The new control scheme is assessed through numerical simulations, which corroborate the new saturated controller’s feasibility.

Probing the high mixing efficiency events in a lock-exchange flow through simultaneous velocity and temperature measurements

Gravity currents produced by a lock-exchange flow are studied using high-resolution molecular tagging techniques. Instead of employing salt to produce density stratification, an initial temperature difference is introduced in the system to generate the ensuing gravity currents. The experiments focus on the interface between the hot and cold fluids to characterize the resultant mixing across the interface. The present measurements spatially resolve the flow to smaller than the Kolmogorov scale and close to the Batchelor scale. This enables reasonably accurate estimates of velocity and density gradients. The measured density (temperature) distribution allowed estimation of the background potential energy of the flow that is used to quantify mixing. These measurements yield a mixing efficiency of about 0.13 with a standard deviation of 0.05 for the present Reynolds number range [Re≤O(104)]. An analysis combining flow visualization and quantitative measurements reveals that spatially local values of high mixing efficiency occur after the occurrence of certain dissipative stirring events. These events, largely associated with vortical overturns, are commonly observed near the interface between the two fluids and are a precursor to locally efficient mixing.

Simultaneous Range and Velocity Measurement Using Frequency Modulated Laser

Simultaneous Range and Velocity Measurement Using Frequency Modulated Laser

Experimental Study of Oscillating Freestream Effect on the Spatiotemporal Distributions of Leading-Edge Film Cooling

Abstract An experimental study was conducted to investigate the influence of mainstream oscillations on spatio-temporal variation of leading-edge film cooling effectiveness. The investigation utilized fast-response pressure-sensitive paint (Fast-PSP) technique at high frame rate. During the experiment, coolant (i.e., CO2, DR = 1.53) was discharged into three rows of cylindrical holes. Various blowing ratios (i.e., M = 0.50, 0.75, 1.00, and 1.50) were tested under the steady (i.e., f = 0 Hz) and oscillating (i.e., f = 7 Hz and 25 Hz) conditions. The measured instantaneous effectiveness was analyzed in terms of time-averaged and phase-averaged results. The results revealed that the mainstream oscillation, consisting of simultaneous pressure and velocity oscillation, significantly influences the behavior of the film cooling effectiveness. The time-averaged effectiveness significantly decreased at high oscillating frequency (i.e., 13.0–19.8% reduction at M = 0.50, f = 25 Hz compared with f = 0 Hz), especially at low blowing ratios (i.e., M = 0.50 and 0.75). The phase-averaged results captured significant decay in the film distributions associated with backflow caused by negative pressure gradients in coolant holes at certain phases. However, the mainstream oscillation effect was relatively insignificant at high blowing ratios (i.e., M = 1.00 and 1.50), which revealed the robustness of coolant coverage at low coolant Strouhal number (i.e., high blowing ratio) under the same oscillating frequency. Furthermore, the unsteady coolant intermittency showed highly unstable film coverage at high coolant Strouhal number. The coolant decay associated with backflow at high coolant Strouhal number should be considered by the gas-turbine designers in order to improve the lifecycle of turbine blades.

Periodic Response and Stability of a Maglev System with Delayed Feedback Control Under Aerodynamic Lift

In this research, the periodic response and stability of a nonlinear maglev system under the combined effects of steady and unsteady aerodynamic lifts is investigated, considering time delay in the feedback control loop. First, a nonlinear maglev system with a single levitation point that accounts for the nonlinearity of the electromagnetic force, time delay in the feedback control loop, and effect of aerodynamic lift is established. Then the periodic solutions of the maglev system with aerodynamic lift and time delays are obtained by an incremental harmonic balance analysis, in which the explicit time-delay action matrices used indicate that the effect of time delay on the response of the maglev system is periodic. The stability of the periodic solutions based on a finite difference continuous time approximation method and Floquet theory is studied, from which the critical time delay is obtained. Also, the relationship between the periodic vibration amplitude and the time delay is examined, along with the steady aerodynamic lift coefficient, and frequency of the unsteady aerodynamic lift, as well as the variation of critical delay with respect to the position feedback and velocity feedback with the control gain parameters. In addition, the stability boundary for the simultaneous time-delayed position and velocity feedback is obtained.

Spatio-Temporal Planning in Multi-Vehicle Scenarios for Autonomous Vehicle Using Support Vector Machines

Efficient trajectory planning of autonomous vehicles in complex traffic scenarios is of interest both academically and in automotive industry. Time efficiency and safety are of key importance and here a two-step procedure is proposed. First, a convex optimization problem is solved, formulated as a support vector machine (SVM), in order to represent the surrounding environment of the ego vehicle and classify the search space as obstacles or obstacle free. This gives a reduced complexity search space and an A* algorithm is used in a state space lattice in 4 dimensions including position, heading angle and velocity for simultaneous path and velocity planning. Further, a heuristic derived from the SVM formulation is used in the A* search and a pruning technique is introduced to significantly improve search efficiency. Solutions from the proposed planner is compared to optimal solutions computed using optimal control techniques. Three traffic scenarios, a roundabout scenario and two complex takeover maneuvers, with multiple moving obstacles, are used to illustrate the general applicability of the proposed method.

Vertically distributed wall sources of buoyancy. Part 1. Unconfined

Abstract

The advanced nutrient removal efficiency and microbial community of a pipeline biofilm system for tailwater transportation

To achieve advanced nutrient removal in wastewater treatment plants (WWTPs) with limited land and reuse wastewater in a low-cost way, a pilot-scale pipeline biofilm system integrating advanced simultaneous nitrogen and phosphorus removal with tailwater pressure transportation from WWTPs was proposed in this research. Results indicated that with the wall-attached polyurethane foams, the system was established after 7 days of starting operation and the enriched biomass reached 12.79 kg/m3. Simultaneous high-efficiency purification and high velocity (0.7 m/s) delivery of tailwater were realized. Furthermore, the removal efficiency was significantly affected by COD/TN and flow velocity. Under the optimal condition, the removal efficiencies of COD, NH4+-N, NO3−-N, TN and PO43--P were 85.97 ± 4.53 %, 78.63 ± 4.00 %, 98.17 ± 1.19 %, 94.99 ± 0.90 % and 82.52 ± 5.45 %, respectively. TN removal rate per unit area biocarrier was 32.17 × 10-3 mg/(L h m2) and PO43--P removal rate was 1.24 × 10-3 mg/(L h m2). High-throughput sequencing validated that heterotrophic nitrification - aerobic denitrification bacteria (Acinetobacter), denitrifying polyphosphate - accumulating organisms (Dechloromonas) and denitrifying bacteria (Hydrogenophaga, Cloacibacterium and Clostridium) synergistically contributed to pollutants removal. This study provided a new strategy for advanced nutrient removal and sewage reuse.

Local myocardial stiffness variations identified by high frame rate shear wave echocardiography

BackgroundShear waves are generated by the closure of the heart valves. Significant differences in shear wave velocity have been found recently between normal myocardium and disease models of diffusely increased muscle stiffness. In this study we correlate in vivo myocardial shear wave imaging (SWI) with presence of scarred tissue, as model for local increase of stiffness. Stiffness variation is hypothesized to appear as velocity variation.MethodsTen healthy volunteers (group 1), 10 hypertrophic cardiomyopathy (HCM) patients without any cardiac intervention (group 2), and 10 HCM patients with prior septal reduction therapy (group 3) underwent high frame rate tissue Doppler echocardiography. The SW in the interventricular septum after aortic valve closure was mapped along two M-mode lines, in the inner and outer layer.ResultsWe compared SWI to 3D echocardiography and strain imaging. In groups 1 and 2, no change in velocity was detected. In group 3, 8/10 patients showed a variation in SW velocity. All three patients having transmural scar showed a simultaneous velocity variation in both layers. Out of six patients with endocardial scar, five showed variations in the inner layer.ConclusionLocal variations in stiffness, with myocardial remodeling post septal reduction therapy as model, can be detected by a local variation in the propagation velocity of naturally occurring shear waves.

An Approach on Velocity and Stability Control of a Two-Wheeled Robotic Wheelchair

Conventional robotic wheelchairs (three or four-wheeled) which are statically stable are poor in mobility. Though a two-wheeled robotic wheelchair has better mobility, it is not statically stable and needs an active stability controller. In addition to mobility and stability, velocity control is also important for the operation of a wheelchair. Conventional stability and velocity controllers rely on the motion of the wheels and require high driving torque and power. In this paper, this problem is tackled by adding a compact pendulum-like movable mechanism whose main function is for stability control. Its motion and those of the wheels are controlled through a quasi-sliding mode control approach to achieve a simultaneous velocity and stability control with much less driving torque and power. Simulation results are presented to show the effectiveness of the proposed controller.

Simultaneous Eulerian-Lagrangian velocity measurements of particulate pipe flow in transitional regime.

We present a unique pipe flow rig capable of simultaneous particle tracking and flow velocity measurements in a dilute, neutrally buoyant particulate pipe flow in regimes of transition to turbulence. The flow consists of solid glass spheres for the disperse phase and a density-matching fluid for the carrier phase. The measurements are conducted using a bespoke, combined two-dimensional particle image velocimetry and particle tracking velocimetry technique. The technique takes advantage of a phase discrimination approach that involves separating the disperse and carrier phases based on their respective image characteristics. Our results show that the rig and the technique it implements can effectively be employed to study transitional particulate pipe flows at dilute concentrations.