Instantaneous Profile Research Articles

Multiwave Ultrasonic Doppler Method for Bubbly Two-Phase Taylor Couette Flow Measurement

Ultrasonic methods, such as the Ultrasonic Velocity Profile - UVP method, have a number of advantages over other conventional measurement methods. They are non-intrusive, applicable to opaque wall or fluid, and capable of obtaining instantaneous velocity profiles along a measurement line in real time. This paper reports on the development of a multiwave Doppler UVP method for the measurement of bubbly two-phase flow in a Taylor-Couette flow configuration. Due to its highly complex nature, two-phase flow still attracts considerable interest in both experimental measurement as well as numerical simulation. In this study the new multiwave Doppler UVP method exploits two basic ultrasonic frequencies 2 MHz and 8 MHz. The 2 MHz frequency is for the measurement of the bubble phase. The 8 MHz frequency is for that of the liquid phase. The signal processing technique is based on the pulse repetition Doppler method. A new phase discrimination method is proposed to eliminate bubble velocity included in the data of the liquid phase measured by the 8 MHz frequency. Measurements of bubbly two-phase Taylor-Couette flow have been demonstrated and discussed.

Coordination of Ultrafast Solid-State Circuit Breakers in Radial DC Microgrids

This article proposes a comprehensive method for optimal coordination of ultrafast solid-state circuit breakers (SSCBs) in radial dc microgrids. The proposed method consists of two consecutive steps. In the first step, SSCBs are optimally coordinated for overload, short circuit, and instantaneous protections. Inverse time-current characteristics (ITCC) curves are formulated to systematically coordinate SSCBs. The trip curve of each SSCB includes overload, short-circuit, and instantaneous profiles. In determining overload protection, the thermal capability of SSCBs is considered; while the short-circuit and instantaneous tripping profiles are realized based on short circuit thermal capability and ultrafast response time of SSCBs. Coordination time interval (CTI) is included between upstream and downstream SSCBs to achieve selectivity. To avoid miscoordination in practice, CTI is chosen by incorporating the SSCBs’ metal-oxide varistor (MOV) conduction time interval during turn-off process and dc current measurement error. In the second step, the operating speed of the protective scheme is optimized by applying distance-based secondary protection (DBSP). The DBSP is used to minimize the tripping time when short circuit faults occur close to upstream SSCBs. This significantly reduces the consumed energy by faults, prevents damage, reduces absorbed energy by SSCBs, and enhances the safety of operators. The proposed coordination removes the need for communication links between SSCBs and presents high reliability. A 400-V dc microgrid benchmark with photovoltaic (PV) and energy storage systems (ESSs) is examined as a case study in simulation. Besides, experiments are conducted in a 400-V dc system to evaluate the effectiveness and accuracy of the DBSP.

Gravity‐Wave‐Driven Seasonal Variability of Temperature Differences Between ECMWF IFS and Rayleigh Lidar Measurements in the Lee of the Southern Andes

AbstractLong‐term high‐resolution temperature data of the Compact Rayleigh Autonomous Lidar (CORAL) is used to evaluate temperature and gravity wave (GW) activity in ECMWF Integrated Forecasting System (IFS) over Río Grande (53.79°S, 67.75°W), which is a hot spot of stratospheric GWs in winter. Seasonal and altitudinal variations of the temperature differences between the IFS and lidar are studied for 2018 with a uniform IFS version. Moreover, interannual variations are considered taking into account updated IFS versions. We find monthly mean temperature differences <2 K at 20–40 km altitude. At 45–55 km, the differences are smaller than 4 K during summer. The largest differences are found during winter (4 K in May 2018 and −10 K in August 2018, July 2019 and 2020). The width of the difference distribution (15th/85th percentiles), the root mean square error, and maximum differences between instantaneous individual profiles are also larger during winter (>±10 K) and increase with altitude. We relate this seasonal variability to middle atmosphere GW activity. In the upper stratosphere and lower mesosphere, the observed temperature differences result from both GW amplitude and phase differences. The IFS captures the seasonal cycle of GW potential energy (Ep) well, but underestimates Ep in the middle atmosphere. Experimental IFS simulations without damping by the model sponge for May and August 2018 show an increase in the monthly mean Ep above 45 km from only ≈10% of the Ep derived from the lidar measurements to 26% and 42%, respectively. GWs not resolved in the IFS are likely explaining the remaining underestimation of the Ep.

Comparative Efficiency and Sensitivity Analysis of AC and DC Power Distribution Paradigms for Residential Localities

The new millennium has witnessed a pervasive shift of trend from AC to DC in the residential load sector. The shift is predominantly due to independent residential solar PV systems at rooftops and escalating electronic loads with better energy saving potential integrated with diminishing prices as well as commercial availability of DC-based appliances. Comprehensive sensitivity analysis considering the real load profile is missing in the present body of knowledge. In order to fill that gap, this paper is an attempt to include a comprehensive sensitivity analysis of the DC distribution system and its simulation-based comparison with its AC counterpart, considering the real load profile. The paper uses the Monte Carlo technique and probabilistic approach to add diversity in residential loads consumption to obtain an instantaneous load profile. Various possible scenarios such as variation of standard deviation from 5% to 20% of mean load value, PV capacity variation from 1000 W to 9000 W, and variation in power electronic converter (PEC) efficiencies are incorporated to make the system realistic as much as possible maintaining a fair comparison between both systems. The paper concludes with the baseline efficiency advantage of 2% to 3% during the day for the case of the DC distribution system as compared to the AC distribution system.

Hybrid Model of Rolling-Element Bearing Vibration Signal

The generation of synthetic vibration signals enables the testing of novel machine diagnostic methods without the costly introduction of real failures. One of major goals of vibration-based condition monitoring is the early detection of bearing faults. This paper presents a novel modeling technique based on the combination of the known mechanical properties of a modeled object (phenomenological part) and observation of a real object (behavioral part). The model uses the real pulse response of bearing housing, along with the external instantaneous machine speed profile. The presented method is object-oriented, so it is applicable to a large group of machinery.

Numerical Investigation of Hydraulic Conductivity Variation on Highway Slopes Made of Expansive Yazoo Clay

Expansive soils cover more than 25% of the total area of the United States and are subjected to shrink-swell behavior with moisture variation. With successive moisture and temperature variations over the seasons, the hydraulic conductivity of the expansive soil is subjected to change because of the development of shrinkage cracks which affect the vertical hydraulic conductivity, whereas the horizontal hydraulic conductivity remains negligibly constant. This affects the percolation behavior of the subgrade soil and, in turn, reduces the soil strength, as one of the major factors of slope failure. However, no study has been done on the change in the hydraulic properties of expansive soil with time and its effect on highway slopes. The current study intends to investigate the hydraulic conductivity and matric suction variation at different wet-dry cycles on highway slopes. An instantaneous profile method to investigate the changes in hydraulic conductivity during 1N to 5N wet-dry cycles was utilized. The finite element method in Plaxis was conducted to evaluate the effect of different frequencies and duration of rainfall on water intrusion, and the corresponding change in the matric suction of the highway slope. The selected rainfall pattern is evaluated at different intensities and durations of rainfall based on 100-years return periods. The flow analysis showed that the suction dropped at the highway slope with the presence of rainfall.

Large Eddy Simulation of a supersonic air ejector

This paper presents a study on the flow topology in the mixing chamber of a supersonic ejector using Large Eddy Simulation (LES). To this end, a supersonic air ejector of squared crossed-section was modelled using a specialized finite-element code. Comparisons with experimental data showed good agreement, both in terms of the primary jet shock cell structures and wall pressure measurements (mean deviation of 12%). Results have been discussed both in terms of time averaged profiles and instantaneous structures in the mixing layer. The general flow features have been identified by means of instantaneous temperature fields and pressure profiles through the device. Results show that, under the assessed conditions, the mixing layer is laminar at first and transitions towards turbulence in the first quarter of the mixing chamber, where Λ vortices have been identified. These evolve into hairpin vortices and finally break down around half of the mixing chamber. Time-averaged velocity profiles show self-similarity in this section. In comparison with an unconfined mixing layer (Fang et al., 2018), the supersonic ejector mixing layer grows slower first but then develops at a similar rate after the transition region. A shock train occurs towards the end of the mixing chamber, which enhances mixing. Given its location, it generates a recirculation bubble in the diffuser which narrows the main flow passage and breaks the flow vertical symmetry. This pioneer study shows the enormous potential that LES offers for the optimization and detailed analysis of supersonic ejectors. • Pioneer Large Eddy Simulation of an air supersonic ejector. • Turbulent structures are identified along the shear mixing layer. • An asymmetric shock wave/recirculation is observed in the diffuser. • Application of compound choke theory to study the choking phenomenon.

Spatiotemporal measurement of concentration-dependent diffusion coefficient

We introduce a method to measure the concentration-dependent diffusion coefficient from a sequence of images of molecules diffusing from a source toward a sink. Generally, approaches measuring the diffusion coefficient, such as fluorescence recovery after photobleaching (FRAP), assume that the diffusion coefficient is constant. Hence, these methods cannot capture the concentration dependence of the diffusion coefficient if present. Other approaches measure the concentration-dependent diffusion coefficient from an instantaneous concentration profile and lose the temporal information. These methods make unrealistic assumptions, are not robust, and lead to 100% error. We introduce an image analysis framework that utilizes spatial and temporal information in a sequence of concentration images and numerically solves the general form of Fick's second law using radial basis functions (RBF) to measure the concentration-dependent diffusion coefficient. We term this approach as concentration image diffusimetry (CID). Our method makes no assumptions about the sink and source size and the diffusion dependence on concentration. CID is superior to existing methods in estimating spatiotemporal changes and concentration-dependent diffusion. CID also provides a statistical uncertainty quantification on the measurements using a bootstrapping approach, improving the reliability of the diffusion measurement. We assessed CID's performance using synthetically generated images. Our analysis suggests that CID accurately measures the diffusion coefficient with less than 2% error for most cases. We validated CID with FRAP experimental images and showed that CID agrees with established FRAP algorithms for samples with a constant diffusion coefficient. Finally, we demonstrate the application of CID to experimental datasets of a concentration gradient-driven protein diffusion into a tissue replicate. In conclusion, this work presents an image-based methodology that uses the spatial and temporal changes of concentration fields to measure the concentration-dependent diffusion coefficient.

Theoretical reassessment of the first Stefan diffusion column experiment with a two-component liquid phase, consisting of a high-density volatile solvent and a low-density nonvolatile diluent

The Stefan column was designed in the 19th century to allow the experimental estimation of binary gas diffusion coefficients starting with a pure volatile liquid A placed at the bottom overlaid with a stagnant/inert gas B. A sweeping B stream was provided at the top to remove the diffused gas A. In 1959, Richardson first studied a two-component liquid mixture in the Stefan column. One of his systems, a high-density volatile liquid A (carbon tetrachloride) dissolved in a low-density nonvolatile liquid O (dibutyl phthalate), is of interest to our ongoing research efforts. He collected interfacial descent-time data in his single isothermal Stefan column experiment, and analyzed them with a diffusion transport model, which contained unnecessary assumptions and simplifications, to obtain the binary liquid diffusivity of A in O, D AO. The present study removes the major restrictions of the previous model, reanalyzing the reported data with an improved numerical diffusion model that includes realistic features of the one-dimensional transport problem and statistical information on the estimated D AO. The average ± standard deviation of D AO were 8.82E-10 ± 1.85E-15 m2/s (12 data points), with an error of −13.3% relative to the Richardson value. The new model also provides detailed insight on the diffusive transport dynamics of liquid A by predicting interfacial descent rates, instantaneous concentration profiles in the liquid phase, and the time-dependent fraction of the mass of A lost from the original solution. The model is valuable to chemical engineering researchers studying diffusion–evaporation phenomena and multicomponent distillation processes.

Using splines in the application of the instantaneous profile method for the hydrodynamic characterization of a tropical agricultural Vertisol

An important aspect in the study and understanding of the physical phenomena involved in water movement in the soil-plant system is the need to carry out the hydrodynamic characterization (HC) of non-saturated field soils. Studies of this type have been widely developed in soils of temperate climates, but they are infrequent in the tropics, hence there is a need for further research in tropical Vertisols under field conditions. Hydrodynamic characterization consists of finding the functional relationship between soil hydraulic [...]

Signature of a mesospheric bore in 557.7 nm airglow emission using all-sky imager at Hanle (32.7oN, 78.9oE)

A prominent signature of dark bore front in the mesospheric O( 1 S) airglow emission is observed on a night in the late winter at Hanle (32.7 o N, 78.9 o E) located in the western Himalaya. The leading front was followed by a series of evident trailing waves and the event lasts for more than two hours. The characteristic features of the bore indicate it to be linear undular type. Instantaneous temperature profile shows presence of stable region through formation of thermal duct in the upper mesosphere possibly supported by chemistry and/or dynamics. With time, the bore fronts became faint in presence of ripples as they reached other side of imager field of view (FOV). During the initial period around 3–4 waves h −1 appear to enter the imager FOV. The observed average phase speed, period and horizontal wavelength are found to be 40 m/s, 12 min and 29 km, respectively. The bore fronts exhibit a clockwise rotation at a rate of around 5° h −1 . The front edge perpendicular to the direction of propagation shows small-amplitude undulation indicating nonuniform duct structure. The tropospheric meteorological conditions may indicate plausible contribution from jet stream, weather front (linked with the Himalayan orography), and nonmigrating tides to excite and sustain the mesospheric bore event although further investigations in this direction are being sought to understand the actual underlying physical processes.

Sparse processing with range migration compensation capability for a frequency agile orthogonal frequency division multiplexing waveform

Digital-to-analogue and analogue-to-digital in a digital array radar limits the transmission and reception of instantaneous broadband signals (IBSs), which makes it a technical bottleneck for digital array radar to obtain an instantaneous broadband high-resolution range profile (HRRP). A frequency-agile orthogonal frequency division multiplexing (OFDM) waveform with a high repetition frequency pulse train is proposed, which uses multiple narrowband OFDM to realise large bandwidth so that the digital array radar can easily realise the broadband working mode. This frequency hopping signal makes the digital array radar have the characteristics of broadband HRRP formation and low interception simultaneously. To solve the problem of range migration caused by high-speed moving targets, a two-stage sparse processing algorithm with range migration compensation capability (FS-RMCSP) in slow time and fast time domains is proposed. By constructing a sparse processing dictionary matrix with range compensation operator according to the phase offset of the moving target echo, the proposed algorithm can complete the compensation of target range migration with high resolution, accurately recover the range-Doppler parameters of target, and realise the coherent accumulation of target echo. The simulation results show that this waveform can obtain the range-Doppler high-resolution characteristics equivalent to the IBS in the radar tracking working mode. Compared with the conventional sparse signal processing algorithm, the FS-RMCSP algorithm significantly improves the performance of target reconstruction in the scene of high-speed moving targets.

Effect of confinement ratio on flame structure and blow-off characteristics of swirl flames

Blow-off of swirl flames as well as its mechanism are fundamental issues and attract continuous attention due to its wide application in modern combustors. This study experimentally investigated the blow-off and flame macrostructure transition behavior of unconfined and confined premixed CH4/air flames stabilized on a swirl and bluff-body burner. PIV and OH-PLIF techniques were used to measure the flow field and instantaneous OH profile, respectively. It was observed that the combustor confinement could significantly broaden the blow-off limits, which was further widened with the increase of confinement ratio (CR) of the confined combustor. The influence of CR on flame stabilization was revealed by analyzing flame structures and flow fields. For the unconfined combustor, when the flames are far away and close to the blow-off, the shear layer and inner recirculation zone (IRZ) play the critical role in stabilizing the flame front, respectively. For the confined combustor, when the flame was far from blow-off, both the shear layer and the outer recirculation zone (ORZ) contributed to the stabilization. With the decrease of equivalence ratio, the stabilization effect of ORZ started to decrease and gradually weakened. When near lean blow-off limit, for CR = 2 (Φ= 0.48), the flame was mainly stabilized by the IRZ, while for CR = 3 (Φ = 0.46), the flame stabilization depended on the upstream IRZ/inner shear layer (ISL) and the downstream IRZ/ISL and ORZ/outer shear layer (OSL). Furthermore, the ISL vortexes would further accelerate the blow-off near the lean limit for confined and unconfined flames. The transition from stable to unstable was extended by increasing the CR in the confined combustor.

New simplified transient method for determining the coefficient of permeability of unsaturated soil

The instantaneous profile (IP) method is widely used for determining the coefficient of permeability of unsaturated soils. IP method requires the measurement or control (i.e., zero flux) of flux at any one end of a soil profile. Besides, there are requirements of variations in volumetric water contents (VWCs) and pore-water pressures (PWPs) at various points from the above-mentioned one end of the soil profile to a particular point in which the unsaturated coefficient of permeability is derived. The measurement or control of flux at one end of the soil profile requires high accuracy which causes difficulty while performing tests in the laboratory and field. To overcome the difficulty of the IP method, this study proposes a new simplified transient method for determining the coefficient of permeability of the unsaturated soil. Variations in volumetric water contents and corresponding pore-water pressures at three points are required in the new simplified transient method. The intellectual advantage of this method as compared to the IP method is that there is no need to measure or control the flux at one end of the soil profile. Therefore, this new method is more practical and is expected to be widely used in both laboratory tests and field tests. The validity of the new simplified transient method is verified through numerical simulations considering a one-dimensional seepage for four different types of soils including coarse-grained soil, sand, clay, and silty sand with gravel. The applicability of the new simplified transient method is demonstrated by comparing the unsaturated coefficients of permeability of soils computed by the new simplified transient method and the IP method. Good agreements in comparisons prove that the new simplified transient method is effective for determining the unsaturated coefficient of permeability of soil regardless of soil types and hydraulic functions features.

Wind tunnel study on the wake characteristics of a wind turbine model subjected to surge and sway motions

An experimental study was performed in a uniform incoming flow wind tunnel to investigate the effect of surge and sway motions on the wake characteristics of a wind turbine model. The platform surge and sway motions can be simulated at prescribed amplitudes and frequencies through a translation stage mounted on the base of the turbine model. The flow fields of near, intermediate, and far wakes of the turbine model were characterized by a particle image velocimetry system. Results show that the mean velocity profiles during the whole surging and swaying process of the downwind wakes were almost unchanged with that of a base-fixed turbine; however, the maximum mean velocity differences appeared near the blade tips for both motions compared with the base-fixed cases. Little difference was found between the mean velocity profiles of the turbine model while moving in different directions, for both the surge and sway motions. Later, the characteristics of instantaneous velocity profiles were investigated, and the lateral offset of the instantaneous velocity profiles for the swaying turbine at the two ends of the sway motion was observed. The offset distance was very close to sway amplitudes within the near wake, and it gradually decreased until it disappeared as the downstream distance increases. This work may provide an instrumental guide in the further research on the wake of floating offshore wind turbines.

Optimal Capacity Configuration of Hybrid Energy Storage System Considering Smoothing Wind Power Fluctuations and Economy

After comparing the economic advantages of different methods for energy storage system capacity configuration and hybrid energy storage system (HESS) over single energy storage system, a method based on improved moving average and ensemble empirical mode decomposition (EEMD) to smooth wind power fluctuations is proposed aiming at the optimal capacity configuration of HESS. Firstly, EEMD was used to decompose the HESS reference power which was derived by improved moving average filtering, and then several intrinsic mode functions (IMFs) were obtained. Each IMF instantaneous frequency-time profile was processed by Hilbert transform, the so- call gap frequency was identified, and then reconstruct the high and low frequency components to obtain the HESS reference power. Subsequently, taken the energy storage system charge-discharge efficiency and state of charge (SOC) into account, the rated power and capacities of each scheme was determined. Finally, based on Life Cycle Cost (LCC) theory, an energy storage system economic cost calculation model was established to compare the costs of each scheme and select the optimal one.

Entrainment and adaptation processes in the evolution of collisional bedload layers

We performed laboratory experiments which describe the evolution, from triggering until full formation, of a bedload layer. The phenomenon is driven by a turbulent open-channel flow at about constant discharge since the very initiation of the process. The flow stays uniform and the slope constant during the transient phase, during which we measured the instantaneous velocity and concentration profiles of the solid phase within the bedload layer. The timing of the process is governed by inertia and resistance forces. The bedload layer progressively thickens, fed by sediments entrained from the bed, which is progressively eroded, until the final steady uniform condition (i.e., equilibrium) is reached. We then applied a recent numerical model, able to cope with collisional suspensions using extended kinetic theories, to replicate the experimental results. The model results are used to further analyze and discuss the physical processes within the flow.

On the method of determining instantaneous wall shear stress from near-wall velocity measurements in wall turbulence

The determination of the instantaneous wall shear stress (WSS) from near-wall velocity measurements has received considerable attention. However, the most appropriate procedure and the achievable accuracy remain open topics. The present work uses direct numerical simulation datasets of channel flow to investigate the influences of the wall-normal distribution of instantaneous velocity, the method for estimating the velocity gradient, and the wall-normal position of velocity vectors on the accuracy of the instantaneous WSS determined from near-wall velocity measurements. In general, the method of dividing instantaneous velocity vectors by their wall-normal positions performs better than the method of linearly fitting instantaneous velocity profiles for estimating the wall velocity gradients when the wall position is correctly determined. However, the nonlinear instantaneous velocity distribution within the viscous layer means that all methods introduce a negative mean bias error and non-negligible root mean square error for the instantaneous WSS and its statistics. The magnitudes of these errors increase with the wall-normal position of the velocity vectors. An empirical method for correcting the instantaneous WSS statistics is proposed based on the negligible Reynolds number dependence of the bias error of all statistics. The influence of the wall-normal position of the velocity vectors on the WSS statistics and the correction method are verified using experimental data from open channel flows. The verification results show that the correction method significantly improves the accuracy of the statistics of instantaneous WSS determined from near-wall velocity measurements under canonical wall turbulence.

An experimental investigation of dam-break induced flood waves for different density fluids

The present study aims to investigate the effect of various fluids on dam-break flow propagation in a rectangular and horizontal channel under dry bed conditions. Laboratory experiments were carried out to produce dam-break flood waves in a tank by the sudden release of a movable gate that divided the tank into a reservoir and a downstream channel. In these experiments, three different fluids were used as Newtonian fluids in the reservoir: normal water, sunflower oil, and salt water. A digital image processing technique was adopted for the experimental characterization of the dam-break waves. Instantaneous free surface profiles of the dam-break flow were captured by a high-speed camera. Free-surface profiles for different times and time evolution of the flow depths at four selected locations were determined. The types of fluids had an effect on the results due to their specific characteristics such as density and viscosity. Furthermore, numerical simulation of the problem was performed by Reynolds-averaged Navier-Stokes (RANS) and Volume of Fluid (VOF) based software Flow-3D. When the experimental data were compared with the numerical simulation results, there was good agreement for the elapsed time and selected measuring locations.

Modeling of Electromagnetic Torque Including Ripple Harmonics in Synchronous Reluctance Machines

An analytical model to predict the instantaneous torque profile in Synchronous Reluctance Machine (SyncRel) is proposed and developed. The model predicts torque performance of the reluctance-based machine based on inductance or flux linkage harmonics. High performance torque ripple sensitive application has stringent torque ripple and noise and vibration requirements to satisfy the overall system performances. The prediction of the torque ripple is critical in these applications to identify the root cause and then mitigate the torque ripple through design alternations under different loading (current) conditions of the machine. The developed analytical model provides a simpler,intuitive and significantly less time consuming yet reasonably accurate alternative compared to the finite element analysis. A 2D finite element model has been developed to validate the proposed analytical model. The proposed model is also validated with experimental data of a 30-slot,4-pole SyncRel machine.