Two-dimensional Velocity Research Articles

Guided wave tomography for quantitative thickness mapping using non-dispersive SH0 mode through geometrical full waveform inversion (GFWI)

Guided wave tomography plays a significantly important role in quantitatively mapping thickness variations in plate-like structures and pipelines in the petrochemical industry for accurate measurement of corrosion, as guided waves enable rapid screening of large areas without needing direct access. Several inverse algorithms have been implemented in guided wave tomography; however, almost all of them use a primary assumption: the three-dimensional (3D) guided wave thickness reconstruction is simplified as a two-dimensional (2D) acoustic wave velocity inversion, which is then mapped to thickness variation using the dispersive nature of guided waves. Although this assumption simplifies the inverse procedure, it makes it impossible to use non-dispersive modes in reconstructions. Geometrical full waveform inversion (GFWI) is promising to overcome this limitation since it can reconstruct corrosion profiles through geometry optimization using a data-fitting procedure, where velocity-to-thickness mapping is not needed. In this work, GFWI-based guided wave tomography is developed in plate-like structures, and is applied to reconstruct thickness maps in a series of corrosion defects using the non-dispersive SH0 mode, demonstrating high performance and achieving an improved reconstruction resolution.

Bathymetry and discharge estimation in large and data-scarce rivers using an entropy-based approach

ABSTRACT This study implements an entropy theory-based approach to infer bathymetry for 29 selected cross-sections along a 1740 km reach of the Congo River. A genetic algorithm optimization approach is used based on an analysis of near-surface velocity measurements to generate a random sample of 1000 bathymetry profiles from which the analysis is carried out. The resulting simulated bathymetry shows good agreement compared to the measurements obtained via Accoustic Doppler Current Profiler (ADCP), with a correlation that varies from 0.49 to 0.88. The bathymetry results are subsequently used to estimate the two-dimensional cross-sectional flow velocity distribution and, consequently, to calculate the river discharge. The mean errors observed for flow area, discharge, and mean velocity are found to be 2.7%, 1.3%, and 1%, respectively. This study demonstrates, for the first time, the successful application of an entropy-based approach to estimate bathymetry and discharge in large rivers and has significant implications for remote sensing applications.

Assessing The Potential Of PIV Data To Resolve Hidden Frequency Scales

The present work investigates the performance of an advection-based flow reconstruction model to increase the temporal resolution of PIV measurements recorded in a turbulent, planar jet. Using a semi-Lagrangian technique in combination with Rapid Distortion Theory, a modified trajectory tracking procedure is implemented. The method introduces a specification for a two-dimensional convective velocity based on the least squares minimization of the linearized advection equation, in contrast to the previously introduced one-dimensional mean velocity profile outlined in Vocke et al. (2023). The new implementation is based on local flow measurements, making it well-suited towards streamwise heterogeneity and spatially developing flows. With this, the flow at some unknown time can be estimated from the know flow measurements at the forward and backward time. Spectral analysis illustrates the model's proficiency in recovering spatiotemporal information far exceeding the Nyquist frequency, with spectral reconstruction errors of less than 5% for the most extreme case. It is demonstrated that the spectral content can be estimated at least two orders of magnitude beyond the sampling frequency of the original recording. Improved performance compared to alternative methods is demonstrated with only minor impact on computational time. This indicates the approach may be used as a tool for experimental researchers a) having no access to a high-speed PIV or b) with high-speed PIV to increase the spectral resolution even further.

Spaceborne Synthetic Aperture Radar Aerial Moving Target Detection Based on Two-Dimensional Velocity Search

Synthetic aperture radar (SAR) can detect moving targets on the ground/sea, and high-resolution imaging on the ground/sea has critical applications in both military and civilian fields. This paper attempts to use a spaceborne SAR system to detect and image moving targets in the air for the first time. Due to the high velocity of aerial targets, they usually appear as two-dimensional range and azimuth direction defocus in SAR images, and clutter will also have a profound impact on target detection. To solve the above problems, a method of detecting and focusing on a spaceborne SAR target based on a two-dimensional velocity search is proposed by combining the BP algorithm. According to the current environment of the aerial target and the number of system channels, the clutter suppression methods are set and combined with two-dimensional velocity search with different precision, the Shannon entropy under different search velocity groups is used to obtain the search velocity group closest to the actual velocity and realize the integrated processing of moving target detection–focused imaging parameter estimation. Combined with simulation data, the effectiveness of the proposed method is verified.

Theoretical studies on wide-operating-range ejector based on operating conditions and multi-parameter coupling effect in proton exchange membrane fuel cell system

When the ejector in a fuel cell system operates under off-design conditions, its performance will significantly decrease. To improve the performance of the ejector under all operating conditions, this paper proposes a theoretical model for predicting performance and optimizing the structure of the ejector that has not been studied before. Based on the jet theory, a two-dimensional three-segment velocity distribution is established, and the exponent of the velocity function is modified by simulation and experimental data, reducing the model’s calculation error from 15% to 6.5%. By combining the Lagrange algorithm, we investigate the influence of operating conditions and multi-parameter coupling effects on ejector performance, obtaining optimal values for structural parameters under different load conditions. The results show that the optimal value of main nozzle exit position (Lx) increases with increasing current and the optimal value ranges from 0.5 to 6 mm. The influence of dimensionless parameter (λc), dimensionless parameter (λd) and diffusion angle (αd) on ejector performance is significant and optimal values exist. Reducing the nozzle throat diameter (dnt) can effectively promote the entrainment performance at low power, and four adjustment conditions are proposed. When dnt decreases from 3.2 to 2.0 mm, the operating range of the current is increased by 38.42%, the power range is increased by 42.12%, and the pressure drop of the ejector (pd) decreased by 9.66 bar. The theoretical model not only improves the accuracy of predicting the entrainment ratio, but also realizes the study of the influence of multi-structural parameter coupling effect on the performance of the ejector, which leads to a significant improvement in the optimization accuracy and efficiency, and extends the applicable power range of the ejector. This provides a new direction for the future performance optimization of wide operating range ejectors considering multi-parameter coupling effects.

Identifying the body force from partial observations of a two-dimensional incompressible velocity field

Identifying the body force from partial observations of a two-dimensional incompressible velocity field

Ultrasound Shear Elastography With Expanded Bandwidth (USEWEB): A Novel Method for 2D Shear Phase Velocity Imaging of Soft Tissues.

Ultrasound shear wave elastography (SWE) is a noninvasive approach for evaluating mechanical properties of soft tissues. In SWE either group velocity measured in the time-domain or phase velocity measured in the frequency-domain can be reported. Frequency-domain methods have the advantage over time-domain methods in providing a response for a specific frequency, while time-domain methods average the wave velocity over the entire frequency band. Current frequency-domain approaches struggle to reconstruct SWE images over full frequency bandwidth. This is especially important in the case of viscoelastic tissues, where tissue viscoelasticity is often studied by analyzing the shear wave phase velocity dispersion. For characterizing cancerous lesions, it has been shown that considerable biases can occur with group velocity-based measurements. However, using phase velocities at higher frequencies can provide more accurate evaluations. In this paper, we propose a new method called Ultrasound Shear Elastography with Expanded Bandwidth (USEWEB) used for two-dimensional (2D) shear wave phase velocity imaging. We tested the USEWEB method on data from homogeneous tissue-mimicking liver fibrosis phantoms, custom-made viscoelastic phantom measurements, phantoms with cylindrical inclusions experiments, and in vivo renal transplants scanned with a clinical scanner. We compared results from the USEWEB method with a Local Phase Velocity Imaging (LPVI) approach over a wide frequency range, i.e., up to 200-2000 Hz. Tests carried out revealed that the USEWEB approach provides 2D phase velocity images with a coefficient of variation below 5% over a wider frequency band for smaller processing window size in comparison to LPVI, especially in viscoelastic materials. In addition, USEWEB can produce correct phase velocity images for much higher frequencies, up to 1800 Hz, compared to LPVI, which can be used to characterize viscoelastic materials and elastic inclusions.

A Vlasov-Fokker-Planck-Landau code for the simulation of colliding supersonic dense plasma flows

A Vlasov-Fokker-Planck-Landau (VFPL) code is developed for the study of colliding supersonic dense plasma flows, in which the VFPL equations for both electrons and ions are solved by the time splitting strategy in the two-dimensional Cartesian coordinate space and the two-dimensional velocity space (2D2V). To accurately handle two colliding supersonic plasma flows with their velocities even much higher than the thermal velocities of ions, the full Fokker-Planck-Landau operator is employed for the collision terms. Using advanced numerical methods such as the fast spectral method and the asymptotic-preserving scheme, the ion-ion and electron-electron collision terms can be properly solved with a relatively large time step so that both high accuracy and efficiency of the developed code can be achieved. Further, the quantum degeneracy effect due to the high density and relatively low initial temperature of the electrons is included in the model. In addition, both the energy and momentum conservation are well satisfied. The developed code provides a unique numerical tool to study the interactions between high-velocity high-density plasma flows, which may be encountered in some advanced schemes of inertial confinement fusion and laser-driven laboratory astrophysics experiments.

Reconstruction and prediction of the rotor wake flow field in hovering state

A clear understanding of the flow structure and evolution of the rotor wake flow field is one of the key problems to be solved in the development of rotor aerodynamics. The tip vortices are the primary structure of the rotor wake flow field. A theoretical model of the vortex ring was established to verify the feasibility of flow field reconstruction. Particle image velocimetry (PIV) is used to measure the two-dimensional velocity field in the rotor wake. Because of the wandering motion of tip vortices, a new conditional average algorithm is proposed to deal with the flow field. On this basis, it is proposed that the plane interval of the rotor wake flow field reconstructed by interpolation should be less than 20 deg. The vortex core radius is obtained by the analysis method based on the circulation. A Back Propagation (BP) neural network was established to predict the axial and radial positions of the tip vortices and the radius of the vortex core. The inputs are the vortex ages measured by the experiment, and the outputs are the position and radius of the vortex core under any vortex ages. The predicted values were in good agreement with the experimental results. The study provides further analytical methods and new insights for the characteristics and evolution of tip vortices.

A numerical model for calculating velocity distribution in cross-section of an open channel

Flow velocity in open channels is a fundamental hydraulic parameter with wide-ranging applications, including the development of rating curves and the study of sediment transport. While some river engineering projects may only require the calculation of average flow velocity, others, such as the design of hydraulic structures and stable channels, as well as the assessment of boundary shear stress, necessitate a more comprehensive understanding of flow dynamics, including the two-dimensional velocity distribution within open channels. To address this, various mathematical models have been proposed for estimating the two-dimensional distribution of flow velocity across transverse and depth directions. However, these models often come with complexities that hinder their practical application. In this research, we introduce a simplified numerical model that combines simplified Navier–Stokes equations with an eddy viscosity formula. This innovative approach aims to estimate velocity distribution in both rectangular and trapezoidal channels. The accuracy of our developed model hinges on the momentum transfer coefficient used in the eddy viscosity formula. Through the execution of the numerical model and the utilization of observational data, we determined the optimal value of the momentum transfer coefficient to be 0.241. To validate the effectiveness of our numerical model, we compared its predictions with laboratory data encompassing diverse hydraulic conditions. The results demonstrated a high level of accuracy, with the calculated velocity distribution and flow discharge differing by no more than 7.6% and 6.8%, respectively.

An Ensemble Study of Turbulence in Extended QSO Nebulae at z ≈ 0.5–1

Turbulent motions in the circumgalactic medium play a critical role in regulating the evolution of galaxies, yet their detailed characterization remains elusive. Using two-dimensional velocity maps constructed from spatially extended [O ii] and [O iii] emission, Chen et al. measured the velocity structure functions (VSFs) of four quasar nebulae at z ≈ 0.5–1.1. One of these exhibits a spectacular Kolmogorov relation. Here, we carry out an ensemble study using an expanded sample incorporating four new nebulae from three additional quasi-stellar object (QSO) fields. The VSFs measured for all eight nebulae are best explained by subsonic turbulence revealed by the line-emitting gas, which in turn strongly suggests that the cool gas (T ∼ 104 K) is dynamically coupled to the hot ambient medium. Previous work demonstrates that the largest nebulae in our sample reside in group environments with clear signs of tidal interactions, suggesting that environmental effects are vital in seeding and enhancing the turbulence within the gaseous halos, ultimately promoting the formation of the extended nebulae. No discernible differences are observed in the VSF properties between radio-loud and radio-quiet QSO fields. We estimate the turbulent heating rate per unit volume, Q turb, in the QSO nebulae to be ∼10−26–10−22 erg cm−3 s−1 for the cool phase and ∼10−28–10−25 erg cm−3 s−1 for the hot phase. This range aligns with measurements in the intracluster medium and star-forming molecular clouds but is ∼103 times higher than the Q turb observed inside cool gas clumps on scales ≲1 kpc using absorption-line techniques. We discuss the prospect of bridging the gap between emission and absorption studies by pushing the emission-based VSF measurements to below ≈10 kpc.

A physics-oriented shadowgraph motion estimation algorithm for turbulent flow structures

Shadowgraph imaging is a simple, cost-effective, and non-invasive technique for visualizing strong gradients in transparent medium. This paper developed a shadowgraph motion estimation algorithm to resolve dense motion fields for turbulent flow structures. The algorithm inherits the framework of the optical flow method, which resolves the two-dimensional velocity vectors from two basic constraints using optimization techniques. In the current motion estimation scheme, a physics-oriented constraint is derived from the optical equation of shadowgraph imaging and the fluid continuity equation, while the other constraint adopts a second-order div-curl equation. The improved constraints are specifically suitable for shadowgraph imaging, which can resolve more accurate estimations. An energy function is constructed with the two constraints, and the velocity components are solved by minimizing the energy function. Several state-of-the-art optimization techniques are adopted, including multi-resolution pyramids, weighted median filter and graduated non-convex algorithms. The algorithm is applied to two test conditions covering a wide velocity range, including an acoustic excited premixed flame and a sonic jet. The comparison to Horn–Schunck optical flow indicates that the current algorithm is able to resolve more details of the turbulent flow field, and the velocity shows better continuity. The proposed algorithm has great potential for motion estimation based on shadowgraph images in high speed turbulent flow and combustion research.

Heat transfer across an air curtain for heat confinement in road tunnels: Influence of the heat source

Experiments were carried out to study the influence of the heat source using double-flow double-jet curtains (DS-TJ) to confine heat in fire safety problems. For this purpose, a small-scale road tunnel facility in 1:34 was built. The heat source used is an electric resistance. Simultaneous two-dimensional temperature and velocity measurements were made across the DS-TJ air curtain and in its immediate vicinity using a fine thermocouple and a 2D laser Doppler anemometer (LDA), respectively. Four cases were studied, by modifying the air curtain velocities at the nozzle exits and the heat source power. It is noted that hot-cold jets and heat source play a role in the curtain heat confinement by modifying the development of the two jets. Both the entrainment of the upward flow rising from the heat source as well as the Kelvin-Helmholtz instabilities contribute to this. On the other hand, the nozzle exit velocities determine the behavior of the Reynolds stress profiles as well as the production of the velocities fluctuations across the curtain, showing a non-correlating effect on the hot side, so that the profiles take values around zero, suggesting a heat source influence. In contrast in the cold side negative values indicate energy-draining behavior. The intensity of thermal turbulence reveals that the hot jet has higher values than the cold jet, constituting a thermal barrier to turbulent heat flow, and all activity is relegated to the zone of interaction between the two jets. In fact, the production derived from temperature fluctuations occurs mainly in the interaction of hot-cold jets, and negative values are due to large turbulent eddies, such as Kelvin-Helmholtz instabilities and Görtler-type structures. The Richardson number shows that buoyancy forces prevail on both sides of the curtain (Ri > 0.1), especially on the hot side, due to the heat source. Lower Ri values within the curtain indicate the presence of a thermal barrier, attenuating heat transfer through the curtain and favoring thermal sealing.

Two-Dimensional Absolute Velocity Estimation of Moving Targets by Real-Aperture Scanning Radar Using Multiorder Range Migration Fitting Method

Two-Dimensional Absolute Velocity Estimation of Moving Targets by Real-Aperture Scanning Radar Using Multiorder Range Migration Fitting Method

Transient Tire Slip Losses Using the Brush Theory

ABSTRACT Tire slip losses have been shown to have a significant impact on vehicle performance in terms of energy efficiency, thus requiring accurate studies. In this paper, the transient dissipation mechanisms connected to the presence of micro-sliding phenomena occurring at the tire–road interface are investigated analytically. The influence of a two-dimensional velocity field inside the contact patch is also considered in light of the new brush theory recently developed by the authors. Theoretical results align with findings already known from literature but suggest that the camber and turn spins contribute differently to the slip losses and should be regarded as separate entities when the camber angle is sufficiently large. The present work shows that an additional amount of power which relates to the initial sliding conditions is generated or lost during the unsteady-state maneuvers. A simple example is presented to illustrate the discrepancy between the microscopic and macroscopic approaches during a transient maneuver.

Unsupervised Neural Manifold Alignment for Stable Decoding of Movement from Cortical Signals.

The stable decoding of movement parameters using neural activity is crucial for the success of brain-machine interfaces (BMIs). However, neural activity can be unstable over time, leading to changes in the parameters used for decoding movement, which can hinder accurate movement decoding. To tackle this issue, one approach is to transfer neural activity to a stable, low-dimensional manifold using dimensionality reduction techniques and align manifolds across sessions by maximizing correlations of the manifolds. However, the practical use of manifold stabilization techniques requires knowledge of the true subject intentions such as target direction or behavioral state. To overcome this limitation, an automatic unsupervised algorithm is proposed that determines movement target intention before manifold alignment in the presence of manifold rotation and scaling across sessions. This unsupervised algorithm is combined with a dimensionality reduction and alignment method to overcome decoder instabilities. The effectiveness of the BMI stabilizer method is represented by decoding the two-dimensional (2D) hand velocity of two rhesus macaque monkeys during a center-out-reaching movement task. The performance of the proposed method is evaluated using correlation coefficient and R-squared measures, demonstrating higher decoding performance compared to a state-of-the-art unsupervised BMI stabilizer. The results offer benefits for the automatic determination of movement intents in long-term BMI decoding. Overall, the proposed method offers a promising automatic solution for achieving stable and accurate movement decoding in BMI applications.

Systematic analysis of non-intrusive polynomial chaos expansion to determine rotary blood pump performance over the entire operating range

This study applies non-intrusive polynomial chaos expansion (NIPCE) surrogate modeling to analyze the performance of a rotary blood pump (RBP) across its operating range. We systematically investigate key parameters, including polynomial order, training data points, and data smoothness, while comparing them to test data. Using a polynomial order of 4 and a minimum of 20 training points, we successfully train a NIPCE model that accurately predicts pressure head and axial force within the specified operating point range ([0–5000] rpm and [0–7] l/min). We also assess the NIPCE model's ability to predict two-dimensional velocity data across the given range and find good overall agreement (mean absolute error = 0.1 m/s) with a test simulation under the same operating condition. Our approach extends current NIPCE modeling of RBPs by considering the entire operating range and providing validation guidelines. While acknowledging computational benefits, we emphasize the challenge of modeling discontinuous data and its relevance to clinically realistic operating points. We offer open access to our raw data and Python code, promoting reproducibility and accessibility within the scientific community. In conclusion, this study advances comprehensive NIPCE modeling of RBP performance and underlines how critically NIPCE parameters and rigorous validation affect results.

Interseismic kinematics along the Tuolaishan-Lenglongling fault determined by Sentinel-1 InSAR observations

Current study of interseismic fault slip behavior constrained by Interferometric Synthetic Aperture Radar (InSAR) derived line-of-sight (LOS) velocities has been favored. However, we found that the fault slip rate inferred by the spatially dense two-dimensional (2-D) horizontal velocities can be more robust than that estimated by LOS velocities. Here, we obtain the LOS velocity maps across the Qilian-Haiyuan fault (QL-HYF) zone through time series analysis of Sentinel-1 A/B data (2015–2020). Combining the GPS observations, we calculate the interseismic 3-D velocity map. Based on a genetic optimization algorithm, we investigate the fault motion at depth on the Lenglongling (LLL) and Tuolaishan (TLS) segments. We show the spatial variation of the strike-slip rate (4.1– 5.5 mm/yr), dip-slip rate (0– 1.7 mm/yr), crustal compression shortening rate (1.2– 3 mm/yr) and locking depth (7.9– 17.1 km) along the TLSF. These parameters are 3.4– 5.6 mm/yr, 0– 0.8 mm/yr, 1.9– 4 mm/yr and 13.3– 23 km along the LLLF, respectively. Based on the inferred strike-slip rate (∼3.4 mm/yr) and locking depth (∼13.3 km) on the main fault of the 2022 Menyuan earthquake, the estimated interseismic accumulated seismic moment (1.44×1019 N m) since the 1540 M7.2 paleoearthquake can produce an Mw6.74 earthquake, in agreement with the moment magnitude (∼Mw6.7) caused by the coseismic rupture. This suggests that there is a good correspondence between inter- and co-seismic kinematics, and the fault with low interseismic slip rate remains have the potential to generate large earthquake.

Solidified magma reservoir derived from active source seismic experiments in the Aira caldera, southern Kyushu, Japan

The Aira caldera, located in southern Kyushu, Japan, originally formed 100 ka, and its current shape reflects the more recent 30 ka caldera-forming eruptions (hereafter, called the AT eruptions). This study aimed to delineate the detailed two-dimensional (2D) seismic velocity structure of the Aira caldera down to approximately 15 km, by means of the travel-time tomography analysis of the seismic profile across the caldera acquired in 2017 and 2018. A substantial structural difference in thickness in the subsurface low-velocity areas in the Aira caldera between the eastern and western sides, suggest that the Aira caldera comprises at least two calderas, identified as the AT and Wakamiko calderas. The most interesting feature of the caldera structure is the existence of a substantial high-velocity zone (HVZ) with a velocity of more than 6.8 km/s at depths of about 6–11 km beneath the central area of the AT caldera. Because no high ratio of P- to S-wave velocity zones in the depth range were detected from the previous three-dimensional velocity model beneath the AT caldera region, we infer that the HVZ is not an active magma reservoir but comprises a solidified and cool remnant. In addition, a poorly resolved low-velocity zone around 15 km in depth suggests the existence of a deep active magma reservoir. By superimposing the distribution of the known pressure sources derived from the observed ground inflation and the volcanic earthquake distribution onto the 2D velocity model, the magma transportation path in the crust was imaged. This image suggested that the HVZ plays an important role in magma transportation in the upper crust. Moreover, we estimated that the AT magma reservoir in the 30 ka Aira caldera-forming eruptions has the total volume of 490 km3 DRE and is distributed in a depth range of 4–11 km.Graphical

Results of 23 yr of Pulsar Timing of PSR J1453-6413

In this paper, we presented the 23.3 yr of pulsar timing results of PSR J1456−6413 based on the observations of Parkes 64 m radio telescope. We detected two new glitches at MJD 57093(3) and 59060(12) and confirmed its first glitch at MJD 54554(10). The relative sizes (Δν/ν) of these two new glitches are 0.9 × 10−9 and 1.16 × 10−9, respectively. Using the “Cholesky” timing analysis method, we have determined its position, proper motion, and two-dimensional transverse velocities from the data segments before and after the second glitch, respectively. Furthermore, we detected exponential recovery behavior after the first glitch, with a recovery timescale of approximately 200 days and a corresponding exponential recovery factor Q of approximately 0.15(2), while no exponential recovery was detected for the other two glitches. More interestingly, we found that the leading component of the integral pulse profile after the second glitch became stronger, while the main component became weaker. Our results will expand the sample of pulsars with magnetosphere fluctuation triggered by the glitch event.