Velocity Measurements Research Articles

Noise Reduction of Velocity Measured by Frequency-Supervised Combined Doppler Sonar Using an Adaptive Sliding Window and Kalman Filter

Velocity is fundamental information for ocean engineering. It is difficult for traditional Doppler sonar to provide accurate and wide-range velocity measurement information with a short time lag. Therefore, a frequency-supervised combined Doppler sonar system using an adaptive sliding window and Kalman filter is proposed. In this method, the initial value of the integer ambiguity is calculated based on the average value of the conventional Doppler sonar. The change value of the integer ambiguity is calculated by the difference of the adjacent velocities measured by coherent Doppler sonar. The velocity of combined Doppler sonar is calculated by the cumulative result of the initial and change values of integer ambiguities. Finally, the velocity bias due to the error of the integer ambiguity calculation is corrected by the frequency supervision using the Kalman filter in a sliding time window under different signal-to-noise ratios. The experimental results show that the proposed method is more accurate than the conventional Doppler sonar, has a wider measurement range compared with coherent Doppler sonar, and suppresses the impulsive noise well. The frequency-supervised combined Doppler sonar using an adaptive sliding window and Kalman filter can provide accurate and precise velocities with a short time lag over a wide range of signal-to-noise ratios.

Detection and characterisation of giant planets with Gaia astrometry

Abstract Astrometric observations with Gaia are expected to play a valuable role in future exoplanet surveys. With current data from Gaia’s third data release (DR3), we are sensitive to periods from less than 1 year to more than 4 years but, unlike radial velocity are not as restricted by the orbital inclination of a potential planet. The presence and potential properties of a companion affect the primary’s renormalised unit weight error (RUWE) making this a valuable quantity in the search for exoplanets. Using this value and the fitted astrometric tracks from Gaia, we use Bayesian inference to constrain the mass and orbital parameters of companions in known systems. Combining this with radial velocity measurements, we show it is possible to independently measure mass and inclination and suggest HD 66141 b is a possible brown dwarf with maximum mass 23.9$^{+7.2}_{-6.4}$ MJ. We show how this method may be applied to directly imaged planets in the future, using β-Pictoris c as an example but note that the host star is bright and active, making it difficult to draw clear conclusions. We show how the next Gaia data release, which will include epoch astrometry, will allow us to accurately constrain orbital parameters from astrometric data alone, revolutionising future searches for exoplanets. Combining predicted observational limits on planet mass with theoretical distributions, we estimate the probability that a star with a given RUWE will host a detectable planet, which will be highly valuable in planning future surveys.

Use of Ultrasound to Identify Microstructure-Property Relationships in (AlN + WC) Fabricated with Electroless Ni Producing

In order to improve the properties of the materials produced by the powder metallurgy method, first of all, powders (16.59% AlN + 6.63% WC) were coated with nickel (Ni) by electroless method, and then box boriding, which is one of the most widely used surface coating methods, was applied. A composite formed with (16.59% AlN + 6.63% WC)76.7Ni was prepared under the Ar shroud in the temperature range of 1000-1400°C. Pulse-echo technique was used for ultrasonic velocity measurements on Ni coated (16.59% AlN + 6.63% WC) samples. It is aimed to examine the change of physical, mechanical and ultrasonic properties of the obtained ceramic-metal composites depending on different sintering temperatures. In addition, the samples were characterized by mechanical and metallographic examination. The results show that the longitudinal and transverse ultrasonic velocity values and ultrasonic modulus (shear, bulk, Young’s etc.) values increase simultaneously with the increase of sintering temperature. The highest microhardness value was observed in composite samples sintered at 1400°C and its value was 1150.80 Hv. The increased strength is mainly due to grain refinement and strong interfacial bonding between Ni particles and AlN and WC matrix.

DESIGN OF AN AUTOMATIC PENDULUM VELOCITY MEASURING DEVICE USING LIGHT SENSORS

The instantaneous velocity of an object is the rate of change of its position over an infinitesimally small-time interval, making direct measurement with tools like stopwatches impractical. Using two LDR sensors paired with an Arduino, it is possible to measure such small-time intervals effectively. Understanding the maximum velocity of a mathematical pendulum is critical for distinguishing between harmonic and non-harmonic oscillations. To validate the accuracy of the sensor-Arduino system, several experiments were conducted, including comparisons between Arduino measurements and those obtained from a movie tracker, as well as variations in sensor separation distances, initial oscillation angles, and pendulum rope lengths. Results showed a high level of agreement between Arduino and movie tracker measurements for pendulum crossing times. Additionally, the sensor-Arduino system successfully differentiated the effects of varying each parameter while holding others constant. The system demonstrated an accuracy of 97.86% for velocity measurements at a release angle of 5°, with an average recorded velocity of 23.350 m/s. These findings confirm the sensor-Arduino system's capability to reliably measure the velocity of a mathematical pendulum.

Structure and Mechanical Properties of a Titanium–8 wt.% Gallium Alloy

This paper describes a study of the microstructure and mechanical properties of a titanium–gallium (Ti-8 wt.% Ga) alloy using X-ray diffraction, optical metallography, micro-hardness measurements, compression and tensile testing, nanoindentation and ultrasonic velocity measurements. X-ray diffraction has shown the alloy to be wholly α Ti with no other phases present. A comparison of the hardness and elastic modulus values of the Ti-8Ga alloy with those of Ti-6Al-4V showed the former to have a significantly higher hardness, although the elastic moduli of the two alloys were broadly comparable. The study also indicated reasonable agreement between the elastic moduli obtained by nanoindentation, ultrasonic velocity measurements and tensile testing. Under compressive loading, the mean 0.2% proof stress values of the Ti-8Ga alloy were between 1066 MPa and 1083 MPa. However, under tensile conditions, the mean tensile strength was found to be only 427 MPa, and the alloy exhibited highly brittle behaviour, with specimens failing before they had undergone any appreciable plasticity. The cause of this was ascribed to high oxygen and nitrogen levels.

Aortic velocity measurements derived from phase-contrast MRI are influenced by a cardiac implantable electronic device in both adult and pediatric human subjects.

Overall there is a lack of evidence on the accuracy and precision of phase-contrast (PC) MRI in patients with cardiac implantable electronic devices (CIEDs). The purpose of this study is to determine whether aortic velocity measurements are influenced by a CIED. We scanned 21 adult patients and 8 pediatric volunteers using clinical standard PC and real-time PC (rt-PC) sequences with and without a CIED generator taped on human subjects (below the left clavicle for adults and children; also on the abdomen for children) to mimic image artifacts. Peak and mean velocities above the aortic valve were calculated. The Bland-Altman analyses on peak velocity measurements in pediatric subjects showed that both the accuracy and precision worsen as the distance between the CIED and aortic valve decreases (i.e., from abdomen to below the left clavicle). Specifically, both the bias and the coefficient of variation (CV) for both clinical PC and rt-PC increased from the abdominal position (clinical: bias = -1.1%, CV = 4.3%; rt-PC: bias = -0.3%, CV = 3.4%) to the clavicle position (clinical: bias = -4.0%, CV = 8.1%; rt-PC: bias = 8.2%, CV = 7.3%). A similar trend was observed for mean velocity. The mean difference in peak and mean velocity measurements between rt-PC with CIED (either position) and clinical standard PC with no CIED was within 7.5%. In adult patients, the mean difference between rt-PC with CIED and clinical standard PC with CIED in peak velocity was 6.9%, and the CV was 7.9%. This study demonstrates that aortic velocity measurements are influenced by CIED in both adult and pediatric subjects.

Study Regarding the Possibility of Using Ultrasonic Pulse Velocity (UPV) on Earthen Construction Evaluation

The determination of drying period, compressive strength, and air-dry density represent crucial parameters for assessing the quality and performance of earthen construction materials. This paper explores the possibilities of using the ultrasonic method as a non-destructive testing technique applied to earthen materials (specimens, elements, or structures) to determine these properties. The method relies on the measurement of ultrasonic pulse velocity (UPV), which is influenced by factors such as density, elasticity, and curing process. By analyzing the propagation of ultrasonic waves through earthen samples, valuable insights can be gained regarding their drying period, compressive strength, and density. The drying period of earthen samples can be determined using the ultrasonic method by monitoring the changes in pulse velocity over time. As the moisture content decreases during the drying process, the velocity of ultrasonic waves increases due to the reduced presence of water. This allows for the estimation of the drying period without the need for time-consuming and destructive testing methods. Compressive strength is also a critical parameter in assessing the structural integrity of earthen materials. The UPV method offers a non-destructive approach to determine the compressive strength of earthen samples. This provides a valuable tool for quality control and assessment of earthen construction materials. Density is another important property that influences their performance and the UPV method can be used to determine the density of earthen materials by measuring the ultrasonic pulse velocity and analyzing its relationship with density. This non-destructive approach allows for quick and efficient estimation of the compactness and quality of earthen mixes. Overall, the ultrasonic method offers a non-destructive and efficient approach in determining the drying period, compressive strength, and density of various soil compositions. By measuring the pulse velocity and analyzing its relationship with these properties, valuable insights can be gained regarding the quality and performance of earthen construction materials. This method has the potential to significantly improve the assessment and quality control processes in earthen construction, leading to more sustainable and reliable structures associated with the earthen techniques.

The Effect Of Co2-Brine-Rock Interaction Towards Sand Onset Modeling In Dolomite-Rich Sandstone: A Case Study In Air Benakat Formation, South Sumatera, Indonesia

Carbon Capture Utilization Storage (CCUS) into geological storage (e.g., Enhanced Oil or Gas Recovery) provides a solution to reduce CO­2 emissions. However, it still remains a potential operational problem, such as sand problem phenomena in producer wells. This study observes the phenomenon of sand problems in production wells possibly triggered by CO2-brine-rock interactions on CO2 injection in rich dolomite sandstone reservoir. This research performs several experimental works (i.e., time-lapse dry mass measurements, X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), and elastic wave measurements) by using CO2-brine-rock batch experimental setup as well as geochemical simulation to observe mineral dissolution, pore structures alteration as well as rock physics alteration due to CO2-brine-rock interactions. We used an outcrop sample of dolomite-rich sandstone from the Air Benakat Formation, South Sumatera, Indonesia. Our experimental and simulation works show that dolomite dissolution (dolomite reduction of ~4% after 14 soaking days), secondary porosity development (11% of visible porosity improvement), as well as rock strength reduction, occur indirectly (shown by elastic wave velocity, i.e. and reduction of ~3.8% and ~4.4%, respectively) due to CO2-brine-rock interactions. Subsequently, the results of elastic wave velocity measurements were then used to modify a considerable sand onset prediction (sand-free envelope) model. The modified model showed that the production well was more prone to sand problems due to CO2-brine-rock interactions. Thus, it is concluded that the sand onset prediction model with considering CO2-brine-rock interactions could help to design a better sand management strategy in producer wells.

Multiplicity of Galactic Cepheids from long-baseline interferometry V. High-accuracy orbital parallax and mass of SU Cygni

We aim to accurately measure the dynamical mass and distance of Cepheids by combining radial velocity measurements with interferometric observations. Cepheid mass measurements are particularly necessary for solving the Cepheid mass discrepancy, while independent distance determinations provide a crucial test of the period--luminosity relation and Gaia parallaxes. We used the multi-telescope interferometric combiner, the Michigan InfraRed Combiner (MIRC) of the Center for High Angular Resolution Astronomy (CHARA) Array, to detect and measure the astrometric positions of the high-contrast companion orbiting the Galactic Cepheid SU Cygni. We also present new radial velocity measurements from ultraviolet spectra taken with the Hubble Space Telescope. The combination of interferometric astrometry with optical and ultraviolet spectroscopy provided the full orbital elements of the system, in addition to component masses and the distance to the Cepheid system. We measured the mass of the Cepheid, $M_A = and its two companions Ba and Bb This is the most accurate existing measurement of the mass of a Galactic Cepheid ( Comparing with stellar evolution models, we show that the mass predicted by the tracks is higher than the measured mass of the Cepheid, which is similar to the conclusions of our previous work. We also measured the distance to the system to be $ obtaining an unprecedented parallax precision of $ which is the most precise and accurate distance for a Cepheid. This precision is similar to what is expected by Gaia for its last data release (DR5 in $ 2030$) for single stars fainter than $G = 13$, but is not guaranteed for stars as bright as SU Cyg. We demonstrate that evolutionary models remain incapable of accurately reproducing the measured mass of Cepheids, often predicting higher masses for the expected metallicity, even when factors such as rotation or convective core overshooting are taken into account. Our precise distance measurement allowed us to compare predictions from some period--luminosity relations. We find a disagreement of 0.2-0.5\,mag with relations calibrated from photometry, while relations calibrated from a direct distance measurement are in better agreement.

Damage characterization of AlSi10Mg plates subjected to rigid impacts up to 300 m/s: comparison between subtractive and additive manufacturing

Mechanical structures built using the additive manufacturing (AM) process are generating significant interest due to their ability to design structural components with complex geometries. Indeed, additive processes, by adding material layer by layer, enables the creation of geometries that would be unfeasible using standard processes. However, while mechanical tests have extensively validated the use of conventional processes, the characterization of parts generated by less conventional processes, such as additive manufacturing, remains open to discussion. Specifically, will a part manufactured by AM meet the specifications in terms of mechanical strength? This paper contributes to answering this question by comparing identical AlSi10Mg plates manufactured using the AM process with a LASER powder bed fusion (L-PBF) machine (additive) and by conventional subtractive process (SM), subjected to high-velocity impacts. The impacts have been conducted on additive and subtractive 70*150*2 mm plates up to 300 m/s.” Based on measurements of projectile impact and residual velocities, as well as the study of deformation profiles of the different plates, the damage domains were identified. These tests highlighted significant differences between the different processes.

Rheology of polyacrylamide-based fluids and its impact on proppant transport in hydraulic fractures

Rheological experiments and measurements of particle settling velocity under static conditions were conducted for two types of polyacrylamide (PAA-based) fluids. The flow behavior of the viscoelastic fluids is described by a simplified, three-parameter model that integrates a constant viscosity at low shear rates with a power-law viscosity dependency at higher shear rates. The estimated dependencies of the rheological parameters and particle settling velocity on PAA concentration align with the classical power-law scaling for semi-dilute polymer solutions. The identified scaling offers valuable insight for optimizing the chemical composition of fracturing fluids, thereby improving the efficiency of hydraulic fracturing technology. By applying the lubrication approximation to the Navier–Stokes equations, a set of equations for the suspension flow in a vertical plane channel, characterized by the three-parameter rheology model, was derived. In typical fracturing conditions, the conventional power-law viscosity model used in current fracturing simulators significantly overestimates the gap-averaged apparent fluid viscosity compared to the proposed model. The novel model of the suspension flow aims to enhance the accuracy of proppant transport models applied in hydraulic fracturing simulators. Based on the three-parameter rheology model, a new model of particle settling in the studied PAA-based fluids is developed. It is based on smart Stokes' law, where viscosity is calculated according to either the plateau or power-law region, depending on the self-induced shear rate. The new model more accurately approximates experimentally determined settling velocity of proppant under static conditions across a broad range of PAA concentrations than existing models.

The GAPS programme at TNG

Ultra-hot Jupiters (UHJs) are gas giant planets orbiting close to their host star, with equilibrium temperatures exceeding 2000 K, and among the most studied planets in terms of their atmospheric composition. Thanks to a new generation of ultra-stable high-resolution spectrographs, it is possible to detect the signal from the individual lines of the species in the exoplanetary atmospheres. We employed two techniques in this study. First, we used transmission spectroscopy, which involved examining the spectra around single lines of Fe II. Then we carried out a set of cross-correlation studies for two UHJs: KELT-9b and KELT-20b. Both planets orbit fast-rotating stars, which resulted in the detection of the strong Rossiter-McLaughlin (RM) effect and center-to-limb variations in the transmission spectrum. These effects had to be corrected to ensure a precise analysis. Using the transmission spectroscopy method, we detected 21 single lines of Fe II in the atmosphere of KELT-9b. All of the detected lines are blue-shifted, suggesting strong day-to-night side atmospheric winds. The cross-correlation method leads to the detection of the blue-shifted signal with a signal-to-noise ratio (S/N) of 13.46. Our results are in agreement with models based on non-local thermodynamical equilibrium (NLTE) effects, with a mean micro-turbulence of νmic = 2.73 ± 1.5 km s−1 and macro-turbulence of νmac = 8.22 ± 3.85 km s−1. In the atmosphere of KELT-20b, we detected 17 single lines of Fe II. Considering different measurements of the systemic velocity of the system, we conclude that the existence of winds in the atmosphere of KELT-20b cannot be determined conclusively. The detected signal with the cross-correlation method presents a S/N of 11.51. The results are consistent with NLTE effects, including means of νmic = 3.04 ± 0.35 km s−1 and νmac = 6.76 ± 1.17 km s−1.

Effects of viscosity and induced magnetic fields on weakly nonlinear wave transmission in a viscoelastic tube using physics-informed neural networks

This study presents an advanced deep learning methodology that utilizes physics-informed neural networks (PINNs), to analyze the transmission of weakly nonlinear waves in a prestressed viscoelastic arterial tube. Using the long wave approximation, a mathematical model is constructed to replicate the propagation of weakly nonlinear waves in a viscoelastic arterial tube filled with viscous nanofluid, taking into account the influence of an induced magnetic field. The perturbed Burger, perturbed Korteweg–de Vries, and perturbed Korteweg–de Vries-Burgers equations are formulated based on the combined effects of nanofluid viscosity and the applied magnetic field using the reductive perturbation technique. Semi-supervised physics-informed neural network models are utilized to solve these perturbed evolutionary equations, trained on a limited dataset within their rectangular domain of definition. Gaussian process-based Bayesian optimization is used to determine the hyperparameters of the neural network, ensuring optimal model is performance. The effectiveness of the optimal models is evaluated by calculating the residual losses associated with the perturbed partial differential equations (PDEs). Visual representations of weakly non-linear wave propagation, considering nanofluid viscosity and induced magnetic fields, enhance the comprehension of dissipative effects in the cardiovascular system. These insights aid in obtaining precise measurements of pulse wave velocity for cardiovascular health monitoring. Consequently, the application of PINN proves to be a valuable tool for solving real-world PDEs and highlights its importance in advancing medical machine learning fields.

Enhancing high-performance concrete with local andesite and calcined marl: Insights from heat treatment and untreated conditions

This study explores the incorporation of local Algerian andesite and calcined marl as supplementary cementitious materials in high-performance concrete (HPC), with a special focus on the effects of heat treatment. Advanced analytical techniques, including X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA), were used for material characterization. The Sherbrooke method was utilized for mix design optimization, and thermal curing effects were critically evaluated. Key results demonstrated that both andesite and calcined marl significantly enhance HPC performance. Fresh mixtures showed excellent workability and consistent density. In the hardened state, these admixtures reduced porosity and water absorption capacity, improving durability. Heat-treated samples exhibited substantial early strength gains, while non-heat-treated samples showed superior long-term strength due to ongoing pozzolanic activity. Ultrasonic pulse velocity (UPV) measurements confirmed the high quality of the concrete. Tomography revealed a dense pore structure and strong interfacial transition zones, contributing to overall performance. Statistical modeling using the Design of Experiments (DOE) methodology validated the experimental findings and identified optimal conditions for maximizing compressive strength. Sulfuric acid exposure tests indicated good chemical resistance, with balanced performance in maintaining residual strengths and managing weight losses. This research underscores the potential of using local andesite and calcined marl to enhance HPC, promoting sustainable construction practices in Algeria by reducing reliance on imports and utilizing regional resources. In summary, this study contributes to sustainable HPC development by demonstrating the effectiveness of local mineral admixtures. The dual benefits of heat treatment for early strength gain and non-heat-treated conditions for long-term durability offer valuable insights for optimizing HPC formulations, advancing our understanding of pozzolanic materials, and promoting environmental stewardship and economic efficiency in the construction industry.

Propagation of untwisting solar jets from the low-beta corona into the super-Alfvénic wind: Testing a solar origin scenario for switchbacks

Context. Parker Solar Probe’s (PSP) discovery of the prevalence of switchbacks (SBs), localised magnetic deflections in the nascent solar wind, has sparked interest in uncovering their origins. A prominent theory suggests these SBs originate in the lower corona through magnetic reconnection processes, closely linked to solar jet phenomena. Jets are impulsive phenomena, observed at various scales in different solar atmosphere layers, associated with the release of magnetic twist and helicity. Aims. This study examines whether self-consistent jets can form and propagate into the super-Alfvénic wind, assesses the impact of different Parker solar wind profiles on jet dynamics, and determines if jet-induced magnetic untwisting waves display signatures typical of SBs. Methods. We employed parametric 3D numerical magnetohydrodynamics (MHD) simulations using the Adaptively Refined Magnetohydrodynamics Solver (ARMS) code to model the self-consistent generation of solar jets. Our study focuses on the propagation of solar jets in distinct atmospheric plasma β and Alfvén velocity profiles, including a Parker solar wind. We explored the influence of different atmospheric properties thanks to analysis techniques such as radius-time diagrams and synthetic in situ velocity and magnetic field measurements, akin to those observed by PSP or Solar Orbiter. Results. Our findings demonstrate that self-consistent coronal jets can form and then propagate into the super-Alfvénic wind. Notable structures such as the leading Alfvénic wave and trailing dense-jet region were consistently observed across different plasma β atmospheres. The jet propagation dynamics are significantly influenced by atmospheric variations, with changes in Alfvén velocity profiles affecting the group velocity and propagation ratio of the leading and trailing structures. U-loops, which are prevalent at jet onset, do not persist in the low-β corona but magnetic untwisting waves associated with jets exhibit SB-like signatures. However, full-reversal SBs were not observed. Conclusions. These findings may explain the absence of full reversal SBs in the sub-Alfvénic wind and illustrate the propagation of magnetic deflections through jet-like events, shedding light on possible SB formation processes.

On increasing the scour funnel size upstream of a bottom orifice by using a cuboid pile

Scour funnels formed before bottom orifices are of vital importance regarding intaking water with low-concentration and small-sized sediment to protect the water turbine. Via flume experiments, this work investigates the effect of a bottom-mounted cuboid pile on the formation of a scour funnel upstream of a bottom orifice. A phenomenon we call as “reverse sediment collapse” is observed for the first time, which causes a rapid increase in the scour depth upstream of the orifice. Instantaneous velocity measurements show that the turbulence kinetic energy near the cuboid pile is significantly higher compared with that in a case without a pile or with a cylinder under a same waterhead condition, indicating that large-scale vortex motions are enhanced due to the use of a cuboid pile. The equilibrium scour funnel depth upstream of the orifice is found to be increased by as much as 124.6% when a cuboid pile exists compared with that in a case without a pile under a same waterhead condition. The scour process is highly accelerated when a cuboid pile exists, and it is found that the time required when a cuboid pile exists to reach for the first time the same equilibrium scour depth without a pile is dramatically reduced by 97.2%–99.7%. A formula was established to calculate the equilibrium scour depth. The findings provide guidance for future optimization of the form and placement of structures upstream of an orifice to efficiently achieve a larger-sized scour funnel.

Test Flight of a Stratospheric Sonic Anemometer Prototype

Abstract Stratospheric sonic anemometers are an emerging technology for making wind velocity measurements in low pressure environments. This paper explores the challenges, design, and high-altitude testing of a digital sonic anemometer for applications including high-altitude balloon navigation, atmospheric gravity wave research, solar activity research, and planetary science on Mars. The system was flown on NASA’s Sensor Package for Attitude, Rotation, and Relative Observable Winds (SPARROW-3) balloon test flight out of Fort Sumner, New Mexico, in August 2022. The mission recorded relative wind data throughout the flight at temperatures as low as −40°C and at the balloon’s float altitude of 38 km (3.8-mb pressure; 1 mb = 1 hPa). The device surpassed all previous sonic anemometers regarding maximum operational altitude. However, only two of the three axes operated well above 32 km, leading to some validation challenges. The system achieved a velocity resolution of 0.1 m s−1 (standard deviation) and recorded three-dimensional wind measurement every 2.25 s. Future plans anticipate addressing the faulty axis and increasing performance to a resolution of 0.01 m s−1 and a wind sampling rate of 10 Hz.

Equilibrium dynamical models in the inner region of the Large Magellanic Cloud based on Gaia DR3 kinematics

Context. The Large Magellanic Cloud (LMC) contains complex dynamics driven by both internal and external processes. The external forces are due to tidal interactions with the Small Magellanic Cloud and the Milky Way, while internally its dynamics mainly depend on the stellar, gas, and dark matter mass distributions. Despite this complexity, simple physical models often provide valuable insights into the primary driving factors. Aims. We used Gaia Data Release 3 (DR3) to explore how well equilibrium dynamical models based on the Jeans equations and the Schwarzschild orbit superposition method are able to describe the LMC’s five-dimensional phase-space distribution and line-of-sight (LOS) velocity distribution, respectively. In the Schwarzschild model, we incorporated a triaxial bar component for the first time and derived the LMC’s bar pattern speed. Methods. We fit comprehensive Jeans dynamical models to all Gaia DR3 stars with proper motion and LOS velocity measurements found in the footprint of the VISTA near-infrared survey of the Magellanic System using a discrete maximum likelihood approach. These models are very efficient at discriminating genuine LMC member stars from Milky Way foreground stars and background galaxies. They constrain the shape, orientation, and enclosed mass of the galaxy under the assumption of axisymmetry. We used the Jeans model results as a stepping stone to more complex two-component Schwarzschild models, which include an axisymmetric disc and a co-centric triaxial bar, which we fit to the LMC Gaia DR3 LOS velocity field using a χ2 minimisation approach. Results. The Jeans models describe the rotation and velocity dispersion of the LMC disc well, and we find an inclination angle of θ = 25.5° ±0.2°, line of nodes orientation of ψ = 124° ±0.4°, and an intrinsic thickness of the disc of q0d = b/a = 0.23 ± 0.01 (minor to major axis ratio). However, bound to axisymmetry, these models fail to properly describe the kinematics in the central region of the galaxy dominated by the LMC bar. We used the derived disc orientation and the Gaia DR3 density image of the LMC to obtain the intrinsic shape of the bar. Using these two components as input to our Schwarzschild models, we performed orbit integration and weighting in a rotating reference frame fixed to the bar, deriving an independent measurement of the LMC bar pattern speed of Ω = 11 ± 4 km s−1 kpc−1. Both the Jeans and Schwarzschild models predict the same enclosed mass distribution within a radius of 6.2 kpc of ∼ 1.4 × 1010 M⊙.

Sound velocity measurement of pipeline fluids based on wavenumber-frequency spectrum

Sound velocity measurement of pipeline fluids based on wavenumber-frequency spectrum

Suppressing interference from sidelobe coupling in phased-array acoustic Doppler velocimetry based on correlation delay optimization

ABSTRACT Velocity information is important for describing the motion state of an object. Modern underwater navigation systems use the Doppler effect to extract the absolute velocity to the bottom or relative velocity to the water layer from the acoustic backscattering signal. Suppressing interference from sidelobe coupling is very important to improve the accuracy of phased-array acoustic Doppler Velocity Log (DVL) and to realize autonomous navigation in complex ocean environments. This paper proposes an interference suppression method based on optimizing the correlation delay of the pulse-pair algorithm to reduce the sidelobe coupling interference. The results of simulations and experiments show that the proposed method reduces the effect of sidelobe coupling on velocity measurements by 70% on average, which is expected to be useful for improving the autonomous navigation performance of unmanned vehicles in complex underwater environments.