Speed Field Research Articles

Ocean sound speed field reconstruction beyond tensor neural network

Obtaining accurate ocean sound speed fields (SSFs) across a three-dimensional (3D) geographic region is vital for various underwater acoustic tasks. However, the scarcity of measurements due to the high cost of underwater sensors, combined with the high dimensionality of complex 3D SSF, makes the reconstruction problem highly ill-conditioned, thus demanding advanced models and methods. Our recent work has analyzed the reconstruction error and identified one promising way: finding a representation model that is both concise and expressive. Following this path, we proposed a tensor neural network (TNN) model, which leverages the conciseness of tensor models and the expressive power of deep learning. However, existing TNN-based approaches have two limitations: (1) they are unable to capture long-range correlations within the SSF and (2) they can only handle discrete-indexed tensor data. To overcome these limitations and fully unleash the power of deep tensor learning, we seamlessly introduce attention schemes into the existing TNN framework without compromising its interpretability. Additionally, we employ Gaussian process models to evolve the original parameterized tensor model into a new functional tensor model, enabling reconstruction with a continuous grid. Numerical results obtained from real-life datasets demonstrate the superior performance of our approach compared to state-of-the-art methods.

Ocean sound speed field reconstruction with graph regularized deep matrix factorization

To reconstruct the ocean sound speed field (SSF), a matrix in horizontal could be formed by gridding the sea area, where some sparse entries were filled by the observation sound speed profiles (SSPs). The reconstruction of the SSF can be modeled as a matrix completion problem, using limited and noisy observation values to reconstruct the entire matrix. Furthermore, the spatial correlation of the SSF could be modeled by graph space model, utilizing with the low-rank property of the SSF matrix, the problem of graph regularization low-rank matrix completion was developed. The observed average SSPs in six cross section were estimated from the four underwater acoustic tomography moorings, and nine local SSPs were obtained from pressure inverted echo sounders (PIESs) inversion. By combining the method of deep matrix factorization and the graph regularization, the Graph Regularized Deep Matrix Factorization (GRDMF) method was proposed. The simulation results showed that the GRDMF performs better than the spatial interpolation algorithm in SSF reconstruction. Considering the application scenarios of deep-sea acoustic tomography, an average constraint (AC) item was designed additionally, and then a customized algorithm named GRDMF-AC is proposed. Finally, data of the experiment at the South China Sea in 2021 is processed to verify GRDMF-AC, the results showed that the reconstructed SSF captures mesoscale eddy in the experiment.

Impacts of EL NIÑO-Southern oscillation on tropical cyclone activity over the coastal zones of Vietnam

The activity of El Niño - Southern Oscillation (ENSO) has been found to alter the characteristics of tropical cyclones (TCs) worldwide. This paper examines how ENSO influences the active time, occurence frequencies, and intensities of TCs over the coastal zones of Vietnam. The study uses Best Track Data in the Western North Pacific region from 1961 to 2020. The wind speed fields of all TCs over the coastal zones are calculated using a semi-empirical model with a square grid of 0.05° resolution. The results show that the frequencies of TCs over the coastal zones decrease during El Niño years, whilethe TC intensities increase significantly compared to those in Neutral years. Meanwhile, TC intensities over all coastal zones during La Niña years, and some coastal zones during El Niño years, decrease significantly compared to those in Neutral years. The magnitudes of both the increase and decrease in TC frequencies and intensities over the coastal zones vary significantly. Moreover, the active time of TCs during La Niña years in some coastal zones is shorter and occurs later than during the Neutral years.

Effect of sinusoidal pulsating speed enhancement on the mixing performance of plastics machinery

Abstract Numerous vibration-assisted methods have been adopted to solve problems in polymer processing, but the introduction of vibration fields is typically done on small extruders or injectors in school laboratories and industrial research rooms, which profoundly limits the application of vibration technology. The purpose of this study is to put forward a simple vibration excitation method for all scale extruders or injection molding machines. To recover the mixing performance of that excitation method, a numerical investigation was carried out using the CFD software ANSYS POLYFLOW 19.2, and the analysis and comparison were made between the mixing performance of a simplified screw element with and without a sinusoidal pulsating speed field. The results showed that not all dynamic states with the superimposed excitation field have better mixing performance than the steady state without any pulsating field. Nevertheless, the introduction of a pulsating speed field under certain parameters setting can indeed enhance the stretching rate, reduce the separation scale, increase the mixing efficiency, and lower the screw force. These findings are of great importance and provide valuable references for the development and application of vibration-assisted molding technology in plastics machinery.

The Radial Interplanetary Field Strength at Sunspot Minimum as Polar Field Proxy and Solar Cycle Predictor

The minimum value of the geomagnetic aa index has served as a remarkably successful predictor of solar cycle amplitude. This value is reached near or just after sunspot minimum, when both the near-Earth solar wind speed and interplanetary magnetic field (IMF) strength fall to their lowest values. At this time, the heliospheric current sheet is flattened toward the heliographic equator and the dominant source of the IMF is the Sun’s axial dipole moment, which, in turn, has its source in the polar fields. As recognized previously, the success of aamin as solar cycle precursor provides support for dynamo models in which the sunspots of a given cycle are produced by winding up the poloidal field built up during the previous cycle. Because they are highly concentrated toward the poles by the surface meridional flow, the polar fields are difficult to measure reliably. Here we point out that the observed value of the radial IMF strength at solar minimum can be used to constrain the polar field measurements, and that this parameter, which is directly proportional to the Sun’s axial dipole strength, may be an even better solar cycle predictor than geomagnetic activity.

An assembled hot wire anemometer design

The hot wire anemometer is a widely utilized device in laboratory settings for measuring air speed. This paper investigates the relationship between air speed and hot wire temperature across various air speed ranges, employing the theory of thermal equilibrium. We designed a measurement circuit and hot wire shape based on the hot wire anemometer principle, and validated the linear relationship between current and temperature at different air speeds within an adjustable air speed field. The measured current serves as a representative of air speed. Experimental validation of the designed hot wire anemometer demonstrates accurate measurement results that align with theoretical values across different air speed ranges. Finally, we determined the sensitivity of the anemometer in various measurement ranges, considering the instrument's uncertainty and measurement formula.

Dynamically orthogonal narrow-angle parabolic equations for stochastic underwater sound propagation. Part II: Applications.

The stochastic dynamically orthogonal (DO) narrow-angle parabolic equations (NAPEs) are exemplified and their properties and capabilities are described using three new two-dimensional stochastic range-independent and range-dependent test cases with uncertain sound speed field, bathymetry, and source location. We validate results against ground-truth deterministic analytical solutions and direct Monte Carlo (MC) predictions of acoustic pressure and transmission loss fields. We verify the stochastic convergence and computational advantages of the DO-NAPEs and discuss the differences with normal mode approaches. Results show that a single DO-NAPE simulation can accurately predict stochastic range-dependent acoustic fields and their non-Gaussian probability distributions, with computational savings of several orders of magnitude when compared to direct MC methods. With their coupling properties and their adaptation in range to the dominant uncertainties, the DO-NAPEs are shown to predict accurate statistics, from mean and variance to multiple modes and full probability distributions, and to provide excellent reconstructed realizations, from amplitudes and phases to other specific properties of complex realization fields.

Influence of wind and waves on ambient noise and bubble entrainment depth in the semi-enclosed Baltic Sea

Semi-enclosed, fetch-limited waters create unique conditions for wind wave development and breaking. Parameters of breaking waves influence bubble entrainment depth and associated noise, which is why they differ in semi-enclosed sea compared to open waters. While the established noise-wind speed relationship holds in oceanic conditions, it differs in land-constrained basins like the Baltic Sea. To explore noise level, bubble entrainment depth and wind speed relationships, we conducted noise and sub-surface bubble measurements, coupled with wind observations, in the selected area of the Baltic Sea during two consecutive summers. A novel method was employed to estimate bubble entrainment depth under conditions of strong backscatter. Model data of wave field parameters were employed to assess their influence on noise level and bubble entrainment depth. Results suggest stronger connections between noise level and wind speed, as well as wave height, compared to wave age and wind sea steepness. The same patterns hold true for the correlation between bubble entrainment depth and both wind speed and wave field parameters. The parameterized noise level-wind speed relationship differs from that obtained for oceanic conditions and also varies across measurement periods. Observed differences were shaped by varying wind-wave conditions, notably differences in wind speed, direction, wave height, and the presence of swell. The noise level-bubble entrainment depth relation is reported for the first time for Baltic Sea conditions. For a thorough analysis of the influence of these factors on noise and bubbles, longer measurements under diverse wind-wave conditions are required to account for site-specific wave field characteristics.

Assessing the parameters of electromagnetic fields and microclimate in the radionuclide department of the positron emission tomography centre

Currently, in the Russian Federation there is an increase in the number of positron emission tomography scans. As a result, the collective dose from radionuclide diagnostics in 2021 compared to 2020 increased by 62.0%, the average effective dose per one study in positron emission tomography (PET) centres of Moscow from 2015 to 2019. increased from 1.71 to 4.41 mSv. This leads to an increase in radiation doses not only for patients, but also for medical workers, and makes it urgent to develop modern effective measures to prevent the adverse effects of ionizing radiation.
 The aim of the study is to evaluate the parameters of electromagnetic fields and microclimate in the premises of the radionuclide department of the PET centre.
 During the study, in the main working areas of the radionuclide department, the following levels were assessed: the strength levels of electric and magnetic fields of industrial frequency, relative humidity, temperature and air speed using generally accepted measures in occupational hygiene.
 zThe main parameters of electromagnetic fields and microclimate (temperature, humidity, air speed) comply with hygienic standards in industrial workplaces. At the same time, in certain working areas of the radionuclide department, higher levels of electromagnetic fields were recorded, as well as a decrease in relative humidity and air velocity.
 Monitoring the parameters of electromagnetic fields and microclimate is important for improving the working conditions of medical workers in the radionuclide department of the PET centre, which helps maintain the functional state of workers at a high level, increases concentration and accuracy of movements, increases the speed of work manipulations, and reduces the time of contact with radionuclides when administered to patients and thereby reduce the dose load on health workers.
 Ethics. The study does not require the opinion of this committee.

Helical sample-stepping for faster speckle-based multi-modal tomography with the Unified Modulated Pattern Analysis (UMPA) model

Speckle-based imaging (SBI) is a multi-modal X-ray imaging technique that gives access to absorption, phase-contrast, and dark-field signals from a single dataset.However, it is often difficult to disentangle the different signals from a single measurement.Having complementary data obtained by repeating the scan under slightly varied conditions (multiframe approach) can significantly enhance the accuracy of signal extraction and, consequently, improve the overall quality of the final reconstruction.In order to retrieve the different channels, SBI relies on a reference pattern, generated by the addition of a wavefront marker in the beam (i.e., a sandpaper or gratings).Here, we show how a continuous helical acquisition can extend the field of view (FOV) and speed up the acquisition while maintaining a multiframe approach for the signal retrieval of a test object.

Effects of coronal mass ejection orientation on its propagation in the heliosphere

Context. In the scope of space weather forecasting, it is crucial to be able to more reliably predict the arrival time, speed, and magnetic field configuration of coronal mass ejections (CMEs). From the time a CME is launched, the dominant factor influencing all of the above is the interaction of the interplanetary CME (ICME) with the ambient plasma and interplanetary magnetic field. Aims. Due to a generally anisotropic heliosphere, differently oriented ICMEs may interact differently with the ambient plasma and interplanetary magnetic field, even when the initial eruption conditions are similar. For this, we examined the possible link between the orientation of an ICME and its propagation in the heliosphere (up to 1 AU). Methods. We investigated 31 CME-ICME associations in the period from 1997 to 2018. The CME orientation in the near-Sun environment was determined using an ellipse-fitting technique applied to single-spacecraft data from SOHO/LASCO C2 and C3 coronagraphs. In the near-Earth environment, we obtained the orientation of the corresponding ICME using in situ plasma and magnetic field data. The shock orientation and nonradial flows in the sheath region for differently oriented ICMEs were investigated. In addition, we calculated the ICME transit time to Earth and drag parameter to probe the overall drag force for differently oriented ICMEs. The drag parameter was calculated using the reverse modeling procedure with the drag-based model. Results. We found a significant difference in nonradial flows for differently oriented ICMEs, whereas a significant difference in drag for differently oriented ICMEs was not found.

Response of sound propagation characteristics to Luzon cold eddy coupled with tide in the Northern South China Sea

The northern part of the South China Sea is a complex ocean environment with a large range of tidal waves and the stable Luzon cold eddy, which significantly influence the sound propagation characteristics through their impact on sound speed. This study uses a 3D ocean-acoustic framework consisting of MITgcm and BELLHOP ray model to investigate the coupled effects of the Luzon cold eddy and tidal waves. Firstly, the model incorporates tidal assimilation to reconstruct the hydrographic field and compute the sound speed field. Subsequently, the sound propagation in a representative region in the northern South China Sea is simulated to compare the response of sound propagation characteristics to the Luzon cold eddy only, tide only, and the coupled effect of both. The results demonstrate that the cold eddy shifts the location of the convergence zone forward by over 5 km at most. Further, it also makes the acoustic energy focus on the first few arrivals and delays the arrival time of rays by about 0.1 s. The tidal waves intensify these effects, resulting in a further increase of the forward distance of the convergence zone by 2-5 km and a delay in arrival time by 0.02 s. Sound propagation in the coupled influence of these two dynamic processes is exposed to steady perturbations from the cold eddy and spatial-temporal perturbations from tidal waves. The model in this study provides valuable insight for underwater detection and positioning in the realistic ocean environment.

Possibility of Energy Recovery from Airflow around an SUV-Class Car Based on Wind Tunnel Testing

For many years, technological progress has been observed in the field of minimizing energy consumption by devices and increasing the efficiency of energy generation from freely available sources. Energy harvesting (EH) is one of the ways to increase the energy available in vehicles. The manuscript presents the results of a series of laboratory tests carried out in a wind tunnel using a 1:10 scale model of an SUV. The aim of the tests was to measure the air velocity in the footsteps of the car. The speed field has been identified at more than 188,000 points in the space behind or next to the car, considering the symmetry of the vehicle. The total energy was aggregated for 2760 points in a vertical plane perpendicular to the plane of symmetry. From the tests carried out, it was found that the highest speed was achieved just behind the trunk of the car, at a distance of about 20% of the length of the car. Interestingly, the speed in this area was higher than the speed of the car.

Simulation study on arc motion process of DC miniature circuit breakers

Based on the theory of magnetohydrodynamics, a mathematical model of air arc in the arc extinguishing chamber of a DC miniature circuit breaker was established. By coupling external circuit characteristics and contact movement process, the motion process of the arc was simulated and analyzed. On this basis, the effects of breaking speed, time constant, and magnetic field on the arc motion characteristics were studied. The study showed that increasing the breaking speed appropriately and adding appropriate magnetic field can improve the breaking performance of DC miniature circuit breakers. The research results can provide reference for the optimization design of DC miniature circuit breakers.

Impact of internal waves on underwater acoustic propagation

The propagation of internal waves in the ocean can produce significant fluctuations in the local sound speed field. Understanding how these fluctuations affect acoustic propagation is an area of considerable interest in underwater acoustics. Previous studies have indicated that large fluctuations (of the order of 20 dB) in transmission loss (TL) of acoustic waves can occur due to focusing and defocusing effects as the acoustic waves propagate through an internal wave. This work looks to extend some of these studies by exploring the frequency and directional dependence of these fluctuations through the implementation of a 3D acoustic model (FOR3D) suitable for modelling low frequency (<1 kHz) acoustic propagation. The study utilises sound speed data produced using the non-hydrostatic model MITgcm, simulating a nonlinear three-dimensional internal wave field that was verified using in situ mooring observations. By also considering results from a study utilising an acoustic ray model (Bellhop3D) on the same data, this work gives a comprehensive picture of the internal wave induced TL fluctuations across a range of acoustic frequencies.

Public procurement artificial ’’fragmentation’’: actual problems and customer’s responsibility

One of the most urgent and controversial problems in the field of ensuring state and municipal needs is the public procurement artificial fragmentation. Fragmentation is carried out by customers in order to bypass certain price thresholds established by legislation in the field of procurement, to simplify or speed up procedures, or to obtain material benefits. At the same time, the discussion of the issue of procurement fragmentation is created by the lack of consolidation of this concept in legislation, which in turn leads to the emergence of different opinions regarding the criteria for qualifying a particular activity as fragmentation. The ambiguity in this matter is reinforced by the presence of generally ambiguous administrative and judicial practice. That is why the issue of procurement fragmentation remains relevant both for state and municipal customers and for regulatory authorities.

An efficient method for simulating fluctuating wind speed fields in two-spatial dimensions based on a frequency-dependent acceptance-rejection scheme

The simulation of fluctuating wind speed fields holds paramount importance in the wind-resistant design of significant structures such as high-rise buildings, long-span bridges, and wind turbines. To address the computational challenges posed by the original spectral representation method (SRM), a novel approach has emerged. This approach, rooted in the frequency-wavenumber spectrum (FWS), offers a solution to the complexities associated with the original SRM. An enhanced non-uniform discrete technique based on the acceptance-rejection (A-R) criterion was introduced to improve the efficiency of the FWS-based SRM. Nonetheless, this technique currently faces certain constrains, including its demand for a substantial allocation of random access memory (RAM) and its inability to be seamlessly integrated with the fast Fourier transform (FFT) algorithm. Given this scenario, a notably more effective strategy for selecting representative points emerges -the frequency-dependent acceptance-rejection (A-R) scheme. This innovative scheme holds the advantage of diminishing RAM utilization, transforming wind field modeling from a supercomputers-exclusive task to one feasible on personal computers. Moreover, its seamless integration with FFT technology bolsters simulation efficiency. The provided numerical simulation instances of two-spatial dimensional fluctuating wind speed fields underscore the proficiency of this proposed frequency-dependent A-R scheme. The outcomes demonstrated the combined A-R and FFT technique’s efficiency and precision, in simulating two-spatial dimensions fluctuating wind speed fields.

Internal solitary waves in the presence of linear and nonlinear shear-currents

In this paper, the effects of background linear and nonlinear shear-currents on internal solitary waves in a two-layer fluid system are studied. In the linear shear-current case, the strongly nonlinear internal-wave equations (SNIWE) and the high-level Green–Naghdi (HLGN) equations are used to study the effect of the current on the wave speed, wave profile and velocity distribution. A comparative study between the results of these two models is presented. The SNIWE, commonly used in the literature, however, is confined to a condition where the horizontal velocity is invariant in the vertical direction in the absence of current, and it varies linearly in the presence of a shear current. It is shown in this study that this assumption is not valid under nonlinear shear-current conditions, or when current is in the opposite direction of the wave, resulting in large errors. In such cases, the use of a nonlinear theory which relaxes this assumption, e.g. the HLGN equations, is necessary. The effects of background nonlinear shear-currents on the speed, profile and velocity field of internal solitary waves are investigated here by use of the HLGN equations. It is found that the nonlinear shear-currents affect the velocity field of the internal solitary wave significantly more than the linear shear-currents do.

Developing a distributed acoustic sensing seismic land streamer: Concept and validation

Motivated by existing cabled seismic land-streamer designs, we develop a distributed acoustic sensing (DAS) land-streamer system for high-resolution near-surface seismic data acquisition. The system consists of a DAS interrogator unit (IU), a fiber-optic cable attached beneath a fire-hose assembly for environmental isolation and improved fiber-ground coupling, and a vehicle-mounted accelerated weight-drop source. The DAS land streamer is easily deployed and towed along the ground surface, allowing for spatially dense data acquisition. We report two field tests with the developed hardware to evaluate the DAS land-streamer performance. The first test investigates the effects of hose weight on the surface-deployed fiber and indicates that this approach improves fiber-ground coupling and leads to an improved signal-to-noise ratio (S/N). The second test demonstrates that the DAS land streamer records waveforms with similar phase and moveouts as those recorded by horizontal geophones but offers a higher native spatial density advantage than standard geophone arrays, leading to spatially dense waveforms, improved S/N after postprocessing, and superior surface-wave acquisition array mobility. Our findings suggest that a DAS land streamer is a promising alternative to traditional geophone-based surveys and may offer several advantages, such as faster survey acquisition speed and lower field costs due to reduced acquisition hardware requirements. However, methodological limitations include recording a single horizontal ground-motion component, a dependence on favorable fiber-ground coupling conditions, and the upfront cost of IU procurement. A DAS land streamer may be useful in numerous subsurface applications, such as (pseudo) 1D multichannel analysis of surface waves or 2D surface-wave inversion for S-wave velocity model estimation for geophysical, geologic, geotechnical, and environmental investigations.

Characteristics of Fluctuating Wind Speed Spectra of Moving Vehicles under the Non-Stationary Wind Field

To promote energy saving, emission reduction, and sustainable development of high-speed trains, as well as achieve low-carbon operation of these trains. It is necessary to establish a fluctuating wind speed spectra model that can accurately describe the characteristics of the fluctuating wind speed field of the moving vehicle. This will help explore the effects of strong winds on the running resistance, energy consumption, safety, and comfort of trains. In this paper, based on Priestley’s evolutionary power spectral density (EPSD) theory, an efficient method was developed for generating the fluctuating wind speeds at the moving point under the non-stationary wind field. On such basis, the effects of different mean wind speeds, ground clearances, temporal modulation function parameters, and vehicle’s moving speeds on the time-varying correlation function ratio of fluctuating wind speed at fixed and moving points were analyzed. Subsequently, the relationship between the time-varying correlation functions of fluctuating wind speed at the fixed and moving points was established by analyzing the sensitivity of the above parameters, and a theoretical model of fluctuating wind speed spectra of the moving point under the non-stationary wind field was proposed. In addition, the relational expression of fluctuating wind speed spectra of the moving point under stationary and non-stationary wind fields was established, which was further validated using the fluctuating wind speed spectra model at the fixed points with different modulation function forms. The results demonstrated that the direct generation method can avoid n times of POD decomposition and Ns∑j=1nNqjj times of FFT calculation, improve the calculation speed, and save memory. The proposed fluctuating wind speed spectra model at the moving point under the non-stationary wind field is in good agreement with the corresponding target one, indicating the high accuracy of the proposed model. Meanwhile, it is also noted that the fluctuating wind speed spectra at the moving point under the non-stationary wind field can be obtained by modulating the spectra under the stationary wind field using temporal modulation function, which is the same as that of the fluctuating wind speed spectra at fixed points under the non-stationary wind field.