A New Region Ocean Sound Velocity Field Model Considering Variation Mechanisms of Temperature and Salt

: The effect of the subsurface current on the sound velocity field in the western Mediterranean was investigated in the summer of 1970. This water movement carries warm waters from the Strait of Sicily to the Strait of Gibraltar at depths below the sound channel axis. A hydrographic section made between the two straits indicates that a change in the properties of the intermediate water at around 7 degrees E results in a doubling of the depth of the sound channel axis and alters the character of the sound velocity profile about this axis. A more extensive study of this region, including towing of an instrument package, gave indications of an intermittent process involved in this change. The sound velocity field was found to change appreciably over distances of ten nautical miles. A second tow exercise probed the region between the Strait of Sicily and the Tyrrhenian Sea. It found the velocity field there to be less variable than might have been expected.

Accurate measurement of temperature and velocity fields in combustion and flow diagnostic plays an important role in analyzing the heat transfer mechanism and ensuring the safe operation of equipment. In this work, considering the refraction effect of sound waves, temperature and velocity fields are reconstructed simultaneously based on the nonlinear acoustic tomography (NAT) by using the covariance matrix adaptation evolution strategy (CMA-ES) algorithm. In the forward problem, the fast two-point ray-tracing algorithm is introduced to track curved sound waves more efficiently. Due to the sparse measurement signals caused by the limited space and curved acoustic paths, Tikhonov regularization is introduced as the constraint of smoothing prior information to reduce the ill-posedness of the problem. The influence of the velocity regularization parameter and temperature regularization parameter on simultaneously visualizing the temperature and corresponding velocity fields are investigated, respectively. Then the selection strategies of these two regularization parameters are given, which are proved to have high selection efficiency. On this basis, inhomogeneous temperature and velocity fields are reconstructed simultaneously by using the CMA-ES algorithm, simulated annealing, and genetic algorithms. By solving the inverse problem of the NAT, which is highly nonlinear and ill-posed, the feasibility and effectiveness of the CMA-ES algorithm in the simultaneous reconstruction of velocity and temperature fields are confirmed. The proposed method for visualizing the temperature and velocity fields will supply key feedback for the combustion process control.

At present, ranging with acoustic signals is the primary means for determining positions on the sea floor. Converting travel time measurements into distances requires accurate knowledge of the effective sound velocity along the propagation path. In fact, marine positioning accuracy is presently most limited by the uncertainty in determinations of the ocean’s sound velocity field. The best sea-going sound velocity meters have accuracies of a part in 104, which translates into position uncertainties of 100 centimeters in 10 kilometers. A recently developed sound velocity meter improves this accuracy by a factor of ten, using a time-averaged, phase com-parison process. A description of this sound velocity meter and a discussion of its calibration and accuracy are presented here. Ultimately, knowledge of sound velocity in the ocean is limited by the variability of the ocean’s temperature and salinity structure. Therefore, the requirement is to measure sound velocity accurately on time and length scales appropriate for the position measurement being made, and a brief discussion of statistical methods of measurement in the ocean in order to adequately model the spatial coherence and temporal variability of sound velocity follows.

Study on sound wave kinematic characteristics and temperature sensing mechanism during the warming process of loose coals

The paper presents research results on sound velocity variability in the water column based on long-term measurements conducted on stationary platforms on the Crimean and southeastern shelves of the Black Sea in the summer–fall seasons. Measurements consisted of long-term hourly soundings with a miniSVP sound velocity probe, continuous temperature recording with a thermistor chain, and current monitoring with ADCPs. A significant and frequently observed variability in the sound velocity fields was revealed during the passage of inertial internal waves and internal bores, both on the Crimean and Caucasian shelves.

Transmission loss depends on the sound velocity structure. Present models are deterministic, and require deterministic inputs. However, from a given set of sound velocity data generally only one sound velocity profile is generated. The resulting transmission-loss curves are frequently compared to acoustic data for model evaluation purposes, sometimes unsuccessfully. A technique has been developed which, from a given data set, will generate many profiles, obeying certain vigorous mathematical constraints. Unfortunately each profile requires the acoustic model to be rerun, but the process generates transmission-loss fields which can be statistically analyzed. The generation of such fields will allow more realistic appraisals of acoustic models when compared to acoustic data. The sensitivity of acoustic models to small perturbations in the sound velocity field is presented for certain special cases. The technique is applicable to all environmental inputs for any models requiring deterministic inputs.

Data sets obtained from towed thermistor strings, instrumented tow bodies, conductivity temperature depth sensors, expendable bathythermographs, sound velocimeters and high-frequency acoustic backscattering systems provide detailed information on the temporal and spatial variability of the sound velocity field in the upper ocean. The data sets show that internal waves and other small scale fluid phenomena such as instabilities can significantly perturb the sound velocity field and consequently sound propagation. Little attention has been focused on the magnitude of short-range, high-frequency acoustic propagation variability caused by internal wave field and/or water mass variability. A ray trace program package has been developed which numerically integrates with a fourth-order Runge–Kutta method the time dependent eikonal equations through a range dependent sound velocity field. The sound-speed profiles, which are calculated from field data, are entered into a matrix with sizes larger than the numerical integration steps. Consequently, the profiles are interpolated between matrix steps with the bicubic interpolation technique of Akima. Calculations for sound-speed fields perturbed by internal waves show that at a fixed position the intensity of the sound intensity field can vary by as much as 20 dB as a function of time.

The Terrestrial Reference Frame (TRF) is essential for solid Earth research, including geodesy and geodynamics, providing a unified spatiotemporal datum. With the continuous expansion of global GNSS infrastructure and data, significant progress has been made in refining TRF and models of crustal plate motion and tectonic deformation. This study provides a global velocity field and a plate motion model through three decades of Global Navigation Satellite System (GNSS) data and nonlinear TRF refinement. Key contributions include: (1) the Integrated and Improved Time Series Analysis (IITSA) model, achieving horizontal fitting precision of 3 mm and vertical precision of 6 mm for three-decade GNSS time series; (2) the Global GNSS Velocity Model 2020 (GGVM2020), with RMS values of 0.12, 0.11, and 0.26 mm/yr in the north, east, and up directions, providing new insights into the crustal movements of Antarctica and North America; (3) the Global Interpolation Velocity Model 2020 (GIVM2020), offering a global horizontal velocity grid (3°×3°) with interpolation accuracy better than 3 mm/yr, enabling velocity estimation for any site globally; and (4) the Global Plate Motion Model 2020 (GPMM2020), which improves the accuracy of Euler motion parameters for the 14 major tectonic plates, achieving precision better than 3 mm/yr. In conclusion, the study’s results, including the global GNSS velocity field and plate motion model, enhance the reliability and application of terrestrial reference frame products.

Drifter data from the Gulf of Mexico are used to assess and enhance the output of a primitive equation general circulation model. The analysis is made in a 450 km × 450 km open subdomain encompassing a Loop Current ring. The model velocity field is compared with position data from four drifters at the drogue depth of 50 m using geometrical orthogonal functions (GOF). An Eulerian velocity field is reconstructed from the model velocity field and drifter velocities. This reconstructed velocity improves 8‐day numerical trajectories relative to the model field by at least an order of magnitude, as quantified by two Lagrangian error metrics referenced to the real drifter paths. An Eulerian metric that compares the two fields, however, does not exceed 7% for the 20‐day assessment period. Thus the drifter data may be reproduced with modest impact on the model velocity. Enhancement of the model velocity field is determined by two tests: the ability of the GOF velocity field to (1) improve the forecast of drifter positions using only a posteriori data and (2) improve the forecast of withheld drifter data. Using a posteriori data, the 20‐day temporal mean of the position error is improved for all drifters by 87–89% for 6‐hour and 26–38% for 30‐hour forecasts. For 6 days, a withheld drifter is 35–40 km from a drifter whose velocity is used in the reconstructed velocity field. The temporal mean of the position error during this period is improved by 20% for 6‐hour and 26% for 30‐hour forecasts.

A turbulent diffusion model in which the velocity field is Gaussian and rapidly decorrelating in time (GRDT) has been widely used recently in an endeavor to understand the emergence of anomalous scaling behavior of physical fields in fluid mechanics from the underlying stochastic partial differential equations. The utility of the GRDT model is the fact that correlation functions of the passive scalar field solve closed partial differential equations; the usual moment closure obstacle is averted. We study here the sense in which the GRDT model describes turbulent diffusion by a general, non-Gaussian velocity field with nontrivial temporal structure in the limit in which the correlation time of the velocity field is taken to zero. When the velocity field is rescaled in a particular manner in this rapid decorrelation limit, then a limit theorem of Khas'minskii indeed shows that the passive scalar statistics are described asymptotically by the GRDT Model for a broad class of velocity field models. We provide, however, an explicit example of a “Poisson blob model” velocity field which has two different well-defined rapid decorrelation in time limits. In one, the passive scalar correlation functions converge to those of the GRDT Model, and in the other, they converge to a distinct nontrivial limit in which the correlation functions do not solve closed PDE's. We provide both mathematical and heuristic explanations for the differences between these two limits. The conclusion is that the GRDT Model provides a universal description of the rapid decorrelation in time limit of general non-Gaussian velocity field models only when the velocity field is rescaled in a particular manner during the limit process.

If effects like ocean fronts, changing water depths, or irregular bottom properties can be excluded, then an ocean area can be treated as horizontally homogeneous in respect to sound transmission. The intensity of a signal then depends on the transmitter and receiver depth and the distance between them, but not on their distinct positions. In a zero order approximation also the sound velocity field may be said to be horizontally homogeneous. Just as its determining factors temperature, salinity, and pressure the sound velocity is mainly a function of depth and only to a much less extent of the horizontal displacement. Moreover the small differences between sound velocity profiles from different stations in the areas under consideration are of statistical nature and mostly not accessible to measurements.

Modeling of layer thickness and strain for the two-layered metal clad plate rolling with the different roll diameters

After conducting the intensive research on the distribution of fluid’s velocity and biochemical reactions in the membrane bioreactor (MBR), this paper introduces the use of the mass-transfer differential equation to simulate the distribution of the chemical oxygen demand (COD) concentration in MBR membrane pool. The solutions are as follows: first, use computational fluid dynamics to establish a flow control equation model of the fluid in MBR membrane pool; second, calculate this model by adopting direct numerical simulation to get the velocity field of the fluid in membrane pool; third, combine the data of velocity field to establish mass-transfer differential equation model for the concentration field in MBR membrane pool, and use Seidel iteration method to solve the equation model; last but not least, substitute the real factory data into the velocity and concentration field model to calculate simulation results, and use visualization software Tecplot to display the results. Finally by analyzing the nephogram of COD concentration distribution, it can be found that the simulation result conforms the distribution rule of the COD’s concentration in real membrane pool, and the mass-transfer phenomenon can be affected by the velocity field of the fluid in membrane pool. The simulation results of this paper have certain reference value for the design optimization of the real MBR system.

This article presents a construction method of the velocity field for poststack time migration for 2D seismic calculated on the basis of interval velocities in boreholes and structural interpretation, as well as the results of poststack time migration based on this solution. Three velocity field models have been developed. The models used differ in the way of spatial interpolation and extrapolation in the adopted calculation grid in the depth domain, which was created on the basis of a structural interpretation of 2D seismic profiles. Three methods of interpolation and extrapolation were used: Gaussian distribution, kriging and moving average. The spatial distribution of the interval velocities in the boreholes was made using the Petrel software by Schlumberger. The interval velocities along the analyzed seismic profile were extracted from the computed spatial interval velocity models, and after conversion from the depth to the time domain, they were used for the poststack time migration. For comparison, poststack time migration was calculated for the same seismic profile based on the stacking velocities obtained in the seismic processing data as a result of velocity analyzes. The velocity field calculated on the basis of interval velocities and structural interpretation was used for the poststack time migration procedure performed with the Implicit FD Time Migration algorithm (finite difference), while the stacking velocities were used for the poststack time migration procedure performed with the Stolt and Kirchhoff algorithms in accordance with the technical conditions of correct operation of these algorithms. The selected percentage ranges of 60%, 100%, and 140% have been used for all velocity fields. Application of the element of directional velocity variation resulting from the spatial distribution of interval velocities in the boreholes to the velocity field for the poststack time migration allowed to obtain a better seismic image in relation to the one obtained as a result of applying the stacking velocities. The most reliable seismic image after poststack time migration was obtained for the velocity field calculated on the basis of the interval velocities with Gaussian distribution, using the finite difference algorithm with 60 percent value of the velocity field.

Modeling and analysis of deformation characteristics for the two-layered metal clad plate produced by asymmetric rolling