Streamer Shape Research Articles

Marine Compass Data Quality Control Method Based on Robust Surface Fitting

Towed streamer positioning is a key step in offshore seismic exploration, and its positioning accuracy directly affects the imaging quality of subsequent seismic data. Accurate and clean magnetic compass observations are an important guarantee for high-precision towed streamer positioning. However, the existing compass data quality control methods have the problem of insufficient utilization of spatial distribution prior information, which heavily relies on mathematical statistical characteristics of the data while neglecting the crucial factors of streamer shape, bringing about an inadequate elimination of gross errors. In this work, a compass data quality control algorithm based on robust surface fitting is proposed to improve the accuracy of positioning. Firstly, the towed streamer positioning algorithm and the prior information of the spatial structure distribution of the compass are introduced. Secondly, the robust surface fitting to control the quality of compass data is proposed, and the specific process of the algorithm is given. Lastly, the effectiveness of the algorithm is verified by simulation and measured data. The results of simulation experiments indicate that compared with the traditional single-streamer threshold robust algorithm, the new algorithm has a significant effect on the quality control of compass data, and the positioning accuracy of the towed streamer is significantly improved. The positioning precision of along-line direction is improved by 52.1%, and that of the across-line direction by 52.4%. These demonstrate that the proposed new algorithm is effective for detecting and eliminating gross errors in compass observations in real-time operation scenarios, improving the stability of towed streamer shape calculation, which can better ensure the smooth progress of offshore towed streamer seismic exploration operations.

SimStr: A C++ program for offshore seismic towed-streamer positioning data simulation

Offshore seismic exploration requires accurate positions of towed streamers and seismic receivers. Because the actual positions of underwater streamers cannot be accurately determined, few effective evaluation methods for streamer positioning algorithms/software have been developed, besides simulations. However, most simulated data used in streamer positioning research are static; they lack physical meaning and neglect to consider the complex motion characteristics of the streamers caused by the towing vessel and current. To address this limitation, we have developed a C++ program for simulating streamer positioning observations, called SimStr. Based on the motion equation of underwater streamers, we use the finite-difference method to obtain a dynamic streamer shape, for which a box method is used to discretize the streamer motion in space and time. The positioning data are then simulated based on the dynamic streamer shape. We elaborate the structure of the program, for which the code of core algorithms was implemented to have good extendibility, efficiency, and portability, while ensuring high performance. As an example, we determine the simulated streamers of a vessel turning around to demonstrate the effectiveness of the code. Furthermore, we input the simulated data into a self-developed streamer positioning program and a commercial software to evaluate their positioning results and ultimately validate the simulated data.

Helical streamers guided by surface electromagnetic standing waves

The streamer that is driven by the specific pulse DC discharge parameters can stably form a three-dimensional helical plasma channel in a long dielectric tube in the low-temperature plasma experiment, in cases when there were neither external background magnetic field or other factors that destroyed the poloidal symmetry of the tube. The formation mechanism and chirality of helical streamers are discussed according to the surface electromagnetic standing wave theory. The shape of the helical streamers and the characteristics of helical branches are quantitatively analyzed to further expand the application of plasma and streamer theory in the helix problem and chiral catalytic synthesis.

Formation of wide negative streamers in air and helium: the role of fast electrons

Available experimental data show that the use of voltage pulses with subnanosecond rise times and amplitudes that essentially exceed the breakdown voltage leads to the formation of wide spherical or conical streamers. In this paper, the structure and dynamics of atmospheric pressure wide negative streamers in air and helium by applying high overvoltages with a short rise time to a sharp needle electrode are investigated experimentally and computationally. In the simulations, the two-dimensional fluid and kinetic electron Monte Carlo simulation models are used. All the streamers were simulated with the conventional photoionization term S ph that was never turned off. By including an additional source S MC, responsible for the generation of fast electrons, wide and diffuse streamers are obtained. We compare the shapes, width and velocities of conventional streamers in air and helium with those for streamers driven by fast electrons. We show that a conventional streamer in air has a cylindrical form. The conventional streamer in helium is wider than that in air and has a shape of an expanding cone. While accounting for fast electrons, different streamer shapes were obtained. In air, the gap was closed by a spherical streamer. In helium, the shape of a streamer resembles that of a pumpkin. We also demonstrate that near the flat anode, velocities of conventional streamers in air and helium were as high as 5 × 109 cm s−1 and reached values greater than 1010 cm s−1 when fast electrons were taken into account. By the application of high (by a factor of four or greater) overvoltages to a sharp needle electrode, the formation of a discharge with several parallel streamers was observed. In this regime, the trajectories of fast electrons originated not only from the cathode, but also from the region of a streamer front where the electric field is high. As a result, the so-called diffuse discharge was formed with high intensity plasma channels surrounded by an aureole of smaller electron density.

Pressure-dependent propagation of streamers under step voltage in a long point-plane gap in transformer oil

The effect of pressure on positive and negative streamer propagation in a mineral transformer oil is studied in an 80 mm point-plane gap under step voltage. Increased pressure causes reduced stopping length for non-breakdown streamers, higher breakdown voltage, reduced background current, reduced branching in positive streamers and virtually no change in negative streamer shape. The velocities and acceleration voltages are close to being independent of pressure, indicating that the velocity controlling mechanisms take place in the liquid phase. Amplitude and frequency of small current pulses (probably small reilluminations) during negative 1st mode is reduced with increasing pressure, but the effect on reilluminations during 2nd and 3rd mode is small in both polarities.

FINITE ELEMENT MODELLING FOR ELECTRIC FIELD DISTRIBUTION AROUND POSITIVE STREAMERS IN OIL

Electric field distribution of positive streamers during propagation was determined with the finite element method by using COMSOL multiphysics. Modelling was performed at 210 kV and 270 kV. The geometrical shape of streamers was modelled with cylinder and sphere for the case of 210 kV while a growing cylinder was used for streamer propagation at 270 kV. In addition, a spherical model was used for determining the correlation between streamer branching and the electric field. It is obtained from the simulation results that the 2nd mode streamers has the electric field at channel tips of about 0.1 MV/cm while 8.3 MV/cm was received for the 4th mode streamers. The simulation results also reveal that the shielding effect resulting from streamer branching significantly reduces the electric field at the channel tips, and the shielding effect disappears with the angle a between channels is about 30o-60o depending on the size of streamer envelope. The hypothesis on correlation among velocity, streamer branching and electric field is suggested.

PROPERTIES OF WAVEFIELD EXTRAPOLATION OPERATORS (ON THE EXAMPLE OF PREDICTION OF GHOST REFLECTIONS)

Seismic deghosting algorithms involve wavefield extrapolation. The operator of such a transformation is integral, and when applied to discrete seismic data, its approximation is used, which corresponds to a method of numerical integration. The paper examines the limits of applicability of the approximation by the method of cells and the method of rectangles. It is shown that when processing 3D seismograms recorded using traditional survey geometries, correct ghost prediction is possible only after interpolation. When processing 2D seismic gathers, it is possible to predict and remove ghost waves for deep and shallow streamers. The streamer shape can be arbitrary. The results of the study and the conclusions made are valid not only for ghost prediction operators, but also for all seismic exploration tasks that involve wavefield extrapolation.

IMPROVING THE EFFICIENCY OF ELECTROSTATIC PRECIPITATORS

This paper provides information on the achievements in development of gas cleaning. A critical analysis of functioning principle of electrostatic precipitators, which are currently being developed and operated, is conducted. The possibility of increasing the effectiveness of gas cleaning using unipolar voltage pulses has been analyzed. It has been found that a streamer mechanism of discharge or streamer shape of corona discharge is the case, when voltage pulses with over-voltage are used and electrostatic precipitators run. The most rational circuit for unipolar voltage pulses generation using low-voltage generators of periodic voltage pulses is identified. To separate space charges formed in the streamers' channel, it is proposed to use pulsating voltage with a direct component and a potential plane with corona needles-grounded plane electrode system. The analysis of transient process within feed circuit of discharge technological gaps has shown that cut-off pulse repetition frequency, in which stability of discharge current is ensured, depends on the parameters of feed circuit elements and the discharge gap capacitance. It was found that the use of corona discharge streamer form allows increasing the speed of the gas to be purified up to 8 m/s, and reducing the aerosol particles deposition zone to 1 m. The gas velocity is 1 m/s with a deposition zone of more than 27 m in an existing gas filling device (GFD) type electrostatic precipitator. When comparing these indicators, the energy intensity of the process decreases by more than 100 times, and the specific power of the gas flow purification process is 33 (W·s)/m3.

A method for deghosting of data recorded with a streamer of arbitrary shape in rough sea conditions

ABSTRACTDeghosting of pressure‐only data has become a routine in marine seismic processing. Most existing techniques suffer from noise susceptibility or excessive simplification of the used ghost model, which leads to difficulties in removing the ghost waves. The algorithm presented in this paper is based on the wavefield extrapolation theory, and is capable of taking into account arbitrary streamer shapes and rough sea surfaces. The computations are performed in the frequency domain and come down to solving systems of linear equations. Regularization and data‐adaptive statistical optimization of the parameters prevent noise amplification. We describe the theory of the method and test it against synthetic and field datasets with different streamer shapes for both rough and flat sea surfaces.

Pre-breakdown streamer propagation and breakdown characteristics of refined bleached and deodorized palm oil under lightning impulse voltage

Vegetable oils are considered nowadays as a potential alternative to Mineral Oil (MO) for dielectric insulation fluids in transformers due to its high biodegradability, non-toxicity and high fire resistance. This paper presents an experimental investigation on the streamer propagation and breakdown of Refined, Bleached and Deodorized Palm Oil (RBDPO) under both positive and negative lightning impulse voltages. The streamer shape, stopping length, velocity and breakdown voltage of 2 types of RBDPO were examined. Needle-plane electrodes configuration with 50 mm gap was used in this study and streamer images were captured by a high speed camera. It is observed that the negative streamer shape patterns are thicker than positive streamer for both RBDPO and MO. At the same applied voltage level and polarity, both RBDPO have longer streamer stopping lengths and the streamers propagate faster than MO.

Characteristics of a Pulse-Periodic Corona Discharge in Atmospheric Air

Pulse-periodic corona discharge in atmospheric air excited by applying a voltage pulse with a subnanosecond or microsecond rise time to a point electrode is studied experimentally. It is shown that, at a voltage rise rate of dU/dt ~1014 V/s, positive and negative ball-shaped streamers with a front velocity of ≥2 mm/ns form near the point electrode. As dU/dt is reduced to 1010−1011 V/s, the streamer shape changes and becomes close to cylindrical. The propagation velocity of cylindrical streamers is found to be ~0.1 mm/ns at dU/dt ~ 2 × 1010 V/s. It is shown that the propagation direction of a cylindrical streamer can be changed by tilting the point electrode, on the axis of which the electric field strength reaches its maximum value. It is established that, for the negative polarity of the point electrode and a microsecond rise time of the voltage pulse, a higher voltage is required to form a cylindrical streamer than for the positive polarity of the point electrode.

Abnormal Polarity Effects of Streamer Discharge in Propylene Carbonate under Microsecond Pulses**Supported by the National Natural Science Foundation of China under Grant No 51677190, and the Hunan Provincial Natural Science Foundation of China under Grant No 2017JJ1005.

Propylene carbonate (PC) has a great potential to be used as an energy storage medium in the compact pulsed power sources due to its high dielectric constant and large resistivity. We investigate both the positive and negative breakdown characteristics of PC. The streamer patterns are obtained by ultra-high-speed cameras. The experimental results show that the positive breakdown voltage of PC is about 135% higher than the negative one, which is abnormal compared with the common liquid. The shape of the positive streamer is filamentary and branchy, while the negative streamer is tree-like and less branched. According to these experimental results, a charge layer structure model at the interface between the metal electrode and liquid is presented. It is suggested that the abnormal polarity effect basically arises from the electric field strength difference in the interface between both electrodes and PC. What is more, the recombination radiation and photoionization also play an important role in the whole discharge process.

Experimental study of an impulse electric discharge with liquid electrodes

Experimental results are presented on transition of a streamer shape multichannel discharge into a multichannel spark discharge. We present current–voltage characteristics of a multichannel streamer discharge at atmospheric and reduced pressures as well as temperature distribution between a plate-like copper electrode and technical water.

Effect of TiO2nanoparticles on streamer propagation in transformer oil under lightning impulse voltage

Recent experiments have shown that some nanoparticles can influence the breakdown strength of transformer oil under lightning impulse voltage. To reveal the working mechanism, this paper presents an experimental study on the effect of TiO2 nanoparticles on the impulse breakdown strength and prebreakdown streamer propagation process in transformer oil-based nanofluid under both positive and negative lightning impulse voltage. The test results verify that the modification of nanoparticles on breakdown strength of transformer oil has a distinct polar effect: positive breakdown voltage of nanofluid is increased by up to 30.8%, whereas the negative one is decreased by 6.8%. Streamer shape, propagation length and velocity in both pure oil and nanofluid were investigated using the shadowgraph technique. It is revealed that the propagation characteristics of positive and negative streamers in nanofluid are markedly affected by the addition of TiO2 nanoparticles. The positive streamers in nanofluid form a bush-like structure with thicker and denser branches, developing much slower than tree-like streamers in pure oil. While negative streamers in nanofluid have a tree-like shape with much longer branches, propagating faster than the original bush-like streamer in pure oil. These differences in streamer propagation characteristics and breakdown strength in pure oil and nanofluid are closely related to the change of space charge distribution caused by shallow trap in nanofluid. More negative charges are formed through capturing fast electrons into slow electrons in shallow traps induced by the presence of TiO2 nanoparticles, which change the local electric field in front of the streamer tip. Thus, streamer propagation process in nanofluid is dramatically modified, leading to the change in breakdown strength.

Effect of Fe3O4 nanoparticles on positive streamer propagation in transformer oil

Fe3O4 nanoparticles with an average diameter of 10 nm were prepared and used to modify streamer characteristic of transformer oil. It was found that positive streamer propagation velocity in transformer oil-based Fe3O4 nanofluid is greatly reduced by 51% in comparison with that in pure oil. The evolution of streamer shape is also dramatically affected by the presence of nanoparticles, changing from a tree-like shape with sharp branches in pure oil to a bush-like structure with thicker and denser branches in nanofluid. The TSC results reveal that the modification of Fe3O4 nanoparticle can greatly increase the density of shallow trap and change space charge distribution in nanofluid by converting fast electrons into slow electrons via trapping and de-trapping process in shallow traps. These negative space charges induced by nanoparticles greatly alleviate the electric field distortion in front of the positive streamer tip and significantly hinder the propagation of positive streamer.

Streamer propagation in a non-uniform electric field under lightning impulse in short gaps insulated with natural ester and mineral oil

Abstract This article describes the comparative experimental studies on streamer propagation in natural ester and mineral oil under a high voltage lightning impulse. These studies were concentrated around the small electrode gaps and the point-plane electrode arrangement. The spatial shapes of the developing streamers, light emission and propagation velocity were analyzed and compared between the two different dielectric liquids. In both of them two streamer propagation modes were registered during the studies performed. Propagation of slow 2nd mode streamers took place below the so-called acceleration voltage while fast 3rd mode streamers developed at acceleration voltage and above. Comparing the streamer shapes corresponding to a given voltage polarity, no visible differences were observed between the liquids tested. Concerning the light emission, higher frequencies of light pulses were registered however in the case of natural ester. The significant differences between both liquids were noticed in the value of the acceleration voltage estimated. In the case of positive polarity streamers started to develop in natural ester as a 3rd mode at lower value of testing voltage than in the case of mineral oil. For negative polarity, within the applied testing voltages, 3rd mode streamers appeared only in natural ester. On this basis, the fundamental conclusion is that natural ester may have a lower ability of preventing the development of fast and energetic 3rd mode streamers, even at small electrode gaps.

Incipient electric field determination for bush and streamer stage in dielectric liquid under energy balance condition

This paper introduces a new approach for streamer advance mechanism in dielectric liquid. The existing of bush-like streamer shape early and then a tree structure shape after that has been given an over view and definition by devising a breakdown index for dielectric liquid which reach a value of 25. The deviation of streamer velocity from low values of tens of meter per second, until several kilometer per second from bush-like shape, until complete breakdown has been discussed too. These different stages have been studied on an energy balance concepts. In this paper using energy balance analysis, different critical applied fields have been obtained. These values reach 2.18 MV/cm for one branch channel in bush-like streamer shape and 21.5 MV/cm, for tree streamer. After that, the initial streamer velocities concerning these stages have been introduced. From these analysis the dissociation of dielectric liquids starts when the streamer velocity reach the sound speed in air, 331 m/s. In addition, the dissociation field depends mainly on the physical values of the dielectric medium, such as density, and permittivity have been introduced. In this paper the dissociation starts at an electric field value of 21.5 MV/cm for nearly all dielectric liquids, This result is equal to tree streamer inception value, which can be considered as a new introduced finding. A new energy equation relating injected energy electric field, velocity and new deduced breakdown index in dielectric liquid has been devised. The streamer may stop or continue its advance until complete breakdown. According to many published data for streamer, there is no clear explanation for streamer stopping and continuing it advance. In this paper, the streamer must advance ahead of the bush zone in the gap toward the opposite electrode when the prospective electric field at 66% of the gap achieves a breakdown index of 25. This result can be considered as a new criterion for streamer growth until crossing the gap. These new equations and findings have been applied to several experimental works and achieve good results.

Shape estimate of a streamer of hydrophones towed by an Autonomous Underwater Vehicle

Abstract: The paper deals with the problem of estimating the shape of a streamer of hydrophones for acoustic geoseismic survey when towed by an Autonomous Underwater Vehicle (AUV). The considered problem arises in the framework of a H2020 European Project, named WiMUST, aimed at using a team of AUVs, each one towing a streamer of hydrophones, to perform geoseismic survey missions that are traditionally performed using streamers towed by a single manned surface vessel. The replacement of the towing system of the vessel with a team of AUVs introduces several issues in the localization of the hydrophones, needed to allow the processing of the acoustic data, since they are no more on the sea surface. In this paper we want to study the solvability of the streamer shape estimation problem depending on the possibly available measurements and information that can be collected via the hydrophones, the AUVs on board sensors, and relying on acoustic communication.

Localized Residual Heat and Formation of Nonbranched Positive Streamer With Highly Repetitive Streamer Discharge

The mechanism of a mode change from a branch-type to a nonbranch positive streamer with increase in pulse repetition rate was investigated from the point of view of background gas heating. In this experiment, a repetitive streamer was generated between a needle and a plane electrode. The repetition rate of impulse positive streamer discharge was changed from 500 to 10 500 pulse/s. The branching of a streamer decreased with the increase in pulse repetition rate and the streamer shape completely changed to a nonbranched type at 10 000 pulse/s. The gas temperature in the repetitive streamer was quantitatively measured at different pulse repetition rates by a spectroscopic method using N2 second positive system band (0, 0). In addition, the gas density change between the electrodes due to gas heating caused by the repetitive streamers was observed using the laser schlieren method. As a result, it was confirmed that the gas temperature in repetitive streamers increased with the increase in pulse repetition rate. The gas temperature in a streamer increased up to 420 K by the accumulation of background gas heating at 10 000 pulse/s. Furthermore, residual gas heat in the shape of a single filament due to a highly repetitive streamer and its dissipation process were clearly visualized.

The vertical shape of a buoyant acoustic streamer between depth control units

When conducting marine seismic surveys it is important to know the vertical profile of the seismic streamer. Typically the streamer has a density that is different from the seawater; therefore the streamer is held at depth by depth control units, and the streamer׳s tail is held at the surface by a tail buoy. In this paper, a semi-analytical solution is presented. It is the first-order solution for the profile of a streamer, towed in a straight line, at a constant speed. The solution is adapted to describe the streamer shape when there are significant changes in cable density due to the presence of components over small regions. The resulting profiles have good agreement with a numerical solution evolved to the steady state.