Gas Cloud Model Research Articles

A joint absorbing boundary for the multiple-relaxation-time lattice Boltzmann method in seismic acoustic wavefield modeling

Conventional seismic wave forward simulation generally uses mathematical means to solve the macroscopic wave equation, and then obtains the corresponding seismic wavefield. Usually, when the subsurface structure is finely constructed and the continuity of media is poor, this strategy is difficult to meet the requirements of accurate wavefield calculation. This paper uses the multiple-relaxation-time lattice Boltzmann method (MRT-LBM) to conduct the seismic acoustic wavefield simulation and verify its computational accuracy. To cope with the problem of severe reflections at the truncated boundaries, we analogize the viscous absorbing boundary and perfectly matched layer (PML) absorbing boundary based on the single-relaxation-time lattice Boltzmann (SRT-LB) equation to the MRT-LB equation, and further, propose a joint absorbing boundary through comparative analysis. We give the specific forms of the modified MRT-LB equation loaded with the joint absorbing boundary in the two-dimensional (2D) and three-dimensional (3D) cases, respectively. Then, we verify the effects of this absorbing boundary scheme on a 2D homogeneous model, 2D modified British Petroleum (BP) gas-cloud model, and 3D homogeneous model, respectively. The results reveal that by comparing with the viscous absorbing boundary and PML absorbing boundary, the joint absorbing boundary has the best absorption performance, although it is a little bit complicated. Therefore, this joint absorbing boundary better solves the problem of truncated boundary reflections of MRT-LBM in simulating seismic acoustic wavefields, which is pivotal to its wide application in the field of exploration seismology.

Liouville partial-differential-equation methods for computing 2D complex multivalued eikonals in attenuating media

We have developed a Liouville partial-differential-equation (PDE)-based method for computing complex-valued eikonals in real phase space in the multivalued sense in attenuating media with frequency-independent qualify factors, where the new method computes the real and imaginary parts of the complex-valued eikonal in two steps by solving Liouville equations in real phase space. Because the earth is composed of attenuating materials, seismic waves usually attenuate so that seismic data processing calls for properly treating the resulting energy losses and phase distortions of wave propagation. In the regime of high-frequency asymptotics, the complex-valued eikonal is one essential ingredient for describing wave propagation in attenuating media because this unique quantity summarizes two wave properties into one function: Its real part describes the wave kinematics and its imaginary part captures the effects of phase dispersion and amplitude attenuation. Because some popular ordinary-differential-equation (ODE)-based ray-tracing methods for computing complex-valued eikonals in real space distribute the eikonal function irregularly in real space, we are motivated to develop PDE-based Eulerian methods for computing such complex-valued eikonals in real space on regular meshes. Therefore, we solved novel paraxial Liouville PDEs in real phase space so that we can compute the real and imaginary parts of the complex-valued eikonal in the multivalued sense on regular meshes. We call the resulting method the Liouville PDE method for complex-valued multivalued eikonals in attenuating media; moreover, this new method provides a unified framework for Eulerianizing several popular approximate real-space ray-tracing methods for complex-valued eikonals, such as viscoacoustic ray tracing, real viscoelastic ray tracing, and real elastic ray tracing. In addition, we also provide Liouville PDE formulations for computing multivalued ray amplitudes in a weakly viscoacoustic medium. Numerical examples, including a synthetic gas-cloud model, demonstrate that our methods yield highly accurate complex-valued eikonals in the multivalued sense.

Flexible alarming mechanism of a general GDS deployment for explosive accidents caused by gas leakage

Gas detection system (GDS) is critical for identifying and suppressing the flammable or hazardous gas leaked by incidents. The spread of a flammable gas cloud is susceptible to external factors and highly uncertain, but the GDSs deployed today often raise alarms based on certainty. It means that the threshold value set in a GDS for triggering alarms is a constant. Such an approach sometimes cannot accurately determine the leakage location, and so it may result in a great delay of gas detection. To reduce the risk of gas leakage, this paper proposes a flexible triggering mechanism for GDSs, where an alarm is raised or not depending on the number of sensors whose reading are reaching or closing to the preset threshold. An equivalent gas cloud (EGC) model is introduced here to provide design inputs for such a flexible triggering GDS. The volume and location distribution of an EGC are estimated with the Gaussian dispersion model, based on the changes of wind speed and direction. A case study in a terminal station of LNG is conducted, to illustrate the effectiveness of the new approach. The findings show that the flexible triggering mechanism is able to make alarms of a GDS more accurate, and meanwhile avoiding unnecessary measures, which can effectively optimize alarming thresholds.

Simulation of pollutant-gas-cloud infrared spectra under plane-array detecting

The research on simulation of pollutant-gas-cloud infrared spectra is very important for studying the spectral identification algorithms by using simulated spectra. Some good results of the simulation of pollutant-gas-cloud infrared spectra under single-detector detecting are achieved, and have been used for studying the spectral identification. With the development of infrared detection technology, the infrared imaging spectrometer is used to detect pollutant gas cloud. The gas identification algorithms in the way of plane-array detecion based on the imaging spectrometer also need a number of measured gas-cloud infrared spectrum data cubes. Due to the lack of measured data in studying the spectral identification algorithm that is based on imaging spectrometer, the multiple-layer model of the cloud infrared spectrum is well studied by using the high-precision physics-based gas-cloud explosion model and its gridding simulation results, and the way of simulating pollutant-gas-cloud infrared spectra under plane-array-detector detecting is proposed to generate the infrared spectrum data cube with both spectral and spatial information, which obtains a new research method for the research field. Validations are made by comparing the measured data with the simulated data, and the comparison contains three parts: i) the comparison of measured gas-cloud explosion with simulated gas-cloud explosion, ii) the comparison of spectral identification imaging results between the measured and the simulated gas-cloud infrared spectrum data cubes, and iii) the comparison between the measured and the simulated gas-cloud infrared spectra. The comparison results have two aspects: the first aspect is that the simulated gas-cloud explosion is consistent with the measured explosion and has little difference in separate parts, and the second aspect is that the simulated gas-cloud spectra have relative errors of less than 10% compared with the measured gas-cloud spectra. The conclusion is that the simulation model of pollutant-gas-cloud infrared spectra under plane-array detecting is correct, which is obtained from the validation results that simulated gas-cloud infrared spectrum data cubes are highly precise, whether in the comparison with spectral identification imaging results or in the comparison with gas-cloud spectra. The simulation of pollutant-gas-cloud infrared spectra under plane-array detecting which directly reflects the explosion of pollutant gas cloud and provides complete and realistic infrared spectrum data cube of pollutant gas cloud, is significant for improving and perfecting the spectral identification algorithms.

Neural network methods to solve the Lane–Emden type equations arising in thermodynamic studies of the spherical gas cloud model

In the present study, stochastic numerical computing approach is developed by applying artificial neural networks (ANNs) to compute the solution of Lane–Emden type boundary value problems arising in thermodynamic studies of the spherical gas cloud model. ANNs are used in an unsupervised manner to construct the energy function of the system model. Strength of efficient local optimization procedures based on active-set (AS), interior-point (IP) and sequential quadratic programming (SQP) algorithms is used to optimize the energy functions. The performance of all three design methodologies ANN-AS, ANN-IP and ANN-SQP is evaluated on different nonlinear singular systems. The effectiveness of the proposed schemes in terms of accuracy and convergence is established from the results of statistical indicators.

Resolving high frequency anomalies of gas cloud using full waveform inversion

<p>High resolution models with structurally improved results significant to the physical properties of rocks in geologically complex areas require advance modeling methodologies. Low frequencies are required to understand the geological properties of the rocks while high frequencies is needed to address the structural challenges. Recent industry success in inversion have shown the accurate and robust results for the low frequencies. In this work, we provide a strategy to resolve geologically complex area such as gas cloud (at high frequencies) using full waveform inversion (FWI) based on 2D wave equation. Our contribution here, is the improvement in FWI imaging by: (i) solving the wave field equation to recover high resolution inversion results which is consistence to physical properties and shows structural enhancements; (ii) estimating the distribution of local minima which is largely affected by initial velocity model. To validate our approach, we demonstrate algorithms on synthetic gas cloud model.</p>

Acoustic 2D full waveform inversion to solve gas cloud challenges

<p>The existing conventional inversion algorithm does not provide satisfactory results due to the complexity of propagated wavefield though the gas cloud. Acoustic full waveform inversion has been developed and applied to a realistic synthetic offshore shallow gas cloud feature with Student-t approach, with and without simultaneous sources encoding. As a modeling operator, we implemented the grid based finite-difference method in frequency domain using second order elastic wave equation. Jacobin operator and its adjoint provide a necessary platform for solving full waveform inversion problem in a reduced Hessian matrix. We invert gas cloud model in 5 frequency band selected from 1 to 12 Hz, each band contains 3 frequencies. The inversion results are highly sensitive to the misfit. The model allows better convergence and recovery of amplitude losses. This approach gives better resolution then the existing least-squares approach. In this paper, we implement the full waveform inversion for low frequency model with minimum number of iteration providing a better resolution of inversion results.</p>

Seismic Illumination Analysis in Poor Oil & Gas Field Data by Using Focal Beam Method

The area underneath shallow gas cloud is an area where the image of subsurface data is generally poor. This distorted image underneath gas zones usually contains precious information of hydrocarbon accumulation. Previously, we analyse the factors contribute to poor subsurface seismic image underneath the gas cloud model and use focal beam technique to understand subsurface illumination information. Encourage by model-based success, we shift our focus to data-based application by applying the focal beam technique into a real field data. The results from this field were analyse in term of resolution function and amplitude versus ray parameter (AVP) imprint for different reflector depth, followed by acquisition analysis on the surface level. For this purpose, a velocity data of a field located in Malay Basin was built before applying the focal beam calculation. We will demonstrate that by using focal beam analysis for this field, we will able to obtain good imaging particularly for target reflector at 2000ms, 4000ms and 6000ms depth, provided the full 3D acquisition geometry was used during focal beam application.

Physics-based, reduced-order gas cloud with radiative transport model for rapid simulation of hyperspectral infrared sensors

Peter A. KottkeGeorgia Institute of TechnologyGeorge W. Woodruff School of MechanicalEngineering701 Ferst DriveAtlanta, Georgia 30332-0405E-mail: pk57@mail.gatech.eduAndrei G. FedorovGeorgia Institute of TechnologyGeorge W. Woodruff School of MechanicalEngineering and Parker H. Petit Institute ofBioengineering and Bioscience701 Ferst DriveAtlanta, Georgia 30332-0405Abstract. We have developed a reduced-order, physics-based model ofgas cloud transport and combined it with an approximate formulation ofthe equation of radiative transport to enable efficient prediction of spectralirradiation for simulation of hyperspectral infrared sensors. The resultingcombined model is easily implemented, providing a rapid and flexiblein silico experimentation capability. The gas cloud model is based onthe entrainment hypothesis and predicts cloud trajectories in three-dimensions, with elevation changes occurring primarily due to buoyancyeffects and with spreading and accompanying dilution and cooling occur-ring due to a turbulence dominated growth mechanism. The radiationtransport model is simplified through an approximate treatment of scatter-ing that transforms the governing equation from an integro-differentialequation to an ordinary differential equation. The conjugate model hasbeen combined with a simple sensor model and has been validatedthrough comparison to results from large-scale field tests. The utility ofthe simulations has also been demonstrated through inclusion in a largeralgorithm development and analysis program, the chem/bio algorithmdevelopment kit.

Analytic solutions to the accretion of a rotating finite cloud towards a central object - I. Newtonian approach

We construct a steady analytic accretion flow model for a finite rotating gas cloud that accretes material to a central gravitational object. The pressure gradients of the flow are considered to be negligible, and so the flow is ballistic. We also assume a steady flow and consider the particles at the boundary of the spherical cloud to be rotating as a rigid body, with a fixed amount of inwards radial velocity. This represents a generalization to the traditional infinite gas cloud model described by Ulrich. We show that the streamlines and density profiles obtained deviate largely from the ones calculated by Ulrich. The extra freedom in the choice of the parameters on the model can naturally account for the study of protostars formed in dense clusters by triggered mechanisms, where a wide variety of external physical mechanisms determine the boundary conditions. Also, as expected, the model predicts the formation of an equatorial accretion disc about the central object with a radius different from the one calculated by Ulrich.

Gas clouds rotating around a principal axis: II. The separation of variables

We present a new formulation of the spinning gas cloud model of Ovsiannikov and Dyson (in the case of rotation around a fixed axis), in terms of a 4×4 symmetric matrix which is a linear function of four coordinates xi. We obtain a pair of separable variables l1, l2 related to the xi by a simple transformation, and discuss their geometrical meaning.

Spinning gas clouds: Liouville integrability

This paper constitutes a generalization to arbitrary states of rotation of an earlier work in which we showed Liouville integrability of the expanding and rotating gas cloud model of Ovsiannikov and of Dyson in cases of rotation around a fixed principal axis.

Spinning gas clouds - without vorticity

Ovsiannikov and Dyson have considered an ordinary differential reduction of the gas-dynamical equations for an ideal gas which is adiabatically expanding and rotating. Gaffet has shown, based on its Painleve property, the complete integrability of that ellipsoidal gas cloud model, when there is neither rotation nor vorticity and the gas is monatomic (γ = 5/3), and has conjectured that the integrability might persist in more general cases including rotation. In this paper we show that the presence of vorticity in general destroys the integrability property, but the conjecture is otherwise verified, under the simplifying assumption of rotation around a fixed axis. In a future work we hope to extend the present result to Dyson's most general spinning gas cloud without vorticity.

Infrared Imaging of z = 2.43 Radio Galaxy B3 0731+438 with the Subaru Telescope — Detection of Hα a Ionization Cones of a Powerful Radio Galaxy

We report on infrared imaging observations of the z = 2.429 radio galaxy B3 0731+438 with the Subaru telescope. The images were taken with the K′-band filter and the 2.25 μm narrow-band filter to examine the structure and properties of the Hα+[NII] λλ 6548, 6583 emission-line components. The Hα+[NII] emission-line image shows biconical lobes with an extent of 40 kpc, which are aligned with the radio axis. The rest-frame equivalent widths of the emission lines at these cones are as large as 1100 Å, and can be well explained by a gas-cloud model photoionized by power-law continuum radiation. The isotropic ionizing photon luminosity necessary to ionize the hydrogen gas in these cones amounts to 1057 (photons s−1), which is larger than that in the majority of radio-loud QSOs. From these results, we propose that the Hα alignment effect in this object is produced by biconical gas clouds, which are swept up by the passage of radio jets, and are ionized by strong UV radiation from a hidden AGN. The continuum image consists of two components, a stellar-like point source and an extended diffuse galaxy. These are supposed to be a type-2 AGN and its host galaxy. The SED is fitted by a combination of spectra of a reddened dust-scattered AGN and an instantaneous starburst population of 500 Myr old. The stellar mass of the galaxy is estimated to be 3 × 1011M⊙, which is as large as that of typical 3C radio galaxies at z = 1.

Modeling the Lake Nyos gas disaster

Post-accident studies have revealed that a carbon dioxide gas cloud released from Lake Nyos, Cameroon, was responsible for the asphyxiation of humans and animals at distances of several kilometers from the lake. The spreading and dispersive properties of such a cloud, as calculated from the dense gas cloud model of Fay and Zemba ( Atmospheric Environment 19, 1257–1261, 1985), are consistent with the observed effects.