Realistic Velocity Research Articles

Validation of a fast semi-analytic method for surface-wave propagation in layered media

SUMMARYGreen’s functions provide an efficient way to model surface-wave propagation and estimate physical quantities for near-surface processes. Several surface-wave Green’s function approximations (far-field, no mode conversions and no higher mode surface waves) have been employed for numerous applications such as estimating sediment flux in rivers, determining the properties of landslides, identifying the seismic signature of debris flows or to study seismic noise through cross-correlations. Based on those approximations, simple empirical scalings exist to derive phase velocities and amplitudes for pure power-law velocity structures providing an exact relationship between the velocity model and the Green’s functions. However, no quantitative estimates of the accuracy of these simple scalings have been reported for impulsive sources in complex velocity structures. In this paper, we address this gap by comparing the theoretical predictions to high-order numerical solutions for the vertical component of the wavefield. The Green’s functions computation shows that attenuation-induced dispersion of phase and group velocity plays an important role and should be carefully taken into account to correctly describe how surface-wave amplitudes decay with distance. The comparisons confirm the general reliability of the semi-analytic model for power-law and realistic shear velocity structures to describe fundamental-mode Rayleigh waves in terms of characteristic frequencies, amplitudes and envelopes. At short distances from the source, and for large near-surface velocity gradients or high Q values, the low-frequency energy can be dominated by higher mode surface waves that can be captured by introducing additional higher mode Rayleigh-wave power-law scalings. We also find that the energy spectral density for realistic shear-velocity models close to piecewise power-law models can be accurately modelled using the same non-dimensional scalings. The frequency range of validity of each power-law scaling can be derived from the corresponding phase velocities. Finally, highly discontinuous near-surface velocity profiles can also be approximated by a combination of power-law scalings. Analytical Green’s functions derived from the non-dimensionalization provide a good estimate of the amplitude and variations of the energy distribution, although the predictions are quite poor around the frequency bounds of each power-law scaling.

Realistic Model of Mobility based on Location and Route for VANET

In this research work, we propose two realistic mobility models named as location based realistic mobility model and route based realistic mobility model. In location based realistic mobility model speed and velocity is updating and route based realistic mobility model implies how many routes are available. With these models the targeted position is set and vehicles are moving according to the same position. Hence the problem of routing is resolved which is encountered in existing realistic mobility model. For implementation of our models, we use open source software named as network simulator NS-3 and traffic simulator MOVE with SUMO. We also compare our models with the existing realistic models in terms of performance matrices: packet loss, throughput and transmission delay. Since the vehicles are moving according to targeted position, so as application aspects we predict accidents and lots of traffic and with the help of prediction we will choose some optimal solutions.

Simulating the nonlinear interaction of relativistic electrons and tokamak plasma instabilities: Implementation and validation of a fluid model

For the simulation of disruptions in tokamak fusion plasmas, a fluid model describing the evolution of relativistic runaway electrons and their interaction with the background plasma is presented. The overall aim of the model is to self-consistently describe the nonlinear coupled evolution of runaway electrons (REs) and plasma instabilities during disruptions. In this model, the runaway electrons are considered as a separate fluid species in which the initial seed is generated through the Dreicer source, which eventually grows by the avalanche mechanism (further relevant source mechanisms can easily be added). Advection of the runaway electrons is considered primarily along field lines, but also taking into account the E×B drift. The model is implemented in the nonlinear magnetohydrodynamic (MHD) code jorek based on Bezier finite elements, with current coupling to the thermal plasma. Benchmarking of the code with the one-dimensional runaway electron code go is done using an artificial thermal quench on a circular plasma. As a first demonstration, the code is applied to the problem of an axisymmetric cold vertical displacement event in an ITER plasma, revealing significantly different dynamics between cases computed with and without runaway electrons. Though it is not yet feasible to achieve fully realistic runaway electron velocities close to the speed of light in complete simulations of slowly evolving plasma instabilities, the code is demonstrated to be suitable to study various kinds of MHD-RE interactions in MHD-active and disruption relevant plasmas.

Bed shear stress, surface shape and velocity field near the tips of dam-breaks, tsunami and wave runup: Reply by Peter Nielsen

A reply is offered to the discussion by Baldock, T E, (2018): Bed shear stress, surface shape and velocity field near the tips of dam-breaks, tsunami and wave runup. Discussion, Coastal Eng, Vol 142, pp 77–81, henceforth B18 of the swash tip model by Nielsen, P (2018): Bed shear stress, surface shape and velocity field near the tips of dam-breaks, tsunami and wave runup. Coastal Engineering, Vol 138, pp 126–131, henceforth N18. The point made by B18, that the near uniform velocity profiles predicted by the N18 model close to the contact point are unrealistic, is substantiated via new data with enhanced vertical resolution due to large bed roughness, ks ≈ 6.5cm. This data shows that the tip does not actually have a vertical tangent at the contact point. Hence, the main argument for a vertically uniform velocity at a tip, propagating with constant form, falls away. When the N18 model is applied using a measured, non-bullnose, near-tip surface shape it provides realistic velocity profiles and bed shear stress magnitudes. Thus, N18 provides a step towards an integrated explicit 2DV description of swash tips, though not a definitive description.

Oblique Reflections of Mars Express MARSIS Radar Signals From Ionospheric Density Structures: Raytracing Analysis

AbstractMars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) radar sounder on board the Mars Express spacecraft revealed oblique reflections coming systematically from apparently stable density structures in the Martian ionosphere. Although these were typically interpreted by assuming a straight line propagation of the sounding signal at the speed of light, the ionospheric plasma is clearly a dispersive medium. Consequently, the ray propagation paths may be significantly bent, and, moreover, the observed time delays need to be interpreted in terms of realistic group velocities of the signal propagation. We select a single particularly well‐pronounced event with oblique reflections observable over a large range of signal frequencies, and we employ raytracing calculations to perform its detailed analysis. An isolated density structure responsible for the reflection of the sounding signal back to the spacecraft is assumed, and the relevant ionospheric signal propagation is properly evaluated. We show that initially oblique sounding signals get progressively more oblique during their propagation, imposing an upper threshold on the angular propagation distance between the spacecraft and the reflecting density structure, in line with the observations. Considering realistic propagation paths further allows us to explain the frequency dependence of the observed time delays and to accurately model the entire event. The obtained results are consistent with the spacecraft passing very close to a spatially limited density structure. We also show that the results obtained using realistic raytracing calculations are significantly different from the results obtained using additional simplifying assumptions.

A Method for Detecting Atmospheric Lagrangian Coherent Structures Using a Single Fixed-Wing Unmanned Aircraft System.

The transport of material through the atmosphere is an issue with wide ranging implications for fields as diverse as agriculture, aviation, and human health. Due to the unsteady nature of the atmosphere, predicting how material will be transported via the Earth’s wind field is challenging. Lagrangian diagnostics, such as Lagrangian coherent structures (LCSs), have been used to discover the most significant regions of material collection or dispersion. However, Lagrangian diagnostics can be time-consuming to calculate and often rely on weather forecasts that may not be completely accurate. Recently, Eulerian diagnostics have been developed which can provide indications of LCS and have computational advantages over their Lagrangian counterparts. In this paper, a methodology is developed for estimating local Eulerian diagnostics from wind velocity data measured by a single fixed-wing unmanned aircraft system (UAS) flying in a circular arc. Using a simulation environment, driven by realistic atmospheric velocity data from the North American Mesoscale (NAM) model, it is shown that the Eulerian diagnostic estimates from UAS measurements approximate the true local Eulerian diagnostics and also predict the passage of LCSs. This methodology requires only a single flying UAS, making it easier and more affordable to implement in the field than existing alternatives, such as multiple UASs and Dopler LiDAR measurements. Our method is general enough to be applied to calculate the gradient of any scalar field.

Generalized explicit guidance with optimal time-to-go and realistic final velocity

This paper presents an approach to compute the optimal time-to-go and final velocity magnitude in the Generalized Explicit (GENEX) guidance. Time-to-go and final velocity magnitude are two critical input parameters in GENEX guidance implementation. Optimal time-to-go selects that optimal solution which yields less cost compared to the costs yielded by other optimal solutions. In addition to it, the input of realistic final velocity lowers the cost further. These developments relax the existing limitations of GENEX, thereby making this optimal guidance law more optimal, effective and generic.

A New Perspective on Heat Transfer Mechanisms and Sonic Limit in Pool Boiling

Pool boiling is postulated as a single-phase heat transfer process with nucleating bubbles providing a liquid pumping mechanism over the heater surface. This results in three fluid streams at the heater surface—outgoing vapor and liquid streams, and an incoming liquid stream. Heat transfer during periodic replacement of the liquid in the influence region around a nucleating bubble is well described by transient conduction (TC) and microconvection (MiC) mechanisms. Beyond this region, free convection (FC) or macroconvection (MaC) contributes to heating of the liquid. A bubble growing on the heater surface derives its latent heat from the surrounding superheated liquid and from the microlayer providing a direct heat conduction path. Secondary evaporation occurs in the bubbles rising in the bulk after departure, and at the free surface. This secondary evaporation does not directly contribute to the heat transfer at the heater surface but provides a means of dissipating liquid superheat. A sonic limit-based model is then presented for estimating the theoretical upper limit for pool boiling heat transfer by considering the three fluid streams to approach their respective sonic velocities. Maximum heat transfer rates are also estimated using this model with two realistic velocities of 1 and 5 m/s for the individual streams and are found to be in general agreement with available experimental results. It is postulated that small bubbles departing at high velocity along with high liquid stream velocities are beneficial for heat transfer. Based on these concepts, future research directions for enhancing pool boiling heat transfer are presented.

The carbon: 234Thorium ratios of sinking particles in the California current ecosystem 2: Examination of a thorium sorption, desorption, and particle transport model

Thorium-234 (234Th) is a powerful tracer of particle dynamics and the biological pump in the surface ocean; however, variability in carbon: thorium ratios of sinking particles adds substantial uncertainty to estimates of organic carbon export. We coupled a mechanistic thorium sorption and desorption model to a one-dimensional particle sinking model that uses realistic particle settling velocity spectra. The model generates estimates of 238U234Th disequilibrium, particulate organic carbon concentration, and the C:234Th ratio of sinking particles, which are then compared to in situ measurements from quasi-Lagrangian studies conducted on six cruises in the California Current Ecosystem. Broad patterns observed in in situ measurements, including decreasing C:234Th ratios with depth and a strong correlation between sinking C:234Th and the ratio of vertically-integrated particulate organic carbon (POC) to vertically-integrated total water column 234Th, were accurately recovered by models assuming either a power law distribution of sinking speeds or a double log normal distribution of sinking speeds. Simulations suggested that the observed decrease in C:234Th with depth may be driven by preferential remineralization of carbon by particle-attached microbes. However, an alternate model structure featuring complete consumption and/or disaggregation of particles by mesozooplankton (e.g. no preferential remineralization of carbon) was also able to simulate decreasing C:234Th with depth (although the decrease was weaker), driven by 234Th adsorption onto slowly sinking particles. Model results also suggest that during bloom decays C:234Th ratios of sinking particles should be higher than expected (based on contemporaneous water column POC), because high settling velocities minimize carbon remineralization during sinking.

Rapid Geodetic Analysis of Subduction Zone Earthquakes Leveraging a 3‐D Elastic Green's Function Library

AbstractThe 2018 M7.2 Pinotepa earthquake ruptured a shallow slab section along the Middle America subduction zone. We demonstrate how a geodetic Green's function (GF) library and efficient modeling algorithm can rapidly resolve earthquake slip and contribute to early warning systems. The source is characterized with InSAR data and a finite‐element model mimicking realistic slab geometry (Slab1.0) and velocity structures (CRUST2.0) that are not considered in the conventional homogeneous (HOM)‐ or layered(1‐D)‐crust solutions. The rupture is imaged 18 min after geodetic data are downloaded to a 16‐CPU‐thread workstation. Nearby Mw8.6‐megathrust scenarios are also studied with synthetic GPS data in the Guerrero/Oaxaca area. Our results show that earthquake slip solutions are sensitive to the materials of elastic‐modeling domains. Attaining smaller misfits or sums of squared errors, models by 3‐D GFs significantly better recover coseismic displacements than those estimated with 1‐D GFs or HOM GFs at 95% confidence.

New approach to materials behaviour studies in high-speed flue gas from oxy-steam combustion

Some new proposals are being considered aiming at improving the efficiency and operability of oxy-combustion power plants, such as the so-called oxy-steam combustion. This process consists in replacing the carbon dioxide by steam in the firing atmosphere. One of the main uncertainties for the feasibility of the oxy-steam technology is the materials resistance to steam corrosion at high temperature, mainly due to chromium vaporization. The novel approach to the issue presented in this work is the generation of realistic flue gas velocity (20 m·s−1) in flames produced with a thermal spray gun using H2 as fuel. Gas composition was selected to match expected final H2O content after combustion: 40 and 60% H2O in CO2 with excess of O2. A set of metallic steels and alloys (SS304, SS310, I800HT, Kanthal and IN617) was preoxidised in air to generate external oxide scales. After preoxidation, the samples were treated under steam flames at 700 °C, placed in a position either parallel or perpendicular to the flame axis. Surface oxides composition was compared to that obtained in a quasi-static furnace, where metallic samples were exposed to steam atmosphere at 700 °C for 20 h (50% steam, 45% CO2 and 5% O2). The characterisation of the surfaces was performed using low-angle XRD and SEM-EDX for a precise measuring of the variation of oxide amount and chromium content. The analyses showed that mixed Cr-Mn and Cr-Fe external oxides formed during the preoxidation stage suffered the depletion of the surface chromium when they were exposed parallel to the steam flame axis, as a simulation of the lateral flue gas pass in the heat-exchanger tubing. Cr depletion was also observed in the windside of tubes (perpendicular to flame axis) but in minor extent. The reduction in the Cr amount of the samples when tested in the vapour furnace was negligible compared to the Cr loss found after treatment under high velocity flames. The presence of external (Mn,Cr)3O4 in preoxidised SS310 and SS304 did not provide an effective protection against Cr volatilization in the steam flame treatment, whereas surface alumina in Kanthal seemed to prevent Cr volatilization.

Repeatability and High‐Speed Validation of Supplemental Lead‐Extrusion Energy Dissipation Devices

Recent research on supplemental damping enabling low to no damage structures has led to new devices, such as lead‐extrusion‐based high force‐to‐volume (HF2V) devices. They provide significant energy dissipation and force capacity in a small volume, enabling a range of novel low to no damage connections and systems. However, despite several research study tests and a limited range of velocity testing, they have never been tested across a realistic velocity range or for robustness to manufacture and design across several devices. These issues are hurdles that limit professional design uptake and add uncertainty and risk to their use in design. To address them, a serious damage‐free dissipation device characterise its force capacity and variability due to manufacture (repeatable quasistatic force) and velocity input (peak force to connections). These outcomes are critical to size all the connections and foundations for the resultant demands and ensure robust, effective design. This manuscript presents the quasistatic testing of 96 devices designed for the same quasistatic force capacity, as well as high‐speed prototype testing at velocities up to 200 mm/sec. Quasistatic tests show device forces vary with standard deviation, σ < 6.2% of design and average force. Peak input velocities of ∼200 mm/s produced peak resistive forces of ∼350 kN and increasingly weak velocity dependence as device input velocity increased, which is an advantage as it limits large demand forces to connecting elements and surrounding structure if larger than expected response velocities occur. Overall, the devices show stable hysteretic performance, with slight force reduction during high‐speed testing due to heat build‐up and softening of the lead working material. This testing quantified important HF2V device dynamics and robustness for designers and is an important step towards design uptake.

Crustal Deformation on the Northeastern Margin of the Tibetan Plateau from Continuous GPS Observations

We installed 10 continuous Global Positioning System (GPS) stations on the northeast margin of the Tibetan Plateau at the end of 2012, in order to qualitatively investigate strain accumulation across the Liupanshan Fault (LPSF). We integrated our newly built stations with 48 other existing GPS stations to provide new insights into three-dimensional tectonic deformation. We employed white plus flicker noise model as a statistical model to obtain realistic velocities and corresponding uncertainties in the ITRF2014 and Ordos-fixed reference frame. The total velocity decrease from northwest to southeast in the Longxi Block (LXB) was 5.3 mm/yr within the range of 200 km west of the LPSF on the horizontal component. The first-order characteristic of the vertical crustal deformation was uplift for the northeastern margin of the Tibetan Plateau. The uplift rates in the LXB and the Ordos Block (ORB) were 1.0 and 2.0 mm/yr, respectively. We adopted an improved spherical wavelet algorithm to invert for multiscale strain rates and rotation rates. Multiscale strain rates showed a complex crustal deformation pattern. A significant clockwise rotation of about 30 nradians/yr (10−9 radians/year) was identified around the Dingxi. Localized strain accumulation was determined around the intersectional region between the Haiyuan Fault (HYF) and the LPSF. The deformation pattern across the LFPS was similar to that of the Longmengshan Fault (LMSF) before the 2008 Wenchuan MS 8.0 earthquake. Furthermore, according to the distributed second invariant of strain rates at different spatial scale, strain partitioning has already spatially localized along the Xiaokou–Liupanshan–Longxian–Baoji fault belt (XLLBF). The tectonic deformation and localized strain buildup together with seismicity imply a high probability for a potential earthquake in this zone.

Making the usage of guidance systems in pedestrian infrastructures measurable using the virtual environment DAVE

This paper presents the development and partial validation of a cave automatic virtual environment (CAVE), which is designed to make the reactions of pedestrians to guidance information (even such that are not technically feasible with current technology) in pedestrian infrastructures (such as airports, train stations or subway stations) measurable. The navigation is designed to be intuitive and easy to learn. It uses the Microsoft Kinect to obtain information on the user’s movement. The user walks in place to move forward in the virtual world and turns her shoulders to invoke rotations in the virtual world to make turns. The virtual world includes simulated pedestrians to enhance the immersion and is equipped with a number of sensors that allow for a multi-method measuring of users. After the implementation of hands free steering two case studies are used to provide first evidence with respect to the possible answers that the research infrastructure is capable of delivering. The validity of the model for steering has been explored using a case study involving parallel test groups that expose individuals to wayfinding exercises in both the real world and the corresponding virtual world. Our results show that the objective distances and times in the real and the virtual worlds, as well as perceptions of distances, times and directions, do not differ statistically significantly. This provides a partial validation of the model for steering. In a second larger case study the hypothesis was tested that using the virtual environment test persons are able to find their way also in complex multi-level infrastructures with only limited learning requirements. Additionally, we tested the hypothesis that also in this setting realistic paths (including elevator and escalator usage) are taken by the test persons while observing realistic average velocities over longer trips. We find that our hypotheses have not been rejected by the data. Therefore, this environment is a useful tool for the design of guiding systems for large pedestrian infrastructures.

Effects of random 3D upper crustal heterogeneity on long-period (\u2265\u20091\xa0s) ground-motion simulations

The effects of the short-wavelength heterogeneity of the crustal structure on predicted ground motion at periods of 1 s and longer were investigated by conducting three-dimensional finite-difference simulations using a detailed realistic velocity model of the Kanto region of Japan. The short-wavelength heterogeneity of the media within the upper crust was randomly modeled using the exponential-type autocorrelation function where the velocity standard deviation was set to 5%. Combinations of heterogeneous media with various correlation lengths and point source models with various depths and durations were considered in order to investigate the variability of the predicted ground motion and the sensitivity to the parameters. The effects of random heterogeneity on the simulated ground motion appeared as a result of changes in the amplitude and phase of both the direct waves and later phases, as well as the spectral peaks of the response spectra. Ground-motion variability, in terms of peak ground velocity (PGV) and velocity response spectra (Sv), was evaluated using the residual, or the difference in logarithm of PGV and Sv between the ground motion computed with and without random heterogeneity. While the residual averaged over the surface of the computed area was almost negligible in the studied period range, the variability of the residual was found to increase with distance and to be larger for point sources with shorter durations.

Effects of Spatiotemporal Filtering on the Periodic Signals and Noise in the GPS Position Time Series of the Crustal Movement Observation Network of China

Analysis of Global Positioning System (GPS) position time series and its common mode components (CMC) is very important for the investigation of GPS technique error, the evaluation of environmental loading effects, and the estimation of a realistic and unbiased GPS velocity field for geodynamic applications. In this paper, we homogeneously processed the daily observations of 231 Crustal Movement Observation Network of China (CMONOC) Continuous GPS stations to obtain their position time series. Then, we filtered out the CMC and evaluated its effects on the periodic signals and noise for the CMONOC time series. Results show that, with CMC filtering, peaks in the stacked power spectra can be reduced at draconitic harmonics up to the 14th, supporting the point that the draconitic signal is spatially correlated. With the colored noise suppressed by CMC filtering, the velocity uncertainty estimates for both of the two subnetworks, CMONOC-I (≈16.5 years) and CMONOC-II (≈4.6 years), are reduced significantly. However, the CMONOC-II stations obtain greater reduction ratios in velocity uncertainty estimates with average values of 33%, 38%, and 54% for the north, east, and up components. These results indicate that CMC filtering can suppress the colored noise amplitudes and improve the precision of velocity estimates. Therefore, a unified, realistic, and three-dimensional CMONOC GPS velocity field estimated with the consideration of colored noise is given. Furthermore, contributions of environmental loading to the vertical CMC are also investigated and discussed. We find that the vertical CMC are reduced at 224 of the 231 CMONOC stations and 170 of them are with a root mean square (RMS) reduction ratio of CMC larger than 10%, confirming that environmental loading is one of the sources of CMC for the CMONOC height time series.

Automatic approach for increasing the location accuracy of slow-moving landslide endogenous seismicity: the APOLoc method

Seismological observations offer valuable insights on the stress-strain states, the physical mechanisms and the possible precursory signs of activation of various Earth surface processes (i.e. volcanoes, glaciers and landslides). Comprehensive catalogues of the endogenous landslide seismicity, that is corresponding to seismic sources generated by the unstable slope from either mechanical or hydrological origins, should include the typology and an estimate of the source parameters (location, magnitude) of the event. These advanced catalogues constitute a strong basis to better describe the slope deformation and its time evolution and better understand the controlling factors. Because the number of seismic events in landslide catalogues is generally large, automatic approaches must be considered for defining both the typology and the location of the sources. We propose here a new location approach called Automatic Picking Optimization and Location method-APOLoc for locating landslide endogenous seismic sources from seismological arrays located at close distance. The approach is based on the automatic picking of the P waves arrivals by optimizing the intertrace correlations. The method is tested on calibration shots realized at the Super-Sauze landslide (Southeast French Alps) and compared to other location approaches. By using a realistic velocity model obtained from a seismic tomography campaign, APOLoc reduces the epicentre errors to 23 m (on average) compared to ca. 40 m for the other approaches. APOLoc is then applied for documenting the endogenous seismicity (i.e. slopequakes and rockfalls) at the landslide.

Theoretical analysis of pollutant mixing zone considering lateral distribution of flow velocity and diffusion coefficient.

Theoretical formulae have shown significant advantages in describing the characteristic geometric scales of the pollutant mixing zone (PMZ) formed by offshore pollutant discharged by a single general form. They, however, fail to predict the influence of the lateral inhomogeneity of the river flow because constant flow velocity and the lateral diffusion coefficient are assumed during the derivation. The realistic flow velocity in a river is fitted by an exponential law in this study and the lateral diffusion coefficient is proposed to have the same form. Similar idea has been used in previous studies on the vertical dispersion of scalar in the lower atmosphere. Pollutant discharged from a steady onshore point source into a wide straight open channel is examined to characterize the concentration taking into consideration of these lateral variations. Theoretical formulae describing the maximum length, maximum width and its corresponding longitudinal position, as well as the area of the PMZ are derived. A non-dimensional standard curve equation for the isoconcentration boundary of PMZ is also obtained. The results show that the shape of the dimensionless standard curve of PMZ depends only on the exponential constants in the exponential laws. The exponential profiles that fit the near-shore velocity give good prediction, while the ones that match the entire lateral range up to the center of the river underpredict the PMZ significantly. These findings are of great importance for practitioners to characterize the geometry of the PMZ in rivers and for water quality modeling.

Up- and downgoing borehole wavefield retrieval using single component borehole and reflection data

A standard procedure in processing vertical seismic profile (VSP) data is the separation of up- and downgoing wavefields. We show that these wavefields in boreholes can be retrieved using only single-component data, given that a full set of surface reflection data is also available. No medium parameters are required. The method is an application of the Marchenko method and uses a focusing wavefield. It is a wavefield that satisfies certain focusing conditions in a reference medium. We show that the method is applicable to boreholes with any orientation, and no receiver array is required. By this work, we present two contributions. One is that we investigate the effect of using only the traveltime from borehole data to form the focusing wavefield. The second is that we validates standard separation methods (PZ summation and f-k filtering) by retrieving the one-way wavefields from a completely different approach. We use the numerically modelled data from a realistic field velocity model in the North Sea. Three borehole geometries (horizontal, deviated and vertical) are tested. We discuss the practical aspects for field application in the end.

Experimental and numerical investigation of turbulent jets issuing through a realistic pipeline geometry: Asymmetry effects for air, helium, and hydrogen

Experiments and numerical simulations were conducted to investigate the dispersion of turbulent jets issuing from realistic pipe geometries. The effect of jet densities and Reynolds numbers on vertical buoyant jets were investigated, as they emerged from the side wall of a circular pipe, through a round orifice. Particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) techniques were employed simultaneously to provide time-averaged flow velocity and concentrations fields. Large eddy simulation (LES) was applied to provide further detail with regards to the three-dimensionality of air, helium, and hydrogen jets. These jets were always asymmetric and found to deflect about the vertical axis. The deflection was influenced by buoyancy, where heavier gases deflected more than lighter gases. Significant turbulent mixing was also observed in the near field. The jets from realistic pipe geometries experienced faster velocity decay and asymmetric jet spreading compared to round jets. These findings indicate that conventional round jet assumptions are, to some extent, inadequate to predict gas concentration, entrainment rates and, consequently, the extent of the flammability envelope of realistic gas leaks.