Simulated Travel Time Research Articles

Field experience and evaluation of the South Pars sea line pigging, based on dynamic simulations

Multi-phase flow is experienced in many instances of the oil and gas industry. There is multi-phase flow in the sea lines, transferring the production from the South Pars offshore platforms to the receiving onshore facilities. By pigging at frequent intervals, liquid inventory buildup in a sea pipeline and the maximum slug size can be reduced. Uncontrolled speed of a pig can cause to large liquid slugging formation and bursting of pipeline due to pig stuck. In June 2008 the slug catcher levels increased unexpectedly to 100–105%. The main objective of this study is composed of calculation for liquid holdup, pig velocity, amount of slug during pigging operation and the influence of the production flow rate during the pigging of South Pars sea lines that is located in south of Iran. Besides the slug catcher liquid level, some parameters such as liquid bottle level were measured during pigging time process. The comparison between the actual and simulated sea line glycol holdup, travel time for the pig, sea line inlet pressure and the liquid slug volume has been done in this work. The difference between the actual and simulated travel time for the pig was 0.7 and 1.3 h for 600 and 300 million standard cubic feet per day (MMSCFD) of the gas flow rate. The absolute average relative errors of condensate and water slug volume are 5.6% and 9.1% respectively, which are very satisfactory. The results showed that the optimum gas flow should be around 500 MMSCFD to handle the slug volume and running the pigs is most effective at a near constant speed.

Upper and Middle Tiete River Basin dam-hydraulic system, travel time and temperature modeling

Summary Tiete River System in the State of Sao Paolo, Brazil is characterized by complex hydraulics and operational problems due to series of dams and point and diffuse inflows along the river. A one dimension Lagrangian river model was developed and applied to the 313 km reach of the Upper and Middle Tiete River Basin from the Penha Dam to the head water of Bara Bonita Reservoir, a stretch of river that includes six small to medium size dams (3.4–22 m high) including the Pirapora Reservoir and 26 inflows into the river (11 tributaries, 9 diffuse source areas, and discharges of 4 cities stormwater and 2 wastewater treatment plants. The conservative tracer transport and temperature model that accounts for the short and long wave radiation and heat transfers at the free surface was included and solved using the Crank–Nicholson scheme. The time variable catchment input to the model was the simulated output of the external hydrological model called Runoff Load Model which results were provided by CETESB. The numerical treatment of series of dams and spillway (that included uncontrolled overflow spillway, gate-controlled ogee spillway; and underflow gates and tunnels) and parameterisation of hydraulic jumps are described. Special attention was focused on the high spatial and temporal variation of flows in Tiete River Basin, a result of the large variation in catchment inflows and channel geometry due to dams and reservoirs along the river. Predicted and measured spatial and seasonal variation of flow and temperature profiles along the river show good agreement. The simulated travel time of conservative tracer is compared against the CETESB’s 1982 and 1984 field study data in a 254 km reach of the Middle Tiete River that again shows good agreement. Being Lagrangian in construction, this new model is computationally efficient making it an ideal tool for long term simulation for water resource planning, management and operation decision making in a large and complex river basin system.

Earthquake Generated Tsunami in the Indian Ocean and Probable Vulnerability Assessment for the East Coast of India

The tsunami hazard for the east coast of India is assessed. The Sumatra-Andaman 1300 km long fault is divided into five segments, each segment assumed to have different fault parameters. The initial vertical displacement of the sea bottom is calculated with the Mansinha and Smylie algorithm. Modeling of tsunami amplitude, travel time, run-up and directivity has been done. We compared simulated tsunami travel times and elevation with data measured at tide gauges and coastal runup. The model results show that the distribution of maximum amplitude in the Indian Ocean basin is primarily controlled by the classical effects of the directivity and by refraction and focusing along bathymetric features. The results suggest 7–8 m run up height at Nagapatanam, Tamil Nadu, which was the worst affected region in the mainland of India during the 2004 Indian Ocean tsunami.

Using a Bayesian Network to Summarize Variability in Numerical Long-Term Simulations of a Meteorological–Marine System: Drift Climatology of Assumed Oil Spills in the North Sea

Climate-related scientific analyses of meteorological–marine systems are often based on numerical long-term simulations at high spatial and temporal detail. Such comprehensive data sets require much resources and specific evaluation tools, which sometimes hampers their use within interdisciplinary projects. In the present study, we propose the use of a Bayesian network to represent simulated transports in the North Sea depending on variable external forcing in terms of conditional probabilities. Eliciting probability tables from multi-decadal numerical simulations ensures that all realistic weather and resulting sea state conditions are covered in agreement with the frequency of their occurrence. The probabilistic representation conveniently allows for conditioning numerical simulations on either external forcing (weather conditions) or observed transports. In the latter case, the Bayesian inversion formula becomes involved to transfer information in a direction opposite to causal dependencies encoded in the underlying mechanistic model. We show that simulated travel time distributions even allow for taking into account a substance’s specific half-life, although this was not an issue in the original passive tracer simulations.

Cellular Automata Model for Work Zone Traffic

This paper proposes a cellular automata (CA) model incorporating work zone configuration to model work zone traffic. The randomization probability parameter of the proposed CA model is able to characterize driver acceleration–deceleration behavior. The randomization probability should be a function of traffic flow and work zone configuration that comprises the activity length and transition length; however, past studies have assigned a hypothetical constant value for the randomization probability. This paper calibrates the randomization probability from field data, which is determined by minimizing the square error between simulated travel time and observed travel time by using a trial-and-error method. A polynomial regression method is employed to formulate the randomization probability functions in and outside the work zone. A case study was performed to test the proposed CA model dependent on work zone configuration. Comparison of field data and the proposed CA model for travel time and traffic delay shows very close agreement. Statistical comparison of the simulated results from the proposed CA model and PARAMICS indicates that the proposed CA model performs well in modeling work zone traffic.

Stochastic simulations of regional scale advective transport in fractured rock masses using block upscaled hydro-mechanical rock property data

A method for upscaling coupled hydro-mechanical properties in fractured rock from the small (metre) scale to the large (decametre to kilometre) scale has been developed and applied within a stochastic modelling framework. The method was implemented to assess the impact on estimates of advective travel times and transport pathways in the geosphere arising from uncertainties in the mechanical properties of a fractured host rock. A 2D hypothetical geological environment for a deep nuclear waste repository, characterized using rock and fracture property data from the site investigations at Sellafield, UK, was used for the assessment. Hydro-mechanical modelling was undertaken to obtain block scale equivalent hydraulic properties for discrete fracture networks described by power-law statistics for fracture length and density. Values of the mechanical properties for the host rock were employed to derive a basic statistical model of the uncertainty in the key fracture property values: joint compressive strength ( JCS ) and joint roughness coefficient ( JRC ). The block upscaling was carried out in two stages. First, mechanical modelling was undertaken to determine aperture distributions throughout each modelled fracture network using the distinct element code UDEC. The Barton–Bandis model for fracture closure was adopted in UDEC and each fracture network was modelled under a range of stress conditions with five ( JCS , JRC ) pairs that reflected the spread of mechanical properties observed in the actual field data. Second, mean block scale hydraulic conductivity tensors were determined for each stress and mechanical property combination by inverting the results from steady state hydraulic models for the mechanically controlled fracture networks. Finally, a Monte-Carlo simulation experiment was performed on a 2D profile model of the geosphere populated by sampling from the block upscaled hydraulic results. Particle tracking was applied to each realisation of the flow field in the geosphere to study the range of advective travel times from the repository to the seabed (biosphere). The simulated travel times were found to depend significantly on the rock and fracture mechanical properties with breakthrough times at the seabed ranging between 4000 years and 2,560,000 years. The spread of travel times in the simulation results demonstrate the significance of both hydro-mechanical rock properties and their spatial distribution. The very low joint compressive strength ( JCS ) of the uppermost formation and the assumed lateral uniformly distributed mechanical and hydraulic parameters of this formation are observed to provide the dominant control on the particle travel times. The present study suggests that observations of hydro-mechanical property data and their spatial distribution can offer useful additional information for developing models of the regional scale hydraulic behaviour of a fractured host rock mass.

Forward modelling of sub-photospheric flows for time-distance helioseismology

Results of forward modelling of acoustic wave propagation in a realistic solar sub-photosphere with two cases of steady horizontal flows are presented and analysed by the means of local helioseismology. The simulations are based on fully compressible ideal hydrodynamical modelling in a Cartesian grid. The initial model is characterised by solar density and pressure stratifications taken from the standard Model S and is adjusted in order to suppress convective instability. Acoustic waves are excited by a non-harmonic source located below the depth corresponding to the visible surface of the Sun. Numerical experiments with coherent horizontal flows of linear and Gaussian dependences of flow speed on depth are carried out. These flow fields may mimic horizontal motions of plasma surrounding a sunspot, differential rotation or meridional circulation. An inversion of the velocity profiles from the simulated travel time differences is carried out. The inversion is based on the ray approximation. The results of inversion are then compared with the original velocity profiles. The influence of steady flow on the propagation of sound waves through the solar interior is analysed. Further, we propose a method of obtaining the travel-time differences for the waves propagating in sub-photospheric solar regions with horizontal flows. The method employs directly the difference between travel-time diagrams of waves propagating with and against the background flow. The analysis shows that the flow speed profiles obtained from inversion based on the ray approximation differ from the original ones. The difference between them is caused by the fact that the wave packets propagate along the ray bundle, which has a finite extent, and thus reach deeper regions of the sub-photosphere in comparison with ray theory.

Approach to Time Dependence and Reliability in Dynamic Route Guidance

This paper presents a methodology for increasing the reliability of route suggestions in route guidance systems. The procedure, based on the A* path-finding algorithm and Chen's link penalty method, involves penalizing links with a high risk of being congested and obtaining a set of reliable route suggestions. Time dependence of travel times is considered by adapting the flow–speed model technique accordingly. The structure of the path-finding algorithms is also modified to account for real road network features. Finally, experiments using simulated travel time and reliability data are carried out on a road network, and the results are discussed.

An Analytical Model for Traffic Delays and the Dynamic User Equilibrium Problem

In urban transportation planning, it has become critical (1) to determine the travel time of a traveler and how it is affected by congestion, and (2) to understand how traffic distributes in a transportation network. In the first part of this paper, we derive an analytical function of travel time, based on the theory of kinematic waves. This travel-time function integrates the traffic dynamics as well as the effects of shocks. Numerical examples demonstrate the quality of the analytical function, in comparison with simulated travel times. In the second part of this paper, we incorporate the travel-time model within a dynamic user equilibrium (DUE) setting. We prove that the travel-time function is continuous and strictly monotone if the flow varies smoothly. We illustrate how the model applies to solve a large network assignment problem through a numerical example.

Basic Investigations of Dynamic Travel Time Estimation Model for Traffic Signals Control Using Information from Optical Beacons

In this paper put forward are neuron-type models, i.e., neural network model, wavelet neuron model and three layered wavelet neuron model(WV3), for estimating traveling time between signalized intersections in order to facilitate adaptive setting of traffic signal parameters such as green time and offset. Model validation tests using simulated data reveal that compared to other models, WV3 model works very fast in learning process and can produce more accurate estimates of travel time. Also, it is exhibited that up-link information obtainable from optical beacons, i.e., travel time observed during the former cycle time in this case, makes a crucial input variable to the models in that there isn't any substantial difference between the change of estimated and simulated travel time with the change of green time or offset when up-link information is employed as input while there appears big discrepancy between them when not employed.

Stochastic ground water flow simulation with a fracture zone continuum model.

A method is presented for incorporating the hydraulic effects of vertical fracture zones into two-dimensional cell-based continuum models of ground water flow and particle tracking. High hydraulic conductivity features are used in the model to represent fracture zones. For fracture zones that are not coincident with model rows or columns, an adjustment is required for the hydraulic conductivity value entered into the model cells to compensate for the longer flowpath through the model grid. A similar adjustment is also required for simulated travel times through model cells. A travel time error of less than 8% can occur for particles moving through fractures with certain orientations. The fracture zone continuum model uses stochastically generated fracture zone networks and Monte Carlo analysis to quantify uncertainties with simulated advective travel times. An approach is also presented for converting an equivalent continuum model into a fracture zone continuum model by establishing the contribution of matrix block transmissivity to the bulk transmissivity of the aquifer. The methods are used for a case study in west-central Florida to quantify advective travel times from a potential wetland rehydration site to a municipal supply wellfield. Uncertainties in advective travel times are assumed to result from the presence of vertical fracture zones, commonly observed on aerial photographs as photolineaments.

A simulation model of the bus transitway (TRNSIM)

AbstractFor planning and design of a bus rapid transit system and for the analysis of multimodal corridors, methodology is required for simulating bus traffic operation on a Transitway. Macroscopic models of vehicle flow are gaining popularity due to their capability to analyze complex operations and yet offer efficiency in development and applications. A macroscopic model is developed for the investigation of travel time, energy and emissions that correspond to bus volume levels on the Transitway. This paper describes the travel time part of the model. The model treats stochastic characteristics of bus traffic and passenger activities. Also, safety regimes in vehicle flow and factors affecting minimum headways in station areas are incorporated. The model is verified by comparing simulated travel time for the Ottawa‐Carleton Transitway with actual data.

Use of 3H/3He Ages to evaluate and improve groundwater flow models in a complex buried‐valley aquifer

Combined use of the tritium/helium 3 (3H/3He) dating technique and particle‐tracking analysis can improve flow‐model calibration. As shown at two sites in the Great Miami buried‐valley aquifer in southwestern Ohio, the combined use of 3H/3He age dating and particle tracking led to a lower mean absolute error between measured heads and simulated heads than in the original calibrated models and/or between simulated travel times and 3H/3He ages. Apparent groundwater ages were obtained for water samples collected from 44 wells at two locations where previously constructed finite difference models of groundwater flow were available (Mound Plant and Wright‐Patterson Air Force Base (WPAFB)). The two‐layer Mound Plant model covers 11 km2 within the buried‐valley aquifer. The WPAFB model has three layers and covers 262 km2 within the buried‐valley aquifer and adjacent bedrock uplands. Sampled wells were chosen along flow paths determined from potentiometric maps or particle‐tracking analyses. Water samples were collected at various depths within the aquifer. In the Mound Plant area, samples used for comparison of 3H/3He ages with simulated travel times were from wells completed in the uppermost model layer. Simulated travel times agreed well with 3H/3He ages. The mean absolute error (MAE) was 3.5 years. Agreement in ages at WPAFB decreased with increasing depth in the system. The MAEs were 1.63, 17.2, and 255 years for model layers 1, 2, and 3, respectively. Discrepancies between the simulated travel times and 3H/3He ages were assumed to be due to improper conceptualization or incorrect parameterization of the flow models. Selected conceptual and parameter modifications to the models resulted in improved agreement between 3H/3He ages and simulated travel times and between measured and simulated heads and flows.

Moment tensor inversion of local earthquake data-I. Investigation of the method and its numerical stability with model calculations

SUMMARY Two methods for moment tensor inversion of waveform data (Sipkin 1982) are examined for applicability to high-frequency near-source data. This study focuses on two subjects, namely the numerical aspects of the inversion method and the various kinds of assumptions being made from the theory. It is shown that the moment tensor inversion methods are theoretically unstable if only far-field SH seismograms are used due to dependencies and vanishing of different Green's functions. Additional instabilities are found even for the P–SV problem, which are caused by numerical effects. In order to remove these problems the inversion methods are modified by a damped least-squares algorithm, estimating the useful range of damping parameters from singular value analysis. Numerical tests are performed on synthetic near-source data with simulated traveltime errors assuming a wrong source location or misidentification of phases. Bias from extended sources with directivity is investigated. It is concluded that the modified inversion method is robust with respect to such data sets.

A Transfer Function Model of Solute Transport Through Soil: 3. The Convection‐Dispersion Equation

The two‐component convection‐dispersion equation (CDE) model is developed as a special case of the transfer function model (TFM) of solute transport. It is shown that the two‐component CDE model can be reformulated as an integral equation for the “fast” solute component which has the same form and interpretation as the TFM integral equation specialized to (1) steady water flow conditions and (2) solute input or loss restricted to the entrance or exit surface of a soil unit. The travel time probability density function (pdf) for a solute according to the two‐component CDE model then is calculated analytically as a Laplace transform. Numerical inversion of the transformed pdf is carried out for several different sets of values of the four adjustable parameters in the CDE model. The effects of convection, dispersion, and linear sorption processes, as well as the influence of the “slow” solute component, are illustrated by the numerically simulated travel time pdf. It is suggested that the fractional transport volume is the most significant physical parameter in the model in terms of impact on the shape of the travel time pdf.