Large-scale Modeling Studies Research Articles

An efficient parallel-computing method for modeling nonisothermal multiphase flow and multicomponent transport in porous and fractured media

This paper presents an efficient massively parallel scheme for modeling large-scale multiphase flow, multicomponent transport and heat transfer in porous and fractured reservoirs. The new scheme is implemented into a parallel version of the TOUGH2 code and the numerical performance is tested on a Cray T3E-900 (a distributed-memory parallel computer with 692 processors) and IBM RS/6000 SP (a distributed-memory parallel computer with 3328 processors). The efficiency and robustness of the parallel-computing algorithm are demonstrated by completing three over-million-cell simulations using site-specific data for site characterization. The first application is the development of a three-dimensional unsaturated zone numerical model simulating flow of moisture in the unsaturated zone of Yucca Mountain, Nevada; the second problem is the modeling of flow of moisture, gas, and heat at the same site. The third application is the study of flow-focusing phenomena through fractures for the same site. Simulation results show that the parallel-computing technique enhances modeling capability by several orders of magnitude in speedup of computing times for large-scale modeling studies.

Pairing Correlations in Nuclear Systems, from Neutron Stars to Finite Nuclei

In this contribution we attempt at giving an overview of pairing correlations in nuclear systems with an emphasis on Superfluidity and superconductivity in neutron stars and the relation to the underlying nucleon-nucleon interaction. Extraction and interpretations of pairing correlations in finite nuclei through large-scale shell model studies of nuclei with mass A ∼ 100 - 132. Effective interactions based on recent nucleon-nucleon interactions are utilized in the shell-model studies. The partial waves which lead to superfluid properties in infinite matter are also crucial for pairing correlations in finite nuclei. Discussion of recent experimental and theoretical studies of thermodynamical properties of finite nuclei and their interpretation in terms of eventual pairing transitions in finite nuclei.

Characterization of flow and transport processes within the unsaturated zone of Yucca Mountain, Nevada, under current and future climates

This paper presents a large-scale modeling study characterizing fluid flow and tracer transport in the unsaturated zone of Yucca Mountain, Nevada, a potential repository site for storing high-level radioactive waste. The study has been conducted using a three-dimensional numerical model, which incorporates a wide variety of field data and takes into account the coupled processes of flow and transport in the highly heterogeneous, unsaturated fractured porous rock. The modeling approach is based on a dual-continuum formulation of coupled multiphase fluid and tracer transport through fractured porous rock. Various scenarios of current and future climate conditions and their effects on the unsaturated zone are evaluated to aid in the assessment of the proposed repository's system performance using different conceptual models. These models are calibrated against field-measured data. Model-predicted flow and transport processes under current and future climates are discussed.

Minimum Submergence before Double-Entrance Pressure Intakes

This paper describes a large-scale physical model study concerning the minimum submergence required for double-entrance pressure intakes, such as used for power tunnel intakes. Use of minimum submergence can avert the occurrence of subatmospheric pressure and air-entraining vortices, and avoid reducing the efficiency of the turbine and its vibration of the turbine, etc. The scale of the double-entrance intake model, 1:30, which is primarily designed for the Three Gorges project, is almost the largest in the world. Based on analysis of the experimental data, an empirical formula is obtained and then it is compared with Gordon's formula, which is used mainly to calculate the minimum submergence before single-entrance intakes. The empirical formula is useful in the design of double-entrance pressure intakes.

The effects of Pleistocene glaciations on the geohydrological system of Northwest Europe

A large-scale hydrological model study is carried out to investigate the geohydrological responses to glacial climate conditions in Northwest Europe. The vertically integrated groundwater model is based on a supraregional hydrogeological model of the Cenozoic and Mesozoic subsurface in Northwest Europe. Three different layers are distinguished above the relatively impervious base of Palaeozoic and Precambrian rocks. Boundary conditions are inferred from indicative palaeoenvironmental reconstructions of the last three glacial cycles to simulate groundwater flow related to ice sheet expansions into the. Northwest European lowlands. Recharge of the groundwater system due to basal glacial melting is deduced from ice sheet model simulations driven by a transient climate function. Results of the large-scale model study show relatively high groundwater velocities and pressures in the subglacial areas and the ice-marginal permafrost areas. Extreme high velocities may develop when the ice sheet has advanced to the southern margins of the upper Plio/Pleistocene aquifer in Northwest Europe. Drainage of the highly pressurized groundwater system mainly occurs in proglacial ice-dammed lakes, ice-marginal seas and zones of discontinuous permafrost, including river valleys.

Deforming beds: Viscous and plastic scales of deformation

Small scale field and laboratory observations of sub-glacial sediment deformation suggest that failure is the predominant method of sediment deformation, while large scale modelling studies using a viscous model of till deformation have been reasonably successful in predicting the geological consequences of ice sheet action. This suggests that the cross-over scale between viscous and plastic deformation occurs at a much larger scale than the grain-grain interaction scale previously thought to be appropriate to deforming till. Sediment deformation and the drainage of sub-glacial areas are considered at different scales, and how these interact to produce failure and viscous behaviour is discussed. A fluctuation length scale is proposed, whose horizontal dimensions are of the order of the depth of the base of deformation (1–10 m). On this length scale, the glacier/deforming bed system is highly variable in time as well as in space. Till deformation occurring at this length scale is plastic, happening though failure events. Three other specific scales are proposed, whose different properties depend on the relative spatial variability of static and seepage pressures and topography. The key theoretical problem which has yet to be solved is how multiple small scale failure events combine into a viscous type flow. This is discussed in the context of self-organised criticality. It is argued that the length scales appropriate for some drainage features are not appreciably larger than the scale for plastic failure events, implying that modelling sub-glacial drainage channels by balancing erosion rates against viscous closure of the channel is misconceived. The outlines of an alternative model involving percolation theory are presented. Certain key questions which can only be settled through observations by glaciologists and glacial geologists are discussed. It is suggested that the difference between lodgement tills and deformation tills reflects the rate of motion of till by deformation, and that lodgement from the ice is unimportant.

Dynamics of the Gulf Stream/Deep Western Boundary Current Crossover. Part I: Entrainment and Recirculation

A regional primitive equation model is applied to the study of the interaction between the Gulf Stream and the deep western boundary current (DWBC) where they cross at Cape Hatteras. It is found that for a wide range of forcing parameters the upper core of the DWBC is split into two mean paths at the crossover, one flowing toward the south along the western boundary and the other flowing toward the cast under the Gulf Stream. The eastward branch is entrained Into the southern recirculation gyre and, after being diverted into the interior for up to 1500 km, eventually returns to the western boundary current and continues to flow southward. This recirculation and mixing is shown to have a significant impact on the separation point and mean path of the Gulf Stream, the basin-scale stratification, and the properties of the DWBC south of the crossover. For most configurations, the lower DWBC remains largely on the western boundary and interacts only weakly with the interior. The entrainment of the upper core is shown to be driven by a baroclinic, time-dependent process of DWBC water eddy formations into the recirculation gyres under the Gulf Stream. Potential vorticity considerations are key to understanding the entrainment mechanism and its sensitivity to variations in the model forcing and configuration. A scaling estimate of the amount of entrained DWBC water as a function of the eddy field is derived. The mean paths of the upper and lower DWBCs and strength of the eddy fluxes compare well with various observational estimates. The importance of such entrainment and mixing processes on large-scale ocean modeling and climate studies is discussed.

The effect of the surfaces enclosing atria on the daylight in adjacent spaces

The reflective characteristics of the surfaces enclosing an atrium space can significantly influence the distribution of daylight in adjacent spaces. Large scale model studies were used to evaluate the effects of floor reflectance and the proportion of opening in the atrium walls during overcast sky conditions. Measurements show that the daylight potential in the middle and lower floors can be enhanced by gradually increasing the proportion of opening to reflective surface of the atrium walls from relatively small openings at the top to fully glazed openings at the ground. Further, the floor reflectivity can dramatically influence the daylighting in the lower floors.

Large-scale model studies of a rockbolted tunnel

Large-scale model studies of a rockbolted tunnel

Pipeline Lateral Stability in Soft Clay

Summary This paper concerns the lateral stability of submerged pipelines in soft clay. The material presented in this pipelines in soft clay. The material presented in this paper is derived from a laboratory and field investigation paper is derived from a laboratory and field investigation using model pipelines. A relationship is presented between the depth/diameter ratio of the pipeline and the maximum resistance developed against lateral movement in the soil. Conclusions are drawn with respect to the effect of the diameter of the pipe, pipe weight, and the rate of displacement on the soil resistance. Introduction The problem of determining the stability of pipelines in soil classically has been investigated with a view toward determining vertical movements. In addition, however, lateral stability of pipelines has become a concern in areas suspected to be susceptible to subaqueous slope failures. Definitive experimental studies have been conducted concerning lateral stability of pipelines in sand, but few such data have been collected for clays. Of that work published for soft clays, little attention has been paid to the effect of embedment depths greater than one paid to the effect of embedment depths greater than one pipe diameter. pipe diameter. Lyons conducted small- and large-scale model studies in sand and clays. Tests conducted with clays were typically at depths of pipeline embedment of less than one diameter. Lyons observed that lateral resistance in clays increased with increasing pipe submerged weight. Karal approached the problem using the upper bound approach of the theory of plasticity. Lyons study was modeled using parametric solutions. Karal's theoretical solution compared favorably with Lyons measurements.The study reported in this paper concerns itself with the effect of the following variables on the resistance developed during lateral displacements of a pipe:(1)pipe weight,(2)pipe diameter,(3)embedment depth, pipe weight,(2)pipe diameter,(3)embedment depth,(4)loading rate. and(5)soil type. Experimental studies were conducted in the field in a montmorillonitic clay in Harris County, TX, near Galveston Bay, and the work was extended in the laboratory with kaolin clay. The thrust of this work was to provide relationships between lateral resistance and the factors just listed. Theoretical Considerations The problem of lateral resistance due to pipe movement is in principle similar to that of the bearing capacity of a foundation. However, because of the geometry of the pipe/soil interface and the position of the free boundary, it is somewhat more complex. The classical theory of plasticity has been adapted by other investigators to solve problems of this nature in soil mechanics, both onshore and offshore. The limit analysis technique was used, along with the concept of perfect plasticity, to model the behavior of the soil perfect plasticity, to model the behavior of the soil for this study.The least upper bound solution for load-carrying capacity of a strip footing expresses the bearing capacity as a function of soil shear strength. If consideration is restricted to short-term loading, the least upper bound solution for bearing capacity is (1) where c is the undrained cohesion, bf is the footing width, and P is the resistance to displacement per foot of length.If the soil is assumed to be weightless and incompressible and the effects of pipe curvature and geometric nonlinearities are neglected, the failure mechanism assumed in the development of Eq. 1 can be applied to the lateral capacity of a pipe moving horizontally in an open trench, as shown in Fig. 1. Thus, P ideally should be maximized as a function of embedment D at D/d=2 and with P max = 5.14cd. JPT P. 217

Large scale model studies of vertical recording

A large scale magnetic recording model (5000x) has been used to study writing and reading using a film ring head on a medium which can be configured in either a horizontal or vertical recording mode. Field measurements from the written transitions indicate that a narrower transition is written on the vertical medium configuration than on the horizontal.

Studies of Annular Gas Flow Following Primary Cementing

Abstract Annular gas flow has been a problem in the Alberta oilfields for several years. Much of the evidence for annular flow can be found in abandoned wells in southeastern Alberta and various producing wells in the Slave Lake area. This paper will review in 'some detail specific examples of gas flow problems and a cement slurry and cementing technique which has been successful in arresting this problem. Much research has been done in the area of cement slurry phase behaviour and the effects that this phase behaviour has on downhole formations. Results of laboratory testing and field applications will be presented as well as an overview of cement behaviour after cementing. Annular Gas Flow Problems in Alberta The flow of annular gas occurs in many different areas in Alberta because of various conditions. The following are a few problem areas which exhibit this phenonemon and their specific circumstances. Medicine Hat Area-Southeast Alberta Several formations in this area have gas leakage problems after cementing and require attention. The Second White Gas flow problems have occurred in the Milk River and Medicine Hat formations of southeast Alberta for years. The most critical problems have occurred after setting open-hole abandonment pings in shallow gas wells. These plugs cover most of the Milk River Formation and extend into the surface casing. Gas leakage is noticed in many cases after cementing. If the gas leakage is severe enough, then remedial action is required, such as drilling out and resetting the abandonment plug over the Milk River Zone. Problems have also occurred where gas is leaking between production and surface casing after production casing is set. This requires several expensive remedial steps, such as perforating and squeezing, and extensive service rig time. Lloydminster Area-Northwest Alberta Several formations in this area have gas leakage problems after cementing and require attention. The Second White Specks Formation near the Lloydminster area is the most critical. Other formations of concern are the Colony and Wabiskaw around Lac La Biche. Both of these areas experience gas leakage after cementing and must be dealt with at great expense to the operator. Grande Prairie-Northwestern Alberta This area has also experienced gas migration and channeling after cementing. Some of the problem areas occur in the Mussreau and Kakwa area. Annular Gas- The Unwanted Product Annular gas migration can occur in wells where the gas escapes at the surface and can be monitored. It can also occur underground by migration from a gas zone to another zone of lower pressure. Both systems are wasteful, dangerous and costly to repair. The problem of annular gas is not new. For many years, operators accepted the fact by completing wells and then performing remedial cement squeezes prior to producing. During the 1960s, extensive laboratory and field research was begun in an attempt to control the complex problem. Large-scale laboratory model studies evaluate several different drilling fluids, spacers, flushes and cement slurries with density, viscosity, flow characteristics, fluid loss and pipe configurations as the main parameters.

LARGE SCALE MODEL TESTS OF PLACED STONE BREAKWATERS

Large scale model studies reveal that Reynolds scaling can affect the apparent stability and wave modifying properties of layered breakwater structures. Results of a study for a breakwater configuration designed to protect offshore power and port facilities in water depths to 60 feet are presented and discussed. The armor layer of this structure is formed from quarried rock of irregular rectangular parallelepiped shape, individually placed perpendicular to 1:2 seaward slope and crest. The resulting armor layer is relatively smooth, densely packed and very stable. Model studies of similar configurations were studied at 1:10, 1:20 and 1:100 scale ratios. Stability, runup, rundown and reflection were measured for a variety of water depths, wave heights and periods. Analysis of the large scale test results establish that the placed stone armor is approximately as stable as dolos armor units. Runup, rundown and reflection respond similar to rough, impermeable slopes. Comparison of large and small scale results demonstrate that relative increases in drag forces at lower Reynolds numbers decrease stability and runup in small scale models.

Transitions for Canals and Culverts

Results of large-scale model studies of variations in open-type and closed-conduit-type inlet and outlet transitions for small canals and culverts are presented. Losses for open transitions are 0.6 to 0.7 Δhv for outlet service, and 0.4 Δhv for inlet service. Reasonable changes in slope of the inverts, slope of the pipelines, or changes in divergence of the sidewalls have little effect on losses or scour. Losses for outlet service decrease to 0.4 Δhv when short closed-conduit transitions are added between the pipeline and the open transition. Outlet losses are reduced to 0.1 Δhv by using Six D-long closed-conduit transitions that discharge directly into the canal through vertical headwalls placed normal to the canal axis. Inlet losses remain at 0.4 Δhv. Scour in earth canals is less with the closed-conduit transitions than with conventional open ones.

Laboratory Research on Interceptor Drains

Results of large scale model study on design of interceptor drains; previously developed analytical relationships for determining shape of resultant water table drawdown curve are analyzed; new relationships are developed for estimating flow from drains; examples given.

Laboratory Research on Interceptor Drains

Results of large scale model study on design of interceptor drains; previously developed analytical relationships for determining shape of resultant water table drawdown curve are analyzed; new relationships are developed for estimating flow from drains; examples given.