Local Deformation Rates Research Articles

The long-term failure processes of a large reactivated landslide in the Xiluodu reservoir area based on InSAR technology

After the first impoundment of the reservoir, many landslides seriously threatened the safety of the reservoir. Accurate determination of the relationship between the landslide deformation characteristics and water-level fluctuations is crucial. However, with the increasing number of water-level fluctuation cycles, the deformation characteristics of the landslides were also changing, and long-term continuous monitoring to capture the failure process of reservoir landslides is necessary. A large reacted landslide in the Xiluodu reservoir was set as an example, using InSAR technology to seek its variations of deformation characteristics over nine years. The local deformation rate and annual maximum deformation area variation were analyzed by InSAR technology based on Sentinel-1 descending SAR data from October 2014 to June 2022. According to the regional deformation characteristics, the landslide was divided into three zones: Zone I above the elevation of 950 m; Zone II below it; the front edge of Zone II, where the collapse happened, was further divided into Zone III. In general, the accumulated deformation in Zone I was the largest, followed by Zone III, and Zone II was the smallest. The average deformation rate of Zone II was the smallest. Zone I of NLJL was mainly affected by the drawdown of reservoir water level, and the impacts of water-level rising and drawdown on Zone II and Zone III were similar. After analyzing a nine-year variation of the deformation area, the deformation mechanism of NLJL changed from a retrogressive type to a progressive one after the first impoundment and then changed back to a retrogressive one after 2017. The impact of reservoir impoundment on NLJL was most substantial in the first three years after the first impoundment.

Liquid foam under simple shear: Local flows in the films

Predicting the effective viscosity of a foam as a function of its bubble size, liquid fraction and chemical composition is still an open question. The confinement of the liquid phase between the bubbles is expected to strongly enhance the local deformation rates. However, these local deformations are induced by interfacial stresses, which are limited by the surface tension accessible range: above a critical bubble size and/or shear rate, it is impossible to shear the whole film separating the bubbles. In this paper, we investigate this large bubble regime by imposing a simple shear to a minimal foam made of five interconnected films. We present a new local deformation pattern, with a relaxation process lasting long after the motor stops, that we characterize for a large range of shear rate and for different foaming solutions. A direct evidence of the absence of shear during the relaxation has been obtained for one solution. At 10 s−1, this original large bubble regime should be relevant for foams with bubbles larger than 300 microns.

The Early Identification and Spatio-Temporal Characteristics of Loess Landslides with SENTINEL-1A Datasets: A Case of Dingbian County, China

Loess landslides represent an important geohazard in relation to the deformation of unstable loess structures occurred on the slope of loess-covered area. It has become one of the important topics to accurately identify the distribution and activity of loess landslides and describe the spatio-temporal kinematics in the western-project construction in China. Interferometric synthetic aperture radar (InSAR) proves to be effective for landslides investigation. This study proposes an improved InSAR-based procedure for large-area landslide mapping in loess-hilly areas, including tropospheric-delay correction based on quadtree segmentation and automatic selection of interferograms based on minimum-error boundary. It is tested in Dingbian County in Shaanxi Province, China. More than 200 SAR images were processed and a total of 50 potential loess landslides were detected and mapped. Results show that the landslides are mainly distributed along the river basins and concentrated in areas with elevation ranging from 1450 m to 1650 m, and with slope angles of 10–40°. Then, a total of eight (16%) loess landslides are classified as active ones based on three parameters derived from InSAR-deformation rates: activity index (AI), mean deformation rate, and maximum deformation rate. Moreover, we characterize the segmentation of detected landslides and describe the discrepancy of local topography and deformation rates by coupling the peak in probability-density curves of deformation rates and profiles of the elevation and deformation rates. Finally, correlation between landslide deformation and rainfall is given through wavelet analysis.

From heterogeneous morphogenetic fields to homogeneous regions as a step towards understanding complex tissue dynamics.

Within developing tissues, cell proliferation, cell motility and other cell behaviors vary spatially, and this variability gives a complexity to the morphogenesis. Recently, novel formalisms have been developed to quantify tissue deformation and underlying cellular processes. A major challenge for the study of morphogenesis now is to objectively define tissue sub-regions exhibiting different dynamics. Here, we propose a method to automatically divide a tissue into regions where the local deformation rate is homogeneous. This was achieved by several steps including image segmentation, clustering and region boundary smoothing. We illustrate the use of the pipeline using a large dataset obtained during the metamorphosis of the Drosophila pupal notum. We also adapt it to determine regions in which the time evolution of the local deformation rate is homogeneous. Finally, we generalize its use to find homogeneous regions for cellular processes such as cell division, cell rearrangement, or cell size and shape changes. We also illustrate it on wing blade morphogenesis. This pipeline will contribute substantially to the analysis of complex tissue shaping, and the biochemical and biomechanical regulations driving tissue morphogenesis.

Precisely Defining Local Gradients of Stimuli-Responsive Hydrogels for Complex 2D-to-4D Shape Evolutions.

The intellectualization and complication of existing self-shaping materials are limited by the inseparable monotonic relationship between their deformation rate and deformation degree (i.e., a higher deformation rate is accompanied by a high deformation degree). This causes that they can only deform from 2D to 3D states. Here, a simple yet versatile strategy to decouple the monotonic correlation between the deformation rate and deformation degree of self-shaping hydrogels is presented for achieving complex deformations from 2D to temporary 3D to 3D (2D-to-4D). It is demonstrated that when the gradient hydrogels prepared by photopolymerization possess dense polymer networks, the local regions with a high deformation rate can exhibit a low deformation degree. The resulting hydrogels can thus deform in a novel 2D-to-4D mode under external stimuli. During the deformation, they first transform into the temporary shapes induced by the local deformation rate difference, and then transform into the final shapes determined by the local deformation degree difference. Through controlling the ultraviolet irradiation direction and time to precisely program the local gradients of self-shaping hydrogels, they can be designed to produce various unprecedented yet controllable 2D-to-4D shape evolutions on demand, such as transformable origami, sequential gesture actions in finger-guessing games, mobile octopuses, time switch, etc.

Determination of the instantaneous strain rate during small punch testing of 316 L stainless steel

The Small Punch Test, SPT, has been widely used by scientists for the mechanical characterization of nuclear materials and different applications. This technique is able to provide an approximation of mechanical properties from a very small amount of material. However, the inhomogeneous distributions of local stresses and strains, coupled to the response of the material hinder accurate predictions of the mechanical properties in terms of tensile tests parameters. Additionally, the determination of the instantaneous strain rate, as the test proceeds, remained a pending issue. This article analyses the predictions of SPT on 316 L steels by a FEM model, validated by an additively manufactured 316 L SLM (Selective Laser Melting) stainless steel, in terms of thickness evolution, local deformation and instantaneous strain rate during SPT testing. This alternative analysis shows that the deformation behaviour and, thus, the final form of the sample is affected by the strain hardening behaviour, which it has an influence on the instantaneous local strain rate. The instantaneous local strain rate was calculated for two dissimilar 316 L austenitic stainless steel, one “hardened”, characterized by low ductility but very high yield strength (YS) and ultimate tensile strength UTS, and another “annealed”, characterized by very low YS and large ductility, typical of annealed 316 L steel. The calculated central and minimum thicknesses, strain and instantaneous local strain rate, are not linear as SPT testing proceeds. Therefore, they are fitted to polynomial equations for both annealed and hardened 316 L steels. These functions allow, for instance, LVDT measurement corrections for appropriate SPT curve analysis, and proper true strain rate measurements for creep (SPCT) data analysis.

Multi-Scale Simulation of Well-Entangled Polymer Melt Flows in a Channel

In order to produce better polymeric goods, it is important to predict and to control a flow behavior of a polymeric fluid. To understand a flow behavior of a polymeric fluid, computational approach is quite effective. It is well-known that polymeric fluids exhibit complex flow behaviors owing to a strong correlation between the state of macroscopic flow and the microscopic state of polymer chains. The complex flow behaviors are originated from the stress tensor in the Cauchy momentum equation. When solving the equation, a constitutive equation is usually used to evaluate the stress tensor from the local deformation rate tensor and a set of parameters. By using a constitutive equation, however, it is difficult to reflect the microscopic state to the macroscopic flow. As one of the methods to overcome the difficulty, it has been proposed to use a multi-scale simulation (MSS) method where local microscopic states and the macroscopic flow are directly connecting each other. So far, the MSS method has succeeded in predicting the flow in simpler geometries such as a flow in between two parallel plates and polymer melt flows passing a circular object in a two-dimensional periodic system. To develop further the MSS method that can deal with more industrially oriented problems, it is necessarily to investigate the applicability of the method to a flow in complicated geometry of boundary. In this context, we have applied the multiscale simulation technique to flows of polymer melts in a channel with 4:1:4 contraction and expansion geometry. In the MSS method, we introduced Lagrangian particles which contain many chains to precisely maintain the microscopic states. As the microscopic polymer model, a slip-link model is used. Using the multiscale simulation method, we investigated the macroscopic spatial distribution of microscopic quantities, such as the spatial distribution of polymer chain orientation and the number of entanglements. We found that the number of entanglements strongly decreases around the middle of the polymer chains. This kind of information can be helpful when designing polymer melts with specific properties.

Anisotropic particles strengthen granular pillars under compression.

We probe the effects of particle shape on the global and local behavior of a two-dimensional granular pillar, acting as a proxy for a disordered solid, under uniaxial compression. This geometry allows for direct measurement of global material response, as well as tracking of all individual particle trajectories. In general, drawing connections between local structure and local dynamics can be challenging in amorphous materials due to lower precision of atomic positions, so this study aims to elucidate such connections. We vary local interactions by using three different particle shapes: discrete circular grains (monomers), pairs of grains bonded together (dimers), and groups of three bonded in a triangle (trimers). We find that dimers substantially strengthen the pillar and the degree of this effect is determined by orientational order in the initial condition. In addition, while the three particle shapes form void regions at distinct rates, we find that anisotropies in the local amorphous structure remain robust through the definition of a metric that quantifies packing anisotropy. Finally, we highlight connections between local deformation rates and local structure.

Influence of additional vibration impact on kinetics of strain bands due to the Chernov-Lüders deformation and Portevin-Le Chatelier effect in metals

The aim of the work is to investigate the influence of additional vibration impact on spatial-time inhomogeneity of plastic flow due to the Chernov-Lüders deformation and Portevin-Le Chatelier effect in metals (carbon steel and Al-Mg alloy) during uniaxial tension tests. Experimental data were obtained (diagrams, evolution of strain fields and local deformation rates, temperature fields, AE parameters) characterizing the kinetics of the strain bands initiation and propagation. The evolution of inhomogeneous strain and temperature fields were analyzed by using the digital image correlation technique and the infrared thermography accordingly. The mechanical behavior and the regularities of the jerky flow were studied using analysis of stress serrations and the accompanying acoustic emission.

Multimaterial 4D Printing with Tailorable Shape Memory Polymers.

We present a new 4D printing approach that can create high resolution (up to a few microns), multimaterial shape memory polymer (SMP) architectures. The approach is based on high resolution projection microstereolithography (PμSL) and uses a family of photo-curable methacrylate based copolymer networks. We designed the constituents and compositions to exhibit desired thermomechanical behavior (including rubbery modulus, glass transition temperature and failure strain which is more than 300% and larger than any existing printable materials) to enable controlled shape memory behavior. We used a high resolution, high contrast digital micro display to ensure high resolution of photo-curing methacrylate based SMPs that requires higher exposure energy than more common acrylate based polymers. An automated material exchange process enables the manufacture of 3D composite architectures from multiple photo-curable SMPs. In order to understand the behavior of the 3D composite microarchitectures, we carry out high fidelity computational simulations of their complex nonlinear, time-dependent behavior and study important design considerations including local deformation, shape fixity and free recovery rate. Simulations are in good agreement with experiments for a series of single and multimaterial components and can be used to facilitate the design of SMP 3D structures.

Simple microfluidic stagnation point flow geometries.

A geometrically simple flow cell is proposed to generate different types of stagnation flows, using a separation flow and small variations of the geometric parameters. Flows with high local deformation rates can be changed from purely rotational, over simple shear flow, to extensional flow in a region surrounding a stagnation point. Computational fluid dynamic calculations are used to analyse how variations of the geometrical parameters affect the flow field. These numerical calculations are compared to the experimentally obtained streamlines of different designs, which have been determined by high speed confocal microscopy. As the flow type is dictated predominantly by the geometrical parameters, such simple separating flow devices may alleviate the requirements for flow control, while offering good stability for a wide variety of flow types.

Diagnostic value of X-ray stereotactic vacuum-assisted biopsy for breast micro-calcification

Objective To compare the accuracy and clinical effect between X-ray stereotactic vacuum-assisted biopsy (SVAB) and metal wire guided lumpectomy. Methods From January 2010 to June 2014, 681 cases of breast micro-calcification biopsy were performed. Among them, 78 cases were performed with SVAB and 603 cases were performed with the method of stereotactic metal wire guided lumpectomy. All cases were non-palpable breast lesions (NPBLs) and breast imaging-reporting and data system (BI-RADS) assessment categories 4. The diagnostic accuracy and clinical effect were compared. Results The sensitivity of both methods was 100 % with no misdiagnosis. The underestimation rate of SVAB was 12.5 %. Compared with the method of metal wire guided lumpectomy, SVAB had many advantages, such as easy to use, quickly performed, low rate of local deformation and lower rate of operative complications. 77.5 % patients benefited from SVAB by avoiding open surgery of benign disease. Conclusions SVAB is an accurate, safe and convenient method of biopsy. It can be recommended as the preferred method of micro-calcification (BI-RADS 4). Additional operation should be performed on patients with the pathological diagnosis of middle and high grade of dysplasia and any kind of carcinoma. Key words: Breast micro-calcification; Vacuum-assisted biopsy; Diagnosis; Wire guided lumpectomy

A hybrid Eulerian–Lagrangian numerical scheme for solving prognostic equations in fluid dynamics

Abstract. A new hybrid Eulerian–Lagrangian numerical scheme (HEL) for solving prognostic equations in fluid dynamics is proposed. The basic idea is to use an Eulerian as well as a fully Lagrangian representation of all prognostic variables. The time step in Lagrangian space is obtained as a translation of irregularly spaced Lagrangian parcels along downstream trajectories. Tendencies due to other physical processes than advection are calculated in Eulerian space, interpolated, and added to the Lagrangian parcel values. A directionally biased mixing amongst neighboring Lagrangian parcels is introduced. The rate of mixing is proportional to the local deformation rate of the flow. The time stepping in Eulerian representation is achieved in two steps: first a mass-conserving Eulerian or semi-Lagrangian scheme is used to obtain a provisional forecast. This forecast is then nudged towards target values defined from the irregularly spaced Lagrangian parcel values. The nudging procedure is defined in such a way that mass conservation and shape preservation is ensured in Eulerian space. The HEL scheme has been designed to be accurate, multi-tracer efficient, mass conserving, and shape preserving. In Lagrangian space only physically based mixing takes place; i.e., the problem of artificial numerical mixing is avoided. This property is desirable in atmospheric chemical transport models since spurious numerical mixing can impact chemical concentrations severely. The properties of HEL are here verified in two-dimensional tests. These include deformational passive transport on the sphere, and simulations with a semi-implicit shallow water model including topography.

Late Quaternary megaturbidites of the Indus Fan: Origin and stratigraphic significance

The Indus sedimentary basin forms one of the largest “source-to-sink” systems of the Quaternary and extends over 106 km2 offshore. It is characterized by a complex tectonic setting marked by the Himalayan active orogenic belt in the source area, and the active strike-slip India-Arabia plate boundary (Owen Fracture Zone; OFZ) in its distal reaches. This paper focuses on a Late Quaternary channel–levee system from the Indus Fan captured by the recent opening of the 20°N pull-apart basin, located at 850 km off the present-day Indus Delta, along the OFZ. In this area the channel-mouth deposits consist of a set of up to 23 m thick megaturbidites trapped in the basin. These deposits form “ponded” lobe deposits in a tectonically-active confined basin. Age determination from radiocarbon dating and extrapolation of local deformation rates show that the older deposits observed on the seismic profiles are up to 358 ka BP old (MIS 10). The origin of these Late Quaternary deposits are investigated in the context of the Indus “source-to-sink” system and their significance is placed in a sequence stratigraphic framework. Integration of the stratigraphic architecture of the 20°N Basin megaturbidites with previous work in the area suggests that the Indus Fan evolved from a delta-fed turbidite system with several active canyons and channel–levee during the forced regressive conditions of the last falling stage of sea-level (122–25 ka BP), to a point source turbidite system during the sea-level lowstand (Last Glacial Maximum) and early transgressive stages (25–12 ka BP). This work sheds new light on the recent evolution of the Indus sedimentary system and illustrates the importance of the delta/river evolution during the fall of sea-level (e.g., incised valley formation) on the timing of sedimentary transfer and sediment distribution at the basin-scale.

Channelized melt flow in downwelling mantle: Implications for 226Ra‐210Pb disequilibria in arc magmas

We present the results of an analytical model of porous flow of viscous melt into a steadily dilating “channel” (defined as a cluster of smaller veins) in downwelling subarc mantle. The model predicts the pressure drop in the mantle wedge matrix surrounding the channel needed to drive melt flow as a function of position and time. Melt is sucked toward the dilatant region at a near‐constant velocity (10−5 s−1) until veins comprising the channel stop opening (t = τ). Fluid elements that complete their journey within the time span t < τ arrive at a channel. Our results make it possible to calculate the region of influence sampled by melt that surrounds the channel. This region is large compared to the model size of the channelized region driving flow. For a baseline dilation time of 1 year and channel half width of 2 m, melt can be sampled over an 80‐m radius and has the opportunity to sample matrix material with potentially contrasting chemistry on geologically short timescales. Our mechanical results are consistent with a downgoing arc mantle wedge source region where melting and melt extraction by porous flow to a channel network are sufficiently rapid to preserve source‐derived 238U‐230Th‐226Ra, and potentially also 226 Ra‐210Pb, disequilibria, prior to magma ascent to the surface. Since this is the rate‐determining step in the overall process, it allows the possibility that such short‐lived disequilibria measured in arc rocks at the surface are derived from deep in the mantle wedge. Stresses due to partial melting do not appear capable of producing the desired sucking effect, while the order of magnitude rate of shear required to drive dilation of ∼10−7 s−1 is much larger than values resulting from steady state subduction. We conclude that local deformation rates in excess of background plate tectonic rates are needed to “switch on” the dilatant channel network and to initiate the sucking effect.

A network scission model for wormlike micellar solutions: I. Model formulation and viscometric flow predictions

In this paper a network model for wormlike micellar solutions is presented which incorporates scission and reforming of the chains, based on a discrete version of Cates’ ‘living polymer’ theory. Specifically we consider two elastically active Hookean species: long chains which can break to form two short chains, which can themselves recombine to form a long chain. The chains undergo rupture at a rate dependent on the local elongation and deformation rate. This two species model, developed ultimately to enable understanding of inhomogeneous flows, is examined in this paper for various deformations; steady-state shear flow, step strain, extension, and linear small amplitude oscillatory flow in homogeneous conditions. We also examine how systematic variations in the model parameters affect the rheological predictions and material functions.

Simultaneous determination of shear and extensional viscosities and wall slip by on-line rheometry with parameter fitting: an application to EPDM rubber

Shear and extensional viscosities and wall slip are determined simultaneously under extrusion processing conditions using an on-line rheometer. Because it is not possible to independently control flow rate and temperature, classical methods for interpretation of capillary data cannot be used with on-line rheometry. This limitation is overcome using computational optimization to fit parameters in a flow model. This consists of three parts, representing shear viscosity, extensional viscosity, and wall slip. Three-parameter, power law forms, based on local instantaneous deformation rates and including temperature dependence, are used for each, and analytic solutions applied for entry flow and flow in the capillary. For entry flow, the Cogswell–Binding approach is used, and for developed flow in the capillary a solution incorporating wall slip is derived. The rheometer, with interchangeable capillaries, is mounted in place of the die on a rubber profile extrusion line. Pressure drops and temperatures for extrusion of an EPDM rubber through 2 mm diameter capillaries of length 0, 2, 3, 4, and 5 mm are logged and flow rates determined for a range of extruder speeds (5 to 20 rpm). Pressures ranged from 60 to 75 bar and temperatures from 86 to 116 °C. Mean flow velocity in the capillaries was between 5 × 10−3 and 5 × 10−1 m s−1. The nine material parameters are optimized for best fit of the analytic pressure drops to experimental data, using about 100 data points, with the Levenberg–Marquardt method. It is concluded that flow is dominated by extension and wall slip. Shear flow appears to play little part. The slip model indicates that slip velocity increases much more rapidly than the wall shear stress (in the range 0.5–1 MPa) and decreases with temperature for a given stress level. Results for the (uniaxial) extensional viscosity represent an engineering approximation to this complex phenomenon at the high strains (approximately 200) and high extension rates (up to 800 s−1) applying in the extrusion. Results indicate a slight extension hardening and a decrease with temperature. Results are put into the context of the available studies in the literature, which, particularly with regard to wall-slip and extensional flow, consider conditions far removed from those applying in industrial extrusion. The present methods provide a powerful means for flow characterization under processing conditions, providing data suitable for use in computer simulations of extrusion and optimization of die design.

100th Anniversary Special Paper: Numerical Models of Extensional Deformation, Heat Transfer, and Fluid Flow across Basement-Cover Interfaces during Basin-Related Mineralization

Fluid circulation within low-permeability basement rocks has been proposed to occur beneath many sediment-hosted mineral deposits, in some cases contributing substantial metals or sulfur to the deposits in overlying cover sequences. However, mechanisms proposed for fluid transport and mass transfer within and through basement rocks are diverse, some models appealing to thermal circulation but others appealing more to deformation- or topography-driven flow. We address some of these issues here by a series of numerical models designed to compare and then couple thermally and mechanically driven fluid flow (and incorporate temperature-dependent fluid properties), starting with generic problems and then using a simulation of coupled deformation, heat transfer, and fluid flow that may be applicable to the formation of Mount Isa-style Pb-Zn ores and other extension-related basinal deposits. Results from deformation-only models show that downward penetration of near-surface fluids into relatively low permeability basement rocks may occur along fault zones at high strain rates during extension, because local deformation rates may exceed the capacity for fluid to move through the basement rocks due to their low permeability, leading to periods of underpressure. For our thermal fluid-flow models, in the absence of deformation and with elevated basal heat flows, large differences in basement and cover permeability tend to restrict thermal convection to the permeable units. Downflow into low-permeability basement may occur by a reduction of the permeability of cover sequences, because larger convection cells are possible as permeability approaches common, optimal values throughout the rock mass. The normal reduction in porosity and permeability of cover sequences with burial may thus lead to progressively deepening convection cells and an enhanced potential for extraction of components from basement rocks. Long-lived, stable convection is generated with ≤2 order of magnitude permeability difference between basement and cover. Such convection has the potential to lead to near-surface mineralization (e.g., sediment-hosted syngenetic or diagenetic deposits), particularly if an initial overpressure stimulates convection cells toward upflow along basin-bounding faults. These models also serve to indicate the inadequacy of models that do not incorporate thermal dependencies of fluid viscosity and density, because the upward fluid velocity generated by buoyancy is of the same order of magnitude as the downward fluid velocity generated by extension-related underpressure in models that do not incorporate these properties. In numerical models of coupled deformation, heat transfer and fluid flow in which high basal heat flow is coupled with extensional deformation, the effects of the deformation dominate flow regimes, rather than the thermal structure. A model with initial heating and fluid flow established large convection cells with basement fluid circulation, prior to deformation being incorporated. The convection cells are effectively destroyed by extension at geologically reasonable strain rates around 10–14s–1, with surface fluids driven downward and meeting remnants of the decaying convection deep in the system. This simulation provides a possible solution for mixing of near-surface and deep fluids in unconformity-related U deposits and Olympic Dam-style iron oxide Cu-Au deposits. Geological models for shale-hosted base metal deposits (e.g., Mount Isa Zn-Pb) appeal to transitions from active rifting to blanketing by mineralized sag-phase shales, requiring reduction or cessation of extension with time. We simulate this here by stopping the deformation component of the coupled model and allowing the heating and fluid-flow parts to continue. Initial or periodic fluid overpressures (140% of hydrostatic) applied at the base of our coupled numerical models during extension (rift phase) cause initial upflow along faults and sufficient heat advection to generate steep near surface thermal gradients. When deformation ceases, convection progressively deepens with time, but upflow continues along faults, producing perfect conditions for exhalation of fluids that have circulated through basement. From all of the coupled models, we infer that active extension or extensional reactivation of basin-bounding faults is generally destructive with respect to potential fluid upflow and generation of near-surface deposits. Exhalative or other near-surface ores are likely to form when extension ceases and the thermal structure becomes the driver of fluid flow.

100th Anniversary Special Paper: Numerical Models of Extensional Deformation, Heat Transfer, and Fluid Flow across Basement-Cover Interfaces during Basin-Related Mineralization

Fluid circulation within low-permeability basement rocks has been proposed to occur beneath many sediment-hosted mineral deposits, in some cases contributing substantial metals or sulfur to the deposits in overlying cover sequences. However, mechanisms proposed for fluid transport and mass transfer within and through basement rocks are diverse, some models appealing to thermal circulation but others appealing more to deformation- or topography-driven flow. We address some of these issues here by a series of numerical models designed to compare and then couple thermally and mechanically driven fluid flow (and incorporate temperature-dependent fluid properties), starting with generic problems and then using a simulation of coupled deformation, heat transfer, and fluid flow that may be applicable to the formation of Mount Isa-style Pb-Zn ores and other extension-related basinal deposits. Results from deformation-only models show that downward penetration of near-surface fluids into relatively low permeability basement rocks may occur along fault zones at high strain rates during extension, because local deformation rates may exceed the capacity for fluid to move through the basement rocks due to their low permeability, leading to periods of underpressure. For our thermal fluid-flow models, in the absence of deformation and with elevated basal heat flows, large differences in basement and cover permeability tend to restrict thermal convection to the permeable units. Downflow into low-permeability basement may occur by a reduction of the permeability of cover sequences, because larger convection cells are possible as permeability approaches common, optimal values throughout the rock mass. The normal reduction in porosity and permeability of cover sequences with burial may thus lead to progressively deepening convection cells and an enhanced potential for extraction of components from basement rocks. Long-lived, stable convection is generated with ≤2 order of magnitude permeability difference between basement and cover. Such convection has the potential to lead to near-surface mineralization (e.g., sediment-hosted syngenetic or diagenetic deposits), particularly if an initial overpressure stimulates convection cells toward upflow along basin-bounding faults. These models also serve to indicate the inadequacy of models that do not incorporate thermal dependencies of fluid viscosity and density, because the upward fluid velocity generated by buoyancy is of the same order of magnitude as the downward fluid velocity generated by extension-related underpressure in models that do not incorporate these properties. In numerical models of coupled deformation, heat transfer and fluid flow in which high basal heat flow is coupled with extensional deformation, the effects of the deformation dominate flow regimes, rather than the thermal structure. A model with initial heating and fluid flow established large convection cells with basement fluid circulation, prior to deformation being incorporated. The convection cells are effectively destroyed by extension at geologically reasonable strain rates around 10−14s−1, with surface fluids driven downward and meeting remnants of the decaying convection deep in the system. This simulation provides a possible solution for mixing of near-surface and deep fluids in unconformity-related U deposits and Olympic Dam-style iron oxide Cu-Au deposits. Geological models for shale-hosted base metal deposits (e.g., Mount Isa Zn-Pb) appeal to transitions from active rifting to blanketing by mineralized sag-phase shales, requiring reduction or cessation of extension with time. We simulate this here by stopping the deformation component of the coupled model and allowing the heating and fluid-flow parts to continue. Initial or periodic fluid overpressures (140% of hydrostatic) applied at the base of our coupled numerical models during extension (rift phase) cause initial upflow along faults and sufficient heat advection to generate steep near surface thermal gradients. When deformation ceases, convection progressively deepens with time, but upflow continues along faults, producing perfect conditions for exhalation of fluids that have circulated through basement. From all of the coupled models, we infer that active extension or extensional reactivation of basin-bounding faults is generally destructive with respect to potential fluid upflow and generation of near-surface deposits. Exhalative or other near-surface ores are likely to form when extension ceases and the thermal structure becomes the driver of fluid flow.

Prédiction du tremblement en écoulement transsonique

Under transonic flow conditions, the shock wave/turbulent boundary layer interaction and flow separation on the wing upper surface induce flow instabilities, designated as buffeting, which result in structure vibrations. This phenomenon can greatly influence the aerodynamic performance. These self-sustained flow excitations can produce enough energy to excite the structure. The objective of the present work is to correctly predict this unsteady phenomenon by using unsteady Navier–Stokes averaged equations with time dependent turbulence model based on suitable ( k– ɛ) turbulent eddy viscosity model. The model used is based on the turbulent viscosity concept where the turbulent viscosity coefficient C μ is related to local deformation and rotation rates. To validate this model, the flow over a flat plate at Mach number of 0.6 is calculated. The solution is in agreement with analytical results. The ONERA OAT15A transonic airfoil was chosen to describe buffet phenomena. Computational results show the ability of the present model to predict physical phenomena of the flow oscillations allowing a suitable description of the unsteady shock wave/boundary layer interaction. To cite this article: A. Kourta et al., C. R. Mecanique 333 (2005).