工程施工路径相关性的数值仿真

本文将损伤理论与时变力学耦联,形成用于模似施工的损伤时变力学方法,文中推导了基本方程和数值化算式。利用时变分析法对某地下煤层开采过程进行计算机仿真分析,给出了三种不同路径下开采引起地表沉陷的时空演化图,并进行对比分析。对体现出的位移、损伤与施工路径相关现象进行了探讨,并定量给出损伤时变分析下不同开采路径造成的最终力学状态的差别。本文中损伤时变力学方法为施工过程分析提供了一种新方法与手段。     

Using a Smoothing Averaging Operator to Evaluate Macroscopic Parameters in Structurally Inhomogeneous Materials

A smoothing averaging operator is used in passing from structural to macroscopic modeling of the stress–strained state of an article from a composite material taking into account finite strains. A model is constructed using an integral operator, in which the macroscopic laws of conservation of energy and mass and the equation of motion have the ordinary form used to describe processes in homogeneous materials. As an example, macroscopic parameters are evaluated in a system consisting of an ensemble of inclusions in an infinite matrix.     

The attractor of a Navier-Stokes system in an unbounded channel-like domain

The Navier-Stokes system describes a flow of a fluid in an unbounded planar channel-like domain. It is proved that in the case when an external force decays at infinity, the semigroup generated by this system has a global attractor and its Hausdorff dimension is finite. Estimates in weighted Sobolev spaces are used as a main tool. Asymptotics, as the distance from the origin in the plane tends to infinity, of functions on the attactor is found. This asymptotics show that all dynamics on the attractor decays at infinity and the turbulence generated by the force does not propagate to infinity.This research was supported in part by the Institute for Mathematics and its Applications with funds provided by the National Science Foundation.     

Analysis of Cracks and Deformations in a Full Scale Reinforced Concrete Beam Using a Digital Image Correlation Technique

This paper deals with the use of a digital image correlation technique for the determination of the actual mechanical behaviour of a full scale reinforced concrete beam after 25 years of service in a severe industrial environment. The objective is to investigate the influence of the service conditions on the cracking process and the flexural behaviour of the beam. For this purpose, one beam is removed from the existing structure before being tested in four point bending in laboratory. Displacement fields derived from digital images captured during five loading cycles are analysed in terms of crack detection and measurement, beam deflection and curvature. Owing to its good resolution, the method proves suitable for early crack detection and measurement. A comparison between experimental results and theoretical values derived from Eurocode 2 design code in the serviceability state suggests the existence of a longitudinal compressive force in the beam. A complementary analysis confirms the validity of this hypothesis. It is concluded that the cracking and the flexural behaviour of the tested beam are significantly affected by the existence of an initial compressive stress, which is possibly resulting from a swelling of the concrete due to long term exposure to wet atmosphere and elevated temperature.     

Three-dimensional Full-field Measurements of Large Deformations in Soft Materials Using Confocal Microscopy and Digital Volume Correlation

A three-dimensional (3-D) full-field measurement technique was developed for measuring large deformations in optically transparent soft materials. The technique utilizes a digital volume correlation (DVC) algorithm to track motions of subvolumes within 3-D images obtained using fluorescence confocal microscopy. In order to extend the strain measurement capability to the large deformation regime (>5%), a stretch-correlation algorithm was developed and implemented into the Fast Fourier Transform (FFT)-based DVC algorithm. The stretch-correlation algorithm uses a logarithmic coordinate transformation to convert the stretch-correlation problem into a translational correlation problem under the assumption of small rotation and shear. Estimates of the measurement precision are provided by stationary and translation tests. The proposed measurement technique was used to measure large deformations in a transparent agarose gel sample embedded with fluorescent particles under uniaxial compression. The technique was also employed to measure non-uniform deformation fields near a hard spherical inclusion under far-field uniaxial compression. Introduction of the stretch-correlation algorithm greatly improved the strain measurement accuracy by providing better precision especially under large deformation. Also, the deconvolution of confocal images improved the accuracy of the measurement in the direction of the optical axis. These results shows that the proposed technique is well-suited for investigating cell-matrix mechanical interactions as well as for obtaining local constitutive properties of soft biological materials including tissues in 3-D.     

From Double Bind to N-Bind: Toward a New Theory of Schizophrenia and Family Interaction

Double Bind Theory has long been discredited as a viable theoretical framework to understand the relationship between schizophrenia and family interaction. Since research continues to indicate that the family environment plays a crucial role in the development and/or maintenance of the disorder, a reconsideration of the status of Double Bind is both necessary and timely. This paper utilizes a Nonlinear Dynamical Systems framework to bring the theory up to date with current dynamical thinking, and renames the resulting model N-Bind theory. The premises of N-Bind theory are discussed, and the symptoms of schizophrenia are described in light of the theory. The compatibility of N-Bind theory with the Vulnerability-Stress model is discussed, and a procedure is proposed to test the two hypotheses which postulate on different levels of analysis that Binds are more likely to occur in families with than without a schizophrenic member. Some of the implications for treatment and prevention are considered, should the theory be supported by empirical evidence.     

A Study of Large Plastic Deformations in Dual Phase Steel Using Digital Image Correlation and FE Analysis

Large plastic deformation in sheets made of dual phase steel DP800 is studied experimentally and numerically. Shear testing is applied to obtain large plastic strains in sheet metals without strain localisation. In the experiments, full-field displacement measurements are carried out by means of digital image correlation, and based on these measurements the strain field of the deformed specimen is calculated. In the numerical analyses, an elastoplastic constitutive model with isotropic hardening and the Cockcroft–Latham fracture criterion is adopted to predict the observed behaviour. The strain hardening parameters are obtained from a standard uniaxial tensile test for small and moderate strains, while the shear test is used to determine the strain hardening for large strains and to calibrate the fracture criterion. Finite Element (FE) calculations with shell and brick elements are performed using the non-linear FE code LS–DYNA. The local strains in the shear zone and the nominal shear stress-elongation characteristics obtained by experiments and FE simulations are compared, and, in general, good agreement is obtained. It is demonstrated how the strain hardening at large strains and the Cockcroft–Latham fracture criterion can be calibrated from the in-plane shear test with the aid of non-linear FE analyses. An erratum to this article can be found at     

Use of 3-D Digital Image Correlation to Characterize the Mechanical Behavior of a Fiber Reinforced Refractory Castable

Refractory castables exhibit very low fracture strain levels when subjected to tension or bending. The main objective of this work is to show that 3-D digital image correlation (3-D DIC) allows such low strain levels to be measured. Compared to mechanical extensometer measurements, 3-D DIC makes it possible to reach similar strain resolution levels and to avoid the problem of position dependance related to the heterogeneous nature of the strain and to strain localization phenomena. First, the 3-D DIC method and the experimental set-up are presented. Secondly, an analysis of the 3-D DIC method is performed in order to evaluate the resolution, the standard uncertainty and the spatial resolution for both displacement and strain measurements. An optimized compromise between strain spatial resolution and standard uncertainty is reached for the configuration of the experimental bending test. Finally, the macroscopic mechanical behavior of a fiber reinforced refractory castable (FRRC) is studied using mechanical extensometry and 3-D DIC in the case of tensile and four-point bending tests. It is shown that similar results are obtained with both methods. Furthermore, in the case of bending tests on damaged castable, 3-D DIC results demonstrate the ability to determine Young’s modulus from heterogeneous strain fields better than by using classical beam deflection measurements.     

Using geometric complexity to enhance the interfacial strength of heterogeneous structures fabricated in a multi-stage,multi-piece molding process

Interfaces in heterogeneous structures are typically engineered for optimal strength through the control of surface roughness and the choice of adhesives. Advances in manufacturing technologies are now making it possible to also tailor the geometries of interfaces from the nanoscale to the macroscale to create geometrically complex interfaces that exhibit enhanced performance characteristics. However, the impact of geometric complexity on the mechanical behavior of interfaces has not yet been ascertained. In this investigation, the first step is taken towards understanding the effects of geometric complexity on interfacial strength. A new multi-stage, multi-piece molding process is used to create heterogeneous polymer structures with geometrically complex interfaces consisting of rectangular and circular interlocking features. The structural integrity of these heterogeneous structures is characterized through interfacial tension testing. The full-field deformation measurement technique known as digital image correlation is also used during the testing to visualize the deformation fields around the geometrically complex features. Through this characterization, it is determined that the complex geometries increase the interfacial strength by approximately 20–25%, while reducing the statistical variation by 50%. These effects are attributed to a transition in the failure mechanism from interfacial fracture to homogeneous ligament failure. Results also indicate that geometrically complexity can be used on completely debonded interfaces to increase the strength to at least 25–35% of the bonded interface. Based on these results, some simple design rules have been proposed that enable geometrically complex interfaces to be engineered with enhanced strengths approaching the weaker of the two base materials. These design rules can also be used in the engineering of interfaces to facilitate the development of heterogeneous structures using new design paradigms, such as design for recyclability and the design of products based on bio-inspired concepts.     

Identification of Heterogeneous Constitutive Parameters in a Welded Specimen: Uniform Stress and Virtual Fields Methods for Material Property Estimation

Local strain data obtained throughout the entire weld region encompassing both the weld nugget and heat affected zones (HAZs) are processed using two methodologies, uniform stress and virtual fields, to estimate specific heterogeneous material properties throughout the weld zone. Results indicate that (a) the heterogeneous stress–strain behavior obtained by using a relatively simple virtual fields model offers a theoretically sound approach for modeling stress–strain behavior in heterogeneous materials, (b) the local stress–strain results obtained using both a uniform stress assumption and a simplified uniaxial virtual fields model are in good agreement for strains ɛ _xx < 0.025, (c) the weld nugget region has a higher hardening coefficient, higher initial yield stress and a higher hardening exponent, consistent with the fact that the steel weld is overmatched and (d) for ɛ _xx > 0.025, strain localization occurs in the HAZ region of the specimen, resulting in necking and structural effects that complicate the extraction of local stress strain behavior using either of the relatively simple models.

A New Technique to Determine Horizontal and Vertical Permeabilities from the Time-Delayed Response of a Vertical Interference Test

To determine the permeabilities from a vertical interference test, earlier investigators proposed correlations or type curves based on point source solutions or partially penetrated well solutions. However, it is impossible for these correlations or type curves to cover all possible scenarios in the real world. In more recent years, people use regression analysis to simultaneously match the pressure responses at the source interval and the observation point. With regression analysis, we face the problem of non-unique solutions. Sometimes, estimated permeability could be outside a reasonable range when analyzing noisy data from real tests. In this paper, a new technique is presented to estimate horizontal and vertical permeabilities from the time-delayed response in a wireline vertical interference test. In a vertical test, a pressure drawdown test period is followed by a pressure buildup test period. Because of the delay in response, the pressure at the observation probe continues to drop for some time while the pressure at the source interval is being built up. The maximum pressure drop at the observation probe with regard to the maximum pressure drop in the source interval is time-delayed. Using this time delay and the maximum pressure drop at the observation probe, vertical and horizontal permeabilities can be estimated. A novel numerical scheme is used. The new technique is compared with the previous methods, and it shows its superiority in accuracy. In addition, it can be used in different test configurations. Application issues in real testing conditions are discussed. Finally, two field tests are analyzed using this technique, while an earlier effort to analyze the tests using a conventional method was not successful due to poor data quality.     

Simulation of Gas Dipole Tests in Fractures at the Intermediate Scale Using a New Upscaling Method

A high-level radioactive waste disposal site may lead to gas generation by different physical mechanisms. As these sites are to be located in areas with low water flow, any small amount of gas can lead to relative high gas pressures, so that multiphase flow analysis becomes relevant. The movement of gas and water through the system has two important implications. Firstly, water flow takes place in unsaturated conditions, and thus travel times of the radioactive particles transported are affected; and secondly, gas can also carry radioactive particles. Therefore, one of the key points in such studies is the time when gas would break through the biosphere under a number of different flow conditions. In fractured zones, gas would flow preferentially through the most conductive features. We consider a two-dimensional system representing an isolated fracture. In each point we assign a local porosity and permeability and a local pressure-saturation relationship. A dipole (injector-producer) gas flow system is generated and the variation in water saturation is studied. A simple method is proposed for obtaining upscaled values for several parameters involved in two-phase flow. It is based on numerical simulation on a block scale assuming steady-state conditions and absence of capillary pressure gradients. The proposed method of upscaling is applied to simulate a dipole test using a coarser grid than that of the reference field. The comparison between the results in both scales shows an encouraging agreement.     

Estimation of crack density due to fragmentation of brittle ellipsoidal inhomogeneities embedded in a ductile matrix

Summary An estimation is found for the energy release due to fragmentation of a brittle inhomogeneity of ellipsoidal shape embedded in a ductile matrix under remote static loading. In the state of completed fragmentation the inhomogeneity is replaced by a void with zero stiffness. Thus, the problem of estimating the energy release reduces to the eigenstrain problem solved by Eshelby. The energy release calculated for prolate spheroidal inhomogeneities is used in the balance of energy to determine the crack density. The application to the geological system of garnet inhomogeneities embedded in a quartz matrix is considered.     

Performance evaluation of shape-memory-alloy superelastic behavior to control a stay cable in cable-stayed bridges

This paper focuses on introducing and investigating the performance of a new passive control device for stay cable in cable-stayed bridges made with shape-memory alloys (SMA). The superelasticity and damping capability of SMA is sought in this study to develop a supplementary energy dissipation device for stay cable. A linear model of a sag cable and a one-dimensional constitutive model for the SMA are used. The problem of the optimal design of the device is studied. In the optimization problem, an energy criterion associated with the concept of optimal performance of the hysteretic connection is used. The maximum dissipation energy depends on the cross-sectional area, the length, and the location of the SMA on the cable. The effectiveness of the SMA damper in controlling the cable displacement is assessed. Furthermore, a study is conducted to determine the sensitivity of the cable response to the properties of the SMA device. The comparison between the SMA damper and a more classical passive control energy dissipation device, i.e., the tuned mass damper (TMD), is carried out. The numerical results show the effectiveness of the SMA damper to damp the high free vibration and the harmonic vibration better than an optimal TMD.     

Multiphase Thermohaline Convection in the Earth’s Crust: I. A New Finite Element – Finite Volume Solution Technique Combined With a New Equation of State for NaCl–H2O

We present a new finite element – finite volume (FEFV) method combined with a realistic equation of state for NaCl–H₂O to model fluid convection driven by temperature and salinity gradients. This method can deal with the nonlinear variations in fluid properties, separation of a saline fluid into a high-density, high-salinity brine phase and low-density, low-salinity vapor phase well above the critical point of pure H₂O, and geometrically complex geological structures. Similar to the well-known implicit pressure explicit saturation formulation, this approach decouples the governing equations. We formulate a fluid pressure equation that is solved using an implicit finite element method. We derive the fluid velocities from the updated pressure field and employ them in a higher-order, mass conserving finite volume formulation to solve hyperbolic parts of the conservation laws. The parabolic parts are solved by finite element methods. This FEFV method provides for geometric flexibility and numerical efficiency. The equation of state for NaCl–H₂O is valid from 0 to 750°C, 0 to 4000 bar, and 0–100 wt.% NaCl. This allows the simulation of thermohaline convection in high-temperature and high-pressure environments, such as continental or oceanic hydrothermal systems where phase separation is common.     

Darcian Dynamics: A New Approach to the Mobilization of a Trapped Phase in Porous Media

We develop a new approach, which we term Darcian Dynamics, to simulate two-phase (liquid-gas) flow in porous media, when the gas phase is disconnected in the form of ganglia. The method is based on the assumption of homogeneous fluid flow for the liquid, although it does allow for heterogeneous capillary thresholds due to the pore microstructure. Using techniques from potential theory, the hydrodynamic interaction between liquid and gas is expressed through an integral representation over the ganglia interfaces. We use a numerical method to solve the resulting integral equation, and explore conditions for the onset of ganglia mobilization as well as for subsequent events, such as break-up, coalescence and stranding. The interaction between the ganglia and the flowing phase is influenced by the capillary and gravity (Bond) numbers, and by geometric factors, such as size, orientation, and ganglia density. The latter effect depends on the hydrodynamic interaction in addition to the intuitively expected crowding effect.