A constitutive model for ice as a damaging visco-elastic material

A general three dimensional theory is proposed for describing constitutive properties for ice as a viscoelastic brittle material. The elastic and viscous properties of ice are assumed to be initially orthotropic. Initiation and growth of a multitude of small microcracks is described using continuum mechanics principles. The material damage caused by microcracks is described using independent vectorial fields of planar microcracks. The constitutive equations are derived from general thermodynamic principles combined with some results from invariant theory for tensors. The developed theory is tested on two simple loading cases for a bar with material properties selected in conformance with test results for S2-ice. Results obtained numerically are compared with results reported in the literature. The results show good correspondence with test results over a wide range of strain rates including regions of ductile and brittle as well as regions of transition from ductile to brittle behaviour. The proposed model can easily be implemented in FEM programs.     

A quasi-linear technique applied to the method of fundamental solution

This paper proposes the use of a quasi-linear technique for the method of fundamental solution (MFS) to treat the non-linear Poisson-type equations. The MFS, which is a fully meshless method, often deals with the linear and non-linear poisson equations by approximating a particular solution via employing radial basis functions (RBFs). The interpolation in terms of RBFs often leads to a badly conditioned problem which demands special cares. The current work suggests a linearization scheme for the non-homogeneous term in terms of the dependent variable resulting in Helmholtz-type equations whose fundamental solutions are available. Consequently, the MFS can be directly applied to the new linearized equation. The numerical examples illustrate the effectiveness of the presented method.     

An artificial neural network approach to multiphase continua constitutive modeling

Constitutive equations describe intrinsic relationships among sets of material system parameters. This study utilizes artificial neural networks in place of a traditional micromechanical approach to calculate the global (macroscopic) elastic properties of composite materials given the local (microscopic) properties and local geometry. This approach is shown to be more computationally efficient than conventional numerical micromechanical approaches. An eight sub-celled representative volume element is used for the local geometry. Multi target artificial neural networks (MTANNs) and single target artificial neural networks are studied for applicability in predicting the global properties. The best performing MTANN achieves a precision of 9%. The single target artificial neural networks (STANNs) perform best and predicts the global properties within a target error of 5.3%. The computation time is 1.8 s for all six STANNs to predict six global properties for 19,683 different microstructures.     

A locally analytic technique applied to grid generation by elliptic equations

One technique for obtaining grids for irregular geometries is to solve sets of elliptic partial differential equations. The solution of the partial differential equations yields a grid which discretizes the physical solution domain and also a transformation for the irregular physical domain to a regular computational domain. Expressing the governing equation of interest in the computational domain requires the derivatives of the physical to computational domain transformation, i.e., the metrics. These metrics are typically determined by numerical differentiation, which is a potential source of error. The locally analytic method uses the analytic solution of the locally linearized equation to develop numerical stencils. Thus, the locally analytic method allows numerical differentiation with no loss of accuracy. In this paper, the locally analytic method is applied to the solution of the Poisson and Brackbill–Saltzman equations. Comparison with an exact solution shows the locally analytic method to be more accurate than the finite difference method, both in solving the partial differential equation and evaluating the metrics. However, it is more computationally expensive.     

Image-driven constitutive modeling of myocardial fibrosis

Myocardial fibrosis is a pathological process that occurs during heart failure (HF). It involves microstructural remodeling of normal myocardial tissue, and consequent changes in both cardiac geometry and function. The role of myocardial structural remodeling in the progression of HF remains poorly understood. We propose a constitutive modeling framework, informed by high-resolution images of cardiac tissue structure, to model the mechanical response of normal and fibrotic myocardium. This image-driven constitutive modeling approach allows us to better reproduce and understand the relationship between structural and functional remodeling of ventricular myocardium during HF.     

Inverse identification of constitutive parameters from heat source fields: A local approach applied to hyperelasticity

In this paper, a new inverse identification method of constitutive parameters is developed from full kinematic and thermal field measurements. It consists in reconstructing the heat source field from two different approaches by using the heat diffusion equation. The first one requires the temperature field measurement and the value of the thermophysical parameters. The second one is based on the kinematic field measurement and the choice of a thermo-hyperelastic model that contains the parameters to be identified. The identification is carried out at the local scale, ie, at any point of the heat source field, without using the boundary conditions. In the present work, the method is applied to the challenging case of hyperelasticity from a heterogeneous test. Due to large deformations undergone by the rubber specimen tested, a motion compensation technique is developed to plot the kinematic and the thermal fields at the same points before reconstructing the heterogeneous heat source field. In the present case, the constitutive parameter of the Neo-Hookean model has been identified, and its distribution has been characterized with respect to the strain state at the surface of a cross-shaped specimen.     

Mathematical modeling of river ice processes

River ice processes involve complex interactions between hydrodynamic, mechanical, and thermal processes. River ice research has largely been driven by engineering and environmental problems that concern society, including ice effects on flooding, hydropower, navigation, ecology, and the environment. Important findings on river ice research before 1980 have been summarized by Ashton (1986) and Donchenko (1987). Significant progress has been made in river ice research in the last three decades. Mathematical modeling has been an essential part of this progress. Mathematical models have been developed for various river ice processes. They not only helped to advance understanding of the physical processes by complementing field and laboratory studies, but also provided tools for planning and design of engineering projects. In this paper, models of various river ice processes during the winter, from freeze-up to breakup, are reviewed after a brief overview of river ice phenomena. Following the discussion of these ‘component’ models, a discussion on ‘comprehensive’ models and an analytical framework which links all river ice processes in a coherent manner is presented.     

快速评价反渗透专用阻垢剂阻垢性能的实验技术

反渗透装置中最重要的给水预处理方法之一是加入阻垢剂,来防止水中难溶盐形成水垢,RO市场上每年都会推出新的阻垢剂．RO装置的技术人员在使用这些阻垢剂前要对其性能进行实验室评估,研究阻垢剂所可能达到的最大回收率及正确的加药量．文章对阻垢剂的实验室快速评价技术进行了研究,使RO装置以周期性浓缩的全循环模式运行,以逐渐提高RO装置浓水侧的结垢趋势,并测定其结垢速率．选择了新型阻垢剂PTP-2000和传统阻垢剂SHMP,对其阻QaCO3的性能进行了比较研究．结果表明,周期性浓缩的全循环是一种快速、方便、可靠的阻垢剂评价技术,     

A new technique for measuring the constitutive parameters of planarmaterials

A technique for measuring the constitutive parameters of materials over a broad range of frequencies is developed. The technique is specifically designed for planar samples. Planar samples can be placed in the measurement fixture without any special preparation; this makes the technique more convenient than other techniques which require that the sample has to be machined to fit into a measurement fixture. Using fourth-order elements, the finite-element method provides a general, very accurate solution. The technique is experimentally verified by measuring the constitutive parameters of two materials with known properties. The measured results are compared to those of other investigators and are shown to be in good agreement     

A two-dimensional adaptive nodes technique in irregular regions applied to meshless-type methods

We propose a two-dimensional (2D) adaptive nodes technique for irregular regions. The method is based on equi-distribution principle and dimension reduction. The mesh generation is carried out by first producing some adaptive nodes in a rectangle based on equi-distribution along the coordinate axes and then transforming the generated nodes to the physical domain. Since the produced mesh is applied to the meshless-type methods, the connectivity of the points is not used and only the grid points are important, though the grid lines are utilized in the adapting process. The performance of the adaptive points is examined by considering a collocation meshless method which is based on interpolation in terms of a set of radial basis functions. A generalized thin plate spline with sufficient smoothness is used as a basis function and the arc-length is employed as a monitor in the equi-distribution process. Some experimental results will be presented to illustrate the effectiveness of the proposed method.     

膜技术在处理造纸黑液污染中的应用

研究用MAE（membrane-assisted electrolysis）单阳膜技术控制造纸黑液的污染,探讨了这种膜技术从造纸黑液中回收氢氧化钠等有用化学品的途径;黑液中大量存在的硅,对离子交换膜可能产生的影响;黑液污染控制的可行性和控制的程度。研究表明：MAE单阳膜技术不但能回收有用的化学品,还可将黑液的CODCr值从112000mg／L处置到2000mg／L左右,具有明显的控制效果。     

Dissimilarity partial least squares applied to non-linear modeling problems

In this paper, dissimilarity partial least squares, which deals with non-linear modeling problems, is discussed. It is based on the classic partial least squares approach, where the dissimilarity matrix representing dissimilarities among data objects replaces explanatory variables. This enables the construction of a global model able to adjust to local data inhomogeneities. The method seems to be an attractive alternative to other hierarchical modeling approaches. It is fast and can be applied to data sets containing numerous objects and variables. The algorithm is very simple (the calculation of the distance matrix and the application of the PLS algorithm with a modified cross-validation procedure). The concept of representing data objects by their similarity or dissimilarity with respect to other objects (using e.g., Euclidean distances) has many other attractive applications, and is the subject of our on-going research. Performance of the proposed approach is illustrated using simulated and experimental data.     

Multigrid technique applied to the compressible Euler equations

Summary An optimized multigrid method (EUFLEX-MG) for the EUFLEX code of MBB is described. The method is based on correction scheme and implicit relaxation procedures and is applied to the two dimensional case. The performance of EUFLEX-MG is demonstrated for subsonic and supersonic flow over a RAE-2822 airfoil and over a NACA-0012 airfoil for a large range of Mach numbers.     

Multi-surface failure criterion for saline ice in the brittle regime

In this paper, the development of a 3-D failure criterion for saline ice is presented. The need for such general 3-D failure formulation stems from the fact that, during ice–ship interactions, ice undergoes a complex state of deformation and stress before it fails and breaks away, and the use of the uniaxial strength of ice to compute impact ice loads may lead to inaccurate load calculations and non-conclusive results.In recent years, with the availability of High Power Computers (HPC), numerical methods are being used more than ever before in marine and ice engineering problems. Numerical models based on computational techniques such as finite elements, boundary elements and discrete elements require 3-D constitutive models and failure criteria to represent the behavior of the materials involved (such as the behavior of the ship structure, ice and water “fluid”).At high-speed impacts (strain rates >10⁻³ s⁻¹), ice behaves as a linear elastic material with a brittle mode of failure. Previously, Derradji-Aouat [Derradji-Aouat, A., 2000. A unified failure envelope for isotropic freshwater ice and iceberg ice. ASME/OMAE-2000, Int. Conference on Offshore Mechanics and Arctic Engineering, Polar and Arctic section, New Orleans, US, PDF file # OMAE-2000-P/A # 1002] developed a unified 3-D failure envelope for both fresh water isotropic ice and iceberg ice. In this paper, that formulation is extended to include failure of saline ice (in addition to fresh water ice and iceberg ice). The results of a significant number of true triaxial tests using Laboratory Grown Ice (LGSI) were obtained from the open literature. The results of these tests formed a database that enables the existing failure model [Derradji-Aouat, A., 2000. A unified failure envelope for isotropic freshwater ice and iceberg ice. ASME/OMAE-2000, Int. Conference on Offshore Mechanics and Arctic Engineering, Polar and Arctic section, New Orleans, US, PDF file # OMAE-2000-P/A # 1002] to be extended from the isotropic fresh water ice and iceberg ice to columnar saline ice.Mroz's [J. Mech. Phys. Solids 15 (1967) 163] concept for the multi-surface failure theory is used in both studies (the present study, for saline ice, as well as in the previous study, for the fresh water isotropic ice and iceberg ice). It appears that the same set of the equations is applicable to the failure of all three types of ice. The possibility of the existence of a universal and general failure criterion for all types of ice is discussed.The validation of the present multi-surface failure criterion was discussed on the basis of comparisons between predicted failure curves and actual true triaxial test results. An overall discrepancy of predicted versus measured strength values of less than 20% was calculated.     

Permanent set and stress-softening constitutive equation applied to rubber-like materials and soft tissues

Many rubber-like materials present a phenomenon known as Mullins effect. It is characterized by a difference of behavior between the first and second loadings and by a permanent set after a first loading. Moreover, this phenomenon induces anisotropy in an initially isotropic material. A new constitutive equation is proposed in this paper. It relies on the decomposition of the macromolecular network into two parts: chains related together and chains related to fillers. The first part is modeled by a simple hyperelastic constitutive equation, whereas the second one is described by an evolution function introduced in the hyperelastic strain energy. It contributes to describe both the anisotropic stress softening and the permanent set. The model is finally extended to soft tissues’ mechanical behavior that present also stress softening but with an initially anisotropic behavior. The two models are successfully fitted and compared to experimental data.