A Comprehensive Comparison of the Analytical and Numerical Prediction of the Thermal History and Solidification Microstructure of Inconel 718 Products Made by Laser Powder-Bed Fusion

The finite-element （FE） model and the Rosenthal equation are used to study the thermal and microstructural phenomena in the laser powder-bed fusion of lnconel 718. A primary aim is to comprehend the advantages and disadvantages of the Rosenthal equation （which provides an analytical alternative to FE analysis）, and to investigate the influence of underlying assumptions on estimated results. Various physical characteristics are compared among the FE model, Rosenthal equation, and experiments. The predicted melt pool shapes compared with reported experimental results from the literature show that both the FE model and the analytical （Rosenthal） equation provide a reasonably accurate estimation. At high heat input, under conditions leading to keyholing, the reported melt width is narrower than predicted by the analytical equation. Moreover, a sensitivity analysis based on choices of the absorptivity is performed, which shows that the Rosenthal approach is more sensitive to absorptivity, compared with the FE approach. The primary reason could be the effect of radiative and convective losses, which are assumed to be negligible in the Rosenthal equation. In addition, both methods predict a columnar solidification microstructure, which agrees well with experimental reports, and the primary dendrite arm spacing （PDAS） predicted with the two approaches is comparable with measurements.

Micromechanical modeling of asphalt concrete fracture using a user-defined three-dimensional discrete element method

A user-defined micromechanical model was developed to investigate the fracture mechanism of asphalt concrete （AC） using the discrete element method （DEM）. A three-dimensional （3D） AC beam was built using the ＂Fish＂ language provided by PFC3D and was employed to simulate the three-point bending beam test at two temperature levels： -10 ℃ and 15℃. The AC beam was modeled with the consideration of the microstructural features of asphalt mixtures. Uniaxial complex modulus test and indirect tensile strength test were conducted to obtain material input parameters for numerical modeling. The 3D predictions were validated using laboratory experimental measurements of AC beams prepared by the same mixture design. Effects of mastic stiffness, cohesive and adhesive strength on AC fracture behavior were investigated using the DEM model. The results show that the 3D DEM fracture model can accurately predict the fracture patterns of asphalt concrete. The ratio of stress at interfaces to the stress in mastics increases as the mastic stiffness decreases; however, the increase in the cohesive strength or adhesive strength shows no significant influence on the tensile strength.

Parametric analysis of steel plated shear structures

Due to outstanding ductility and high strength,the steel plate shear wall(SPSW)is recognized as a good lateral system for building structures; particularly as it interacts with earthquake resistant design.This study aims to reveal the dynamic and cyclic behavior of steel plated shear wall.Finite element method of analysis was implemented in order to simulate the behavior of such a wall structure.To determine the dynamic behavior of un-stiffened plate shear wall,two different analytical models were implemented.The post buckling strength of steel plate subjected to lateral loading was also employed.The story shear-drift diagrams of steel shear wall system were presented.The strength and ductility of the system obtained from the analysis were compared with those of steel shear wall tests reported before.The pertinent parameters of the steel shear wall system such as plate thickness,column and beam stiffness and the plate aspect ratio were recognized and their effects were recorded.The effect of stiffeners on the behavior of the SPSW was also investigated.

A Simplified Approach to Analysis of High-Rise Frame Tube Structures

Based on finite element method and finite strip method, a simplified approach was presented to analyze high rise frame tube structures. The generalized strip element is introduced and then the generalized stiffness matrices for beam and column line are derived by using the displacement functions that describe the nodal displacements and displacement transforms. Furthermore, the formulas for the generalized stiffness matrix of generalized strip element and load arrays corresponding to the displacement parameters were developed. It is shown through a series of numerical computation that the nodal angular displacements at the same floor in a generalized strip element are approximately identical. A comparison of the finite element method and the finite strip method shows that the simplified approach not only is accurate, but also reduces the number of basic unknown quantities.

Modeling p VT Properties and Vapor-Liquid Equilibrium of Ionic Liquids Using Cubic-plus-association Equation of State

Combining Peng-Robinson （PR） equation of state （EoS） with an association model derived from shield-sticky method （SSM） by Liu et al., a new cubic-plus-association （CPA） EoS is proposed to describe the ther-modynamic properties of pure ionic liquids （ILs） and their mixtures. The new molecular parameters for 25 ILs are obtained by fitting the experimental density data over a wide temperature and pressure range, and the overall aver-age deviation is 0.22%. The model parameter b for homologous ILs shows a good linear relationship with their mo-lecular mass, so the number of model parameters is reduced effectively. Using one temperature-independent binary adjustable parameter kij, satisfactory correlations of vapor-liquid equilibria （VLE） for binary mixtures of ILs ＋ non-associating solvents and ＋ associating solvents are obtained with the overall average deviation of vapor pressure 2.91% and 7.01%, respectively. In addition, VLE results for ILs ＋ non-associating mixtures from CPA, lattice-fluid （LF） and square-well chain fluids with variable range （SWCF-VR） EoSs are compared.

Adaptive Finite Element Modeling of Marine Controlled-Source Electromagnetic Fields in Two-Dimensional General Anisotropic Media

In this paper, we extend the scope of numerical simulations of marine controlled-source electromagnetic (CSEM) fields in a particular case of anisotropy (dipping anisotropy) to the general case of anisotropy by using an adaptive finite element approach. In comparison to a dipping anisotropy case, the first order spatial derivatives of the strike-parallel components arise in the partial differential equations for generally anisotropic media, which cause a non-symmetric linear system of equations for finite element modeling. The adaptive finite element method is employed to obtain numerical solutions on a sequence of refined unstructured triangular meshes, which allows for arbitrary model geometries including bathymetry and dipping layers. Numerical results of a 2D anisotropic model show both anisotropy strike and dipping angles have great influence on the marine CSEM responses.

Thermal-hydraulic modeling and analysis of hydraulic system by pseudo-bond graph

To increase the efficiency and reliability of the thermodynamics analysis of the hydraulic system, the method based on pseudo-bond graph is introduced. According to the working mechanism of hydraulic components, they can be separated into two categories: capacitive components and resistive components. Then, the thermal-hydraulic pseudo-bond graphs of capacitive C element and resistance R element were developed, based on the conservation of mass and energy. Subsequently, the connection rule for the pseudo-bond graph elements and the method to construct the complete thermal-hydraulic system model were proposed. On the basis of heat transfer analysis of a typical hydraulic circuit containing a piston pump, the lumped parameter mathematical model of the system was given. The good agreement between the simulation results and experimental data demonstrates the validity of the modeling method.

Stability analysis of slope in strain-softening soils using local arc-length solution scheme

Soils with strain-softening behavior — manifesting as a reduction of strength with increasing plastic strain — are commonly found in the natural environment. For slopes in these soils,a progressive failure mechanism can occur due to a reduction of strength with increasing strain. Finite element method based numerical approaches have been widely performed for simulating such failure mechanism,owning to their ability for tracing the formation and development of the localized shear strain. However,the reliability of the currently used approaches are often affected by poor convergence or significant mesh-dependency,and their applicability is limited by the use of complicated soil models. This paper aims to overcome these limitations by developing a finite element approach using a local arc-length controlled iterative algorithm as the solution strategy. In the proposed finite element approach,the soils are simulated with an elastoplastic constitutive model in conjunction with the Mohr-Coulomb yield function. The strain-softening behavior is represented by a piece-wise linearrelationship between the Mohr-Coulomb strength parameters and the deviatoric plastic strain. To assess the reliability of the proposed finite element approach,comparisons of the numerical solutions obtained by different finite element methods and meshes with various qualities are presented. Moreover,a landslide triggered by excavation in a real expressway construction project is analyzed by the presented finite element approach to demonstrate its applicability for practical engineering problems.

Combined back-analysis method of ground stress based on refined geological modeling

A new back-analysis method of ground stress is proposed with comprehensive consideration of influence of topography, geology and nonlinear physical mechanical properties of rock on ground stress. This method based on non-uniform rational B-spline (NURBS) technology provides the means to build a refined three-dimensional finite element model with more accurate meshing under complex terrain and geological conditions. Meanwhile, this method is a back-analysis of ground stress with combination of multivariable linear regression model and neural network (ANN) model. Firstly, the regression model is used to fit approximately boundary loads. Regarding the regressed loads as mean value, some sets of boundary loads with the same interval are constructed according to the principle of orthogonal design, to calculate the corresponding ground stress at the observation positions using finite element method. The results (boundary loads and the corresponding ground stress) are added to the samples for ANN training. And on this basis, an ANN model is established to implement higher precise back-analysis of initial ground stress. A practical application case shows that the relative error between the inversed ground stress and observed value is mostly less than 10 %, which can meet the need of engineering design and construction requirements.

Potentials of Cellular Vortex Element Modeling of Fluid Flow in Confined 2D Aquifer

Numerical methods such as finite difference, finite volume, finite element or hybrid methods have been globally used to successfully study fluid flow in porous stratum of which aquifers are typical examples. Those methods involve mathematical expressions which increases computation time with requirement of specific human expertise. In this paper, numerical models for single phase flow in 1D and 2D using the conservation of mass principles, Darcy＇s flow equation, equation of state, continuity equation and the STB/CFB （stock tank barrel/cubic feet barrel） balance were developed. The models were then recast into pressure vorticity equations using convectional algorithms. Derived equations were used to formulate transport equations which resemble the conventional vorticity transport equation. Formulated numerical models were used to investigate the daily instantaneous aquifer pressure drawdowns and pressure heads for 365 days. The developed equations were subsequently solved using cellular vortex element technique. The developed computer program was used to investigate confined aquifer of dimensions 10× 10 × 75 m with single vertex image. For the aquifer rate of 0.5 m3/s, 0.1 m3/s, 0.15 m3/s, 0.2 m3/s, 0.25 m3/s, 1.0 m3/s, 2.0 m3/s, 2.5 m3/s, 3.0 m3/s, 4.0 m3/s, the respective average head drawdowns and heads were, 1.127 ±0.0141 m, 1.317 ±0.0104 m, 1.412± 0.0041 m, 1.427 ± 0.116 m,1.527 ± 0.0141 m, 2.107 ± 0.0171 m, 2.197 ±0.0191 m, 3.007±0.0171 m, 3.127 ± 0.0041 m, 3.626 ± 0.0121 m, and 25 kN/m2, 35 kN/m2, 33 kN/m2, 5 kN/m2, 6 kN/m2, 11 kN/m2, 25 kN/m2, 42 kN/m2, 50 kN/m2, 62 kN/m2, respectively. Cellular vortex technique with relative little mathematics has been established to have recorded successes in numerical modeling of fluid flow in aquifer simulation.

Analysis of raft foundation design based on considering influence of superstructure stiffness

The finite element method was used for analysis of raft foundation design in high-rise building.Compared with other conventional methods,this method is more adapted to the practical condition since both superstructure stiffness and soil conditions were considered in calculation.The calculation results by example show that the base reaction is more uniform and the maximum reaction decreases obviously.Accordingly,the raft foundation design is more economic without any loss of security for high-rise building.

Modeling crack in viscoelastic media using the extended finite element method

In this paper,the problem of modeling crack in 2D viscoelastic media is studied using the extended finite element method.The paper focuses on the definition of enrichment functions suitable for cracks assessment in viscoelastic media and the generalized domain integrals used in the determination of crack tip parameters.The opening mode and mixed mode solutions of crack tip fracture problems in viscoelastic media are also undertaken.The results obtained by the proposed method show good agreement with the analytical methods and provide reasonable background information to enhance the modeling of crack growth in viscoelastic media.

Synthesis and catalytic activity of Ln (III) complexes with an unsymmetrical Schiff base including multi“非汉字符号” C=N—groups

A synthetic method for a new unsymmetrical Schiff base and its Ln(Ⅲ)complexes including multi > C = N — groups is reported. The complexes are characterized byelemental analysis, IR spectra, ~1H and ^(13)C NMR, especially 2D-COSY ~1H, ~1H NMR spectra. Thegeneral formula of the obtained complexes is [Ln_3(TBLY)(NO_3)_3] · nH_2O (Ln = La, n = 3; Ln = Nd,n=5; Ln = Gd, Dy, Yb, Y, n = 7), where TBLY = tetraglycol aldehyde-2,4-dihydroxy benzaldehydebis-lysine Schiff base. In addition, the evidence for existence of > C = CH — NH — group issupported by the AM1 method. The complexes obtained may be used as a catalyst. Conversion rate of80% with the viscosity-average molecular weight 220000 for the polymerization of methyl methacrylate(MMA) without addition of any cocatalyst has been obtained.

Distributed parametric modeling and simulation of light polarization states using magneto-optical sensing based on the Faraday effect

To solve the problems encountered in practical processes of magneto-optical sensing, the infinitesimal distributed-parameter model and finite-element accumulation of different dielectric properties of micromaterials were used to describe the evolution of light polarization states, instead of the previously commonly used method of lumped-parameter simulation, thus essentially explaining the mechanism of sensing, magneto-optical effects, and related factors, and achieving multiphysics coupling using the COMSOL finite-element analysis method. Considering the cases of the Faraday effect without and with line birefringence, the magneto-optical effect and output characteristics of an infinitesimal magneto-optical sensor were simulated and studied. The results verified the effectiveness of the infinitesimal sensor model. Because the magnetic field, stress, and temperature changes alter the dielectric properties of magneto-optical materials, the finite-element accumulation method lays a good foundation for research on theoretical analysis and performance of magneto-optical sensors affected by factors such as the magnetic field, temperature, and stress.