Consideration Of Physical Phenomena Research Articles

Multi-scale and multi-physics simulation of central segregation in an equiaxed dendritic mushy zone during continuous casting of steel

Centreline segregation during continuous casting of steel is highly detrimental to the end-product mechanical properties. In this study, a 3D multi-scale and multi-physics model is developed and validated that directly predicts alloy segregation occurring in peritectic steel grades having centreline equiaxed grain morphology. The model consists of four models: (1) a 1D macroscale heat transfer and solidification model, (2) a 3D mesoscale dendritic solidification model, (3) a 3D mesoscale dendritic fluid flow model, and (4) a 3D mesoscale solute transport and redistribution model. The use of a mesoscale domain where the solid and liquid phases are separately discretized allows for consideration of physical phenomena affecting segregation that are classically hidden by the averaging procedures of fully continuum approaches. Thus the new model is able to account for the multiple phenomena occurring during continuous casting while also directly considering the stochastic effects resulting from grains having randomly-placed nuclei as well as interactions between the liquid and solid phases. The results demonstrate that solute partitioning combined with intra-dendritic fluid flow leads eventually to liquid channels enriched with solute that result in centreline segregation. The predicted composition in these discrete liquid channels shows excellent agreement with a Mn centreline segregation profile experimentally-measured via microscopic X-ray fluorescence of a commercially-cast steel slab. Finally, the effects of alloy composition, and soft reduction on the degree of centreline segregation are examined.

FEM Simulations of Bond Behaviour between Concrete and Seven-Wire Prestressing Strand

The article deals with the subject related to numerical tests of the concrete bond to seven-wire strands. Nonlinear contact concrete-steel calculations with using Finite Element Method (FEM) is applicable for concrete bond to reinforcing steel analyses. At the moment, the analyzes are the subject of independent research projects. The research using several scientific and commercial computing systems allows us to look deeper into the sample and obtain information about cracks development, stresses, and internal deformations. Such analyzes are impossible when tests only experimentally. The concrete-steel behaviour of materials can be modeled with a bond-slip mechanism where the relative slip of reinforcement and concrete is phenomenologically described. The behaviour of the slip zone is then mapped with a zero thickness interface (contact) element. The constitutive laws of bond-slip adhesion are based mainly on the theory of total deformation, which expresses the pulling force as a function of total relative displacement. The correct construction of the bond model requires consideration of physical phenomena occurring not only at the interface of the materials but also inside within each of them. When designing numerical research, it is necessary to keep in mind the limits in computing memory of computers. Performing static calculations for complex numerical models containing a number of geometric, material and contact nonlinearities may prove to be too time-consuming on a PC. For this reason, it is now reasonable to construct approximate, simplified models. FEM models with a strand modeled as a solid bar (with a sidewall accurate to the real one) made it possible to observe and research, destructive mechanisms identified in experimental pull-out tests.

Creep modelling for multi-physical simulation of mass concrete structures using the explicit finite element approach

In the context of increasingly required evaluation of existing critical concrete infrastructures, prediction of the long-term behaviour can sometimes be very sensitive to the proper consideration of physical phenomena that occur during the first weeks during construction. For the specific example of mass concrete structures, it is important to consider the heat of hydration process and the possible development of thermally induced stresses and cracking at an early age. Consideration of the early age to the long-term time spectrum to recreate the history of stress/crack development is a challenging task in the field of numerical simulation of concrete structures and involves a consideration of multiple non-linear and physical phenomena. This work constitutes a continuation of previous works involving multi-physical simulation of concrete structures using the explicit finite element solver algorithm, which is known for its efficiency in solving highly nonlinear problems compared to the conventional implicit solver. A simple and innovative framework was developed in previous studies and involves the decomposition of strain into mechanical, thermal, creep, shrinkage and a coupling chemo-physical strain. This work focuses on the development of a simple and feasible computational framework for considering the creep in the specific field of mass concrete structures. Verification and validation examples are considered at the material and element levels. Application at the structural level on a new numerical benchmark demonstrates the feasibility of the approach and the efficiency of the developed computational framework.

THERMOPHYSICAL PHENOMENA IN METAL ADDITIVE MANUFACTURING BY SELECTIVE LASER MELTING: FUNDAMENTALS, MODELING, SIMULATION, AND EXPERIMENTATION

Among the many additive manufacturing (AM) processes for metallic materials, selective laser melting (SLM) is arguably the most versatile in terms of its potential to realize complex geometries along with tailored microstructure. However, the complexity of the SLM process, and the need for predictive relation of powder and process parameters to the part properties, demands further development of computational and experimental methods. This review addresses the fundamental physical phenomena of SLM, with a special emphasis on the associated thermal behavior. Simulation and experimental methods are discussed according to three primary categories. First, macroscopic approaches aim to answer questions at the component level and consider for example the determination of residual stresses or dimensional distortion effects prevalent in SLM. Second, mesoscopic approaches focus on the detection of defects such as excessive surface roughness, residual porosity or inclusions that occur at the mesoscopic length scale of individual powder particles. Third, microscopic approaches investigate the metallurgical microstructure evolution resulting from the high temperature gradients and extreme heating and cooling rates induced by the SLM process. Consideration of physical phenomena on all of these three length scales is mandatory to establish the understanding needed to realize high part quality in many applications, and to fully exploit the potential of SLM and related metal AM processes.

Nonlinear sliding mode observer for exhaust manifold pressure estimation in a light-duty diesel engine

In this paper, a sliding mode observer is proposed to estimate exhaust pressure for a diesel engine equipped with variable geometry turbocharger (VGT) and exhaust gas recirculation (EGR) systems. Since the exhaust pressure directly affects generation of the VGT power and the EGR rate in the cylinder, the exhaust pressure information is important for precise control of the VGT and EGR systems. In order to estimate the exhaust pressure accurately, a dynamic model of intake and exhaust pressure was derived. Furthermore, the mass flow rate and temperature of the air system in the diesel engines were modeled by consideration of physical phenomena and the thermodynamic law. Based on the developed models, a nonlinear sliding mode observer was designed to estimate the exhaust pressure. Convergence of the proposed observer was verified by the Lyapunov stability criterion. The proposed observer was implemented on a real-time embedded system and validated with the engine experiments. The experimental results show that the observer estimates the exhaust pressure accurately in both steady and transient engine operating conditions. Moreover, as a case study, the estimation results of the proposed observer could be applied for detecting a fault of the EGR system. The fault of the EGR system was detected precisely using the estimation result and the limited sensor information in mass-produced engines.

Description of magnetorheological behavior with internal variables

The macroscopic theory of magnetorheological (MR) fluids is investigated by the use of the tensorial and vectorial internal variables. After both variables are defined, the balance equations, entropy inequality and evolution equations can be obtained. Under the consideration of physical phenomena of MR fluids (the existence of yield stress and the elasticity of MR solids), some parameters in the evolution equations are suitably chosen. The discussion is focused on the expression of stress tensor and the mechanism of energy dissipation. Comparisons among the vectorial internal variable, the tensorial internal variable, and the Cauchy's deformation tensor are made to explicate the connection among the different approaches. Finally, taking account of the effect of the gradient of the vectorial internal variable, modified expressions for entropy inequality and rotational invariant are also discussed.

Two-dimensional subsonic flows of a compressible fluid and their singularities

1. Methods for generating stream functions of two-dimensional flows of a compressible fluid. The consideration of physical phenomena, in particular the study of electric and magnetic fields, was one of the starting points from which Riemann developed his approach to the theory of integrals of algebraic functions. In particular the consideration of two-dimensional electric and magnetic fields without singularities or with such singularities as vortices, sinks, sources, doublets, and so on, suggests the introduction of integrals of the first, second, and third kinds. The investigation of certain phenomena in fluid dynamics, namely the consideration of two-dimensional, irrotational, steady flow patterns of an incompressible fluid, leads to the same mathematical notions as those mentioned above since these flows are, from an abstract mathematical point of view, not essentially different from electric and magnetic fields. Generalizing this approach, one can introduce flow patterns of a compressible fluid with corresponding singularities and investigate relations between potentials and stream functions of these flows. The compressibility equation is, however, much more complicated than Laplace's equation, and it is very questionable whether such an immediate generalization would lead to results comparable with those in the theory of functions of a complex variable. It seems that it is preferable in this case to use the hodograph method (see below) and to link this approach with the theory of operators which transform solutions of one partial differential equation into solutions of another one. A two-dimensional steady irrotational flow of a perfect fluid can be described either by its potential (in the following denoted by 0) or by the stream function, 41. In the case of an incompressible fluid 0 and 41 are connected by the Cauchy-Riemann equations, so that O+i4l is an analytic function, f, of a complex variable. Taking the real and imaginary part of f we obtain 0 and 41, respectively. This process can obviously be interpreted as an operation