Search Results for numerical stability

Computational fluid dynamics (CFD) is reserved for computationally intensive three-dimensional simulations of thermal fluids systems where nonlinear momentum transport plays an important role. This article presents the governing equations of fluid dynamics and an introduction to the CFD techniques for their solution. It introduces discretization techniques that are used by finite-difference, finite-volume, finite-element, spectral, and some particle methods. Associated concepts of numerical stability and accuracy are also reviewed. The article describes two approaches for grid generation with complex geometries: the use of unstructured grids and the use of special differencing methods on structured grids. The article describes the four-step procedures of the CFD process: geometry acquisition, grid generation and problem specification, flow solution, and post-processing and synthesis. It provides information on the applications of the engineering CFD. Issues and directions for the engineering CFD are also described.

This article describes the systems for designating the aluminum and aluminum alloys that incorporate the product forms (wrought, casting or foundry ingots) and its respective temper for strain-hardened alloys, heat-treatable alloys and annealed alloys. All these systems are covered by American National Standards Institute (ANSI) standard H35.1. Furthermore, the article provides a short note on the designation of unregistered tempers.

Computational fluid dynamics (CFD) is a computationally intensive three-dimensional simulation of thermal fluids systems where non-linear momentum transport plays an important role. This article presents the governing equations of fluid dynamics and an introduction to the CFD techniques. It introduces some common techniques for discretizing the fluid-flow equations and methods for solving the discrete equations. These include finite-difference methods, finite-element methods, spectral methods, and computational particle methods. The article describes the approaches for grid generation with complex geometries. It discusses the four-step procedures used in the CFD process for engineering design: geometry acquisition, grid generation and problem specification, flow solution, and post-processing and synthesis. The article also provides information on the engineering applications of the CFD. It concludes with a discussion on issues and directions for engineering CFD.

Nonplanar microstructures form most frequently during the solidification of alloys, and play a crucial role in governing the properties of the solidified material. This article emphasizes the basic ideas, characteristic lengths, and the processing conditions required to control the columnar and equiaxed microstructures. The formation of cellular and dendritic structures in one- and two-phase structures is presented with emphasis on the effect of processing conditions and composition on the selection of microstructure and microstructure scales.

This article provides a discussion on probes for laboratory tests and resultant curves of industrial quenching processes. It describes the scope of the tests, and the calculation of heat-transfer coefficient (HTC) based on the tests. The article highlights the differences between the laboratory tests and characterization of industrial quenching processes. It reviews the importance of initial heat-flux density and first critical heat-flux density. The theoretical principle behind and the purpose of the temperature gradient method are discussed. The article provides information on the design of the probe, heat-extraction dynamics, and influence of wetting kinematics. It also includes discussions on the simplified 1-D temperature-distribution model, calculation of the HTC, and the finite-volume method for the heat-conduction equation.

This article provides a summary of the biocompatibility or biological response of metals, ceramics, and polymers used in medical implants, along with their clinical issues. The polymers include ultrahigh-molecular-weight polyethylene, nonresorbable polymer, and resorbable polymers.

Designing of induction heating, or, generally electro technological installations, requires mathematical modeling for solving problems related to various physical phenomena, including electromagnetic (EM), thermal, mechanical, fluidic, and metallurgical fields. This article focuses on the solution of Maxwell's equations (MEs) and provides some basic information regarding the heat transfer and fluid equations, because these physical phenomena usually are strongly coupled to magnetic and electric fields. The solutions are usually obtained by using specific numerical methods such as finite-element method, finite difference method, boundary-element method or volume-integral method, and direct-solution method. The article also discusses the typical structure of commercial codes (preprocessor, solver, and postprocessor) to solve field problems mainly in finite-element method.

Composite materials offer amazing opportunities for delivering structures that are optimized to meet design requirements. This article provides a summary of the concepts discussed in the articles under the section “Engineering Mechanics, Analysis, and Design” in ASM Handbook, Volume 21: Composites. The section introduces many of the engineering approaches used in composite industry.

This article describes the characteristics of three types of gas bearings, such as aerostatic bearing, precision aerodynamic bearing (PAB), and compliant aerodynamic bearing (CAB). It discusses the applications for aerostatic bearings and advantages in lubricating a bearing with a compressible gas. The article also describes the different types of aerostatic bearings, such as annular thrust bearings and orifice-compensated journal bearings. It presents a discussion on load capacity and stiffness, friction and power loss, and stability and damping of the aerostatic bearings. The article provides a discussion on the types of PAB and CAB. The types include spiral groove annular thrust bearings, cylindrical journal bearings, three-sector journal bearings, tilting-pad journal bearings, and helical-grooved journal bearings. The types of CAB include foil bearings and pressurized-membrane bearings. The article concludes with a description of factors that influence materials selection for gas-lubricated bearings.

Automated tape laying is a mature process used in both commercial and military aircraft applications. This article provides a brief history of the process and describes the use of commercially available flat and contour tape-laying equipment. It discusses the advantages and disadvantages of the tape laying. The article describes the various components of a ten-axis gantry-type tape laying machine and the tape laying process. It provides a discussion on typical material types and forms for tape laying and provides information on design guidelines for tape laying.

This article focuses on the electroless gold plating technique, describing the advantages and limitations, applications, and properties of plated deposits. It also reviews process variables of the technique, including gold concentration, reducing agent, agitation, and contaminants.

A potential pH diagram is a graphical representation of the relations, derived from the Nernst equation, between the pH and the equilibrium potentials (E) of the most probable electrochemical reactions occurring in a solution containing a specific element. This article describes three types of reactions for calculation and construction of E-pH diagrams: electrochemical reactions of pure charge (electron) transfer; reactions involving both electron and solvated proton transfer; and acid-base reactions of pure solvated proton transfer. It illustrates the practical use of E-pH diagrams for temperature aqueous solutions and adsorbed species and in prediction of corrosion of nickel and copper.

One impressive example of plane front solidification (PFS) is the industrial production of large silicon single crystals, used mainly as substrates for integrated circuits. This article explores the PFS of a single phase, without taking convection into account. It discusses the solute build-up at the solid-liquid interface forming transients and steady state, the morphological stability/instability and perturbation theory, and rapid solidification effects, including solute trapping and oscillatory instabilities. The article presents a microstructural selection map that presents an overview of interface stability as a function of composition for a given alloy.

This article focuses on the unique characteristics of composites and laminated plates, including orthotropic, anisotropic, and unsymmetric plates. It discusses the stability issues associated with practical, structural laminates based on the finite stack effects and transverse shear stiffness effects. The article presents the study of instability associated with postbuckling behavior and hygrothermal buckling in composite sandwich panels and shell panels.

Plastic product failures are directly attributed to one of the following four reasons: omission of a critical performance requirement, improper materials specification, design error, and processing/manufacturing error. Therefore, product failures can be minimized or eliminated if all of these parameters are comprehensively examined during the design process. This article focuses on all of these factors, except processing-related failures, which are outside the design and engineering domain. It is dedicated to the identification and avoidance of common problems associated with the selection and designing of plastic parts. The article provides information on the material-related design criteria that depend on the applications, environmental conditions of use, and performance requirements. It discusses physical properties of plastics based on their relevance to real-world environmental conditions. The most-common design problems related to design considerations are also covered.

In cast iron, residual stresses normally arise due to hindered thermal contraction, meaning that they are associated with the presence of constraints that prevent the natural, free volumetric variation of the material upon solid-state cooling. This article explains their mechanism of formation by introducing the scalar relation, known as the additive strain decomposition. The main factors influencing casting deformation are volume changes during solidification and cooling, phase transformations, alloy composition, thermal gradients, casting geometry, and mold stability. The article reviews the dimensional stability in cast iron and discusses macroscopic and microscopic stresses in cast iron.

High-temperature-resistant polymers are used in aerospace, electronic, and other applications that demand outstanding elevated-temperature physical and mechanical properties. This article discusses the general characteristics of condensation-type polyimides and polymerization of monomer reactants (PMR) polyimides. It provides information on the applications of PMR-15 with illustrations.