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Über dieses Buch

Computer-aided design has come of age in the magnetic devices industry. From its early beginnings in the 1960s, when the precision needs of the experimental physics community first created a need for computational aids to magnet design, CAD software has grown to occupy an important spot in the industrial designer's tool kit. Numerous commercial CAD systems are now available for magnetics work, and many more software packages are used in-house by large industrial firms. While their capabilities vary, all these software systems share a very substantial common core of both methodology and objec­ tives. The present need, particularly in medium-sized and nonspecialist firms, is for an understanding of how to make effective use of these new and immensely powerful tools: what approximations are inherent in the methods, what quantities can be calculated, and how to relate the com­ puted results to the needs of the designer. These new analysis techniques profoundly affect the designer's approach to problems, since the analytic tools available exert a strong influence on the conceptual models people build, and these in turn dictate the manner in which they formulate prob­ lems. The impact of CAD is just beginning to be felt industrially, and the authors believe this is an early, but not too early, time to collect together some of the experience which has now accumulated among industrial and research users of magnetics analysis systems.

Inhaltsverzeichnis

Frontmatter

Introduction

Abstract
Magnetic devices have traditionally been designed by combining empirical rules based on experimental evidence with simplified magnetic circuit models. This technique may be labelled design by rule. But as devices become increasingly varied and complex, conventional design rules are no longer adequate and design by analysis, based on reasonably detailed solution of the underlying electromagnetic field problems, becomes the normal practice. Design by analysis really means design by numerical analysis since no other tools are capable of dealing with both the geometric complexity and nonlinearity found in such disparate devices as vertical recording heads and direct current machines. Design by analysis therefore inevitably means at least computer-aided analysis, and increasingly has come to mean full-fledged computer-aided design.
D. A. Lowther, P. P. Silvester

Magnetic Material Representation

Abstract
Analysis of magnetic devices normally requires a knowledge of the physical properties of the materials used: their magnetization curves as well as various other characteristics. Computer-readable files of material properties therefore must be maintained ready for use as and when required, in a convenient form. Ideally, the manufacturers’ catalogues for all materials to be used in design should be computer-readable and computer-accessible, so that analysis programs need only refer to materials by name or type identification.
D. A. Lowther, P. P. Silvester

The Potential Equations of Magnetics

Abstract
Practically all currently available CAD systems for magnetics and electromagnetics represent physical problems in terms of electric or magnetic potentials. The mathematical physics underlying potential theory, and potential theory as it applies to problems of magnetics, are reviewed in this chapter, with a few brief examples to illustrate the classes of problems to which one formulation or another might apply. The mathematical tools which are subsequently used to solve potential problems are generally numerical. This chapter is intended as a convenient summary review, not as an introduction to electromagnetics.
D. A. Lowther, P. P. Silvester

Problem Modelling and Mesh Construction

Abstract
Setting up magnetics problems for solution by computer involves several tasks. First, the geometric shape of the device to be analyzed must be described to the computer, and a discrete numerical model must be created which satisfactorily approximates the real device. Next, the materials to be used in the analysis must be identified and their properties described. Finally, the boundary conditions and the excitation values must be defined. It is often necessary to compute a solution for each of several closely related cases, for example, to find the magnetic state of a device for various different values of exciting current; therefore, boundary conditions and excitations are usually prescribed several times, one set for each distinct physical case. Once the physical problem has been fully stated in this way, most CAD systems further require the user to stipulate certain purely system-related parameters, such as the type of equation-solving technique to be used or the accuracy levels desired. The entire ensemble of steps needed to set up problems in a form ready for solution is usually termed preprocessing. This chapter outlines typical preprocessing steps in CAD systems, omitting only the construction of material property curves which is described elsewhere in this book.
D. A. Lowther, P. P. Silvester

Field Problems in Magnetic Devices

Abstract
Field problems as handled by the analyst are mathematical or computational abstractions of reality. The real physical world’s rich complexity of detail precludes taking account of any but a few selected features of a device in the process of analysis, so it becomes the responsibility of the design engineer to decide what aspects to include, which to ignore, and which to represent in an approximate fashion. Although there are many good computer programs to perform every mathematical step of the analysis itself, no computer can undertake to select which features of a device are important, and which results are desirable. The art of magnetic design in the brave new world of CAD bears some resemblance to the craft of the graphic artist in a world endowed with photography. Compared to an earlier age, there is less need for detailed mastery of the trade secrets and craft tricks of algebraic manipulation and calculation—the machines can handle much of that—and an ever increasing need for sensitive perception in selection, abstraction, and interpretation. Accordingly, the formulation of problems, rather than their solution, comes to occupy a primary role, as this chapter seeks to illustrate.
D. A. Lowther, P. P. Silvester

Postprocessing Operations in CAD

Abstract
The ensemble of activities by which the engineering significance of a mathematical field solution is evaluated is generally termed postprocessing. It includes the derivation of specific numerical results as well as their graphical presentation. A postprocessor is a major part of any design system since it allows relevant data to be extracted from the solution and presented in a way that has meaning to the user. Postprocessing should desirably be an interactive process, allowing the designer to query the solution. This chapter outlines the major requirements of postprocessing, while the following one describes a particular postprocessor structure by way of illustration.
D. A. Lowther, P. P. Silvester

Postprocessing Systems for Magnetics

Abstract
When a solver program terminates its run, it leaves in a computer file a digital version of the magnetic field as calculated. The postprocessor is expected to perform any further manipulations—which may be many, and which may involve far from trivial amounts of computation—and must therefore be endowed with the capacity for performing them. Some of the varied techniques available for the extraction of engineering information from mathematical solutions were examined at length in the previous chapter. However, no attempt was made there to provide an exhaustive list of all the operations that might be needed; the stress was rather on results which are common to many designers’ requirements. The present chapter is directed the other way: it seeks to ask how rather than why, and therefore to examine the implementation of a postprocessing system capa­ble of meeting the requirements implicitly defined by its predecessor.
D. A. Lowther, P. P. Silvester

CAD Systems Present and Future

Abstract
Engineering is said to be the art of coordinating men, machines, and materials to produce useful goods and services. It includes both scientific and managerial components so engineering computing must reflect the characteristics of both. Development of the CAD art, from computer- aided analysis (which it was in the early 1970s) to computer-aided engineering (which it might become in the late 1980s), is moving it steadily closer to the professional practice of engineering. Software for computer-aided design, which in the seventies amounted to straightforward scientific applications programs, has increasingly begun to take on the system orientation associated with business operating systems in the past.
D. A. Lowther, P. P. Silvester

The Literature of CAD in Magnetics

Abstract
Design is an art and must be studied through examples like any other art. Engineering design naturally includes a large element of engineering science, which is best acquired in an analytic and deductive fashion. Expertise in the art of design, on the other hand, is best learned by case studies and by emulation of others. To aid the reader in finding examples related to specific classes of problems, this bibliography is provided.
D. A. Lowther, P. P. Silvester

Backmatter

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