Numerical Design Tools Research Articles

Corrugated soft sector horn with different beam properties in the two principal planes

The authors present a corrugated horn antenna with different beam properties in the two principal planes of radiation. It is designed to give a frequency independent wide beamwidth in the horizontal plane, by making it flare-angle controlled in that plane, and a beamwidth that is decreasing with increasing frequency in the vertical plane, by making it aperture controlled in that plane. The throat of the horn is designed to ensure excitation of the desired mode in the flared part of the horn and achieve the desired aperture distribution. The flare in the horizontal plane is gradually increased to the chosen value and the corrugations on the horizontal walls are curved to follow the curved phase front of the desired mode. Improved mode excitation by introducing several thin dielectric lenses in the throat is studied. The radiation patterns are calculated from an approximate aperture field, representing the lowest-order mode in a radial sector waveguide. A horn was built and measured. Results show that it is possible to make corrugated sector horns with different beam properties in the two principal planes over a relative bandwidth of 1.5. However, it is also clear that it would have been desirable to have available numerical design tools for such complicated geometries in order to get better results.

Plasma generators for re-entry simulation

The qualification of thermal protection systems (TPS) and numerical design tools for re-entry vehicles and space probes requires the ability to understand and duplicate the prevailing complex physico-chemical phenomena, including thermal and chemical nonequilibrium near the surface of a body that enters the atmosphere of the Earth or another celestial body. At the Institut fur Raumfahrtsysteme of the University of Stuttgart, four plasma wind tunnels (PWK1-4) are in operation to simulate the thermal, aerodynamic, and chemical loads on the surface of a space vehicle. Three different plasma sources have been developed for this purpose: 1) a magnetoplasmadynamic generator for the simulation of the highenthalpy and low-pressure environment during the first phase of re-entry, 2) a thermal arcjet device for the follow-on flight path at moderate specific enthalpies and higher stagnation pressures, and 3) an inductively heated generator for basic materials experiments over a wide range of specific enthalpies and pressures. Special efforts were made to avoid electrode erosion to preclude impairing the erosion and catalytic behavior of TPS materials. A detailed description of these plasma generators and an overview of the simulation regions and operation areas of the plasma wind tunnels are presented.

Sharing the learning activity using intelligent CAD

AbstractIn this paper the need for Intelligent Computer Aided Design (Int.CAD) to jointly support design and learning assistance is introduced. The paper focuses on presenting and exploring the possibility of realizing “learning” assistance in Int.CAD by introducing a new concept called Shared Learning. Shared Learning is proposed to empower CAD tools with more useful learning capabilities than that currently available and thereby provide a stronger interaction of learning between a designer and a computer. “Controlled” computational learning is proposed as a means whereby the Shared Learning concept can be realized. The viability of this new concept is explored by using a system called PERSPECT. PERSPECT is a preliminary numerical design tool aimed at supporting the effective utilization of numerical experiential knowledge in design. After a detailed discussion of PERSPECT's numerical design support, the paper presents the results of an evaluation that focuses on PERSPECT's implementation of “controlled” computational learning and ability to support a designer's need to learn. The paper then discusses PERSPECT's potential as a tool for supporting the Shared Learning concept by explaining how a designer and PERSPECT can jointly learn. There is still much work to be done before the full potential of Shared Learning can be realized. However, the authors do believe that the concept of Shared Learning may hold the key to truly empowering learning in Int.CAD.

Application of numerical simulation in the bending of aluminium-alloy profiles

This paper deals with 3D elasto-plastic finite-element analyses of the production bending of aluminium extrusions. The overall objective of the study is to determine the applicability of using the general purpose software MARC K5.2 in analysing industrial rotary draw bending and stretch bending. The main focus is placed on the effects of material behaviour, slenderness of cross-sectional members, and die geometry on geometrical tolerances. The influence of applying external pre-stretching and internal support for obtaining better tolerances is demonstrated also. The results have been validated by a number of tests carried out in the laboratory and using industrial bending machines. The results show that wrinkles and sagging, or ‘suck-in’ of the flanges, can be eliminated by applying a stationary internal mandrel in combination with an internal web, even with tight radii. Furthermore, external pre-stretching is shown to be advantageous in order to reduce local buckling and spring-back. It has been found that the thickness variation expected after extrusion is of the same importance as anisotropy with respect to sagging in stretch bending. Elastic spring-back is influenced by the strain-hardening characteristic and the amount of axial loading applied, both decreased strain hardening and increased tension ensuring reduced spring-back. The experimental and numerical results appear to be in excellent agreement, indicating that extrapolation of the results to cases, other than those tested, may be possible. It is concluded that finite-element analysis has proven to be a well-suited numerical tool for design and product optimisation in industrial bending.

Three-dimensional simulation of a molten carbonate fuel cell stack using computational fluid dynamics technique

The performance of a molten carbonate fuel cell stack with regard to safe and efficient electricity generation has been investigated using the computational fluid dynamics (CFD) technique. A numerical model is developed, and it is employed to calculate the three-dimensional distributions of the crucial parameters (e.g., temperature, pressure, concentration, and density) across a stack. In particular, the model can consider simultaneously the dominant processes of a stack, such as mass transport, chemical reactions, heat transfer, and the voltage-current relations. Moreover, it is also capable of calculating the mass distribution across the stack rather than assuming a uniform distribution. In this paper, the model is demonstrated by applying it to calculate fuel cells with three different manifolds (e.g., co-, counter- and cross-flow) in a stack. The model is an effective numerical tool for optimal design and operational analysis of fuel-cell stacks, e.g. for comparing performance with different manifolds and to identify operational characteristics.

Integrating and enhancing for ASIC design using MOSIS fabrication

It is pointed out that application-specific integrated circuits (ASICs) can now be designed using high-quality, inexpensive tools and can be fabricated in small quantities using MOSIS (metal oxide semiconductor implementation service). Numerous computer-aided design tools developed under government sponsorship are available to organizations within the United States for just a media handling fee. These tool integration and enhancement activities have resulted in a proven set of high-quality aids that permit the design of custom and semicustom analog and digital ASICs. Examples of projects implemented using this tool set are given along with the support activities that are being conducted to transfer this technology to other federal agencies and universities.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The design and simulation of high-voltage Applied-B ion diodes for inertial confinement fusion

We present the design of the high-voltage (30 MV) Applied-B ion diode that is now being tested on the PBFA-II accelerator at Sandia National Laboratories. This diode design is the first application of a new set of numerical design tools that have been developed over the past several years. Furthermore, this design represents significant departures from previous designs due to much higher voltage and the use of a nonprotonic ion, Li+. The higher voltage increases the magnetic field strength required to insulate the diode from 1 to 2 T of previous diodes to 3–7 T. This represents a very large increase in the magnetic field energy and the magnetic forces exerted on the field-coil structures. Our new design incorporates changes in the field-coil locations to significantly reduce the field energy and the forces on the field-coil structures. The use of nonprotonic ions introduces a new complication in that these ions will be stripped when they penetrate material, i.e., the gas cell membrane. The importance of current neutralization, charge-exchange reactions, and the conservation of canonical angular momentum are discussed in the context of designing light ion diodes suitable as drivers for inertial confinement fusion. We have simulated the performance of this diode design using the electromagnetic particle-in-cell code, magic. We find that the most sensitive point in the power flow is the transition from the self-magnetically insulated transmission line to the applied field region of the diode.

A finite element model for the analysis of tailored pulse stimulation of boreholes

AbstractA constitutive model is described for the prediction of dynamic crack formation in geological media. The model includes a simple tensile failure criterion for crack formation and a soil plasticity model for both deviatoric and volumetric plasticity. Numerical results are presented which show that the model reproduces the observed dependence of fracture formation on loding rate for dynamic pressure loading of boreholes. The use of the model as a numerical tool for design is demonstrated through two example parameter studies.