Geometry Generation

Aerodynamic design is development of a suited shape. For SCT development, extensive appli­cation of numerical opumi/ers is required. When using optimizers, the first very important step is to describe the space of possible shapes by as few parameters as possible, but still without in – acccptahlc restrictions. In the first step of interdisciplinary optimisation, only global parameters
arc needed to described the basic aircraft geometry. The more refined the investigations arc, the more sophisticated the numerical methods are. the more detailed the geometry must be de­scribed. But for all levels the same requirements for geometry generation hold:

• For geometry generation by a human design engineer:

Geometry must be described by a limited set of parameters. But those parameters must be meaningful and well ordered in order to allow a human to reach geometric design goals. Alternative ways are allowed, e g multiple parameter sets or parameter set selections.

• For automatic geometry generation by a numerical optimizer

Geometry must be described by as few independent parameters as possible. Those param­eters may have any level of abstraction. Not allowed arc alternatives to the optimizer for selection between different, but equivalent parameter scis.

• Any geometry generator must provide smooth shapes without tending to wiggles:

If wiggles cannot be avoided, smoothing procedures must be provided. For human appli­cations, the smoothing procedures can be applied off-line as the Iasi step of geometry gen­eration. For numerical optimizers smoothing, if not avoidable, must be included in the geometry generation.

• Any geometry generator must provide interfaces to and from CAD-systems:

When aerodynamics has developed a shape, this shape will be transferred to oilier com­pany work groups like project, structure, acroelastics, model design and fabrication All aircraft related data transfer uses CAD-systems. The aerodynamic shape therefore has to be transferred into the CAD-system without intolerable accuracy losses.

On the other side, aerodynamics has to use input from other departments for geometry constraints like fainng size etc. Or the real model geometry has to be checked prior to a wind tunnel test. Or geometries generated by a partner must be investigated. Or wind tun­nel results • like pressure measurements – have to be applied to a given geometry for aero­dynamic improvements. In all those cases it must be possible to transfer the CAD- geometry mm the aerodynamic geometry generator as an input geometry, e. g. to start an improvement calculation.

Especially for application of numerical optimisation strategies more progress in sys­tematic shape definition is needed. Sometimes a is proposed to use CAD-systems directly for geometry generation, but CAD-systems arc oriented towards structural design: these do not contain geometry definition tools suitable for aerodynamic optimisation. Powerful aerodynamic 3D-geometry generators arc under development as preprocessors for CAD systems, see hook chapter 9.

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