Multilevel functional preconditioning for shape optimisation

We study the application of a multi-level preconditioner to a practical optimal shape design problem. The preconditioner is based on the Bramble-Pasciak-Xu (BPX) series. We extend it to the unstructured parametrization of 3D shapes by using the volume–agglomeration heuristics. The choice of the smoothing parameter is analysed from functional arguments. Application to the shape design for optimising aerodynamic and sonic boom performances of a wing is demonstrated.     

Principles of minimum transformed energy and minimum principles for dynamics of plates

In the present paper, we first by Laplace transform present a derivation of principle of transformed virtual work, three principles of minimum transformed energy with influence of rotatory enertia for dynamics of anisotropic linear elastic plates with three generalized displacements. Moreover, the forms with the original in place-time domain corresponding these variational principles are presented.Then by the introduction of the set of admissible weight functions the three minimum principles for the original place-time domain are derived.In each of the preceding groups of the variational principles there are two which are the dynamic counterparts to the static principles of minimum potetial energy and minimum complementary energy; the other principles are formulated in terms of the internal force alone, but have no counterpart in elastostatics of plates.     

Holberg's optimisation for high-order compact finite difference staggered schemes

Two optimised high-order compact finite difference (FD) staggered schemes are presented in this communication. Following Holberg's optimisation strategy, the least squares problem to minimising the group velocity (MGV) error, for the fourth- and sixth-order pentadiagonal schemes, is formulated. For a fixed level of group velocity accuracy, the optimised spectrum of wave number and the optimised coefficients for the schemes, are analytically evaluated. The spectral accuracy of these schemes has been verified by several comparisons with the FD staggered schemes obtained following Kim and Lee's (1996) optimisation procedure. Fewer group and phase velocity errors, greater resolution in terms of absolute error and resolving efficiency have been achieved by the optimised schemes proposed. High-order accuracy in time is obtained by marching the solution with an optimised Runge–Kutta scheme. Next, the comparison in terms of the number of grid points per wavelength required to achieve a standard accuracy for distances expressed in terms of the number of wavelengths travelled is presented. Numerical results from benchmark tests for the one-dimensional shallow water equations are presented.     

Strength-optimal running surface contour for track links

The various stresses resulting from weight, driving and tracking forces are transmitted over the contact point between track roller and track link running surface which is, compared with the dimensions of a track-type undercarriage, very small. The design of this contact point and hence the running surface profile of a track link, therefore, is particularly important. References were analyzed with the aim of discussing theoretical diversions on contact problems between plain and curved bodies to get the basis for an optimized design of the running surface profile of track-type undercarriages. Therefore stresses at point and line contact, i.e. for curved and plane running surfaces, are compared by Hertz' theory. In the case of line contact, the maximum Hertzian stress and thus also the maximum effective stresses strongly depend on the actual tilted position of the track roller to the track link running surface. The lowest stress is applied in the case of ideal line contact which is only theoretically interesting. Already at small angles of misalignment, the stresses for line contact are higher than for point contact. In field operation, at constantly changing angles of misalignment, the edge stresses cause the formation of curved running surfaces due to plastic deformation. If track links are already designed with such a running surface contour, the result will be constant stresses over the whole service life which are largely independent of the angle of misalignment avoiding excessive stresses caused by roller misalignments.     

An improved analysis for thermal track buckling

In a previous analysis of track buckling by the author, a simplifying assumption was made that the axial resistance which the ballast exerts on the rail-tie structure is constant. In the present paper this assumption is dropped, by presenting the axial resistance as a bi-linear response, which agrees better with the corresponding test data over the entire range of axial displacements. The obtained analytical results were evaluated numerically for the track parameters currently in use and the results are compared with the results of previous analyses, in order to establish the effect of the introduced analytical improvement.     

Fast dynamic modeling for off-road track vehicles

The paper presents a simple, fast, and reliable dynamic model for an off-road track vehicle operating on terrain with obstacles. The method has been proven previously for wheeled-vehicle formulation. The model is based on a discrete body dynamics (DBD) method, which leads to simplistic linear decoupled motion equations. In this method, joints and bodies with relatively small mass are replaced with stiff springs and dampers, eliminating the system’s constraints and reducing the number of system bodies; this is important for accelerating the simulation runtime of the track vehicle model. The track in this approach is based on modeling each link as a point-mass. Two consecutive links are connected by stiff springs and dampers. This approach reduces the calculation time and increases system stability. The track–soil interaction was modeled using Bekker’s and Janosi’s formulation (Bekker, 1956; Hanamoto and Janosi, 1961). Specific soil properties were obtained for each link–soil interaction from soil classification and GIS. The link–ground contact was determined from topographic surface and adjustment of the force and direction acting on the track. The results of the simulation using the DBD method were compared with Siemens' VL commercial multibody dynamics program and with experiments reported in the literature. Results using the proposed method were found to be similar to the commercial program based on published experiments. The solution runtimes obtained for unpaved soil were two orders faster with the DBD method compared with the Siemens' VL program. The model was written as an independent software infrastructure, enabling easy integration with any other software component, such as a control system. The algorithm is in a suitable form for parallel processing calculation to speed up the runtime simulation close to real-time.     

Wings of minimum drag for given lift

The variational problem of determining the optimal shape (camber and twist) of the midsurface of a wing having minimum wavedrag is examined in the linear formulation. It is shown that for wings with supersonic leading edge and straight trailing edge, whose shape is given in the form of a double polynomial, the over-all aerodynamic characteristics can be simply expressed in terms of the equation for the leading edge of the wing. This makes it possible not only to solve the variational problem by the Ritz method and obtain the minimum wave drag [1] but also to find the optimal shape of the wing. As examples we consider delta and double-delta wings.     

Polymer track developments

This article summarizes the development of tracks for cross-country vehicles and emphasizes the importance of a very well defined specification of the needs to be able control the development work. It also points out that it is absolutely essential for the manufacturers involved to work very closely together to ascertain the most suitable design of track vehicle.     

Dielectric-barrier-discharge vortex generators: characterisation and optimisation for flow separation control

We investigated the use of dielectric-barrier-discharge plasma actuators as vortex generators for flow separation control applications. Plasma actuators were placed at a yaw angle to the oncoming flow, so that they produced a spanwise wall jet. Through interaction with the oncoming boundary layer, this created a streamwise longitudinal vortex. In this experimental investigation, the effect of yaw angle, actuator length and plasma-induced velocity ratio was studied. Particular attention was given to the vortex formation mechanism and its development downstream. The DBD plasma actuators were then applied in the form of co-rotating and counter-rotating vortex arrays to control flow separation over a trailing-edge ramp. It was found that the vortex generators were successful in reducing the separation region, even at plasma-to-free-stream velocity ratios of less than 10%.     

Numerical optimisation of a classical stochastic system for targeted energy transfer

The paper studies stochastic dynamics of a two-degree-of-freedom system, where a primary linear system is connected to a nonlinear energy sink with cubic stiffness nonlinearity and viscous damping. While the primary mass is subjected to a zero-mean Gaussian white noise excitation, the main objective of this study is to maximise the efficiency of the targeted energy transfer in the system. A surrogate optimisation algorithm is proposed for this purpose and adopted for the stochastic framework. The optimisations are conducted separately for the nonlinear stiffness coefficient alone as well as for both the nonlinear stiffness and damping coefficients together. Three different optimisation cost functions, based on either energy of the system’s components or the dissipated energy, are considered. The results demonstrate some clear trends in values of the nonlinear energy sink coefficients and show the effect of different cost functions on the optimal values of the nonlinear system’s coefficients.     

Patch repair design optimisation for fracture and fatigue improvements of cracked plates

The problem of improving fracture and/or fatigue life of structural components by means of patch repairs is addressed in the present paper by applying a biology-based method, known as the Genetic Algorithm. The optimum design procedure consists in evaluating the patch topology, to be applied to the highest stressed region, which maximises the fracture resistance or the expected fatigue life of the improved structural component by keeping constant the total patched area (constrained optimisation problem). The proposed procedure is implemented in a finite element code and some numerical simulations are carried out in order to assess its reliability. The method is applied to two simple cases of cracked plates under pure Mode I or Mode II: for such analysed configurations, the method allow to improve significantly the fracture or fatigue behaviour of structural components repaired by employing the optimised shape patches instead of a simple shape (e.g. square or rectangular) patches.     

Free-piston driver optimisation for simulation of high Mach number scramjet flow conditions

The University of Queensland (UQ) is currently developing high Mach number, high total pressure scramjet flow conditions in its X2 and X3 expansion tube facilities. These conditions involve shock-processing a high-density air test gas followed by its unsteady expansion into a low-pressure acceleration tube. This relatively slow shock-processing requires the driver to supply high pressure gas for a significantly greater duration than normally required for superorbital flow conditions. One technique to extend the duration is to operate a tuned free-piston driver. For X2, this involves the use of a very light piston at high speeds so that, following diaphragm rupture, the piston displacement substitutes for vented driver gas, thus maintaining driver pressure much longer. However, this presents challenges in terms of higher piston loading and also safely stopping the piston. This article discusses the tuned driver concept, the design of a very lightweight but highly stressed piston, and details the successful development of a new set of tuned free-piston driver conditions for X2.     

镁粉尘云最低着火温度的实验测试

采用标准装置Godbert-Greenwald恒温炉测试了不同条件下镁粉尘云最低着火温度。实验测试结果显示:D50为6、47、104、173 m时镁粉尘云最低着火温度分别为480、520、620、700 ℃;选取D50为6 m的镁粉,在分散压力恒定为0.1 MPa时,镁粉浓度由424 g/m3变化到5 085 g/m3,粉尘云最低着火温度由600 ℃降低到480 ℃;而粉尘质量恒定为0.3 g时,分散压力从0.1 MPa增加到0.2 MPa,粉尘云最低着火温度由540 ℃升高到580 ℃。还分析了镁粉粒径、浓度及分散压力对粉尘云最低着火温度的影响。     

A minimum principle for microstructuring in rigid-viscoplastic crystalline solids

A minimum plastic power principle is proposed for a rigid-viscoplastic crystalline domain subdivided into two sets of lath-shaped regions, called bands. The lattice orientation in each band is assumed uniform and to differ infinitesimally from that in the other band. The proposed minimum principle yields the slip activity in the bands and semi-analytical expressions for the misorientation axis and orientation of band boundaries. These band boundary characteristics are predicted for f.c.c. lattice orientations near the ideal rolling texture components. Surprisingly, it found that the predicted band boundary characteristics closely match those of microstructural features called cell block boundaries reported in the experimental literature, except when the dislocations of activated slip systems are known to interact very strongly. This suggests that except when precluded by strong dislocation interactions, continuum extremum principles may also govern microstructural characteristics.     

On the risk-based steam generator lifetime optimisation

A probabilistic fracture mechanics model is employed to estimate the failure probability of axially cracked steam generator tubes. The model estimates the failure probability from the random changes of the influencing parameters such as tube and crack geometry, material properties and non-destructive examination results, reliability and sizing accuracy and stable crack propagation. The performance of the model is illustrated by a numerical example. A steam generator tubing severely affected by the stress corrosion cracking is studied during most unfavourable accidental conditions. Two different plugging approaches are analyzed and the quality is compared, showing the superior performance of crack length oriented approach over tube wall thickness reduction both in terms of SG failure probability and extent of plugging. Thus, apart from setting the acceptable SG failure probability, all elements for the risk-based SG lifetime optimisation are provided on the example of stress corrosion cracking in the tube expansion transition zone.