Application of gradient based algorithms for robust shape optimization of a tensile test specimen

In case of technical applications such as automotive or aeronautic part optimization, uncertainties in design variables and other parameters have to be taken into account. Especially, scattering of material properties and mechanical loads have large influences on the component behavior. Due to the difficulty in calculating of sensitivities, usually stochastic algorithms are used for robust and reliability optimization. That entails a large number of function calls and long computation time. Therefore, the stochastic responses with expectation value and variances will be approximated by response surfaces in this contribution. Based on the practical example of a tensile test specimen a deterministic optimization and optimization under uncertainties will be done. The results of the different optimizations will be compared and the influence of the uncertainties will be shown and discussed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Comparisons of Heat Transfer Enhancement of an Internal Blade Tip with Metal or Insulating Pins

Cooling methods are needed for turbine blade tips to ensure a long durability and safe operation. A common way to cool a tip is to use serpentine passages with 180-deg turn under the blade tip-cap taking advantage of the three-dimensional turning effect and impingement like flow. Improved internal convective cooling is therefore required to increase the blade tip lifetime. In the present study, augmented heat transfer of an internal blade tip with pin-fin arrays has been investigated numerically using a conjugate heat transfer method. The computational domain includes the fluid region and the solid pins as well as the tip regions. Turbulent convective heat transfer between the fluid and pins, and heat conduction within pins and tip are simultaneously computed. The main objective of the present study is to observe the effect of the pin material on heat transfer enhancement of the pin-finned tips. It is found that due to the combination of turning, impingement and pin-fin crossflow, the heat transfer coefficient of a pin-finned tip is a factor of 2.9 higher than that of a smooth tip at the cost of an increased pressure drop by less than 10%. The usage of metal pins can reduce the tip temperature effectively and thereby remove the heat load from the tip. Also, it is found that the tip heat transfer is enhanced even by using insulating pins having low thermal conductivity at low Reynolds numbers. The comparisons of overall performances are also included.     

On the dimerization of carbon dioxide in nitrogen and argon matrices

The ir spectrum of carbon dioxide in solid nitrogen and solid argon has been studied. In nitrogen, the NN stretching vibration becomes ir-active in the presence of carbon dioxide. Concentration dependency and diffusion studies allow the identification of a carbon dioxide dimer in solid argon. In solid nitrogen no clear evidence for a dimer was obtained.     

Binding of methyl green to deoxyribonucleic acid analyzed by linear dichroism

From linear dichroism data a distinct structure of the strongest complex between the methyl green (MG) dication and the B-form DNA is concluded. MG is not intercalated but binds (probably to hydrophobic surfaces in the major groove) with its x and z axes at an angle to the local helix axis of 48° and 90°, respectively. At higher occupation density, exciton coupling between transition dipoles of adjacent molecules is visualized in the linear and circular dichroism spectra. The final spectra may be understood in terms of a right-handed (MG)_N helix in the major groove of the double helix.     

Terminating general recursion

In Martin-Löf's type theory, general recursion is not available. The only iterating constructs are primitive recursion over natural numbers and other inductive sets. The paper describes a way to allow a general recursion operator in type theory (extended with propositions). A proof rule for the new operator is presented. The addition of the new operator will not destroy the property that all well-typed programs terminate. An advantage of the new program construct is that it is possible to separate the termination proof of the program from the proof of other properties.Dedicated to Peter Naur on the occasion of his 60:th birthday.