Enflu\ der Oberflächenspannung auf die Ausbildung von Flüssigkeits-Hohlstrahlen

Zusammenfassung Unter der Voraussetzung reibungsfreier Str?mung gelingtes, den Verlauf von Flüssigkeits-Hohlstrahlen, wie sie an Zerst?uber-Dralldüsen und an Zerst?uber-Ringdüsen entstehen, zu berechnen. Nach dem entwickellen Verfahren in Abh?ngigkeit von der Oberfl?chenspannung und der Dichte der Zerst?ubungsfüssigkeit, von der Austrittsgeschwindigkeit und von den konstruktiven Daten der Düse ermittelle Strahlkonturen stimmlen bis zu der Stelle, an der der Zerfall in Tropfen beginnt, gut mit beobachtelen Strahlkonturen überein. Bei kleinen Geschwindigkeiten wird der Hohlstrahl u. U. durch den Einflu\ der Oberfl?chenspannung derart deformiert, da\ keine Zerst?ubung zustandekommt und der Hohlstrahl zu einem Vollstrahl zusammenschl?gt. Durch geeignetes Zusammenfassen der verschiedenen Einflu\gr?\en bleiben als Parameler des Strahlkontur lediglich eine Weberzahl, der Halbmesser der Ringdüse sowie zwei durch die Düsenkonstruktion festgelegte Str?mungswinkel. Dissertation des Verfassers, Techn. Hochschule Karlsruhe 1956 Auszugsweise wurde über diese Arbeit auf der gemeinsam von den Fachausschüssen für Str?mungsforschung der Gesellschaft für angewandte Mathematik und Mechanik (GAMM), der Wissenschaftlichen Gesellschaft für Luftfahrt (WGL) und des VDI vom 6. bis 8. Oktober 1955 in Güttingen veranstalteten Tagung für Str?mmungsforschung vorgetragen.     

Rewriting systems with a clocking mechanism

A new type of rewriting system is introduced in which every string in a derivation is preceded by one (clocking) symbol which must be rewritten at every moment of time, (hence in a parallel mode). The rest of the string is rewritten in a sequential mode, (i.e., one symbol at every moment of time). The communication from the clocking symbol to the rest of the string, and vice versa, is achieved by incorporating various types of context conditions in every production.     

Wertprüfungssysteme bei Winterraps

Quality Test Systems of Winter Rape Seed Winter rape seed is cultivated in Germany for grain use as well as green intermediate summer crop or as intermediate winter crop. According to the destination of the crop by the declarer the Federal Board of Sorts carries out the qualification test of one or more of these three kinds of use. It is reported where the tests in the Federal Republic of Germany are carried out, where and by whom they are looked after, in which way the seed is distributed, which properties are received by observations, measurements and weighings, and in which way the declarer is informed about the results of the qualification test of a usual period of three years.     

Einfluß polymerisathaltiger Schmieröle auf den Verschleiß von Verbrennungsmotoren

The wear protecting properties of motor oils containing oil soluble polymethacrylates were investigated by means of measuring the wear of the crankshaft bearings of internal combustion machines. From this results follows that lube oils containing enough polymer (up to 12%) give lower wear than straight mineral oils of equal viscosity. That means that polymethacrylate has a wear protecting effect which is more efficient than the thickening effect of the polymer. The efficiency of this effect depends on polymer content and on the molecular weight of the polymer. Furthermore, the results clearly show that the wear protecting effect of the polymethacrylate is strongly influenced by the solving properties of the base oil.     

Zur phasentrennung von polymergemischen in lösung

Usually, mixtures of solutions of two different polymers in the same solvent are incompatible. This incompatibility leads to an intensive turbidity of the mixture and finally, to the formation of two phases. The turbidity disappears on dilution with the same solvent, because the polymers are compatible below a certain polymer concentration c_kr. In principle, the same effects occur also with mixtures of polymers in the solid state (polymer blends), but here the aggregation of the microphases is impossible due to the high viscosity. Up to now, there is little known about the composition of the two phases above c_kr. Therefore, we studied the distribution of two different polymersin solution regarding molecular weight and concentration into both phases. It was varied the polymer ratio, the molecular weight, the overall concentration and the nature of the solvent. Polystyrene and polyvinyl acetate were used as polymers because they can easily be separated from each other which is necessary when analysing the different phases; this analytical separation was carried out for each individual phase. The following results were obtained: Each phase contains both polymers; in addition there occurs a fractionation according to molecular weight during the phase separation for both polymers. The polymer distribution in the two phases regarding molecular weight, amount of polymer, and concentration depends not only upon initial concentration, molecular weight and weight ratio of the two polymers but also upon the different degree of solvation of the macromolecules in different solvents. When mixtures of solvents are used, an additional partially separation of the solvent into both layers takes place.     

Struktur und Eigenschaften von ABS-Polymeren. IV. Zum Einfluß der thermischen Vorbehandlung auf das Deformationsverhalten von ABS-Pfropfpolymerisaten

The influence of thermal history on the thermomechanical properties of a graft polymer (ABS) is investigated. The thermal pretreatments are: sharp quenching from above the glas-transition of the matrix resin, annealing below the glas transition. A first characterization of the influence of these two pretreatments is done by measuring density, probe length as function of temperature and by DTA. The less modulus in the region below the glas transition of the matrix resin is very sensitive to thermal pretreatment. Small but reproducible influences are observed in the glas transition region of the polybutadien particles. At room temperature stress-strain measurements are achieved until fracture happens. Crazing is observed (which is often called stress-whitening) in all cases, but the extent of craze growing is dependent on thermal history. The measurements are completed by scanning micrographs of the fracture surfaces. Annealing of the fracture surfaces gives additional informations. The results are discussed using the concept of free volume which is variated by thermal pretreatment. At room temperature the phase-boundary between polybutadion particle and matrix resin is considered as transition zone from high to small hole concentration. The sharpness of this zone is supposed to be a decisive parameter for the macroscopic deformation behaviour.     

On FEM-BEM coupling for fluid-structure interaction analyses in the time domain

The investigation of coupled fluid-structure systems, subjected to dynamic loads, calls for the use of discrete techniques such as the finite element method (FEM) and the boundary element method (BEM). This paper reports on the development of a FEM-BEM coupling procedure, where finite elements are used to model the linear elastic structure, while the adjacent fluid is represented by boundary elements. The new approach is formulated entirely in the time domain to be extensible to non-linear problems. Various numerical calculations are presented which clearly demonstrate the applicability and the merits of the hybrid method. The obtained results are in excellent agreement with solutions stemming from a boundary element analysis which uses subdomain techniques.     

Dynamic, polarization, and transverse mode characteristics ofvertical cavity surface emitting lasers

The dynamic, polarization, and transverse mode characteristics of strained InGaAs-GaAs quantum well vertical cavity surface emitting lasers (VCSELs) emitting at 0.98 μm are investigated. The dynamic behavior of VCSELs with high and low operating voltages and series resistances is compared. A large wavelength chirp in the lasing spectrum was observed for the lasers with high voltage/resistance, even under low-duty-cycle pulse operation. This is thought to be due to resistive heating close to the laser junction. It is observed that the transverse mode structure of VCSELs and their dependence on laser dimensions and drive current are highly analogous to those of edge emitting lasers, whereas the polarization characteristics of the two types of lasers are significantly different