Short shots and industrial case studies: Understanding fluid flow and solidification in high pressure die casting

The geometric complexity and high fluid speeds involved in high pressure die casting (HPDC) combine to give strongly three dimensional fluid flow with significant free surface fragmentation and splashing. A simulation method that has proved particularly suited to modelling HPDC is Smoothed Particle Hydrodynamics (SPH). Materials are approximated by particles that are free to move around rather than by fixed grids, enabling more accurate prediction of fluid flows involving complex free surface motion. Three practical industrial case studies of SPH simulated HPDC flows are presented; aluminium casting of a differential cover (automotive), an electronic housing and zinc casting of a door lock plate. These show significant detail in the fragmented fluid free surfaces and allow us to understand the predisposition to create defects such as porosity in the castings. The validation of flow predictions coupled with heat transfer and solidification is an important area for such modelling. One powerful approach is to use short shots, where insufficient metal is used in the casting or the casting shot is halted part way through, to leave the die cavity only partially filled. The frozen partial castings capture significant detail about the order of fill and the flow structures occurring during different stages of filling. Validation can occur by matching experimental and simulated short shots. Here we explore the effect of die temperature, metal super-heat and volume fill on the short shots for the casting of a simple coaster. The bulk features of the final solid castings are found to be in good agreement with the predictions, but the fine details appear to depend on surface behaviour of the solidifying metals. This potentially has significant implications for modelling HPDC.     

氮中多元标准混合气体的制备

研究用重量法制备氮中多元标准混合气体，对其制备原理、制备装置、气体称量装置，制备过程以及组分气体纯度的分析方法进行了介绍。分析了重量法制备氮中多元标准混合气体定值不确定度的来源，其定值的扩展不确定度小于3％。     

Spreadsheet Implementable Inventory Control for a Distribution Center

This paper develops and tests a simple procedure for establishing stocking rules for a multi-component distribution center that supplies spare parts for an equipment maintenance operation. Our basic formulation seeks to minimize inventory investment subject to constraints on average service level and replenishment frequency. We simplify this formulation by classifying parts according to a new ABC methodology and applying heuristics to the classical (Q,r) model that lead to closed-form expressions for the stocking parameters. Our numerical results show that: (1) the proposed ABC scheme does not introduce large errors provided that it is done in a manner that reflects the key parameters in the model, and (2) any of a number of simple reorder point heuristics can provide the basis for an effective spreadsheet implementable system for controlling inventory in a complex multi-component environment as long as the service level is checked against the exact formula.     

Analytische Berechnung einfacher scherströmungen aufgrund eines fließgesetzes vom carreauschen typ

Zusammenfassung Es wird eine modifizierte Form des Potenzgesetzes zur Beschreibung des Fließverhaltens strukturviskoser Fluide, der sog. Carreau-Ansatz näher untersucht. Die Angemessenheit dieser Modifikation wird durch den Vergleich von Berechnungen einfacher Strömungsformen, nämlich der Druckströmung durch eine Schlitzdüse sowie der überlagerten Druck- und Schleppströmung zwischen zwei parallelen Platten erwiesen. Dabei ergeben sich erhebliche Unterschiede, je nachdem die Fließkurve des betrachteten Stoffes durch ein einfaches Potenzgesetz oder durch einen dem Fließverhalten besser anzupassenden Carreau-Ansatz approximiert wird.Anschließend werden analytische, mit dem Taschenrechner auszuwertende Berechnungsformeln aufgrund des Carreau-Ansatzes für die genannten Strömungsformen und für die Druckströmung durch eine Bohrung hergeleitet. Ferner wird eine in sehr guter Näherung gültige Vereinfachung der exakten Durchsatzcharakteristik (scheinbaren Fließkurve) für Schlitzdüse und zylindrische Bohrung angegeben.Die gewonnenen Ergebnisse lassen sich z.B. auf dem Gebiet der Auslegung von Kunststoffverarbeitungsmaschinen und Ausformwerkzeugen sowie bei der Auswertung kapillarviskometrischer Messungen anwenden.

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A modified power law, the so-called Carreau formula, for the viscosity of pseudoplastic fluids in simple shear flow is considered. The appropriateness of introducing this modification is demonstrated by comparative calculations of some simple types of flow, namely the pressure flow through a slit die and the superimposed pressure and drag flow between two parallel plates. These calculations yield substantially different results according to whether the flow curve of the fluid is approximated by the usual power law or by the Carreau formula, which can be more closely matched to the rheological properties.Subsequently, analytic expressions for the above-mentioned flow types are derived on the basis of the Carreau formula enabling the flow to be computed using a pocket calculator. Moreover, a simplified but still very accurate formula for the throughput characteristic (or equivalently the apparent flow curve) of a slit die and a circular capillary is presented.The results obtained here are applicable to the design of polymer processing machines and dies as well as to the interpretation of viscosity measurements made with capillaries.

Auszugsweise vorgetragen auf dem 8. Stuttgarter Kunststoffkolloquium am 10. März 1983     

Generalized Multi-component TC Hierarchy and Its Multi-component Integrable Coupling System

A new 3M-dimensional Lie algebra X is constructed firstly. Then, the corresponding loop algebra X is produced, whose commutation operation defined by us is as simple and straightforward as that in the loop algebra A1. It follows that a general scheme for generating multi-component integrable hierarchy is proposed. By taking advantage of X, a new isospectral problem is established, and then well-known multi-component TC hierarchy is obtained. Finally, an expanding loop algebra FM of the loop algebra X is presented. Based on the FM, the multi-component integrable coupling system of the generalized multi-component TC hierarchy has been worked out. The method in this paper can be applied to other nonlinear evolution equations hierarchies. It is easy to find that we can construct any finite-dimensional Lie algebra by this approach.     

Proposal for Fourier-Transform Phase-Modulation Fluorometer

I propose a concept of a novel Fourier-transform phase-modulation fluorometer by which a fluorescence decay waveform can be obtained. In the fluorometer, the modulation frequency of the excitation light source is swept continuously from a start frequency f_min to an end frequency f_max with a time duration T. The resultant fluorescence signal waveform is Fourier-transformed to obtain amplitude and phase spectra. The ratio of the amplitude spectrum and the difference of the phase spectrum over those of the reference spectra that are obtained from a non-fluorescent material are calculated, respectively, and the pair of both spectral data is inverse-Fourier-transformed again to obtain the fluorescence decay waveform. To verify and demonstrate the effectiveness of the concept, I carried out (1) numerical simulations, (2) determination of a time constant of a passive resistor-capacitor (RC) differential circuit, and (3) measurement of a fluorescent decay waveform of YAG materials packed in Nichia’s white LED.     

单滴燃料热壁蒸发、微爆与着火的实验研究

多组分燃料在热板的蒸发与着火规律与空间相比,具有一些新的特点,特别是乳化油的贴壁燃烧现象更有重要意义。本文通过实验将多组分与单组分的燃烧情况进行了对比研究。结果表明：（１）易挥发组分的着火延迟在较低的温度条件下长于不易挥发份,在较高温度时情况相反。混合物则居于其中;（２）对于含水的乳化油,燃烧与微爆发生先后同的外界条件有关,其着火过程极为迅速。（３）乳化油中易挥发燃料含量较高,环境温度也较高时,微爆滞后很明显。