Development of a new direct test method for estimating cutter life, based on the Sievers’ J miniature drill test

The Sievers’ J-miniature drill test (SJ) has been used extensively at NTNU/SINTEF since the 1960s in connection with drillability testing of rock samples. Nearly 3000 samples have been tested, and the method is at present internationally recognised as a reliable method for determination of surface hardness of rock samples. A new test method for estimation of cutter life has evolved as a result of a recent update of the SJ test. This update was made possible by the development of instrumentation of the test apparatus. The new test method analyses the penetration depth and speed during the testing. The point in time where an interception occurs between the tangent lines for what could be defined as the “effective drilling” part and the “worn out” part of the penetration curve is defined as the Sievers’ J interception point or SJIP. Testing of 212 rock samples, representing different rock types, and correlations of the results to some of the most widely used methods for estimation of cutter life, show that it is possible to obtain a direct cutter life estimate by use of the SJIP value. The demand for representative parameters for rock properties in connection with underground excavations is increasing, as this constitutes the fundamental input for obtaining the most reliable cost estimates. The new test method provides information that was previously unavailable. This will improve the understanding on how different rock types and properties affect the drilling process and the wear on cutter tools. This test method is not meant to act as a substitute for well established and currently used test methods, but rather constitute an additional tool that can contribute to “bridge the gap” between laboratory testing, modelling and the actual excavation process estimates.     

Removal of inclusions from silicon

The removal of inclusions from molten silicon is necessary to satisfy the purity requirements for solar grade silicon. This paper summarizes two methods that are investigated: (i) settling of the inclusions followed by subsequent directional solidification and (infiltration by ceramic foam filters. Settling of inclusions followed by directional solidification is of industrial importance for production of low-cost solar grade silicon. Filtration is reported as the most efficient method for removal of inclusions from the top-cut silicon scrap.     

Solidification of silicon for electronic and solar applications

Silicon is widely used for its semiconducting properties in electronic and photovoltaic devices. These applications require strict control of the structure and impurity levels. Silicon must, therefore, be solidified using processes that give a minimum of impurity contamination and microstructural defects, as well as a planar solidification front to avoid microsegregation. Czochralski growth, and to some extent float zone crystallization, are processes used to obtain defect-free single crystals for integrated circuits and advanced solar cell wafers, whereas the Bridgman process can be used for production of multicrystalline silicon for standard solar cells. Direct solar cell wafer solidification processes have also been developed and reached limited commercial use. The paper will review these silicon crystallization processes and discuss recent developments and trends.     

The effect of stochastic relative permeabilities in reservoir simulation

During recent years Norsk Hydro has developed a 3D model for the simultaneous generation of stochastic absolute and relative permeabilities.By using a unique set of core data containing relative permeability curves measured on 85 core plugs from one single well in the North Sea, the authors have been able to model relative permeability curves (represented by endpoints and exponents) stochastically for four different depositional environments ranging from highly permeable mouthbar sands to low permeable tidal deposits.The authors will show that for all the four depositional environments represented here, the stochastic variation of the relative permeabilities have only marginal, if any, effect on the production characteristic, compared to keeping the relative permeabilities constant at their mean.Based on the fractional flow theory, for unit mobility ratio and ingnoring capillary forces, this paper presents both a theoretical and empirical statistical analysis of the correlation between the water shock front velocity and the absolute permeability for the different depositional environments. It is shown that in specific cases this correlation can serve as an indication of the potential effects of stochastically varying relative permeability curves.The main conclusion, which must be very comforting to practicing engineers, is that in within a wide range of depositional environments, stochastic modelling of the relative permeability curves is of minor importance. However, the choice of mean relative permeabilities may be crucial.     

A pattern based, robust approach to cyclic master surgery scheduling

The Master Surgery Scheduling problem consists of finding a suitable allocation of operating resources to surgical groups. A?myriad of variants of the problem has been addressed in literature. Here we focus on two major variants, arising during a cooperation with Sykehuset Asker og B?rum HF, a large hospital in the city of Oslo. The first variant asks for balancing patient queue lengths among different specialties, whereas the second for minimizing resort to overtime. To cope with these problems we introduce a new mixed integer linear formulation and show its beneficial properties. Both problems require the estimation of demand levels. As such estimation is affected by uncertainty, we also develop a light robustness approach to the second variant. Finally we present computational results on a number of real-world instances provided by our reference hospital.     

Equipartition of entropy production as an approximation to the state of minimum entropy production in diabatic distillation

We show that the theorem of equipartition of entropy production is important for the understanding of the state of minimum entropy production in diabatic distillation. The theorem is not valid in a strictly mathematical sense. We explain why, when and in what sense this theorem is a good approximation to the optimal state in diabatic distillation. In order to make these predictions, we use a hypothesis for the state of minimum entropy production of an optimally controlled system, which was formulated on the basis of results of entropy production minimisation in chemical reactors. The hypothesis says that the state of minimum entropy production is characterised by approximately constant local entropy production and thermodynamic forces, given that there is sufficient freedom in the system. We present numerical results which are in agreement with the predictions. The results show that a column with constant tray entropy production in the stripping section and in the rectifying section is a good approximation to the optimal column, except when the total heat transfer area is low. The agreement between the two columns becomes better and better as the total heat transfer area and the number of trays increase. The fact that the predictions and the numerical results agree very well gives support to the validity of the hypothesis.     

Numerical study of cluster formation in a gas–particle circulating fluidized bed

Simulations with two-way coupling are performed for two-dimensional gas–solid flow in a circulating fluidized bed with a total solids concentration of 3% in the riser. The motion of particles is treated by a Lagrangian approach, and particles are assumed to interact through binary, instantaneous, non-frontal, and inelastic collisions with friction. The model for the interstitial gas phase is based on the Navier–Stokes equations for two-phase flow with fluid turbulence calculated by using LES. Several porosity functions exist in the literature relating the drag force for a particle in a cloud to the drag force on an isolated particle. We have studied the influences of this porosity function, observing large differences in the local flow structure. The fluctuating gas–solid motion has been investigated showing a strong anisotropic flow behaviour, which is similar to experimental findings. The instabilities in these flows are strongly linked to the non-linear drag function due to the group effect of particles in a cloud. The collision parameters have been found to have an important influence on the cluster structures.     

Numerical evidence for a “highway in state space” for reactors with minimum entropy production

We report on the nature of the state of minimum entropy production. Thousands of solutions for this state in chemical reactors controlled by the temperature of the coolant medium, show that the solutions fall more or less on what we have called a “highway in state space”. The solutions were found using optimal control theory for reactors that produce a fixed amount of product. A subset of the solutions, for the oxidation of sulphur dioxide, is presented. Each solution gives the most energy-efficient way of operating a reactor for the given boundary conditions. For reasonable process intensities, the highway is characterised by approximately constant entropy production and driving forces, but not necessarily by linear flux-force relations. Knowledge about the highway has implications for energy-efficient reactor design. The results give theoretical support to engineering practices.     

斯堪的纳维亚硬岩海底隧道工程

论述了北欧海底隧道特别是基岩中开挖的公路隧道的工程经验,目前在北欧已建成25条以上的海底隧道,总长超过100km,大部分在挪威,最长的7.9km,最深的在海平面下264m。所有这些隧道都是用钻爆法进行开挖的。同时,叙述了勘探、规划、设计和施工等诸方面的重要问题,讨论了从这些工程中的经验教训。最后,介绍了规划中的海底隧道,包括长24km、埋深400m的2条隧道。相应地,介绍了其他北欧国家的海底隧道,这些隧道大多也是根据挪威海底隧道的经验进行设计和施工的。