Papers by Author: Long Chen Duan

Abstract: One of the important objectives of lunar exploration is to obtain the lunar soil samples. However, the sampling process is very different from that on the Earth due to special characteristics of the lunar soil and surface environment. In order to ensure that the lunar exploration and sampling are successful, large numbers of ground experiments and computer simulations must be taken. In this paper, the surface lunar soil excavation simulation is investigated by three-dimensional discrete element method (DEM). It is implemented based on the open source LIGGGHTS, which takes the lunar soil as spherical particles. The interaction between the excavation tool and lunar soil is demonstrated. The excavation force and torque have also been calculated in real time. Moreover, the comparison of the excavation in different environments between the Earth and Moon corresponding to their different gravity accelerations was done. This paper shows that three-dimensional discrete element method can be used for the surface lunar soil excavation simulation and can provide important reference results for actual operations.

Abstract: The software CFDesign was used for the analysis of flow field simulation of two different kinds of drilling bit. The results showed that, if the waterway design of drilling bit was unreasonable, it could result in the following phenomenon: the local position of drilling bit could get severe erode of drilling fluid; the return of flow and eddy currents could be observed in the bottom of drilling well; negative pressure could be detected and might result in cavitation corrosion; the direction vector of flow field were diffused and resulted in cross flow. The waterway structure of arc-bottom bit was more reasonable comparing that of flat-bottom bit.

Abstract: This paper introduces a new kind of diamond bit body material. The characteristics of this material are as follows: the outer bit body cast with tungsten-carbide and the inside is steel shot. So the bit body has got high wear resistance on the outside and good mechanical properties inside at the same time. The mechanical properties inside and the wear resistance outside of the bit were tested. The paper also introduces how to apply a film of mixture of glue-included tungsten-carbide on the surface of the bit mold and graphite stick. The improvements of mechanical properties inside and maintenance of wear resistance outside have made much choice to design wider and deeper junk slots. Thus the performance of bit has been improved.

Abstract: Auger drilling is widely employed in pile foundation engineering and sampling test for geological sciences, and is even considered as one of the idealest methods for space sampling. However, in practice, drilling parameters are usually determined by experience which might cause unnecessary accidents as a result of transportation blocking of chips. To achieve smooth chips transportation, the existed critical speed models are firstly analyzed and summarized in this paper followed by the main introduction of the proposed new model of critical drilling parameters. The influence of rotational speed and vertical feeding rate on the actual trajectory of chips transportation as well as the selection of critical models for different applied drilling fields are subsequently investigated and discussed herein. Analyses indicate that the critical models of overall combined chips and chips divided into inner and outer layer are more reliable, vertical feeding rate and rotational speed should be taken into account simultaneously. The analyses on the actual trajectory of chips transportation are helpful to understand the motion state of chips. To achieve safe and efficient drilling production, suggested drilling parameters should be provided by manufacturers according to the solving models mentioned in this paper and the specific drilling fields.

Abstract: In order to understand the friction characteristics of hot-pressing bit matrix and granite under dry sliding conditions, the influence law of hardness and diamond concentration to the friction coefficient was analyzed and discussed with the data of friction coefficient and torque under different conditions. Three groups of hot-pressing matrix samples of different hardness and three groups of hot-pressing matrix samples with different diamond concentration were chosen. The friction and wear tests were carried out between hot-pressing matrix samples and granite samples. The results showed that the friction torque and coefficient firstly increased, and then decreased with the increase of hardness in dry friction experiments between granite sample and matrix sample without diamond. Compared with data from matrix sample without diamond, the friction torque and friction coefficient decreased significantly when test was carried between granite sample and impregnated diamond matrix sample. The friction torque and coefficient increased with the increase of diamond concentration.

Abstract: In oil drilling the failures of PDC drill bits are exhibited as erosive wear, dropping and breaking of cutters, so the erosion and corrosion resistance of the matrix is one of the key factors affecting the quality of PDC bits. In order to understand the degradation mechanism of matrix materials for drill bits, a kind of loop recirculation rig is adopted to measure total mass loss TML, mass loss E by pure mechanical erosion, and then through calculation the mass loss C+S by corrosion and synergy is obtained. The tested and calculated results show that TML of matrix materials is not only caused by pure mechanical erosion, but also by corrosion and their synergy of mechanical erosion and corrosion. In the discussed scope of this paper the volume loss produced by corrosion and synergy is 24.16% of the total volume loss (TVL) at most, which tells us that the corrosion resistance of matrix materials should be considered carefully besides their erosive resistance in the design and selection of PDC drill bits used in the corrosive drilling muds.