| Whether in China or on the earth, both are rich in glacier resources. Glacial ice isthe largest reservoir of freshwater, and it is widely distributed. Plenty of potentialvaluable information for research will be hidden in these glacier, so the data of ice corehas become the core data for us to understand the glacier. All kinds of informationcontainedin glacieris the“key”forhumanto understandtheearthchanges, forexample:studying the history of climate change and predicting the future climate. In the past fiftyyears, scientists and engineers have drilled lots of borehole and have collected a largenumber of cores. There are some limitations when we drilled the snow-firn layer, whosemaximum thickness related to the snow accumulation rate and temperature is rangefrom64m to115m. Drilling shallow ice and obtaining ice core samples quickly is veryimportant for Geochemistry, Microbiology, Climatology and environmental science. Ithas important scientific significance and social value for the development of humansociety and the natural world understanding. The upper part of the inland Antarctic Icesheet consists from permeable snow-firn layer. This snow-firn layer cannot be drilledby the ice drilling-fluid technology because drilling fluid will be spared in the pores anddisappeared, besides it will lead to unexpected pollution and destruction for theAntarctic environment. In addition, the Antarctic is located away from the mainland ofhuman life, the environment is extraordinary adverse and the supply is rather difficulty.Therefore this thesis researches one novel, ice core obtained quickly, portable, highefficiency, low energy consumption, easy to operate and maintain, and environmentallyfriendly drilling tool---the armored cable suspended electro-mechanical ice coring drillwith near-bottom air reverse circulation.Development and application of the drill can lay the foundation for post-drillingdeep ice and subglacial bedrock drilling. In this paper, the development of electro-mechanical coring drill technology can drill500m, which can provide a chance for morein-depth studies of polar research. The technology not only can be used in the Antarcticand Greenland ice drilling, but also be used for sampling engineering in mountainglaciers exploration, permafrost and natural gas hydrate drilling.In order to research the drilling tool, the existing glacier drilling tool are reviewed,the research status of shallow ice coring drill at home and abroad are mainly introduced,especially detailed introducing the air ice drilling and putting forward the researchcontents of the article. The drilling tool is used in shallow ice drilling and it has obviousadvantages in comparison to the other existing shallow ice drilling tool. So after thedesign of the drilling tool is proposed, we need to research air reverse circulation interms of theory, set up an air reverse circulation test stand for acquiring some required data from the experiment, which was done to prove that the air can form reversecirculation and suck ice chip particles into the chip chamber in time. Then fluiddynamics software “Fluent” was used to verify the parameters gained from thetheoretical calculation. We can design the drilling tool and conduct simulationexperiment after the drilling tool was produced, if the parameters are reasonable. At lastwe will select drilling technology and the optimum drilling parameters as soon aspossible. The key target is to prove the feasibility of the drilling tool, which can beworked well in the drilling process.(1) The existing shallow ice coring drill have some disadvantages, therefore anovel electro-mechanical ice coring drill with air reverse circulation of conceptualdesign is being proposed, and five kinds of methods, which are engineering practicemethod, the method of gas volume requirements for underbalanced drilling, mechanicsanalysis method, the hydromechanics method and start-up mechanism of cuttings, wereused for theoretical calculation. In consideration of safety drilling, the minimum airflow rate should be more than8.32m/s, the minimum air flow should be bigger than1.26m3/min, the pressure loss3.82kPa can be as a reference.(2)Theory analysis are universal, but the calculation object often required simpleand abstraction, and rarely can deal with nonlinear conditions. Therefore one CFDmethod is used not only to make up the defect of the theory analysis method, but alsoto solve the cost of manpower and material resources, funds investment and thelimitation of the time. It proves that the accuracy of theoretical calculation by using“Fluent” software simulation analysis, which also provides theoretical foundation forthe following experiment. The results of “Fluent” software simulation analysis showthat the greater the final vacuum degree is, the stronger the suction force is, the biggerthe air flow rate in the process of air circulation is, the more quickly and timely washingclearance. The final vacuum degree directly influence the air flow rate, and the finalvacuum degree should be at least more than3kPa if we want fully to wash holeclearance and suck all ice cuttings into the chip chamber. Fluent simulation showed theplaces of circulation system where the resistance are highest. This places need to becarefully designed in order to reduce air losses.(3)The results of “Fluent” simulation are closed to the theoretical calculation, wecan regard the results are reasonable. Whether the air reverse circulation can be formedand suck ice cuttings into the chip chamber, it still remains for further experimentalvalidation. Then we design and set up air reverse circulation test stand, and validate thefeasibility of circulation theory. The simulation cuttings are2mm diameter millets,which have similar physical properties with ice chips. This experimental results showthat: the air reverse circulation can be formed and the circulation air can remove thecuttings into the chip chamber. Therefore we can deduce that the air flow rate meets therequirements the minimum air flow rate. The detailed experimental results are asfollows:(a) the air can form reverse circulation in the simulation tube, whose length isfour meters and inner diameter is110mm;(b) the circulation air can effectively carryout millets in the chip chamber;(c) when the height of drill bit window is more than60mm, the air can’t carry cuttings into the chips chamber quickly, even can’t remove cuttings out.(4) The drilling tool was designed and produced in Polar Research Center of JilinUniversity with direct involvement of the author. It includes five main parts: armoredcable termination, slip ring component, anti-torque system, driven unit and coringcomponent. The main and key component is driven unit, we have to select suitablemotor, confirm the gear ratio, choose appropriate impeller and deal with sealing. Inaddition the design of armored cable is indispensable for raising and lowering drillingtool, transmitting power to motor and collect and recycle signal, which are obtainedfrom sensors.(5) From the experiment we successfully obtained ice core and sucked ice cuttingsinto the chip chamber, which evidence feasibility of the drilling tool, the rationality ofdesign and validity of the theoretical calculation and Fluent simulation analysis. Duringthe analogue simulation experiment we prove two type of impellers can be used in ourdesign, and the rotation speed range of impellers under the precondition of satisfyingthe need of ice core drilling. Besides we derive the relationship between final vacuumdegree and rotation speed of impeller, making preparations for solving the relationshipbetween maximum penetration rate and final vacuum degree. We also obtained someexperimental data including rotation speed of impeller, motor power, motor torque andmaximum penetration rate. Then we use these data to match the trend of the relationshipbetween each parameter. According to the results of fitting we know that: within acertain limits, when the output power of motor getting increaser, the impeller rotationspeed will be more faster, the final vacuum degree will be more stronger, the motortorque also changed bigger and the maximum penetration rate will be raised. Therelationship between each of two parameters is presented increasing linear relationship.At last we still got some parameters during the process of drilling. In order to suck allcuttings into chip chamber, the required maximum air flow cannot be lower than1.86m3/min, the final vacuum degree should be more than740Pa (which is solved fromthe inlet of air flow), and the minimum motor power must be more than885W.Some of the parameters and conditions are ignored during the theoretical analysis,numerical simulation and experimental test. Therefore the results of this thesis will notbe definitely right. In the future, we still need optimize calculation parameters andnumerical simulation, improve test process. |
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