Design And Experimental Study On Self-synchonizing Subglacial Sediment Vibrocorer

Sediments beneath the Antarctic ice shelves,ice streams,and subglacial lakes can contain important paleo-climatic and paleo-environmental records,which can offer a long-term perspective on Antarctic ice sheet retreat history and sub–ice shelf ocean circulation patterns.In addition,these sediments also provide the new opportunities for study on microbial life forms in extreme environment and for primitive life forms exploration.At present,subglacial sediment sampling in Antarctic mainly relies on hot-water drilling projects.The sampling devices should first pass through the pre-drilled access hole and reach to the water floor,then sediment sampling process can be started.Unique working condition put forward series technological challenges for sampler selection and designing.In this paper,we analyzed the technological characteristics of subglacial sediment sampling in Antarctic,then summarized the technical problems exist in this research field.Finally,we combined the research status of corers working in conventional and subglacial conditions,proposed the design scheme of selfsynchronizing subglacial sediment vibrocorer.The main achievements of this thesis are as following:1.The general vibrocorer structure designed according to the relevant parameter requirements of Chinese ‘863' project ‘Key Technology and System Development of Ice Shelf Hot Water Drilling System'.Vibrocorer includes four main units: water-proof pressure chamber,vibrator,core-barrel unit and spring buffer.The four units were designed one by one based on their logical sequence.In the design process of vibrator,we utilized the self-synchronous theory of dual-mass vibrating machine that allowed to compress the vibrocorer radial size.Finally,structure parameters of vibrocorer are as follows: maximal radial size 270 mm,total length 4.3m,it weighs 203 kg and designed for sampling 3m length,94 mm sediment core,total power 400 W.2.Based on the ANSYS Workbench simulation and analysis platform,we simulated load state of the vibrating pressure chamber working in 2200 m water depth,built static structural and transient structural finite element analysis models to evaluate the model mechanical response under static and static-dynamic load.We found the stress dangerous zone under static pressure load on pressure chamber,and then original design was improved on the base of the analysis results.The next stage of simulation included application and analyzing of water pressure and vibration combine load(vertical vibration and water pressure;horizontal vibration load)in the structural analysis module.Finally,the pressure resistance ability under combination load of water pressure and vibrations was verified.3.The subglacial sediment sampling simulation test stand was developed in order to test the synchronous performance and sampling ability of the vibrocorer.The experiment results showed that: The experiment results showed that:(1)the vibrocorer can reach to synchronous states rapidly both in suspending and penetrating status,0-46.5Hz converterable vibrating frequency,average 1.33 gravity acceleration amplitude;(2)under the condition that simulated sediment composition is similar to the Antarctic subglacial sediments,the vibrocorer can penetrate to the depth of more than 3m providing low compressed sediment cores and well-keeping water-sediment interface;(3)comparing with gravity coring,penetration depth of vibrocoring was twice deeper.4.The vibrocorer can achieve three different vibration modes: vertical,horizontal and alternative vibrations.Experiments with different vibrating modes were carried out using simulation test stand.The experiment results showed that vibration mode changing influences on rate of penetration of the vibrocorer.Among the three different modes,alternative vibration showed the highest average rate of penetration which can reach as high as 77.8mm/s,horizontal and vertical vibration showed lower rate averaging 71.2mm/s and 54.9mm/s,respectively.Vibrocorer can penetrate 3m depth in 80 s under all of these three vibration modes.Further,after the core barrel penetrated into the sediments,appropriate transform the vibration modes can be helpful to enhance the penetration abilityAt present,China is increasing investments on research of Antarctic region and the coming years Chinese hot-water drilling project will be carry out at Amery ice shelf,Antarctica.Self-synchronous subglacial sediment vibrocorer proposed in this paper was designed and aimed to the ‘863' project ‘Key Technology and System Development of Ice Shelf Hot Water Drilling Rig'.With the finite element analysis and the field experiment testing results,preliminary verified the feasibility of vibrocorer structure design and working principle.This study will provide important reference value for devices development of Antarctic subglacial sediment sampling.