Penetration-Type Lunar Regolith Coring Technique Based On Particle Unidirectional Flow Effect

The collection and analysis of lunar regolith,is an important part of lunar resources exploration and can also provide a reliable technical support for the oncoming lunar basement's establishment and lunar resources' exploration.Compared with loose and disorderly lunar regolith sample,the profile sample with stratification information will be a better choice for sampling missions,because it can reflect more geological structures,the evolution history,and the distribution of in-situ mineral resources.Currently,there are two main methods to collect the lunar profile regolith,the drilling-type coring and the penetration-type coring,in which the first one is more widely used in application.In drilling into deep lunar regolith with a high compaction state,it often needs to employ a percussive motion that may lead to a serious disturbance of its stratification structure.Generally,the penetrating ability of penetration type coring is not a good choice compared with drilling type coring.However,it has a great advantage with a light weight and can keep soil a good stratification due to its simple structure.It should be noted that in penetration type coring the sample is easily to be blocked in the coring tube increasing the penetration resistance,reducing the filling rate,and may also resulting in a difficult pulling finally.To solve above difficulties,this thesis,based on the unidirectional flow effect of particles,proposes a novel method to reduce the coring resistance and increase coring efficiency.By using the visual simulation technology in discrete element method,the mechanism of unidirectional flow of lunar regolith at the asymmetric interface of longitudinal vibration was revealed,and the influence of vibration parameters,interface parameters,particle size and morphology on the unidirectional flow performance was analyzed then.Based above theoretical analysis,a prototype of this novel sampler and its testing system were developed.Finally,the coring efficiency of this proposed sampling method was investigated in experiments.By modeling the physical model of the interaction between coring tube and lunar regolith,the mechanism of penetration-type coring and the cause of high resistance and low filling rate are analyzed,respectively.By establishing the coring load model,the coring tube's structure parameter can be optimized and the limit sampling capacity can be predicted.Herein,an effective method to reducing the resistance and to increasing the coring efficiency based on the particles' unidirectional flow effect was proposed.A simplified mechanical model describing unidirectional flow was established which enhanced the feasibility of this proposed method.In addition,a coring efficiency evaluation index system was also established to quantify the resistance reduction and efficiency improvement of the new method.It is easily to understand that an object can be pushed upward along the slope by applying a horizontal force on it,in which the required forces are determined by the slope degrees.According to this principle,an asymmetric functional interface that can realize a unidirectional flow of particles under the condition of longitudinal simple harmonic vibration was designed in this paper.Its working functions can be verified by experiments.A discrete element simulation model of the interaction between asymmetric functional interface and lunar regolith was established to simulate the behavior and explain the mechanism of unidirectional flow of particles.The effects of interface parameters,vibration parameters,particle size and morphology on the unidirectional flow performance were studied by the discrete element simulation.Based on the test design method of Box-Behnken response surface,the regression equations between the vibration parameters and the principle interface parameters,the unidirectional flow velocity,and the flow region were established to provide guidance for the optimal design of coring tube interface parameters.Based on the established coring load model and the unidirectional flow of particles regression equations,the coring tube structure and its optimal design of interface parameters are developed.A prototype of sampler and its coring efficiency test system are also developed.A lunar regolith profile simulant was prepared by a three-dimensional vibration compacting process,by which the coring verification experiments were carried out.Compared with the traditional impact-type coring,the actual resistance reduction and efficiency performance of the sampler were both verified,and the influences of the procedure parameters(amplitude,frequency and axial pressure)on the coring efficiency were analyzed.This thesis proposed a penetration-type coring method based on the unidirectional flow effect of lunar particles to reduce the resistance and to increase the coring efficiency.By researching on the particle unidirectional flow characteristics,the quantitative relationship between the vibration parameters,the significant interface parameters,and the particle unidirectional flow velocity along with flow region are acquired.Based the theoretical model,a prototype of sampler was developed.Verification experiments show that this method has a higher efficiency than the traditional impact penetration-type coring.It can be inferred that this research results can provide a new scheme method for the future high-efficiency collection of lunar regolith profile sample.