【作者】 潘岩；

【导师】 马飞；

【作者基本信息】 北京科技大学 ， 机械工程， 2021， 博士

【摘要】 随着矿产资源需求的增加和陆地矿产资源的日趋减少,深海矿产资源开采已成为国家重大发展需求。作为深海资源勘探开发装备中的关键技术,射流技术在结核采集系统中发挥了重要作用,其中,自振射流具有强烈的振荡特性和空化作用,在高围压下可显著提高冲蚀效果。然而在深海高围压条件下,自振射流频率特性难以预测、高频振荡及其冲蚀行为未得到深入研究,现有理论模型与实际射流动力学特性之间联系不强,无法对射流的实际打击冲蚀行为进行指导,严重制约了自振射流技术在围压下的应用。针对围压下自振射流频率特性及冲蚀行为研究过程中存在的关键问题,本文首先对射流装置的声谐固有频率特性开展理论分析,并基于不同建模方法建立理论模型。通过围压下自振射流冲击试验,获取自振射流的全频谱结构,揭示了射流自激频率的影响因素及变化规律,最终建立实际射流的频率模型,并据此对射流高频振荡模态进行了深入分析。基于自振射流冲蚀试验,研究了自振射流的冲蚀模式,进一步探究了射流冲蚀行为的影响因素及变化规律。主要研究内容如下:(1)为解决现有理论模型过于简化的问题,对射流装置理论模型开展研究。首先对射流装置声谐固有频率特性进行理论分析,基于装置结构的谐振特性,采用不同建模方法分别对管网结构和喷嘴谐振腔建立频率特性数学模型,探明装置声谐固有频率的宽带特征及频率范围。(2)为解决理论模型与实际射流动力学特性之间存在脱节的问题,对实际射流频谱特征展开研究。通过围压下自振射流冲击试验,基于信号分析方法,获取射流的全频谱结构。自振射流频率特性包括低频脉动与高频振荡,其诱发机理分别为管网内流体扰动与喷嘴出口处流体涡激振动,二者影响因素与应用条件均有较大差别。射流的全频谱结构为不同围压下自振射流频率特性的研究提供了理论支撑。(3)在获取自振射流全频谱结构的基础上,对围压下射流的高频振荡特性展开研究。通过对射流频率理论计算公式及相关因素的分析,确定了斯特劳哈尔数对射流频率计算的重要作用。依据三波共振理论确定射流自激频率及斯特劳哈尔数,通过研究斯特劳哈尔数的影响因素及变化规律,获得了斯特劳哈尔数随空化数的变化关系;依据流体相似理论,建立实际射流自激频率的估算模型,该模型为自振射流振荡模态分析奠定了理论基础。(4)基于射流自激频率的估算模型,开展了射流高频振荡模态研究。首先依据射流装置谐振特性与理论模型,改变喷嘴装置结构参数,使其产生特定声谐固有频率;其次,改变射流工作参数,使射流振荡频率分别与装置不同声谐固有频率相匹配,产生多种振荡模态。重点分析了次谐波共振及基频共振的发生机理及振荡效果,探究了射流高频振荡模态调制的可行性。(5)在自振射流振荡模态可调的前提下,基于冲蚀试验法对射流冲蚀行为展开研究,获得自振射流冲蚀效果随环境参数的变化规律,定义了自振射流的三种冲蚀模式,并研究得到不同冲蚀模式的演化规律及生成机理;结合射流声谐共振特性,分析得到射流冲蚀行为与高频振荡特性的联系。在此基础上,针对围压条件下喷嘴下游边界结构及靶盘倾斜角对射流冲蚀行为的影响展开研究,分析各因素的影响规律,为围压下自振射流的空化冲蚀应用提供了参考。更多还原

【Abstract】 With the increasing demand of mineral resources and the decreasing of land mineral resources,deep-sea mineral resources exploitation has become a major development demand of the country.As the key technology in deep-sea resources exploration and development equipment,jet technology plays an important role in the tuberculosis collection system,among which,the self-resonating jet has strong oscillation characteristics and cavitation effect,and can significantly improve the erosion effect under high confining pressure.However,under the condition of deep-sea high-confining pressure,the frequency property of the self-resonating jet are difficult to predict,high frequency oscillation and erosion behavior have not been studied in depth.The relationship between the existing theoretical model and the actual jet dynamics is not strong,which can not guide the actual impact erosion behavior of the jet,which strictly restrict the application of the self-resonating jet under confining pressure.In order to solve the key problems in the research on the frequency property and erosion behavior of self-resonating jet under confining pressure,in this paper,the acoustic natural frequencies of the device are carried out theoretically firstly,and theoretical models are established based on different modeling methods.Through the impinging experiment under high confining pressure,the full spectrum structure of self-resonating jet is obtained,and the influencing factors and variation rules of self-excited frequency of jet are revealed.Finally,the frequency model of the actual jet is established,and the high-frequency oscillation modes of jet are analyzed.Based on the erosion experiment of self-oscillating jet under high confining pressure,the jet’s erosion patterns are explored,and the influencing factors and changing rules of jet erosion behavior as cavitation number and impinging distance varies are further revealed.The main research contents are as follows,(1)In order to solve the problem that the theorectical model is too simplified,the theoretical model of the system device is studied.Firstly,the acoustic natural frequency of the device are analyzed theoretically.Based on the resonance characteristics of the device structure,the mathematical models of the pipe network structure and the nozzle resonator are established by using different modeling methods,respectively,and the broadband property and frequency range of the device are verified.(2)In order to solve the problem of disconnection between the theoretical model and the dynamic characteristics of the actual jet,the frequency spectrum of the actual jet are studied.The full spectrum structure of the jet is obtained through the jet impinging test under confining pressure and based on the signal analysis method.The frequency property of the self-resonating waterjet includes low-frequency pulsation and high-frequency oscillation,which are induced by fluid disturbance in pipe network and vortex-induced-vibration at nozzle outlet,respectively.The influencing factors and application conditions of these two types of oscillation are quite different.The full frequency spectrum provides a theoretical support for further study of the frequency property of the self-resonating jet under confining pressure.(3)On the basis of obtaining the full frequency spectrum of the self-resonating jet,the high-frequency oscillation characteristics of the jet are mainly studied.Through the analysis of the theoretical formula of the jet oscillating frequencies and the related factors,the important role of the Strouhal number in the calculation of the jet oscillating frequency is determined.According to the "triad resonance"theory,the fundamental frequency and the according Strouhal number of the jet are determined.By studying the influence factors and variation rules of Strouhal number,the relationship between the Strouhal number and the cavitation number is obtained.Based on the fluid similarity theory,an estimation model of the self-excited frequency of the actual jet is established,which lays a theoretical foundation for the oscillation mode analysis of the self-resonating jet.(4)Based on the estimation model of the self-excited frequency,the jet oscillation modes are studied,and the feasibility of high frequency oscillation mode modulation is explored.Firstly,according to the resonance characteristics and theoretical model of the jet device,the nozzle structure is designed to produce specific acoustic harmonics.The working parameters of the jet are modified to make the jet oscillation frequencies match with different acoustic harmonics of the device to produce a variety of oscillation modes.The mechanism and oscillation effect of subharmonic resonance and fundamental resonance are mainly analyzed,the feasibility of effective modulation of jet oscillation mode is explored.(5)On the premise that the oscillation modes of self-resonating jet can be modulated,the erosion behavior of self-resonating jet is studied based on the erosion experiments,and the variation law of the jet’s erosion effect with environmental parameters is obtained.Three erosion modes of self-resonating jet are defined,and the evolution law and generation mechanism of different erosion modes are studied.On this basis,the influence of nozzle downstream boundary structure and target tilt angle on jet erosion behavior under confining pressure is studied,and the influence law of various factors is obtained,which provides experimental reference for cavitation erosion of self-resonating jet under confining pressure.更多还原