空化声震效应对煤体温度及应力分布的影响研究

发布时间：2018-03-16 07:31

本文选题：空化水射流　切入点：声震效应　出处：《重庆大学》2015年硕士论文　论文类型：学位论文

【摘要】：煤矿浅部资源随着持续开采即将耗尽,煤矿开采必然向深部转移,含瓦斯煤层微孔隙、低渗透性、高吸附导致难以开采的难题愈发明显。高压水射流割缝卸压增透技术在煤矿瓦斯抽采中已经比较广泛地应用,产生的空化声震效应能强化瓦斯解吸与促进渗流。但是目前空化声震效应对煤体瓦斯的影响机理还尚未完全研究清楚,例如声波是如何作用煤体,横波与纵波进入煤体后对煤体结构产生的影响,对煤体的抗拉强度,抗剪强度的影响,以及热效应的影响机理等还未见相关报道。本文通过理论分析、数值模拟与实验验证相结合的方式,对空化水射流空化声频的频率特性、空化声震对煤体应力的影响以及对煤体温度的影响进行研究,其取得的主要成果有:①通过对空化水射流声震效应进行了声波特性研究,理论分析了空化声震的机械振动与热效应对煤体温度应力的影响,空化声震产生的空化声波进入煤体后会对煤体产生拉伸与剪切的交替作用,使煤体所受有效应力发生变化,煤基质收缩;同时空化过程中产生的热效应使得煤体温度提高,使煤体内瓦斯分子从吸附态转向游离态,空化过程中产生的温度越高,解吸的瓦斯气体愈多。②分析了空化声波进入煤体后能量的传播过程,得到空化声波在煤体中传播的能量方程;在假设能量传递过程中衰减全部转换为热效应的情况下,得到煤体受到空化声震的机械振动作用后的应力变化方程与空化声震热效应的煤体温度变化方程。③通过对空化声震的声频功率谱进行统计分析,得到不同空化数下(围压与泵压的不同的组合)声频的分布特征。采用COMSOL数值模拟软件分析了不同空化声频下对煤体应力及温度变化规律。得到了空化声震下煤体的呈交替正负的声压分布特征;空化声震机械振动作用对煤体有效应力提高0.8MPa~1.2MPa,由于声波反射与衰减的原因,煤体应力呈轴对称交替分布,有效应力的提高与声频呈正向关系;在温度方面,煤体温度上升在不同的声频下表现不同,在低频阶段上升速度先小后大,在高频阶段没有这样的趋势而保持上升速度较为稳定。同时温度提高在5~8度之间,声频越高,热效应越明显。温度的分布呈由内向外逐级减小的趋势。④开展了不同空化数下声震效应的振动测试、空化声震效应对煤体温度与瓦斯渗流的影响实验研究。不同空化数能产生不同的空化集中声频,影响煤体温度及应力的主要的空化声频集中在2000Hz~6000Hz;通过不同空化数下的煤体温度实验表明,空化声震热效应促使温度提高4~5摄氏度,与数值模拟结果较为吻合;煤体渗透率随着空化数的增加而减小,拟合出渗透率与空化数之间的关系式。
[Abstract]:With the continuous exploitation, the shallow resources of coal mine will be exhausted, and the coal mining will inevitably transfer to the deep, and the gas-bearing coal seam will have micropores and low permeability. It is more and more obvious that the difficult problem of mining is caused by high adsorption. The pressure relief and antireflection technology of high pressure water jet cutting joint has been widely used in coal mine gas drainage. The cavitation acoustic shock effect can enhance gas desorption and promote seepage. However, the mechanism of cavitation acoustic shock effect on coal gas has not been fully studied, such as how sound wave acts on coal body. The influence of shear wave and longitudinal wave on coal structure, the influence of shear strength and shear strength on coal structure, and the influence mechanism of thermal effect have not been reported in this paper. The frequency characteristics of cavitation frequency of cavitation water jet cavitation, the influence of cavitation acoustic shock on the stress of coal body and the influence of coal temperature on cavitation water jet cavitation frequency are studied in combination of numerical simulation and experimental verification. The main achievements are as follows: (1) the acoustic wave characteristics of cavitation water jet are studied through the acoustic shock effect of cavitation water jet, and the influence of mechanical vibration and thermal effect of cavitation acoustic shock on the thermal stress of coal body is theoretically analyzed. The cavitation sound wave produced by cavitation acoustic shock will produce alternating action of stretching and shearing on the coal body when it enters the coal body, so that the effective stress of the coal body changes and the coal matrix shrinks. At the same time, the thermal effect in the cavitation process increases the temperature of the coal body. The gas molecules in coal are changed from adsorption state to free state. The higher the temperature produced in cavitation process, the more gas gas desorbed. 2. The energy propagation process after cavitation sound wave enters coal body is analyzed. The energy equation of cavitation sound wave propagating through coal body is obtained. Under the assumption that the decay of cavitation sound wave is converted into thermal effect during the energy transfer process, The stress change equation of coal body subjected to mechanical vibration of cavitation acoustic shock and the temperature change equation of coal body under cavitation acoustical shock heat effect are obtained by statistical analysis of acoustic power spectrum of cavitation acoustic shock. The distribution characteristics of audio frequency under different cavitation numbers (different combinations of confining pressure and pump pressure) are obtained. The variation of stress and temperature on coal body under different cavitation acoustic frequency is analyzed by using COMSOL numerical simulation software, and the coal under cavitation acoustic shock is obtained. The sound pressure distribution of the body is positive and negative alternately. The mechanical vibration of cavitation acoustics increases the effective stress of coal body by 0.8 MPa and 1.2 MPa. Due to the reflection and attenuation of acoustic wave, the stress of coal body is distributed alternately axisymmetrically, and the increase of effective stress is positively related to the sound frequency. The temperature rise of coal body is different under different audio frequency. The rising speed of coal body is first small and then large in low frequency stage, but it is stable in high frequency stage without such trend. At the same time, the higher the audio frequency is when the temperature is increased between 5 degrees and 8 degrees, The more obvious the thermal effect is, the smaller the temperature distribution is from inside to outside, .4 the vibration measurement of acoustic shock effect under different cavitation numbers is carried out. Experimental study on the effect of cavitation Acoustic shock effect on Coal temperature and Gas seepage. Different cavitation numbers can produce different cavitation concentrated audio frequency. The main cavitation sound frequency affecting the temperature and stress of coal body is 2000Hz0 6000Hz.The experimental results show that the thermal effect of acoustical shock of cavitation makes the temperature increase by 4 ~ 5 degrees Celsius, which is in good agreement with the results of numerical simulation. The permeability of coal decreases with the increase of cavitation number, and the relationship between permeability and cavitation number is fitted.
【学位授予单位】：重庆大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TD311;TD821

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