Research advances in enhanced coal seam gas extraction by controllable shock wave fracturing

With the continuous increase of mining in depth,the gas extraction faces the challenges of low permeability,great ground stress,high temperature and large gas pressure in coal seam.The controllable shock wave(CSW),as a new method for enhancing permeability of coal seam to improve gas extraction,features in the advantages of high efficiency,eco-friendly,and low cost.In order to better utilize the CSW into gas extraction in coal mine,the mechanism and feasibility of CSW enhanced extraction need to be studied.In this paper,the basic principles,the experimental tests,the mathematical models,and the on-site tests of CSW fracturing coal seams are reviewed,thereby its future research directions are provided.Based on the different media between electrodes,the CSW can be divided into three categories:hydraulic effect,wire explosion and excitation of energetic materials by detonating wire.During the process of propagation and attenuation of the high-energy shock wave in coal,the shock wave and bubble pulsation work together to produce an enhanced permeability effect on the coal seam.The stronger the strength of the CSW is,the more cracks created in the coal is,and the greater the length,width and area of the cracks being.The repeated shock on the coal seam is conducive to the formation of complex network fracture system as well as the reduction of coal seam strength,but excessive shock frequency will also damage the coal structure,resulting in the limited effect of the enhanced gas extraction.Under the influence of ground stress,the crack propagation in coal seam will be restrained.The difference of horizontal principal stress has a significant impact on the shape,propagation direction and connectivity of the CSW induced cracks.The permeability enhancement effect of CSW is affected by the breakage degree of coal seam.The shock wave is absorbed by the broken coal,which may hinder the propagation of CSW,resulting in a poor effect of permeability enhancement.When arranging two adjacent boreholes for CSW permeability enhancement test,the spacing of boreholes should not be too close,which may lead to negative pressure mutual pulling in the early stage of drainage.At present,the accurate method for effectively predicting the CSW permeability enhanced range should be further investigated.

Study on Extraction of Oolong Tea Assisted by Ultrasonic Wave and 4C Technique and Its Application

[Objectives]The extraction conditions of formula oolong tea were investigated by an orthogonal experiment.[Methods]The technical conditions were optimized by the 4C method,and the application of formula oolong tea extract in cigarettes was studied.[Results]①In the experimental range,the best sensory evaluation effect of formula oolong tea extract was obtained with extraction conditions of 70%ethanol as extraction solvent,extraction time h,extraction temperature 25℃,and ultrasonic frequency 80 kHz,and follow-up low-temperature concentration,low-temperature sedimentation and low-temperature centrifugation.②The effects of different centrifugal speeds on the quality of formula oolong tea extract were explored.The formula oolong tea extract obtained under the conditions of 3000 r/min and centrifugal time of 10 min showed the best evaluation effect with soft and delicate smoke,rich smoke fragrance,good comfort and refreshing mouthfeel.③The effective aroma components in the formula oolong tea extract were qualitatively analyzed by GC-MS.[Conclusions]This study provides high-quality raw materials and a theoretical basis for the research of independent flavor blending in cigarette industry enterprises.

Wave Extraction and Attenuation Performance of An Edinburgh Duck Wave Energy Converter

Edinburgh Duck wave energy converter(ED WEC)has excellent energy extraction performance and shows a great potential to integrate with other marine structures.This paper aims to investigate its wave energy extraction performance as a WEC and wave attenuation performance as a protection method for shoreline or marine structures.The wave and ED WEC interactions in regular waves are modeled using the Star-CCM+software and verified by comparisons with published experimental results.The motion response,energy conversion efficiency,and transmission coefficient of the ED WEC with different attack angles,rotation center,and incident wave heights are investigated.Results indicate that the ED WEC with an attack angle of 42°and a rotation center of 0.55 m below the mean water line can achieve both good wave energy extraction and wave attenuation performances.The wave energy extraction and wave attenuation performance of the ED WEC decrease significantly with the increase of wave nonlinearity characterized by the wave steepness.This paper can guide the practical application of the ED WEC at the early stage of design.

Hydrodynamic Performance of An Integrated System of Breakwater and A Multi-Chamber OWC Wave Energy Converter

A multi-chamber oscillating water column wave energy converter(OWC-WEC)integrated to a breakwater is investigated.The hydrodynamic characteristics of the device are analyzed using an analytical model based on the linear potential flow theory.A pneumatic model is employed to investigate the relationship between the air mass flux in the chamber and the turbine characteristics.The effects of chamber width,wall draft and wall thickness on the hydrodynamic performance of a dual-chamber OWC-WEC are investigated.The results demonstrate that the device,with a smaller front wall draft and a wider rear chamber exhibits a broader effective frequency bandwidth.The device with a chamber-width-ratio of 1:3 performs better in terms of power absorption.Additionally,results from the analysis of a triplechamber OWC-WEC demonstrate that reducing the front chamber width and increasing the rearward chamber width can improve the total performance of the device.Increasing the number of chambers from 1 to 2 or 3 can widen the effective frequency bandwidth.

Wave Extraction and Attenuation Performance of A Hybrid System of An Edinburgh Duck WEC and A Floating Breakwater

Installing the Edinburgh Duck Wave Energy Converter(ED WEC)on a floating breakwater provides a potential solution to reduce costs and improve the reliability of the ED WEC.To investigate the interactions between the ED WEC and the breakwater,a two-dimensional numerical model of a hybrid WEC-breakwater system is established based on Star-CCM+Computational Fluid Dynamics(CFD)software.The wave energy extraction performance,wave attenuation performance,and wave forces on the breakwater of the hybrid system are compared with those of the corresponding single device.The effects of the initial attack angle,the distance between the WEC and the breakwater,and the incident wave height on the pitch motion,energy conversion efficiency,transmission coefficient,and wave forces on the breakwater of the hybrid system are analyzed.The results indicate that combing the ED WEC with a breakwater can improve the energy extraction performance of the ED WEC and reduce the wave forces on the breakwater in shorter-period waves.The conversion efficiency of the hybrid system with the initial attack angle of 42°is the largest in shorter-period waves,but is reduced with the increase of initial attack angle in longer-period waves.The wave attenuation performance of the hybrid system is determined by the draft of the breakwater.The distance between the WEC and the breakwater has little effect on the hybrid system.Wave energy extraction of the ED WEC of the hybrid system decreases significantly with the increase of the incident wave height.

A Survey of Gesture Recognition Using Frequency Modulated Continuous Wave Radar

With technology advances and human requirements increasing, human-computer interaction plays an important role in our daily lives. Among these interactions, gesture-based recognition offers a natural and intuitive user experience that does not require physical contact and is becoming increasingly prevalent across various fields. Gesture recognition systems based on Frequency Modulated Continuous Wave (FMCW) millimeter-wave radar are receiving widespread attention due to their ability to operate without wearable sensors, their robustness to environmental factors, and the excellent penetrative ability of radar signals. This paper first reviews the current main gesture recognition applications. Subsequently, we introduce the system of gesture recognition based on FMCW radar and provide a general framework for gesture recognition, including gesture data acquisition, data preprocessing, and classification methods. We then discuss typical applications of gesture recognition systems and summarize the performance of these systems in terms of experimental environment, signal acquisition, signal processing, and classification methods. Specifically, we focus our study on four typical gesture recognition systems, including air-writing recognition, gesture command recognition, sign language recognition, and text input recognition. Finally, this paper addresses the challenges and unresolved problems in FMCW radar-based gesture recognition and provides insights into potential future research directions.

Parameters of Exterior Ballistic Feature Points Extraction in Radar Measurement Data by EMD

The problem of measuring exterior ballistic feature points is always difficult to solve and it is essentiale on exterior ballistic measurement.By analysis of radar reflection characteristics and non-stationary echo signals of exterior ballistic feature points,the echo data of exterior ballistic feature points is measured by using the continuous wave radar.The parameters of feature points are extracted by the empirical mode decomposition method(EMD)of Hilbert-Huang transform(HHT)spectrum analysis technique.The radar echo signal model and EMD extraction model are established to analyze the exterior ballistic mutation point detection and EMD extraction method of aliasing echo signal.Typical feature point parameters of exterior ballistic in rocket flight tests are carried out and the effectiveness of the method is verified.A new method of measuring the parameters of exterior ballistic feature point is therefore presented.

Extraction of copper from copper-bearing biotite by ultrasonic-assisted leaching

Copper-bearing biotite is a refractory copper mineral found on the surface of the Zambian Copperbelt.Biotite is a copper oxide from which copper is extracted by various methods,especially by leaching.Leaching is the process of extracting a substance from a solid material dissolved in a liquid.To improve the efficiency of the leaching process by a more effective method,a new method called ultrasonic-assisted acid leaching is proposed and applied in this study.Compared with regular acid leaching,the ultrasound method reduced the leaching time from 120 to 40 min,and sulfuric acid concentration reduced from 0.5 to 0.3 mol·L^(-1).Besides,leaching temperature could be reduced from 75 to 45°C at the leaching rate of 78%.The mechanism analysis indicates that an ultrasonic wave can cause the delamination of a copper-bearing biotite and increase its specific surface area from 0.55 to 1.67 m^(2)·g^(-1).The results indicate that copper extraction from copper-bearing biotite by ultrasonic-assisted acid leaching is more effective than regular acid leaching.This study proposes a promising method for recycling valuable metals from phyllosilicate minerals.

适用于直流保护的数学形态学降噪与噪声干扰识别方法

柔性直流输电系统是调节我国能源分布不均问题的重要手段,直流保护是保证柔直系统安全的重要技术。现有工程中多采用行波保护作为主保护,然而行波保护存在易受噪声影响、故障波头不易捕捉等问题,制约了其广泛应用。针对上述问题,提出数学形态学降噪与噪声干扰识别方法,并根据直流保护采样信号特点进行参数设计,用于直流保护采样信号降噪和噪声干扰的识别。首先,确定基于自适应多尺度形态滤波的直流信号降噪方法,并设计结构元素长度和形态学滤波器类型、自适应多尺度形态滤波器的滤波器阶数和步长。其次,确定基于形态学梯度变换的噪声干扰识别方法,并设计形态学梯度变换的阈值。接着,从不同角度对形态学降噪方法与现有典型信号处理方法的滤波效果进行对比分析。最后,对形态学降噪与噪声干扰识别方法和保护的配合效果进行验证。形态学降噪与噪声干扰识别方法所需采样频率较低,运算量适中,滤波效果好,对直流保护适用性好。

松软煤层底板爆破致裂增透模拟试验研究及应用

针对松软煤层爆破增透钻孔施工困难,爆破增透产生的裂隙不发育且易于重新压实的问题,提出在底板岩层开展爆破作业,达到松软煤层增透进而增加瓦斯有效抽采时间的目的。为了监测跨界面应力波传播规律及煤层损伤状况,在实验室构建了物理模型并开展了煤层底板爆破相似模拟试验。同时使用数值模拟的研究方法对煤层底板爆破过程中煤、岩体内部的损伤及裂隙的演化过程进行补充。结果表明:松软煤层底板爆破裂纹沿爆破孔向四周岩体扩展,爆破孔位置和底板煤岩交界面以及煤层内部的破坏较为严重,产生跨界面损伤裂纹。爆炸应力波从松软煤层底板岩层传播到松软煤层时,岩体和松软煤体的交界面产生透射压缩应力波和反射拉伸应力波,透射波作用于松软煤体,使煤层裂隙增加;反射波反作用于岩体,在煤岩交界面形成交叉裂纹,使底板岩层裂隙和松软煤层裂隙贯通,有利于松软煤层的瓦斯垂向运移流动和卸压瓦斯抽采。潘一东煤矿现场应用表明,煤层底板爆破增透后瓦斯抽采纯量及其浓度快速上升,抽采纯量从0.06 m^(3)/min提高到1.46 m^(3)/min,增加了23.33倍;瓦斯浓度从爆破前的10.46%上升到45.50%左右,增加了3.34倍,并且长时间维持在较高水平。研究成果可为深部松软煤层瓦斯高效抽采提供理论基础和技术支持。

基于CRS-LMD和SVD的MMC-HVDC线路故障测距方法

直流输电线路故障行波波速不确定、波头提取困难以及噪声干扰等因素制约了直流电网中故障测距技术的应用。为了降低上述因素对定位准确性的影响,提出一种基于局部特征有理样条插值均值分解(LMD based on characteristic rational spline,CRS-LMD)和奇异值分解(singular value decomposition,SVD)的故障测距方法。首先,利用特征尺度选取最优极点系数,结合有理样条插值调节拟合曲线的松紧程度,实现对故障电压行波的局部均值分解。其次,采用奇异值分解对故障行波波头进行准确提取。最后,在PSCAD/EMTDC中搭建了张北±500 kV柔性直流电网的仿真模型,模拟各种故障情况并输出故障数据,利用Matlab对故障数据进行处理并验证定位算法。最后,仿真结果表明,所提故障测距算法在不同故障距离和故障类型下均能实现故障测距,且在叠加噪声和过渡电阻的情况下也能保障较高的精确性。

双浮体直驱波浪发电装置建模分析与基于模型预测控制的能量提取算法研究

基于振荡浮体结构的直驱波浪发电装置具有损耗低、控制灵活等优点,近年来,逐渐成为波浪发电领域的研究热点。双浮体直驱波浪发电装置不需要海上固定平台,能够通过锚系结构在海水中工作,是一种工程可行的直驱波浪发电方案,但其动力学模型更为复杂,相关控制算法缺少实际装置测试。该文通过等效电路的方法对双浮体装置进行建模分析,指出采用张力锚结构可将双浮体装置等效为单浮体装置进行分析,简化控制器的分析与设计,从而建立基于模型预测控制的高效波浪能提取问题。提出一种结合波浪激励力辨识、预测与快速模型预测求解的控制算法,并且设计了双浮体直驱波浪发电装置,在不同波浪条件下进行了相关实验测试。实验结果表明,所提控制算法能够在有效降低运算复杂度的前提下提高装置的波浪能提取效率。

基于贝塞尔曲面拟合的子光斑背景噪声去除方法

受天光背景影响,夏克-哈特曼波前传感器子光斑图像背景光增强,导致子光斑质心位置无法准确提取,使得波前传感器探测精度下降。为提高强天光背景影响下波前传感器探测精度,提出了一种基于贝塞尔曲面拟合的背景噪声去除算法。该算法利用贝塞尔曲面拟合背景噪声,不受拟合基函数约束,实现背景噪声与目标光斑信号的有效分离。仿真和实验结果均表明,所提方法对背景噪声的拟合精度不受目标光斑信号的影响,在保证目标光斑信号完整的前提下,能有效拟合非均匀分布背景噪声,相比传统阈值法、加窗法等,在背信比范围为30至120的强天光背景干扰下,将波前探测精度提升约33%。

基于特征参数分析的中国MPDB工况特征波形获取与应用

为了表征汽车碰撞工况下具有代表性的特征波形,明确相应的乘员损伤响应特征,基于正面50%重叠渐近可变形移动壁障(Mobile Progressive Deformable Barrier,MPDB)碰撞工况4种车型的波形数据,提出一种可行的特征波形处理办法.归纳统计各车型波形的特征参数分布规律,针对样本进行时间和加速度的归一化特征平均处理再进行时间缩放,保持波形形状特征和连续性,获得MPDB工况的特征波形.根据动量守恒定律,将特征波形等效为双梯形波,以满足台车试验和仿真的应用稳定性需求.通过MPDB特征波形和等效双梯形波作用下人体模型的仿真应用,对比分析乘员运动响应与损伤,乘员损伤参数结果相差最小可至1%.结果表明,采用归一化特征平均方法获得的波形时间和强度符合波形样本的特征参数规律,等效双梯形波能够很好地捕捉特征波形作用下的乘员运动损伤响应.

频域特征提取联合双流CNN的轴承故障诊断方法

针对传统方法提取到的轴承各类故障特征混杂,部分类别故障不易区分的问题,设计一种双流卷积神经网络(Convolutional Neural Network,CNN)的故障诊断模型。首先将振动信号转换到频域,为减少低频微弱信号的干扰,过滤频域信号,设定滤波器通带和阻带衰减值以保证信号不失真,进而确定频率带宽,在该带宽值下求得信号振幅占比最大值的范围,同时以正常信号振幅平均值作为高频信号的阈值确定频率最高值。用上述参数分别作为滤波器的参数,过滤信号得到频谱信号和构建时频图像。将提取频谱信号和时频图作为模型两个通道的输入,在卷积层和池化层后加入特征融合层,通过加权融合的方式将两个通道的特征融合,使得各类故障特征区分度显著提高。实地搭建故障平台采集数据验证,实验结果表明,该方法能提取到每类故障独有的特征,轴承故障识别准确率达到98.95%。

基于连续太赫兹波频谱信息提取方法研究

调频连续太赫兹系统受激励器件限制导致其带宽普遍较窄,在检测样件时由于单点处数据量有限,存在不易提取特征信号的问题,针对此问题,本文提出了一种基于Kaiser窗的线性调频z变换算法。首先对原始信号进行加窗处理,采用线性调频z变换对不同样件中深度缺陷特征信号进行提取,引入不同信号处理方法进行比较分析,结果可得本文提出方法在有限的数据量中保留样件特征信息的同时,降低了计算复杂度,通过与不同种复合材料检测数据处理对比,证明了该方法的有效性与普适性。

蓝莓酒渣不同提取方法对花青素含量的影响

以蓝莓、果酒及酒渣为原料,分析果酒酿造整个过程中花青素含量及抗氧化活性。采用甲醇、乙醇、丙酮有机溶剂,果胶酶、纤维素酶、淀粉酶、酸性和中性蛋白酶、超声波、微波以及溶剂-微波、溶剂-超声波复合不同提取方法,对蓝莓酒渣中的花青素预处理不同方法进行比较分析。实验结果表明,酒渣中花青素提取以柠檬酸作为提取酸、100%乙醇为提取液,无水乙醇与柠檬酸的比例为2∶8,再加入400 W超声波进行提取,提取的花青素含量最高,为123.35 mg·100 g^(-1)。在发酵的过程中,花青素含量、总酚以及DPPH自由基清除能力排序:蓝莓>蓝莓酒渣>蓝莓酒。

基于变分模态提取的动力响应重构方法研究

基于经验模态分解的响应重构方法依赖于参数繁多的带通滤波器,且不适用于具有密集模态的结构,因此,提出一种基于变分模态提取的动力响应重构方法。首先,在时域内使用变分模态提取将由传感器测得的动力响应分解为各阶模态响应;随后,通过根据有限元建模或模态试验导出的模态转换矩阵计算得到响应未知位置的各阶模态响应,再根据模态叠加法完成其余位置动力响应的重构;最后,对非密集模态的悬臂梁和密集模态的3层剪切框架进行数值模拟,并通过简支梁进行试验分析,验证了所提方法的有效性和较好的鲁棒性。

基于空间属性特征的毫米波雷达身体干扰识别

手势识别中,身体的移动容易被误判为手势动作,对手势识别造成干扰。因此,针对存在的身体干扰问题,提出了基于空间属性特征的身体干扰识别算法。在对毫米波雷达接收信号进行预处理后,首先分别对一维距离像和二维距离角度谱提取一维潜在目标和二维潜在目标,并对二维潜在目标进行连通域标记。然后,基于潜在目标及连通域提取出用于区分身体干扰和手势目标的空间属性特征。最后,采用支持向量机(support vector machine,SVM)分类器进行身体干扰识别。实验结果表明,所提方法能有效区分身体干扰和手势目标,单帧预测下准确率为97.3%,多帧预测下准确率为98.94%。

波浪式拖管法铺设海底管道力学性能研究

海底管道铺设是海洋油气资源开发的重要环节,传统的拖管法不能很好地适应海洋深度和复杂环境的变化。针对Acergy公司在Girassol项目中提出的一种波浪式拖管方法,对其应用于2.0 km长海底管道铺设进行分析。首先,结合深水海洋环境特征,采用集中质量法建立管道拖航数值模型,并介绍管道、拖缆和浮筒力学计算及水动力荷载计算方法;其次,基于非线性有限元OrcaFlex软件对拖管过程建模,以模拟实际项目拖管过程;然后,通过对比相同条件下的单波式和双波式两种拖管方式,探讨管道和拖缆的动态力学性能变化;最后,针对不同浮重比、拖航速度、拖缆长度和悬垂角、海流流速和流向角等因素展开敏感性分析。结果表明:波浪式拖管法可以有效地降低施工时对拖缆的张力需求,但也会因此增加管道局部弯矩和应力响应;相对于单波式拖管,双波式拖管在缓解由于拖航速度等变化而产生的管道局部损伤效应上更有优势,并能较好地适应不同水深环境;复杂的海流工况对拖航时管道的力学性能影响十分显著,施工前应选择合适的铺设窗口期以防止管道产生损伤。