Blast wave characteristics of multi-layer composite charge:Theoretical analysis,numerical simulation,and experimental validation

This article investigates the characteristics of shock wave overpressure generated by multi-layer composite charge under different detonation modes.Combining dimensional analysis and the explosion mechanism of the charge,a peak overpressure prediction model for the composite charge under singlepoint detonation and simultaneous detonation was established.The effects of the charge structure and initiation method on the overpressure field characteristics were investigated in AUTODYN simulation.The accuracy of the prediction model and the reliability of the numerical simulation method were subsequently verified in a series of static explosion experiments.The results reveal that the mass of the inner charge was the key factor determining the peak overpressure of the composite charge under single-point detonation.The peak overpressure in the radial direction improved apparently with an increase in the aspect ratio of the charge.The overpressure curves in the axial direction exhibited a multi-peak phenomenon,and the secondary peak overpressure even exceeded the primary peak at distances of 30D and 40D(where D is the charge diameter).The difference in peak overpressure among azimuth angles of 0-90°gradually decreased with an increase in the propagation distance of the shock wave.The coupled effect of the detonation energy of the inner and outer charge under simultaneous detonation improved the overpressure in both radial and axial directions.The difference in peak overpressure obtained from model prediction and experimental measurements was less than 16.4%.

Efficient oil-water separation by novel biodegradable all cellulose composite filter paper

Industrial production and domestic discharge produce a large amount of oily wastewater, which seriously affects the stability of the ecological environment. Membrane separation technology provides another path to treating oily wastewater. And appropriate surface modification of the membrane helps to achieve high efficiency of treating oily wastewater. With green, economy and stability been more concerned.The focal research reports a completely biodegradable all cellulose composite filter paper(ACCFP) composed of Ⅰ-cellulose macrofibers and Ⅱ-cellulose matrix. It is a simple one-step impregnation method to adjust the surface microstructure of the pristine filter paper(PFP), and it does not involve with chemical reaction. The pre-wetted ACCFP consist of Ⅱ-cellulose hydrogel and Ⅰ-cellulose reinforcement in the process of oil-water separation. This layer of hydrogel is the fundamental to underwater superoleophobicity, which determines their eligibility for applications of efficient oil-water mixture or oil-in-water(oil/water) emulsion separation. The separation efficiency of oil-water mixture and oil/water emulsion exceed 95% and 99.9%, respectively. In addition, excellent mechanical properties of ACCFP in dry and wet conditions ensure its stability in service and prolong service life in applications. The focal study provides a new method for high-performance oil-water separation and it is more in line with sustainable chemistry.

Low-Velocity Impact Response of Stitched Multi-layer Foam Sandwich Composites

Low-velocity impact damage known as“imperceptible”damage usually destroys the structural integrity of the material and seriously affects the service life of the materials.To improve the low-velocity impact resistance of foam sandwich composites,an innovative concept of a stitched multi-layer sandwich structure by organically combining the discrete splitting of foam layer with full thickness stitching was proposed,and its low-velocity impact resistance obtained through drop-hammer impact tests was explored.The results showed that the multi-layer foam sandwich structure acted as a stress disperser and reduced the irreversible impact damage.The depth and area of low-velocity impact damage of multi-layer foam sandwich composites gradually decreased with increasing the number of the layers.The stitched structure would improve the integrity of the foam sandwich composites and inhibit the propagation of cracks.The maximum impact load of the stitched foam sandwich composite increased by approximately 5% compared with that of the non-stitched material.In addition,the low-velocity impact damage depth,damage area and absorbed energy of the stitched three-layer foam sandwich composite were reduced by 37.7%,34.6% and 20.7%,respectively,compared with those of the non-stitched single-layer sandwich material.

Experimental and Computational Study of the Microwave Absorption Properties of Recycled α-Fe2O3/OPEFB Fiber/PCL Multi-Layered Composites

The aim of this study was to fabricate multi-layered recycled α-Fe2O3/OPEFB fiber/PCL composites for microwave absorbing applications in the 1 - 4 GHz frequency range. The multi-layered composites were 6 mm thick and each consisted of a 2 mm thick layer of recycled α-Fe2O3/PCL composites at various loadings (5 wt% - 25 wt%) of 16.2 nm recycled α-Fe2O3 nanofiller, placed between two layers of 2 mm thick OPEFB fiber/PCL composites blended at a fixed ratio of 7:3. The real (ε') and imaginary (ε") components of the relative complex permittivity were measured using the open-ended coaxial probe technique and the values obtained were applied as inputs for the Finite Element Method to calculate the reflection coefficient magnitudes from which the reflection loss (RL) properties were determined. Both ε' and ε" increased linearly with recycled α-Fe2O3 nanofiller content and the values of ε' varied between 3.0 and 3.9 while the ε" values ranged between 0.26 and 0.64 within 1 - 4 GHz. The RL (dB) showed the most prominent values within the 1.38 - 1.46 GHz band with a minimum of -38 dB attained by the 25 wt% composite. Another batch of minimum values occurred in the 2.39 - 3.49 GHz range with the lowest of -25 dB at 2.8 GHz. The recycled α-Fe2O3/OPEFB fiber/PCL multi-layered composites are promising materials that can be engineered for solving noise problems in the 1 - 4 GHz range.

Bilateral Filter for the Optimization of Composite Structures

In the present study,we propose to integrate the bilateral filter into the Shepard-interpolation-based method for the optimization of composite structures.The bilateral filter is used to avoid defects in the structure that may arise due to the gap/overlap of adjacent fiber tows or excessive curvature of fiber tows.According to the bilateral filter,sensitivities at design points in the filter area are smoothed by both domain filtering and range filtering.Then,the filtered sensitivities are used to update the design variables.Through several numerical examples,the effectiveness of the method was verified.

Endpoint forecasting on composite regeneration by coupling cerium-based additive and microwave for diesel particulate filter

Numerical simulation has been carried out to investigate the major factors affecting the time of composite regeneration due to coupling cerium-based additive and microwave for diesel particulate f3ilter(DPF). Effect on the composite regeneration time from various factors such as mass flow rate of exhaust gas, temperature of exhaust gas, oxygen concentration of exhaust gas, microwave power and amount of cerium-based additive are investigated. And a mathematical model based on fuzzy least squares support vector machines has been developed to forecast the endpoint of the composite regeneration. The results show that the relative error of endpoint forecasting model of composite regeneration is less than 3.5%, and the oxygen concentration of exhaust gas has the biggest effect on the endpoint of composite regeneration, followed by the mass flow rate of exhaust gas, the microwave power, the temperature of exhaust gas and the amount of cerium-based additive.

Design of Miniaturized Band-Pass Filter with Composite Right/Left-Handed Transmission Line

In this paper, a new miniaturized wide-pass-band filter at U band based on composite right/left- handed transmission line (CRLH TL) is implemented. The CRLH TL contributed to a broadband filter is a balanced structure with a small size of only 1.428 mm*0.5530 mm. The frequency characteristics are simulated and the results show that the 3 dB band width of the proposed filter is about 13.5 GHz from 45.8 GHz to 59.3 GHz. The insertion loss is quite flat through the pass-band and the return loss is relatively low.

Mechanical Properties of Composite SiNx/DLC Films Prepared by Filtered Cathodic Arc of Graphite Incorporated with RF Sputtering of Silicon Nitride

Composite SiNx/DLC films were deposited on Si substrate by RF magnetron sputtering of silicon nitride (Si3N4) target simultaneously with filtered cathode arc (FCA) of graphite. The RF power was fixed at 100 W whereas the arc currents of FCA were 20, 40, 60 and 80 A. The effects of arc current on the structure, surface roughness, density and mechanical properties of SiNx/DLC films were investigated. The results show that the arc current in the studied range has effect on the structure, surface roughness, density and mechanical properties of composite SiNx/DLC films. The composite SiNx/DLC films show the sp3 content between 53.5% and 66.7%, density between 2.54 and2.98 g/cm3, stress between 1.7 and 2.2 GPa, and hardness between 35 and 51 GPa. Furthermore, it was found that the density, stress and hardness correlate linearly with the sp3 content for composite SiNx/DLC films.

Microstructure and mechanical properties of Al/Cu/Mg laminated composite sheets produced by the ARB proces

In the present study, an Al/Cu/Mg multi-layered composite was produced by accumulative roll bonding(ARB) through seven passes, and its microstructure and mechanical properties were evaluated. The microstructure investigations show that plastic instability occurred in both the copper and magnesium reinforcements in the primary sandwich. In addition, a composite with a perfectly uniform distribution of copper and magnesium reinforcing layers was produced during the last pass. By increasing the number of ARB cycles, the microhardness of the layers including aluminum, copper, and magnesium was significantly increased. The ultimate tensile strength of the sandwich was enhanced continually and reached a maximum value of 355.5 MPa. This strength value was about 3.2, 2, and 2.1 times higher than the initial strength values for the aluminum, copper, and magnesium sheets, respectively. Investigation of tensile fracture surfaces during the ARB process indicated that the fracture mechanism changed to shear ductile at the seventh pass.

Generating multi-layer nested chaotic attractor and its FPGA implementation

Complex chaotic sequences are widely employed in real world, so obtaining more complex sequences have received highly interest. For enhancing the complexity of chaotic sequences, a common approach is increasing the scroll-number of attractors. In this paper, a novel method to control system for generating multi-layer nested chaotic attractors is proposed.At first, a piecewise(PW) function, namely quadratic staircase function, is designed. Unlike pulse signals, each level-logic of this function is square constant, and it is easy to realize. Then, by introducing the PW functions to a modified Chua's system with cubic nonlinear terms, the system can generate multi-layer nested Chua's attractors. The dynamical properties of the system are numerically investigated. Finally, the hardware implementation of the chaotic system is used FPGA chip.Experimental results show that theoretical analysis and numerical simulation are right. This chaotic oscillator consuming low power and utilization less resources is suitable for real applications.

Choice of reference surfaces for machined surface roughness in milling of SiC_p/Al composites

In order to choose the appropriate reference surface on the machined surface roughness of Si Cp/Al composites, the cutting experiments of Si Cp/Al composites were carried out, and the machined surface topography was measured by OLS3000 Confocal laser scanning microscope. The 3D measured data of machined surface topography were analyzed by the area power spectrum density. The result shows that the texture of machined surface topography in milling of Si Cp/Al composites is almost isotropic. This is the reason that the values of Rq at different locations on the same machined surface are obviously different. Through the comparison of performance of different filtering methods, the robust least squares reference surface can be used to extract the surface roughness of SiC p/Al composites effectively.

Edge Detection of Composite Insulators Hydrophobic Image Based on Improved Canny Operator

The detection of hydrophobicity is an important way to evaluate the performance of composite insulators, which is helpful to the safe operation of composite insulators. Image processing technology is used to judge the hydrophobicity of composite insulators, which makes detection results more accurate and overcomes the subjective drawbacks of traditional detection methods.?As the traditional Canny operator requires manual intervention in selecting the variance of the Gaussian filter and the threshold, the paper presents a method of edge detection based on improved Canny operator. First, the adaptive median filter replaces the Gaussian filter, which can eliminate the impact from the variance of Gaussian filter and remove noise according to the characteristics of the image itself. Then the Ostu threshold method is used to select the best threshold automatically, which makes the edge detection be more continuous and reduce the presence of fake edges. The results show that the operator is applicable to all hydrophobic images.

Experimental investigation of sound absorption in a composite absorber

A composite absorber made of a polyurethane sponge and multi-layer micro-perforated plates is pre-sented in this study.Results from an acoustic impedance tube test show that the polyurethane sponge can exhibits higher low-frequency sound absorption in front of the micro-perforated plate,while sound absorption at medium and high-frequencies remains low.The physical mechanism behind this is that the micro-perforated plate increases the denpth cavity.If the polyurethane sponge is placed behind the micro-perforated plate,the amplitude of the original absorption peak will remain constant,but the ab-sorption peaks will shift to lower frequencies.The reason for this phenomenon is that porous materials with low flow resistance can be approximately equivalent to fluid,which not only does not affect the res-onance absorption coefficient of micro-perforated plate,but also makes the peaks move to low frequency.This study has the potential applications in the sound absorption design of composite structure.

过滤结构对贮箱增压用燃气发生器输出性能的影响

针对某液体姿控发动机贮箱增压用低燃温燃气发生器,开展了内部过滤结构对其输出性能影响的试验研究。试验验证及结果分析表明:燃气发生器内部压强曲线的升高是由贮箱与过滤结构的共同影响造成的;即使贮箱反向压力不超过喷管临界压强,但在反向压力作用下药剂燃烧产生的固体残渣更易堵塞过滤层成为二次喉道,使燃气发生器内部工作压强依然持续升高;在满足燃气洁净度及降温吸热的前提下,采用低燃温复合推进剂的贮箱增压用燃气发生器的过滤层相对密度不宜超过0.45。

PAN/MgO/Ag复合纳米纤维过滤膜的制备及性能分析

为提高聚丙烯腈(PAN)纳米纤维膜的性能,在PAN溶液中掺杂了MgO和Ag纳米颗粒(MgONPs和AgNPs),通过静电纺丝方法制备了不同质量分数的PAN/MgO/Ag复合纳米纤维过滤膜,采用扫描电镜、X射线衍射仪、红外光谱仪、紫外线透反射分析仪、过滤性能测试仪测试复合纤维过滤膜的微观形态、结晶结构、透气性、透湿性及过滤性能等。结果表明:纯PAN纳米纤维的直径为222.9 nm,PAN/MgO/Ag复合纳米纤维的直径为151.5 nm~258.6 nm。相对于纯PAN纤维膜,PAN/MgO/Ag复合纤维膜具有优良的过滤性能和紫外线防护性能,其紫外线防护系数为38.73~55.37,过滤效率为95.36%~97.59%,阻力压降为46.06 Pa~58.31 Pa。当MgONPs和AgNPs的质量分数都是0.75%时,PAN/MgO/Ag复合纤维膜的品质因子最高,为0.071 4 Pa^(-1),过滤性能最好,属于高效低阻且具有防紫外线功能的过滤膜材料。

不同改性方法对生物砂滤池生物膜特性及处理受污染原水效果的影响

通过对普通石英砂(QS)进行氨基及铝钙双氢氧化物改性制得氨基改性砂(AMS)和铝钙双氢氧化物改性砂(CAS),分别以QS、AMS、CAS为滤料填充滤池进行挂膜,研究了不同石英砂表面的生物膜量、生物活性、胞外聚合物(EPS)的特性及对受污染原水的处理效果。结果表明,挂膜成功后CAS表面的生物活性最高,为42.00 mgO_(2)/(g·h),生物膜量和胞外聚合物的含量最大,分别为12.43 mg/g、105.09 mg/(g·SS),对COD_(Cr)、NH^(+)_(4)-N的去除率分别稳定在58.20%、89.50%;AMS表面的生物活性、生物膜量、EPS平均含量分别为32.97 mgO_(2)/(g·h)、9.07 mg/g、93.41 mg/(g·SS),对COD_(Cr)、NH^(+)_(4)-N的去除率分别为54.60%、85.10%。三种石英砂表面生物量分布均沿水流方向递减,EPS的含量从溶解性胞外聚合物(SL-EPS)到紧密附着性胞外聚合物(TB-EPS)呈上升趋势。

基于壳聚糖的复合抑菌空气滤料制备与评估

由于新冠疫情的暴发,人们对于室内空气质量有了更高的要求.探索既能过滤细微颗粒物,还能抑制和消杀微生物细菌、防止二次污染的过滤材料具有重要意义.以质量分数为1%的聚四氟乙烯(PTFE)乳液配制出不同壳聚糖质量浓度的浸渍液,利用直接浸渍后处理工艺制备出壳聚糖/涤纶/聚四氟乙烯复合抑菌空气滤料.利用大肠杆菌为实验菌落验证其抑菌性能,并对其织物特性、捕集效率及压差特性进行了研究.结果表明,壳聚糖质量浓度为12.5 mg/mL时复合滤料初始阻力最小,对PM_(2.5)粒子捕集效率达到93.88%,品质因子为0.02013,分别比原始滤料提高19.56%,0.0044,且对大肠杆菌的抑菌率为84.12%.综上所述,壳聚糖质量浓度为12.5 mg/mL,PTFE乳液质量分数为1%的浸渍液制备的壳聚糖/涤纶/聚四氟乙烯复合抑菌空气滤料兼具良好的过滤能力与抑菌效果.

基于改进型QPR的并网逆变器复合控制策略

针对准比例谐振(QPR)控制对高次谐波和直流抑制能力差等问题,提出了一种改进型QPR控制与直流前馈补偿的复合控制策略。该策略在QPR控制的基础上加入了高次谐波补偿,并在控制基波电流的电流外环上加入含积分控制器的直流分量补偿环节。在对并网电流所含3、5、7次谐波进行抑制的同时,降低了并网电流中所含直流分量。仿真结果表明,与QPR控制相比,所提控制策略直流含量从0.05降为0.01,总谐波畸变率下降了1.48%,具有较好的抑制效果。

复合改性砂滤料制备及生物砂滤池对受污染原水的净化效果

为改善普通石英砂(QS)表面特性,提高生物砂滤池生物附着量及对水中污染物的去除效果,对QS进行氨基、铝离子及铝钙双氢氧化物改性,制得氨基改性砂(AMS)、铝离子改性砂(ALS)和铝钙双氢氧化物改性砂(CAS),以四种滤料填充滤池考察对受污染原水的净化效果。结果表明,与QS相比,ALS与CAS表面覆盖了金属离子,AMS、ALS、CAS表面形态及比表面积均得到改善,成膜后表面生物附着量分别增加3.6、5.5、6.9 mg/g;滤速为5 m/h时,CAS滤池对浊度和COD平均去除率分别为90.1%、51.8%。与AMS、ALS滤池相比,CAS滤池表面生物量最大,对水中污染物去除效果良好。

多特征下室内声源定位的复合模型粒子滤波

为提高混响噪声下声源定位的精度和稳健性,提出多特征复合模型粒子滤波算法。该算法以麦克风接收信号的多特征构建似然函数,采用卷积神经网络提取多假设时延估计图像的深度特征,建立基于支持向量回归的时延估计模型;引入波束输出能量融合机制,弥补单特征不能同时抑制噪声和混响的缺陷。针对说话人运动随机性的问题建立声源跟踪的复合模型,改善说话人跟踪系统的鲁棒性。仿真和实测结果表明:在复合模型跟踪下,多特征算法比可控响应功率时延估计算法位置平均均方根误差减少83%以上;在多特征观测下,复合模型比郎之万模型和随机行走模型位置平均均方根误差减少46%以上;新算法实现了对复杂环境下随机运动声源的有效跟踪。