Effect of interstitial air holes on Bragg gratings in photonic crystal fibre with a Ge-doped core

The effect of interstitial air holes on Bragg gratings in photonic crystal fibre （PCF） with a Ge-doped core is numerically investigated by using the beam propagation method （BPM）. It is shown that the interstitial air holes （IAHs） can make Bragg resonance wavelength λB shift a little towards short wavelengths and increase λB -λ1 （the wavelength spacing between the main peak with Bragg resonance wavelength λB and the first side peak with wavelength λ1） and the coupling coefficient κ of Bragg resonance. Moreover, when the ratio of air hole diameter （d） to pitch （∧）, d/∧, is small, IAHs can suppress the cladding mode resonance. When d/∧ is large, IAHs increase the number of mode that could strongly interact with the fundamental mode. By comparing the transmission spectral characteristics of PCF-based fibre Bragg grating （FBG） with IAHs with those without IAHs at the same air-filling fraction, it is clarified that the change of transmission spectral characteristics of PCF-based FBG with IAHs is not due to a simple change in air-filling fraction. It is also closely related to the distribution of interstitial air holes.

Analysis of the Effect of Air Hole Diameter and Lattice Pitch in Optical Properties for Hexagonal Photonic Crystal Fiber

We have investigated the different optical properties such as confinement loss, waveguide dispersion of a five rings hexagonal photonic crystal fiber under varied air hole diameter (d), lattice pitch (Λ), and air hole diameter to lattice pitch ratio for three different materials fused quartz glass, borosilicate glass and sapphire glass. We observed low confinement loss and high negative dispersion at higher d/Λ. Achieving high d/Λ can be done in two ways: increasing the air hole diameter or decreasing the lattice pitch. It has been observed, increasing the air hole diameter has significant effect over reducing lattice pitch in achieving low confinement loss. On the other hand, decreasing the lattice pitch over increasing the air hole diameter has significant effect in achieving high negative dispersion. It has also been found that, effective refractive index (neff) decreases significantly when lattice pitch decreases.

Comparison of outcomes of idiopathic macular holes treated by vitrectomy with air or silicone oil tamponade based on the hole size

AIM:To compare the efficacy of vitrectomy combined with air or silicone oil in the treatment of idiopathic macular hole(IMH).METHODS:According to the results of high-definition optical coherence tomography(HD-OCT),75 cases(75 eyes)of IMH in stage II-IV(Gass stage)in the General Hospital of Chinese PLA from January 2017 to December 2019 were collected for this retrospective study.The best corrected visual acuity(BCVA)and minimum diameter of IMH(MMHD)were measured.Eyes underwent vitrectomy combined with internal limiting membrane peeling operation,and were divided into disinfection air group(30 eyes)and silicone oil group(45 eyes)according to the intraocular tamponade.For MMHD≤400μm(MMHD1),there were 23 eyes in air group and 16 eyes in silicone oil group.For MMHD2>400μm(MMHD2),there were 7 eyes in air group and 29 eyes in silicone oil group.One month after surgery,the closure rates of IMH and BCVA were compared and analyzed.According to HD-OCT,the closure shape was graded with A(bridge closure)and B(good closure).RESULTS:The closure rates of air group and silicone oil group were 86.67%and 95.56%respectively with no significant difference(P>0.05);For MMHD1,those of air group and silicone oil group were 95.65%and 100%respectively with no significant difference(P>0.05);For MMHD2,those of air group and silicone oil group were 57.14%and 93.10%respectively,and those of the silicone oil group were higher than the air group(P<0.05).There was no significant difference in the closure shape grade between MMHD1 air group and silicone oil group(P>0.05).The proportion of Grade B in MMHD2 silicone oil group was higher than that in the air group(P<0.05).BCVA of each group after operation was better than that before operation,and there was no significant difference between air group and silicone oil group.While among them,MMHD1 air group was better than silicone oil group(P<0.05),and there was no significant difference between MMHD2 air group and silicone oil group(P>0.05).CONCLUSION:For smaller IMH(≤400μm),the efficacy of vitrectomy combined with air should be considered better than silicone oil;for larger IMH(>400μm),the efficacy of silicone oil may be better than air.

FGC-15D large-diameter DTH air hammer drilling system and its application in offshore rock-socketed pile hole drilling

In the past two decades, numerous large-diameter rock-socketed piles were constructed in China to support foundations of skyscrapers, great bridges or to retain soil in potential geological hazard areas. However, drilling large-diameter rock-socketed pile holes with conventional drilling method such as rotary drilling or cable tool drilling is time-consuming and the cost is usually very high. In order to drill large-diameter rocksocketed pile holes faster at relatively low cost, the FGC15A large-diameter DTH air hammer drilling system was developed in 1987 and was given the second-clasa award by Ministry of Geology and Mineral Resources in 1991. Since it was innovated the drilling system has been used in more than twenty important and tough pro- jects on land, and wonderful results were acquired. At the same time the large-diameter DTH air hammer drilling system was improved continuously. The FGC15D is the latest version of the technique.

Incomplete fluid-air exchange technique for idiopathic macular hole surgery

AIM: To explore an improved procedure involving incomplete fluid-air exchange for idiopathic macular hole(IMH), and the closure rate, visual function, and the visual field of macular holes(MHs) were evaluated.METHODS: This prospective randomized controlled study, included 40 eyes of 40 patients with IMH who were treated with pars plana vitrectomy and peeling of the internal limiting membrane. They were grouped by random digital table. Twenty-one eyes underwent incomplete fluidair exchange(IFA) and 19 eyes underwent traditional complete fluid-air exchange(CFA) as the control group. Outcomes included best-corrected visual acuity(BCVA), intraocular pressure, and optical coherence tomography, light adaptive electroretinography, and visual field evaluations.RESULTS: All MHs <400 μm were successfully closed. BCVAs before and 6 mo after surgery were 0.82±0.41 logMAR and 0.28±0.17 logMAR in IFA group and 0.86±0.34 logMAR and 0.34±0.23 logMAR in CFA group, respectively. The electroretinogram analysis of patients in IFA group revealed increases in b-wave amplitudes at 1, 3, and 6 mo after surgery. Additionally, patients in IFA group showed an amplitude increase of 28.6% from baseline at 6 mo(P<0.05), while no obvious improvements were noted in CFA group. Although there were no statistically significant improvements in either group, the IFA group showed a slight increase in mean sensitivity(P>0.05).CONCLUSION: IFA is a reliable method that offers comparable closure rate to CFA and facilitates improvements in visual function.

深孔轴向多段间隔装药孔壁冲击压力分布

为确定地下垂直长深孔爆破时合理的空气间隔长度,基于爆轰波理论,分析了多段间隔装药爆破条件下孔壁冲击压力随间隔长度变化的内在分布规律函数;依据Mises准则,得出了不同岩性时合理的间隔长度参考值,并通过数值模拟和现场爆破试验进行了验证。结果表明,空气间隔段孔壁冲击压力沿炮孔轴线从两端向中间骤降,但在中点周围略微增大,压力曲线呈两端大、中间小、中点周围略微凸起的“W”形对称分布。

抽吸孔排列对喷气涡流纺喷嘴流场影响的数值模拟

为探究抽吸孔排列参数对负压抽吸式喷气涡流纺包芯纱成纱过程与质量的影响规律,建立喷嘴气流场的计算流体动力学模型,对抽吸孔周向列数与抽吸孔轴向间距对气流流动特性的影响进行数值模拟研究,并与纺纱试验结果进行对比分析。结果表明:成纱过程中落纤量的大小受锭子中引纱通道入口端面处气流轴向速度和径向速度的方向和大小影响显著,落纤量随该处气流轴向和径向速度值的增大而降低;成纱断裂强度受锭子入口附近抽吸孔中气流径向速度大小的影响较大,成纱断裂强度随径向速度的增大而提高。抽吸孔周向列数为3列和4列时落纤量均低于2列时,但抽吸孔周向列数为2列时成纱断裂强度最高;当抽吸孔轴向间距从1 mm增加至2 mm时,落纤量与成纱断裂强度均明显增加。抽吸孔排列参数对包芯纱成纱过程落纤量与成纱断裂强度影响的数值模拟结果与前期纺纱试验结果较为一致,为揭示参数对喷气涡流纺成纱过程与质量的影响机制提供了可行的方法。

中镍无限冷硬球墨铸铁轧辊辊颈缺陷原因分析及应用

分析了中镍无限冷硬球墨铸铁轧辊离心铸造时产生气孔、夹渣的工艺原因,采取了预脱氧处理、控制稀土镁球化剂使用率、提高浇注速度、提高型砂透气性、控制混合保护渣使用量、配箱时间控制在3 min以内等措施,辊颈气孔和夹渣产生的废品率从40%降低到6%以内,有效降低了废品率。

带同轴引气激光制孔中的气动特性分析

针对锥形激光加工器在航空发动机热部件冷却孔加工过程中的吹渣效果,研究了射流冲击孔板附近的流场特性及其影响因素。针对同轴高压气体撞击带盲孔平板的射流结构,采用数值模拟方法,分析了不同进气压力p_(int)(0.2~1.5 MPa)、射流间距H/De(3.6,5.6,7.6)和冲击角度α(30°,45°,60°,90°)对盲孔附近气体动力学性能的综合影响。研究结果表明,当H/De为3.6时,随进气压力的增大,盲孔附近的气体动力学性能呈现先逐步提高后剧烈下降的趋势,较好工作压力为1 MPa;当射流间距H/De达到5.6及以上时,适当地增大喷嘴压力可以提高盲孔附近气流的气动水平,但提升有限。随着冲击角度α减小,盲孔内流出质量流量逐渐增大,α为30°时较垂直射流提升约11倍,但在冲击表面上气体的剪切流动随冲击角度减小逐渐变弱。

不同温度下气调剂对常见储粮害虫控制效果研究

气调剂通过消耗有限空间内的氧气,对空间害虫有很好的控制效果。为了解不同温度下,气调剂对常见储粮害虫的杀灭效果,针对5种常见储粮害虫,研究了在20、25、30℃温度条件下,100 g气调剂在24000 cm^(3)密闭空间内对每种害虫死亡率与时间的关系,结果表明:在24000 cm^(3)密闭空间内,100 g气调剂3 d可使氧体积分数降至0.5%以下,且能维持氧体积分数≤0.5%,降氧迅速。随着温度的降低,相同时间下同种害虫的死亡率降低,其中,谷蠹和玉米象低温条件时LT_(99)值明显增大,表明2种蛀食性害虫对低氧和低温耐受能力较强。同一温度条件下,不同害虫对气调剂低氧环境下耐受力不同,玉米象耐受力最大,锯谷盗最低,5种害虫的低氧耐受力为:玉米象>谷蠹>长角扁谷盗>赤拟谷盗>锯谷盗。

V形气膜孔气膜冷却效率的数值分析研究

采用数值模拟方法研究了不同角度和吹风比条件下V形气膜孔的气膜冷却效率,并与椭圆形气膜孔进行了对比。结果表明:相同吹风比下,3种V形气膜孔的冷却效率都要高于椭圆形气膜孔,角度对V形气膜孔冷却效率有较大影响。计算结果对目前涡轮叶片气膜孔的设计有一定指导意义。

侧壁排烟口下方倾斜空气挡板促进侧向排烟效果研究

为了研究侧壁排烟效果随空气挡板倾斜角度的变化规律,探究了不同倾斜角度空气挡板作用下侧壁排烟口附近温度场与流速矢量场特征及排烟效率。结果发现:侧壁排烟口下方设置空气挡板可以有效抑制冷空气的流入,侧壁排烟效率得到明显提升。侧壁排烟口下方设置空气挡板后,排烟口附近热烟气流线明显增加,冷空气流线变得稀疏,排烟口区域高温烟气面积明显增加。当排烟口宽高比为1:2时,侧壁排烟效率随挡板倾斜角度(0≤θ≤45°)的增大而增大,在45°≤θ≤60°基本保持高位稳定,具有最佳排烟效果;当排烟口宽高比为2:1时,侧壁排烟效率随挡板倾斜角度(0≤θ≤30°)的增大而增大,在30°≤θ≤60°出现下降趋势,30°时达到排烟效率峰值。通过数据分析构建了现有条件下不同倾斜角度空气挡板作用下的侧壁排烟效率表征模型,可为隧道侧壁排烟系统设计提供相应技术参考。

滤筒除尘器喷吹孔孔径的优化

【目的】为控制各个喷吹管气流量的均匀性,对喷吹管上的喷吹孔径进行优化,提高滤筒除尘器清灰效果。【方法】自制高压脉冲喷吹气流量测量装置对现有喷吹管气流量进行测定,采用光纤传感分析仪测试除尘器滤筒各部分的侧壁压力峰值,分析各滤筒清灰效果不均匀的原因;以滤筒各部位侧壁压力峰值作为清灰均匀性效果评估指标,优化喷吹孔径。【结果】优化前4个喷吹孔径均为19 mm,喷吹孔的气流量依次为13.69、 14.78、 16.03、 16.93 L,对应4个滤筒上、中、下部侧壁压力峰值的最小值分别为最大值的37%、 26%、 20%,气流量均匀度标准差为1.41;优化后4个喷吹孔径分别为23、 20、 18、 17 mm,喷吹气流量依次为14.05、 15.08、 15.87、 16.13 L,对应4个滤筒上、中、下部测壁压力峰值的最小值为最大值的56%、 56%、 53%,气流量均匀度标准差降为0.93。【结论】优化后的喷吹管气流量均匀化程度提高,可实现滤筒除尘器的均匀清灰。

装药结构对硬质岩隧洞轮廓成型效果的影响研究

硬质岩隧洞的轮廓成型效果对提高围岩稳定性和降低支护成本具有重要意义。以优化隧洞轮廓孔单孔装药量和装药结构为目标,首先,理论分析了隧洞爆破中轮廓孔装药参数的取值范围;其次,分别以1200 g、900 g、750 g、600 g的单孔装药量进行了硬质岩隧洞爆破试验,并借助激光扫描仪对隧洞轮廓成型效果进行了扫描分析;最后,利用断裂力学模型分析了不同单孔装药量的隧洞轮廓成型效果。结果表明:当硬质岩隧洞的轮廓孔装药参数在合理范围内时,单孔装药量越小,爆破产生的孔间裂缝数量越少,岩体损伤范围也越小;当装药量由1200 g降低至600 g时,隧洞轮廓超挖体积由6.53 m^(3)降低至2.02 m^(3),但由孔位误差导致的轮廓欠挖体积由0.15 m^(3)增大0.26 m^(3);断裂力学模型在硬质岩隧洞轮廓爆破的模拟中优于损伤模型,模型计算得隧洞轮廓上的半孔数与观察值吻合较好。研究成果可为类似硬质岩隧洞爆破开挖中轮廓成型效果优化提供技术与方法借鉴。

下向低浓钻孔“抽-注”排水排渣抽采一体化技术研究

为了防止永夏矿区陈四楼煤矿煤与瓦斯突出事故的发生,在采用水力排渣钻孔进行抽采瓦斯时,发现在钻孔内存在着大量的水和煤渣,堵塞了煤体内部的孔隙通道,对煤层瓦斯运移和钻孔孔壁的稳定性产生不利影响,从而严重影响了瓦斯抽采的效果。针对煤矿急需解决的俯孔排水排渣问题,提出采用压风吹孔技术,将孔内水和煤渣带出孔外,疏通钻孔堵塞通道。该技术在陈四楼煤矿井下现场应用效果良好,吹孔后钻孔平均在抽浓度由11.86%提升到了18.73%~56.38%,低浓钻孔提升效果明显;代替了以往水力排渣钻进技术,达到高效抽采瓦斯、保证煤矿安全生产的目的,对钻孔抽采瓦斯过程中能够及时排出水和煤渣有一定指导意义。在此基础上,形成的一套下向低浓钻孔“抽—注”排水排渣一体化技术及工艺,为下向低浓钻孔排水排渣工作提供参考借鉴。

固定式打磨台排风除尘效果研究

在固定式打磨台上进行高精细度的金属打磨已成为机械制造工艺中的重要环节。为改善某公司固定式打磨台的排风除尘效果,提出了2种优化方案。采用CFD-DPM相互耦合的数值模拟方法,对打磨过程中固定式打磨台上的粉尘质量浓度分布情况进行分析,并对原固定式打磨台及2种优化方案的固定式打磨台排风除尘效果进行对比研究。研究结果表明,原固定式打磨台的排风除尘效果较差,而2种优化方案都能在一定程度上降低打磨过程中的粉尘质量浓度。当排风孔数量增加到4个和5个(上2下3)时,排风除尘效果较佳。在此基础上,通过在固定式打磨台安装风幕,对比得出安装风幕的4个排风孔固定式打磨台的排风除尘效果最佳,其呼吸带高度粉尘质量浓度和最大粉尘质量浓度相比未安装风幕分别降低了99.88%和91.81%,值得在相关工业实践中推广使用。

基于阻断漏风路径原理的新型钻孔封孔装置

瓦斯抽采钻孔的封孔质量直接影响其抽采效率,为了有效保障瓦斯抽采钻孔的封孔质量,对瓦斯抽采钻孔封孔后可能存在的漏风裂隙及其可控性进行定性分析,并据此对其漏风路径形成的难易程度进行对比。结果表明:封孔后瓦斯抽采钻孔内部及外部可能存在的裂隙主要有巷道围岩松动圈裂隙、支护装置周边裂隙、煤层内部原生裂隙、钻孔周边裂隙、封孔材料裂隙及抽采管裂隙6种;相应地,瓦斯抽采钻孔可能产生的漏风路径主要有7种,其中最容易形成的漏风路径为巷道内空气→巷道围岩松动圈裂隙→钻孔周边裂隙→抽采钻孔→抽采管。基于此,结合现有瓦斯抽采钻孔封孔装置的不足及其现场应用实际条件,从切断漏风节点之间的联系、消除漏风节点进而阻断漏风路径的原理出发,提出了1种可回收及多次补封的新型钻孔封孔装置。

基于双层孔结构的850nm超细径保偏光子晶体光纤

光子晶体光纤由高纯度石英玻璃制备而成,具备弯曲损耗小、环境适应性强等优点,尤其适用于恶劣应用环境下的高稳定光纤陀螺。传统光子晶体光纤内部微孔占据了较大的空间,导致光纤直径大,并且主要工作波段为1550nm,无法满足小型化、高精度光纤陀螺需求。提出了双层空气孔结构缩小光纤直径,通过微孔尺寸调节降低光纤损耗,并使光纤限制损耗具有偏振相关性,从而实现超细径保偏光子晶体光纤设计。采用“堆积拉制”法制备了Φ60/100μm光子晶体光纤样品,经截断法测试光纤损耗为6.5dB/km@850nm,偏振串音-15dB@100m。

基于无机纳米封孔材料提高煤层瓦斯抽采率的试验研究

为解决钻孔使用传统材料封孔产生裂隙导致瓦斯抽采率低、钻孔寿命有限的问题,分析了抽采钻孔漏气途径与周围应力分布,确定钻孔漏气的主要部位;通过向硅酸盐无机材料中添加纳米氧化物对其改性,得到一种能够长期保持水分且不凝固、不收缩等特点的无机纳米封孔材料;基于山西竹林山煤业有限公司53032巷道,开展顺层钻孔封孔及后续补浆封孔试验。结果表明:无机纳米封孔材料试验组平均瓦斯抽采浓度整体优于普通封孔水泥对照组,封孔16 d后,试验组平均瓦斯抽采纯量为0.04~0.06 m^(3)/min,而对照组平均瓦斯抽采纯量为0.02~0.04 m^(3)/min,试验组的封孔质量优于对照组钻孔。试验组经过补浆封孔,平均瓦斯抽采浓度提高了20%,补浆封孔可以提高钻孔的封堵质量和瓦斯抽采的平均浓度。

凹坑对并排气膜孔冷却性能的影响研究

为提高燃气轮机热端部件的冷却性能,探索了一种并排气膜孔和波浪形凹坑的组合冷却结构,添加椭圆形凹坑考虑凹坑形状变化的影响。利用压力敏感漆(PSP)技术实验测量了组合结构的冷却性能,结合数值模拟分析了流场结构。在吹风比0.5~2.0内,PSP实验结果显示,并排气膜孔结构产生的气膜冷却效果优于单圆孔结构,布置波浪形凹坑可以显著改善气膜孔下游的流场结构。经过计算,在吹风比为1.0时,波浪形并排凹坑孔对比单圆孔面平均冷却效率提高147.8%,对比椭圆形并排凹坑孔提高46.7%。在四个吹风比下,波浪形并排凹坑孔产生了最佳的气膜冷却效果。