Numerical simulation of the propagation of electromagnetic waves in ionospheric irregularities

The characteristics of high-frequency(HF)electromagnetic(EM)wave propagation can be affected when EM waves propagate in the ionosphere.When ionospheric irregularities appear in the ionosphere,they can have a serious impact on the propagation of HF EM waves.In this study,the propagation of HF EM waves in ionospheric irregularities was investigated by numerical simulation.First,a twodimensional model of plasma bubbles was used to produce ionospheric irregularities in the ionosphere.A ray-tracing method was then utilized to simulate the propagation of HF radio waves in these ionospheric irregularities.Results showed that the propagation of HF radio waves in the ionosphere was more complex in ionospheric irregularities than without ionospheric irregularities.In addition,corresponding ionograms were synthesized by radio rays propagated in the ionosphere with these irregularities.The synthesized ionograms were then compared with the experimental ionograms recorded by an ionosonde.Results showed that spread F could be simulated on the ionograms when ionospheric irregularities occurred in the ionosphere.This result was consistent with the ionosonde observations.

The numerical simulation on electromagnetic wave attenuation characteristics of coal face in time-frequency domain

This paper took the abnormal geological objects with high or low resistivity in the coal face as the background to establish the physical model. 2D forward numerical simulation for electromagnetic wave equation was implemented by the finite-difference scheme. According to the simulative results, the attenuation-absorption coefficient were calculated respectively based on field intensity and frequency shift parameter. Research result indicates, when coal-bed contains high electric resistivity geological abnormal object or low electric resistivity geological abnormal object, absorption attenuation function researched by frequency shift parameter of electromagnetic wave signal is more sensitive than by electromagnetic field intensity parameter.

Flame behavior, shock wave, and instantaneous thermal field generated by unconfined vapor-liquid propylene oxide/air cloud detonation

Energy output and heating effects are essential for vapor-liquid fuel/air cloud detonation in the fuel-air explosive(FAE) applications or explosion accidents. The purpose of this study is to examine the dynamic large-size flame behavior, shock wave propagation law, and instantaneous thermal field generated by unconfined vapor-liquid propylene oxide(PO)/air cloud detonation. Based on computational fluid dynamics(CFD) and combustion theory, a numerical simulation is used to study the detonation process of a PO/air cloud produced by a double-event fuel-air explosive(DEFAE) of 2.16 kg. The large-scale flame behavior is characterized. The flame initially spreads radially and laterally in a wing shape. Subsequently,the developed flame increases with a larger aspect ratio. Moreover, the propagation laws of shock waves at different heights are discussed. The peak pressure of 1.3 m height level with a stepwise decline is obviously different from that of the ground with an amplitude of reversed ’N’ shape. In the vast majority of the first 6.9 m, the destructive effect of the shock wave near the ground is greater than that of the shock wave at 1.3 m height. Furthermore, the dynamic instantaneous isothermal field is demonstrated.The scaling relationship of various isotherms in the instantaneous thermal field with the flame and initial cloud is summarized. The comprehensive numerical model used in this study can be applied to determine the overpressure and temperature distribution in the entire fuel/air cloud detonation field,providing guidance for assessing the extent of damage caused by DEFAE detonation.

Numerical simulation of interior ballistic process of railgun based on the multi-field coupled model

Railgun launcher design relies on appropriate models. A multi-field coupled model of railgun launcher was presented in this paper. The 3D transient multi-field was composed of electromagnetic field, thermal field and structural field. The magnetic diffusion equations were solved by a finite-element boundary-element coupling method. The thermal diffusion equations and structural equations were solved by a finite element method. A coupled calculation was achieved by the transfer data from the electromagnetic field to the thermal and structural fields. Some characteristics of railgun shot, such as velocity skin effect, melt-wave erosion and magnetic sawing, which are generated under the condition of large-current and high-speed sliding electrical contact, were demonstrated by numerical simulation.

Electromagnetic interaction between local surface plasmon polaritons and an atmospheric surface wave plasma jet

We analyze the electromagnetic interaction between local surface plasmon polaritons （SPPs） and an atmospheric surface wave plasma jet （ASWPJ） in combination with our designed discharge device. Before discharge, the excitation of the SPPs and the spatial distribution of the enhanced electric field are analyzed. During discharge, the critical breakdown electric field of the gases at atmospheric gas pressure and the surface wave of the SPPs converted into electron plasma waves at resonant points are studied. After discharge, the ionization development process of the ASWPJ is simulated using a two- dimensional fluid model. Our results suggest that the local enhanced electric field of SPPs is merely the precondition of gas breakdown, and the key mechanism in maintaining the discharge development of a low-power ASWPJ is the wave-mode conversion of the local enhanced electric field at the resonant point.

Thermal recovery process of a backfilled open-pit in permafrost area at the Gulian strip coal mine in Northeast China

Timely and proper backfilling of open-pits in strip coal-mines has been an effective measurement for the recovery of the hydrothermal regimes and ecological environment in permafrost regions. In this study, numerical simulations and statistical regressions were applied for analyzing the recovery processes of the backfill and its major influencing factors for the thermal equilibrium in recently backfilled open pits at the Gulian strip coalmine in Mo'he, Northeast China. Results show that the thermal recovery time of backfilled areas is positively correlated to the backfill depth(BD) of the soils, the backfilled soil temperature(BST), and the mean annual ground surface temperature(MAGST); meanwhile, climate warming can impact on thermal regimes of the backfill area. The impact of climate warming on ground temperature of the backfill will show up significantly in about 50 years afterbackfilling(BD at 10.0 and 20.0 m, BST at 20.0°C) under the climate warming scenario(CWS) of 0.025°C·year ^(-1). Grey-relation analyses show that the sensitivity of the backfill recovery time declines in the order of the BD, BST and MAGST. On the basis of the abovementioned studies, the layer-by-layer backfilling in cold seasons is advised for more effective and more rapid recovery of thermal regimes of the backfilled open-pits in cold regions.

Attenuation characteristics of electromagnetic waves in plasma generated by coating radionuclide on surface structures

Stealth technology plays an important role in modern military conflicts, especially when used in fighter jets. Since airfoil structures have a leading edge, inlet, and surface bulge that are easily detected by radar, it is necessary to study the stealth of these structures. In this study,we investigate structures coated with radionuclides to generate plasma. Using simulation and calculation methods, the attenuation of 0.1–10 GHz electromagnetic waves propagating in plasma was studied. The results showed that the attenuation of low-frequency electromagnetic waves is greater than that of high-frequency electromagnetic waves.The attenuation of 0.1–1 GHz electromagnetic waves is found to be less than-2.7 d B,-3.0 d B, and-15.6 d B at the airfoil leading edge, inlet, and surface bulge structures, respectively. We also found that the attenuation of electromagnetic waves with 0°-incidence is greater than that of waves with 10°, 20°, and 30° incidence angles.Additionally, the attenuation of electromagnetic waves decreases gradually as the incident angle increases.

单摆永磁直驱式波浪能发电装置的性能研究

为解决海洋仪器的长期能源供应问题,基于永磁材料的电磁特性,结合易于起振的摆式俘能机制,提出了一种与小体积球形浮标相结合的永磁式波浪能发电装置。详细论述了装置的发电原理和设计方案,推导了装置在波浪激励下的运动模型。依靠AQWA与Maxwell软件进行了联合仿真并对装置进行了参数优化,最终仿真结果表明:在波浪入射角度β=0°,波浪周期T=3.5s,波浪高度H=0.6m的波况下摆锤做周期T_(p)=2s,幅值A_(p)=15°的往复振荡运动,单相绕组产生的感应电动势最大可达27.7V,最佳输出功率为2.07W,可有效满足海洋仪器的供电要求。

模块化随钻电磁波测井仪器结构对测量信号的影响

常规的随钻电磁波测井是一种重要的地层流体评价方法,但其不具有方位特性。为此,提出了一种具有较好方位探测特性的新型模块化随钻电磁波测井仪器结构。为准确了解模块化随钻电磁波测井仪器结构对测量电压信号的影响情况,采用有限元法建立了三维模型,探究了仪器各部分的影响规律。研究得出:随着钻铤和天线槽填充物电阻率增大,接收电压信号出现了突变区间且与仪器的频率和几何尺寸密切相关;盖板材料的电阻率对接收信号强度的影响较大,盖板应选择电阻率比金属稍低的材料,而测量信号随传感器本体电阻率增大而增大,因此传感器本体应选择非金属材料;钻铤和填充物的电阻率较小时,接收电压信号有明显的衰减,填充物电阻率较大时其影响可以忽略;通过扣除空气介质中的仪器响应,可以较好地消除仪器结构的影响,扣除仪器结构影响后线圈中磁通量减小,导致仪器信号低于扣除前。该研究结果可为实际测井仪器的设计制造提供理论依据。

稠油采出流体余热回收流动传热特性

为回收稠油热采生产的井口流体余热,采用数值模拟方法,研究稠油井口采出流体在矩形流道内的流场与温度场,分析不同参数对流动传热特性的影响规律,得到流动压降及传热系数计算式。结果表明:不凝气质量分数影响最大,随着不凝气质量分数增加,热交换器传热性能降低,流动阻力增大;当不凝气质量分数>10%后,流动传热特性几乎不再受其影响;进口采出液流速增加、通道水力直径减小,传热性能变强、流动阻力变大;进口温度升高使冷凝段长度降低,热交换器整体压降降低。

井下表面电磁波协同中继传输方法

在井下进行表面电磁波通信时,中继器布局不合理会导致信号强度减弱,为此,提出了表面电磁波的协同中继传输方法。首先,结合数值模拟与模拟试验结果,分析了表面电磁波的传播特性;然后,利用电场积分方法,建立了井下表面电磁波中继传输系统的数学模型,分析了不同中继器布局和数量对接收机信号强度的影响。研究结果表明,表面电磁波比传统无线电磁波具有更小的衰减和更高的传输速率,可成为一种高效的井下通信方式;应用表面电磁波协同中继传输技术,信号强度可平均提高5.91 dB。研究结果为增大表面电磁波井下通信的传输距离提供了新的技术途径。

套管-钻杆窄间隙环形空间电磁波传输特性

在气体钻井时,基于电磁波的井下信息传输技术有效解决了井下钻井参数的实时传输问题。但目前关于环境因素对窄间隙环形空间内电磁波传输影响规律的研究相对较少。为进一步研究套管—钻杆窄间隙环空电磁波传输特性,进而明确影响电磁波强度衰减速率的关键因素,基于电磁场与电磁波传输理论,采用有限元数值模拟方法,建立了套管—钻杆窄间隙环形空间模型,然后以电磁波强度为评价指标,对电磁波在环形空间截面的分布以及随传输距离的衰减规律进行深入研究,分析了钻杆偏心度、管材表面粗糙度与电磁响应参数、环空填充介质属性对电磁波强度衰减速率的影响,最后探讨分析了能够有效提升电磁波传输距离的途径。研究结果表明:①电磁波能量随距离增加近似线性衰减,但受多种因素影响可能转变为指数衰减;②钻杆偏心度会直接影响电磁波的能量分布和衰减速率;③管材的表面粗糙度、电导率、相对磁导率以及空气的电导率是影响电磁波传输能量衰减的关键因素。结论认为,该研究成果明确了电磁波在井筒环形空间传输时的衰减规律,为拓宽电磁波传输信道和基于电磁波测控的井下仪器、设备研发提供了理论依据。

非供暖季中深层热储自然恢复与蓄热对比分析

中深层岩土热储恢复对地埋管的取热效率至关重要,非供暖季结束时中深层热储温度场呈现不同的衰减程度。主要研究对比分析中深层地埋管运行1个供暖季后在非供暖季埋管周围热储自然恢复与有人为干预的蓄热恢复两种不同恢复情况温度场的变化,利用ANSYS Fluent建立传热模型,基于有限体积法进行求解,并与项目实测数据进行对比验证。通过对比分析两种不同恢复模式在非供暖季结束时热储的温度值,结果表明:非供暖季中深层热储通过自然恢复结束时,热储温度热恢复率最低点为96.81%;进行人为干预的蓄热恢复在非供暖季结束时,热储温度的最高恢复率可以达到158.09%。对比两种不同的热恢复模式在非供暖季结束时温差最大达到10.09℃,温差随深度及径向距离的增加而减小。

C1单元沙二段开发井网完善优化研究

针对C1单元沙二段储层薄、地层压力低、部分区域井网仍不完善的问题,本文通过建立数值模拟模型,模拟C1单元沙二段2、3号小层未控制区域,优化布井原则,完善该区域井网;优化开发方式,调整注入成分的用量,改善已动用区块的开发效果。数值模拟结果表明:布井厚度为3.2m以上,边部井纵向上位于储层下部最优,而内部井纵向上位于储层上部最优,距边水距离要大于180 m,井水平段长度应该在180 m左右,蒸汽吞吐前期注汽强度为10 t/m左右,蒸汽吞吐后期注汽量应逐周期增加5%;目前情况下,前置N2增能防窜+伴注N2扩大蒸汽波及体积效果最好,最优用量为前置N26万m^(3)+伴注N26万m^(3)。根据现场应用结果,新布井网单井产油为11.5 t/d,比老井网单井产油量增加6.59t/d,为其他区块后续开发提供了经验借鉴。

不同尺度飞行器周围等离子体分布及电磁波传输效应

研究气动电磁波传输效应对于评估和解决黑障问题具有重要意义。基于求解三维N-S方程及波动方程的数值方法,分析了天线位置、电磁波频率、飞行器特征尺度等因素对飞行器周围等离子体分布和电磁波传输的影响。研究结果表明:在同一再入条件下,随着球头半径增加,飞行器周围电子数密度、等离子体鞘套厚度以及对电磁波的衰减也随之增大,影响天线附近等离子体分布的主要机制是NO电离反应;轴向天线位置和频率对电磁波衰减具有重要影响,可以通过提高电磁波频率和合理选择天线位置降低等离子体对通信影响;飞行器沿弹道再入过程中,等离子对电磁波的衰减出现峰值,高频电磁波的通信中断区间缩小;典型条件下等离子体分布及通信中断的预测与测量结果一致,该预测手段可为飞行器电磁通信系统设计提供技术支持。

Transmission characteristics of EM wave in a finite thickness plasma

One of the key factors for solving the problems of re-entry communication interruption is electromagnetic（EM） wave transmission characteristics in a plasma.Theoretical and experimental studies were carried out on specific transmission characteristics for different plasma sheath characteristic under thin sheath condition in re-entry state.The paper presents systematic studies on the variations of wave attenuation characteristics versus plasma sheath thickness L,collision frequency ν,electron density n e and wave working frequency f in a φ 800 mm high temperature shock tube.In experiments,L is set to 4 cm and 38 cm.ν is 2 GHz and 15 GHz.n e is from 1×10 10 cm（-3） to 1×10 13 cm（-3）,and f is set to 2,5,10,14.6 GHz,respectively.Meanwhile,Wentzel-Kramers-Brillouin（WKB） and finite-difference time-domain（FDTD） methods are adopted to carry out theoretical simulation for comparison with experimental results.It is found that when L is much larger than EM wavelength λ（thick sheath） and ν is large,the theoretical result is in good agreement with experimental one,when sheath thickness L is much larger than λ,while ν is relatively small,two theoretical results are obviously different from the experimental ones.It means that the existing theoretical model can not fully describe the contribution of ν.Furthermore,when L and λ are of the same order of magnitude（thin sheath）,the experimental result is much smaller than the theoretical values,which indicates that the current model can not properly describe the thin sheath effect on EM attenuation characteristics.

深部含水层储热系统的数值模拟研究

深部含水层储热系统,是一种以深部含水层介质为载体的“地热+”多能互补储/供能系统。该系统可将各种形式的能量储存于地下并按需求取出加以利用,能够弥补能源供需的时空分布的不平衡,是综合利用多种可再生能源,实现节能减排的有效途径。深部含水层储热是一种水热型地热资源开发利用的新方式。传统的水热型地热资源开采,受限于地热尾水回灌导致的热突破,热田寿命有限。而利用深部含水层储能,不但可以增强热储能力,而且能够延长热田寿命。本研究通过数值模拟研究表明,与传统的水热型地热系统相比,通过采取深部含水层储热技术,在相同开采流量下,可以提升单井供热能力20%。其储热效率可以达到60%~90%,能够保证更高的地热能提取率;同时,与传统水热型地热井寿命受限于热突破时间的情况不同,深部含水层储热系统可以延长地热井寿命,实现可持续开采。通过参数敏感性分析的方法进一步评估了不同参数对深部含水层储热性能的影响。通过参数研究发现,储层渗透率和储热温度等是影响储热能力和效率的关键参数。本研究为后续开展深部含水层储热系统工程的设计与优化提供科学参考。

双频透射无线电波勘探方法及应用研究

煤层可作为高频电磁波的导波层,无线电波透视技术适用于工作面煤层内的地质构造探测。目前无线电波透视法通常采用单一频率进行探测,在煤层工作面勘探过程中常存在频率选择不当和探测精度不足等方面问题。为此,提出了双频透射无线电波勘探方法。基于理论分析,利用双频透视场强数据和衰减系数参数,推导了基于双频无线电波测量数据的煤岩介质吸收因子γ计算公式;采用有限元数值模拟方法,模拟并分析了无异常构造煤层和含断层煤层工作面两种工况。实验结果表明:利用双频法计算得到的吸收因子对煤层地质异常的响应更加敏感,验证了透射无线电波勘探方法的有效性。通过比对现场试验数据及回采钻探结果,再次验证了双频吸收因子γ对地质异常的响应特征优于单频衰减系数。研究结果表明,双频法可提高煤层工作面无线电波探测地质异常的效果,为无线电波精细化勘探和矿井地质透明化提供一个新的方法和思路。

基于灰色关联度分析和多目标优化的浅层含水层储热性能整体优化

含水层储能(Aquifer Thermal Energy Storage,缩写为ATES)系统因其良好的储热能力和经济性受到国内外学者的广泛关注,其中含水层储热系统中运行参数和布井参数的设置直接影响储热效果,如何优化参数获得最佳工艺方案,对于推广储热工程现场应用具有重要意义。为此,以浅层含水层储热性能作为优化目标,通过灰色关联度方法对比关键参数对储热性能的影响程度,采用多目标优化方法得到最佳储热方案。研究结果表明:①注入温度与含水层之间温差较大会削弱系统储热能力,同类型储热井之间的热干扰反而有利于储热性能;②含水层厚度和布井数量对热损失率影响较大,而注入排量和井距对热回收率影响较大,注入温度对二者的影响最小;③注入温度25℃、含水层厚度106.597 m、注入排量30 kg/s的单井系统为最佳储热方案。结论认为:①关键参数对热损失和热回收的影响程度不同,为提高储热性能有必要对二者进行均衡优化;②优化方案有效扩大了储热体积,减少了热损失同时提高了热回收,使整个系统热损失率和热回收率分别在原有基础上优化了12.69%和3.19%,可为ATES系统的合理设计提供参考。

助剂对电磁原位加热稠油储层温度分布的影响

为了解决电磁原位加热导热、导电性能差的稠油储层时存在温度偏低的问题,提出了基于助剂注入的电磁原位加热技术,并建立了考虑稠油储层热性质随温度动态变化的电热耦合数学模型,开展了电磁加热室内试验以验证数学模型的准确性,比较了助剂注入前、后储层的电场和温度分布以评估电磁加热性能,最后分析了助剂导电和导热性质对储层温度分布的影响规律。研究结果表明:室内试验证实了电热耦合数学模型的准确性,助剂注入后电磁原位加热稠油储层的温度明显升高;在一定径向范围内,助剂电导率的增大有助于提高储层温度;储层径向温度随着助剂比热容和导热系数的减小而升高。研究结果证实了基于助剂注入的电磁原位加热技术在解决加热温度偏低的问题上可行。