This paper introduces a new approach for the determination of the source region of beat wave(BW)modulation.This type of modulation is achieved by transmitting high-frequency(HF)continuous waves with a frequency differ...This paper introduces a new approach for the determination of the source region of beat wave(BW)modulation.This type of modulation is achieved by transmitting high-frequency(HF)continuous waves with a frequency difference f,where f is the frequency of modulated ELF/VLF(extremely low frequency/very low frequency)waves from two sub-arrays of a high power HF transmitter.Despite the advantages of BW modulation in terms of generating more stable ELF/VLF signal and high modulation efficiency,there exists a controversy on the physical mechanism of BW and its source region.In this paper,the two controversial theories,i.e.,BW based on D-E region thermal nonlinearity and BW based on F region ponderomotive nonlinearity are examined for cases where each of these two theories exists exclusively or both of them exist simultaneously.According to the analysis and simulation results presented in this paper,it is found that the generated VLF signal amplitude exhibits significant variation as a function of HF frequency in different source regions.Therefore,this characteristic can be utilized as a potential new approach to determine the physical mechanism and source location of BW.展开更多
The generation of low frequency waves by a single or double wave groups incident upon two Plane beaches with the slope of 1/40 and 1/100 is investigated experimentally and numerically. A new type of wave maker signal ...The generation of low frequency waves by a single or double wave groups incident upon two Plane beaches with the slope of 1/40 and 1/100 is investigated experimentally and numerically. A new type of wave maker signal is used to generate the groups, allowing the bound long wave (set-down) to be included in the group. The experiments show that the low frequency wave is generated during breaking and propagation to the shoreline of the wave group. This process of generation and propagation of low frequency waves is simulated numerically by solving the short-wave averaged mass and momentum conservation equations. The computed and measured results are in good agreement. The mechanism of generation of low frequency waves in the surf zone is examined and discussed.展开更多
A nonlinear short-wave-averaged (surf beat) model is presented. The model is based on that of Roelvink (1993), but the numerical techniques used in the solution are based on the so-called weighted-averaged flux (WAF) ...A nonlinear short-wave-averaged (surf beat) model is presented. The model is based on that of Roelvink (1993), but the numerical techniques used in the solution are based on the so-called weighted-averaged flux (WAF) method (eg Watson et al., 1992), with time-operator splitting used for the treatment of some of the source terms. This method allows a small number of computational points to be used, and is particularly efficient in modelling breaking long waves. The short-wave (or primary-wave) energy equation is solved using a more traditional Lax-Wendroff technique. Results of validation indicate that the model performs satisfactorily in most respects.展开更多
基于高电离层质动力非线性加热理论,引入差频双波束概念,建立双频双波束加热电离层激发甚低频/极低频(VLF/ELF)辐射理论仿真模型,通过对已有实验参数进行仿真计算,验证了模型的正确性.据此模型,全面分析了不同纬度、有效辐射功率、加热...基于高电离层质动力非线性加热理论,引入差频双波束概念,建立双频双波束加热电离层激发甚低频/极低频(VLF/ELF)辐射理论仿真模型,通过对已有实验参数进行仿真计算,验证了模型的正确性.据此模型,全面分析了不同纬度、有效辐射功率、加热频率、极化模式、频率差、实验时段等对激发VLF/ELF辐射强度的影响,并对比分析了中低纬度地区双频双波束和幅度调制两种方法激发VLF/ELF信号的差异.分析结果表明:VLF/ELF辐射效果随着地磁倾角的增加而增强,随着系统有效辐射功率的增大而增强;X波模式优于O波模式;实验时段冬季最好,夜晚优于白天;加热频率和频率差存在最优值选取问题.对于背景自然电流较弱的中低纬度地区,相对现有幅度调制方法,利用双频双波束方法激发VLF/ELF辐射更加有效,两者相差10 d B以上.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.41804149)China Scholarship Council。
文摘This paper introduces a new approach for the determination of the source region of beat wave(BW)modulation.This type of modulation is achieved by transmitting high-frequency(HF)continuous waves with a frequency difference f,where f is the frequency of modulated ELF/VLF(extremely low frequency/very low frequency)waves from two sub-arrays of a high power HF transmitter.Despite the advantages of BW modulation in terms of generating more stable ELF/VLF signal and high modulation efficiency,there exists a controversy on the physical mechanism of BW and its source region.In this paper,the two controversial theories,i.e.,BW based on D-E region thermal nonlinearity and BW based on F region ponderomotive nonlinearity are examined for cases where each of these two theories exists exclusively or both of them exist simultaneously.According to the analysis and simulation results presented in this paper,it is found that the generated VLF signal amplitude exhibits significant variation as a function of HF frequency in different source regions.Therefore,this characteristic can be utilized as a potential new approach to determine the physical mechanism and source location of BW.
基金This project was financially supported by the National Natural Science Foundations of China(Grant No.5967900559839330)
文摘The generation of low frequency waves by a single or double wave groups incident upon two Plane beaches with the slope of 1/40 and 1/100 is investigated experimentally and numerically. A new type of wave maker signal is used to generate the groups, allowing the bound long wave (set-down) to be included in the group. The experiments show that the low frequency wave is generated during breaking and propagation to the shoreline of the wave group. This process of generation and propagation of low frequency waves is simulated numerically by solving the short-wave averaged mass and momentum conservation equations. The computed and measured results are in good agreement. The mechanism of generation of low frequency waves in the surf zone is examined and discussed.
文摘A nonlinear short-wave-averaged (surf beat) model is presented. The model is based on that of Roelvink (1993), but the numerical techniques used in the solution are based on the so-called weighted-averaged flux (WAF) method (eg Watson et al., 1992), with time-operator splitting used for the treatment of some of the source terms. This method allows a small number of computational points to be used, and is particularly efficient in modelling breaking long waves. The short-wave (or primary-wave) energy equation is solved using a more traditional Lax-Wendroff technique. Results of validation indicate that the model performs satisfactorily in most respects.
文摘基于高电离层质动力非线性加热理论,引入差频双波束概念,建立双频双波束加热电离层激发甚低频/极低频(VLF/ELF)辐射理论仿真模型,通过对已有实验参数进行仿真计算,验证了模型的正确性.据此模型,全面分析了不同纬度、有效辐射功率、加热频率、极化模式、频率差、实验时段等对激发VLF/ELF辐射强度的影响,并对比分析了中低纬度地区双频双波束和幅度调制两种方法激发VLF/ELF信号的差异.分析结果表明:VLF/ELF辐射效果随着地磁倾角的增加而增强,随着系统有效辐射功率的增大而增强;X波模式优于O波模式;实验时段冬季最好,夜晚优于白天;加热频率和频率差存在最优值选取问题.对于背景自然电流较弱的中低纬度地区,相对现有幅度调制方法,利用双频双波束方法激发VLF/ELF辐射更加有效,两者相差10 d B以上.
