Wave height estimation using the singular peaks in the sea echoes of high frequency radar

The popular methods to estimate wave height with high-frequency（HF） radar depend on the integration over the second-order spectral region and thus may come under from even not strong external interference. To improve the accuracy and increase the valid detection range of the wave height measurement, particularly by the smallaperture radar, it is turned to singular peaks which often exceed the power of other frequency components. The power of three kinds of singular peaks, i.e., those around ±1,±√2 and ±1√2 times the Bragg frequency, are retrieved from a one-month-long radar data set collected by an ocean state monitoring and analyzing radar,model S（OSMAR-S）, and in situ buoy records are used to make some comparisons. The power response to a wave height is found to be described with a new model quite well, by which obvious improvement on the wave height estimation is achieved. With the buoy measurements as reference, a correlation coefficient is increased to 0.90 and a root mean square error（RMSE） is decreased to 0.35 m at the range of 7.5 km compared with the results by the second-order method. The further analysis of the fitting performance across range suggests that the peak has the best fit and maintains a good performance as far as 40 km. The correlation coefficient is 0.78 and the RMSE is 0.62 m at 40 km. These results show the effectiveness of the new empirical method, which opens a new way for the wave height estimation with the HF radar.

REPRESENTATION OF STATISTICAL PROPERTIES OF WAVE GROUPS FOR SEA PROCESSES WITH DOUBLE-PEAKED SPECTRA

A method using group-induced second-order long waves(GSLW) to represent statistical properties of wave groups with double-peaked spectra is put forward in this paper on the basis of the GSLW theory. The GSLW is regarded as a weighted linear superimposition of the second-order long Wave induced by the low peak frequency section and that induced by the high peak frequency section. There is a parabolic relationship between the GSLW and the wave envelope. Then the probability density function and the distribution function of the GSLW amplitude are derived. Thus the formulas for the average time duration and the mean length of runs can be derived. Good agreement between theoretical results and measured values was achieved. as verified with the measured double-peaked spectra in different regions.

Taylor Dispersion of Contaminants by Dual-peak Spectral Random Waves

Recent extensive and important studies have provided detailed information and compelling evidence on how the presence of waves influences the vertical diffusivity/dispersivity in the coastal environment, which can affect various water quality considerations such as the distribution of suspended sediments in the water column as well as the potential of eutrophication. Comparatively, how the presence of waves influences the horizontal diffusivity/dispersivity has received only scant attention in the literature. Our previous works investigated the role played by the Taylor mechanism due to the wave-induced drift profile which leads to the longitudinal dispersion of contaminants in the horizontal direction, under regular sinusoidal waves and random waves with single-peak spectra. Natural waves in the coastal environment, however, often possess dual-peak spectra, comprising both higher frequency wind waves and lower frequency swells. In this study, the Taylor dispersion of contaminants under random waves with dual-peak spectra is examined through analytical derivation and numerical calculations. The effects of various dual-peak spectral parameters on the horizontal dispersion, including the proportion of lower frequency energy, peak frequency ratio and spectral shape parameter, are investigated. The results show that the relative energy distribution between the dual peaks has the most significant effect. Compared with single-peak spectra with equivalent energy, the Taylor dispersion with dual-peak spectra is stronger when the lower frequency is close to the peak frequency of the single-peak spectrum, and weaker with the higher frequency instead. Thus, it can be concluded that with a dual-peak wave spectrum, wind-dominated seas with higher frequency lead to stronger dispersion in the horizontal direction than swell-dominated seas with lower frequency.

冻融循环下秸秆纤维混凝土损伤特性及动态力学性能研究

为研究冻融循环对不同纤维掺量的秸秆纤维混凝土动态力学性能的影响,采用非金属超声波检测仪测量不同冻融循环次数下秸秆纤维混凝土试件纵波波速,利用直径74 mm变截面分离式霍普金森压杆试验装置对试件开展动态单轴压缩试验,分析试件纵波波速、峰值应力、劣化度、韧性及破碎耗能密度与冻融循环次数及秸秆纤维掺量间的关系。结果表明:纤维的掺入能够提高混凝土材料的纵波波速及整体性,随着冻融循环次数的增加,秸秆纤维混凝土纵波波速随之降低,冻融循环会对试件造成损伤;秸秆纤维的掺入会增强混凝土材料的力学性能,掺量为0.2%时效果最佳,冻融循环作用试件峰值应力不断降低,劣化度不断增加,相较于冻融循环0次素混凝土试件,冻融循环30、60、90、120次试件峰值应力分别降低6.96%、19.4%、34.2%、53.3%,冻融循环后期应力降幅显著增加,纤维的掺入在一定程度上减缓了冻融作用下试件劣化程度;纤维掺量为0.2%时试件的韧性与破碎耗能密度提升最大,冻融循环会对试件造成劣化,降低其韧性及吸能效果。秸秆纤维的掺入使混凝土材料力学性能大幅增加,秸秆纤维的绿色可再生性对秸秆纤维混凝土的推广具有重大意义。

TNT和温压炸药浅埋爆炸效应差异性研究

为研究TNT和温压炸药浅埋爆炸效应的差异性,文章开展了浅埋爆炸试验,系统分析了TNT和温压炸药在爆坑形貌和地表空气冲击波波形等方面的差异。结果表明:相同工况的浅埋爆炸,温压炸药产生的爆坑直径、深度以及体积都大于TNT,装药埋深为0.1 m和0.3 m时,温压炸药产生的爆坑体积分别是TNT的1.2倍和2.3倍。通过对测得的冲击波参数进行比较,分析得出:当埋深为0.1 m和0.3 m时,比例距离为1的测点处温压炸药产生的冲击波峰值压力分别是TNT的2.16倍和1.41倍;在研究范围内,比例距离和埋深变化对不同类型装药的冲击波冲量衰减量影响很小,但对衰减率有较大影响,当埋深从0.1 m增加为0.3 m时,2种类型装药的冲量衰减率都增加了近1倍。

不同气流量下气泡帷幕对水下冲击波衰减特性研究

为了研究不同气流量下气泡帷幕对水下冲击波的衰减特性,采用高速摄像探究气泡帷幕在受到冲击波冲击后形态变化,结合冲击波压力时程曲线进行分析。结果表明,气泡帷幕中的气泡受到冲击波作用后会发生数次膨胀收缩行为,随着气流量增加,气泡膨胀的最大直径增大,第一次膨胀收缩周期变长;且气泡帷幕对水下冲击波压力有很强的衰减作用,气流量上升幅度越大,冲击波压力峰值衰减越明显,在气流量40 L/min下,冲击波峰值衰减高达88.98%;气流量大于20 L/min后,冲击波冲量衰减幅度均大于50.00%。针对气流量大小与压力峰值下降幅度的关系进行曲线拟合,提出适用于该工况下的经验方程,以期指导实际工程。

波浪能发电装置垂荡浮子PTO系统的建模与计算

为了便捷求出垂荡式波浪能发电装置垂荡浮子的平均功率,对现有的设计计算方法进行了研究。基于波浪理论和Froude-Krylov假定法求解波浪力,应用单自由度有阻尼系统受迫振动理论,将波浪激励力作为对垂荡浮体的输入动力,将发电机的电磁阻力作为主要的阻尼力,建立了质量-弹簧-阻尼振动力学模型,确定了垂荡浮子响应的计算方法,并对实际波浪能发电装置垂荡浮子Power Take Off(PTO)系统列举出计算实例。在算例基础上,对假设条件进行了扩展,应用频率响应曲线、MATLAB软件做出不同参数条件下平均功率三维曲线和输出平均功率数值表,清晰地表明了系统响应状况。研究显示,在波高和频率比一定的条件下,PTO系统平均机械功率随着浮体质量和阻尼力矩的变化具有峰值,围绕峰值区域设计装置的各项参数,能够取得较理想的效果。该建模与计算方法可为实际工程优化设计提供参考。

滑坡面瑞雷波波场模拟及H/V谱比探测

滑坡是一种分布广泛、数量众多、危害巨大的地质灾害,准确确定滑坡滑动面对滑坡防治具有重大意义。传统的勘探手段,如钻探和地球物理方法在起伏较大的滑坡地形中具有诸多限制。本文以四川省屏山县东池庄滑坡为参考,建立了起伏地形软弱性土质滑坡模型,进行了瑞雷波波场模拟并经过模式分离后计算求得水平/垂直(H/V)谱比曲线。对比分析了波场传播及H/V谱比曲线的特征,发现在110道检波器排列中,中心部位检波器的峰值频率可作为计算土石分界面的卓越频率。设计了土层厚度分别为25、31、35 m的滑坡模型,发现土层厚度与峰值频率呈负相关关系。给出了地层为黏性土与泥岩时的频率-深度经验公式,得到了连续滑动面信息,经验公式计算结果与实际模型吻合较好。

冠心病患者动态心电图检查中P波离散度、T波峰-末间期的变化及诊断价值研究

目的:探讨冠心病(CHD)患者动态心电图检查中P波离散度(Pd)、T波峰-末(Tp-Te)间期的变化及诊断价值。方法:选取CHD患者203例作为研究组,其中,心肌缺血95例作为心肌缺血组,心肌缺血合并心律失常108例作为心肌缺血合并心律失常组。另取同期体检健康者90例作为对照组。所有受试者均接受动态心电图检查,并记录Pd、Tp-Te间期情况。比较研究组和对照组以及心肌缺血组和心肌缺血合并心律失常组Pd、Tp-Te间期。绘制受试者工作特征曲线(ROC)分析Pd、Tp-Te间期对CHD及CHD心律失常的诊断价值。结果:研究组Pd、Tp-Te间期大于对照组(均P<0.05)。Pd、Tp-Te间期联合诊断CHD的AUC高于两者单独诊断的AUC(均P<0.05)。心肌缺血合并心律失常组Pd、Tp-Te间期大于心肌缺血组(均P<0.05)。Pd、Tp-Te间期联合诊断CHD患者心律失常的AUC高于两者单独诊断的AUC(均P<0.05)。结论:CHD患者动态心电图Pd增加及Tp-Te间期延长,且心肌缺血合并心律失常患者Pd增加及Tp-Te间期延长较心肌缺血患者更为明显,两者联合对CHD及CHD心律失常诊断价值较高。

爆炸冲击波与水膜相互作用的试验研究

为了研究爆炸冲击波与水膜的相互作用,基于水平激波管搭建冲击波与水膜相互作用的试验平台,设计一个水膜发生器,能够产生厚度为8 mm的稳定水膜。研究了1.31和1.42马赫的入射冲击波分别与距管口45、55和65 mm处的水膜相互作用,并采用纹影仪和高速摄影机对冲击波与水膜的相互作用进行了可视化研究,采用压力测试系统记录水膜前方和后方20 mm处的压力和冲量变化。研究结果表明:水膜前方的压力变化取决于冲击波的反射,且水膜产生的反射波低于刚性-固体壁面产生的反射波;水膜后方的压力变化取决于受冲击的水膜破碎时所吸收的能量,且这部分能量主要来源于冲击波后高速气流的作用,冲击波本身的作用并不明显;水膜后方的峰值压力和冲量显著增强,峰值压力的增强效果能达到50%以上,冲量的增强效果能达到10倍以上;水膜距管口越远,对峰值压力的增强效果越显著,对冲量的增强效果越微弱。

激波/湍流边界层干扰中的自适应控制技术

从激波/湍流边界层干扰机理以及流动控制的迫切需求入手,从自适应涡流发生器、自适应鼓包、自适应微射流以及自适应次流循环四个方面对激波/湍流边界层干扰中的自适应控制技术研究进展进行了总结。分析认为,结合AI技术发展自适应流动控制技术,加速控制方式智能化,可作为新一代高超声速飞行器宽速域飞行的重要技术手段。具体来说,就是通过调节外加激励对高超声速飞行器不同区域实现局部流动加/减速、气动热防护、气动控制等功能,根据流场参数建立控制反馈回路,自适应调整局部流场结构,以满足工程实际需求。

结构参数对闭口体系新型激波吹灰器工作特性的影响研究

锅炉吹灰器可以有效实现清除锅炉内部的积灰,提高锅炉运行效率,对锅炉安全运行具有重要意义。SPG型激波吹灰器是在传统激波吹灰器基础上发展而来的闭口体系新型高性能吹灰器,使用数值方法对该装置的可行性进行验证,并分析工作特性,可以为实际应用与改进提供参考。基于CFD技术,将SPG型激波吹灰器作为研究对象,使用动网格技术对设备内活塞的真实运动过程进行仿真模拟,利用Fluent软件模拟计算SPG型激波吹灰器内部流场的连续变化这一动态过程,并通过调整喷管、燃烧室以及压力蓄能器的结构参数,在出口处监测得到各部件结构参数变化对排气特性的影响规律,获取其工作特性。结果表明:喷管的长径比从2增加到4时,出口参数峰值出现滞后现象,但压力峰值与速度峰值获得显著提升,且喷管的扩张段改为直管可以降低膨胀损失,适当增加喷管长径比并直接连接直管是一种较好的方案;燃烧室径向和轴向壁面之间的间距缩短均可使出口压力峰值提高,但轴向距离缩短压力峰值增加幅度更大;在压力蓄能器中,去除阻尼装置压力提升较少,且无法减缓活塞复位,使排出气体减少,去除限位器后喷管出口压力大幅提高,但其峰值持续时间变短。

基于BP神经网络的场地等效剪切波速变化预测研究

利用日本KiK-net台网提供的407个台站的30952条地震动记录,提出了一种基于BP神经网络的场地等效剪切波速比变化预测模型。模型采用了均方误差函数及Adam优化算法,由3个输入参数、5个隐藏神经元及1个输出参数组成。输入参数为地面峰值加速度PGA、Arias烈度I_(a)及场地剪切波速V_(S30),输出为场地等效剪切波速比(V_(S r))。研究结果表明:该神经网络模型残差对于各输入变量整体呈现出无偏的特性,在大部分的软硬场地中均有较好的预测性能,该模型预测得到的PGA关于V_(S30)的相关系数曲线与用传统的最小二乘法回归得到的函数曲线相比,其相关系数有更好的表现。该模型预测曲线显示,B类场地在PGA达到175 cm/s^(2)时,场地剪切波速下降5%,D、E类场地在PGA达到140 cm/s^(2)时,场地剪切波速下降5%,多数场地的非线性阈值为50~100 cm/s^(2)。PGA在该网络模型中占据着较高的权重,为场地等效剪切波速变化的最主要控制参数。该网络模型捕捉到场地等效剪切波速比随PGA的增大有下降的趋势,而较为松软的D、E类场地受PGA影响更大,下降幅度更大。

加热速率对中心直裂纹巴西圆盘试样断裂行为影响规律研究

为了研究不同加热速率处理后花岗岩的断裂特性与损伤机理,对中心直裂纹巴西圆盘(CSTBD)试样在4组加热温度下分别进行4种加热速率的高温处理,冷却至室温后使用电液伺服压力机进行巴西劈裂实验,分析其静力学断裂过程。结果表明:(1)经过不同高温处理的花岗岩,从脆性破坏向延性破坏转变。(2)在同一目标温度下,经不同加热速率处理的花岗岩,峰值破坏载荷随着加热速率的增大而降低。表观颜色无明显区别,而表观裂缝逐渐增多。(3)不同加热速率下,200℃和400℃下的纵波波速和弹性模量变化较小,而600℃以上时,随着加热速率的增大,纵波波速和弹性模量显著降低。(4)花岗岩的断裂韧度随着温度升高呈现逐渐衰减特征,同一温度下花岗岩试样的I型断裂韧度值随加热速率的增大而减小,400℃下加热速率对花岗岩断裂韧度的影响最大。

Analysis of Blast Wave Propagation Inside Tunnel

The explosion inside tunnel would generate blast wave which transmits through the longitudinal tunnel. Because of the close-in effects of the tunnel and the reflection by the confining tunnel structure, blast wave propagation inside tunnel is distinguished from that in air. When the explosion happens inside tunnel, the overpressure peak is higher than that of explosion happening in air. The continuance time of the blast wave also becomes longer. With the help of the numerical simulation finite element software LS-DYNA, a three-dimensional nonlinear dynamic simulation analysis for an explosion experiment inside tunnel was carried out. LS-DYNA is a fully integrated analysis program specifically designed for nonlinear dynamics and large strain problems. Compared with the experimental results, the simulation results have made the material parameters of numerical simulation model available. By using the model and the same material parameters, many results were adopted by calculating the model under different TNT explosion dynamites. Then the method of dimensional analysis was used for the simulation results. As overpressures of the explosion blast wave are the governing factor in the tunnel responses, a formula for the explosion blast wave over-pressure at a certain distance from the detonation center point inside the tunnel was derived by using the dimensional analysis theory. By comparing the results computed by the formula with experimental results which were obtained before, the formula was proved to be very applicable at some instance. The research may be helpful to estimate rapidly the effect of internal explosion of tunnel on the structure.

Effects of tidal currents on winter wind waves in the Qiongzhou Strait:a numerical study

Effects of currents on winter wind waves in the tide-dominated Qiongzhou Strait(QS)were numerically evaluated via employing the coupled ocean-atmosphere-wave-sediment transport(COAWST)modeling system.Validations showed satisfactory model performance in simulating the intense tidal currents in the QS.Different effects of sea level variations and tidal currents on waves were examined under the maximum eastward(METC)and westward(MWTC)tidal currents.In the east entrance area of the QS,the positive sea levels under the MWTC deepened the water depth felt by waves,benefiting the further propagation of wave energy into the inner strait and causing increased wave height.The METC and the MWTC could both enhance the wave height in the east entrance area of the QS,mainly through current-induced convergence and wavenumber shift,respectively.By current-induced refraction,the METC(MWTC)triggered counterclockwise(clockwise)rotation in peak wave directions in the northern part of the QS while clockwise(counterclockwise)rotation in the southern part.

Non-conventional modeling of extreme significant wave height through random sets

The analysis and design of offshore structures necessitates the consideration of wave loads. Realistic modeling of wave loads is particularly important to ensure reliable performance of these structures. Among the available methods for the modeling of the extreme significant wave height on a statistical basis, the peak over threshold method has attracted most attention. This method employs Poisson process to character- ize time-varying properties in the parameters of an extreme value distribution. In this paper, the peak over threshold method is reviewed and extended to account for subjectivity in the modeling. The freedom in selecting the threshold and the time span to separate extremes from the original time series data is incorpo- rated as imprecision in the model. This leads to an extension from random variables to random sets in the probabilistic model for the extreme significant wave height. The extended model is also applied to different periods of the sampled data to evaluate the significance of the climatic conditions on the uncertainties of the parameters.

Directional Spectrum of Wind Waves: Part Ⅱ- Comparison and Confirmation

A model on the directional frequency spectrum of wind waves for deep water is introduced. The comparisons of the proposed model with other existing models show that the proposed model is very close to the JONSWAP model and DHH model for describing the developing waves under the normal spectral bandwidth, and has a better description for the transition of the unidirectional spectrum from ω -4 to ω -5 at a position around 3ω p, i.e., three time the peak frequency. Comparisons also show that the proposed model describes closely both field data measured by a four-frequency radar and a laser-optical sensor, and laboratory data measured by a laser slope gauge and an imaging optical method. The comparisons further demonstrate that the inverse spectral bandwidth as a new wave parameter is robust for describing the spectral steepness. Finally, the formula on the local spectral-peak angular frequency is confirmed using the observed two-dimensional spectra.

A fuzzy quantification approach of uncertainties in an extreme wave height modeling

A non-traditional fuzzy quantification method is presented in the modeling of an extreme significant wave height. First, a set of parametric models are selected to fit time series data for the significant wave height and the extrapolation for extremes are obtained based on high quantile estimations. The quality of these results is compared and discussed. Then, the proposed fuzzy model, which combines Poisson process and gener-alized Pareto distribution （GPD） model, is applied to characterizing the wave extremes in the time series data. The estimations for a long-term return value are considered as time-varying as a threshold is regarded as non-stationary. The estimated intervals coupled with the fuzzy theory are then introduced to construct the probability bounds for the return values. This nontraditional model is analyzed in comparison with the traditional model in the degree of conservatism for the long-term estimate. The impact on the fuzzy bounds of extreme estimations from the non stationary effect in the proposed model is also investigated.

Shenzhou-4 spaceborne altimeter waveform processing and significant wave height retrieval

The Shenzhou -4 spaceborne （SZ -4） altimeter waveforms were processed, and then the significant wave heights （SWH） was retrieved on the basis of waveform fitting and waveform retracking. Waveforms processing includes the waveform ls averaging, the elimination of thermal noise and the waveforms normalization. Double peaks were found on each SZ - 4 waveform, and it was pointed out that the region of waveforms with the second peak is abnormal and its effects on the whole waveform in the waveform fit should be taken into consideration. To obtain the width of the waveform leading-edge, a method was proposed to find the starting point of waveform, and the half-power point of waveform was found by retracking the waveform. The normalized wavefornis were fitted with the Haynes model by using the weighting least square fit method. Then the selections of the weighting coefficients and their effects on significant wave hight retrieving were discussed, and the optimal five-region weighting method was proposed. At last, the SWH data of SZ -4 altimeter retrieved by using the proposed method were compared with those of ERS -2 and Jason - 1 altimeter, and it was concluded that the SZ -4 altimeter can detect significant wave height.