Damping long waves by a multi-channel structure     

Sheng-Wen Twu  Cheng-Chi Liou 《Ocean Engineering》2003,30(3):351-367

In this paper, a multi-channel structure was developed to attenuate waves with various wave periods. By ignoring energy losses and the factor of channel width, a simple and straightforward method was used to tackle this problem. The theoretical solution showed that a single reflected channel structure could attenuate waves of a certain wave period, while a multi-channel structure could attenuate waves with various wave periods. If an interval of 0.05<relative water depth<0.15 is concerned, a structure consisting of four reflected channels could provide a transmission coefficient of less than 0.2. Experimental tests were conducted to verify the theoretical solutions. Both theoretical solution and experimental data indicated that waves with various wave periods would be effectively attenuated after passing through the multi-channel structure. Although some factors are neglected in treating this problem, the method is applicable. An allowed transmission coefficient can be provided by a multi-channel structure only if the computed peak value is not larger than that value.  相似文献   

NI4472在海洋噪声和传播损失测量中的应用   总被引：1，自引：0，他引：1  

崔华义  周长兴 《海洋技术学报》2003,22(3):74-75

利用NI公司的高性能数据采集板NI4472来进一步改善海洋噪声和传播损失的测量情况。  相似文献   

湖北2015年冬季PM_2.5重污染过程的气象输送条件及日变化特征分析     

白永清  祁海霞  赵天良  杨浩  刘琳  崔春光 《气象学报》2018,76(5):803-815

PM_2.5污染仍然是湖北省冬季大气污染的首要污染类型,且具有明显区域传输特征,重污染过程的空气污染气象条件有别于华北地区,值得关注。采用WRF/Chem不同排放情景下的模拟结果,并结合观测分析,研究了2015年12月—2016年1月湖北省PM_2.5重污染过程的气象输送条件及日变化特征,从大尺度输送条件和局地边界层动力作用分析了外来污染物水平传输、悬浮聚集和向下传输的过程,并解释了该地区观测到的午后PM_2.5浓度特殊峰值的气象成因。结果表明,湖北重污染爆发以区域传输为主,地面观测PM_2.5极值对应10 m风速可达8—10 m/s,边界层0—1 km为较强偏北风输送,污染传输通量极值位于400 m高度附近,为重要传输通道,低空无明显逆温,重污染过程具有“非静稳”边界层气象特征。重污染形成的大尺度输送条件为,长江中下游及北部地区偏北风异常偏强,南部地区风速减缓,使污染物在中游平原堆积,鄂北边界风速越大,越有利污染输送增长。传输性污染主要来自偏北和东北方向的污染源输送,潜在源区贡献主要为途经偏北通道上的豫中、南阳盆地和关中地区,以及途经东北通道上的鲁、皖、苏等部分地区。PM_2.5浓度日变化双峰结构的天气成因不同,21—24时（北京时）峰值为静稳性污染,11—14时峰值为传输性污染。污染输送受大气边界层高度影响,日出前大气边界层高度较低,层结稳定并伴有上升运行,使得低空外来输送悬浮聚集在400 m高度附近;日出后随大气边界层高度升高,静稳层结被破坏,在干沉降作用下高浓度PM_2.5开始向下传输,并在午后地面形成峰值。   相似文献   

Scattering of internal waves in a two-layer fluid flowing through a channel with small undulations     

Smrutiranjan Mohapatra  Swaroop Nandan Bora 《Ocean Dynamics》2009,59(4):615-625

Using two-dimensional linear water wave theory, we consider the problem of normal water wave (internal wave) propagation over small undulations in a channel flow consisting of a two-layer fluid in which the upper layer is bounded by a fixed wall, an approximation to the free surface, and the lower one is bounded by a bottom surface that has small undulations. The effects of surface tension at the surface of separation is neglected. Assuming irrotational motion, a perturbation analysis is employed to calculate the first-order corrections to the velocity potentials in the two-layer fluid by using Green’s integral theorem in a suitable manner and the reflection and transmission coefficients in terms of integrals involving the shape function c(x) representing the bottom undulation. Two special forms of the shape function are considered for which explicit expressions for reflection and transmission coefficients are evaluated. For the specific case of a patch of sinusoidal ripples having the same wave number throughout, the reflection coefficient up to the first order is an oscillatory function in the quotient of twice the interface wave number and the ripple wave number. When this quotient approaches one, the theory predicts a resonant interaction between the bed and the interface, and the reflection coefficient becomes a multiple of the number of ripples. High reflection of the incident wave energy occurs if this number is large. Again, when a patch of sinusoidal ripples having two different wave numbers for two consecutive stretches is considered, the interaction between the bed and the interface near resonance attains in the neighborhood of two (singular) points along the x-axis (when the ripple wave number of the bottom undulation become approximately twice as large as the interface wave number). The theoretical observations are presented in graphical form.  相似文献   

无线网络技术在气象信息服务中的应用   总被引：1，自引：0，他引：1       下载免费PDF全文

王会品  张涛 《气象与环境学报》2009,25(2):54-56

介绍了利用无线网络这一先进技术为政府和部分行业部门提供及时天气信息、预报预警等气象信息服务,以及如何应用该技术进行气象信息自动采集、无线传输、发布显示,如何对发布的气象信息进行自动采集与实时更新。由于无线网络技术本身的优越性,被应用于越来越多的气象服务中,可以提高气象信息服务的及时性和高效性。  相似文献   

中国对虾育苗期球形病毒的感染及垂直传播途径的初步探讨   总被引：3，自引：1，他引：2  

汝少国  姜明  李永祺  马英杰 《海洋与湖沼》1999,30(3):255-260

１９９４－１９９５年山东文登市高岛盐厂对虾育苗池和养虾池,随机和定点采集中国对虾的卵,无节幼体,蚤状幼体,糠虾幼体,仔虾及幼虾,成虾样品,利用透射电子显微镜对其进行病毒的检测。结果表明,卵细胞中含有大量的卵黄,没有明显的细胞分化,卵细胞质中有球形病毒感染;无节幼体的肝胰腺和上皮细胞的分化程度较低,有大量球形病毒分布;糠虾幼体已有明显的肝胰腺和上皮细胞的分化,肝胰腺上皮细胞的胞质中发现有球形病毒包涵  相似文献   

Scattering of water wave by a submerged horizontal plate and a submerged permeable breakwater     

Hu-Hsiao Hsu  Yung-Chao Wu 《Ocean Engineering》1998,26(4):325-341

Based on a two-dimensional linear water wave theory, this study develops the boundary element method (BEM) to examine normally incident wave scattering by a fixed, submerged, horizontal, impermeable plate and a submerged permeable breakwater in water of finite depth. Numerical results for the transmission coefficients are also presented. In addition, the numerical technique's accuracy is demonstrated by comparing the numerical results with previously published numerical and experimental ones. According to that comparison, the transmission coefficient relies not only on the submergence of the horizontal impermeable plate and the height of the permeable breakwater, but also on the distance between horizontal plate and permeable breakwater. Results presented herein confirm that the transmission coefficient is minimum for the distance approximately equal to four times the water depth.  相似文献   

含裂缝地层的过套管电阻率测井响应特征研究          下载免费PDF全文

刘福平  刘晓博  王安玲  刘华群  游福成  杨长春 《地球物理学报》2017,60(2):851-861

由于石油压裂开采等开发措施的实施,会使在套管周围存在着许多被油气等高阻流体填充的微裂缝.尽管这些裂缝或孔隙可能很小,但对套管井电阻率测量会有非常大的影响,甚至会改变原地层的电阻率测井特征,因此裂缝测井响应的计算及考察对过套管电阻率测井十分重要.为解决裂缝测井响应的计算问题,本文提出了计算等效电阻的电流通量管模型,利用该电流通量管模型给出了含垂直裂缝地层横向电阻的计算方法,基于传输线方程法及地层电阻的过套管测量方法实现了含裂缝地层的过套管电阻率测井响应的数值计算,通过计算实例考察了地层裂缝对过套管电阻率测井响应的影响.算例表明:裂缝中的高阻流体对地层视电阻率测量结果会有较大的影响;环形裂隙比垂直裂缝有更大的电阻率测井响应.本文的研究为解决微裂缝过套管电阻率测井响应的计算这一关键技术问题提供了一种可行的计算与考察方法.  相似文献   

单通道无线存储式地震仪关键技术   总被引：2，自引：1，他引：1       下载免费PDF全文

田入运  吕世学  林君  张林行 《地球物理学报》2017,60(11):4273-4281

当前地震勘探装备多数价格昂贵、体积大、功耗高,导致大规模的地震勘探产生很大困难.新型的无缆存储式地震仪,省去了大线传输,解决了复杂环境下进行大道数地震数据采集的问题.但是由于缺乏有效的监测手段,无法对其进行现场实时质量监控,施工质量和效率难以保证,具有封闭性的技术缺陷.针对此问题,本文研制了一款基于无线网络通讯技术的低功耗、低成本、小体积、高精度的现场可实时质量监控型单通道无线存储式地震仪.地震仪以Cortex-M4型内核MCU为核心,构成系统的主控模块,负责管理系统运行.采用32位A/D采集模块、大容量SD卡存储模块、高效率DC-DC电源管理模块、低功耗无线WiFi模块以及有线以太网模块,完成地震数据的采集、存储、质量监控和回收.研制的基于无线通讯技术的单通道无线存储式地震仪以其便携性、低成本、可现场实时质量监控以及地震数据本地存储的特点,降低了勘探成本,提高了大规模勘探的可操作性,在大道数、高密度、宽方位的地震勘探中具有广泛的应用前景.  相似文献   

系留式无人机中继通信系统在地震应急现场的应用试验研究   总被引：1，自引：0，他引：1  

徐秀杰  贾荣光  杨玉永  娄世平  董翔  胡鹏  李永强 《震灾防御技术》2018,13(3):718-726

在地震现场应急通信中,为满足无线图传系统等通信设备在复杂地形进行大范围和远距离通信作业的需求,提出利用系留式无人机中继通信系统保障无线电（超短波）的远距离传输。目前,对该系统的研究还处于理论分析和试验阶段,尚未在地震应急中得到大范围的推广应用。本研究利用多次试验的数据,分析验证系留式无人机供电系统的可行性及实用性,定量计算中继通信系统的升空效益,并形成一套完整的、可操作性强的系统实施方案。在城区、郊区以及起伏较低的山地、丘陵等地区,实现了移动图传系统在距离通信车5—10km范围内稳定、实时、快速的数据传输。  相似文献