液固两相射流冲击磨损的数值计算与实验研究

应用实验与数值模拟研究液固两相射流对不锈钢材料的冲蚀磨损行为,分析不同质量分数、粒径情况下样品的平均磨损率,并基于数值模拟预测不同射流速度工况下的冲刷磨损率,最终建立冲刷磨损率与射流速度的关系模型。研究结果表明:单相射流流场的数值模拟结果与实验结果吻合较好;在距离射流中心区域不同径向距离上,平均速度的变化趋势较一致;在近壁面处,射流轴向速度突然减小,造成雷诺切应力增大。在远离壁面处,其法向速度逐渐增大,脉动速度相应增大,雷诺切应力增大;当射流继续远离壁面时,雷诺切应力开始减小直到趋近于0;在喷嘴正下方,压力分布存在1个滞止区,此处压力高于四周压力;下游冲刷磨损率先升高再稍微下降,而上游冲刷磨损率明显下降;实验样品表面微观测试结果验证了不同区域冲刷磨损率分布的正确性。国家自然科学基金资助项目(51776225,51376153,51406235);;中国石油大学(北京)科学基金资助项目(C201602)~

基于Au1200无线车载视频监控的设计与实现

基于Au1200设计无线车载媒体处理系统,介绍系统中视频监控部分的设计方案,提出基于ffMPEg的软压缩方法,设计并实现了视频监控的实时采集、压缩和存储。利用ffMPEg软压缩方法,将采集到的视频数据实时压缩成视频文件存储于硬盘中,降低了系统成本,对实际嵌入式媒体处理系统的开发具有较大价值

Image qual ity evaluation based on visual masking effect and singular value decomposition

中文摘要:将人眼视觉特性和图像本征特性相结合 ,设计了一套基于视觉掩盖和奇异值分解的图像质量评测方法。根据人眼的视觉敏感性函数(CSF)将参考图像和待测图像做噪声掩盖处理 ,剔除视觉敏感区外的图像信息;然后 ,根据人眼视觉特性提取参考图像的纹理区和平坦区 ,并作为待测图像检测区的划分依据 ,分别计算参考图像和待测图像在各自纹理区 和平坦区的奇异值;最后 ,通过奇异值测度得到待测图像在纹理区和平坦区的质量劣化程度。实验表明:通过纹理区和平坦区的区分检测 ,可提高检测敏感度并据此判断劣化及影响程度。同时 ,检测结果的主观相似性(CC)可达到 0. 896 ,均方根误差(RMSE)为 5. 58 ,较 PSNR和 SSIM 具有更好的性能。该方法实现简单 ,便于系统集成 ,可在涉及视频及图像质量检测的领域得到较好应用。 英文摘要：A image quality evaluation method based on visual masking effect and singular value decom-position is proposed. According to t he Cont rast Sensibility Function (CSF) ,t he original image and the processed image are prep rocessed to remove the signals out side the sensible region. On the basis of t he property of t he Human Visual System ( HVS) , t he text ure and plat regions of the original image are extracted to used as a division standard. Then , the singular values of t he original and p rocessed images are calculated bot h in text ure and plat regions. Finally , by measuring the difference between the singular value met rics of the original and the processed images , the image quality can be evaluated. The experimental result s show that this method is sensible to t he errors perceived by human2being and can improve discrimination for t he distortion region. The cor relation between t he result and t he subjective score is 0. 896 and t he root mean square error (RMSE) is 5. 58 ,which shows t he method can be realized easily and can be embedded into t he application system.基金项目:广州京信研究基金资助项目(No. K81004

Method for Video Quality Evaluation Based on HVS Properties

摘要：本文针对视频质量的评测应用，对传统峰值信噪比(PSNR)算法加以改进。通过在视频帧内图像和帧间图像的处理过程中引入人眼视觉系统(HVS)的主要特性，克服传统 PSNR 算法在序列质量检测应用方面的缺陷。方法在帧内图像处理上利用人眼对边缘轮廓失真具有较强敏感性的特点，设计了基于图像边缘的检测方案以提高对典型空域失真的检测性能；在帧间图像处理上，通过测量帧间时域能量的变化，获得序列在时域轴上的典型特征，并据此对空域检测结果进行修正。通过上述改进，算法能在保持传统 PSNR 算法简易性的同时，提升其检测结果与主观感受的相关性；同时算法的计算量并不复杂，易于在检测设备中实现系统集成 Abstract: A method for the objective video quality assessment is proposed. By using the Human Vision System (HVS) properties into the intra and inter frame processing, the proposed method can overcome the traditional Peak Signal-to-noise Ratio (PSNR) in the application of video quality evaluation. Based on the principle that human's eyes tend to be more sensible to the degradation happening in the edge of image, a detection scheme is designed to evaluate the distortion in the intra frame. By measuring the temporal energy, know the typical features in the temporal domain and then use them to modify the evaluation result of the spatial domain. The proposed method inherits the advantages of the traditional PSNR such as simpleness and convenience and has better correlation with the subjective perception. And it can be easily implemented and integrated in the equipment system of detection.京信研究基金资

Investigation of behaviour of particle impact on material by impinging jet

颗粒冲击材料现象广泛存在于自然界以及工业领域中。应用实验测量与数值计算相结合的方法研究了颗粒射流冲击材料(304不锈钢)的磨损行为。考虑了颗粒粒; 径、运动轨迹、颗粒-壁面撞击点分布以及所导致材料物相结构变化。实验测试包括材料质量损耗、材料元素X射线衍射(XRD)分析、表面微观结构扫描电镜(; SEM)观察。对相应的颗粒射流冲击材料行为进行了数值计算,获得流场,颗粒场以及相应材料磨损。结果表明:颗粒射流冲击下颗粒运动轨迹与撞击点的分布不; 同,造成了材料样品表面磨损区域明显不同。颗粒-壁面碰撞不仅会导致材料损失而且会造成材料物相结构的变化。Particle-material impact is popular in the nature and industries. In; this work, experimental measurement and numerical calculation were; carried out to investigate the particle impinging jet effect on the; behaviour of material (304 stainless steel). Herein, particle diameter,; particle tracking trajectories, particle-wall collision point; distribution were considered to study material loss and the phase change; of material structure. In the experimental work, the measurements were; carried out for material mass loss, material element X-ray; diffractometry (XRD) analysis, surface micro-structure scanning electron; microscopy (SEM) observation and so on. In addition, the behaviour of; particle impinging jet impact on wall material was studied by numerical; simulations. Particularly, flow fields, particle trajectories and wall; material loss were obtained. The results show that particle collision; point distribution is quite different from their tracking trajectories; under particle impinging jet impact, which causes the wear zones on; sample surface different from each other obviously. It is concluded that; particle-wall impact will not only lead to material loss but also cause; the phase change of material structure.国家自然科学基

Optimized Local Superposition in Wireless Sensor Networks with t-average-mutual-coherence

Compressed sensing (CS) is a new technology for recovering sparse data from undersampled measurements. It shows great potential to reduce energy for sensor networks. First, a basic global superposition model is proposed to obtain the measurements of sensor data, where a sampling matrix is modeled as the channel impulse response (CIR) matrix while the sparsifying matrix is expressed as the distributed wavelet transform (DWT). However, both the sampling and sparsifying matrixes depend on the location of sensors, so this model is highly coherent. This violates the assumption of CS and easily produces high data recovery error. In this paper, in order to reduce the coherence, we propose to control the transmit power of some nodes with the help of t-average-mutual-coherence, and recovery quality are greatly improved. Finally, to make the approach more realistic and energy-e±cient, the CIR superposition is restricted in local clusters. Two key parameters, the radius of power control region and the radius of local clusters, are optimized based on the coherence and resource consideration in sensor networks. Simulation results demonstrate that the proposed scheme provides a high recovery quality for networked data and verify that t-average-mutual-coherence is a good criterion for optimizing the performance of CS in our scenario.Qualcomm-Tsinghua-Xiamen University Joint Research Program; National Natural Science Foundation of China under grant 61172097;Fellowship of Postgraduates' Oversea Study Program for Building High-Level Universities from the China Scholarship Council

A Congestion-aware Cross-layer Routing Scheme of Ad Hoc Networks with Multi-rate Mechanism

利用跨层设计的思想,论文提出了一种自适应多速率机制下,基于节点信息的AdHoc路由算法。根据物理层SNR的测量,结合MAC层的信息进行延迟估计,引入一种新的路由度量来选择路径,避开拥塞,减少延迟,提高网络吞吐量,从而能改善网络的整体性能。This paper proposes a cross-layer routing scheme based on information monitored by nodes for Ad Hoc networks supporting multi-rate mechanism.A new routing metric is introduced to take SNR measure on physical layer and delay estimate on MAC layer into account.With this metric,the routing algorithm tends to choose routes with wider bandwidth,lower delay,and less congestion.It demonstrates that the proposed scheme improves the performance of Ad Hoc work.清华-高通无线通信研究中心资助项

Sparsity-based Online Missing Sensor Data Recovery

In sensor networks, due to power outage at a sensor node, hardware dysfunction, or bad environmental conditions,not all sensor samples can be successfully gathered at the sink. Additionally, in the data stream scenario, some nodes may continually miss samples for a period of time. In this paper, a sparsity-based online data recovery approach is proposed. We construct an overcomplete dictionary composed of past data frames and traditional fixed transform bases. Assuming the current frame can be sparsely represented using only a few elements of the dictionary, missing samples in each frame can be estimated by Basis Pursuit. Our method was tested on data from a real sensor network application:monitoring the temperatures of the disk drive racks at a data center. Simulations show that in terms of estimation accuracy and stability, the proposed approach outperforms existing average-based interpolation methods, and is more robust to burst missing along the time dimension.This work was supported by Tsinghua-Qualcomm Joint Research Program,Fundamental Research Funds for the Central Universities (No. 2011121050),and National Natural Science Foundation of China (No. 61001142)

Sparsity-Based Spatial Interpolation in Wireless Sensor Networks

The authors would like to thank Ming-Ting Sun at University of Washington and Zicheng Liu at Microsoft for constructive suggestions.In wireless sensor networks, due to environmental limitations or bad wireless channel conditions, not all sensor samples can be successfully gathered at the sink. In this paper, we try to recover these missing samples without retransmission. The missing samples estimation problem is mathematically formulated as a 2-D spatial interpolation. Assuming the 2-D sensor data can be sparsely represented by a dictionary, a sparsity-based recovery approach by solving for l1 norm minimization is proposed. It is shown that these missing samples can be reasonably recovered based on the null space property of the dictionary. This property also points out the way to choose an appropriate sparsifying dictionary to further reduce the recovery errors. The simulation results on synthetic and real data demonstrate that the proposed approach can recover the missing data reasonably well and that it outperforms the weighted average interpolation methods when the data change relatively fast or blocks of samples are lost. Besides, there exists a range of missing rates where the proposed approach is robust to missing block sizes.Qualcomm-Tsinghua- Xiamen University Joint Research Program;Fellowship of Postgraduates’ Oversea Study Program for Building High-Level Universities from the China Scholarship Council

国内外聚羧酸系高性能减水剂的性能比较

选取了国内外4个品牌5种聚羧酸系高性能减水剂作为研究对象,分别从水泥净浆流动度、与水泥的相容性、保坍性以及产品的性价比等方面进行了对比研究.研究表明:不同品牌的国内外聚羧酸系减水剂具备了低掺量、高减水率、保坍性好、增强效果显著等共同特点,但是与水泥的相容性存在着较大差异.分析认为,国产聚羧酸系高性能减水剂产品与国外同类产品相比,技术性能差距不大,基本上处于同一档次,但是却拥有明显的价格优势.与此同时,我国庞大的建筑市场为国内外聚羧酸系高性能减水剂的推广应用提供了广阔的发展空间,使其具有良好的应用前景