基于核磁共振弹性成像技术的肝纤维化分级体模研究

Accurate detection of liver fibrosis stage and fibrosis procession is crucial for assessing prognosis and candidacy for treatment of patients with chronic hepatic disease. A significant need exists for developing a noninvasive technique for quantitative detection of liver fibrosis stage. Magnetic resonance elasto-graphy (MRE) is one of the most repidly advancing technologies for classifying the liver fibrosis. This study establishes a platform for liver fibrosis classification, and discusses some details in developing stimulator and displacement-phase imaging pulse. At last, the preliminary result and analysis of phantom experiment are given, which would form a basis for subsequent research on phantom MRE and its clinic application.     

基于非接触式麦克风冲击共振测试的钢-混组合结构界面脱空损伤识别方法研究

针对现有无损检测技术在钢-混组合结构界面混凝土脱空损伤识别问题上普遍存在的测试成本高、识别精度有限及操作过程复杂等不足之处,提出了一种基于麦克风冲击共振测试的非接触式检测方法。首先,基于四边约束矩形薄板振动理论,将钢-混凝土板局部脱空处钢板简化为四边固支约束的板壳模型进行分析。通过在ABAQUS中建立考虑流-固耦合的钢-混凝土板有限元模型,将模拟所得脱空处钢板自振频率值与理论解析结果进行对比,证明该经验公式可有效适用于脱空区域处局部钢板自振频率的估计当中。其次,依据相关声学理论研究成果,利用所建立的有限元模型进行了外部激励下钢-混组合结构声压场信号分布特征研究,结果表明设置及未设置脱空损伤的有限元模型所产生的声压响应存在明显不同,且未脱空模型中信号响应具有幅值大、周期长等特征;同时,针对一钢-混凝土板设置了8种不同类型的损伤工况,并利用麦克风传感器分别进行了基于冲击共振测试的脱空损伤识别。试验结果表明,麦克风摆放位置对测试所得声压信号频响函数基本特征的影响程度并不显著;且针对本试验所设置的损伤工况,该方法基本均能实现有效识别,但对平面尺寸在60 mm以下区域的测试效果并不明显。最后,在对一特定损伤区域进行栅格化处理的基础上,通过开展基于麦克风冲击共振法的损伤成像测试,对该脱空区域的平面轮廓进行了有效识别。除此之外,将试验测试效果分别与传统红外热像检测法、超声波探测法进行了对比分析,验证了该麦克风冲击共振法能够较好地适用于钢-混组合结构的脱空损伤识别问题当中,且具有非接触式、测试成本低、识别效果显著及操作便捷等优点。     

构造煤的动力变质作用及其演化规津

采用X射线衍射分析、电子顺磁共振等方法研究了构造煤的动力变质作用特征和演化规律。构造煤与煤层的变形变质历史有关,动力变质作用形成的构造煤,其结构特征与其它变质类型煤不同,演化途径也不同,但它们的演化规律一致。      

Natural frequencies measured from ambient vibration response of the arch dam of Mauvoisin

The resonance frequencies of the 250‐m‐high arch dam of Mauvoisin are obtained by way of ambient vibration tests. It is observed that the resonance frequencies initially increase with rising water level and then decrease with a further rise. This is linked to the two competing features of increasing entrained mass of water (reduction of the resonance frequencies) and of dam stiffening due to closing of the vertical construction joints (augmentation of the resonance frequencies). The ambient vibration test results are complemented by those obtained during earthquakes at an array of 12 accelerographs. Copyright © 2000 John Wiley & Sons, Ltd.     

Experimental studies of a damaged ship section in forced heave motion

This work documents a detailed series of experiments performed in a wave flume on a thin walled prismatic hull form. The model consists of a rectangular opening located on the side. The length of the model is slightly smaller than the flume breadth to achieve two-dimensional (2D) behavior in the experiments. Forced oscillatory heave tests in calm water have been carried out by varying the model-motion parameters and examining both intact and damaged conditions. Video recordings, measurements of the wave elevation inside the damaged compartment and of the force on the model were performed in all the experiments. The effect of damage opening in the model on hydrodynamic loads is examined by comparing with an intact section. A theoretical analysis is used to explain the behavior of added mass and damping coefficients in heave for a 2D damaged section. The presented results demonstrate occurrence of sloshing and piston mode resonances in the tests and their influence on the hydrodynamics loads of a damaged ship. Detailed physical investigations are presented at these resonance frequencies for the damaged section. Effect of filling level in the damage compartment, damage-opening length and air compressibility in the airtight compartment is examined. Nonlinear effects are documented and appear dominant, especially, for lowest filling level where we have shallow-water depth conditions in the damaged compartment. Resonance phenomena that can lead to significant local loads are identified for the shallow water condition. Air compressibility in the airtight compartment and floodwater act as a coupled system and influence inflow/outflow of floodwater in the compartment. It has a significant effect on local floodwater behavior in the damaged compartment.     

长周期波浪激发矩形港池多模态共振研究

长和宽接近的矩形港池存在横向、纵向及横纵向混合共振模态。采用基于混合有限元的椭圆型缓坡方程数值模型模拟不同波浪入射角的低频波浪激发矩形港池的多模态共振,并分析不同平面布置形式的矩形港池模态响应特性。结果表明,斜向波浪会激发港池的横向共振模态,其放大因子受入射角度影响较大,而纵向共振模态的放大因子受入射角度影响较小。口门宽度对港池的共振模态个数与放大因子均有影响,具体为:随着口门宽度增加,各阶模态放大因子减小。口门位置对纯横向以及纯纵向共振的振荡模式有显著影响,而对横向纵向混合模态影响较小。各阶模态放大因子的大小和波节线与波腹线与口门的相对位置密切相关。     

高阶电离层延迟对中国区域双差定位影响研究

给出顾及高阶电离层延迟改正的双差定位模型,探讨中国区域VTEC的时空变化规律,分析高阶电离层延迟对L3观测值的影响。利用41个陆态网测站2015年全年的GNSS数据,基于Bernese 5.2软件的双差定位技术,系统研究高阶电离层延迟对中国区域双差定位的影响及其时空分布规律。结果表明,高阶电离层延迟对中国区域双差定位的影响与测站网型结构相关,明显存在0.5 a的周期变化,影响年均值大小为0～2 mm,且具有方向性差异,对高纬度测站的影响有向北偏移趋势,对低纬度测站的影响有向南偏移趋势。     

Spar平台垂荡-纵摇耦合运动失稳机理

研究参数激励和强迫激励共同作用下Spar平台垂荡-纵摇耦合运动的失稳机理.考虑静稳性和排水体积的变化,推导平台的垂荡回复力和纵摇回复力矩表达式,建立规则波浪中平台垂荡-纵摇耦合的运动方程.以经典Spar平台为例,分析平台垂荡-纵摇耦合运动发生马休类型不稳定运动的条件以及平台运动失稳的形式,给出波高和波浪周期平面上平台因大幅运动失稳的参数域.结果表明,当波高相对较小时,波浪的临界周期接近于垂荡固有周期,平台失稳的形式为马休失稳;当波高相对较大时,波浪的临界周期远离垂荡固有周期,平台由于大幅摇摆运动而失稳.     

A note on edge waves on a flat shelf

Abstract

A variational approximation to the dispersion relation for trapped waves on a flat shelf of depth h ₁, bounded internally by a vertical coast and externally by a semi-infinite ocean of depth h ₂>h ₁, is obtained through an integral-equation formulation that accounts for all of the non-propagated modes that are excited at the discontinuity in depth (the conventional formulation of the edge-wave problem allows only for the propagated mode on the shelf and the dominant, non-propagated mode in the deep water). Coriolis effects are neglected. The exact result in the limit ω² h ₂/g↓0 (ω = angular frequency) is obtained by conformal mapping and compared with the variational approximation, which proves to be quite accurate over the entire range 1>h ₂/h ₁>x. The effects of the higher-order, non-propagated modes are found to be small for the long waves observed over the Southern California shelf by Snodgrass, Munk and Miller (1962).     

基于模拟退火法的磁共振测深多源谐波噪声压制方法

磁共振测深找水方法在高电磁噪声环境下应用时,往往会因为电磁噪声的干扰导致实测数据信噪比降低,反演结果难以准确地确定实际地下水体的分布状况,降低方法的应用效果。针对磁共振测深找水方法在实际野外数据采集工作中常面临的多源谐波噪声干扰问题,在模型去噪的基础上推导出网格搜索同步删除法,进一步提出了效率更高的模拟退火同步删除法。仿真结果表明,2种方法均能有效压制多源谐波噪声,而模拟退火同步删除法能够更快速地搜索谐波基频值,相较网格搜索同步删除法在双基频谐波情况下工作效率提高2.35倍,大大降低了去噪流程的时间成本,且对多源谐波噪声也能取得较好的去噪效果。将该去噪算法应用于实例中,反演结果和钻孔资料的对比表明,模拟退火同步删除法可以有效压制磁共振测深方法实测数据中的多源谐波噪声,显著提高磁共振测深方法的应用效果。