Micro-bubble Drag Reduction on a High Speed Vessel Model

Ship hull form of the underwater area strongly influences the resistance of the ship. The major factor in ship resistance is skin friction resistance. Bulbous bows, polymer paint, water repellent paint （highly water-repellent wall）, air injection, and specific roughness have been used by researchers as an attempt to obtain the resistance reduction and operation efficiency of ships. Micro-bubble injection is a promising technique for lowering frictional resistance. The injected air bubbles are supposed to somehow modify the energy inside the turbulent boundary layer and thereby lower the skin friction. The purpose of this study was to identify the effect of injected micro bubbles on a navy fast patrol boat （FPB） 57 m type model with the following main dimensions： L=2 450 ram, B=400 mm, and T=190 mm. The influence of the location of micro bubble injection and bubble velocity was also investigated. The ship model was pulled by an electric motor whose speed could be varied and adjusted. The ship model resistance was precisely measured by a load cell transducer. Comparison of ship resistance with and without micro-bubble injection was shown on a graph as a function of the drag coefficient and Froude number. It was shown that micro bubble injection behind the mid-ship is the best location to achieve the most effective drag reduction, and the drag reduction caused by the micro-bubbles can reach 6%-9%.

Multimodality Vessel Modeling Analysis for Cerebral Arteriovenous Malformation

Cerebral arteriovenous malformations (AVMs) are a type of vascular anomaly consisting of large intertwined vascular growth (Nidus) that is prone to serious hemorrhaging and can result in patient death if left untreated. Intervention through surgical clipping of feeding and draining vessels to the Nidus is a common treatment. However, identification of which vessels to clip is challenging even to experienced surgeons aided by conventional image guidance systems. The lumped modeling for the Cerebral Arteriovenous Malformation (CAVM) hemodynamic analysis is of high importance in clinical world. As part of the treatment planning for CAVM, it is difficult for doctors to assess the NIDUS part, which may get rupture while inserting catheter. In this paper, we have proposed a non-invasive method for assessing the hemodynamic condition of AVM. The measurement of flow and pressure without intervention along the vessel is a big challenge due to occlusion, bending and thinning of the vessel in Arteriovenous Malformation patients. In this paper, we analyzed a lumped model for the vascular malformation using various imaging multi-modalities that help to analyze CAVM Structures.

Exploration on the Optimization Strategy for the Layup of Composite Material Pressure Vessels Based on Advanced Algorithms

This study aims to explore the influence of the laying angle on the pressure shell structure made of composite materials under the condition of a fixed shape. By using a composite material composed of a mixture of T800 carbon fiber and AG80 epoxy resin to design pressure vessels, this material combination can significantly improve the interlaminar shear strength and heat resistance. The article elaborates on the basic concepts and failure criteria of composite materials, such as the maximum stress criterion, the maximum strain criterion, the Tsai-Hill criterion, etc. With the help of the APDL parametric modeling language, the arc-shaped, parabolic, elliptical, and fitting curve-shaped pressure vessel models are accurately constructed, and the material property settings and mesh division are completed. Subsequently, APDL is used for static analysis, and the genetic algorithm toolbox built into Matlab is combined to carry out optimization calculations to determine the optimal laying angle. The research results show that the equivalent stress corresponding to the optimal laying angle of the arc-shaped pressure vessel is 5.3685e+08 Pa, the elliptical one is 5.1969e+08 Pa, the parabolic one is 5.8692e+08 Pa, and the fitting curve-shaped one is 5.36862e+08 Pa. Among them, the stress distribution of the fitting curve-shaped pressure vessel is relatively more uniform, with a deformation of 0.568E−03 m, a minimum equivalent stress value of 0.261E+09 Pa, a maximum equivalent stress value of 0.537E+09 Pa, and a ratio of 0.48, which conforms to the equivalent stress criterion. In addition, the fitting curve of this model can adapt to various models and has higher practical value. However, the stress distribution of the elliptical and parabolic pressure vessels is uneven, and their applicability is poor. In the future, further exploration can be conducted on the application of the fitting curve model in composite materials to optimize the design of pressure vessels. This study provides important theoretical support and practical guidance for the design of composite material pressure vessels.

Crystal Structure Evolution of the Cu-rich Nano Precipitates from bcc to 9R in Reactor Pressure Vessel Model Steel

The crystal structure evolution of the Cu-rich nano precipitates from bcc to 9R during thermal aging was studied in nuclear reactor pressure vessel （RPV） model steels. The specimens, contained higher copper and nickel contents than commercially available one, were heated at 890 ~C for 0.5 h and then water quenched followed by tempering at 0（50 ~C for I0 h and aging at 400 ~C for 1000 h. It was observed that bcc and 9R orthogonal structure, as well as 9R orthogonal and 9R monoclinic structure, coexist in a single Cu-rich nano precipitate. Further analyses pointed out that Cu-rich nano precipitates of bcc structure were not stable, it may preferentially transform to 9R orthogonal structure and then to 9R monoclinic structure. This results showed that the crystal structure evolution of the Cu-rich nano precipitates was complex.

NONLINEAR MOTION MECHANICS MODEL OF CURVED BLOOD VESSEL

A geometric model of curved blood vessels is established based on some reasonable hypotheses; the nonlinear motion mechanics model of the curved blood vessel is established according to basic mechanics laws. This model includes much more physiological factors. It couples the interaction of blood flow with mechanical factors such as the displacement, deformation, strain and stress etc. of the curved blood vessel. It is of great importance for investigating the circulation rules of the cardiovascular system and the nonlinear pulse wave propagation in curved blood vessels.

Finite Element Modeling of Variable Membrane Thickness for Field Fabricated Spherical (LNG) Pressure Vessels

This study investigated thickness requirements for field fabricated (large) spherical liquefied natural gas (LNG) pressure vessels using the finite element method. In the FEM modeling, 3-dimenisonal analysis was used to determine thickness requirements at different sections of a 5-m radius spherical vessels based on the allowable stress of the material as given in ASME Section II Part D. Shallow triangular element based on shallow shell formation was employed using area coordinate system which had been proved better than the global coordinate system in an earlier work of the authors applied to shop built vessels. This element has five degrees of freedom at each corner node-five of which are the essential external degrees of freedom excluding nodal degree of freedom associated with in plane shell rotation. Set of equations resulting from Finite Element Analysis were solved with computer programme code written in FORTRAN 90 while the thickness requirements of each section of spherical pressure vessels subjected to different loading conditions were determined. The results showed membrane thickness decreasing from the base upwards for LNG vessels but constant thickness for compressed gas vessels. The obtained results were validated using values obtained from ASME Section VIII Part UG. The results showed no significant difference (P > 0.05) with values obtained through ASME Section VIII Part UG.

Environmental stress model for evaluation of vessel traffic in ports and waterways

Environmental stress model is proposed as an effective tool to the analysis and evaluation of navigational safety in ports and waterways. Marine traffic simulations are carried out in a virtual port area with various arrangements and conditions. Calculations of stress values and traffic volume criteria are illustrated. The simulation results provide a valuable hint for safety management of vessel traffic. The model provides quantitative information and helps administrators in decision making to achieve desired safety level and improve the efficiency of vessel traffic in ports and waterways.

Finite Element Modeling of Shop Built Spherical Pressure Vessels

This work builds on an earlier work done which used global coordinates where a large number of elements were needed to form a convergence of results for shop built spherical pressure vessels. In this work area coordinates were used. Any action that leads to an inability on the part of a structure to function as intended is known as failure. This research, therefore, investigates stresses developed in a shop built carbon steel spherical storage vessels using finite element approach as the analytical tool. 3-D finite element modeling using 3-node shallow triangular element with five degrees of freedom at each node is employed. These five degrees of freedom are the essential nodal degrees of freedom without the sixth in-plane rotation. The resulting equations from finite element analysis are coded using FORTRAN 90 computer programme. Spherical storage vessels are subjected to various internal loading pressures while nodal displacements, strains and the corresponding maximum Von-mises stresses are determined. The calculated maximum Vonmises stresses are compared with the yield strength of the shell plate material. Using specified safety factor, safety internal pressures with the corresponding shell thicknesses for shop built spherical pressure vessels are determined. The finite element modeling carried out in this research can be used to predict in-service stresses, strains, and deformations of shop built spherical pressure vessels using Von-mises yield stress as the failure criteria. The results obtained were validated by analytical method and it showed there was no significant difference (P > 0.05) with values obtained through analytical method.

水合物开采模拟超重力试验装置的研发及应用

天然气水合物是突破世界能源瓶颈的重要潜在能源,广泛分布于深海沉积物和陆域永冻土。水合物赋存在高压低温环境下,储层厚度达数十至百米,大尺度储层重力场显著影响其开采时的液气渗流、储层变形和传热过程,进而影响开采产气效率且可能诱发工程灾变。研发了一套能够在超重力场下模拟大尺度水合物储层长历时开采演变过程的离心模型试验装置,主要由高压釜系统、水合物制备模块、水压力控制模块、水合物开采模块、监测与响应模块组成。该装置能够在100g超重力下伺服调控高压釜内气液压力和温度环境,在模型尺度上有效再现水合物储层应力、温度和荷载条件。在系统介绍装置研发思路和技术特色的基础上,通过100g下水合物储层模型降压分解试验探析了原位等效重力场下储层不同深度处孔压演化规律及开采产气特性,再现了Nankai海槽原位试采产气速率峰值模式,为揭示水合物储层开采相变多相多场耦合机制和灾变防控提供了新的研究手段。

多重防护机制下LNG动力船风险态势分析方法

为探讨多重防护机制下的液化天然气(Liquefied Natural Gas,LNG)动力船营运风险特征,提出了一种基于复杂性控制系统作用模式的风险态势分析方法。从系统控制过程视角,采用系统控制过程分析方法(System-Theoretic Process Analysis,STPA)确立LNG动力船系统安全控制的风险致因,揭示基于LNG泄漏三重防护机制的风险因子体系和风险形成机制;引入隐马尔可夫模型(Hidden Markov Model,HMM),进行无监督学习并确立模型参数,推理多重防护机制下的LNG动力船风险转移特征;结合LNG动力船营运的具体场景,对三重防护机制分别进行仿真并统计风险态势。仿真结果表明,三重防护机制在降低LNG动力船营运风险态势方面具有因子诱导的针对性,在防漏因子、止漏因子和治漏因子诱导下LNG动力船分别趋向一般风险状态、较高风险状态和高风险状态。基于复杂性控制系统作用模式的风险态势分析可为LNG动力船营运的安全控制和风险管理提供管控模式和手段。

基于历史数据挖掘的海上船舶交通事故预测

为优化船舶航行路线,减少因交通事故导致的延误和拥堵,提升海上运输效率和效益,研究基于历史数据挖掘的海上船舶交通事故预测方法。从海事机构获取海上船舶交通事故历史数据后,采用数据挖掘方法中的一维局阿尼自编码器对海上船舶交通事故历史数据展开挖掘,得到海上船舶交通事故特征,再建立灰色SCGM(1,1)C模型,将海上船舶交通事故特征输入到该模型中,并运用当前预测状态中间值作为修正产生,对灰色SCGM(1,1)C模型预测结果进行修正后,得到海上船舶交通事故预测结果。实验表明,该方法具备较强的海上船舶交通事故历史数据挖掘能力,灰色SCGM(1,1)C模型输出的海上船舶交通事故预测结果 DBI数值较高,预测海上船舶交通事故能力较好。

基于巴特沃斯幅频特性的自适应粒子群算法

针对传统粒子群算法存在求解精度低和易陷入局部最优等问题,提出一种基于巴特沃斯幅频特性的自适应粒子群算法(Butterworth amplitude-frequency characteristics based adaptive particle swarm optimization algorithm,BAC-PSO).一方面,借助巴特沃斯幅频特性设计一种惯性权重非线性递减策略,均衡算法中粒子的局部与全局搜索能力;另一方面,通过S型函数的粒子群优化策略和Sigmoid函数改进位置更新方法,进一步提升算法的求解精度.以5个经典的测试函数为基准,将BAC-PSO算法与5种经典粒子群算法的性能进行对比,并将其应用到求解压力容器模型的设计问题中.实验结果表明,相较于其他经典粒子群算法,BAC-PSO算法的求解精度更高,收敛速度更快,稳定性更好.

急性前循环大血管狭窄脑卒中患者不良预后的危险因素分析

目的分析急性前循环大血管狭窄脑卒中患者不良预后的危险因素。方法回顾性选取2021-01—2023-09安庆一一六医院收治的急性前循环大血管狭窄脑卒中患者,将其中治疗后3个月随访评估为不良预后的23例患者纳入预后不良组,采用倾向匹配法从良好预后的患者中匹配46例患者纳入良好组。对比并分析2组患者的临床资料,构建风险模型。结果基线NIHSS评分≥13.705分、梗死核心区体积≥52.720 mL、入院收缩压≥160.060 mmHg为ALVSS患者不良预后的危险因素。rLMC评分≤9.429分为不良预后的保护因素,对于ALVSS患者不良预后具有中等评估价值(0.7<AUC≤0.9,P<0.05)。危险因素与保护因素联合构建的风险模型对于ALVSS患者不良预后具有较高的预估价值(AUC>0.9,P<0.05)。结论基线NIHSS偏高、梗死核心区体积较大、入院收缩压较高以及rLMC评分较低可提示急性前循环大血管狭窄脑卒中患者不良预后,可针对性给予干预,改善患者预后。

船模水动力噪声及孔腔激励载荷试验与计算对比分析

开展某远洋客船光体船模水下噪声测试及带孔腔船模的水动力激励载荷测试,并进行孔腔处稳态和瞬态流场计算,孔腔处脉动压力频谱计算曲线与试验曲线吻合较好。孔腔脉动压力线谱频率测试值与经验公式频率计算值对比良好,说明该公式在一定情况下适用于船体条形格栅孔腔线谱频率的预估。采用统计能量法分析法计算光体船模中高频流激噪声,将流体激励以频率-波数功率谱的形式施加,可大大减少流场计算工作量,适合于工程快速预估。在工程一般范围内,阻尼损耗因子取值可导致噪声结果相差5.5 dB,说明阻尼损耗因子的取值会较大影响计算结果,有必要形成材料损耗因子随频率变化的数据库,为船舶噪声快速计算提供支撑。

基于直接数值模拟的压力容器入口射流湍流模型评价

采用基于谱元法的开源软件Nek5000对压力容器入口射流进行直接数值模拟(DNS)。压力容器模拟在环向简化为1/3的尺度,主管段雷诺数为63700,下降段雷诺数为14014,工质为碘化钠溶液。通过对常见物理量进行统计,构建高精度湍流数据库。并采用FLUENT对常见的壁面函数和湍流模型进行适应性评价,评价标准包括速度、湍动能和湍流黏度。结果表明:在上升段Stress-ω模型适用性最好;在下降段,Standard k-ω模型适用性最优。

氢动力船加注过程高压氢气泄漏数值模拟

该文针对氢动力船加注过程中可能发生的高压氢气泄漏问题进行了数值模拟研究。首先,通过与已有实验结果对比,验证了CFD虚喷嘴模型和分层流动模型的有效性。其次,结合氢动力船实际加注场景,着重分析风速、障碍物对高压氢气扩散行为的影响。最后,利用半球扩散模型划分疏散区域,提高氢动力船加注过程的安全性。结果表明:分层流动模型与实验结果拟合性更好;高速的风可阻止氢气上浮,增加氢气泄漏距离,降低氢气浓度;泄漏源下游设置障碍物一定程度上缩短了易燃云在水平方向上的扩散距离。

碎冰模型形状对船舶碎冰阻力数值预报的影响

在数值模拟中,碎冰模型形状对于船舶碎冰阻力预报结果的准确性具有显著影响。本文以某极地环保多用途运输船为案例对象,研究7种数值碎冰模型形状对船舶碎冰阻力预报的影响,建立片状正方形、圆形、正五边形、正六边形、椭圆形、梯形和不规则多边形数碎冰模型,采用CFD-DEM的方法对船舶碎冰阻力进行预报,并将结果与冰水池模型试验相对比。研究表明,7种形状碎冰模型均能很好模拟出模型试验现象,数值计算得到的碎冰阻力值均比模型试验结果高,片状圆形碎冰模型数值计算值高2.04%,在7种形状中误差最小。因此,在以阻力预报为目的船舶碎冰航道航行CFD-DEM数值计算中,建议采用片体形状为圆形的数值碎冰模型。

脑内扩大的血管周围间隙患者运动认知功能减退综合征的临床评估

目的 探究老年脑内扩大的血管周围间隙(EPVS)患者运动认知功能减退综合征(MCR)的患病率及运动和认知功能减退情况。方法 连续纳入2023年3月1日至2023年11月30日在北京朝阳医院神经内科就诊的≥60岁头部磁共振成像显示有EPVS的患者113例,根据是否患有MCR分为MCR组44例和MCR阴性组69例。评估患者认知功能及运动功能,认知功能评估包括蒙特利尔认知量表(MoCA)、简易智能状态检查量表(MMSE)、连线测试(TMT),运动功能评估包括Tinetti量表、简易体能状况量表(SPPB)、8 m步行任务、“起立-行走”计时测试(TUGT)、步行和连续减法任务(WSS)、步行和语义流畅任务(WSF)、TUGT和串行减法任务(TUGSS)。比较2组患者的运动和认知功能,多因素logistic回归分析EPVS患者发生MCR的相关危险因素。结果 与MCR阴性组比较,MCR组MoCA评分、SPPB评分、8 m步行速度降低,TMT-A时间、TMT-B时间、WSS时间、WSF时间、TUGSS时间升高(P<0.05,P<0.01)。多因素logistic回归分析显示,在模型1中(将单因素分析存在差异的变量纳入回归分析),MoCA评分、8 m步行速度、TUGSS时间是EPVS患者发生MCR的影响因素(P<0.05,P<0.01);在模型2中(将单因素分析存在差异的变量纳入回归分析同时调整年龄、性别、教育程度、既往史因素),MoCA评分(OR=0.621,95%CI:0.432~0.929,P=0.010)、8 m步行速度(OR=1.332,95%CI:1.115~1.591,P=0.002)、TUGSS时间(OR=0.393,95%CI:0.232~0.665,P=0.001)仍为EPVS患者发生MCR的影响因素。结论 在老年EPVS患者中,MCR患者认知及运动功能显著减退,MoCA评分、8 m步行速度、TUGSS时间是EPVS患者发生MCR的相关因素。

改进D-Linknet的眼底视网膜血管分割

临床医生可通过观察眼底视网膜血管及其分支对人体是否患有疾病进行早期诊断,但由于视网膜中的血管错综复杂,模型在分割时会出现对微细血管分割精确度不足的问题。为此,提出一种结合残差模块Res2-net以及高效通道注意力机制(efficient channel attention,ECA)的D-Linknet模型。首先,利用Res2-net代替基础模型中的残差模块Res-net以提升每个网络层的感受野;其次,在Res2-net中添加一种结合压缩激励(squeeze and excitation,SE)和门通道(gated channel transformation,GCT)的注意力机制模块,改善处于复杂背景下的血管分割效果和效率;在网络的解码层加入ECA确保模型计算的性能,避免因降维导致的精度下降;最后,融合改进的模型输出图与掩膜图细化分割结果。在公开数据集DRIVE、STARE上进行分割实验,模型准确度(accuracy,AC)分别为97.11%、96.32%,灵敏度(sensitivity,SE)为84.55%、83.92%,曲线下方范围的面积(area under curve,AUC)为0.9873和0.9766,分割效果优于其他模型。实验证明了算法的可行性,为后续研究提供科学依据。

基于血管模型的网格平滑算法研究

血管三维模型是诊断心血管疾病的重要辅助参考,但表面存在的较多噪声会对诊断产生一定影响,需进行网格平滑。根据现有网格平滑算法,保留清晰特征和减小体积收缩仍具有挑战性。因此,本文提出一种组合平滑算法,并将其应用于人体不同组织结构的三维模型中进行验证。结果表明:该算法结合曲面重建与联合双边滤波,可实现去除噪声,并保持特征,减轻收缩。