Time-Domain Analysis of Body Freedom Flutter Based on 6DOF Equation

The reduced weight and improved efficiency of modern aeronautical structures result in a decreasing separation of frequency ranges of rigid and elastic modes.Particularly,a high-aspect-ratio flexible flying wing is prone to body freedomflutter(BFF),which is a result of coupling of the rigid body short-periodmodewith 1st wing bendingmode.Accurate prediction of the BFF characteristics is helpful to reflect the attitude changes of the vehicle intuitively and design the active flutter suppression control law.Instead of using the rigid body mode,this work simulates the rigid bodymotion of the model by using the six-degree-of-freedom(6DOF)equation.A dynamicmesh generation strategy particularly suitable for BFF simulation of free flying aircraft is developed.An accurate Computational Fluid Dynamics/Computational Structural Dynamics/six-degree-of-freedom equation(CFD/CSD/6DOF)-based BFF prediction method is proposed.Firstly,the time-domain CFD/CSD method is used to calculate the static equilibrium state of the model.Based on this state,the CFD/CSD/6DOF equation is solved in time domain to evaluate the structural response of themodel.Then combinedwith the variable stiffnessmethod,the critical flutter point of the model is obtained.This method is applied to the BFF calculation of a flyingwing model.The calculation results of the BFF characteristics of the model agree well with those fromthe modalmethod andNastran software.Finally,the method is used to analyze the influence factors of BFF.The analysis results show that the flutter speed can be improved by either releasing plunge constraint or moving the center ofmass forward or increasing the pitch inertia.

基于Flutter的智能场景记账APP的设计与实现

综合了市面上记账类APP的功能并根据当下用户的一些需求设计了一款满足个人财务管理需求的同时基于智能记账且便捷、简单好用的记账APP,并通过Flutter搭建前端,Spring Boot搭建后端和MySQL数据库实现了这款智能场景记账APP,同时也将其部署在了服务器上。

基于Flutter的中老年智慧生活APP软件设计与实现

当前,中国的人口老龄化仍呈上升趋势,中老年人越来越频繁地使用手机和家电,容易出现困惑和忘记操作步骤的情况。基于此,文章基于FlutterUI框架、使用SpringBoot作为后台开发框架来开发了一款跨平台APP软件“步步有伴”,其中整个APP采用MVVM架构,后端程序采用MVC架构。开发的目标是帮助中老年人更好地了解和使用这些设备,提高生活质量。开发结果表明,软件可以帮助中老年人更好地管理自己的日常事务,并且帮助子女可以随时随地了解父母的待办事项和提醒事项,并及时提供帮助和支持。

基于Flutter 框架的高校师生协同平台的设计与实现

为保证高校师生信息传输安全,提高教学质量与工作效率,文章结合移动应用程序现有跨平台开发框架,并以济南大学已建成的数据中心作为数据支撑,设计出一套基于Flutter框架的高校师生协同平台。平台可实现用户信息、沟通记录、文档传输等内容本地化存储,同时集成教务、邮箱等办公应用,为高校师生提供集沟通、信息查询和应用办公于一体的移动服务,该平台的引入加速了济南大学数字化转型,进一步提升师生办公效率。

基于Vue和Flutter的经验库设计与实现

随着全球汽车工业的持续繁荣与快速发展,车辆设计和生产过程中的碰撞安全性能已成为评估车辆整体安全性的重要指标之一,其研究和优化显得尤为重要。然而,在车辆碰撞试验过程中积累的大量经验知识如何有效进行管理和共享,成为提升车辆安全性能的关键挑战。为应对这一挑战,文章深入研究了车辆碰撞试验过程中的经验知识管理需求,设计并实现了一个基于Vue和Flutter技术的经验库平台,为车辆碰撞试验过程中的经验知识提供全面、高效的管理和共享机制。该平台通过Vue开发网页端经验管理页面,提供丰富的数据展示和交互功能;同时,利用Flutter框架开发移动端应用,支持问题发布与解决方案的快速更新^([1])。

Mechanistic Insights into Roof-Dependent Macroreentrant Atrial Flutter with Endocardial Block of the Roof Line:A Case Report

Background:Epicardial roof-dependent atrial tachycardia is rare among macroreentrant tachycardias.The importance of epicardial structure or fiber involving septopulmonary bundle(SPB)has not been realized generally.Case presentation:A 74-year-old woman who underwent catheter ablation of atrial fibrillation previously accepted a second-time radiofrequency ablation due to atrial flutter.The mapping and entrainment results of the tachycardia tended to be an epicardial SPB-dependent macroreentrant atrial tachycardia and it was ablated to sinus rate at the first single targeting site,just located in the breakout site of SPB into the posterior wall(PW)of left atrial(LA).The twice-activation mapping of PW of LA also proved the presence of SPB.No recurrent arrhythmia was seen at follow-up at 3 months.Conclusion:In this case,an uncommon phenomenon was observed post-ablation for persistent atrial fibrillation,where the epicardial muscular structure of the LA-SPB was involved in atypical atrial flutter.This should be considered as a potential factor in such cases.Further similar cases may be required to improve diagnostic accuracy and to formulate effective ablation strategies for this type of tachycardia.

基于Flutter的今日早饭App功能设计与开发

当今中国社会正在飞速地向前发展,在这个信息化时代,由于人们对科技的热爱以及科技的发展,智能手机的发展趋势势不可挡,由此也促使了很多美食App的出现。该设计是基于AndroidFlutter移动平台美食菜谱系统来进行分析和设计的,设计一款早饭App,用户通过手机软件可以获得美食具体的菜谱信息、进行线上分享、获取流行菜谱等。文章简要介绍了App的功能以及实现方法,先对整个项目进行总体设计,对一些框架和界面进行整体的基本搭建,然后具体介绍每个模块,每个界面都有一定的功能,使读者了解基于Flutter的美食App设计与开发的一个流程,界面的清晰展示以及流畅的跳转,给用户操作带来一个更好的视觉体验,再配合一些好的组件或者框架,使项目更加完善,更好服务于客户。

基于Flutter的山羊孕测App设计与实现

目前大部分软件产品服务形式已逐步从传统单一的B端向多平台转变,但针对各平台单独开发将会是一个较大工作量、运维成本高、人力成本高的方案,涉及智慧畜牧的情况也是这样。文章介绍选用Flutter开发框架和Golang语言设计和实现一个跨平台的山羊孕测App,包括视频监控、即时通讯、异常通知等功能。利用Golang开发操作后端数据与Socket通信SDK包,使用Flutter开发框架调用SDK包编写一套程序代码进行跨端编译在Android、iOS两个平台运行。有效地提高了开发效率、性能的稳定,降低维护成本,加快对山羊孕测即时响应度。

基于Flutter的“文旅大同”APP设计与开发

大同市作为山西省第二大城市,是中国首批24个国家历史文化名城之一、中国古都之一、中国优秀旅游城市。为了更好地宣传大同,不断提升大同文化旅游产品的社会影响力,进而创造源源不断的经济收益,基于Flutter框架设计实现手机端软件——“文旅大同”移动APP。该APP的功能主要包括:大同小记、大同圈子(攻略、游记、分享、求助)和大同日志(美食、景区、文化、资讯)。该APP使得广大游客更方便快捷地查询大同各类文化旅游信息,对于宣传大同文化旅游,推动大同走向全国、走向世界具有重要意义。

基于Flutter的老年人服务平台

针对居家老人对附近医院及医疗服务系统不了解,对所处医院的强势科室不了解等问题,文中融合Android和Flutter技术开发了一款多功能老年人服务平台,该平台可以帮助居家老人对医院进行全面了解,并及时获悉所在医院相关信息。该老年人服务平台可以减少人力、物力的投入,提高医护工作效率,大大方便了老年人和医护工作者,拥有广阔的发展前景。

Revealing the Fluttering Motions of Mid-Water Trawl Codend Through Sea Trials:Case Study of Antarctic Krill Trawl Codend

The dynamic coupling between the fluttering motions and hydrodynamic characteristics of codend is essential in understanding the trawl selectivity through fish response and the drag force acting on the whole trawl.This study investigated the effect of towing speed,warp length,warp tension,and catch size on the fluttering motions of Antarctic krill trawl codend during net shooting,towing,and hauling by using sea trial data.The time-periodicity of codend oscillation was analyzed by the Morlet wavelet transform method.Results indicated that the period of codend oscillation was between 50 s and 90 s and showed an increasing trend with the warp tension but a decreased value at the towing stage.The coefficient amplitude of codend oscillation was between 0 and 4 at the net shooting and hauling stages,and between 0.2 and 0.6 at the towing stage.The amplitude of codend oscillation increased with the warp tension,towing speed,and catch size,but decreased with the increase of the warp length.In addition,the period of codend oscillation increased with the towing speed at the net shooting and hauling stages,but decreased at the towing stage.These results from codend fluttering motions can improve the understanding of fish behavior and gear shape that modify the hydrodynamic force on the codend instantaneously.

Geometrically Nonlinear Flutter Analysis Based on CFD/CSD Methods and Wind Tunnel Experimental Verification

This study presents a high-speed geometrically nonlinear flutter analysis calculation method based on the highprecision computational fluid dynamics/computational structural dynamics methods.In the proposed method,the aerodynamic simulation was conducted based on computational fluid dynamics,and the structural model was established using the nonlinear finite element model and tangential stiffness matrix.First,the equilibrium position was obtained using the nonlinear static aeroelastic iteration.Second,the structural modal under a steady aerodynamic load was extracted.Finally,the generalized displacement time curve was obtained by coupling the unsteady aerodynamics and linearized structure motion equations.Moreover,if the flutter is not at a critical state,the incoming flow dynamic pressure needs to be changed,and the above steps must be repeated until the vibration amplitude are equal.Furthermore,the high-speed geometrically nonlinear flutter of the wing-body assemblymodel with a high-aspect ratio was investigated,and the correctness of the method was verified using high-speed wind tunnel experiments.The results showed that the geometric nonlinearity of the large deformation of the wing caused in-plane bending to become a key factor in flutter characteristics and significantly decreased the dynamic pressure and frequency of the nonlinear flutter compared to those of the linear flutter.

柔性光伏系统颤振性能的节段模型试验研究

柔性光伏支架的频率低、质量轻,极易在风荷载作用下发生大幅振动。以某实际柔性光伏项目为工程背景,借鉴桥梁抗风的研究经验,对该柔性光伏支架的颤振性能进行研究。首先,考虑严格的相似比关系,设计并制作了弹性悬挂节段模型系统,并对其动力特性进行了测试;然后,进行不同光伏组件倾角(-39°~+39°)下的弹性悬挂节段模型测振风洞试验,研究光伏组件风致响应随风速的变化规律,得到各倾角下柔性光伏节段模型的颤振临界风速值,探讨2种气动措施对提高柔性光伏支架颤振稳定性的效果。结果表明:在0°~39°的正倾角工况下,柔性光伏支架的颤振临界风速随光伏组件倾角的增大,呈现先减小后增大的趋势,最小颤振临界风速出现在12°~21°光伏组件倾角范围内,折算成实际风速为9.6m/s;在-39°~0°的负倾角工况下,颤振临界风速随光伏组件倾角的增大,也呈现先减小后增大的趋势,最小颤振临界风速出现在-21°~-12°光伏组件倾角范围内,折算成实际风速为10.1m/s;设置中央稳定板的气动措施难以有效提高柔性光伏支架的颤振临界风速。

开口断面钢-混结合梁悬索桥颤振特性及颤振形态研究

为准确评估开口断面双边箱钢-混结合梁悬索桥颤振性能和多模态参与效应,以典型的钢-混结合梁悬索桥——怀化洞庭溪沅水特大桥为背景,开展风洞模型试验及数值分析。制作加劲梁节段缩尺模型并进行风洞试验,测试原桥梁结构的颤振性能,分析调整阻尼比、采用气动措施及结构措施对结构颤振特性的影响,采用三维和二维两种颤振分析方法分析设置中央扣结构的颤振模态及多模态参与效应。结果表明:该钢-混结合梁悬索桥存在较明显的颤振起振点,且颤振是以扭转为主的弯扭耦合振动,同时其扭转和竖向振动存在较大的相位差(相差近180°);节段模型风洞试验与三维和二维颤振分析一致得到设置中央扣后,频率较高的正对称扭转模态先于反对称模态发生颤振,且三维与二维颤振分析结果相差不大。

螺旋桨发动机安装系统动力学设计技术综述

随着螺旋桨发动机安装系统国产化研制进程的加快,需要开展相关的安装系统技术研究,而动力学设计是其中的重要组成部分。本文对比分析了不同结构形式安装系统的动态性能特点,进一步从军民用标准规范和工程实践经验出发,归纳了安装系统动力学设计的技术要求,梳理了安装系统动力学设计技术的发展历程和国内外现状,指出国内外差距主要体现在设计理念、关键技术和应用实践经验等方面。在此基础上,展望了螺旋桨发动机安装系统动力学设计技术的发展趋势,为当前及未来螺旋桨发动机安装系统的设计技术研究提供了参考。

Identification of the dominant loop of a dual-loop macro-reentry left atrial flutter without prior intervention using high-density mapping technology:A case report

BACKGROUND Left atrial flutter without prior cardiac interventions is uncommon,especially dual-loop macro-reentry atrial flutter.The critical step to ablate dual-loop macroreentry atrial flutter is to identify the dominant loop and key isthmus.Although entrainment mapping could help identify the dominant loop and key isthmus,it may alter or terminate tachycardia.High-density mapping allows the generation of electroanatomic maps without altering or terminating tachycardia.CASE SUMMARY Here,we report a case of symptomatic left atrial flutter without prior intervention.In this case,high-density mapping revealed a dual-loop macro-reentry around the mitral annulus and central scar of the anterior wall.The propagation result showed that the dominant loop was around the mitral annulus,and the key isthmus was between the central scar and mitral annulus.The atrial flutter terminated successfully after ablation was performed.CONCLUSION In this case,we demonstrate that high-density mapping technology may help identify the dominant loop of dual-loop atrial flutter without entrainment,which makes ablation easier.

基于贝叶斯优化支持向量回归的流线型箱梁颤振气动外形优化方法

为解决风洞试验耗时费力和计算流体动力学(CFD)计算量大的问题,提出了一套新型流线型箱梁断面颤振性能气动外形优化方法.以风嘴参数为设计变量,利用CFD获取断面三分力系数,以准定常理论估算的颤振临界风速为优化目标.根据贝叶斯优化支持向量回归构建代理模型,利用混合加点法更新模型,通过寻优算法确定最优断面.以虎门大桥为例,得到桥梁在可行域内颤振性能最佳的断面方案.结果表明,风嘴升高,颤振临界风速先增后减,相对高度为0.6时整体性能较优,相对高度为0.7时可获得最优断面.底板宽增加,颤振性能显著降低,下斜腹板倾角为14°~16°时颤振性能最优.断面优化后桥梁颤振临界风速相比原始断面提升约31%.

基于Flutter跨平台记账软件的设计与实现

记账在资金快速流动的现代社会成为人们生活中不可缺少的一部分。随着各式各样移动设备的普及,如何在各种设备之间实现财政数据的共享也成为一大问题。基于该设计并开发了一款基于Flutter跨平台智能记账软件,该软件在实现跨平台数据同步的同时,引入OCR(Opentical Character Rescognition,光学字符识别)技术实现批量记账,能够帮助用户进行高效的财务管理。

参数耦合下风力发电机叶片机械颤振检测研究

受气候、风速等因素影响,会使风力发电机叶片的运行条件发生较大变化,增加了颤振检测的难度。为此,该文提出参数耦合下风力发电机叶片机械颤振检测方法。建立风力发电机叶片结构模型,推导结构动力学方程,并利用优化后的参数耦合算法对其求解,获取非稳态气动载荷,通过动力学模型反馈得到叶片的结构响应和振动情况;构建非稳态气动降阶模型,采用能量法分析叶片的结构响应与气动载荷的时域或频域,计算能量交换角度,确定叶片的颤振程度,实现颤振检测。实验结果表明,该方法气动阻尼系数计算结果准确、检测正确率高、计算时间短。

基于同频弯扭耦合强迫振动的桥梁断面颤振导数识别方法改进

为拓展强迫振动法在桥梁断面颤振导数识别领域中的应用能力,采取让断面做2次同频异相的弯扭耦合简谐运动模式,理论推导出任意非零相位差条件下的桥梁断面颤振导数识别公式。以理想平板的Theodorsen解为气动力数据源,对该方法的识别能力进行数值验证,并在此基础上研究弯扭耦合运动相位差、高斯白噪声、整数倍频有色噪声对平板颤振导数识别结果的影响规律。基于Fluent软件,将该方法与计算流体动力学(Computational Fluid Dynamics,CFD)技术结合,识别得到丹麦大带东桥主梁断面的颤振导数。研究结果表明:当平板气动力不包含噪声时,在任意非零相位差取值条件下,按照该方法识别所得颤振导数结果与理论值完全吻合;当平板气动力含有高斯白噪声时,在考察的3个低水平噪声条件下(5%、10%、15%),颤振导数识别误差与高斯白噪声比例水平、折算风速均成正相关,但不同颤振导数对高斯白噪声敏感程度各异;当平板气动力包含整数倍频有色噪声时,3倍频、4倍频噪声对颤振导数的识别精度影响显著,其他低倍频噪声和超高倍频噪声的影响较小,在8个颤振导数的识别结果中,H_(2)^(*)、H_(4)^(*)、A_(2)^(*)、A_(4)^(*)对倍频有色噪声更敏感。应用该方法结合CFD数值模拟识别得到的大带东桥主梁颤振导数与既有文献结果吻合良好,经计算得到的颤振临界风速也较为接近。研究结果可满足同类桥梁颤振设计的工程计算需求。