ANALYSIS OF COUPLED-MODE FLUTTER OF PIPES CONVEYING FLUID ON THE ELASTIC FOUNDATION

The governing equation of solid-liquid couple vibration of pipe conveying fluid on the elastic foundation was derived. The critical velocity and complex frequency of pipe conveying fluid on Winkler elastic foundation and two-parameter foundation were calculated by po,ver series method. Compared,with pipe without considering elastic foundation, the numerical results show that elastic foundation can increase the critical flow velocity of static instability and dynamic instability of pipe. And the increase of foundation parameters may increase the critical flow velocity of static instability and dynamic instability of pipe, thereby delays the occurrence of divergence and flutter instability of pipe. For higher mass ratio beta, in the combination of certain foundation parameters, pipe behaves the phenomenon of restabilization and redivergence after the occurrence of static instability, and then coupled-mode flutter takes place.

Analysis on flutter performance of flexible photovoltaic support based on full-order method

Taking a three-cable flexible photovoltaic(PV)support structure as the research subject,a finite element model was established.Utilizing a full-order flutter analysis method,the flutter critical wind speed and flutter frequency of the flexible PV support structure at a tilt angle of 0°were calculated.The results showed good agreement with wind tunnel test data.Further analysis examined the pretension effects in the load-bearing and stabilizing cables on the natural frequency and flutter critical wind speed of the flexible PV support structure.The research findings indicate increasing the pretension in the load-bearing cables significantly raises the natural frequencies of the first four modes.Specifically,as the pretension in the load-bearing cables increases from 22 to 102 kN,the flutter critical wind speed rises from 17.1 to 21.6 m/s.By contrast,the pretension in the stabilizing cable has a smaller effect on the natural frequency and flutter critical wind speed of the flexible PV support structure.When the pretension in the stabilizing cable increased from 22 to 102 kN,the flutter critical wind speed increased from 17.1 to 17.7 m/s.For wind-resistant design of flexible PV support structures,it is recommended to prioritize increasing the pretension in the load-bearing cables to enhance the structural flutter performance.

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。

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])。

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。

Analysis and engineering of coupled cavity waveguides based on coupled-mode theory

The analytical expression for the transmission spectra of coupled cavity waveguides （CCWs） in photonic crystals （PCs） is derived based on the coupled-mode theory （CMT）. Parameters in the analytical expression can be extracted by simple numerical simulations. We reveal that it is the phase shift between the two adjacent PC defects that uniquely determines the flatness of the impurity bands of CCWs. In addition, it is found that the phase shift also greatly affects the bandwidth of CCWs. Thus, the engineering of the impurity bands of CCWs can be realized through the adjustment of the phase shift. Based on the theoretical results, an interesting phenomenon in which a CCW acts as a single PC defect and its impurity band possesses a Lorentz lineshape is predicted. Very good agreement between the analytical results and the numerical simulations based on transfer matrix method has been achieved.

A three-dimensional coupled-mode model for the acoustic field in a two-dimensional waveguide with perfectly reflecting boundaries

This paper presents a three-dimensional （3D） coupled-mode model using the direct-global-matrix technique as well as Fourier synthesis. This model is a full wave, two-way three-dimensional model, and is therefore capable of providing ac- curate acoustic field solutions. Because the problem of sound propagation excited by a point source in an ideal wedge with perfectly reflecting boundaries is one of a few three-dimensional problems with analytical solutions, the ideal wedge prob- lem is chosen in this work to validate the presented three-dimensional model. Numerical results show that the field results by analytical solutions and those by the presented model are in excellent agreement, indicating that the presented model can serve as a benchmark model for three-dimensional sound propagation problems involving a planar two-dimensional geometry as well as a point source.

Three-dimensional coupled-mode model and characteristics of low-frequency sound propagation in ocean waveguide with seamount topography

Large-scale topography, such as a seamount, substantially impacts low-frequency sound propagation in an ocean waveguide, limiting the application of low-frequency acoustic detecting techniques. A three-dimensional(3D) coupledmode model is developed to calculate the acoustic field in an ocean waveguide with seamount topography and analyze the3D effect. In this model, a correction is introduced in the bottom boundary, theoretically making the acoustic field satisfy the energy conservation. Furthermore, a large azimuth angle calculation range is obtained by using the operator theory and higher-order Pade approximation. Additionally, the model has advantages related to the coupling mode and parabolic equation theory. The couplings corresponding to the effects of range-dependent environment are fully considered, and the numerical implementation is kept feasible. After verifying the accuracy and reliability of the model, low-frequency sound propagation characteristics in the seamount environment are analyzed. The results indicate lateral variability in bathymetry can lead to out-of-plane effects such as the horizontal refraction phenomenon, while the coupling effect tends to restore the abnormal sound field and produces acoustic field diffraction behind the seamount. This model effectively considers the effects of the horizontal refraction and coupling, which are proportional to the scale of the seamount.

Complete leaky mode coupling in dual-core photonic crystal fibre based on the coupled-mode theory

This paper theoretically investigates the dependence of leaky mode coupling between inner core fundamental mode and outer core defect mode on phase and loss matching in pure silica dual-core photonic crystal fibres with the multi-pole method. The complete mode coupling can take place when both the phase and loss matching conditions are satisfied at the avoided anti-crossing wavelength. It shows the influences of cladding structure parameters including the diameters of cladding air holes d1, diameters of outer core holes d2 and hole to hole pitch A on the characteristics of leaky modes coupling. The coupled-mode theory is used to analyse the mode transition characteristics and the complete coupling can be clearly indicated by comparing the real and imaginary parts of propagation constant of the leaky modes.

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.

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.

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。