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.

Stability analysis of the fluttering and autorotation of flow-induced rotation of a hinged flat plate

This work describes investigations performed on the interaction of uniform current and freely rotating plate about a fixed vertical axis. Fluttering and autorotation are two different motions that may occur during the flow induced rotation. The dimensional analysis proves that the motion in flow induced rotation motion is governed essentially by the dimensionless moment of inertia and Reynolds number. Certain combinations define the stability boundaries between fluttering and autorotation. Fluttering is oscillation of body about a vertical axis and the autorotation is a name given to the case when the body turns continuously about the vertical axis First, the loads and moment coefficients are calculated by experiments and streamline theory for different angles of attack for a fixed fiat plate. Then for dynamic case, a bifurcation diagram is presented based on experiments to classify different motion states of flow induced rotation. Finally, a dynamical model is proposed for stability analysis of flow induced rotation of a flat plate.

少数民族代表性传统文化展示与学习系统的设计与实现

针对目前公众对少数民族传统文化认知不足、展示和宣传弘扬缺乏等问题,通过软件开发和数据可视化技术设计和实现了一款少数民族代表性传统文化展示与学习系统,以更好地让公众了解、宣传和弘扬少数民族传统文化。采用当下主流框架技术,包括SpringCloud、SpringBoot、Flutter等前后端框架和MySQL、Redis等数据库技术,以及ElasticSearch搜索引擎技术,JWT身份认证技术和Figma、Material Design等UI设计技术实现了少数民族代表性传统文化展示与学习系统。该系统分为APP端和PC端,其中APP端主要有五大功能模块,分别为少数民族传统文化展示模块、少数民族传统文化学习模块、少数民族分布地图展示模块、社区论坛模块和用户信息管理模块;PC端主要用于各个模块的管理。此外,该系统还设计了基于协同过滤的个性化推荐算法和敏感词过滤算法等以增强用户体验。该系统具备操作简便、易维护、高效和安全等特点。

Experimental investigation of dynamic characteristics of leaching tubing for solution mining of salt cavern carbon and energy storage

Salt caverns are extensively utilized for storing various substances such as fossil energy,hydrogen,compressed air,nuclear waste,and industrial solid waste.In China,when the salt cavern is leached through single-well water solution mining with oil as a cushion,engineering challenges arise with the leaching tubing,leading to issues like damage and instability.These problems significantly hinder the progress of cavern construction and the control of cavern shape.The primary cause of this is the flowinduced vibration instability of leaching tubing within a confined space,which results in severe bending or damage to the tubing.This study presents a model experimental investigation on the dynamic characteristics of leaching tubing using a self-developed liquid-solid coupling physical model experiment apparatus.The experiment utilizes a silicone-rubber pipe(SRP)and a polycarbonate pipe(PCP)to examine the effects of various factors on the dynamic stability of cantilevered pipes conveying fluid.These factors include external space constraint,flexural rigidity,medium outside the pipe,overhanging length,and end conditions.The experiments reveal four dynamic response phenomena:water hammer,static buckling,chaotic motion,and flutter instability.The study further demonstrates that the length of the external space constraint has a direct impact on the flutter critical flow velocity of the cantilevered pipe conveying fluid.Additionally,the flutter critical flow velocity is influenced by the end conditions and different external media.

Nonlinear dynamics of a circular curved cantilevered pipe conveying pulsating fluid based on the geometrically exact model

Due to the novel applications of flexible pipes conveying fluid in the field of soft robotics and biomedicine,the investigations on the mechanical responses of the pipes have attracted considerable attention.The fluid-structure interaction(FSI)between the pipe with a curved shape and the time-varying internal fluid flow brings a great challenge to the revelation of the dynamical behaviors of flexible pipes,especially when the pipe is highly flexible and usually undergoes large deformations.In this work,the geometrically exact model(GEM)for a curved cantilevered pipe conveying pulsating fluid is developed based on the extended Hamilton's principle.The stability of the curved pipe with three different subtended angles is examined with the consideration of steady fluid flow.Specific attention is concentrated on the large-deformation resonance of circular pipes conveying pulsating fluid,which is often encountered in practical engineering.By constructing bifurcation diagrams,oscillating shapes,phase portraits,time traces,and Poincarémaps,the dynamic responses of the curved pipe under various system parameters are revealed.The mean flow velocity of the pulsating fluid is chosen to be either subcritical or supercritical.The numerical results show that the curved pipe conveying pulsating fluid can exhibit rich dynamical behaviors,including periodic and quasi-periodic motions.It is also found that the preferred instability type of a cantilevered curved pipe conveying steady fluid is mainly in the flutter of the second mode.For a moderate value of the mass ratio,however,a third-mode flutter may occur,which is quite different from that of a straight pipe system.

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.

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.

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])。

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。

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。

Interval Finite Element Analysis of Wing Flutter

The influences of uncertainties in structural parameters on the flutter speed of wing are studied. On the basis of the deterministic flutter analysis model of wing, the uncertainties in structural parameters are considered and described by interval numbers. By virtue of first-order Taylor series expansion, the lower and upper bound curves of the transient decay rate coefficient versus wind velocity are given. So the interval estimation of the flutter critical wind speed of wing can be obtained, which is more reasonable than the point esti- mation obtained by the deterministic flutter analysis and provides the basis for the further non-probabilistic interval reliability analysis of wing flutter. The flow chart for interval fmite element model of flutter analysis of wing is given. The proposed interval finite element model and the stochastic finite element model for wing flutter analysis are compared by the examples of a three degrees of freedom airfoil and fuselage and a 15° sweptback wing, and the results have shown the effectiveness and feasibility of the presented model. The prominent advantage of the proposed interval finite element model is that only the bounds of uncertain parameters are required, and the probabilistic distribution densities or other statistical characteristics are not needed.

A New Approach for Aeroelastic Robust Stability Analysis

Air vehicles undergo variations in structural mass and stiffness because of fuel consumption and the failure of structural components, which might lead to serious influences on the aeroelastic characteristics. An approach for aeroelastic robust stability analysis taking into account the perturbations of structural mass and stiffness is developed. Applying the perturbation method and harmonic unsteady aerodynamic forces, the frequency-domain linear fractal transformation （LFT） representation of perturbed aeroelastic system is modeled. Then, the robust stability is analyzed by using the structured singular value ,u-method. The numerical results of a bi-spar wing show its effectiveness and low computational time in dealing with the robust problems with mass and stiffness perturbations. In engineering analysis for solving aeroelastic problems, the robust approach can be applied to flutter analysis for airplane with the fuel load variation and taking the damage conditions into consideration.

Flight Flutter Modal Parameters Identification with Atmospheric Turbulence Excitation Based on Wavelet Transformation

In view of the feature of flight flutter test data with atmospheric turbulence excitation, a method which combines wavelet transformation with random decrement technique for identifying flight flutter modal parameters is presented. This approach firstly uses random decrement technique to gain free decays corresponding to the acceleration response of the structure to some non-zero initial conditions. Then the continuous Morlet wavelet transformation of the free decays is performed; and the Parseval formula and residue theorem are used to simplify the transformation. The maximal wavelet transformation coefficients in different scales are searched out by means of band-filtering characteristic of Morlet wavelet, and then the modal parameters are identified according to the relationships with maximal modulus and angle of the wavelet transform. In addition, the condition of modal uncoupling is discussed according to variation trend of flight flutter modal parameters in the flight flutter state. The analysis results of simulation and flight flutter test data show that this approach is not only simple, effective and feasible, but also having good noise immunity.

长笛的吐音技法

长笛的自身构造决定了它的吐音是管乐器中最容易发音的、吹奏速度最快的乐器。正是由于它的演奏方法比较简单、容易,因此许多人都会忽视这一技巧的科学原理和正确的练习方法,以致严重地阻碍以后的发展。本文阐述了单吐、双吐、三吐、滚舌等几种长笛的吐音技法及其练习方法,希望读者能在其中得到一些借鉴。

基于Flutter开发框架的数据存储访问机制研究

移动端应用程序需要存储与访问的数据越来越多,而移动端设备的存储空间有限,很难满足用户需要,在进行移动端应用程序开发时,选择合适、高效的数据存储与访问机制受到普遍关注。针对Google推出的Flutter跨平台移动开发框架提供的key-value键值对、File文件、SQLite数据库和网络4种数据存储访问机制,深入阐述了它们的内在工作原理,给出了具体实现方法和实现代码。最后,根据4种数据存储访问机制各自的特点和实际的应用程序开发需求,分析了每种机制的应用场景。

BLE通信的移动跨平台考勤方法及系统应用

针对当前企事业单位对成本低廉、识别精确的考勤管理方案的实际需求,提出一种轻量级、高效便捷的基于BLE通信的移动跨平台考勤方法。通过依托跨平台移动框架Flutter构建Android/iOS移动端APP,实现考勤用户注册、加密考勤二维码扫描与BLE连接请求发起,采用基于CC2640R2F芯片的BLE数据透传模块作为Android/iOS移动端与PC端的桥接,PC端完成加密考勤二维码的生成、签到信息校验及考勤二维码的实时更新。应用实践表明,本文提出的解决方案切实可行,具有较高的实际应用价值。

心房扑动与左、右心房扩大的关系

目的探讨心房扑动与双心房扩大的关系。方法对2006年1月～2010年3月在我院住院的1159例心房扑动者,通过彩色超声心动图(UCG)测量心脏左右心房内径,研究与相应疾病的关系。结果 1159例心房扑动者男性多于女性。冠心病者538例(占46.4%)。UCG测量左心房内径值为28～79(平均57.87±10.11)mm。右房内径值为32～68(平均46.32±9.53)mm。其中850例左心房内径≥38mm及或右心房内径≥40mm,与内径正常者比,有统计学意义。结论提示心房扑动与左、右心房扩大相关。左心房扩大例数与右心房扩大例数比,有统计学意义,提示左房扩大比右房扩大明显。