2-Dimensional FEM modeling of macrosegregation in the directional solidification with mesh adaptation

In order to improve the prediction accuracy of macrosegregation channel, an algorithm for dynamic remeshing is proposed. The basic idea is to generate fine elements near the liquidus isotherm. The norm of the gradient of solid fraction is used for piloting the remeshing in the mushy zone; whereas, the objective mesh size in the liquid is considered as a function of the distance to the liquidus isotherm. The efficiency of mesh adaptation is demonstrated by prediction of macrosegregation channel in a case of unidirectional solidification.

翼尖铰接组合式无人机气动建模方法及布局参数影响

翼尖铰接组合式无人机是一类新概念飞行器,其由多个单体无人机以翼尖铰接形式连接而成并允许相对滚转运动,在布局参数及飞行力学特性上与常规飞行器有较大不同,单体无人机间存在气动耦合。首先基于状态空间形式涡格法给出了针对该类型飞行器的气动导数计算方法。然后,结合Newton-Euler方程建立的飞行力学模型进行配平计算及飞行力学稳定性分析,说明其具有以相对滚转运动主导的不稳定复合运动飞行模态特征。最后,开展布局参数对飞行动力学稳定性影响研究,经分析,减小单体无人机配平滚转角,增加后掠角可以改善飞行稳定性,同时机翼与尾翼距离存在改善飞行稳定性最优值。研究结果可为翼尖铰接组合式无人机设计提供指导和参考。

Experimental and numerical flutter analysis of a folding fin with multiple asymmetric free-plays

Experimental folding fin models with an adjustable free-play are tested in a wind tunnel.The fin structure is modeled using the free-interface component mode synthesis method,and its free-play is modeled as four independent nonlinear springs with asymmetric stiffness.A nonplanar unsteady vortex-lattice method considering compressibility is employed to address nonlinear deformation and high subsonic flow.Surface spline interpolation is improved through projection and partition.The aeroelastic characteristics of folding fins with different free-play magnitudes,initial conditions and elastic-axis positions are analyzed using an established time-marching method because of its relatively small computation scale and high precision.The results show good consistency among the presented method,the wind tunnel test and the harmonic balance method.There is a negative correlation between the critical speed of divergent motion and the ratio of the initial condition to the free-play magnitude.If either the free-play magnitude or the initial condition is extreme(tiny or vast),the system nonlinearity degenerates to linearity.Generally,the flutter prevention design of a linear model can be applied to a nonlinear model,such as moving the elastic-axis position aftward.The presented fin configuration exhibits an unstable limit cycle oscillation because the orders of coupled flutter modes do not change with variations in equivalent linear stiffness.

A review of bird-like flapping wing with high aspect ratio

Bird-like flapping-wing vehicles with a high aspect ratio have the potential to fulfill missions given to micro air vehicles,such as high-altitude reconnaissance,surveillance,rescue,and bird group guidance,due to their good loading and long endurance capacities.Biologists and aeronautical researchers have explored the mystery of avian flight and made efforts to reproduce flapping flight in bioinspired aircraft for decades.However,the cognitive depth from theory to practice is still very limited.The mechanism of generating sufficient lift and thrust during avian flight is still not fully understood.Moving wings with unique biological structures such as feathers make modeling,simulation,experimentation,and analysis much more difficult.This paper reviews the research progress on bird-like flapping wings from flight mechanisms to modeling.Commonly used numerical computing methods are briefly compared.The aeroelastic problems are also highlighted.The results of the investigation show that a leading-edge vortex can be found during avian flight.Its induction and maintenance may have a close relationship with wing configuration,kinematics and deformation.The present models of flapping wings are mainly two-dimensional airfoils or three-dimensional single root-jointed geometric plates,which still exhibit large differences from real bird wings.Aeroelasticity is encouraged to consider the nonignorable effect on aerodynamic performance due to large-scale nonlinear deformation.Introducing appropriate flexibility can improve the peak values and efficiencies of lift and thrust,but the detailed conclusions always have strong background dependence.

利那洛肽胶囊联合低剂量聚乙二醇电解质散用于结肠镜肠道准备的可行性与安全性

目的探讨利那洛肽胶囊联合低剂量复方聚乙二醇电解质散(PEG)作为肠镜检查前肠道清洁剂的可行性与安全性。方法选取2022年3月至2022年5月经保定市第一中心医院门诊拟行肠镜检查的300例受试者作为研究对象。采用随机数字表,将受试者随机分为三组,每组各100例患者。A组作为对照组单用3盒PEG、B组利那洛肽胶囊2粒(290μg/每粒)联合2盒PEG清肠、C组3粒利那洛肽胶囊联合2盒PEG清肠,比较三组患者肠道清洁程度及不良事件的发生率。结果B组左半结肠、横结肠、右半结肠及总Boston肠道准备量表(BBPS)均与A组差异无统计学意义(P>0.05);C组左半结肠、横结肠、右半结肠及总BBPS均高于A组,具有统计学意义(P<0.05),B组的左半结肠、横结肠、右半结肠及总BBSP评分均低于A组,具有统计学意义(P<0.05)。不良事件发生率方面,B、C组均低于A组,差异有统计学意义(P<0.05)。B、C组之间差异无统计学意义(P>0.05)。结论利那洛肽胶囊2粒联合2盒PEG肠道清洁度与单用3盒PEG相似,利那洛肽胶囊3粒联合2盒PEG清肠效果优于单用3盒PEG。2种联合用药方式不良事件发生率均低于单用3盒PEG。

Flutter and gust response analysis of a wing model including geometric nonlinearities based on a modified structural ROM

In this paper,a framework is established for nonlinear flutter and gust response analyses based on an efficient Reduced Order Model(ROM).The proposed method can be used to solve the aeroelastic response problems of wings containing geometric nonlinearities.A structural modeling approach presented herein describes the stiffness nonlinearities with a modal formulation.Two orthogonal spanwise modes describe the foreshortening effects of the wing.Dynamic linearization of the ROM under nonlinear equilibrium states is applied to a nonlinear flutter analysis,and the fully nonlinear ROM coupled with the non-planar Unsteady Vortex Lattice Method(UVLM)is applied to gust response analysis.Furthermore,extended Precise Integration Method(PIM)ensures accuracy of the dynamic equation solutions.To demonstrate applicability and accuracy of the method presented,a wind tunnel test is conducted and good agreements between theoretical and test results of nonlinear flutter speed and gust response deflection are reached.The method described in this paper is suitable for predicting the nonlinear flutter speed and calculating the gust responses of a large-aspect-ratio wing in time domain.Meanwhile,the results derived highlight the effects of geometric nonlinearities obviously.

RIP1-dependent linear and nonlinear recruitments of caspase-8 and RIP3 respectively to necrosome specify distinct cell death outcomes

There remains a significant gap in our quantitative understanding of crosstalk between apoptosis and necroptosis pathways.By employing the SWATH-MS technique,we quantified absolute amounts of up to thousands of proteins in dynamic assembling/de-assembling of TNF signaling complexes.Combining SWATH-MS-based network modeling and experimental validation,we found that when RIP1 level is below~1000 molecules/cell(mpc),the cell solely undergoes TRADD-dependent apoptosis.When RIP1 is above~1000 mpc,pro-caspase-8 and RIP3 are recruited to necrosome respectively with linear and nonlinear dependence on RIP1 amount,which well explains the co-occurrence of apoptosis and necroptosis and the paradoxical obser-vations that RIP1 is required for necroptosis but its increase down-regulates necroptosis.Higher amount of RIP1(>~46,000 mpc)suppresses apoptosis,leading to necroptosis alone.The relation between RIP1 level and occurrence of necroptosis or total cell death is biphasic.Our study provides a resource for encoding the com-plexity of TNF signaling and a quantitative picture how distinct dynamic interplay among proteins function as basis sets in signaling complexes,enabling RIP1 to play diverse roles in governing cell fate decisions.

Aeroservoelastic stability analysis for flexible aircraft based on a nonlinear coupled dynamic model

A unified theoretical aeroservoelastic stability analysis framework for flexible aircraft is established in this paper. This linearized state space model for stability analysis is based on nonlinear coupled dynamic equations, in which rigid and elastic motions of aircraft are both considered.The common body coordinate system is utilized as the reference frame in the deduction of dynamic equations, and significant deformations of flexible aircraft are also fully concerned without any excessive assumptions. Therefore, the obtained nonlinear coupled dynamic models can well reflect the special dynamic coupling mechanics of flexible aircraft. For aeroservoelastic stability analysis,the coupled dynamic equations are linearized around the nonlinear equilibrium state and together with a control system model to establish a state space model in the time domain. The methodology in this paper can be easily integrated into the industrial design process and complex structures.Numerical results for a complex flexible aircraft indicate the necessity to consider the nonlinear coupled dynamics and large deformation when dealing with aeroservoelastic stability for flexible aircraft.

Conceptual design and flight test of two wingtipdocked multi-body aircraft

To overcome the drawbacks such as large wing deformations,poor performance encountering gusts,limits in taking off and landing,inconvenience of transportation of High-Altitude Long-Endurance(HALE)Unmanned Aerial Vehicles(UAVs),a new conceptual aircraft called wingtip-docked Multi-Body Aircraft(MBA)has attracted lots of attentions.Aiming to investigate the feasibility of this concept,two UAV models were designed,manufactured and connected by a wingtip-docking mechanism,which only allows the relative roll motion between the two aircraft.The trim solution of the two connected aircraft is firstly obtained by solving the developed nonlinear flight dynamic equations,followed by the stability analysis based on the linearized model.The results show that the connected aircraft is inherently unstable and cannot fly without a reasonable flight control system.A set of Proportional-Integral-Derivative(PID)control laws was then developed and implemented in the two experimental aircraft.The success of the flight tests show that the flight control can effectively eliminate the unstable motion and the wingtip-docked MBA is controllable and feasible。

Time-domain nonlinear aeroelastic analysis and wind tunnel test of a flexible wing using strain-based beam formulation

A theoretical formulation for time-domain nonlinear aeroelastic analysis of a flexible wing model is presented and validated by wind tunnel tests. A strain-based beam model for nonlinear structural analysis is combined with the Unsteady Vortex Lattice Method(UVLM) to form the complete framework for aeroelastic analysis. The nonlinear second-order differential equations are solved by an implicit time integration scheme that incorporates a Newton-Raphson sub-iteration technique. An advanced fiber optic sensing technique is firstly used in a wind tunnel for measuring large structural deformations. In the theoretical study, the nonlinear flutter boundary is determined by analyzing the transient response about the nonlinear static equilibrium with a series of flow velocities. The gust responses of the wing model at various gust frequencies are also studied. Comparisons of the theoretical and experimental results show that the proposed method is suitable for determining the nonlinear flutter boundary and simulating the gust response of flexible wings in the time domain.