Influence of deflection angles on flow behaviours in openchannel bends

The deflection angle of a river bend plays an important role on behaviours of the flow within it, and a clear understanding of the angle's influence is significant in both theoretical study and engineering application. This paper presents a systematic numerical investigation on effects of deflection angles(30°, 60°, 90°, 120°, 150°, and 180°) on flow phenomena and their evolution in open-channel bends using a Re-Normalization Group(RNG) κ-ε model and a volume of fluid(VOF) method. The numerical results indicate that the deflection angle is a key factor for flows in bends. It is shown that the maximum transverse slope of water surface occurs at the middle cross section of a bend, and it increases with the deflection angle. Besides a major vortex, or, the primary circulation cell near the channel bottom, a secondary vortex, or, an outer bank cell, may also appear above the former and near the outer bank when the deflection angle is sufficiently large, and it will gradually migrate towards the inner bank and evolve into an inner bank cell. The strength of the secondary circulations increases with the deflection angle. The simulation demonstrates that there is alow-stress zone on the bed near the outer bank and a high-stress zone on the bed near the inner bank, and both of them increase in size with the deflection angle. The maximum of shear stress on the inner bank increases nonlinearly with the angle, and its maximums on the outer bank and on the bed take place when the deflection angle becomes 120°.

PROBLEMS OF U-SHAPED BELLOWS WITH NONLINEAR DEFORM TION OF LARGE AXISYMMETRICAL DEFLECTION(Ⅰ)--COUNTING NONLINEAR DEFORMATIONS OF RING SHELLS AND COMPRESSED ANGLE OF BELLOWS

This paper follows the work of[1,2].There are some progress in dealing with moderately small rotations(the squares of rotation angles are the order of magnitude of strains)of middle surface normals of inside and outside ring shells and compressed angle of bellows.Calculation results agree with experiments well.To bellow design,the method given in this paper is of practical value and the discussion of the influence of compressed angle on characteristic relation is helpful.

Spherically Symmetric Wormhole Gravitational Lens Deflection Angle Signifying Braneworld Cosmology

Previously, the gravitational lens of a wormhole was introduced by various researchers. Their treatment was focused basically on the lens signature that describes wormhole geometrical character such as the differences from a black hole or between any various types of wormhole models. The braneworld scenario provides the idea of spacetime with underlying extra-dimensions. The inclusion of extra-dimensional terms in the lens object spacetime line element will result in some variation in the expression for its gravitational lens deflection angle. Thus in this paper we investigate such variation by deriving this deflection angle expression. As such, this paper not only shows the existence of such variation but also suggests the potential utilization of gravitational lensing to prove the existence of extra dimensions by studying the deflection angle characteristic in accordance with the spacetime expansion rate of the universe.

Thermal fluctuations,deflection angle,and greybody factor of a high-dimensional Schwarzschild black hole in scalar-tensor-vector gravity

In this study,we examined the thermal fluctuations,deflection angle,and greybody factor of a high-dimensional Schwarzschild black hole in scalar-tensor-vector gravity(STVG).We calculated some thermodynamic quantities related to the correction of the black hole entropy caused by thermal fluctuations and discussed the effect of the correction parameters on these quantities.By analyzing the changes in the corrected specific heat,we found that thermal fluctuations made the small black hole more stable.It is worth noting that the STVG parameter did not affect the thermodynamic stability of this black hole.Additionally,by utilizing the Gauss-Bonnet theorem,the deflection angle was obtained in the weak field limit,and the effects of the two parameters on the results were visualized.Finally,we calculated the bounds on the greybody factor of a massless scalar field.We observed that as the STVG parameter around the black hole increased,the weak deflection angle became larger,and more scalar particles can reach infinity.However,the spacetime dimension has the opposite effect on the STVG parameter on the weak deflection angle and greybody factor.

Massless Dirac perturbations of black holes in f(Q)gravity:quasinormal modes and a weak deflection angle

This article considers a static and spherical black hole(BH)in f(Q)gravity.f(Q)gravity is the extension of symmetric teleparallel general relativity,where both curvature and torsion are vanishing and gravity is described by nonmetricity.In this study,we investigate the possible implications of quasinormal mode(QNM)modified Hawking spectra and deflection angles generated by the model.The Wentzel–Kramers–Brillouin method is used to solve the equations of motion for massless Dirac perturbation fields and explore the impact of the nonmetricity parameter(Q_(0)).Based on the QNM computation,we can ensure that the BH is stable against massless Dirac perturbations and as Q_(0)increases the oscillatory frequency of the mode decreases.We then discuss the weak deflection angle in the weak field limit approximation.We compute the deflection angle up to the fourth order of approximation and show how the nonmetricity parameter affects it.We find that the Q_(0)parameter reduces the deflection angle.

Effect of the Wick Deflection Angles on Heat Transfer Characteristics for the Flat LHP

Loop Heat Pipe(LHP)is an efficient two-phase heat transfer device,which can be used in waste heat recovery,electronics cooling,aerospace and other fields.The wick,the core component of LHP,plays an important role in its start-up and operation.In this paper,the wick fabricated by 3D printing technology had uniform and interconnected pores.In the experiment,the position of the parallel vapor removal grooves was always fixed towards the vapor outlet.When the cylindrical wick was placed in the evaporator,the rotation angle relative to its central axis could be changed,thus changing the number and shape of the pores facing the vapor removal grooves.The wick deflection angle represented its change in spatial position relative to the fixed vapor removal grooves.The effect of the wick deflection angles on the heat transfer characteristics of the flat LHP was experimentally investigated.It was found that with the change of deflection angle,the number of pores in the evaporation-oriented zone would also change,which had a significant impact on the start-up process and heat transfer performance of LHP.When the deflection angle was 30°,LHP could start fastest at a low heat load of 20 W and operate stable at a high heat load of 180 W.

Weak deflection angle and shadow cast by the charged-Kiselev black hole with cloud of strings in plasma

In this study,the gravitational deflection angle of photons in the weak field limit(or the weak deflection angle)and shadow cast by the electrically charged and spherically symmetric static Kiselev black hole(BH)in the string cloud background are investigated.The influences of the BH charge Q,quintessence parameterγ,and string cloud parameter a on the weak deflection angle are studied using the Gauss-Bonnet theorem.in addition to studying the influences on the radius of photon spheres and size of the BH shadow in the spacetime geometry of the chargedKiselev BH in string clouds.Moreover,we study the effects of plasma(uniform and non-uniform)on the weak deflection angle and shadow cast by the charged-Kiselev BH surrounded by the clouds of strings.In the presence of a uniform/nonuniform plasma medium,an increase in the string cloud parameter a increases the deflection angleα.In contrast,a decrease in the BH charge Q decreases the deflection angle.Further,we observe that an increase in the BH charge Q causes a decrease in the size of the shadow of the BH.We notice that,with an increase in the values of the parametersγand a,the size of the BH shadow increases,and therefore,the intensity of the gravitational field around the charged-Kiselev BH in string clouds increases.Thus,the gravitational field of the charged-Kiselev BH in the string cloud background is stronger than the field produced by the pure Reissner-Nordstrom BH.Moreover,we use the data released by the Event Horizon Telescope(EHT)collaboration,for the supermassive BHs M87*and Sgr A*,to obtain constraints on the values of the parametersγand a.

Angle measurement technology based on magnetization vector for narrow space applications

With the wide application of laser in the field of skin plastic surgery, micro laser galvanometer scanner has made great progress in this field with its portability. However, the measurement method used to measure the deflection angle of laser galvanometer in the narrow space of scanner with high precision remains to be studied. In this paper, an angle measurement method based on magnetic field is proposed, and the effect of the shapes of permanent magnets(PMs) on the measurement is studied by theoretical and experimental study under the condition that the maximum available space for the PMs is a 10 mm side cube. An angle measuring experimental device is set up, and the contrast experiment is carried out with different PMs which are the same as simulation. The experimental results show that cylindrical PM is more suitable than other PMs, which is consistent with the simulation results, and the maximum nonlinearity error is 0.562%. This method has the advantages of small volume,non-contact measurement, small moment of inertia, good dynamic response and no external excitation for the PMs, so it has a broad application prospect in micro laser galvanometer scanner.

Quantum effects on the black hole shadow and deflection angle in the presence of plasma

In this study,the optical properties of a renormalization group improved(RGI)Schwarzschild black hole(BH)are investigated in a plasma medium.Beginning with the equations of motion in a plasma medium,we aim to present the modifications in the shadow radius of the RGI BH.To this end,we compute the deflection angle of light in the weak gravity regime for uniform and non-uniform plasma media.Importantly,owing to the plasma media,we discover that the equations of motion for light obtained from the radiating and infalling/rest gas have to be modified.This,in turn,changes and modifies the expression for the intensity observed far away from the BH.Finally,we obtain the shadow images for the RGI BH for different plasma models.Although quantum effects change the background geometry,such effects are minimal,and practically detecting these effects using the current technology based on supermassive BH shadows is impossible.The parameterΩencodes the quantum effects,and in principle,one expects such quantum effects to play significant roles only for very small BHs.However,the effects of plasma media can play an important role in the optical appearance of BHs,as they affect and modify the equations of motion.

取秧侧向零偏移的空间轨迹再生稻分插机构设计与试验

为了解决现有空间行星轮系式分插机构在再生稻宽窄行机械化种植取秧过程中出现侧向偏移量和侧向偏转角的技术难题,本文提出一种具有局部平面轨迹特性的空间轨迹不等速行星轮系机构,并开展基于取秧口和机构回转中心位置约束下的宽窄行分插机构综合研究。构建了基于关键位姿点(取秧起始点、取秧结束点、推秧点)的空间轮系机构运动综合模型,利用关键位姿点求解机构杆长参数与空间交错轴信息,并通过优选二杆相对角位移参数实现机构传动比分配。将不完全非圆齿轮副引入空间行星轮系机构,利用间歇机构锁止弧约束行星轴,实现机构取秧过程侧向零偏移量、侧向零偏转角的平面轨迹段。通过仿真分析与机构样机试验验证了机构实际作业性能与理论设计相一致,结果表明:分插机构取秧侧向零偏移量,取秧侧向零偏转角,推秧侧向总偏移量为50.24 mm、取秧角为5.18°、推秧角为71.56°、推秧侧向角为16.26°、插秧穴口宽度为22.43 mm、轨迹高度为289.76 mm,满足预期设计要求。最后通过田间试验验证,分插机构可实现等行距取秧口和既定机构回转中心下宽行(40 cm)与窄行(20 cm)间隔机插,满足再生稻宽窄行种植要求。

垂直起降系统的互补滑模与情感神经网络控制

针对具有未知扰动的垂直起降机双闭环控制系统,提出一种基于连续径向基情感神经网络的互补积分滑模控制策略。建立了包含未知扰动项的垂直起降机的数学模型,为系统内外环分别设计滑模控制器和互补积分滑模控制器,基于对系统鲁棒性的考量,利用连续径向基情感神经网络逼近系统未知扰动项,给出神经网络权重的自适应律,形成一套新型的复合控制策略,利用Lyapunov方法分析了系统的稳定性。通过对垂直起降机的仿真实验与实物实验进行分析对比,证明了所设计的控制器具有更快的收敛速度、更高的跟踪精度和更佳的鲁棒性。

基于偏转角抑制的改进人工势场法路径规划

针对传统人工势场法在实际应用中存在的局部最极小值、目标不可达以及路径震荡等问题,文种提出了一种基于偏转角抑制的改进人工势场法。该方法以传统人工势场法为基础,采用改进斥力势场函数保证目标点为全局势能最低点。在路径解算中引入偏转角抑制因子来抑制无人车行驶过程中过大的偏转角,在无人车陷入局部极小值点后每一步的路径解算中都添加新的虚拟目标点,直至无人车累积一定的偏转角摆脱障碍物群。仿真实验结果表明,该算法可以在不影响无人车避障的情况下减少规划路径的震荡性,并能够使无人车逃脱复杂障碍物群顺利到达目标点,规划出一条有效、简短以及震荡较少的路径。

大偏角短引渠侧向进水泵站流场流态优化

为了改善大偏角短引渠侧向进水泵站前池、进水池内偏流、回流和漩涡等不良流态,以某大型大偏角短引渠侧向进水泵站工程为研究对象,采用物理模型试验和数值模拟相结合的方式对初步设计方案下的前池、进水池流态进行分析,提出流速偏差系数λ作为评价指标,对工程进行优化,探讨前池的结构性改造对水流的整流效果,得出“弧形隔墩+改变底坡坡度+开设消涡孔”的组合方案为推荐整流方案,有效解决了前池及进水池内原设计存在的不良流态。研究结果表明,该整流方案使各个机组进水池偏差系数分别下降了37.03%、12.99%、22.29%、22.04%,显著改善了前池,进水池流态。研究结果可为类似大偏角短引渠侧向进水泵站前池及进水池流场流态优化提供参考,也可为类似短引渠泵站工程和进水建筑物的设计提供参考。

仿形夹持器的设计研究

多数夹持器适用于夹取表面规则单一的物件,因为夹持形状复杂的物件接触面受力不均匀,难以实现稳定夹取的过程,所以根据这一难题,文章通过分析夹取物件表面形状特征,应用逆向建模还原被夹取物件的模型。从模型结构特性出发,用ZWSOFT软件设计出与夹取物件特征形状相符的仿形夹持器,依靠夹持器内部造型特征,对物件贴合夹取,并通过CAE受力仿真分析与夹取试验得出:气压大小为0.58MPa,转偏角为10°时,仿形夹持器夹取稳定性效果最好。应用得出的参数,与普通夹持器进行夹取试验对比,结果表明:仿形夹持器对夹取复杂表面的物件具有一定优势。

基于含避障角人工势场法的机器人路径规划

针对基于距离的人工势场法(Artificial potential field, APF)存在的局部极小值问题,提出了一种含避障角的人工势场法的避障路径规划方法。在平面环境中,采用斜率判定路径规划过程中的位置关系,通过机器人当前点到障碍物的距离与障碍物的影响半径二者之差得出人工势场法中的排斥力,并对排斥力的偏转角进行调整;另外,在空间环境中利用圆弧插补理论将机器人平面避障问题转换为空间避障问题;基于机器人构型配置对改进人工势场法进一步完善以满足实际避障要求。仿真和实验研究结果表明,含避障角的人工势场法,在单个或多个障碍物环境中进行避障路径规划时解决了局部极小值的问题,同时实现了6自由度机器人末端在避障时的轨迹曲线平滑无振荡,验证了所提出避障路径规划方法的可行性。

攻角和着角联合作用下弹体侵彻混凝土靶的弹道特性研究

为探究攻角和着角联合作用下弹体侵彻混凝土靶的弹道特性,基于LS-DYNA有限元软件,在速度1000 m/s时以不同攻角和着角对弹体侵彻混凝土靶进行数值模拟。重点研究了攻角和着角对弹体轴向侵彻深度、径向偏移距离和偏转角的影响,通过对弹体侵彻过程中受力情况的研究,主要对轴向阻力和径向阻力以及弹体所受偏转力矩进行分析,得到其对弹道的影响规律:随着着角的增大,弹体偏转角受攻角影响呈显著增加趋势;着角在一定的范围内,初始方向与着角相反的攻角对弹体侵彻能力有提升作用,初始方向与着角相同的攻角对侵彻能力有减弱作用;当着角过大时,无论初始攻角的方向与着角是否相同,均会对侵彻能力有减弱作用,且随着角度的增加更明显。研究结果可以为钻地弹的研制提供参考。

负风压作用下隐框玻璃幕墙承载行为和脱胶损伤实验研究

隐框玻璃幕墙连接用的硅酮结构胶发生损伤导致玻璃面板坠落是当前幕墙服役过程中的常见问题.现有研究大多采用动力学方法对幕墙的脱胶损伤进行检测和评估,该方法通常需要额外施加荷载激励,且测量的动力响应数据易受环境影响,难以实现幕墙安全状态的可靠评估.为解决上述问题,提出在负风压作用下利用玻璃面板的挠度和转角对玻璃面板的脱胶损伤进行检测和评估的方法.首先,设计一系列隐框玻璃幕墙脱胶损伤实验,验证了在风荷载作用下利用挠度和转角对玻璃面板的安全状态进行检测的可行性;之后,基于实验结果构建了隐框玻璃幕墙安全风险监测评估系统,实现玻璃面板脱胶位置和数量的实时监测和快速识别.

Study of bending angle and shadow in a new Schwarzschild-like black hole affected by plasma and non-plasma mediums

In this study,we analyze the models of the deflection angle of a new Schwarzschild-like black hole(BH)and employ the optical metric of the BH.To achieve this,we use the Gaussian curvature of the optical metric and the Gauss-Bonnet theorem,known as the Gibbons-Werner technique,to determine the deflection angle.Furthermore,we examine the deflection angle in the presence of a plasma medium and the effect of the plasma medium on the deflection angle.The deflection angle of the BH solution in the gauged super-gravity is computed using the Keeton-Petters approach.Utilizing the ray-tracing technique,we investigate the shadow of the corresponding BH and analyze the plots of the deflection angle and shadow to verify the influence of the plasma and algebraic thermodynamic parameters on the deflection angle and shadow.

不同通气量下双发航行体水下齐射降载增稳特性研究

基于重叠网格技术,VOF(volume of fluid)多相流模型以及改进型分离涡模型相结合方法,建立了基于主动通气下双体水下齐射降载增稳数值方法,分析了通气量对空泡形态、载荷特性及运动稳定性的影响规律。结果表明:在一定范围内,随着通气量的增加,当通气空泡完全包裹航行体孔口下方区域后,横向载荷幅值和交变峰值均减小,同时,产生的扶偏力矩能够大幅度减小双发航行体之间狭长流域产生的流动干扰现象。另外,为了避免发生共振现象,设计航行体时应尽量使其固有频率在通气效应产生的低频范围之外。综合分析,主动通气方式对多体水下齐射运动姿态的不稳定性具有较好的改善作用。

基于变桨与襟翼协同的降载特性研究及机理分析

研究了尾缘襟翼长度、偏转角和攻角对翼型降载特性的影响,并分析其影响机理。结果表明:变桨与尾缘襟翼的协同控制可有效实现挥舞方向上的降载;尾缘襟翼长度越大,尾缘偏转角越小,攻角越远离临界值,降载性能越佳;偏转角增大会导致临界攻角位置前移;为实现快速降载,在正偏转角、大攻角下优先选择尾缘控制,其他情况下均优先选择变桨控制;降载特性与翼型及翼缝流体分布密切相关,压差越小,降载性能越好。