A simulation method on target strength and circular SAS imaging of Xrudder UUV including multiple acoustic scattering

Target strength(TS)and circular synthetic aperture sonar(CSAS)images provide essential information for active acoustic detection and recognition of non-cooperative unmanned undersea vehicles(UUVs),which pose a significant threat to underwater preset facilities.To access them,we propose an iterative physical acoustics(IPA)-based method to simulate the multiple acoustic scattered fields on rigid surfaces in high-frequency cases.It uses the Helmholtz integral equation with an appropriate Green's function in terms of the Neumann series,and then incorporates the ideas of triangulation and iteration into a numerical implementation.Then two approximate analytic formulae with precise physical meanings are derived to predict the TS and CSAS images of concave targets,respectively.There are no restrictions on the surface's curvature and the order of multiple scattering.The method is validated against the finite element method(FEM)for acoustic scattering from a sphere segment and against an experiment involving an X-rudder UUV's stern.On this basis,we simulate and analyze the TS and CSAS images of an X-rudder UUV.In addition,the influence of the angle of adjacent rudders on the multiple scattering characteristics is discussed.Results show that this method can potentially predict accurate UUV features,especially the multiple scattered features.

Scattering of SH-wave by multiple circular cavities in half space

In this paper,an analytic method is developed to address steady SH-wave scattering and perform dynamic analysis of multiple circular cavities in half space.The scattered wave function used for scattering of SH-waves by multiple circular cavities,which automatically satisfies the stress-free condition at the horizontal surface,is constructed by applying the symmetry of the SH-wave scattering and the method of multi-polar coordinates system.Applying this scattered wave function and method of moving coordinates,the original problem can be transformed to the problem of SH-wave scattering by multiple circular cavities in the full space.Finally,the solution of the problem can be reduced to a series of algebraic equations and solved numerically by truncating the infinite algebraic equations to the finite ones.Numerical examples are provided for case with two cavities to show the effect of wave number,and the distances between the centers of the cavities and from the centers to the ground surface on the dynamic stress concentration around the cavity impacted by incident steady SH-wave.

Free Vibration Analysis of Functionally Graded Plates with Multiple Circular and Non-circular Cutouts

Cutouts are inevitable in structures due to practical consideration.In order to investigate the free vibration of functionally graded plates with multiple circular and non-circular cutouts,finite element method is used.The volume fraction of the material constituents is assumed to follow a simple power law distribution.The parameters considered in this paper are as follows：cutout size,cutout location,number of cutouts and different boundary conditions.It should be mentioned that free vibration for FG plates（such as rectangular？skew？trapezoidal？circular plates） with multiple cutouts has not been studied yet and hence the results out coming from this paper may be used as bench marks for future works.

APPLICATION OF THE MODIFIED METHOD OF MULTIPLE SCALES TO THE BENDING PROBLEMS FOR CIRCULAR THIN PLATE AT VERY LARGE DEFLECTION ANDTHE ASYMPTOTICS OF SOLUTIONS (Ⅰ)

In this paper, the modified method of multiple scales is applied to study the bending problems for circular thin plate with large deflection under the hinged and simply supported edge conditions. Theseries solutions are constructed, the boundary layer effects are analysed and their asymptotics are proved.

基于回归分析法的矩形槽圆管吸能特性研究

为了研究矩形槽圆管吸能特性规律,提出了一种基于回归分析法的结构参数与吸能特性关系的拟合方法。针对轴向冲击下的圆管动态响应,首先,建立了6005A-T6材料的Cowper-Symonds本构模型,并验证了仿真模型的准确性;其次,设计了正交试验,建立了吸能特性与结构参数之间的计算模型;然后,利用多元线性与非线性回归分析方法对计算模型参数求解,并对比了两种拟合结果,得到了峰值力和吸能量的经验公式;接着,对比经验公式与有限元数值计算值表明,经验公式在研究范围内具有较高准确性,误差在8%以内;最后,引入吸能性能指标并使用遗传算法对圆管进行了结构优化,优化结果表明,在研究范围内当直径和槽端距最小、壁厚和槽宽最大、槽深最浅时,矩形槽圆管的吸能性能最优。

滑雪产业高质量发展多重循环驱动体系的质性研究

在中国式现代化轨道上发展滑雪产业循环经济,构建多重循环驱动体系,有助于更平衡、更充分地实现滑雪产业高质量发展。本研究利用综合型学术访谈录探究滑雪产业高质量发展的多重循环驱动体系,通过对滑雪产业专家进行深度访谈获取研究资料,并对访谈资料进行编码分析。研究结果表明:滑雪产业高质量发展的多重循环驱动体系主要涵盖了行动主体、资源要素、营商环境、科技创新、现代金融、市场需求六个维度,呈现市场循环、产业循环、需求循环三种表现共同推动滑雪产业高质量发展,研究结论为促进我国滑雪产业高质量发展提供了实践参考。

Nonlinear Resonance of the Rotating Circular Plate under Static Loads in Magnetic Field

The rotating circular plate is widely used in mechanical engineering, meanwhile the plates are often in the electromagnetic field in modern industry with complex loads. In order to study the resonance of a rotating circular plate under static loads in magnetic field, the nonlinear vibration equation about the spinning circular plate is derived according to Hamilton principle. The algebraic expression of the initial deflection and the magneto elastic forced disturbance differential equation are obtained through the application of Galerkin integral method. By mean of modified Multiple scale method, the strongly nonlinear amplitude-frequency response equation in steady state is established. The amplitude frequency characteristic curve and the relationship curve of amplitude changing with the static loads and the excitation force of the plate are obtained according to the numerical calculation. The influence of magnetic induction intensity, the speed of rotation and the static loads on the amplitude and the nonlinear characteristics of the spinning plate are analyzed. The proposed research provides the theory reference for the research of nonlinear resonance of rotating plates in engineering.

Constrained circular-patch-based texture synthesis

Texture synthesis has been developed for several years.The traditional technique can generate a larger image from a small image while avoid feeling of repetition or uncontinuity.Some constrained synthesis methods which can synthesize image according to special location demand or other demands have been also proposed in recent years.However,in general,these constrained texture synthesis methods are simple and have few controllable factors to meet user＇s diverse needs.To control multiple-sample texture synthesis more flexibly in various aspects such as synthesis location,proportion and semantic objects,we present an interactive texture synthesis approach based on circular patches and constrained by objects according to a certain ratio.With this approach,source exemplars and the target image are firstly divided into several regions with different characters.Users can click the blocks in the source exemplars and the want-to-be-synthesized region in the target image,and then texture in the target image is synthesized with the corresponding regions in the source exemplars.In the process of texture synthesis,circular patch instead of square patch is used to eliminate the aliasing phenomena.Images are synthesized from multiple sample images with ratio constraint and experiments on images show that our approach can get effective results of ratio-constrained multi-sample synthesis.

ESTIMATION OF 2-D DOA USING NON-CIRCULAR MUSIC METHOD FOR UNIFORM CIRCULAR AND RECTANGULAR ARRAYS

This paper extends the Non-Circular MUltiple SIgnal Classification(MUSIC)(NC-MUSIC) method for the common array geometries including Uniform Circular Arrays(UCAs) and Uniform Rectangular Arrays(URAs),which enables the algorithm to estimate 2-D Direction Of Arrival(DOA).A comparison between UCAs and URAs of NC-MUSIC is made in this paper.The simulations show that the NC-MUSIC method doubles the maximum estimation number of standard MUSIC.Using non-circular signals,the performance of URAs is improved remarkably while the improvement of UCAs is not so significantly.Moreover,the influence of arrays structures on the NC-MUSIC method is discussed.

Fast BSC-based algorithm for near-field signal localization via uniform circular array

In this paper,we propose a beam space coversion(BSC)-based approach to achieve a single near-field signal local-ization under uniform circular array(UCA).By employing the centro-symmetric geometry of UCA,we apply BSC to extract the two-dimensional(2-D)angles of near-field signal in the Van-dermonde form,which allows for azimuth and elevation angle estimation by utilizing the improved estimation of signal para-meters via rotational invariance techniques(ESPRIT)algorithm.By substituting the calculated 2-D angles into the direction vec-tor of near-field signal,the range parameter can be conse-quently obtained by the 1-D multiple signal classification(MU-SIC)method.Simulations demonstrate that the proposed al-gorithm can achieve a single near-field signal localization,which can provide satisfactory performance and reduce computational complexity.

多发性骨髓瘤环状RNA的差异表达情况及生物学功能研究

目的研究多发性骨髓瘤(MM)中环状RNA(circRNAs)的差异表达情况,并对其生物学功能进行预测。方法收集2023年1月—2月在北京大学第三医院血液科就诊的5例MM患者和同期3例健康志愿者的骨髓样本进行转录组测序,确定MM中差异表达的circRNAs;对circRNAs的miRNA结合位点进行预测;对差异circRNAs进行GO和KEGG富集分析;利用实时荧光定量PCR(qRT-PCR)对部分circRNAs进行验证。结果在MM和正常对照骨髓样本中发现926个差异表达circRNAs,其中上调的818个,下调的108个。这些差异circRNAs具有大量的miRNA结合位点,如miR-619-5p、miR-17-5p、miR-20a-5p等。GO分析显示这些差异circRNAs主要参与细胞的蛋白质代谢、有机物代谢、含氮化合物代谢等生物代谢过程。KEGG分析显示Rap1、FoxO、AMPK等信号通路明显富集。通过qRT-PCR实验对表达显著上调的4个circRNAs进行验证,发现circ_0004524和circ_0003823明显上调,与测序结果一致。结论MM患者具有独特的circRNAs表达谱,对其进行深入的功能和机制研究有助于为MM的诊断和治疗提供潜在的分子标志物。

用于微波烧结黄土的圆波导缝隙天线设计

在土木建筑领域,湿陷性黄土地基受水浸湿后需进行热加固处理,避免地基承载力下降导致工程安全事故的发生。针对该问题,设计了一种工作在2.45 GHz、结构简单、在黄土中匹配效果良好及加热效果良好的圆波导缝隙天线,用于微波烧结湿陷性黄土,并使用多物理场仿真软件COMSOL Multiphysics对烧结效果进行了仿真与分析。结果表明,使用该天线加热半径为45 cm的黄土40h后,黄土的平均温度可达到使湿陷性黄土水分蒸发的100℃,最高温度出现在缝隙周围,由于黄土对电磁波的衰减,距离天线越远加热效果越不明显。此外,通过对黄土介电常数和尺寸的扫参,发现该天线在土体中的S11参数随黄土介电常数和尺寸的变化不大,因此该天线在不同的土壤环境下都能实现良好的匹配和烧结效果。

Surface accuracy optimization of mechanical parts with multiple circular holes for additive manufacturing based on triangular fuzzy number

Surface accuracy directly affects the surface quality and performance of mechanical parts.Circular hole,especially spatial non-planar hole set is the typical feature and working surface of mechanical parts.Compared with traditional machining methods,additive manufacturing(AM)technology can decrease the surface accuracy errors of circular holes during fabrication.However,an accuracy error may still exist on the surface of circular holes fabricated by AM due to the influence of staircase effect.This study proposes a surface accuracy optimization approach for mechanical parts with multiple circular holes for AM based on triangular fuzzy number(TFN).First,the feature lines on the manifold mesh are extracted using the dihedral angle method and normal tensor voting to detect the circular holes.Second,the optimal AM part build orientation is determined using the genetic algorithm to optimize the surface accuracy of the circular holes by minimizing the weighted volumetric error of the part.Third,the corresponding weights of the circular holes are calculated with the TFN analytic hierarchy process in accordance with the surface accuracy requirements.Lastly,an improved adaptive slicing algorithm is utilized to reduce the entire build time while maintaining the forming surface accuracy of the circular holes using digital twins via virtual printing.The effectiveness of the proposed approach is experimentally validated using two mechanical models.

争议性科学事件中科学家间争论焦点研究

爆发于科学共同体成员之间的争论在进入公众视野后,争论焦点由认知要素向社会要素过渡,呈现出复杂的问题情境。为了厘清公共科学争论中持有不同观点的科学家群体的争论焦点,对王贻芳与杨振宁二人关于大型环形加速器−环形正负电子对撞机−超级质子对撞机(CEPC-SPPC)的争议性科学事件展开个案研究。根据编码数据梳理出双方争论的焦点是平等观念和经济问题,并对围绕上述焦点的科学话语展开文本分析。研究发现,在公共科学争论中,科学共同体成员之间争论的焦点本质是对多元主体利益的不同衡量方式,这种不同恰又体现为科学共同体成员能否超出科学共同体的立场来思考科学决策。

环抱式记忆合金肋骨接骨板内固定治疗多发性肋骨骨折的临床效果

目的:探讨环抱式记忆合金肋骨接骨板内固定治疗多发性肋骨骨折(FMR)的疗效。方法:选取2021年1月—2022年12月云浮市新兴县人民医院收治的FMR患者96例为研究对象,采用抽签法分为对照组和观察组,各48例。对照组行胸腔闭式引流术,观察组行环抱式记忆合金肋骨接骨板内固定治疗。比较两组临床指标、疼痛程度、血气情况和并发症。结果:观察组术后置管、胸痛持续、下床活动、住院、骨折愈合时间均短于对照组,差异有统计学意义(P<0.001)。治疗前,两组数字疼痛评分表(NRS)评分、动脉血氧分压(PaO_(2))、动脉血二氧化碳分压(PaCO_(2))水平比较,差异无统计学意义(P>0.05);治疗后3 d,两组NRS评分均降低,PaO_(2)水平升高,PaCO_(2)水平降低,且观察组优于对照组,差异有统计学意义(P<0.05)。两组肺部感染、肺不张发生率比较,差异无统计学意义(P>0.05);观察组胸廓畸形发生率低于对照组,差异有统计学意义(P=0.022)。结论:环抱式记忆合金肋骨接骨板内固定可缩短FMR康复时间,减轻疼痛感,改善血气指标,值得推广。

反平面圆形夹杂和多圆孔多裂纹相互作用问题

运用复变函数及积分方程方法求解了反平面圆形夹杂和多圆孔多裂纹相互作用问题。为解决该问题 ,建立了两种类型的基本解。利用叠加原理和所得的基本解沿圆孔和裂纹表面取待定的基本解密度函数 ,可得一组 Fredholm积分方程。通过积分方程组的数值求解 ,可以得到密度函数的离散值 ,进而得到应力强度因子。

基于频率敏感度和振型的圆柱壳损伤检测方法研究

基于频率敏感度和振型,在损伤定位准则的基础上,提出一种确定圆柱壳中损伤位置和程度的方法。通过对比由于损伤引起的理论和测量频率改变百分比,可以确定损伤的轴向位置。由于圆柱壳的轴对称性,引入某些特定位置的振型信息来确定损伤的环向位置,并且利用一阶近似方法估计损伤程度。对三种边界条件下(自由、简支、悬臂)的圆柱壳数值算例结果表明,文中方法能准确定位单、多位置损伤,而且可以在较小的误差范围内估计出损伤程度。最后利用含噪声的测量频率研究该方法的稳定性。

气象因素与急性脑梗死发病相关性的研究

目的探讨天津市急性脑梗死发病与气象因素的相关性。方法回顾性分析我院2009年~2013年急性脑梗死患者1198例及同期的气温、气压、相对湿度等气象资料;采用圆分布分析急性脑梗死发病的季节规律、直线相关分析及多元逐步回归分析气象因素与急性脑梗死发病之间的关系。结果 （1）急性脑梗死冬季高发,平均角在1月份（P〈0.05）;（2）急性脑梗死月发病例数与月平均气温、月平均最高气温、月平均最低气温呈负相关（P〈0.05）,与月平均气压正相关（P〈0.05）;（3）多元逐步回归筛选出来影响急性脑梗死月发病例数的气象因素是月平均最低气温,其次为月平均日较差。结论气象因素是脑梗死发病的影响因素,在冬季、低气温、高气压气象条件下脑梗死发病率高,这为制定脑血管病相应防治措施提供了依据。

多次水下爆炸钢制圆板应变与挠度增长规律分析

在海上战争中,水面舰艇以及潜艇可能会受到多枚水中兵器的攻击,产生的累计损伤问题影响着水面舰艇以及潜艇的持续作战能力和生命力。对膨胀直径为390 mm,厚度为5 mm空气背衬钢制圆板,在50 g药量下,进行持续多次水下爆炸加载试验,对板中心应变、挠度以及厚度减薄率进行测量,试验结果分析表明:第一次爆炸加载时,局部空化使钢板产生的应变是冲击波加载的1倍,当钢板被炸弯后,再次爆炸加载局部空化的二次加载现象不明显。此外,气泡脉动及气泡射流会使钢板发生明显的弹性应变,应变值是初始冲击波作用的10%。对中心挠度和厚度减薄率的数据分析发现,钢板厚度减薄率是随着中心挠度呈线性增加的。该研究对舰船持续作战能力及生命力的评估提供了一定的试验支撑。

用C语言实现洪水实时预报的最小二乘估计

介绍了一种在洪水预报的模型参数估计中常用的方法即衰减记忆递推最小二乘估计.该方法在计算机上是通过在C语言中设置循环变量来实现.从而达到充分利用信息,实时跟踪实测流量值的变化,不断对预报误差进行修正,以提高洪水预报精度的目的.此外,其通过人为给数据加权,利用已获得的所有观测数据来进行整批运算处理,从而得出新数据,达到重点突出当前数据的作用.