螺旋复合型槽纹管换热器壳程热力性能分析

为研究1.0×10^(4)≤Re≤3.5×10^(4)范围内不同结构参数的螺旋复合型槽纹管的管外流动和换热情况,为结构优化设计提供参考,文中采用Realizable k-ε湍流模型模拟了恒壁温条件下壳程流体的对流换热过程,考察了结构参数(螺距和槽深)对流场、温度场和其他湍流特征的影响。结果表明:壳程的流动情况不如管程剧烈,但由于螺旋槽纹部分的长度选取得当,整个流域内都存在二次流,流体的换热能力得到了增强,同时也导致了压力损失的增加;当螺旋复合型槽纹管的螺距比为3.50时,综合换热能力评价指标最高;当槽深比为0.22时,换热能力提升得最多,但引起的压力损失也最大。

螺旋复合型槽纹管的壳程流动和传热特性分析

针对一种由六头螺旋槽纹管和光管组合而成的新型螺旋复合型槽纹管,在10 000≤Re≤30 000的范围内,观察螺纹部分长度分别为0.1、0.2、0.3m时对壳程流体的流动和传热产生的影响。基于得到验证的数值模拟方法,研究不同Re下流体在壳程的流动情况,通过分析二次流的产生与消失过程,发现流体在壳程中流动的规律与螺纹部分长度无关。随着Re的增长,二次流变得更加剧烈,能有效强化传热,而螺旋复合型槽纹管引起的阻力损失也随之增大。

游离腕横纹复合组织瓣桥接创面修复无缩短断指再植术治疗断指患者的疗效分析

目的探讨游离腕横纹复合组织瓣桥接创面修复无缩短断指再植术治疗断指患者的临床效果。方法选取2017年11月至2020年11月在河南科技大学第一附属医院就诊的98例断指患者为研究对象,采用随机排列法分为对照组和研究组,各49例。对照组采用常规缩短指骨断指再植术治疗,研究组采用游离腕横纹复合组织瓣桥接创面修复无缩短断指再植术治疗。观察两组患者治疗效果、术后并发症情况、手功能主观状态情况以及静态两点辨别距离(2PD)。结果研究组术后恢复良好率(87.76%)高于对照组(65.31%),差异有统计学意义(P<0.05)。研究组术后并发症发生率8.16%低于对照组26.53%,差异有统计学意义(P<0.05)。两组术前手功能主观状态评分六个维度对比差异无统计学意义(P>0.05);研究组术后疼痛维度评分低于对照组,外观、满意度、日常活动、工作状态和整体手功能评分均高于对照组,差异有统计学意义(P<0.05)。术后1个月、术后2个月两组患者手指2PD距离对比差异无统计学意义(P>0.05);术后3个月研究组患者手指2PD距离小于对照组,差异有统计学意义(P<0.05)。结论游离腕横纹复合组织瓣桥接创面修复无缩短断指再植术治疗断指患者有助于改善患者的手功能,减少并发症的发生,保障患者术后的恢复效果,临床治疗效果显著。

浅析殷周时期复合兽面纹饰

兽面纹是我国殷时期到西周的青铜器上面主要纹饰,最早由良渚玉器文化发展,经历了从兽面纹到人面纹的发展过程,到殷商周时期在青铜器上大量运用让其得到空前发展。本文主要探讨殷时期和周代的复合兽面纹,从这两个时期复合兽面纹的特点、主题等方面进行分析,进而总结复合兽面纹的特点。

基于装饰纹样的剪纸图案设计方法

以传统剪纸图案为研究对象,分解出构成剪纸图案的纹样,将这些纹样分为独立纹样和复合纹样。通过对二维图形进行布尔运算等方法构建丰富的独立纹样库。以独立纹样为基础,应用扩大对称、渐变等图案设计技术建立复合纹样库,同时,对折叠剪纸效果进行模拟。实验结果表明,该方法能够根据需要生成不同形式的折叠剪纸图案。

西周陶器的审美特征

西周陶器对传统纹饰进行夸张、变形、简化,具象写实化为抽象写意,形成一种抽象几何纹。而复合法的运用,统一中见变化,变化中见和谐。西周先民对自然大化的生命和形式法则的自觉体认和把握,在造型和纹饰上追求一种圆满具足的审美效果;而礼制文化的严格限制,又使得西周陶器呈现出规范化和程式化的倾向,风格上表现为一种端庄大方、中庸静穆的特征,而有限的形式规范却指向无限的审美意蕴和生命追求。

Flexural destructive process of unidirectional carbon/carbon composites reinforced with in situ grown carbon nanofibers

Unidirectional carbon/carbon（C/C） composites modified with in situ grown carbon nanofibers（CNFs） were prepared by catalysis chemical vapor deposition. The effect of in situ grown CNFs on the flexural properties of the C/C composites was investigated by detailed analyses of destructive process. The results show that there is a sharp increase in the flexural load-displacement curve in the axial direction of the CNF-C/C composites, followed by a serrated yielding phenomenon similar to the plastic materials. The failure mode of the C/C composites modified with in situ grown CNFs is changed from the pull-out of single fiber to the breaking of fiber bundles. The existence of interfacial layer composed by middle-textured pyrocarbon, CNFs and high-textured pyrocarbon can block the crack propagation and change the propagation direction of the main crack, which leads to the higher flexural strength and modulus of C/C composites.

STUDY ON CRACKED PLATES WITH BONDED PATCHES UNDER IN PLANE BIAXIAL LOADINGS

Based on the finite element method, a numerical investigation into the bonded repair efficiency of cracked plates under in plane biaxial loadings is presented. The main considerations are: reduction in stress intensity factor (SIF) at the crack tip, the maximum tensile stress in the composite patch and the maximum shear stress in the adhesive bond between the patch and the plate. Without the patch, a tensile or compressive stress parallel to the crack has no effect on the SIF at the crack tip. While with a composite patch, there exists coupling effect between the normal stress parallel to the crack and the SIF, and the coupling effect depends significantly on ply orientation of the patch and the biaxial stress ratio of the plate.

A METHOD FOR PREDICTING BUCKLING LOADS OF COMPOSITE LAMINATED STRIPS WITH A SURFACE NOTCH

Surface notches lower the stiffness of laminated strips, so they lower the buckling loads of the laminated strips, too. In this paper a new method is proposed to predict the buckling loads of the laminated strips with a surface notch. The theoretical and experimental results show that the buckling loads decrease as the depth or width of the surface notches increase; when the stacking sequence of the laminated strips is [0°/0°/+ θ/-θ/0°/0°/+θ/-θ] s , the buckling load decrease as θ increases. It proves that the method is reliable and significant.

RESEARCH ON MATRIX CRACK EVOLUTION OF CROSS-PLY CERAMIC MATRIX COMPOSITE

The matrix crack evolution of cross-ply ceramic matrix composites under uniaxial tensile loading is investigated using the energy balance method.Under tensile loading,the cross-ply ceramic matrix composites have five damage modes.The cracking mode 3 contains transverse cracking,matrix cracking and fiber/matrix interface debonding.The cracking mode 5 only contains matrix cracking and fiber/matrix interface debonding.The cracking stress of modes 3 and 5 appearing between existing transverse cracks is determined.And the multiple matrix crack evolution of mode 3 is determined.The effects of ply thickness,fiber volume fraction,interface shear stress and interface debonding energy on the cracking stress and matrix crack evolution are analyzed.Results indicate that the cracking mode 3 is more likely to appear between transverse cracks for the SiC/CAS material.

Microstructure and mechanical behavior of Ti/Cu/Ti laminated composites produced by corrugated and flat rolling

Ti/Cu/Ti laminated composites were fabricated by corrugated rolling(CR) and flat rolling(FR) method.Microstructure and mechanical properties of CR and FR laminated composites were investigated by scanning electron microscopy, numerical simulation methods, peel and tensile examinations. The effect of CR and FR was comparatively analyzed. The results showed that the CR and FR laminated composites exhibited different effective plastic strain distributions of the Ti layer and Cu layer at the interface. The recrystallization texture, prismatic texture and pyramidal texture were developed in the Ti layer by CR, while the R-Goss texture and shear texture were developed in the Cu layer by CR. The typical deformation texture components were developed in the Ti layer and Cu layer of FR laminated composites. The CR laminated composites had higher bond strength, tensile strength and ductility.

Fatigue crack growth mechanism in cast hybrid metal matrix composite reinforced with SiC particles and Al_2O_3 whiskers

The fatigue crack growth(FCG) mechanism of a cast hybrid metal matrix composite(MMC) reinforced with SiC particles and Al2O3 whiskers was investigated. For comparison, the FCG mechanisms of a cast MMC with Al2O3 whiskers and a cast Al alloy were also investigated. The results show that the FCG mechanism is observed in the near-threshold and stable-crack-growth regions.The hybrid MMC shows a higher threshold stress intensity factor range, ?Kth, than the MMC with Al2O3 and Al alloy, indicating better resistance to crack growth in a lower stress intensity factor range, ?K. In the near-threshold region with decreasing ?K, the two composite materials exhibit similar FCG mechanism that is dominated by debonding of the reinforcement–matrix interface, and followed by void nucleation and coalescence in the Al matrix. At higher ?K in the stable- or mid-crack-growth region, in addition to the debonding of the particle–matrix and whisker–matrix interface caused by cycle-by-cycle crack growth at the interface, the FCG is affected predominantly by striation formation in the Al matrix. Moreover, void nucleation and coalescence in the Al matrix and transgranular fracture of SiC particles and Al2O3 whiskers at high ?K are also observed as the local unstable fracture mechanisms.However, the FCG of the monolithic Al alloy is dominated by void nucleation and coalescence at lower ?K, whereas the FCG at higher ?K is controlled mainly by striation formation in the Al grains, and followed by void nucleation and coalescence in the Si clusters.

游离腕横纹复合组织瓣桥接创面修复无缩短断指再植术治疗断指患者的疗效分析

目的 探究游离腕横纹复合组织瓣桥接创面修复无缩短断指再植术治疗断指患者的疗效.方法 选取我院2016年10月~2019年6月断指患者58例,根据治疗方案不同分组,各29例.对照组给予传统缩短指骨断指再植术治疗,观察组给予游离腕横纹复合组织瓣桥接创面修复无缩短断指再植术治疗.对比两组疗效、关节活动度.结果 观察组总有效率较对照组高(P<0.05);观察组关节活动度优良率高于对照组(P<0.05).结论 游离腕横纹复合组织瓣桥接创面修复无缩短断指再植术治疗断指患者,可提高关节活动度,疗效显著.

Nonlinear free vibration of graphene platelets reinforced composite corrugated plates

The nonlinear vibration of graphene platelets reinforced composite corrugated(GPRCC)rectangular plates with shallow trapezoidal corrugations is investigated.Since graphene platelets are prone to agglomeration,a multi-layer distribution is adopted here to match the engineering requirements.Firstly,an equivalent composite plate model is obtained,and then nonlinear equations of motion are derived by the von Kármán nonlinear geometric relationship and Hamilton’s principle.Afterwards,the Galerkin method and harmonic balance method are used to obtain an approximate analytical solution.Results show that the unit cell half period,unit cell inclination angle,unit cell height,graphene platelet dispersion pattern and graphene platelet weight fraction and geometry play important roles in the nonlinear vibration of the GPRCC plates.

Determination of fatigue cracking direction in composite laminates

The interface plays the central role in the failure analysis of composite laminates, therefore, the interface material properties are taken as the independent parameters. A simple, universal and practicable criterion, i.e. a ratio criterion of strain energy release rate, is proposed to determine the growing direction of a fatigue crack in the composite laminates. The method of arbitrary lines, which is very effective to solve the problems with high gradient feature, is used to analyze the experimental results at the key moments when a crack kinks, turns into the interface, or bifurcates. An approximate method of computing the energy release rate is given. The fatigue fracture tests of composite laminates are carried out, and the numerical predictions of crack growing directions agree well with the experimental results. It is concluded that the methods suggested in this paper are effective to obtain the cracking history and the growing path of a fatigue crack in composite laminates.

油菜联合收割机脱粒装置的改进设计

油菜联合收割是在油菜黄熟后期至完熟期,用油菜联合收割机一次完成收割、脱粒、清选等工序。这种收获方式,对机器性能要求比较高,尤其是其中的脱粒装置应适应油菜收获的特点。即便在油菜最佳收获期间成熟度也不均匀,油菜青黄角果荚脱粒比较困难。笔者设计一种新型油菜收割机的脱粒装置,该种新型脱粒装置由下列3部分构成:

文化传承中的时尚：西汉玉璧功能以及文化寓意的再思考

本文从收藏于加拿大皇家安大略博物馆的三件分区复合纹玉璧的断代所属问题和纹饰风格类型发端,尝试钩沉以汉代玉璧为代表的葬玉制度背后的文化寓意。本文的研究对象是考古遗址墓葬出土的分区复合纹玉璧。作者通过对考古资料的整合,综合考察了 129件分区复合纹玉璧的出土信息,对比了其随葬时代、性质、墓主身份以及玉璧出土所在位置、尺寸、肉好比值区间范围等,对其功能和文化象征意义提出新认识。对以上数据信息的爬梳,实际上松绑了分区复合纹玉璧在汉代承担祭祀和随葬礼器的传统寓意,作者认为,这些玉璧既是承载着文化意义的重器,更是精英社会中风靡一时的装饰物品,主人死后随其一起封存于墓葬中。汉代社会精英权贵对分区复合纹玉璧的喜好和追捧,是千百年来古人对玉璧文化传承和时尚追求的反映,也是汉代人对史前和商周玉璧去宗教化、去礼仪化的过程。

典型脑疾病——自发性脑出血研究进展与新理念

自发性脑出血是致死率、致残率最高的脑血管疾病,提高自发性脑出血的防治效果是目前临床上最迫切需要解决的问题之一。本文简述了自发性脑出血的定义及自然史,综述自发性脑出血的病理损伤机制及目前治疗现状。提出豆纹动脉神经复合体的概念,以便系统整体地研究脑出血发生发展的机制,解决脑出血发生发展的关键科学问题,建立出血性脑卒中预防、诊断和治疗体系,最终提高出血性脑卒中的整体防治水平,降低致死致残率。