Computation of Stiffness and Damping Derivatives of an Ogive in a Limiting Case of Mach Number and Specific Heat Ratio

This work aims to compute stability derivatives in the Newtonian limit in pitch when the Mach number tends to infinity.In such conditions,these stability derivatives depend on the Ogive’s shape and not the Mach number.Generally,the Mach number independence principle becomes effective from M=10 and above.The Ogive nose is obtained through a circular arc on the cone surface.Accordingly,the following arc slopes are consideredλ=5,10,15,−5,−10,and−15.It is found that the stability derivatives decrease due to the growth inλfrom 5 to 15 and vice versa.Forλ=5 and 10,the damping derivative declines with an increase inλfrom 5 to 10.Yet,for the damping derivatives,the minimum location remains at a pivot position,h=0.75 for large values ofλ.Hence,whenλ=−15,the damping derivatives are independent of the cone angles for most pivot positions except in the early twenty percent of the leading edge.

Base Pressure Control with Semi-Circular Ribs at Critical Mach Number

When better fuel-air mixing in the combustion chamber or a reduction in base drag are required in vehicles,rockets,and aeroplanes,the base pressure control is activated.Controlling the base pressure and drag is necessary in both scenarios.In this work,semi-circular ribs with varying diameters(2,4,and 6 mm)positioned at six distinct positions(0.5D,1D,1.5D,2D,3D,and 4D)inside a square duct with a side of 15 mm are proposed as an efficient way to apply the passive control technique.In-depth research is done on optimising rib size for various rib sites.According to this study,the base pressure rises as rib height increases.Furthermore,the optimal location for the semi-circular ribs with a diameter of 2 mm is at 0.5D.The 1D location appears to be optimal for the 4 mm size as well.For the 6 mm size,however,the 4D position fills this function.

Enhanced entropy generation and heat transfer characteristics of magnetic nano-encapsulated phase change materials in latent heat thermal energy storage systems

The objective of the current study is to investigate the importance of entropy generation and thermal radiation on the patterns of velocity,isentropic lines,and temperature contours within a thermal energy storage device filled with magnetic nanoencapsulated phase change materials(NEPCMs).The versatile finite element method(FEM)is implemented to numerically solve the governing equations.The effects of various parameters,including the viscosity parameter,ranging from 1 to 3,the thermal conductivity parameter,ranging from 1 to 3,the Rayleigh parameter,ranging from 102 to 3×10^(2),the radiation number,ranging from 0.1 to 0.5,the fusion temperature,ranging from 1.0 to 1.2,the volume fraction of NEPCMs,ranging from 2%to 6%,the Stefan number,ranging from 1 to 5,the magnetic number,ranging from 0.1 to 0.5,and the irreversibility parameter,ranging from 0.1 to 0.5,are examined in detail on the temperature contours,isentropic lines,heat capacity ratio,and velocity fields.Furthermore,the heat transfer rates at both the cold and hot walls are analyzed,and the findings are presented graphically.The results indicate that the time taken by the NEPCMs to transition from solid to liquid is prolonged inside the chamber region as the fusion temperatureθf increases.Additionally,the contours of the heat capacity ratio Cr decrease with the increase in the Stefan number Ste.

Effect of the number of positive lymph nodes and lymph node ratio on prognosis of patients after resection of pancreatic adenocarcinoma

BACKGROUND： The prognostic factors related to lymph node involvement [lymph node status, the number of positive lymph nodes, lymph node ratio （LNR）] and the number of nodes evaluated in patients with pancreatic adenocarcinoma after pancreatectomy are poorly defined. METHODS： A total of 167 patients who had undergone resection of pancreatic adenocarcinoma from February 2010 to August 2011 were included in this study. Histological examination was performed to evaluate the tumor differentiation and lymph node involvement. Univariate and multivariate analyses were made to determine the relationship between the variables related to nodal involvement and the number of nodes and survival. RESULTS： The median number of total nodes examined was 10 （range 0-44） for the entire cohort. The median number of total nodes examined in node-negative （pN0） patients was similar to that in node-positive （pN1） patients. Patients with pN1 diseases had significantly worse survival than those with pN0 ones （P=0.000）. Patients with three or more positive nodes had a poorer prognosis compared with those with the negative nodes （P=0.000）. The prognosis of the patients with negative nodes was similar to that of those with one to two positive nodes （P=0.114）. The median survival of patients with an LNR ≥0.4 was shorter than that of patients with an LNR 〈0.4 in the pN1 cohort （P=0.014）. No significance was found between the number of total nodes examined and the prognosis, regardless of the cutoff of 10 or 12 and in the entire cohort or the pN0 and pN1 groups. Based on the multivariate analysis of the entire cohort and the pN1 group, the nodal status, the number of positive nodes and the LNR were all associated with survival. CONCLUSIONS： In addition to the nodal status, the number of positive nodes and the LNR can serve as comprehensive factors for the evaluation of nodal involvement. This approach may be more effective for predicting the survival of patients with pancreatic adenocarcinoma after pancreatectomy.

Fluid flow and heat transfer characteristics of spiral coiled tube: Effects of Reynolds number and curvature ratio

Numerical analysis was performed to investigate flow and heat transfer characteristics in spiral coiled tube heat exchanger. Radius of curvature of the spiral coiled tube was gradually increased as total rotating angle reached 12n. As the varying radius of curvature became a dominant flow parameter, three-dimensional flow analysis was performed to this flow together with different Reynolds numbers while constant wall heat flux condition was set in thermal field. From the analysis, centrifugal force due to curvature effect is found to have significant role in behavior of pressure drop and heat transfer. The centrifugal force enhances pressure drop and heat transfer to have generally higher values in the spiral coiled tube than those in the straight tube. Even then, friction factor and Nusselt number are found to follow the proportionality with square root of the Dean number. Individual effect of flow parameters of Reynolds number and curvature ratio was investigated and effect of Reynolds number is found to be stronger than that of curvature effect.

Design and Blade Number Ratio Analysis of Organic Rankine Cycle Radial-Inflow Turbine on Vehicle

The organic Rankine cycle is widely used in industrial waste heat, engine waste heat and other waste heat recovery applications, and as a key component of the system, it affects the efficiency and output power of the system. In this paper, a centripetal turbine is designed for the organic Rankine cycle, using vehicle exhaust gas as the heat source. Numerical simulations are performed to analyze the effect of the ratio of the number of guide vane blades to the number of impeller blades (vane number ratio) on the turbine performance and flow field. The results show that the effect of the number of impeller blades on the turbine entropy efficiency, the average exit velocity and the temperature of the guiding grate becomes less and less as the ratio of the number of blades increases. The optimum turbine performance is obtained when the number of impeller blades and the ratio of the number of blades are 17 and 1.5882, respectively, and the expansion performance of the guide impeller is improved and the isentropic efficiency of the turbine is improved by 3.84% compared with the preliminary number of blades.

Simulation and Experimental Study on Influence of Multi⁃port Integrated Hydraulic Transformer Port Number on Transformer Ratio Characteristics

The integrated hydraulic transformer has a compact structure and no throttling loss in the process of pressure regulation.It is widely used in the common pressure rail hydrostatic transmission system.The integrated hydraulic transformer is realized by designing more than three ports on the distribution plate,and the voltage transformation characteristics of the integrated hydraulic transformer with different port numbers are different.In this paper,the influence of port number on the pressure ratio of integrated hydraulic transformer was studied,and the pressure ratio characteristics of 3⁃ports,4⁃ports,and 5⁃ports integrated hydraulic transformer were obtained,and an experimental platform was built for experimental verification,which shows that the simulation results are consistent with the experimental results and provides a theoretical basis for the design of integrated hydraulic transformer.

中危肺栓塞患者30天内不良预后的预测因素分析

目的:探讨中危肺栓塞早期不良结局的危险因素及可能的预测因素。方法:连续性纳入2016年1月至2021年12月,在我院住院的209例中危肺栓塞患者,按照30d是否存在不良预后分为短期不良结局组和存活组,应用多因素Logistic分析中危肺栓塞早期不良结局的危险因素;应用ROC曲线分析危险因素联合简化版肺栓塞严重程度评分(simplified pulmonary embolism severity index,sPESI)对中危肺栓塞患者早期不良结局的预测价值。结果:多因素Logistic回归分析得出sPESI评分、NLR为预测中危肺栓塞早期不良结局的危险因素(P<0.05)。将NLR≥3.79作为新的指标,计为1分,纳入NLR的sPESI评分预测中危肺栓塞早期不良结局预测价值的ROC曲线下面积为0.968(95%CI:0.932~0.988),当评分≥2分时,灵敏度为100%,特异度为80.61%。结论:纳入NLR的s PESI评分对中危肺栓塞患者早期不良结局具有一定的预测价值。

Physical Properties of the Function and Number of Empirical Macrohardness of the Material: Universal Physical Unit of Measurement of Macro Hardness (Part 2)

Results of analytical studies of the physical properties of the function and number of empirical macrohardness based on the standard experimental force diagram of kinetic macroindentation by a sphere.An analytical comparison method and a criterion for the similarity of the physical and empirical macrohardness of a material are proposed.The physical properties of the hardness measurement process using the Calvert-Johnson method are shown.The physical reasons for the size effect when measuring macrohardness are considered.The universal physical unit and standard of macrohardness of kinetic macroindentation by a sphere is substantiated.

基于冲刷指数的雨水管渠冲刷淤积分析

流速、雷诺数、充满度等单因素指标虽然与雨水管渠的冲刷和淤积量有一定的关联,但是通过单因素指标不足以全面地判断雨水管道的冲刷和淤积。在起动流速和止动流速的基础上,提出了冲刷指数的概念。结合连续非恒定流不同工况下冲刷和淤积量模拟,计算了流速、雷诺数、充满度、冲刷指数4个因素与冲刷量的灰色关联度,其关联度大小依次为:冲刷指数>雷诺数>充满度>流速。根据不同工况的恒定流模型实验的结果,其关联度大小依次为:冲刷指数>>流速>雷诺数>充满度。可以认为,在恒定流与非恒定流工况下,冲刷量和冲刷指数有显著的强相关性,冲刷指数能代替具体的冲刷量计算实现对冲刷程度和趋势的合理判断。

几何参数对轮缘推进器水动力性能影响的研究

轮缘推进器是近年来发展起来的一种无轴组合式特种推进器。与传统推进器相比,轮缘推进器在水动力设计和性能分析方面存在诸多挑战,水动力性能的研究对轮缘推力器的设计和应用具有重要意义。为了研究几何参数对轮缘推力器水动力性能的影响,本文以7叶轮缘驱动推力器为基本模型,基于面元法原理,利用编译的面元法代码对轮缘推力器在开阔水域的工作状态进行了数值模拟。通过求解每个面元的速度场,计算了水动力性能和叶片表面压力分布。此外,本文选择了几个典型的几何特征,如螺距比和叶片数,通过进行变参数分析,比较了不同几何参数下轮缘推力器的敞水性能。结果表明:本文的相关研究对轮缘推力器的设计和开发具有参考价值。

沙土比对混凝土试件空蚀影响的试验研究

在小型循环式水洞中试验研究了沙土比对混凝土试件空蚀影响的机理。首先,在循环式水洞内筒中配制11种沙土比(0%,10%,20%,30%,40%,50%,60%,70%,80%,90%,100%)试样,用红外测沙仪测定相同沙土比的3种不同含沙量(2,12,30 kg/m 3)的挟沙水样,用压力传感器和压力数据采集系统实时采集水洞文丘里工作段空化区和空蚀区的压力;然后,制作了水灰比为0.4、灰砂比为1.5,7 d龄期强度f cu,k=17.8 MPa的混凝土试件,将其安放在水洞文丘里工作段混凝土试件盒中进行4 h的空蚀试验。试验结果表明:沙土比的增大对空化和空蚀破坏均具有促进作用;消失空化数随沙土比的增加而增加,对空化发生具有抑制作用;相同沙土比时,混凝土试件的空蚀量随着含沙量的增加而增加。

循环小数化为分数教学中等比数列的应用

纯循环小数与混循环小数是初等数论中常讲解的内容,但怎样把此两类小数化为分数却没有讲解,通过利用中学的等比数列把纯循环小数和混循环小数化为分数,并给出了纯循环小数和混循环小数化为分数的计算公式。为中小学数学教师教学中,把循环小数化为分数提供了一个有力的计算公式。

平头孔板的初生空化特性定量分析

随着现代水利水电工程的日益优化创新,高坝设计中需要解决的重大技术瓶颈是消杀高坝泄放洪流所携带的超大能量。利用水流的突扩、突缩消能的孔板制造简便,并且消能效率高。孔板的抗空化特性跟它的最小壁面压强系数大小紧密相关,其作为孔板设计制造的一个关键性指标。通过数值模拟和物理模型试验的方法,研究了平头孔板初生空化数与相关体型要素和水力要素之间的关系,并得到了经验表达式。研究结果表明,平头孔板初生空化数的经验表达式与实际吻合较好,为孔板的工程应用提供了参考。

hs-CRP、NT-proBNP及NAR对急性冠状动脉综合征患者诊断价值分析

目的 探讨超敏C反应蛋白(hs-CRP)、氨基末端脑钠肽前体(NT-proBNP)及中性粒细胞与白蛋白比值(NAR)对急性冠状动脉综合征(ACS)患者的诊断价值。方法 选取2020年6月—2022年9月收治的ACS 71例作为研究组,同期健康体检者56例作为对照组,并依照不同疾病类型和血管病变支数将研究组分为ST段抬高型心肌梗死(STEMI)组、非ST段抬高型心肌梗死(NSTEMI)组、不稳定型心绞痛(UAP)组及单支、双支、多支病变组各3个亚组。比较研究组与对照组、不同疾病类型和血管病变支数各3个亚组hs-CRP、NT-proBNP及NAR,探讨hs-CRP、NT-proBNP及NAR单独或联合对ACS的诊断价值。结果 研究组hs-CRP、NT-proBNP及NAR均高于对照组;STEMI组、NSTEMI组和UAP组hs-CRP、NT-proBNP及NAR逐渐降低,单支、双支和多支病变组hs-CRP、NT-proBNP及NAR逐渐升高(P<0.05)。受试者工作特征曲线分析显示,hs-CRP、NT-proBNP和NAR单独或联合诊断ACS的曲线下面积分别为0.820、0.815、0.883及0.914,三者联合诊断ACS的曲线下面积高于单独诊断(P<0.05,P<0.01)。结论 hs-CRP、NT-proBNP及NAR三者联合对ACS的诊断价值较高。

基于UBSS算法的电力系统低频振荡辨识方法

低频振荡监测和分析对电力系统故障诊断和电网恢复至关重要。该文提出一种基于欠定盲源分离原理的低频振荡模式辨识方法,包括欠定盲源分离(underdetermined blind source separation,UBSS)和希尔伯特变换(Hilbert transform,HT)。首次系统地提出并论证含欠定盲源分离、模式定阶和振荡参数的辨识方法。提出的UBSS-HT方法利用能量比函数确定故障时刻,利用贝叶斯信息准则(Bayesian information criterion,BIC)实现模式定阶,阐述维度空间理论,论证构建虚拟多通道的可行性,通过盲源分离来实现源信号分离,最后通过HT在希尔伯特空间来辨识振荡参数。通过大量的系统建模仿真和现场录波数据试验评估所提方法的性能,验证该方法的有效性、准确性和抗干扰能力。

一种自适应选取参数的改进变分模态分解方法

针对传统的变分模态分解(VMD)方法中模态数和惩罚参数难以确定的问题,提出了一种自适应选取参数的改进变分模态分解方法。首先,综合考虑了故障的冲击性和周期性特点,以Gini指数和谱峰比指标为基础构建了加权谱峰比(WSPR)指标;然后,采用非洲秃鹫优化算法(AVOA)进行了寻优,得到了最佳的模态数和惩罚参数组合,克服了人为主观选择参数的弊端;最后,在VMD分解信号后,利用加权谱峰比最大原则自适应选取了敏感内涵模态分量,对最佳IMF进行了包络解调分析,提取了滚动轴承早期故障特征,利用仿真信号、单一故障滚动轴承试验信号及复合故障滚动轴承试验信号对所述方法进行了验证。实验结果表明:该方法可以准确地提取出仿真信号的故障频率(100 Hz)、单一故障信号的故障频率(236.4 Hz)和复合故障信号的故障频率(内圈故障频率149.14 Hz、外圈故障频率86.39 Hz),并且在与其他方法和指标的对比中,其最佳IMF的包络谱图中故障特征频率及其倍数频的谱峰更加明显,准确率更高且鲁棒性更强。研究结果表明:该方法能够有效提取轴承早期故障信号的微弱特征,实现故障类型准确识别的目的。

小车式起落架地面载荷与漂浮性分析

飞机起落架与道面的相容性对飞机的地面运动能力具有重要影响。针对某大型飞机计算不同工况下其起落架载荷及轮胎载荷分配,采用基于韦斯特加德层板理论的波特兰水泥协会法和基于加利福尼亚承载比的美国陆军工程兵团方法,计算不同着陆工况、地面机动工况、轮胎数量、轮胎泄气工况、轮胎间距对飞机等级数的影响,分析刚性道面和柔性道面下的飞机漂浮性。结果表明:垂直过载和机轮泄气带来的轮胎载荷增大与载荷分配不均,都会在不同程度上减弱飞机的漂浮性,尤其是转弯和机尾下沉着陆工况需要予以限制;轮胎数量和轮胎间距的增加可以改善漂浮性,需同时考虑结构设计、强度裕度等来优化设计小车式起落架构造。

单孔双窄缝消能工收缩比对水力特性影响研究

单孔双窄缝消能工在高水头、大流量、窄河谷的水利工程中具有一定的推广价值,但在应用过程中发现中墩迎水面容易受水流冲击而破损,而收缩比对此现象和消能效果影响较大。采用TruVOF方法及RNG k-ε紊流模型进行三维数值模拟,研究在不同来流Fr数下收缩比对水舌流态、消能率、河床底板及挑坎收缩段压力分布变化规律的影响。结果表明:数值模拟与物理模型试验结果基本吻合,可通过调整收缩比β获得合适的高坎中墩水深来减弱高速水流对中墩迎水面的冲击;当β=0.3时,下游河床底板峰值压力P_(max)最小,且峰值压力核心区与传统窄缝相比前移60 m;β<0.3时,P max随着β的减小反而开始增大,而消能率随之减小,同时在挑坎收缩段中部附近位置出现冲击波交汇点,且流道内各断面中线压力沿水深分布在压力最大值前后其规律不同,与宽尾墩类似。虽然来流Fr数对分流比影响较小,但当2.43<Fr<2.82时,各体型方案的分流比k q增大幅度较大,导致双窄缝体型河床底板压力变化幅度较明显。

Genomic signatures of selection,local adaptation and production type characterisation of East Adriatic sheep breeds

Background The importance of sheep breeding in the Mediterranean part of the eastern Adriatic has a long tradition since its arrival during the Neolithic migrations.Sheep production system is extensive and generally carried out in traditional systems without intensive systematic breeding programmes for high uniform trait production(carcass,wool and milk yield).Therefore,eight indigenous Croatian sheep breeds from eastern Adriatic treated here as metapopulation(EAS),are generally considered as multipurpose breeds(milk,meat and wool),not specialised for a particular type of production,but known for their robustness and resistance to certain environmental conditions.Our objective was to identify genomic regions and genes that exhibit patterns of positive selection signatures,decipher their biological and productive functionality,and provide a"genomic"characterization of EAS adaptation and determine its production type.Results We identified positive selection signatures in EAS using several methods based on reduced local variation,linkage disequilibrium and site frequency spectrum(eROHi,iHS,nSL and CLR).Our analyses identified numerous genomic regions and genes(e.g.,desmosomal cadherin and desmoglein gene families)associated with environmental adaptation and economically important traits.Most candidate genes were related to meat/production and health/immune response traits,while some of the candidate genes discovered were important for domestication and evolutionary processes(e.g.,HOXa gene family and FSIP2).These results were also confirmed by GO and QTL enrichment analysis.Conclusions Our results contribute to a better understanding of the unique adaptive genetic architecture of EAS and define its productive type,ultimately providing a new opportunity for future breeding programmes.At the same time,the numerous genes identified will improve our understanding of ruminant(sheep)robustness and resistance in the harsh and specific Mediterranean environment.