掺气减蚀保护作用的新概念

利用针式掺气流速仪测量原型和模型掺气浓度场、流速场，气泡尺寸及其概率分布的研究成果表明，原型水流韦伯数高，形成微小气泡的能力比模型强，气泡上浮慢，接近底部的小尺寸气泡概率及掺气浓度比模型大。初步研究认为：0.2mm或0.5mm以下的微小气泡在掺气减蚀中起着主要作用，可能只要很小掺气浓度即可达到掺气减蚀的效果。因此以小尺寸气泡的掺气浓度，作为判断掺气减蚀保护作用的指标将更为准确。     

自振空化射流提高钻井速度的实验研究

空化射流用于提高钻井速度的可行性研究结果表明，在钻进作业中，利用空泡破裂产生强大破坏作用来提高钻探的效率，其效果显著，可行性高。室内实验表明，自振空化射流在比普通喷嘴射流更深的井底或更高的围压条件下，有更大的起始空化数和更强的空化能力。自振空化喷嘴起始空化数大都在1.0以上，最高达到1.67，而锥形喷嘴最高仅为0.43，围压下其冲蚀效率是锥形喷嘴的1~2倍。现场试验同样证实设计的自振空化射流喷嘴在保护钻头、减少钻头磨损及增加进尺、提高机械钻速方面有显著作用。     

A NEW LARGE CAVITATION CHANNEL IN CHINA SHIP SCIENTIFIC RESEARCH CENTER

1 .　INTRODUCTIONIntherecentdecades ,itisrealizedthatitisquitenecessarytocarryouttestsathighReynoldsnumberwithalowbackgroundnoiselevelinordertomeetmoreandmoreurgentneedsofmodernnavyandmaritimeindustry .Anewlargecavita tionchannelisdevelopedinCSSRCfortestingcompletehull/ propulsor/appendagesarrange ments[1] .Itrepresentsoneofthelatestintechno logicallyadvancedlargecavitationtestfacilities.Inthefollowingsections ,thefeaturesandthefirsttestresultsofthechannelwillbedescribed .2 .　DICRIP…     

日产PD6型柴油机气缸穴蚀原因浅析及对策

本文分析日产车用PDG型柴油机的结构特点及其缸套穴蚀的形成原因、危害和检查与判断方法,并提出在使用中应采取的预防措施。     

On using peak amplitude and rise time for AE source characterization

Acoustic Emission (AE) signals, which are electrical version of acoustic emissions, are usually analysed using a set of signal parameters. The major objective of signal analysis is to study the characteristics of the sources of emissions. Peak amplitude(P _a ) and rise time(R _t ) are two such parameters used for source characterization. In this paper, we theoretically investigate the efficiency ofP _a andR _t to classify and characterize AE sources by modelling the input stress pulse and transducer. Analytical expressions obtained forP _a andR _t clearly indicate their use and efficiency for source characterization. It is believed that these results may be of use to investigators in areas like control systems and signal processing also     

WC对铜基和镍基喷焊覆层材料耐气蚀性能的影响

在CuNiSiB,NiCrSiB自熔合金粉末中添加WC陶瓷颗粒，利用氧乙炔焰粉末喷焊工艺制备覆层材料，用超声波振动气蚀仪对覆层材料进行耐气蚀性能研究，用扫描电子显微镜对覆层材料表面气蚀破坏形貌进行观察，结果表明：复合覆层材料的耐气蚀能力比基体强；提高CuNiSiB覆层材料耐气蚀能力的途径是强化晶界，还探讨了覆层材料的气蚀破坏机理。     

结构陶瓷的空蚀性研究

利用转盘装置测量了ZrO2、Si3N4和Al2O3／Ti(NC)等陶瓷材料受到水的空蚀破坏的体积损失,通过SEM观察和XRD分析,探讨了微观结构和抗空蚀性能的关系。     

THE TENSILE STRENGTH OF WATER IN DEPRESSION TANK

This paper presents the data of tensile strength of water in depression tank whichwere measured by small venturi during cavitation investigation of a series of real project models.These measurements show that in depression tank water has slight tensile strength in case of highvacuum.But it influences the incipient cavitation number.In tests we also studied the influenceof tensile strength on scale effect of cavitation models.     

Reduction of low-frequency pressure fluctuations in wind tunnels

The determination of dynamic wind loads on buildings, i.e. pressure and deflection, has gained increasing interest (European Prestandard ENV 1991-2-4, Eurocode 1: basis of design and actions on structures—Part 2-4: actions on structures—wind actions, European Committe for Standardization, Brussels, 1995; DIN 1055 Teil 4 Lastannahmen für Bauten, Verkehrslasten, Windlasten bei nicht schwingungsanfälligen Bauwerken, 1991; N. Hölscher, M. Hortmanns, J. Sahlem, Praxisnahe Erfassung von Windwirkung an Industrie- und Hochbauten, Windwirkung im Bauwesen, Braunschweig, 7, Dreiländertagung D-A-CH 2001, Windtechnologische Gesselschaft, 2001 [1], [2] and [3]). Therefore, the spectral distributions of velocity and pressure fluctuations in wind tunnels are an important quality aspect. While velocity fluctuations can be manipulated by the obstacles used to create the turbulence, pressure fluctuations are influenced by acoustic noise as well. Especially, the first eigenfrequency of the longitudinal mode of the wind tunnel tends to disturb the pressure spectrum.In this paper, a solution for the reduction of low-frequency acoustic pressure fluctuation is presented and its application in the atmospheric boundary layer wind tunnel at the IAG is shown.