【作者】 李剑钊；

【导师】 闻雪友； 林志鸿；

【作者基本信息】 中国舰船研究院 ， 轮机工程， 2005， 博士

【摘要】 本论文通过理论分析和试验,研究船用汽轮机除湿级带冠叶片的振动特性及疲劳寿命。叶片的安全可靠性是汽轮机安全运行的重要保证,叶片振动以及由此引起的疲劳损伤是导致回转机械叶片失效的一个重要原因。船用汽轮机除湿级采用的带冠叶片工作在高转速、变负荷、湿蒸汽等恶劣条件下,加之结构上与传统叶片明显不同,其安全性变得更为重要,对叶片强度、振动以及疲劳寿命等特性进行系统分析,具有重要的现实意义。本研究利用非线性阻尼模型,建立了带有碰撞阻尼的叶片三维实体单元的叶片结构整体动力学方程;进行了基于平板叶片的碰撞减振机理研究,计算分析了两只、三只叶片在不同叶冠间隙、不同激振力幅值和不同激振力频率条件下的振动特性;引入罚函数法进行带冠叶片的固有频率计算,并对带冠叶片的叶冠结构及质量、叶冠间隙以及叶身纵向槽道等因素进行了影响分析。结果表明:叶片的碰撞表现出非线性的振动特点,出现明显的频谱分量,具有碰撞条件的叶片可以抑制外力做功,外力做功能力随着叶冠间隙的减少而减少;叶冠间隙对叶片动应力有很大的影响,并呈现明显的规律性,当间隙一定时,对应的最大动应力不随激振力的增加而变化;叶身纵向槽道对叶片的固有特性影响较小,但槽道处有应力集中现象。本课题还对损伤力学理论与累积损伤理论进行了对比研究,并应用全耦合损伤力学理论对汽轮机叶片的疲劳寿命以及损伤进行了分析。累积损伤理论在寿命预测时高估了叶片的寿命,而多轴复杂应力状态加速了叶片材料的损伤演化,缩短了叶片的疲劳寿命;连续损伤累积模型更准确地反映了叶片材料的非线性损伤累积发展过程;采用损伤力学方法能对构件的损伤和寿命进行较精确的描述,能更真实地反映材料的损伤发展过程,与当前普遍采用的累积损伤理论相比,不论是在损伤理论模型还是分析方法方面都更为合理。实验研究工作主要在叶片的减振机理和振动特性方面。利用组建的实验装置和测试系统,对平板叶片的减振机理和带冠叶片动态特性进行了试验研究。试验结果表明:碰撞条件使得叶片振动出现明显的频谱分量,碰撞条件可以抑制外力做功;间隙安装的整圈带冠叶片具有单只叶片固有频率特性;叶冠间隙更多还原

【Abstract】 By way of theoretical analysis and tests a study is conduced of the vibrationcharacteristics and fatigue failure of shrouded blades in the wetness removal stageof a marine steam turbine.Blade safety and reliability constitutes an important guarantee for the safeoperation of a steam turbine. Blade vibrations and the resulting fatigue damage are amajor cause leading to the failure of the blades of a rotating machine. The wetnessremoval stage fitted with shrouded blades operates under rigorous conditions of highrotating speeds, changing loads and wet steam, etc. Furthermore, the structure of theshrouded blades is markedly different from that of traditional ones. The systematicanalysis of its characteristics, such as strength, vibration and fatigue failure, etc is ofmajor realistic significance.A nonlinear damping model has been used during the present study and a bladestructure integral dynamics equation set up for the blade three-dimensional entityunit with collision damping. An investigation was undertaken of the mechanismbased on the collision vibration-abatement of flat-plate blades. The vibrationcharacteristics of two or three blades were calculated and analyzed under theconditions of different clearances, different vibration-exciting force amplitudes andfrequencies. The natural frequencies of the shrouded blades were calculated with apenalty function method being introduced. An analysis was carried out of theinfluence of such factors as the shroud structure and mass of the shrouded blades,blade shroud clearance and the longitudinal groove of the blade body, etc. Theresults of the analysis indicate that the collision of blades exhibits nonlinearvibration features with the appearance of distinct frequency spectrum components.The blade with collision conditions can suppress doing-work by external forces. Theability to do work by external forces will decrease with the decrease in blade shroudclearance. The blade shroud clearance exercises a great influence on the bladedynamic stress, showing in this connection a distinct regularity. When theabove-mentioned clearance is constant, the corresponding maximum dynamic stresswill not change with an increase in a vibration-exciting force. The longitudinalgroove of the blade body has a relatively small influence on blade intrinsiccharacteristics. However, there appears a phenomenon of stress concentration at thegroove location. A contrast study was also conducted of damage mechanics theory andaccumulative damage theory. In addition, by applying a full coupled damagemechanics theory an analysis was performed of the fatigue life and damage of steamturbine blades. The accumulative damage theory has overestimated blade servicelife during its service life prediction. Meanwhile, a multi-axial complex stress statehas accelerated the damage evolution of blade material, thus shortening the fatiguelife of blades. A continuous damage accumulation model can more accurately reflectthe evolving process of nonlinear damage accumulation. The use of the damagemechanics method can result in a more precise description of the damage andservice life of structural members and more realistically reflect the damagedevelopment process of materials. Compared with the now universally adoptedaccumulative damage theory, the above-mentioned method is more rational both inrespect of damage theory model or analytical method. The experimental research has mainly been focused on the blade vibrationabatement mechanism and vibration characteristics. By utilizing a test rig andmeasurement system being set up an experimental study was conducted of themechanism of the flat-plate blade vibration abatement and the dynamiccharacteristics of the shrouded blades. The results of the study indicate that thecollision condition can lead to the emergence of distinct frequency spectrumcomponents in blade vibrations. The collision condition can also suppress the doingof work by external forces. The whole ring of shrouded blades installed withclearances has the natural frequency characteristics of a single blade. A decrease inblade shroud clearance can effectively reduce vibration stresses. The results of the present study have laid a solid foundation for the design ofshrouded blades and the analysis of their safety and reliability for the wetnessremoval stage of a marine steam turbine. Some beneficial methods for furtherresearch are also provided.更多还原