Abstract
A cracked blade non‐linear dynamic analysis was performed, taking into account contact interaction between crack sides. The contact‐induced non‐linear problem was solved by using the harmonic balance method. Accuracy and computational efficiency are demonstrated by comparing the results with the time integration of the system's motion equation Problem size reduction was performed using system fixed‐interface method. They suppose that a crack forms an interface between two sub‐structures and use a relative degree of freedom to describe the motion of crack sides. The influence of centrifugal forces was investigated in order to understand the necessity of problem non‐linear formulation depending on crack location and frequency of rotation. Santrauka Mentelės su įtrūkimu netiesinė dinamikos analizė atlikta įvertinant įtrūkimo kraštų kontaktinę sąveiką. Netiesinis uždavinys sprendžiamas harmoninės analizės metodu. Tokio metodo rezultatų tinkamumas ir efektyvumas demonstruojamas lyginant su sistemų dinaminių lygčių skaitinio sprendimo rezultatais. Sprendžiamo uždavinio eilė mažinama kraštų fiksavimo metodas. Šiuo atveju buvo laikoma, kad plyšys suformuoja ribą tarp dviejų konstrukcijos dalių ir plyšio ribų kitimo aprašymui naudojamos santykinės koordinatės. Buvo ištirta išcentrinių jėgų įtaka netiesiniam formulavimui, priklausomai nuo plyšio padėties ir kampinio greičio.
Highlights
In a majority of the works in the field of cracked blade dynamic analysis, the presence of a crack is simulated by a reduction in the stiffness of a structure leading to a reduction in natural frequencies and correspondingly a shift in resonances at frequency response function construction
− open crack models–linear statement, stiffness is maintained constant during analysis;
− opening and closing or breathing crack models– non-linear statement, stiffness is changed depending on external loading conditions (Laine et al 2006, Cheng et al 1999)
Summary
In a majority of the works in the field of cracked blade dynamic analysis, the presence of a crack is simulated by a reduction in the stiffness of a structure leading to a reduction in natural frequencies and correspondingly a shift in resonances at frequency response function construction. − opening and closing or breathing crack models– non-linear statement, stiffness is changed depending on external loading conditions (Laine et al 2006, Cheng et al 1999). As it was said, generally, open crack models are used because of their simplicity and because they provide important diagnostic signa such as natural frequency decrease. Open crack models are used because of their simplicity and because they provide important diagnostic signa such as natural frequency decrease It can be used for the identification of the presence of cracks in the blade, which is a very challenging task and is in the scope of both industry and scientific circles
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