3850 英文单词，英文单词，2.1 万英文字符万英文字符，，中文中文 6000 字字 文献出处：文献出处：Rusiński E, Moczko P, Odyjas P, et al. Investigation of vibrations of a main centrifugal fan used in mine ventilation[J]. Archives of Civil and Mechanical Engineering, 2014, 14(4): 569-579. Investigation of vibrations of a main centrifugal fan used in mine ventilation E. Rusiński, P. Moczko, P. Odyjas, D. Pietrusiak Abstract Operation of machines in resonance ranges is a great challenge for design engineers. The paper focuses on the analysis of centrifugal fan casing vibrations which during machine operation, particularly in unsteady states, are very strong. Within a series of investigations performed according to the experimental modal analysis natural frequencies of fan casing vibrations were specifi ed. Additional numerical simulations helped to defi ne theoretical values of the natural vibrations frequency and its mode shapes. The results were analyzed and the numerical model was adjusted. The information was later used in the analysis of vibration measurements in real operating conditions. The results achieved for a nine-blade impeller (new type) were compared to results of an old construction eight-blade fan impeller. New solutions, which shall facilitate casing operation beyond resonance frequencies vibrations areas, were proposed. Keywords: Rotary machines；Unsteady states；Vibrations；Modal analysis 1. Introduction Fan vibrations, both in steady and unsteady states, signifi cantly infl uence durability of movable and fi xed elements. One of the elements exposed to dynamic effects is an impeller steel casing, which is a part of an outlet scroll (Fig. 1). The fact that part of the scroll is constructed as a steel casing enables the impeller maintenance and potential replacement. However, design and placement of the casing exposes it to constant infl uence of dynamic effects resulting from fl ow phenomena occurring inside. Proper casing operation requires limitation of losses resulting from leakage and vibrati