Wyniki wyszukiwania - BazTech

1

Structure fatigue crack in the effect of acoustic load : case study

Wiśniowski W.

Journal of KONES

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2014

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Vol. 21, No. 4

533--536

EN

The paper presents a method for detection mechanisms and prevention of the fatigue cracks caused by acoustic loads acting on the aircraft elevator structure. During aircraft inspection, the fatigue cracks in elevator rib caps were discovered. The theory emerged, that cracks were caused by acoustic extortion on elevator sheet covering, caused by jet engine exhaust airstream, engine gas flow expanding in convergent nozzle and acting as the source of the strong acoustic load. To prove this theory, investigations were arranged, in which the strains in the elevator sheet skin, between the ribs area, were determined in harmonic excitation. The results, after frequency analysis, showed strong resonance in 270 Hz area. Mode of this resonance caused drumming of covering, resulting in bending of the ribs caps and causing them to fail from fatigue. Changes in elevator design raised the resonance frequency and lowered strains in modified elevator covering. The changes mainly increased sheet-covering stiffness by increase of thickness and lowering the sheet-metal covering mass in selected places, mainly by technological means - metal bonding (gluing) and metal covering chemical milling.

2

Próby rezonansowe - nowe zastosowania

Wiśniowski W.

Prace Instytutu Lotnictwa

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2011

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Nr 5 (214)

3-14

PL

Próby rezonansowe są metodą badania dynamicznych właściwości konstrukcji. Podstawowym ich celem jest wyznaczanie współczynników mas, sztywności i tłumienia występujących w równaniach ruchu konstrukcji. W pracy przedstawiono kilka nowych możliwości wykorzystania prób rezonansowych do identyfikacji oraz interpretacji zjawisk występujących w konstrukcjach obciążanych w sposób dynamiczny.

EN

The resonance tests are the investigation method of dynamic properties of structures. Their basic aim is to determine the coefficients of mass, stiffness and damping occurring in the structure equations of motion. The paper presents some new possibilities of using resonant tests to identify and interpret the phenomena occurring in dynamically loaded structures.

3

Untypical cases and incorrect results of vibration tests

Wiśniewski W.

Journal of KONES

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2009

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Vol. 16, No. 1

591-597

EN

The vibration analysis is the study of the behaviour and dynamic properties of mechanical structures under actuation by harmonic vibration forces. The aim of resonance tests of the structures is the experimental delimitation of frequencies and the modes of resonance vibrations. vibration analysis, or more precisely experimental vibration analysis, is the field of measuring and analyzing the dynamic response of mechanical structures when excited by a mechanical input. The broadly applied method of research relies on the harmonic actuation of vibrations and the measurement of respective parameters. Examples would include measuring the vibration of an aircraft load bearing structure when it is attached to an electromagnetic force actuator. Current vibration testing systems are composed of actuators set with their control and powering circuits, the vibration measurement transducers (typically accelerometers), an analog-to-digital converter to digitize analog instrumentation signals) and a system host computer to analyze the data and view it. The result of researcher own accumulated experiences and those experiences knownfrom the literature create the possibility for design o f a stochastic frame model describing, what type of resonances are possible to expect in the given or other type of structure. The cases submitted below became perceived and tested in the course of research of several aircraft, glider and helicopter designs in the Resonance Tests Program of the Institute of Aviation

4

Resonance tests - vibration mode shapes from the wing torsion group

Wiśniewski W.

Journal of KONES

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2009

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Vol. 16, No. 4

557-561

EN

Resonances of the „ wings torsion " mode shapes to a large extent depend on the structural parameters of the wing, and more specifically to the existence or not of fuel tanks at the wings ends, munitions hard points or engines mounted on the wings. In the paper the group of resonances is presented with mode shapes in which the one, two or three node aircraft wing torsion is present. It is shown in the paper, that these vibration mode shapes consist both of fuselage bending or torsion. Resonance frequencies with mode shapes in which one, two or three node wing torsion occurs depend fundamentally on existence of wing hardpoints. If hardpoints are occupied by fuel tanks, these frequencies are varying continuously in wide range. The various interesting from cognitive point of view combinations have place then, including variable frequencies and variable mode shapes as a function of fuel consumption. The aim for the analysis of 3 cases of resonance a wing torsion mode shapes of airplanes and gliders was to investigate the relationships and mechanisms that are taking place and operate between the torsioningl vibration of the wings and bending or torsion vibrations of the fuselage. Recognition of these phenomena should facilitate the researcher to understand and search effectively and explore the resonances of„ wing torsion " mode shapes.