A method for measuring the natural frequency of a slender object

Abstract

The invention proposes a method for measuring the natural frequency, which can be widely used in the natural frequency detection of structures formed of magnetically conductive or nonmagnetically conductive materials such as pipelines, anchor rods, steel wire ropes, stay cables, plates, and tanks. The present invention uses the sensor to realize the contact or non-contact excitation and detection of the vibration signal according to the magnetostrictive effect and the inverse magnetostrictive effect, and obtains the Fourier spectrum distribution curve corresponding to the system frequency response function Ha,b(f), wherein , a is the measurement point, b is the excitation point, determine the peak point in the Fourier spectrum distribution curve corresponding to Ha,b(f), so as to obtain the natural frequency of the system. The method of the invention not only allows contact measurement, but also allows a larger lift-off distance between the sensor and the measured object, and can detect weaker vibration signals, and has broad application prospects in natural frequency measurement.

Description

technical field [0001] The invention belongs to the field of non-destructive testing, in particular to a method for measuring natural frequency. Background technique [0002] Pipelines, tanks, etc. are important fluid transportation media, and have been widely used in the transportation of oil, natural gas, water, etc.; steel wire ropes, anchor rods, stay cables, etc. in the drilling platform. However, when components such as pipelines and steel wire ropes are subjected to external continuous excitation forces such as external wind loads and transported fluid vibrations, once the frequency of the excitation force is close to its natural frequency, it will cause coupling resonance between the fluid and the structure, and the internal stress of the material will easily reach The limit of strength will cause damage to the material and reduce its service life. Therefore, in order to improve the safety of structure operation and avoid the damage of external excitation force, th...

AI Technical Summary

Problems solved by technology

The traditional natural frequency measurement methods generally use hammering, air cannon, laser ablation, or piezoelectric sensor excitation, and use piezoelectric acceleration sensor to detect the guided wave signal propagating in the structure; however, these methods are contact excitation and detection The method does not allow a large distance between the sensor and the measured object, which is not applicable to the measured objects such as pipes with outer cladding and steel wire ropes with uneven outer surfaces.

At the same time, the above-mentioned contact detection method also has a disadvantage, that is, because the generated vibration signal contains both longitudinal waves and transverse waves, it is difficult to distinguish the natural frequencies corresponding to longitudinal waves or transverse waves according to the detection signals.

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