Preliminary Research On Laser Doppler Flow Velocity Measurement

Laser doppler velocimetry is an advanced technology for velocity measurement using optical doppler effect.Compared with traditional speed measuring methods such as accelerometer and GPS,laser doppler velocimetry has significant advantages such as high accuracy,rapid dynamic response,large measuring range and non-contact.Because of these excellent characteristics,laser doppler velocimetry has been widely used in industry,military,medical,chemical,aviation and other fields.In order to solve the velocity measurement problem of underwater vehicle,a laser doppler velocimetry system is designed and implemented in this paper so that the inertial navigation system of underwater vehicle can be corrected to improve the accuracy of navigation in the future.Firstly the dissertation introduces the historical background and significance of laser doppler velocimetry,then introduces the research status of laser doppler velocimetry,then discusses the basic theory of laser doppler velocimetry,choose dual-beam model to build the system.First the basic light path is structured to establish the system,then the appropriate parameters of each parts are chose to make sure the system works,and the transmission unit and receiving unit of the system are elaborately explained.To make sure that the interference phenomenon at the intersection of the two beams is obvious enough to be observed,we design a dispersion prism to make the length of optical path of the two beams equal in the transmitting unit.In the receiving unit,avalanche photodiode(APD)is selected as the core receiving device of the system.In order to select the added tracer particles,the particle tracking in the fluid was simulated based on the BBO equation.In terms of data processing,fast Fourier transform(FFT),which is widely used nowadays,is adopted as the signal processing algorithm.At last,the experimental system of laser doppler flow velocity measurement is established and the experimental research of flow velocity measurement is carried out.In order to verify the measurement accuracy of the system,a high precision turntable is used as the measuring object.Experimental results show that the laser doppler velocity measurement system is feasible for autonomous navigation system of underwater vehicle.