Study On The Acoustic Velocity Measurement And Its Data Econstruction For The Deep-sea Hydrothermal

As the research on the deep-sea hydrothermal vents has become animportant part of marine science research, estimating the flux of heatand material is one of the important contents of marine hydrothermalactivity research. The calculation of the ocean's heat flux which istransmitted from hydrothermal system depends on the sdudy on the scale,temperature, velocity of hydrothermal area. Therefore, measurement andresearch of velocity field at hydrothermal vent has become an importantcomponent of observation calculation for heat flux at hydrothermal vent.The traditional methods for measure fluid velocity are tracer method,photoelectric method and so on. However, these ways are influenced byoperator and environmental factors considerably. So we need explore amethod via non invasive detection to gain velocity and other physicalparameters at hydrothermal over a long period of time. In this thesis,velocity field at hydrothermal vents is measured non-contactly andreconstructed via acoustic method. The main completed works are asfollows:First of all, based on understanding the tracitional ways to measuringvelocity of flow, acoustic velocity field measurement in deep-seahydrothermal vents is propsed. At the same time, the principle of acousticmeasuring velocity and detection system are introduced. Acousticmeasurement and Reconstruction Algorithm are researched emphatically,reconstruction simulation of all kinds of velocity field model arecompleted based on both the least square method and the Fourierregularization method. Furthermore, flow flux of reconstruction resultsis analysed. Considering the hydrothermal vents may have various forms,the velocity field modles selected in this thesis are as follows:single-summit with smaller velocity gradient, single-summit with largervelocity gradient, double-summit with smaller velocity gradient,double-summit with larger velocity gradient, quadruple-summit,offsetting single-summit,offsetting double-summit,offsetting quadruple-summit.Secondly, reconstruction algorithm for velocity field is studieddetailedly, reconstruction simulation of all kinds of velocity fieldmodels based on both the least square method and the Fourierregularization method are completed engineering mathematics softwareMATLAB. The results show that, the former's restruction effect is pooreras well as it can only woks on simple modles when the number of transducersis fewer. The reconstruction accuracy improves and reconstruction ofcomplicated velocity field models can be accomplished with increasingtransducers'number. The latter's restruction effect and accuracy arebetter for all kinds of velocity field models.Thirdly, considering there may be various factors such as dividingmeasuring areas, number of transducers, decorate means, interplanarspacing and noises which will influence the restruction accuracy inpractical operation, the restruction simulation are studied based thesefactors. The results show that, the restruction accuracy of velocity fieldhas direct relation with factors mentioned above. When the time errorscaused by noises are added to the ideal time differences of flight, therestruction effects of two restruction algorithms are both affected toa certain extent, that is to say both the two algorithms are demandingto the accuracy of time difference of flight.Finally, the measurement and restruction of three-dimensionalvelocity field is introduced and studied. In addition, the restructionsimulation based the least square method and the Fourier regularizationmethod is analyzed and compared. The results show that, the later is betterthan the fomer in 3-D velocity field reconstruction. Besides, the bendingeffect of the acoustic wave in non-uniform temperature field is alsoresearched, thus improving the restruction accuracy of velocity field.