Experimental Study On Flow Induced Motion And Energy Conversion With Variable Excitation Voltage For Multiple Triangular Prisms

With the rapid development of our economic society,the demands of electricity in daily life and work are increasing.Due to the of overuse of non-renewable energy,traditional generation modes meet the challenge of energy lacking.Therefore,the research on clean and renewable energy is extremely urgent.With the continuous development of technology and academic research,offshore wind power and photovoltaic power projects in multiple sea areas have been successfully installed in China.However,for the abundant marine current power,the application of flow induced motion and energy conversion is still under research.Based on this,the experimental tests in this thesis are mainly based on the Flow Induced Motion Energy Conversion System.In this thesis,the Flow-induced motion（FIM）responses and energy conversion of multiple prisms have been studied experimentally.In the tests,two rigidly coupled triangular prisms were arranged in tandem and paralleled,furthermore,three same triangular prisms were coupled rigidly in different arrangements.All the cross-sections of the prisms are regular triangles,and the width of the prism is 0.1m.The effects of spacing ratio,system stiffness and damping on the FIM responses and energy conversion of the multiple prisms were studied by adjusting the space of multiple prisms,the elastically mounted springs and the voltage of the external excitation power supply.All the experiments in this thesis were conducted in a recirculating water channel and the range of Reynolds number is 40618≤Re≤118885,corresponding the flow velocity range of0.465m/s≤U≤1.361m/s.The displacement time history of the prism and the voltage time history of the resistance were measured and analyzed.Based on this,the amplitude ratio,frequency ratio,active power,and efficiency were counted and analyzed.The main conclusions of the test can be summarized as follows:（1）In the FIM response tests for two triangular prisms arranged in tandem:For L/D=1,the amplitude is small,which is about 1/2 of the case of L/D=4.For L/D=3,significant“sharp jump”can be observed in the curves of the amplitude ratio and frequency ratio.In all the tests,the maximum amplitude ratio is A^*=2.48（L/D=4,K=2200N/m,U_r=11）.With the increase of spacing ratio and the decrease of the damping ratio,the oscillation becomes more violent.（2）In the FIM response tests for two triangular prisms arranged in paralleled:For the spacing ratio T/D=1 and T/D=2,the amplitudes of the prisms increase with the flow velocity continuously,and the values are higher totally.For T/D=3,the amplitudes are lower at different stiffness.The maximum amplitude ratio in the tests for two rigidly coupled triangular prisms arranged in paralleled is A^*=2.51,and the oscillation is very violent.In the tests,the decrease of system stiffness and the increase of damping lead a larger amplitude.（3）Three types of three coupled triangular prisms have been experimented,they can appear significant displacements with different stiffness.The oscillations of TypeⅠand TypeⅢprisms perform as typical vortex-induced vibration.The arrangement of TypeⅠhas the best FIM response,and the maximum amplitude is A^*=1.69.The amplitude will be lower and the dominant frequency will be larger if the damping ratio continues to increase.（4）In the energy conversion tests for two triangular prisms arranged in tandem:When the spacing ratio is L/D=4,there exists the maximum active power P_max=18.23W,and the maximum efficiencyη_max=9.05%also appears at this case,which performs better energy conversion characteristics than other cases.Compared with other cases,both the optimal active power and efficiency appear higher values at L/D=4,so the arrangement of L/D=4 is determined as the optimal energy conversion case for the two rigidly coupled triangular prisms arranged in tandem.（5）For T/D=2,the maximum active power P_max=26W is larger than the optimal active power P=18.2W at T/D=1.For T/D=1,as the damping increases,both the active power and efficiency keeps at a stable value and perform without significant restrain,which proves that this case has better energy conversion characteristics.In the tests,the system performs better energy conversion characteristics with smaller stiffness.（6）In the energy conversion tests for three coupled triangular prisms:The TypeⅠprism has the maximum active power P_max=4.89W,the maximum efficiency isη_max=6.01%.The maximum active power for TypeⅢis P_max=1.99W,and the maximum efficiency isη_max=2.77%.Both the two cases do not perform significant advantages over the two rigidly coupled triangular prisms,which proves that the decrease of aspect ratio is helpful for energy conversion.