Dynamics Of Adaptive Head Jet System Of Fire Water Monitor

The fire water monitor has many advantages,such as large flow,long range and high altitude,which has been widely used in various large-scale fire rescue operations.The degree of nozzle opening of normal fire water monitor cannot be ajusted.When the flow or pressure of the incident fluid changes greatly,there will be the jet separate,the short range,and the decrease of fire-fighting efficiency,so it is not suitable for large-scale fire fighting.The adaptive head has adopted an adaptive mechanism that can adjust the nozzle opening inside,so that the fire water monitor can automatically adjust the nozzle opening with the change of the flow rate and pressure,and improve the jet stability and fire-fighting efficiency.Due to the pressure and flow pulsation of the incident fluid,the adaptive head jet system of fire water monitor could inevitably vibrate.When the frequency of fluid pulsation is close to the natural frequency of the jet system,the jet system may vibrate violently,which could affect the stability of the jet and even cause structural damage.Therefore,in this dissertation,the free vibration,forced vibration and parametric vibration of the adaptive head jet system of fire water monitor are studied.Dynamic bulk modulus analysis of gas-liquid mixed fluid.Based on the full cavitation model and the lumped parameter method,a theoretical model of dynamic bulk modulus of gas-liquid mixed fluid is established considering the actual change process of gas-liquid mixed fluid components.The influence of the main parameters on the dynamic bulk modulus is analyzed,and the validity and correctness of the theoretical model are verified by the experimental data.Free vibration analysis of the adaptive head jet system of fire water monitor.Considering the fluid structure coupling and discrete continuous coupling,the free vibration dynamic model and equations of jet system are established.The modal analysis of the jet system is carried out.The sensitivity formula of each natural frequency of the jet system to the design parameters is deduced and the variation law is obtained.Forced vibration analysis of the adaptive head jet system of fire water monitor.The forced vibration equations of jet system are established.When the external excitation frequency is the fluid pressure fluctuation frequency and close to the steady value of the natural frequency respectively,the time-domain and frequency-domain responses of the forced vibration of the jet system are obtained.Parametric vibration analysis of the adaptive head jet system of fire water monitor.The parameter vibration dynamic model and equations of the jet system are established,considering the periodic fluctuation of the equivalent stiffness of the fluid element.The formulas of the main resonance and the combined resonance of the jet system are deduced by the multi-scale method,and resonance of the main resonance and the combined response of the jet system are obtained.Dynamics experiment of adaptive head jet system of fire water monitor.The experiment platform of jet system dynamics has been built,and the frequency of fluid pressure fluctuation and the natural frequency of jet system have been tested.The first-order natural frequency of the jet system obtained from the modal experiment is compared with the theoretical calculation results,which verifies the accuracy of the study on the dynamics of the adaptive head jet system of the fire water monitor.