| The inherent longitudinal pulsation of the propulsion shafting seriously threatened the acoustic stealth of naval vessels.The implementation of dynamic vibration absorption was the current mainstream method and research hotspot of pulse force suppression.Most of the vibration control methods used in propulsion shafting were passive vibration absorbers,which had poor selfadjusting ability of stiffness and damping,and could not adapt to the variable vibration working conditions.In addition,the active control studies were few,and there were some shortcomings in the ocean condition,such as huge energy requirement,complex system,low stability and so on.In the sea,due to the variable working conditions,the inherent frequency of propulsion shafting drifted.The complex and variable of excitation frequency would lead to the invalidation of the original coherent frequency of vibration absorption,the non-optimal matching of the vibration absorbing damping,the large amplitude of the new vibration point and the secondary frequency resonance caused by the multi-frequency excitation,and other bottlenecks remain to be solved.Therefore,how to achieve variable and controllable stiffness and damping to adapt to the high-efficiency vibration absorption of variable working conditions,which is the key and difficult point in improving the acoustic stealth of naval vessels.In the above,a new dynamic vibration absorption method with controllable stiffness and damping was proposed based on magnetorheological fluid(MRF)and its effect,realizing a wide range of frequency coherence and synchronous variable damping,carry out the design of semi-active vibration absorbing device with continuously controllable stiffness and damping,and research on its dynamic and static characteristics.Through theoretical analysis and experimental verification,accurate and efficient semi-active vibration absorption control of propulsion shafting longitudinal vibration is realized.The main work was as follows:In order to solve the problem that it is difficult to identify the dense sound sources accurately or the array of acoustic sensors to be installed is complex,a method of sparse layout and highprecision reconstruction of sound field measurement points based on compressed sensing theory was proposed.Establishing the dynamic model of propeller-shaft longitudinal vibration,analyzing its characteristics,which provided vibration response for the hull acoustic radiation.Using FEM or BEM analyzed the dynamic vibration response of the outer surface structure of hull,obtaining the surface structure simulated the information of acoustic radiation and field intensity point.Compressed sensing theory was used to guide the sparse expression and sampling of acoustic field,random design of acoustic field observation matrix based on Gaussian mixture model.Then,the orthogonal matching pursuit algorithm was used to reconstruct the acoustic field of randomly distributed measurement points.The results showed that the longitudinal vibration of propulsion shafting is one of the main sources of hull noise.The compressed sensing guidance can reduce the number of acoustic sensors by 3/4,and the effective sound field information of the ship can be recovered with an error of less than 2d B(A).Aiming at the problem of complex and variable excitation frequency of propulsion shafting vibration under variable working conditions,a new vibration absorption principle and device with variable stiffness and damping is proposed based on magnetorheological effect.Based on the Bingham model of magnetorheological effect,the principle of variable stiffness and damping was proposed,accordingly a new type of vibration absorber(MRF vibration absorber)with double-shear valve and spring in series or parallel was designed.The dynamic model of MR fluid vibration absorber under different working modes was established,revealing the coupling relationship of stiffness and damping and the law of current action.A hybrid dynamic model of propulsion system and vibration absorber was established.Analyzing the influence of key parameters on the vibration state of propulsion shafting.Based on modal acoustic contribution method,the influence of MRF absorber on the acoustic contribution of longitudinal vibration excited hull with different circumferential wave numbers was studied.The theory proved that it is necessary and feasible to continuously change the stiffness and damping of MRF vibration absorber,and it is most effective to suppress the contribution of ship hull sound power at the first order frequency of propeller.In order to reveal the influence of magnetic field,external excitation characteristics and structural parameters on the stiffness and damping of MRF vibration absorber,a new static model of multi field coupling of MRF absorber was established and verified by experiments.The static model including structural parameters and MRF mechanical properties of MRF absorber under different conditions was derived,and the damping coefficient of each layer was calculate by the energy equivalent method.The MRF was prepared with improved sedimentation stability.A detection device was designed according to the difference in conductivity of the MRF under different sedimentation states.The whole magnetic field characteristics of vibration absorber were simulated by FEM,obtaining the relationship between the magnetic induction intensity of the damping gap and the control current.The prototype of MRF vibration absorber was made,and the relationship between the force and sinusoidal displacement of the vibration absorber under different current was tested,obtaining the relationship between the overall output and current,excitation frequency and amplitude.The experimental results showed that the static model of MRF is accurate,and the variable range of MRF stiffness and damping is about 200%.Aiming at the situation of single frequency,multi-frequency and stiffness damping over-range during vibration absorption control,the time history optimal criterion of stiffness damping under multiple conditions was proposed,and the integral sliding mode controller(ISM)was designed.Taking the experimental data of mechanical properties of vibration absorbers as the database group,the parameters of the unified force model were identified by the intergenerational projection genetic algorithm,the accurate positive force-displacement-current model was obtained.Based on the interaction law between propulsion shafting and MRF vibration absorber,the optimal control direction of stiffness damping of the MRF vibration absorber under multiple conditions was proposed.Based on the rotation invariant subspace method,the excitation frequency was identified to judge the vibration condition.According to different vibration states,taking the stiffness and damping optimal criterion as constraint,and the displacement zero tracking of the controlled object as control objective,the ISM controller was designed and the stability was proved.The results show that the forward model of MRF absorber is accurate,the error is less than 3%,and ISM controller converges exponentially.In order to verify the effectiveness of MRF absorber,control criteria and algorithm of frequency coherence and damping optimization,the vibration absorption control simulation and scale-down experiment of propulsion shafting were carried out.Based on the positive model of force identification and the optimal criteria under different states of stiffness and damping,the ISM controller of vibration absorption is simulated and the control effect is analyzed.The frequency shift characteristic test bench is built,and the frequency sweep experiment is carried out on the MRF vibration absorber to obtain the frequency variation range of the vibration absorber;the propulsion shafting model is developed based on geometry and motion similarity,and its vibration absorption and vibration reduction control experiment is carried out.The experimental results showed that the ISM semi-active control MRF vibration absorber has strong adaptability,the relative change rate of frequency shift is 189%,and it can effectively suppress the vibration acceleration level(VAL)transmitted to the rear end of thrust bearing within 6～30Hz,and the maximum decrease is 29.6d B.The simulation results show that the sound power of the hull can be reduced by 7d B(A). |
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