Research On Vibration Characteristics Of The Hull Pedestal And Equipment Unilateral Constraint System

The research on the input load transferred from equipment to hull is meaningful forvibration and noise reducing and has received extensive concern on the vibration and noiseprediction. The equipment connected with marine pedestal through bolts with pretighteningforce, two-stage vibration isolator and gap retainer. Because vibration isolation effect andvibration displacement upper limit should been considered, it is asked that the vibrationisolator has different tensile compression stiffness properties on different vibrationdisplacement scales, namely nonsmooth unilateral constraint stiffness characteristics. Whenexciting forces exceeds a certain threshold value，amplitude of vibration will exceed gap orprestrain of vibration isolator. The stiffness parameters of vibration system will change andpiecewise linear characteristics of vibration system need be considered. Therefore, this thesisfocuses on the following works.Based on structural dynamics, this paper analyses vertical and pitch two degrees offreedom piecewise vibration of equipment under the combined action of the exciting forceand moment by means of the hull pedestal and equipment mathematical simplified models.Because of stiffness properties on different vibration stage, system may generate fourdifferent vibration forms. In this case, the number of natural frequency of piecewise linearsystem will be at most8. Even under single-frequency excitation force, the system willrepresent multi-frequency vibration response, include forced vibration frequency componentand additional natural frequency component. Through MATLAB software to write programsto solve vibration differential equation.Through the solution of the vibration equation, the vibration characteristics of the hullpedestal and equipment system under different exciting force is analyzed. Theoreticalanalyses, displacement curve and phase plane diagrams are used to analysis vibrationcharacteristic of constant parameter system and variable parameter system. And the effect ofthe system parameters on vibration characteristics is discussed. Under asymmetric excitationforce, the vibration of spring on the sides of equipment differs greatly.KBM nonlinear method is adopt to solve the piecewise vibration differential equation andresonance curve. Make use of the stability property of singular point to qualitatively and quantitatively analysis stability region of resonance curve. The influence of gap and stiffnessratio on resonance curve is analyzed.The variety law of vibration amplification coefficient is obtained. Vibration amplificationcoefficient is related to stiffness ratio and frequency ratio. The amplification coefficient withtheir effects may increases or decreases. For hard spring system, the frequency point isintersection point of two vibration amplification coefficient is related to stiffness ratio andfrequency ratio. The resonance curves of hard piecewise linear spring system will be skewedtoward high frequency and exhibits jumping and hysteresis phenomenon. The smaller gapvalue, the earlier resonance curve is skewed. The smaller stiffness ratio, the larger resonancecurve is skewed.In the end, the typical double circular cylindrical shells finite element model isestablished by ANSYS software. The input load that transferred from equipment to hull isobtained by vibration displacement. The load frequent characteristic of constant parametersystem and variable parameter system is analyzed. The input load contains higher frequencycomponent compared with constant parameter system. By the harmonic response analysis, thevibration response of typical reference points is obtained. Under single-frequency excitingforce, the vibratory response characteristic of the hull pedestal and equipment unilateralconstraint system is analyzed.