Vibration Attenuation Research And Damping Optimization Design Of Pipe System Air Conditioner

Pipe system is an important part of air conditioner, and it is also the insubstantial and fragile unit for a long time, the improvement of pipe system is a difficult design process of air conditioner. Visiul design is becoming the trend of the design and developmeng of air conditioner. Simulation design for pipe system can replace the examination of model macnine, decrease the cost and shorten the design time. Meantime, the productive tempo will be cuttingdown greatly, which will strengthen the competitive power for company.This dissertation was supported by Daikin Co. A new vibration attenuation method was suggested in this paper, with partly circling damping layer on the pipe to absorb the vibration, and strengthen the reliability. Finite element (FE) modeling and damping optimization of pipe system were researched in this paper. Examination and FE verfivation were carried out in gross for pipe system with different type and size. It is the key technique for the simulation of air conditioner system. This research will change the traditional design concept, and the design process and performance evaluation can carry out in the same time.The main research work involves calculation method of dynamic property for viscoelastic compound structure, and optimization design of dynamic property parameters based on approximate model. Begin with the experimental study of viscoelastic material; the parameters'optimization and verification are carried out according to the test result. Vibration test and finite element modeling on U-shaped pipe and pipe system with this kind of viscoelastic material are performed carefully. At last, three kinds of approximate model about the viscoelastic damping position and shape parameters vs. dynamic response parameters are trained according to experiment design result. A multi-objective optimization model is established, which defines mass and modal damping as optimal objective. And the improved Non-dominated Sorting Genetic Algorithm (NSGA-â…¡) is employed as optimal method.The mechanical properties experiment was carried out in Dynamic Mechanical Thermal Analyzer (DMTA). The frequency sweeping result shows both storage modulus and loss modulus increase with the activating frequency, and ascends at a higher rate. And the loss factor has not an obvious peak in 1-200 Hz range. An approach based on GA-BFGS hybrid algorithm is introduced to determine the parameters in a constitutive relation for viscoelastic materials according to the experimentally obtained material mechanical properties. This hybrid algorithm can reduce the iteration times greatly and the results are more exact than single GA algorithm, meantime, the initial values of the design variables are free without limits, which is very important for multi-variable optimization. STD model, GHM model and ADF model were analized and compared from the complexity and computer speed in the sedond chapter. And the ADF model was chosen as the optimum constitutive model for this kind of viscoelastic asphalt material.In order to validate the parameter estimation results, dynamic response analysis of free layer damping (FLD) cantilever beam was performed using experimental and numerical simulation approach. The numerical simulation results have good agreements with experimental results which verified the effectiveness of this method. In view of the virtues of completely compatible with finite element method (FEM), the ADF model is suitable to analyze complicated structure.In view of the frequency dependence of viscoelastic damping material, a suggest method of frequency iterative--modal strain energy--modal superposition was used to calculate the frequency, damping ratio and displacement response. Firstly, considering the frequency dependency property of viscoelastic material, FE iterative and modal strain energy method is adopted to solve the modal frequencies and loss factors. And modal mode and corresponding load are extracted from each modal. Moreover, the displacement response of node at each modal frequency was calculated directly. The displacement response in some points of viscoelastic compound structure can be solved by mode superposition. The comparison of numerical simulations with experiment results indicates that the proposed method is effective for analyzing the viscoelastic material with frequency dependency property. This method can be preformed easily using FE software and a simple program. Therefore it has the potential capability to deal with actual structures with a more complex geometry or boundary conditions.Finite element analysis are often time consuming and costly, especially in structure optimization. Therefore, there is necessary to use approximate model, derived from small numbers of computer runs, to replace additional FE tests during optimization. In this work, an optimization framework is proposed to combine experimental design, approximate model and genetic algorithm to form a computationally efficient global optimization method. Firstly, FE calculation is preformed according to experimental design to create a data set of optimization parameters and corresponding model responses. This data set is then used to train the metamodel to receive model optimization parameters as input and an approximation to the response of the numerical as output. An approximation to the solution is then obtained with the metamodel used in place of the expensive numerical model in optimization algorithm. The approximate model used in this paper includes response surface method, Kriging and neural network. At last, dynamic response calculation is carried out to demonstrate the quality of the approximation optimization models.Damping is an important valuation index of vibration attenuation property. With the same parameters values, the bigger the damping value is, the better the vibration attenuation property is. But, damping layer on the pipe system will add the mass greatly, which increase the design cost. Therefore, the minimun mass and the maximum damping were defined as the optimal objective. And NSGA-â…¡algorithm is employed as optimal method. From the Pareto curves between mass and damping, we can see the damping of the pipe structure is growing with the increase of width of the damping layer. But when the width is more than 58mm, the rise rate of the damping is very slow. So, we can choose the mass range is 140 g~160 g as the optimal design range, and the mass ratio range is 13.4%~29.5%, the damping ratio is 7.5%~10.8%. The test result shows with optimal damping layer, the vibration displacement reduced 19.8dB, accelerate reduced 26dB.It is an important part of virtual design of air conditioner's pipe system. A precise FE model and a simple, feasible calculation method were established in this paper for pipe system. Meantime, new vibration attenuation way was suggested and the corresponding optimal algorithm was given. The results of this thesis may have some guideline value to similar dynamic character analysis of viscoleastic material, and to test, modeling and optimization dynamic response of compound structure.