Research On Low Vibration Design Of Marine Screw Chiller

The range of refrigerating capacity of screw refrigeration compressor is between centrifugal compressor and scroll compressor,which is more suitable for the field of marine refrigeration.With the increasingly stringent requirements for vibration and noise of ships,more stringent requirements for vibration and noise of refrigeration units is put forward.For commercial interests and exclusive purposes,major companies regard high-efficiency and low vibration noise screw refrigeration compressors as core secrets and block them.Taking the160 k W screw chiller as the research object,this paper attempts to take vibration as the core index and integrate quantitative design with efficiency,reliability and other indexes from the beginning of design,so as to explore a new vibration reduction mode of "vibration quantitative design" for this kind of equipment.The main work of this paper is as follows:The excitation force characteristics of the three main vibration sources of the unit were predicted.And the gas excitation force of the screw compressor,the meshing force of the screw rotor and the flow field pulsation of the refrigerant water pump were modeled and simulated.It was found that the excitation force of the gas excitation was the largest at the exhaust pulsation frequency,the meshing force of the rotor presents the prominent characteristics of three times the meshing frequency,and the pump excitation was mainly concentrated at the pump rotation frequency and blade frequency.According to the main vibration source characteristics of the compressor,on the premise of ensuring that the thermodynamic performance of the compressor was ensured,the rotor profile of the screw compressor was designed.The dynamic characteristics of the rotor were analyzed.And the compressor rotor was optimized and improved.On the basis of ensuring the safety of the traditional compressor structure,the vibration mode of the structure was analyzed.The new compressor structure was improved,and the dynamic characteristics were optimized.Aiming at the air flow pulsation of the compressor,the orifice plate pulsation attenuation structure was designed,and the prototype was developed and verified by experiments.The propagation characteristics of bending wave in the flat plate were analyzed,and its dispersion characteristics were integrated into the vibration reduction structure design of the unit.The structural design idea of variable stiffness mass distribution characteristics was introduced into the vibration transmission path of the unit,and the vibration reduction method of increasing the structural mechanical impedance and reducing the vibration transmission coefficient was proposed.The initial sample machine of the unit was developed,and the matching and optimization design of vibration source and transmission path was carried out for the initial sample machine.Based on the modal test,the dynamic of the machine base structure was modified again,the resonance of the base structure was avoided and the optimal matching was realized.And the vibration reduction effect of 12 d B was achieved at the three times of the meshing frequency.The on-line dynamic balance optimization of the pump rotor system was carried out,and the effect of reducing the single frequency line spectrum by 16 d B was obtained.By optimizing and matching the positive prototype,the vibration reduction effect of 9d B of the total frequency band was achieved compared with the initial prototype.