Any kind of exciting force from the outside, including the unbalanced inertial force of the piston compressor, the pulsating impact force of the airflow, and the mechanical pulse power caused by the poor alignment of the rotating shaft, can cause mechanical vibration of the pipeline. If the main frequency of these exciting forces is consistent with the natural frequency of the pipe, a strong mechanical resonance is induced, which is called structural resonance. Strong piping resonance will cause serious damage to the production: fatigue damage to the pipeline structure and pipeline accessories; deterioration of the compressor's working conditions, premature failure of the valve; distortion of the meter on or near the pipeline; Increased noise, affecting the physical and mental health of workers, and so on. The loss caused by the resonance of the pipe system causes the leakage, but the explosion is caused by the explosion, causing a major accident. The problem of structural resonance is generally analyzed by the finite element method. The basic idea of ​​finite element is to divide the elastic continuum into a finite number of unit bodies. They are connected to each other on a finite number of nodes. Under certain precision requirements, each unit is described with a finite number of parameters, its mechanical characteristics, the entire continuum. The mechanical characteristics can be considered as the sum of the mechanical characteristics of these small units, thus establishing the equilibrium equation of the continuum. Based on the previous summary of the finite element method, this paper establishes a complete calculation equation of the natural frequency of the structure by taking the pipeline in the actual project as an example, which provides a theoretical basis for the design of the compressor piping system in the future. 1 Establishment of vibration vector equation of pipe system structure 1. 1 Establishment of modal matrix The natural frequency and main vibration mode of the piping structure are only related to the stiffness characteristics and mass distribution of the structure. Therefore, the differential equation of free vibration can be used to analyze the equation of the undamped free vibration of the pipeline structure as follows: The free vibration equation of the pipe system is a second-order constant coefficient differential equation. Let each displacement component make a simple harmonic vibration in the same phase, namely: {x } = {X } sin( t+ )( 2) where {x} = Substituting equation (2) into equation (1) yields an algebraic equation: ( 1. 2 Calculation of the natural frequency of the structure There are many solutions to the natural frequency and the main vibration mode. There are many standard procedures available. For the multi-degree-of-freedom complex model, the subspace iteration method, Subspace method, is commonly used, which is generally used to extract the minority mode of the large model. Select p initial iteration vectors to form an np order matrix 2 Numerical calculation of the natural frequency of the piping system 2. 1 Process and method of numerical calculation of natural frequency The ANSYS program can be divided into three phases, usually in the modal analysis of the natural frequency of the compressor piping: pre-processing stage, analysis and solving stage, and post-processing stage. Pre-processing stage: a. Create a job name and specify the unit type; M ain m enu: Preprocessor> E lem ent Type > add (usually using three-dimensional beam element Beam188) b. Define material performance constants, mainly density, elastic modulus And Poisson's ratio; M ain m enu: Preprocessor> M aterial Prop> M a terialM odels c. Define the Sections variable (interface radius); M ain m enu: Preprocessor> Sections> Beam > Common Sections d. Create the model, first establish the node , and then establish a unit to connect the nodes. M ain m enu: Preprocessor> M odeling> Nodes/ Element analysis solution phase: a. Specify the analysis type (M odal); M ain m enu: Solution> Analysis Type> New A nalysis b. Specify the analysis option (Subspace); M Ain m enu: Solution> Analysis Type> Analysis Op itions c. Apply constraints as needed; Main menu: Solution> Define Loads> Apply> S tructural> D isplacement> On N odes d. Start solving calculations. M ain m enu: Solution> Solve> Current LS post-processing stage: a. View the results in post-processing; Ma ain menu: General Postproc> Resu lts Sum mary b. Draw a modal map. M ain menu: General Postproc> Plot Resu lts> Deform ed Shape 2. 2 Application examples In order to further study the mechanical resonance of the piping structure, a modal analysis is carried out by taking a part of the pipeline of a low-pressure solvent compressor of Tianhua Chemical Machinery and Automation Research and Design Institute as the example, the specific parameters of the compressor. The beam structure is divided by the beam unit Beam188, and the number of units is 84. In the structural mass concentration point of the pipeline, the mass unit is ass21. The performance constant density of the material is defined as 7. 8 10 3 kg/m 3 , the elastic modulus E = 210 GPa, Poisson's ratio = 0. 27. A constraint is imposed on the support point of the pipe, and then the pipe structure is meshed to obtain the finite element model of the pipe structure (the bow % represents the constraint). The total length of the main pipe is about 13.4m, and the route is 6 brackets. The length of each pipe segment. The subspace iterative method (Subspace method) is used to solve the modality of the pipe system structure, and the natural frequency value of the first 6th order structure of the pipe system structure is obtained, and the vibration mode map corresponding to the first 6 natural frequencies of the pipe system structure is obtained. 2. 3 Calculation of the excitation frequency of the pipe system First calculate the excitation main frequency of the compressor: f = N i / 60 = 740 ! 2 /60= 24. 7 Hz type N compressor spindle speed; i compressor cylinder single or double acting mode, i = 1 for single action, i = 2 for double action. See the excitation frequency of the front 4th compressor of the compressor from the above formula. 3 Conclusion 3. 1 The vibration vector equation of the compressor pipeline structure is established by the variational method and the polycondensation mass method. Then the subspace iterative method is used to establish the complete structural natural frequency calculation equation, so that the method of obtaining the natural frequency of the structure is feasible. 3. 2 The natural frequency and excitation frequency of the piping system are not in the resonance zone at the low stage. Therefore, the compressor piping design is reasonable and has good vibration control effects. Lwcy Screw Compressors Lwcy Screw Compressors,Diesel Screw Air Compressors,Mobile Diesel Screw Compressors,Automatic Screw Compressors ZHEJIANG SHANHAI MACHINERY CO., LTD. , http://www.sunhi-mach.com
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Predictive study on the numerical value of the structure frequency of a certain compressor
The compressor piping system has its own natural frequency depending on the piping condition, the type of support, the support position, and the boundary conditions.