sponse because the compressor operates most efficiently at its resonant frequency [6-10]. A linear compressor consists of moving parts compressing refrigerant and a shell with a grommet. The moving part is mounted on plastic springs of the shell, which is placed on the floor through the grommet made of rubber. To maximize the efficiency of the compressor, the natural frequency of the moving part driven by a motor should be tuned to the motor current frequency. Therefore, the operation condition results in extremely high vibration displacement at the shell of the linear compressor. This work discusses errors that researchers may easily make for linear compressor vibration reduction and points out the key ideas in dynamic absorber design. To the end, the basic theory of dynamic absorber will be presented for one and two degree-of-freedom mass-spring-damper systems. Practical dynamic absorber design scheme will be discussed. Basic Theory of Dynamic Absorbers In this section, basic equations are developed to make a close investigation on design technique of dynamics absorbers. Although dynamic absorber design scheme is well explained in vibration textbooks, the key ideas based on equations are required for the close investigation. Frequency response functions are derived for four simple models in Fig. 1, which consist of mass, spring and damping elements using a linear vibration theory. The 1st model is one-degree-of freedom massspring-damper system, the 2nd and 3rd models are two-degree-of freedom massspring-damper system and the 4th model is a three-degree-of freedom mass-springdamper system. The difference between the 2nd model and the 3rd model is the location of an excitation force. Fig. 1 Theoretical models for close investigation on dynamic absorber design technique: (a) 1st model; (b) 2nd model; (c) 3rd model; and (d) 4th model. 274
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