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Acoustic losses inside a simulated liquid rocket chamber are investigated by numerical simulation coupled with theoretical calculation. In this study, the losses by injector, resonator and chamber are considered and compared. The oscillation amplitude is assumed to be small (within linear range). For injector and chamber, the loss mechanisms, such as the radiation & convection from the inlet or outlet, and viscous & thermal loss at the wall are considered. For a resonator, the viscous & thermal loss would be the major loss factor. A simulated liquid rocket chamber configuration with an injector installed off-center is investigated especially for tangential oscillation modes. It is found that with well-tuned resonator the resonant frequencies and modes would change from those without the resonator. Therefore, the coupled simulation is indispensable for resonator design. Also an order estimation of each acoustic loss factors is conducted. It is found that the viscous & thermal loss of the chamber and resonator dominate the total acoustic loss in the present configuration. However, if several hundreds of injectors is equipped as in actual rocket chamber, the loss related to injectors would become comparable to that related to resonator on the total loss.