Energy simulation and experimental evaluation of the dynamic properties of a hydraulic rubber bellow

Abstract

In many industrial systems, a bellow is necessary to minimise the amplitude and/or forces on the structures that are transferred by vibrations. This study focusses on the application of an in-line rubber bellow and how the change in operating conditions affects the dynamic properties. The vibration and fluid energy are also simulated to understand the energy that is transferred to the fluid of the system and not absorbed by the bellow. Mathematical models were constructed and implemented. These models were used to characterise and evaluate the dynamic properties of an in-line rubber bellow system. The vibration energy and power were evaluated along with the amount of vibration energy that was transferred to the fluid in the system. A single degree-of-freedom mathematical model was implemented and numerically calculated to predict the transient behaviour of the bellow; these predicted calculations were compared to experimental results. The input values of the numerical model were characterised, where the phase angle of the system was calibrated for a damping-free condition. The acceleration and excitation force of the system were also measured and used as part of the input parameters for the numerical model. This characterisation process was conducted at multiple frequencies between 2.5 Hz and 25 Hz, pressures between -30 kPa and 50 kPa, and excitation forces ranging from 50% to 100% of the unbalance motors' capacity. The experimental results were evaluated and discussed, where the change in dynamic properties of the system was compared to the change in amplitude, frequency, and pressure difference, respectively. Although the change in stiffness was not definable, the dependence of the damping in the system with respect to the change in amplitude and frequency was significant and evaluated to aid future design selection for the application of in-line rubber bellows. The damping ratio at lower amplitudes (<5 mm) was lower. (<30%) than at higher amplitudes (6-9 mm). The damping ratio also decreased with the increase in frequency. If the operating design criteria are known in terms of amplitude or operating frequency, the damping ratio of the system can be predicted by using the results in the table below. The vibration energy was simulated to determine where the vibration energy will be dissipated. Here, the amount of vibration energy transferred to the fluid in the system was also determined, where up to 72% of the vibration energy was transferred to the fluid in certain conditions. The evaluation of the energy transferred to the fluid was significant to understand what effect the vibrations will have on the internal fluid, depending on the system design this could have a positive or negative effect on the system.