Novel Methods for Modeling and Online Measurement of Effective Bulk Modulus of Flowing Oil

Abstract

Oil is a key medium for transmitting power and coupling information in the hydraulic transmission system. Accurate calculation and measurement of the dynamic compressibility of the oil have profound significance to the system performance analysis. The present study primarily focuses on the effect of steady pressure on the bulk modulus of static oil. However, changing pressure and flowing oil are the general working conditions in most of hydraulic apparatus. There are few researchers paying attention to the influence of pressure on the compressibility of flowing oil. Considering the log-normal distribution of bubble size in oil, an improved static oil model (Model B) is developed to calculate the bulk modulus of the motionless oil under the dynamic pressure. Then, by deriving Model B, this paper proposes an original flowing oil model (Model C) to determine the effective bulk modulus of flowing oil. Finally, based on the inherent pressure pulsation of the axial piston pump, an innovative online method for measurement of the bulk modulus of flowing oil is presented as it has the advantage of avoiding interference with flow stability. It has been proved that the changes in the flow velocity corresponds to the crucial effect on the effective bulk modulus of flowing oil, especially under the low-flow and low-pressure operation conditions. Those results and analysis provide promoting support for identifying and determining the effective bulk modulus of oil, analyzing the system stiffness, improving the control accuracy, as well as optimizing the mathematical models. INDEX TERMS Bulk modulus, bubble size distribution, flowing oil, online measurement.

Dynamic modeling of fluid nonlinear compression loss and flow loss oriented to fault diagnosis of axial piston pump

“…Assuming that all bubbles in liquid are compressed only. The bulk modulus of two-phase mixed liquid has been given: 27 …”

“…It is maintained at 55 ± 3°C by the cooling fan. According to the online measurement of bulk modulus of flowing oil mentioned in literature ,27 the estimated value of the air content within oil is 2.9%. The three types of KC range are bounded in [0.001,0.5]mm in the model.…”

“…Bubbles in the liquid lose volume in both compression and dissolution. 27 , 28 Pressure increasing would cause the shrinkage of bubbles obviously. At the same time, the saturation solubility of the gas in the liquid increases and the bubbles slowly dissolve into the liquid as the increase of pressure over a period of time.…”

“…28 Though many studies have attempted to reduce the air content by degassing for a better compressibility, 29–31 it is conventionally not available due to its cost consideration, environment/space limitations, and inefficiency. 27…”

The Effects of Oil Entrained Air on the Dynamic Performance of a Hydraulically Driven Multibody System

“…A number of researchers have studied the improvement of a tuned vibration absorber and other techniques to reduce structural and control the vibrations [15]- [20]. In addition, several scholars have also studied on controlling the stiffness, damping characteristics, and flow stability that is induced by fluids [21]- [23]. Yuming Yin et al have studied a hydro-pneumatic suspension system utilizing gas and oil.…”