Effective fluid bulk modulus has significant influence on the stiffness and dynamic performance of hydraulic systems. It is always varied with different working parameters as air content, fluid pressure, and temperature. To estimating effective bulk modulus accurately is very important when designing high performance hydraulic systems. In this study, a measuring device was developed based on the definition of bulk modulus, and the measurement accuracy was estimated. Experiments were carried out using L-HM46 antiwear hydraulic fluid at approximately constant temperature, the results show that the good repeatability and pressure resolution can be achieved. Results also show that when pressure is low, the bulk modulus increases strongly as pressure increases; pressures over 8.5 MPa have slight influence on the bulk modulus. Effective fluid bulk modulus can be expressed as a function of working pressure when the air content is certain.

Electro-hydraulic vibration equipment (EHVE) is widely used in vibration environment simulation tests, such as vehicles, weapons, ships, aerospace, nuclear industries and seismic waves replication, etc., due to its large output power, displacement and thrust, as well as good workload adaptation and multi-controllable parameters. Based on the domestic and overseas development of high-frequency EHVE, dividing them into servo-valve controlled vibration equipment and rotary-valve controlled vibration equipment. The research status and progress of high-frequency electro-hydraulic vibration control technology (EHVCT) are discussed, from the perspective of vibration waveform control and vibration controller. The problems of current electro-hydraulic vibration system bandwidth and waveform distortion control, stability control, offset control and complex vibration waveform generation in high-frequency vibration conditions are pointed out. Combining the existing rotary-valve controlled high-frequency electro-hydraulic vibration method, a new twin-valve independently controlled high-frequency electro-hydraulic vibration method is proposed to break through the limitations of current electro-hydraulic vibration technology in terms of system frequency bandwidth and waveform distortion. The new method can realize independent adjustment and control of vibration waveform frequency, amplitude and offset under high-frequency vibration conditions, and provide a new idea for accurate simulation of high-frequency vibration waveform.

Autonomous excavation operation is a major trend in the development of a new generation of intelligent tunnel boring machines (TBMs). However, existing tec