Study On Characteristics Of Rotary Valve-controlled Differential Hydraulic Vibration Impact System

The pile sinking of precast piles with hydraulic impact hammer and hydraulic vibration hammer plays an indispensable role in the increasingly expanding infrastructure projects.However,due to the working characteristics of their respective power systems,there are problems to be solved urgently in the applicability of these two piling hammer technologies in various working conditions.For the hydraulic impact hammer,the impact frequency of the hydraulic power system is relatively low,so the improvement of impact energy is often used as the symbol of its upgrading.The improvement of impact energy is achieved by increasing weight and lifting height of the hammer head.With the increasing of impact energy,the required working space and the noise pollution will also increase,as well as the damage to its pile body.Because of the energy waste caused by the excitation force generation principle and the mechanical forced synchronization structure cannot be avoided in the joint operation of single hammer or multiple hammers,the eccentric block vibration exciter used in the hydraulic vibration hammer power system is facing certain challenges in many aspects,such as service life,manufacturing cost,deepening application and so on.Aiming at the above situation and related problems,this research proposed a rotary valve controlled differential hydraulic vibration impact system with both vibration and impact output characteristics.The dynamic output characteristics of this system is investigated,combined with two kinds of working conditions of pile sinking,in-depth research is carried out.The main research works include the following aspects.(1)Using the improved abstract variable method and the principle of equivalent force,the linear model of rotary valve controlled differential hydraulic vibration impact system was established,the coupling relationship between kinematics and dynamics of the system was accurately described,and the calculation model of the key structural parameters of the system was derived.Then,the nonlinear model of rotary valve-controlled differential hydraulic vibration impact system(RVCDHVIS)based on power bond graph was established.The results of simulation and physical test show that,the vibration process of the load mass in the RVCDHVIS can be divided into three stages: return acceleration,return deceleration and stroke.By changing the rotating speed of the valve core and the oil supply flowrate of the system,the vibration frequency,amplitude and amplitude of the exciting force of the system can be adjusted steplessly.By adjusting the oil supply flowrate and rotating speed of the system respectively,the impact energy and impact frequency by the system can be controlled independently.(2)A rotary excitation valve,which is the core control element of the hydraulic vibration impact system with unique valve port structure,was proposed,and its static,dynamic and flow field characteristics were studied.Based on the variation law of the excitation valve throttle flow area,the equivalent slide valve model was established,and the static characteristics of the hydraulic vibration excitation valve at the stage of the flow area changing with the spool rotation were described.According to the functional relationship between the zero valve coefficient and structural parameters,it can be proved that the valve port design scheme can ensure that the vibrating valve has a large zero flow gain.The transfer function model of excitation valve control system based on harmonic linearization theory was established.It is found that the amplification gain of the system will decrease with the increase of saturation region,but the stability will be improved.Using CFD flow field simulation technology,the velocity field and pressure field of hydraulic rotary excitation valve under different spool angles,different inlet flow rates and different connection states were obtained.The simulation results showed that when the spool rotates through the oil groove,the injection angle and the absolute value of the steady-state hydrodynamic moment on the spool will firstly increase and then decrease.With the increase of the throttle opening,the pressure loss and flow coefficient of the throttle gradually decreases.During the operation of the rotary excitation valve,the pressure loss and the steady-state hydrodynamic moment are relatively small,especially when the throttle valve of the excitation valve is fully opened,the pressure loss and the steady-state hydrodynamic moment both reach a low level.It is proved that the design scheme of the valve port structure of the vibration valve has a positive effect on improving the energy utilization and control performance of the vibration impact system.(3)A design scheme of vibration impact hammer was proposed,which treats the RVCDHVIS as the power system,and can exert both exciting force and impact force on the pile simultaneously.The mechanical model of pile-hammer system under the coupling effect of vibration and impact was established.The dynamic behavior of the effective work of vibration impact hammer system was analyzed,especially the parametric criterion of the effective work of the vibration impact pile hammer was proposed,and then the value range of the structural parameters of the pile hammer system was obtained,such as the mass of the pile and the hammer,the equivalent stiffness coefficient of the soil,the frequency of the excitation force(rotating speed of the hydraulic excitation valve),the collision recovery coefficient,and stiffness and pre-tightening force of the spring in the hydraulic vibration impact system,etc.A multi-hammer combined operation system based on vibration impact pile hammer was built,and its synchronization performance was tested.The results show that through the synchronous control of the rotary vibration valve,the synchronous output of the vibration force of multiple piles can be realized,and the synchronous performance is excellent..(4)Based on the response characteristics of single-degree-of-freedom viscous damping system under periodic excitation,a technical scheme of high-frequency periodic impact on piles with the natural frequency of pile-soil system was proposed.At the same time,based on the stepless frequency modulation and independent frequency modulation characteristics of the rotary valve-controlled differential hydraulic vibration impact system,the structural scheme of the impact vibration pile hammer with it as the power system was proposed.,and the mechanical simulation model of hammer-pile-soil system considering the sinking behavior of pile hammer were established.The simulation results showed that the system can induce the continuous vibration of piles,thus reducing the requirement for impact speed.When the weight of the pile is close to that of the hammer,the efficiency of pile sinking reaches the highest.The harder the foundation soil is,the better the pile driving effect will be.