The movement and force transmission of planetary roller screw mechanism （PRSM） are realized by the planetary motion of multiple rollers and the meshing of their helical surfaces between the screw and the nut.Based on the characteristics of spatial helical surface of screw，nut and roller，the kinematic analysis model of PRSM is established by using the parametric equations of the screw，nut and roller in this paper.The positions of contact points are obtained according to the principle of continuous tangency.Then，the relationship between the structu-ral parameters of PRSM is deduced from the kinematics characteristics of the contact points.On this basis，the spatial motion trajectories of the screw，nut and roller are simulated，and the stress cycle behaviors on their threads are further obtained.Furthermore，the working life of the PRSM is predicted.The results show that there is a relative velocity at the contact point of the screw and roller，and the contact point of the nut and roller is the instantaneous center; and that each specific contact point on the roller and nut bears stable pulsating cyclic contact stress，while each specific contact point on the screw is subjected to cyclic contact stress with periodic amplitude variation.

By taking the two-stage planetary roller screw mechanism （PRSM） as the research object，this paper supplements the strength conditions and the stability requirements of the compressed rod required for its parameter design.And，on the basis of motion principle of the two-stage PRSM，the theoretical calculation methods of the rotation and revolution angular velocity of the rollers，the axial displacement and axial velocity of the nut at each stage are proposed.Then，according to the design parameters，a three-dimension model of the two-stage planetary roller screw mechanism is established，and a multi-body dynamics simulation model is constructed based on ADAMS software.By comparing the theoretical values with the simulation results，it is found that the relative errors are within the acceptable range，which verifies the rationality of the parameter matching of the two-stage PRSM and the accuracy of the theoretical calculation method.

Buoyancy regulating device can be used in unmanned underwater vehicles to realize the energy-saving rising，diving or suspending in the water.In this study，a buoyancy-regulating device with lager volume and high precision was designed with a five-cylinder structure.Firstly，the piston position was monitored by a displacement sensor and the telescopic characteristics of the multicylinder were assumed，so that the piecewise method of buo-yancy and the maximum possible error range were obtained.Then，based on the design and experiments of the prototype，the fact that the multicylinder tends to retain the characteristics after running was verified.Meanwhile，the piecewise method of buoyancy calculation was optimized to improve precision ability largely.Experimental results show that the prototype can meet the requirements of the continuous buoyancy regulating of 0~80L，the minimum regulating step of 1L，and the comprehensive precision of no less than 0.5%FS.

Confluence and distribution of multi-branch pipeline （CDMBP） can effectively reduce pipeline density and improve space utilization，but unreasonable structural design can easily cause too much pressure loss and excessive flow distribution difference.A numerical method for the optimal design about CDMBP is proposed in this paper.The paper studies the influence law of multiple parameters，including Reynolds number，outlet and inlet area ratio，closed cavity length at the end of the common chamber，branch pipe spacing and the number of branch pipes，on the flow distribution and pressure loss with parametric analysis.The results show that：there is a pre-ssure recovery zone in the confluence and diversion cavity，which has an impact on the flow distribution and pre-ssure loss of each branch; the Reynolds number has an impact on the flow distribution; the increase of the Reynolds number may increase the pressure loss and the difference of flow distribution; the influence of flow distribution and pressure loss from the length of the end common chamber is negligible; the outlet and inlet area ratio，branch pipe spacing，and the number of branch pipes are importantly related to flow distribution and pressure loss.These factors need to be comprehensively considered in the optimization design of the pipeline structure.These results can be used to guide the optimal design of the CDMBP.

In order to realize the rapid on-site detection for pathogens in complex biological hazards，it is necessary to prepare a variety of biological samples，establish a multimodal biospectral database，and eventually achieve targeted rapid inactivation of pathogens.Ultrafine atomizer design is a key technology to prepare high-quality biological samples.The technology can atomize liquid biological samples into small droplets，and then the bioaerosol particles can be formed after low-temperature freezing and sublimation drying.Through the optimal design of the air-assisted atomizer，the ultrafine and uniform atomization can be obtained under the conditions of low flowrate and low pressure without damaging the biological activity.In this paper，the spray process was simulated by means of RANS+DDM method，and the atomization characteristics of the air-assisted atomizer were analyzed at normal temperature and low temperature with heating power.At the same time，LES+VOF method was also adopted to test the turbulence effect of gas swirling near the nozzle on the liquid fluidics，and the atomization mechanism was analyzed.Moreover，the atomizing effect of the air-assisted atomizer was tested by an aerodynamic particle size tester.The results show that the air-assisted atomizer has good atomizing effect and can realize ultrafine atomization of particles with a diameter of around 1μm.The quality of biological samples prepared by spray-freeze-drying method can meet the design requirements，so it can effectively prepare bioaerosol samples in mass quantities and improve the detection and defense capability for pathogens on the site of biological hazards.

For the problem that NdFeB permanent magnet is brittle and has moulding difficulties in making micro structure，magnetorheological fluid was used as the actuated material for the micro magnetic robot，and a spherical robot for targeted drug delivery in human stomach was designed． According to the rheological principle of magnetorheological fluid，the mechanical relationship of magnetic particles in magnetic field was analyzed，and the dynamic model of spherical robot was established and simulated． The magnetic robot motion image acquisition system was built and robot displacement was calculated with Hough transform circle detection algorithm． Finally，a prototype robot was made and its motion characteristics were tested on an experimental platform with space magnetic field． Ｒesults show that the spherical actuated robot based on magnetorheological fluid is easy to control and its motion is stable and reliable.

The magnetorheological damper is a kind of intelligent semi-active vibration damping device with good prospects，but the current magnetorheological dampers mostly use shear valves as the working mode． The vibration damping effect of this type of damper is poor when used in hydraulic mechanical legs，press leveling and other areas due to the insufficient output force caused by the size of the structure． In this paper，a shear-extrusion hybrid mode magnetorheological damper was designed to solve the problem，and a full-channel magnetic circuit structure was used to replace the traditional magnetic circuit structure to increase the maximum output and dynamic range． This research carried out the structure design and principle analysis of the new magnetorheological damper，established the mechanical model，simulated the magnetic field，and made optimization on the structure． The superiority of the new magnetorheological damper was proved by the prototype test． The above tests and simulations show that the damping force of the new magnetorheological damper can be up to 1065N in the shear valve type and 4939N in the squeeze type． Especially，when the piston coil is fed with reverse current，the magnetic induction intensity of the new damper in the piston damping channel is all above 0. 2 T，while the magnetic induction intensity of the traditional damper only nearly 40% reaches 0. 2 T． When set the current in the same direction，the magnetic induction intensity of the new damper more than 80% can reaches 0. 3T，while the damping channel of the traditional damper only nearly 40% reach 0. 3T． Compared with the traditional magnetorheological damper，the shear-extrusion hybrid mode magnetorheological damper has a larger output value and a higher dynamic adjustable coefficient．

The mathematical model of electromagnetic field and electromagnetic force of the continuous damping control shock absorber’s pilot valve was established on the basis of electromagnetic theory． The appropriate pilot valve material was selected based on the magnetic circuit analysis，and the rationality of the material selection was verified by the magnetic field distribution of the pilot valve which was obtained through simulation． The influence of various structural parameters on the electromagnetic force was analyzed by simulation，and the structural parameters of the pilot valve with greater influence on electromagnetic force were obtained by variance analysis method． Furthermore，the optimized parameter combination scheme was obtained through collaborative optimization for the selected parameters which was carried out with the orthogonal experiment method． The results show that the electromagnet has better constant force characteristics when D2 = 12. 6 mm，δ4 = 0. 25 mm，L2 = 4 mm．

Viscous heating of valve orifice not only wastes energy but also causes thermal deformation． It increases the risk of spool clamping and exerts a strong impact on the stability and safety of hydraulic machines． A deep research on the temperature distribution of valve orifice is the foundation of accuracy prediction of thermal deformation，so a temperature measurement method was put forward by embedding miniature thermocouples in different locations of the planar valve orifice． The experiments were conducted with the valve opening x ranges from 1 mm to 3 mm and inlet pressure pin ranges from 0. 5MPa to 3MPa． The results show that the valve orifice temperature rises with the increase of the inlet pressure; the heating rate can reach 0. 79 ℃ /min when x = 2 mm and pin = 3. 0 MPa; the temperature of valve orifice caused by viscous heating distributes unevenly，and the temperature gradient seems more sensitive to pressure drop under a small orifice． The maximum temperature difference of valve orifice can reach 7. 86 ℃ when x = 1 mm and pin = 3. 0MPa． In most cases，the sharp edge of the valve orifice is likely to generate a higher temperature，which can reach 72. 9 ℃ after heating 110 min under 3. 0 MPa． However，a higher temperature will also appear along the vertical edge under a larger valve opening or a higher pressure drop． To analyze the phenomenon，a comprehensive analysis was carried out by combining fluid-solid-heat coupling module and mixture multiphase flow model in ANSYS Fluent software． The results show that the vortex and cavitation have a strong impact on the temperature distribution in the wall of the valve orifice．

Piston pump is the power source and key component of hydraulic system in construction machinery． Its working status and service performance directly affect the construction quality and operation safety of the construction machinery． Aiming at the harsh working environment and the variable load working condition of the piston pump，different severity levels of loose slipper faults were simulated based on the virtual prototype model of piston pump． The dynamic responses of the piston pump under different loading and structural health conditions were investigated through simulated analysis． And a fault diagnosis method of piston pump in construction machinery under variable load condition was proposed in this paper． According to the method，the axial vibration signal of piston pump is collected at first． Then the vibration signal is divided into several equal parts and the ＲMS of each segmented signal is calculated． At last，the loose slipper failure can be detected based on the gradient of the ＲMS trend line． The experimental results show that the proposed method can effectively detect the loose slipper of piston pump in construction machinery under variable load working condition．

The working performance and stability of the axial piston motor are significantly affected by the frictional lubrication characteristics of the valve-plate pair． Considering the oil film pressure distribution and moment action of the auxiliary support belt with surface veins，this study established the oil film dynamic model of the valve-plate pair，and analyzed the change rules of the flow leakage and friction loss of the valve-plate pair under different working pressure，working speed and swash plate angle． The research results show that the leakage flow of the valveplate pair of the axial piston motor increases approximately linearly with the increase of speed，and the increase rate decreases with the increase of pressure． At the same time，the viscous-friction torque of oil film increases with the increase of the rotational speed and pressure，and there is an approximate linear relationship between the friction torque and the rotating speed． The leakage flow and the thickness of the central film decrease with the increase of the inclined angle of the swash plate，while the friction torque increases with the increase of the inclined angle．

Firstly，the development background and research significance of axial piston pump were described，and friction pair was pointed out as the key factor to restrict the development of axial piston pump． Then the research status of friction pair of axial piston pump at home and broad and the problems in current research were summarized． After that，the technical background，principle，development and application prospect of hydrodynamic-magnetic compound support ( HMCS) applied in axial piston pump was introduced． It was showed that the successful application of HMCS in axial piston pump can solve the difficult problems in traditional piston pump technology． Finally，the key technologies and research difficulties faced by the realization of the hydrodynamic-magnetic compound support were prospected，and the relevant research achievements that are helpful to conquer the key technologies were summarized． The hydrodynamic-magnetic compound support is of great theoretical significance and practical application value for the axial piston pump with high reliability and low viscosity medium using．