Research on Feature Extraction Method for Low-Speed Reciprocating Bearings Based on Segmented Short Signal Modulation Signal Bispectrum Slicing

Bearing condition monitoring and fault diagnosis (CMFD) can investigate bearing faults in the early stages, preventing the subsequent impacts of machine bearing failures effectively. CMFD for low-speed, non-continuous operation bearings, such as yaw bearings and pitch bearings in wind turbines, and rotating support bearings in space launch towers, presents more challenges compared to continuous rolling bearings. Firstly, these bearings have very slow speeds, resulting in weak collected fault signals that are heavily masked by severe noise interference. Secondly, their limited rotational angles during operation lead to a restricted number of fault signals. Lastly, the interference from deceleration and direction-changing impact signals significantly affects fault impact signals. To address these challenges, this paper proposes a method for extracting fault features in low-speed reciprocating bearings based on short signal segmentation and modulation signal bispectrum (MSB) slicing. This method initially separates short signals corresponding to individual cycles from the vibration signals based on encoder signals. Subsequently, MSB analysis is performed on each short signal to generate MSB carrier-slice spectra. The optimal carrier frequency and its corresponding modulation signal slice spectrum are determined based on the carrier-slice spectra. Finally, the MSB modulation signal slice spectra of the short signal set are averaged to obtain the overall average feature of the sliced spectra.

Fluid-solid Interaction Model for Hydraulic Reciprocating O-ring Seals

Elastohydrodynamic lubrication characteristics of hydraulic reciprocating seals have significant effects on sealing and tribology performances of hydraulic actuators, especially in high parameter hydraulic systems. Only elastic deformations of hydraulic reciprocating seals were discussed, and hydrodynamic effects were neglected in many studies. The physical process of the fluid-solid interaction effect did not be clearly presented in the existing fluid-solid interaction models for hydraulic reciprocating O-ring seals, and few of these models had been simultaneously validated through experiments. By exploring the physical process of the fluid-solid interaction effect of the hydraulic reciprocating O-ring seal, a numerical fluid-solid interaction model consisting of fluid lubrication, contact mechanics, asperity contact and elastic deformation analyses is constructed with an iterative procedure. With the SRV friction and wear tester, the experiments are performed to investigate the elastohydrodynamic lubrication characteristics of the O-ring seal. The regularity of the friction coefficient varying with the speed of reciprocating motion is obtained in the mixed lubrication condition. The experimental result is used to validate the fluid-solid interaction model. Based on the model, The elastohydrodynamic lubrication characteristics of the hydraulic reciprocating O-ring seal are presented respectively in the dry friction, mixed lubrication and full film lubrication conditions, including of the contact pressure, film thickness, friction coefficient, liquid film pressure and viscous shear stress in the sealing zone. The proposed numerical fluid-solid interaction model can be effectively used to analyze the operation characteristics of the hydraulic reciprocating O-ring seal, and can also be widely used to study other hydraulic reciprocating seals.

RECIPROCATING EXTRUSION OF IN SITU Mg_2Si REINFORCED Mg-Al BASED COMPOSITE

M92Si reinforced Mg-Al based composite with high amount o/silicon was prepared by permanent mould casting, and then extruded by reciprocating extrusion （RE） after the composite was processed by homogenization heat treatment. The effect of RE processing on the morphology and size of M92Si and the mechanical properties of the com- posite were investigated, to develop new ways to refine the M928i phase and improve its shape. The result showed that RE was very useful in refining the M92Si phase. The more the RE processing passes, the better the refining effect would be. Moreover, the uniform distribution of M928i phases would be more in the composite. After the composite was processed by RE for 12 passes, most M92Si phases were equiaxed, with granular diameter below 20 μm, and distributed uniformly in the matrix of the composite. The mechanical properties of the composite could be increased prominently by RE processing, and were much higher than that in the as-cast state. As the temperature rises, the tensile strength is reduced. For the composite RE processed for 12 passes, the tensile strength, yield strength, and elongation are 325.9 MPa, 211.4 MPa, and 3.3% at room temperature, whereas, 288.2 MPa, ,207.7 MPa, and 7.8%, respectively, at 150℃. In comparison with the properties at room temperature, the tensile strength and yield strength are high and only decrease by 11.6% and 1.8% at 150℃. The M928i reinforced Mg-Al based composite possesses good heat resistance at 150℃. The excellent resistance to effect of heat is attributed to the high melting tempera- ture and good thermal stability of fine Mg2Si phases, which are distributed uniformly in the composite, and effectively hinder the grain boundary gliding and dislocation movement.

Valve Dynamic and Thermal Cycle Model in Stepless Capacity Regulation for Reciprocating Compressor

The existing researches of stepless capacity regulation system by depressing the suction valve for reciprocation compressor always adopt hypothesis that the compressor valves are open or close instantaneously, the valve dynamic has not been taken account into thermal cycle computation, the influence of capacity regulation system on suction valves dynamic performance and cylinder thermal cycle operation has not been considered. This paper focuses on theoretical and experimental analysis of the valve dynamic and thermal cycle for reciprocating compressor in the situation of stepless capacity regulation. The valve dynamics equation, gas forces for normal and back flow, and the cylinder pressure varying with suction valve unloader moment during compression thermal cycle are discussed. A new valve dynamic model based on L-K real gas state equation for reciprocating compressor is first deduced to reduce the calculation errors induced by the ideal gas state equation. The variations of valve dynamic and cylinder pressure during part of compression stroke are calculated numerically. The calculation results reveal the non-normal thermal cycle and operation condition of compressor in stepless capacity regulation situation. The numerical simulation results of the valve dynamic and thermal cycle parameters are also verified by the stepless capacity regulation experiments in the type of 3L-10/8 reciprocating compressor. The experimental results agree with the numerical simulation results, which show that the theoretical models proposed are effective and high-precision. The proposed theoretical models build the theoretical foundation to design the real stepless capacity regulation system.

MICROSTRUCTURE OF Mg-6.4Zn-1.1Y ALLOY FABRICATED BY RAPID SOLIDIFICATION AND RECIPROCATING EXTRUSION

In order to explore the methods to prepare high-strength quasicrystal-reinforced magnesium alloys, the flakes of rapidly solidified Mg-6.4Zn-1.1 Y magnesium alloy with a thickness of 50-60μm were obtained by a melt spinning single-roller device, and the flakes were then processed into rods by reciprocating extrusion and direct extrusion. The microstructure of the alloy was analyzed by optical microscope and SEM, and the constituent phases were identified by XRD. Phase transformation and its onset temperature were determined by differential thermal analyzer （DTA）. The analysis result shows that rapid solidification for Mg-6.4Zn-I.IY alloy can inhibit the eutectic reactions, broaden the solid solubility of Zn in α-Mg solute solution, and impede the formation of Mg3 Y2Zn3 and MgZn2 compounds, and thus help the icosahedral Mg3 YZn6 quasicrystal formed directly from the melt. The microstructure of the flakes consists of the α-Mg solid solution and icosahedral Mg3 YZn6 quasicrystal. Dense rods can be made from the flakes by two-pass reciprocating extrusion and direct extrusion. The interfaces between flakes in the rods can be welded and jointed perfectly. During the reciprocating extrusion and direct extrusion process, more Mg3 YZn6 compounds are precipitated and distributed uniformly, whereas the rods possess fine microstructures inherited from rapidly solidified flakes. The rods contain only two phases： α- magnesium solid solution as matrix and fine icosahedral Mg3 YZn6 quasicrystal which disperses uniformly in the matrix.

A new diagnostic method for identifying working conditions of submersible reciprocating pumping systems

The submersible pumping unit is a new type of pumping system for lifting formation fluids from onshore oil wells, and the identification of its working condition has an important influence on oil production. In this paper we proposed a diagnostic method for identifying the working condition of the submersible pumping system. Based on analyzing the working principle of the pumping unit and the pump structure, different characteristics in loading and unloading processes of the submersible linear motor were obtained at different working conditions. The characteristic quantities were extracted from operation data of the submersible linear motor. A diagnostic model based on the support vector machine （SVM） method was proposed for identifying the working condition of the submersible pumping unit, where the inputs of the SVM classifier were the characteristic quantities. The performance and the misjudgment rate of this method were analyzed and validated by the data acquired from an experimental simulation platform. The model proposed had an excellent performance in failure diagnosis of the submersible pumping system. The SVM classifier had higher diagnostic accuracy than the learning vector quantization （LVQ） classifier.

An Integrated Dynamic Model of Ocean Mining System and Fast Simulation of Its Longitudinal Reciprocating Motion

An integrated dynamic model of China＇s deep ocean mining system is developed and the fast simulation analysis of its longitudinal reciprocating motion operation processes is achieved. The seafloor tracked miner is built as a three-dimensional single-body model with six-degree-of-freedom. The track-terrain interaction is modeled by partitioning the track-terrain interface into a certain number of mesh elements with three mutually perpendicular forces, including the normal force, the longitudinal shear force and the lateral shear force, acting on the center point of each mesh element. The hydrodynamic force of the miner is considered and applied. By considering the operational safety and collection efficiency, two new mining paths for the miner on the seafloor are proposed, which can be simulated with the established single-body dynamic model of the miner. The pipeline subsystem is built as a three-dimensional multi-body discrete element model, which is divided into rigid elements linked by flexible connectors. The flexible connector without mass is represented by six spring-damper elements. The external hydrodynamic forces of the ocean current from the longitudinal and lateral directions are both considered and modeled based on the Morison formula and applied to the mass center of each corresponding discrete rigid element. The mining ship is simplified and represented by a general kinematic point, whose heave motion induced by the ocean waves and the longitudinal and lateral towing motions are considered and applied. By integrating the single-body dynamic model of the miner and the multi-body discrete element dynamic model of the pipeline, and defining the kinematic equations of the mining ship, the integrated dynamic model of the total deep ocean mining system is formed. The longitudinal reciprocating motion operation modes of the total mining system, which combine the active straight-line and turning motions of the miner and the ship, and the passive towed motions of the pipeline, are proposed and simulated with the developed 3D dynamic model. Some critical simulation results are obtained and analyzed, such as the motion trajectories of key subsystems, the velocities of the buoyancy modules and the interaction forces between subsystems, which in a way can provide important theoretical basis and useful technical reference for the practical deep ocean mining system analysis, operation and control.

MICROSTRUCTURES AND PROPERTIES OF RECIPROCATINGLY EXTRUDED Mg-6.4Zn-1.1Y ALLOYS

An icosahedral Mg3 YZn6 quasicrystalline phase can be produced in Mg-Zn- Y system alloys when a proper amount of Zn and Y is contained, and it is feasible to prepare the quasicrystal phase-reinforced low-density magnesium alloy. In this article, phase constituents and the effect of reciprocating extrusion on microstructures and properties of the as-cast Mg-6.4Zn-1.1 Y alloy are analyzed. The microstructure of the as-cast Mg-6.4Zn-1.1 Y alloy consists of the α-Mg solid solution, icosahedral Mg3YZn6 quasicrystal, and Mg3 Y2Zn3 and MgZn2 compounds. After the alloy was reciprocatingly extruded for four passes, grains were refined, Mg3 Y2 Zn3 and MgZn2 phases dissolved into the matrix, whereas, Mg3 YZn6 precipitated and distributed uniformly. The alloy possesses the best performance at this state; the tensile strength, yield strength, and elongation are 323.4 MPa, 258.2 MPa, and 19.7%, respectively. In comparison with that of the as-cast alloy, the tensile strength, yield strength, and elongation of the reciprocatingly extruded alloy increase by 258.3%, 397.5%, and 18 times, respectively. It is concluded that reciprocating extrusion can substantially improve the properties of the as-cast Mg-6.4Zn-1.1 Y alloy, particularly for elongation. The high performance of the Mg-6.4Zn-1.1 Y alloy after reciprocating extrusion can be attributed to dispersion strengthening and grain-refined microstructures.

Experimental Studies of Electrostatic Fluctuations and Turbulent Transport in the Boundary of J-TEXT Tokamak Using Reciprocating Probe

As the basic of a deeper investigation on the turbulent transport, the fluctuation property in the boundary of the newly-reconstructed Joint Texas Experimental Tokamak （J- TEXT） is studied experimentally using the reciprocating Langmuir four-tip probe, which has been built and operated as the primary diagnostic tool in the boundary of J-TEXT tokamak. In this paper, spatial profiles of the plasma-edge parameters are obtained, such as electron temperature, plasma density, plasma potential, poloidal electric field and their fluctuations. The results indicate the existence of a Er ×BT shear layer at the vicinity of last closed flux surface （LCFS）, with the fluctuations suppressed in varying degrees. The turbulence-induced particle and energy fluxes can be calculated by the local plasma parameters above. Convection dominates the cross-field turbulent transport in boundary plasma. Electrostatic fluctuations properties are also studied in detail with the help of numerical analysis. Statistical analysis on density fluctuation shows that, the intermittency can affect the turbulence in the scrape-off layer （SOL）.

STUDY ON RECIPROCATING SEALS FOR A LARGER DIAMETER AXIAL PISTON

Sealing performance of the reciprocating seals on a larger diameter (100 mmin diameter) axial piston is theoretically investigated. Based on the characteristics of theclearance flow between the seal and the piston, reasonable boundary conditions for Navier-Stokesequations are determined and the equations are modified, so that the final equations can describethe real flow state of the clearance flow. Through combining the final equations with finite elementmethod, the pressure distributions within the clearance field during the reciprocating motion ofthe piston and the leakage rate with the pressure are studied. The deflections of the seal whichaffect sealing performance are calculated as well. Sealing performance of piston seals using oil asthe working liquid is compared with using water. It is concluded that the seal using water as theworking liquid is under dry friction, which cannot be dealt with the theory of fluid mechanics. Theseal structure is only acceptable using oil as the working liquid..

Study on effect analysis and parameter optimizing of stepless capacity control system on reciprocating compressors

An improved model of reciprocating compressor operation cycle with a stepless capacity control system is presented and influence of the key parameters of the system is evaluated. In the stepless capacity control system of a reciprocating compressor,mechanical unloaders are used to partially hold suction valves open for a certain time during the compression stroke. The typical working process of the reciprocating compressor is changed by capacity regulation apparatus. However,some critical parameters like the hydraulic force acting at the unloader have not been rigorously studied in previous researches. Here an improved numerical model of a double acting reciprocating compressor under the control stepless capacity is proposed and verified by experimental trials. Numerical simulations are carried out to select and evaluate the acting force which definitely has an influence on indicator diagrams of compressors. It is observed that the optimized range of 350 N to 380 N is preferable for the unloader force such that the intensity of opening and closing impacts are minimized.

Optimization and kinetic modeling of waste lard methanolysis in a continuous reciprocating plate reactor

Continuous biodiesel production from a waste pig-roasting lard,methanol and KOH was carried out in a reciprocating plate reactor(RPR)using a factorial design containing three process factors,namely methanol/lard molar ratio,catalyst loading,and normalized height of the reactor.The main goals were to optimize the influential process factors with respect to biodiesel purity using the response surface methodology and to model the kinetics of the transesterification reaction in order to describe the change of triacylglycerols(TAG)and fatty acid methyl esters(FAME)concentrations along the RPR height.The first-order rate law was proved for both the reaction and the mass transfer.The model of the changing reaction mechanism and mass transfer of TAG was also applicable.Both kinetic models agreed with the experimental concentrations of TAG and FAME determined along the RPR height.

Two Dimensional Nanoscale Reciprocating Sliding Contacts of Textured Surfaces

Detailed behaviors of nanoscale textured surfaces during the reciprocating sliding contacts are still unknown although they are widely used in mechanical components to improve tribological characteristics. The current research of sliding contacts of textured surfaces mainly focuses on the experimental studies, while the cost is too high. Molecular dynamics（MD） simulation is widely used in the studies of nanoscale single-pass sliding contacts, but the CPU cost of MD simulation is also too high to simulate the reciprocating sliding contacts. In this paper, employing multiscale method which couples molecular dynamics simulation and finite element method, two dimensional nanoscale reciprocating sliding contacts of textured surfaces are investigated. Four textured surfaces with different texture shapes are designed, and a rigid cylindrical tip is used to slide on these textured surfaces. For different textured surfaces, average potential energies and average friction forces of the corresponding sliding processes are analyzed. The analyzing results show that ＂running-in＂ stages are different for each texture, and steady friction processes are discovered for textured surfaces II, III and IV. Texture shape and sliding direction play important roles in reciprocating sliding contacts, which influence average friction forces greatly. This research can help to design textured surfaces to improve tribological behaviors in nanoscale reciprocating sliding contacts.

Grain refinement impact on the mechanical properties and wear behavior of Mg-9Gd-3Y-2Zn-0.5Zr alloy after decreasing temperature reciprocating upsetting-extrusion

Based on the deforming technique of severe plastic deformation(SPD), the grain refinement of a Mg-9Gd-3Y-2Zn-0.5Zr alloy treated with decreasing temperature reciprocating upsetting-extrusion(RUE) and its influence on the mechanical properties and wear behavior of the alloy were studied. The RUE process was carried out for 4 passes in total, starting at 0 ℃ and decreasing by 10 ℃ for each pass. The results showed that as the number of RUE passes increased, the grain refinement effect was obvious, and the second phase in the alloy was evenly distributed. Room temperature tensile properties of the alloy and the deepening of the RUE degree showed a positive correlation trend, which was due to the grain refinement, uniform distribution of the second phase and texture weakening. And the microhardness of the alloy showed that the microhardness of RUE is the largest in 2 passes. The change in microhardness was the result of dynamic competition between the softening effect of DRX and the work hardening effect. In addition, the wear resistance of the alloy showed a positive correlation with the degree of RUE under low load conditions. When the applied load was higher, the wear resistance of the alloy treated with RUE decreased compared to the initial state alloy. This phenomenon was mainly due to the presence of oxidative wear on the surface of the alloy, which could balance the positive contribution of severe plastic deformation to wear resistance to a certain extent.

Reciprocating Probe Measurements of L-H Transition in LHCD H-Mode on EAST

As the power available in the initial phase of the ITER operation will be limited, accessing the high confinement mode （H-mode） with low heating power will be a critical issue. In the recent experiment on EAST, the H-mode was obtained for the first time with lower hybrid current drive （LHCD） wave only. Reciprocating Langmuir probe measurements at the outer midplane showed that the electron density ne and electron tempel：ature Te in the scrape-off layer （SOL） were significantly reduced in the ELM-free phase, resulting in the increase of lower-hybrid wave （LHW） reflection. It was found that the power loss Ploss was comparable during the L-H transition, by comparing the adjacent L-mode and H-mode discharge. The Da emission, Te and ne decreased rapidly in the time scale of about 1 ms, and the radial electric field Er turned positive in this process near the last closed flux surface. Multiple L-H-L transitions were observed during a single shot when the applied LHW power was marginal to the threshold. The floating potential （Vf） had negative spikes corresponding with the Da signal, and Er oscillation evolved into several intermittent negative spikes just before the L-H transition. In some shots, dithering was observed just before the L-H transition.

Research on gas leakage through suction valves of reciprocating compressor under varying load conditions

A research concerning the coupling conditions of gas leakage through suction valves and capacity regulation is performed in an industrial reciprocating compressor.Both internal flow and thermodynamic characteristic are discussed in detail.The results show that the capacity of compressor can be regulated steplessly by controlling suction valve closure moment.And then the quantitative relationship between the capacity load and the closing angle of suction valve is revealed.The capacity load and valve leakage rate show obvious different features in P-V diagrams,which makes it easier to define appropriate features for detecting cracked or broken reciprocating compressor valves under varying load conditions.A set of curves of compression work and discharge gas mass are obtained and a method for rating thermal performance of a compressor is presented using these curves.

Magnetic Force Transmission of a Reciprocating Motion

Magnetic force transmission of a reciprocating motion is studied by theoretical analysis and experiment. A mathematical model for calculating the magnetic force is derived using the theory of equivalent magnetic charges. An experimental rig is constructed to test the transmission and the model is verified by experiment. Effect of the transmission parameters on the magnetic force is analyzed theoretically from the model, and characteristic of the transmission is studied experimentally. Since the transmission is without direct contact between two elements, it is suitable for application in an organism.

A CFD Study on the Mechanisms Which Cause Cavitation in Positive Displacement Reciprocating Pumps

A transient multiphase CFD （computational fluid dynamics） model was set up to investigate the main causes which lead to cavitation in PD （positive displacement） reciprocating pumps. Many authors agree on distinguishing two different types of cavitation affecting PD pumps： flow induced cavitation and cavitation due to expansion. The flow induced cavitation affects the zones of high fluid velocity and consequent low static pressure e.g. the valve-seat volume gap while the cavitation due to expansion can be detected in zones where the decompression effects are important e.g. in the vicinity of the plunger. This second factor is a distinctive feature of PD pumps since other devices such as centrifugal pumps are only affected by the flow induced type. Unlike what has been published in the technical literature to date, where analysis of positive displacement pumps are based exclusively on experimental or analytic methods, the work presented in this paper is based entirely on a CFD approach, it discusses the appearance and the dynamics of these two phenomena throughout an entire pumping cycle pointing out the potential of CFD techniques in studying the causes of cavitation and assessing the consequent loss of performance in positive displacement pumps.

Study of Seals on Long Stroke and Reciprocating Motion Condition

The equipment has a high and strict requirement of dynamic seals, especially working with Long stroke reciprocating motion under a sandy condition and with a great deal of gas. The seal form of power cylinder on the underground part of hydraulic power rodless type oil extraction equipment is studied. We design three seal structures, do the performance testing and the life testing with related equipment. It turned out that the seal form that combines gap seal with sand prevention techniques has high performance, longer life. The power cylinder works stably and reliably.

Study of Failure Diagnostic Methods and Intelligent Diagnostic System for Reciprocating Compressors

Three categories of failure diagnostic methods for reciprocating compressors are classified according to the signals adopted by the diagnosis. They are parameter method, vibration method, and oil analysis method. In this paper, the applicable range and operational difficulties of these methods are discussed on the basis of analysis and induction upon normal failure. It is proposed that a compressor's normal failure can be divided into thermodynamical property failure and mechanical function failure. As to the former, the parameter method that takes a cylinder pressure signal as the main diagnostic signal may be applied; and as to the latter, the vibration signal frequency spectrum can be used to diagnose. At the same time, the structure of an intelligent diagnostic system based on neural networks is introduced, and its schematic is given.