The underwater anechoic coating technology,which considers pressure resistance and low-frequency broadband sound absorption,has become a research hotspot in underwater acoustics and has received wide attention to addr...The underwater anechoic coating technology,which considers pressure resistance and low-frequency broadband sound absorption,has become a research hotspot in underwater acoustics and has received wide attention to address the increasingly advanced low-frequency sonar detection technology and adapt to the working environment of underwater vehicles in deep submergence.One the one hand,controlling low-frequency sound waves in water is more challenging than in air.On the other hand,in addition to initiating structural deformation,hydrostatic pressure also changes material parameters,both of which have a major effect on the sound absorption performance of the anechoic coating.Therefore,resolving the pressure resistance and acoustic performance of underwater acoustic coatings is difficult.Particularly,a bottleneck problem that must be addressed in this field is the acoustic structure design with low-frequency broadband sound absorption under high hydrostatic pressure.Based on the influence of hydrostatic pressure on underwater anechoic coatings,the research status of underwater acoustic structures under hydrostatic pressure from the aspects of sound absorption mechanisms,analysis methods,and structural designs is reviewed in this paper.Finally,the challenges and research trends encountered by underwater anechoic coating technology under hydrostatic pressure are summarized,providing a reference for the design and research of low-frequency broadband anechoic coating.展开更多
In this paper,a type of reinforcing structure for composite shell with single and through hole is presented.The experimental tests for the composite shells without hole,with single hole and reinforced structure,with t...In this paper,a type of reinforcing structure for composite shell with single and through hole is presented.The experimental tests for the composite shells without hole,with single hole and reinforced structure,with through hole and reinforced structure subjected to hydrostatic pressure were carried out by the designed experimental test system.The mechanical responses of the composite shells under hydrostatic pressure are obtained by the high-speed camera and strain measurement.The results show that the entire deformation process of the shell can be divided into three:uniform compression,"buckling mode formation"and buckling.The"buckling mode formation"process is captured and reported for the first time.For the composite shell with single hole,the proposed reinforcing structure has a significant reinforcement effect on the shell and the buckling capacity of the shell is not weaker than the complete composite shell.For the composite shell with through hole,sealing effect can be achieved by the proposed reinforcing structure,but the buckling capacity of the shell after reinforcement can only reach 77%of the original buckling capacity.展开更多
Two-dimensional van der Waals ferromagnet Fe_(3)GeTe_(2)(FGT)holds a great potential for applications in spintronic devices due to its high Curie temperature,easy tunability,and excellent structural stability in air.T...Two-dimensional van der Waals ferromagnet Fe_(3)GeTe_(2)(FGT)holds a great potential for applications in spintronic devices due to its high Curie temperature,easy tunability,and excellent structural stability in air.Theoretical studies have shown that pressure,as an external parameter,significantly affects its ferromagnetic properties.In this study,we have performed comprehensive high-pressure neutron powder diffraction(NPD)experiments on FGT up to 5 GPa to investigate the evolution of its structural and magnetic properties with hydrostatic pressure.The NPD data clearly reveal the robustness of the ferromagnetism in FGT,despite of an apparent suppression by hydrostatic pressure.As the pressure increases from 0 to 5 GPa,the Curie temperature is found to decrease monotonically from 225(5)K to 175(5)K,together with a dramatically suppressed ordered moment of Fe,which is well supported by the first-principles calculations.Although no pressure-driven structural phase transition is observed up to 5 GPa,quantitative analysis on the changes of bond lengths and bond angles indicates a significant modification of the exchange interactions,which accounts for the pressure-induced suppression of the ferromagnetism in FGT.展开更多
In order to study the laws of the extrusion pressure changing with the extrusion parameters in the process of hydrostatic extrusion for the tungsten alloys, the large deformation elasto plastic theory and the sof...In order to study the laws of the extrusion pressure changing with the extrusion parameters in the process of hydrostatic extrusion for the tungsten alloys, the large deformation elasto plastic theory and the software of ANSYS 5 5 are used to carry out the numerical simulation research. The laws of the extrusion pressure changing with the extrusion parameters, such as the die angle, extrusion ratio, and friction coefficient, are obtained. The simulation results are in good agreement with the experimental ones, and the simulated results are believable.展开更多
How to properly consider the impacts of non-hydrostatic perturbations is one of the challenging issues in developing non-hydrostatic dynamics solvers（NHDSs） for high-resolution atmospheric models. To overcome the dr...How to properly consider the impacts of non-hydrostatic perturbations is one of the challenging issues in developing non-hydrostatic dynamics solvers（NHDSs） for high-resolution atmospheric models. To overcome the drawbacks of current approaches to tackling this issue, this study analyzed the differences between hydrostatic dynamics solvers（HDSs） and their non-hydrostatic counterparts.The analysis then motivated a flexible approach to adjusting existing hydrostatic atmospheric models,especially those adopted in climate simulations for the impacts of non-hydrostatic perturbations.In this approach, the impacts of non-hydrostatic perturbations, reflecting the differences between HDSs and NHDSs, were encapsulated into a single term in the vertical momentum equation for the atmosphere. At each time step, this term was estimated by a separate sub-model, and then it was used to adjust the dynamics of the atmosphere. The adjustment was optional, and could be turned on and off flexibly by utilizing different initial conditions. The approach was illustrated using the Weather Research and Forecasting（WRF） model as an example, and was preliminarily validated by running the 3D baroclinic-wave test case in the model. Results showed that the modified dynamics solver produced simulation results that were very close to those given by the standard NHDS in the WRF model, implying that the approach was basically effective in capturing the non-hydrostatic features of the atmosphere.展开更多
Capability of a novel severe plastic deformation(SPD)method of hydrostatic cyclic extrusion compression(HCEC)for processing of hcp metallic rods with high length to diameter ratios was investigated.The process was con...Capability of a novel severe plastic deformation(SPD)method of hydrostatic cyclic extrusion compression(HCEC)for processing of hcp metallic rods with high length to diameter ratios was investigated.The process was conducted in two consecutive cycles on the AZ91 magnesium alloy,and microstructural evolution,mechanical properties and corrosion behavior were investigated.The results showed that the HCEC process was successively capable of producing ultrafine-grained long magnesium rods.Its ability in improving strength and ductility simultaneously was also shown.The ultimate tensile strength and elongation to failure of the sample after the second cycle of the process were improved to be 2.46 and 3.8 times those of the as-cast specimen,respectively.Distribution of the microhardness after the second cycle was uniform and its average value was increased by 116%.The potentials derived from the polarization curves were high and the currents were much low for the processed samples.Also,the diameter of the capacitive arcs derived from the Nyquist curves was large in the HCEC processed samples.The finite element analysis indicated the independency of HCEC load from the length in comparison to the conventional CEC.HCEC is a unique SPD method,which can produce long ultrafine-grained rods with a combination of superior mechanical and corrosion properties.展开更多
Hydrostatic cyclic expansion extrusion(HCEE) process at elevated temperatures is proposed as a method for processing less deformable materials such as magnesium and for producing long ultrafine-grained rods. In the HC...Hydrostatic cyclic expansion extrusion(HCEE) process at elevated temperatures is proposed as a method for processing less deformable materials such as magnesium and for producing long ultrafine-grained rods. In the HCEE process at elevated temperatures, high-pressure molten linear low-density polyethylene(LLDPE) was used as a fluid to eliminate frictional forces. To study the capability of the process,AM60 magnesium rods were processed and the properties were investigated. The mechanical properties were found to improve significantly after the HCEE process. The yield and ultimate strengths increased from initial values of 138 and 221 MPa to 212 and 317 MPa, respectively.Moreover, the elongation was enhanced due to the refined grains and the existence of high hydrostatic pressure. Furthermore, the microhardness was increased from HV 55.0 to HV 72.5. The microstructural analysis revealed that ultrafine-grained structure could be produced by the HCEE process. Moreover, the size of the particles decreased, and these particles thoroughly scattered between the grains. Finite element analysis showed that the HCEE was independent of the length of the sample, which makes the process suitable for industrial applications.展开更多
Hydrostatic mechanical face seals for reactor coolant pumps are very important for the safety and reliability of pressurized-water reactor power plants.More accurate models on the operating mechanism of the seals are ...Hydrostatic mechanical face seals for reactor coolant pumps are very important for the safety and reliability of pressurized-water reactor power plants.More accurate models on the operating mechanism of the seals are needed to help improve their performance.The thermal fluid–solid interaction（TFSI）mechanism of the hydrostatic seal is investigated in this study.Numerical models of the flow field and seal assembly are developed.Based on the mechanism for the continuity condition of the physical quantities at the fluid–solid interface,an on-line numerical TFSI model for the hydrostatic mechanical seal is proposed using an iterative coupling method.Dynamic mesh technology is adopted to adapt to the changing boundary shape.Experiments were performed on a test rig using a full-size test seal to obtain the leakage rate as a function of the differential pressure.The effectiveness and accuracy of the TFSI model were verified by comparing the simulation results and experimental data.Using the TFSI model,the behavior of the seal is presented,including mechanical and thermal deformation,and the temperature field.The influences of the rotating speed and differential pressure of the sealing device on the temperature field,which occur widely in the actual use of the seal,are studied.This research proposes an on-line and assembly-based TFSI model for hydrostatic mechanical face seals,and the model is validated by full-sized experiments.展开更多
The shear failure of rocks under both a static triaxial stress and a dynamic disturbance is common in deep underground engineering and it is therefore essential for the design of underground engineering to quantitivel...The shear failure of rocks under both a static triaxial stress and a dynamic disturbance is common in deep underground engineering and it is therefore essential for the design of underground engineering to quantitively estimate the dynamic ModeⅡfracture toughness KⅡCof rocks under a triaxial stress state.However,the method for determining the dynamic KⅡCof rocks under a triaxial stress has not been developed yet.With an optimal sample preparation,the short core in compression(SCC)method was designed and verified in this study to measure the dynamic KⅡCof Fangshan marble(FM)subjected to different hydrostatic pressures through a triaxial dynamic testing system.The formula for calculating the dynamic KⅡCof the rock SCC specimen under hydrostatic pressures was obtained by using the finite element method in combination with secondary cracks.The experimental results indicate that the failure mode of the rock SCC specimen under a hydrostatic pressure is the shear fracture and the KⅡCof FM increases as the loading rate.In addition,at a given loading rate the dynamic rock KⅡCis barely affected by hydrostatic pressures.Another important observation is that the dynamic fracture energy of FM enhances with loading rates and hydrostatic pressures.展开更多
The stresses around bubbles formed on a coating/substrate interface under hydrostatic pressure(HP)and alternating hydrostatic pressure(AHP)were calculated using the finite element method.The results reveal that HP pro...The stresses around bubbles formed on a coating/substrate interface under hydrostatic pressure(HP)and alternating hydrostatic pressure(AHP)were calculated using the finite element method.The results reveal that HP promotes coating failure but does not mechanically destroy the interface,whereas AHP can provide tensile stress on bubbles formed at the interface and accelerate disbonding of the coating.Because of water resistance,a lag time exists for the coating that serves in an AHP environment.The coating can have a better protective performance if the lag time suits the AHP to minimize the impact of the AHP on the interface.展开更多
This paper concerns the dynamic characteristics of incompressible laminar flow hydrostatic bearings. An improved method based on the mathematical perturbation technique for calculating the stiffness and damping coeffi...This paper concerns the dynamic characteristics of incompressible laminar flow hydrostatic bearings. An improved method based on the mathematical perturbation technique for calculating the stiffness and damping coefficients of hydrostatic bearings is presented;it raises the calculation efficiency by uncoupling the recess flow continuity equations from the solving of the Reynolds equation. The dynamic coefficients of a water-lubricated four-recess hydrostatic bearing are calculated with both the improved method and the conventional method. The comparisons between these two methods validate the effectiveness and correctness of the improved method. Furthermore, the dynamic response and stability characteristics of a rotor supported by the hydrostatic bearing are calculated and compared with experimental results. First, the dynamic responses calculated with the linear and nonlinear bearing dynamic coefficients models show that the linear model is inaccurate if the rotor whirls in a large eccentricity ratio range, owing to the nonlinearity of stiffness and damping. Second, according to the numerical and experimental results, the nonlinearity of bearing stiffness and damping coefficients could induce double rotational frequency component in the unbalance response frequency spectrum. Finally, the numerical results indicate that the stability threshold speed of the bearing increases with eccentricity ratio. The improved method proposed can be used to evaluate the dynamic performance of hydrostatic bearings efficiently, and the bearing characteristics presented could contribute to a better understanding of the performance of waterlubricated hydrostatic bearings.展开更多
Hydrostatic guideways have various applications in precision machine tools due to their high motion accuracy. The analysis of motion straightness in hydrostatic guideways is generally ignoring the external load on the...Hydrostatic guideways have various applications in precision machine tools due to their high motion accuracy. The analysis of motion straightness in hydrostatic guideways is generally ignoring the external load on the slider. A variation force also exists, caused by the different working positions, together with the dead load of the slider and that of other auxiliary devices. The effect of working position on vertical motion straightness is investigated based on the equivalent static model, considering the error averaging effort of pressured oil film in open hydrostatic guideways. Open hydrostatic guideways in LGF1000 are analyzed with this approach. The theoretical results show that the slider has maximum vertical motion straightness when the working position is closer the guiderail of Y axis. The vertical motion straightness reaches a minimum value as the working position is located at the center of the two guiderails on the Y axis. The difference between the maximum and minimum vertical motion straightness is 34.7%. The smaller vertical motion straightness is attributed to the smaller spacing of the two pads centers, along the Y direction. The experimental results show that the vertical motion straightness is 4.15 μm/1200 mm, when the working position is located in the middle of the Xbeam, and 5.08 pro/1200 mm, when the working position is approaching the Y guiderails, denoting an increase of 18.3%. The changing trends of the measured results validate the correctness of the theoretical model. The research work can be used to reveal the variation law of accuracy of the open hydrostatic guideways, under different working positions, to predict the machining precision, and provides the basis for an error compensation strategy for gantry type grinding machines.展开更多
This paper reviewed the corrosion behavior of metals in simulated deep-water environments and briefly discussed the effect of hydrostatic pressure on the different corrosion types for the active and the passive alloys...This paper reviewed the corrosion behavior of metals in simulated deep-water environments and briefly discussed the effect of hydrostatic pressure on the different corrosion types for the active and the passive alloys.A consensus on the corrosion mechanism is that hydrostatic pressure accelerates the dissolution kinetics,changes the chemical compositions of the product layer or passive films,and promotes the adsorption of Cl^(-)on the metal surface.In addition,a newly-developed mechanism that hydrostatic pressure facilitates the dissolution process by thinning the electric double layer was reviewed,the synergistic effect of hydrostatic pressure and tensile stress on the stress corrosion cracking was discussed,and the modified coating with chemical bonding interface to prolong the service life in this environment was introduced.展开更多
In heavy duty machine tools, hydrostatic turntable is often used as a means for providing rotational motion and supporting workpiece, so the accuracy of turntable is crucial for part machining. In order to analyze the...In heavy duty machine tools, hydrostatic turntable is often used as a means for providing rotational motion and supporting workpiece, so the accuracy of turntable is crucial for part machining. In order to analyze the influence of load-indcued errors on machining accuracy, an identification model of load-induced errors based on the deformation caused by applied load of hydrostatic turntable of computerized numerical control(CNC) gantry milling heavy machine is proposed. Based on multi-body system theory and screw theory, the space machining accuracy model of heavy duty machine tool is established with consideration of identified load-induced errors. And then, the influence of load-induced errors on space machining accuracy and the roundness error of a milled hole is analyzed. The analysis results show that load-induced errors have a big influence on the roundness error of machined hole, especially when the center of the milled hole is far from that of hydrostatic turntable.展开更多
Hydrostatic spindles are increasingly used in precision machine tools. Thermal error is the key factor affecting the machining accuracy of the spindle, and research has focused on spindle thermal errors through examin...Hydrostatic spindles are increasingly used in precision machine tools. Thermal error is the key factor affecting the machining accuracy of the spindle, and research has focused on spindle thermal errors through examination of the influence of the temperature distribution, thermal deformation and spindle mode. However, seldom has any research investigated the thermal effects of the associated Couette flow. To study the heat transfer mechanism in spindle systems, the criterion of the heat transfer direction according to the temperature distribution of the Couette flow at different temperatures is deduced. The method is able to deal accurately with the significant phenomena occurring at every place where thermal energy flowed in such a spindle system. The variation of the motion error induced by thermal effects on a machine work-table during machining is predicated by establishing the thermo-mechanical error model of the hydrostatic spindle for a high precision machine tool. The flow state and thermal behavior of a hydrostatic spindle is analyzed with the evaluated heat power and the coefficients of the convective heat transfer over outer surface of the spindle are calculated, and the thermal influence on the oil film stiffness is evaluated. Thermal drift of the spindle nose is measured with an inductance micrometer, the thermal deformation data 1.35 μm after running for 4 h is consistent with the value predicted by the finite element analysis’s simulated result 1.28 μm, and this demonstrates that the simulation method is feasible. The thermal effects on the processing accuracy from the flow characteristics of the fluid inside the spindle are analyzed for the first time.展开更多
The corrosion form and mechanical properties deterioration of mooring chain steel in simulated deep-sea environments were investigated.With the increase of ocean depth,not only the pressure increases,but also the diss...The corrosion form and mechanical properties deterioration of mooring chain steel in simulated deep-sea environments were investigated.With the increase of ocean depth,not only the pressure increases,but also the dissolved oxygen content decreases.These two factors affect corrosion evolution of mooring chain steel in simulated deep-sea environments,which was studied for the first time.Compared with uniform corrosion of mooring chain steel in shallow sea with sufficient oxygen,low dissolved oxygen leads to the corrosion dominated by pitting with pit covers.Meanwhile,hydrostatic pressure distinctly accelerates pitting initiation and propagation.The higher the hydrostatic pressure is,the more serious the pitting is.For failure mechanism of unstressed mooring chain steel serving in simulated deep-sea environments,both absorbed hydrogen and corrosion morphology can degrade the ductility of mooring chain steel,in which the leading factor depends on the service time.The severe pitting is the main factor and causes remarkable ductility loss of the steel after long-term immersion.But hydrogen plays an important role on elongation loss in early stage.展开更多
Response surface methodology (RSM) was employed in the present work and a second orderquadratic equation for high hydrostatic pressure (HHP) inactivation was built. Theadequacy of the model equation for predicting the...Response surface methodology (RSM) was employed in the present work and a second orderquadratic equation for high hydrostatic pressure (HHP) inactivation was built. Theadequacy of the model equation for predicting the optimum response values was verifiedeffectively by the validation data. Effects of temperature, pressure, and pressureholding time on HHP inactivation of Escherichia coli ATCC 8739 were explored. Byanalyzing the response surface plots and their corresponding contour plots as well assolving the quadratic equation, the optimum process parameters for inactivation E. coliof six log cycles were obtained as: temperature 32.2℃, pressure 346.4 MPa, and pressureholding time 12.6min.展开更多
CoSb3-based mark mid-temperature skutterudites have been a benchthermoelectric material under intensive experimental and theoretical studies for decades. Doping and filling, to the first order, alter the crystal latti...CoSb3-based mark mid-temperature skutterudites have been a benchthermoelectric material under intensive experimental and theoretical studies for decades. Doping and filling, to the first order, alter the crystal lattice constant of CoSb3 in the context of ＂chemical pressure.＂ In this work, we employed ab initio density functional theory in conjunction with semiclassical Boltzmann transport theory to investigate the mechanical properties and especially how hydrostatic loadings, i.e., ＂physical pressure,＂ impact the electronic band structure, Seebeck coefficient, and power factor of pristine CoSb3. It is found that hydrostatic pressure enlarges the band gap, suppresses the density of states （DOS） near the valence band edge, and fosters the band convergence between the valley bands and the conduction band minimum （CBM）. By contrast, hydrostatic tensile reduces the band gap, increases the DOS near the valence band edge, and diminishes the valley bands near the CBM. Therefore, applying hydrostatic pressure provides an alternative avenue for achieving band convergence to improve thermoelectric properties of N-type CoSb3, which is further supported by our carrier concentration studies. These results provide valuable insight into the further improvement of thermoelectric performance of CoSb3-based skutterudites via a synergy of physical and chemical pressures.展开更多
The manipulation of the chromosome set for commercially valuable marine animals is important for enhancing aquacultural production. In this study, triploid and tetraploid sea cucumber Apostichopus japonicus were induc...The manipulation of the chromosome set for commercially valuable marine animals is important for enhancing aquacultural production. In this study, triploid and tetraploid sea cucumber Apostichopus japonicus were induced by hydrostatic pressure shock, and the conditions of appropriate induction were tested with different starting times, and hydrostatic pressure intensities and durations. The highest rate of triploid induction reached 20% and that of tetraploid was 60%. In consideration of the survival rate and hatch rate, the appropriate treatment for triploid was 55 Mpa of hydrostatic pressure for 5 rain at 55 min after fertilization （a.f.）, while for tetraploid it was 60 Mpa for 5 rain at 61 min a.f. The triploid of the sea cucumber could survive through the pelagic larval stage and attachment stage, and develop like the control group of the experiment. The tetraploid, however, could not survive the attachment stage.展开更多
Effects of working parameters on performance characteristics of hydrostatic turntable are researched by applying the fluid-structure-thermal coupled model.Fluid-structure interaction(FSI)technique and computational fl...Effects of working parameters on performance characteristics of hydrostatic turntable are researched by applying the fluid-structure-thermal coupled model.Fluid-structure interaction(FSI)technique and computational fluid dynamics(CFD)method are both employed by this new model,and thermal effects are also considered.Hydrostatic turntable systems with a series of oil supply pressures,various oil recess depth and several surface roughness parameters are studied.Performance parameters,such as turntable displacement,system flow rate,temperature rise of lubrication,stiffness and damping coefficients,are derived from different working parameters(rotational speed of turntable and exerted external load)of the hydrostatic turntable.Numerical results obtained from this FSI-thermal model are presented and discussed,and theoretical predictions are in good agreement with the experimental data.Therefore,this developed model is a very useful tool for studying hydrostatic turntables.The calculation results show that in order to obtain better performance,a rational selection of the design parameters is essential.展开更多
基金Supported by the National Natural Science Foundation of China(Grant No.52271309)Natural Science Foundation of Heilongjiang Province of China(Grant No.YQ2022E104)Doctoral Science and Technology Innovation Fund of Harbin Engineering University(Grant No.3072023GIP0302).
文摘The underwater anechoic coating technology,which considers pressure resistance and low-frequency broadband sound absorption,has become a research hotspot in underwater acoustics and has received wide attention to address the increasingly advanced low-frequency sonar detection technology and adapt to the working environment of underwater vehicles in deep submergence.One the one hand,controlling low-frequency sound waves in water is more challenging than in air.On the other hand,in addition to initiating structural deformation,hydrostatic pressure also changes material parameters,both of which have a major effect on the sound absorption performance of the anechoic coating.Therefore,resolving the pressure resistance and acoustic performance of underwater acoustic coatings is difficult.Particularly,a bottleneck problem that must be addressed in this field is the acoustic structure design with low-frequency broadband sound absorption under high hydrostatic pressure.Based on the influence of hydrostatic pressure on underwater anechoic coatings,the research status of underwater acoustic structures under hydrostatic pressure from the aspects of sound absorption mechanisms,analysis methods,and structural designs is reviewed in this paper.Finally,the challenges and research trends encountered by underwater anechoic coating technology under hydrostatic pressure are summarized,providing a reference for the design and research of low-frequency broadband anechoic coating.
基金supported by the Ningbo Major Research and Development Plan Project(Grant No.2024Z135)the Natural Science Basic Research Program of Shaanxi Province(Grant No.2024JC-YBMS-322)+1 种基金China Postdoctoral Science Foundation(Grant No.2020M673492)National Natural Science Foundation of China(Grant No.51909219)。
文摘In this paper,a type of reinforcing structure for composite shell with single and through hole is presented.The experimental tests for the composite shells without hole,with single hole and reinforced structure,with through hole and reinforced structure subjected to hydrostatic pressure were carried out by the designed experimental test system.The mechanical responses of the composite shells under hydrostatic pressure are obtained by the high-speed camera and strain measurement.The results show that the entire deformation process of the shell can be divided into three:uniform compression,"buckling mode formation"and buckling.The"buckling mode formation"process is captured and reported for the first time.For the composite shell with single hole,the proposed reinforcing structure has a significant reinforcement effect on the shell and the buckling capacity of the shell is not weaker than the complete composite shell.For the composite shell with through hole,sealing effect can be achieved by the proposed reinforcing structure,but the buckling capacity of the shell after reinforcement can only reach 77%of the original buckling capacity.
基金Project supported by the National Natural Science Foundation of China(Grant No.12074023)the Large Scientific Facility Open Subject of Songshan Lake(Grant No.KFKT2022B05)+1 种基金the Fundamental Research Funds for the Central Universities in ChinaNeutron diffraction experiments at the Materials and Life Science Experimental Facility of the J-PARC were performed through the user program(Proposal No.2023A0185).
文摘Two-dimensional van der Waals ferromagnet Fe_(3)GeTe_(2)(FGT)holds a great potential for applications in spintronic devices due to its high Curie temperature,easy tunability,and excellent structural stability in air.Theoretical studies have shown that pressure,as an external parameter,significantly affects its ferromagnetic properties.In this study,we have performed comprehensive high-pressure neutron powder diffraction(NPD)experiments on FGT up to 5 GPa to investigate the evolution of its structural and magnetic properties with hydrostatic pressure.The NPD data clearly reveal the robustness of the ferromagnetism in FGT,despite of an apparent suppression by hydrostatic pressure.As the pressure increases from 0 to 5 GPa,the Curie temperature is found to decrease monotonically from 225(5)K to 175(5)K,together with a dramatically suppressed ordered moment of Fe,which is well supported by the first-principles calculations.Although no pressure-driven structural phase transition is observed up to 5 GPa,quantitative analysis on the changes of bond lengths and bond angles indicates a significant modification of the exchange interactions,which accounts for the pressure-induced suppression of the ferromagnetism in FGT.
文摘In order to study the laws of the extrusion pressure changing with the extrusion parameters in the process of hydrostatic extrusion for the tungsten alloys, the large deformation elasto plastic theory and the software of ANSYS 5 5 are used to carry out the numerical simulation research. The laws of the extrusion pressure changing with the extrusion parameters, such as the die angle, extrusion ratio, and friction coefficient, are obtained. The simulation results are in good agreement with the experimental ones, and the simulated results are believable.
基金supported by the National Key Research and Development Program[grant number 2016YFB0200805]the National Natural Science Foundation of China[grant number 41622503]
文摘How to properly consider the impacts of non-hydrostatic perturbations is one of the challenging issues in developing non-hydrostatic dynamics solvers（NHDSs） for high-resolution atmospheric models. To overcome the drawbacks of current approaches to tackling this issue, this study analyzed the differences between hydrostatic dynamics solvers（HDSs） and their non-hydrostatic counterparts.The analysis then motivated a flexible approach to adjusting existing hydrostatic atmospheric models,especially those adopted in climate simulations for the impacts of non-hydrostatic perturbations.In this approach, the impacts of non-hydrostatic perturbations, reflecting the differences between HDSs and NHDSs, were encapsulated into a single term in the vertical momentum equation for the atmosphere. At each time step, this term was estimated by a separate sub-model, and then it was used to adjust the dynamics of the atmosphere. The adjustment was optional, and could be turned on and off flexibly by utilizing different initial conditions. The approach was illustrated using the Weather Research and Forecasting（WRF） model as an example, and was preliminarily validated by running the 3D baroclinic-wave test case in the model. Results showed that the modified dynamics solver produced simulation results that were very close to those given by the standard NHDS in the WRF model, implying that the approach was basically effective in capturing the non-hydrostatic features of the atmosphere.
文摘Capability of a novel severe plastic deformation(SPD)method of hydrostatic cyclic extrusion compression(HCEC)for processing of hcp metallic rods with high length to diameter ratios was investigated.The process was conducted in two consecutive cycles on the AZ91 magnesium alloy,and microstructural evolution,mechanical properties and corrosion behavior were investigated.The results showed that the HCEC process was successively capable of producing ultrafine-grained long magnesium rods.Its ability in improving strength and ductility simultaneously was also shown.The ultimate tensile strength and elongation to failure of the sample after the second cycle of the process were improved to be 2.46 and 3.8 times those of the as-cast specimen,respectively.Distribution of the microhardness after the second cycle was uniform and its average value was increased by 116%.The potentials derived from the polarization curves were high and the currents were much low for the processed samples.Also,the diameter of the capacitive arcs derived from the Nyquist curves was large in the HCEC processed samples.The finite element analysis indicated the independency of HCEC load from the length in comparison to the conventional CEC.HCEC is a unique SPD method,which can produce long ultrafine-grained rods with a combination of superior mechanical and corrosion properties.
基金This work was financially supported by the Iran National Science Foundation(No.96000854).
文摘Hydrostatic cyclic expansion extrusion(HCEE) process at elevated temperatures is proposed as a method for processing less deformable materials such as magnesium and for producing long ultrafine-grained rods. In the HCEE process at elevated temperatures, high-pressure molten linear low-density polyethylene(LLDPE) was used as a fluid to eliminate frictional forces. To study the capability of the process,AM60 magnesium rods were processed and the properties were investigated. The mechanical properties were found to improve significantly after the HCEE process. The yield and ultimate strengths increased from initial values of 138 and 221 MPa to 212 and 317 MPa, respectively.Moreover, the elongation was enhanced due to the refined grains and the existence of high hydrostatic pressure. Furthermore, the microhardness was increased from HV 55.0 to HV 72.5. The microstructural analysis revealed that ultrafine-grained structure could be produced by the HCEE process. Moreover, the size of the particles decreased, and these particles thoroughly scattered between the grains. Finite element analysis showed that the HCEE was independent of the length of the sample, which makes the process suitable for industrial applications.
基金Supported by National Basic Research Program of China(973 Program,Grant No.2009CB724304)National Key Technology R&D Program(Grant No.2011BAF09B05)National Natural Science Foundation of China(Grant No.50975157)
文摘Hydrostatic mechanical face seals for reactor coolant pumps are very important for the safety and reliability of pressurized-water reactor power plants.More accurate models on the operating mechanism of the seals are needed to help improve their performance.The thermal fluid–solid interaction（TFSI）mechanism of the hydrostatic seal is investigated in this study.Numerical models of the flow field and seal assembly are developed.Based on the mechanism for the continuity condition of the physical quantities at the fluid–solid interface,an on-line numerical TFSI model for the hydrostatic mechanical seal is proposed using an iterative coupling method.Dynamic mesh technology is adopted to adapt to the changing boundary shape.Experiments were performed on a test rig using a full-size test seal to obtain the leakage rate as a function of the differential pressure.The effectiveness and accuracy of the TFSI model were verified by comparing the simulation results and experimental data.Using the TFSI model,the behavior of the seal is presented,including mechanical and thermal deformation,and the temperature field.The influences of the rotating speed and differential pressure of the sealing device on the temperature field,which occur widely in the actual use of the seal,are studied.This research proposes an on-line and assembly-based TFSI model for hydrostatic mechanical face seals,and the model is validated by full-sized experiments.
基金supported by the Natural Sciences and Engineering Research Council of Canada(NSERC)(No.72031326)the National Natural Science Foundation of China(No.52079091)+2 种基金supported by Academy of Finland under Grant No.322518supported by the opening project of State Key Laboratory of Explosion Science and Technology(Beijing Institute of Technology)The opening project number is KFJJ20-01M。
文摘The shear failure of rocks under both a static triaxial stress and a dynamic disturbance is common in deep underground engineering and it is therefore essential for the design of underground engineering to quantitively estimate the dynamic ModeⅡfracture toughness KⅡCof rocks under a triaxial stress state.However,the method for determining the dynamic KⅡCof rocks under a triaxial stress has not been developed yet.With an optimal sample preparation,the short core in compression(SCC)method was designed and verified in this study to measure the dynamic KⅡCof Fangshan marble(FM)subjected to different hydrostatic pressures through a triaxial dynamic testing system.The formula for calculating the dynamic KⅡCof the rock SCC specimen under hydrostatic pressures was obtained by using the finite element method in combination with secondary cracks.The experimental results indicate that the failure mode of the rock SCC specimen under a hydrostatic pressure is the shear fracture and the KⅡCof FM increases as the loading rate.In addition,at a given loading rate the dynamic rock KⅡCis barely affected by hydrostatic pressures.Another important observation is that the dynamic fracture energy of FM enhances with loading rates and hydrostatic pressures.
基金financially supported by the National Natural Science Foundation of China(Nos.51871049 and 51622106)the National Key R&D Program of China(No.2017YFB0702303)Aclass pilot of the Chinese Academy of Sciences(No.XDA22010303)。
文摘The stresses around bubbles formed on a coating/substrate interface under hydrostatic pressure(HP)and alternating hydrostatic pressure(AHP)were calculated using the finite element method.The results reveal that HP promotes coating failure but does not mechanically destroy the interface,whereas AHP can provide tensile stress on bubbles formed at the interface and accelerate disbonding of the coating.Because of water resistance,a lag time exists for the coating that serves in an AHP environment.The coating can have a better protective performance if the lag time suits the AHP to minimize the impact of the AHP on the interface.
文摘This paper concerns the dynamic characteristics of incompressible laminar flow hydrostatic bearings. An improved method based on the mathematical perturbation technique for calculating the stiffness and damping coefficients of hydrostatic bearings is presented;it raises the calculation efficiency by uncoupling the recess flow continuity equations from the solving of the Reynolds equation. The dynamic coefficients of a water-lubricated four-recess hydrostatic bearing are calculated with both the improved method and the conventional method. The comparisons between these two methods validate the effectiveness and correctness of the improved method. Furthermore, the dynamic response and stability characteristics of a rotor supported by the hydrostatic bearing are calculated and compared with experimental results. First, the dynamic responses calculated with the linear and nonlinear bearing dynamic coefficients models show that the linear model is inaccurate if the rotor whirls in a large eccentricity ratio range, owing to the nonlinearity of stiffness and damping. Second, according to the numerical and experimental results, the nonlinearity of bearing stiffness and damping coefficients could induce double rotational frequency component in the unbalance response frequency spectrum. Finally, the numerical results indicate that the stability threshold speed of the bearing increases with eccentricity ratio. The improved method proposed can be used to evaluate the dynamic performance of hydrostatic bearings efficiently, and the bearing characteristics presented could contribute to a better understanding of the performance of waterlubricated hydrostatic bearings.
基金Supported by National Natural Science Foundation of China(Grant No.51275395)National Science and Technology Major Project of Ministry of Science and Technology of China(Grant No.2012ZX04002–091)the Scientific Research Foundation of Shandong University of Science and Technology for Recruited Talents,China(Grant No.2014RCJJ022)
文摘Hydrostatic guideways have various applications in precision machine tools due to their high motion accuracy. The analysis of motion straightness in hydrostatic guideways is generally ignoring the external load on the slider. A variation force also exists, caused by the different working positions, together with the dead load of the slider and that of other auxiliary devices. The effect of working position on vertical motion straightness is investigated based on the equivalent static model, considering the error averaging effort of pressured oil film in open hydrostatic guideways. Open hydrostatic guideways in LGF1000 are analyzed with this approach. The theoretical results show that the slider has maximum vertical motion straightness when the working position is closer the guiderail of Y axis. The vertical motion straightness reaches a minimum value as the working position is located at the center of the two guiderails on the Y axis. The difference between the maximum and minimum vertical motion straightness is 34.7%. The smaller vertical motion straightness is attributed to the smaller spacing of the two pads centers, along the Y direction. The experimental results show that the vertical motion straightness is 4.15 μm/1200 mm, when the working position is located in the middle of the Xbeam, and 5.08 pro/1200 mm, when the working position is approaching the Y guiderails, denoting an increase of 18.3%. The changing trends of the measured results validate the correctness of the theoretical model. The research work can be used to reveal the variation law of accuracy of the open hydrostatic guideways, under different working positions, to predict the machining precision, and provides the basis for an error compensation strategy for gantry type grinding machines.
基金financially supported by the National Natural Science Foundation of China(No.U20b2026)the A-class pilot of the Chinese Academy of Sciences(No.XDA22010303)。
文摘This paper reviewed the corrosion behavior of metals in simulated deep-water environments and briefly discussed the effect of hydrostatic pressure on the different corrosion types for the active and the passive alloys.A consensus on the corrosion mechanism is that hydrostatic pressure accelerates the dissolution kinetics,changes the chemical compositions of the product layer or passive films,and promotes the adsorption of Cl^(-)on the metal surface.In addition,a newly-developed mechanism that hydrostatic pressure facilitates the dissolution process by thinning the electric double layer was reviewed,the synergistic effect of hydrostatic pressure and tensile stress on the stress corrosion cracking was discussed,and the modified coating with chemical bonding interface to prolong the service life in this environment was introduced.
基金Projects(51575010,51575009)supported by the National Natural Science Foundations of ChinaProject(Z1511000003150138)supported by Beijing Nova Program,China
文摘In heavy duty machine tools, hydrostatic turntable is often used as a means for providing rotational motion and supporting workpiece, so the accuracy of turntable is crucial for part machining. In order to analyze the influence of load-indcued errors on machining accuracy, an identification model of load-induced errors based on the deformation caused by applied load of hydrostatic turntable of computerized numerical control(CNC) gantry milling heavy machine is proposed. Based on multi-body system theory and screw theory, the space machining accuracy model of heavy duty machine tool is established with consideration of identified load-induced errors. And then, the influence of load-induced errors on space machining accuracy and the roundness error of a milled hole is analyzed. The analysis results show that load-induced errors have a big influence on the roundness error of machined hole, especially when the center of the milled hole is far from that of hydrostatic turntable.
基金supported by National Natural Science Foundation of China (Grant Nos. 51105005, 51275014)Ministry of Education of China (Grant No. 20111103120002)
文摘Hydrostatic spindles are increasingly used in precision machine tools. Thermal error is the key factor affecting the machining accuracy of the spindle, and research has focused on spindle thermal errors through examination of the influence of the temperature distribution, thermal deformation and spindle mode. However, seldom has any research investigated the thermal effects of the associated Couette flow. To study the heat transfer mechanism in spindle systems, the criterion of the heat transfer direction according to the temperature distribution of the Couette flow at different temperatures is deduced. The method is able to deal accurately with the significant phenomena occurring at every place where thermal energy flowed in such a spindle system. The variation of the motion error induced by thermal effects on a machine work-table during machining is predicated by establishing the thermo-mechanical error model of the hydrostatic spindle for a high precision machine tool. The flow state and thermal behavior of a hydrostatic spindle is analyzed with the evaluated heat power and the coefficients of the convective heat transfer over outer surface of the spindle are calculated, and the thermal influence on the oil film stiffness is evaluated. Thermal drift of the spindle nose is measured with an inductance micrometer, the thermal deformation data 1.35 μm after running for 4 h is consistent with the value predicted by the finite element analysis’s simulated result 1.28 μm, and this demonstrates that the simulation method is feasible. The thermal effects on the processing accuracy from the flow characteristics of the fluid inside the spindle are analyzed for the first time.
基金supported by the National Key R&D Program of China(No.2021YFB3702200)National Natural Science Foundation of China(No.52271050).
文摘The corrosion form and mechanical properties deterioration of mooring chain steel in simulated deep-sea environments were investigated.With the increase of ocean depth,not only the pressure increases,but also the dissolved oxygen content decreases.These two factors affect corrosion evolution of mooring chain steel in simulated deep-sea environments,which was studied for the first time.Compared with uniform corrosion of mooring chain steel in shallow sea with sufficient oxygen,low dissolved oxygen leads to the corrosion dominated by pitting with pit covers.Meanwhile,hydrostatic pressure distinctly accelerates pitting initiation and propagation.The higher the hydrostatic pressure is,the more serious the pitting is.For failure mechanism of unstressed mooring chain steel serving in simulated deep-sea environments,both absorbed hydrogen and corrosion morphology can degrade the ductility of mooring chain steel,in which the leading factor depends on the service time.The severe pitting is the main factor and causes remarkable ductility loss of the steel after long-term immersion.But hydrogen plays an important role on elongation loss in early stage.
文摘Response surface methodology (RSM) was employed in the present work and a second orderquadratic equation for high hydrostatic pressure (HHP) inactivation was built. Theadequacy of the model equation for predicting the optimum response values was verifiedeffectively by the validation data. Effects of temperature, pressure, and pressureholding time on HHP inactivation of Escherichia coli ATCC 8739 were explored. Byanalyzing the response surface plots and their corresponding contour plots as well assolving the quadratic equation, the optimum process parameters for inactivation E. coliof six log cycles were obtained as: temperature 32.2℃, pressure 346.4 MPa, and pressureholding time 12.6min.
基金supported by the Office of Science of the US Department of Energy (Nos. DEAC05-00OR22750 and DE-AC02-05-CH11231)the support of National Science Foundation (No. DMR-1307740)
文摘CoSb3-based mark mid-temperature skutterudites have been a benchthermoelectric material under intensive experimental and theoretical studies for decades. Doping and filling, to the first order, alter the crystal lattice constant of CoSb3 in the context of ＂chemical pressure.＂ In this work, we employed ab initio density functional theory in conjunction with semiclassical Boltzmann transport theory to investigate the mechanical properties and especially how hydrostatic loadings, i.e., ＂physical pressure,＂ impact the electronic band structure, Seebeck coefficient, and power factor of pristine CoSb3. It is found that hydrostatic pressure enlarges the band gap, suppresses the density of states （DOS） near the valence band edge, and fosters the band convergence between the valley bands and the conduction band minimum （CBM）. By contrast, hydrostatic tensile reduces the band gap, increases the DOS near the valence band edge, and diminishes the valley bands near the CBM. Therefore, applying hydrostatic pressure provides an alternative avenue for achieving band convergence to improve thermoelectric properties of N-type CoSb3, which is further supported by our carrier concentration studies. These results provide valuable insight into the further improvement of thermoelectric performance of CoSb3-based skutterudites via a synergy of physical and chemical pressures.
基金the National High-Tech Research and Development Program of China (863 Program, No.2506AA10A411)by the Dalian Natural Science Foundation (No. 99058)
文摘The manipulation of the chromosome set for commercially valuable marine animals is important for enhancing aquacultural production. In this study, triploid and tetraploid sea cucumber Apostichopus japonicus were induced by hydrostatic pressure shock, and the conditions of appropriate induction were tested with different starting times, and hydrostatic pressure intensities and durations. The highest rate of triploid induction reached 20% and that of tetraploid was 60%. In consideration of the survival rate and hatch rate, the appropriate treatment for triploid was 55 Mpa of hydrostatic pressure for 5 rain at 55 min after fertilization （a.f.）, while for tetraploid it was 60 Mpa for 5 rain at 61 min a.f. The triploid of the sea cucumber could survive through the pelagic larval stage and attachment stage, and develop like the control group of the experiment. The tetraploid, however, could not survive the attachment stage.
基金Projects (51175518,51705147) supported by the National Natural Science Foundation of China
文摘Effects of working parameters on performance characteristics of hydrostatic turntable are researched by applying the fluid-structure-thermal coupled model.Fluid-structure interaction(FSI)technique and computational fluid dynamics(CFD)method are both employed by this new model,and thermal effects are also considered.Hydrostatic turntable systems with a series of oil supply pressures,various oil recess depth and several surface roughness parameters are studied.Performance parameters,such as turntable displacement,system flow rate,temperature rise of lubrication,stiffness and damping coefficients,are derived from different working parameters(rotational speed of turntable and exerted external load)of the hydrostatic turntable.Numerical results obtained from this FSI-thermal model are presented and discussed,and theoretical predictions are in good agreement with the experimental data.Therefore,this developed model is a very useful tool for studying hydrostatic turntables.The calculation results show that in order to obtain better performance,a rational selection of the design parameters is essential.
