The accelerator-driven subcritical system (ADS) with a hard neutron energy spectrum was used to study transmutation of minor actinides (MAs). The aim of the study was to improve the efficiency of MA transmutation whil...The accelerator-driven subcritical system (ADS) with a hard neutron energy spectrum was used to study transmutation of minor actinides (MAs). The aim of the study was to improve the efficiency of MA transmutation while ensuring that variations in the effective multiplication factor (keff) remained within safe margins during reactor operation. All calculations were completed using code COUPLE3.0. The subcritical reactor was operated at a thermal power level of 800 MW, and a mixture of mononitrides of MAs and plutonium (Pu) was used as fuel. Zirconium nitride (ZrN) was used as an inert matrix in the fuel elements. The initial mass composition in terms of weight percentages in the heavy metal component (IHM) was 30.6% Pu/IHM and 69.4% MA/IHM. To verify the feasibility of this MA loading scheme, variations in keff, the amplification factor of the core, maximum power density and the content of MAs and Pu were calculated over six refueling cycles. Each cycle was of 600 days duration, and therefore, there were 3600 effective full power days. Results demonstrated that the effective transmutation support ratio of MAs was approximately 28, and the ADS was able to efficiently transmute MAs. The changes in other physical parameters were also within their normal ranges.It is concluded that the proposed MA transmutation scheme for an ADS core is reasonable.展开更多
Subcritical crack growth(SCG)in fluid-rock interactions plays a crucial role in understanding crustal deformation and fracture network development.Using a double-torsion technique,the subcritical crack growth and frac...Subcritical crack growth(SCG)in fluid-rock interactions plays a crucial role in understanding crustal deformation and fracture network development.Using a double-torsion technique,the subcritical crack growth and fracture characteristics of Zhangzhou granite were investigated under fluids with different pH values.Subcritical crack growth index(SCI)was reduced in both acidic and alkaline fluids compared with the neutral environment,with reduction percentages of 9.8%e31.9%under acidic environment(pH=1-5)and 8.3%e17.5%under alkaline environment(pH=10-14),respectively.In contrast,the weakening effect of fluid pH values on critical stress intensity was less than that of SCI.Scanning electron microscopy(SEM)results showed that grain boundaries were prone to dissolution compared to the basal surface,proving that subcritical cracks preferentially propagate along the grain boundaries.Fracture toughness was insensitive to fluid pH values in the short term but sensitive to solution salinity.Considering mineral compositions and contents,a rock dissolution rate was defined,and a SCI prediction model was proposed,which was demonstrated to be capable of estimating variations in SCI under various fluid environments for different rock types and could provide valuable insights for engineering applications and environmental assessments.展开更多
This study examines the nonlinear behaviors of a clamped-clamped porous pipe made of a functionally graded material(FGM)that conveys fluids and is equipped with a retaining clip,focusing on primary resonance and subcr...This study examines the nonlinear behaviors of a clamped-clamped porous pipe made of a functionally graded material(FGM)that conveys fluids and is equipped with a retaining clip,focusing on primary resonance and subcritical dynamics.The nonlinear governing equations for the FGM pipe are derived by the extended Hamilton's principle,and subsequently discretized through the application of the Galerkin method.The direct method of multi-scales is then used to solve the derived equations.A thorough analysis of various parameters,including the clip stiffness,the power-law index,the porosity,and the clip location,is conducted to gain a comprehensive understanding of the system's nonlinear dynamics.Through the analysis of the first natural frequency,the study highlights the influence of the flow velocity and the clip stiffness,while the comparisons with metallic pipes emphasize the role of FGM composition.The examination of the forced response curves reveals saddle-node bifurcations and their dependence on parameters such as the detuning parameter and the power-law index,offering valuable insights into the system's nonlinear resonant behavior.Furthermore,the frequency-response curves illustrate the hardening nonlinearities influenced by factors such as the porosity and the clip stiffness,revealing nuanced effects on the system response and resonance characteristics.This comprehensive analysis enhances the understanding of nonlinear behaviors in FGM porous pipes with a retaining clip,providing key insights for practical engineering applications in system design and optimization.展开更多
Accelerator-driven systems based on molten salt fuel have several unique advantages and features for advanced nuclear fuel utilization.The aim of this work was to study the Th-U breeding capability in such systems,kno...Accelerator-driven systems based on molten salt fuel have several unique advantages and features for advanced nuclear fuel utilization.The aim of this work was to study the Th-U breeding capability in such systems,known as‘‘accelerator-driven subcritical molten salt reactors’’(ADS–MSRs).Breeding capacities including conversion ratio and net^(233)U production for various subcriticalities and different minor actinides(MA)loadings were analyzed for an ADS–MSR.The results show that the subcriticality of the core has a considerable effect on the Th-U breeding.A high subcriticality is favorable to improving the conversion ratio,increasing the net^(233)U production,and reducing the doubling time.Specifically,the doubling time for k_(eff)of 0.99 is larger than 80 years,while the counterpart for k_(eff)of 0.93 is only approximately22 years.Nevertheless,in an ADS–MSR with a high initial MA loading,MA results in a non-negligible^(233)U depletion in the first two decades,while increasing the net^(233)U production compared to reactors without MA loading.During the 50 years of operation,for the subcritical reactor(k_(eff)0:97)with MA fraction increasing from 1 to 14%,the net^(233)U production increases from 3.94 to 8.24 t.展开更多
The study of accelerator-driven subcritical reactor systems(ADSs) has been an important research topic in the field of nuclear energy for years. The main code applied in ADS research is MCNPX, which was developed by L...The study of accelerator-driven subcritical reactor systems(ADSs) has been an important research topic in the field of nuclear energy for years. The main code applied in ADS research is MCNPX, which was developed by Los Alamos National Laboratory. We studied the application of the open-source Monte Carlo codes FLUKA and OpenMC to a coupled ADS calculation. The FLUKA code was used to simulate the reaction of highenergy protons with the nucleus of the target material in the ADS, which produces spallation neutrons. Information on the spallation neutrons, such as their energy, position,direction, and weight, can be recorded by a user-defined routine called FLUSCW provided by FLUKA. Then, the information was stored in an external neutron source file in HDF5 format by using a conversion code, as required by the OpenMC calculation. Finally, the fixed-source calculation function of OpenMC was applied to simulate the transport of spallation neutrons and obtain the distribution of the neutron flux in the core region. In the coupled calculation, the high-energy cross-section library JENDL4.0/HE in ACE format produced by NJOY2016 was applied in the OpenMC transport simulation. The OECD–ADS benchmark problem was calculated, and the results were compared with those obtained using MCNPX. It was found that the flux calculations performed by FLUKA–OpenMC and MCNPX were in agreement, so the coupling calculation method for ADS is reasonable and feasible.展开更多
Effect of cryogenic treatment on the microstructure, hardening behavior and abrasion resistance of 14Cr2Mn2V high chromium cast iron （HCCI） subjected to subcritical treatment was investigated. The results show that ...Effect of cryogenic treatment on the microstructure, hardening behavior and abrasion resistance of 14Cr2Mn2V high chromium cast iron （HCCI） subjected to subcritical treatment was investigated. The results show that cryogenic treatment after subcritical treatment can obviously improve the hardness and abrasion resistance of HCCI because abundant retained austenite is transformed into martensite and fine secondary carbides E（Fe, Cr）23 C6 ] precipitate. The amount of martensite and precipitated secondary carbide in HCCI experiencing subcritical treatment followed by cryogenic treatment was more than that experiencing the subcritical treatment followed by air cooling. When the abrasion resistance of HCCI reaches the maximum, its microstructure contains about 15 % retained austenite. Cryogenic treatment can further reduce the austenite content but the retained austenite cannot be transformed in to martensite completely.展开更多
The hydrolysis technology and reaction kinetics for amino acids production from fish proteins in subcritical water reactor without catalysts were investigated in a reactor with volume of 400 ml under the conditions of...The hydrolysis technology and reaction kinetics for amino acids production from fish proteins in subcritical water reactor without catalysts were investigated in a reactor with volume of 400 ml under the conditions of reaction temperature from 180-320℃, pressure from 5-26 MPa, and time from 5-60 rain. The quality and quantity of amino acids in hydrolysate were determined by bioLiquid chromatography, and 17 kinds of amino acids were obtained. For the important 8 amino acids, the experiments were conducted to examine the effects of reaction temperature, pressure and time on amino acids yield. The optimum conditions for high yield are obtained from the experimental results. It is found that the nitrogen and carbon dioxide atmosphere should be used for leucine, isoleucine and histidine production while the air atmosphere might be used for other amino acids. The reaction time of 30 rain and the experimental temperature of 220℃, 240℃ and 260℃ were adopted for reaction kinetic research. The total yield of amino acids versus reaction time have been examined experimentally. According to these experimental data and under the condition of water excess, the macroscopic reaction kinetic equation of fish proteins hydrolysis was obtained with the hydrolysis reaction order of 1.615 and the rate constants being 0.0017, 0.0045 and 0.0097 at 220℃, 240℃ and 260℃ respectively. The activation energy is 145.1 kJ·mol^- 1.展开更多
Effects of reaction parameter on yield of benzaldehyde produced from toluene oxidization using hydrogen peroxide in subcritical water are investigated. The experimental results show that if the molar ratio of hydrogen...Effects of reaction parameter on yield of benzaldehyde produced from toluene oxidization using hydrogen peroxide in subcritical water are investigated. The experimental results show that if the molar ratio of hydrogen peroxide to toluene is controlled within a reasonable range, the by-products may be neglected. The optimum technology of toluene oxidization to benzaldehyde is reaction time 60 min, reaction temperature 350℃, molar ratio of hydrogen peroxide to toluene 3.5. The yield of benzaldehyde can reach 17.2 % under the optimum condition. Research results of chemical reaction kinetics show that the consecutive reaction consists of two first-order reaction, and activation energy of these two reactions are 89 kJ·mol^-1 and 76 kJ·mol^-1 respectively,展开更多
Diapycnal mixing plays an important role in the ocean circulation.Internal waves are a kind of bridge relating the diapycnal mixing to external sources of mechanical energy.Difficulty in obtaining eigen solutions of i...Diapycnal mixing plays an important role in the ocean circulation.Internal waves are a kind of bridge relating the diapycnal mixing to external sources of mechanical energy.Difficulty in obtaining eigen solutions of internal waves over curved topography is a limitation for further theoretical study on the generation problem and scattering process.In this study,a kind of transform method is put forward to derive the eigen solutions of internal waves over subcritical topography in twodimensional and linear framework.The transform converts the curved topography in physical space to flat bottom in transform space while the governing equation of internal waves is still hyperbolic if proper transform function is selected.Thus,one can obtain eigen solutions of internal waves in the transform space.Several examples of transform functions,which convert the linear slope,the convex slope,and the concave slope to flat bottom,and the corresponding eigen solutions are illustrated.A method,using a polynomial to approximate the transform function and least squares method to estimate the undetermined coefficients in the polynomial,is introduced to calculate the approximate expression of the transform function for the given subcritical topography.展开更多
The Ostwald ripening of carbide particles occurs during the process of subcritical annealing in SCM435 steel, and the degree of ripening influences the microstructure and mechanical properties of the steel. The effect...The Ostwald ripening of carbide particles occurs during the process of subcritical annealing in SCM435 steel, and the degree of ripening influences the microstructure and mechanical properties of the steel. The effects of Ostwald ripening were studied by simulating different soaking time at 680 ~C using SCM435 steel. The spheroidized specimens were analysed by conducting microstructure and mechanical tests. After increasing the soaking time from 2 to 6 h at 680 ~C during subcritical annealing, the number of carbide particles and the spheroidization ratio increased gradually, and the formability was improved. When the soaking time ranged from 6 to 8 h, the spheroidization ratio was similar; however, the number of carbide particles decreased, and the formability gradually worsened. Therefore, by comprehensively comparing the microstructures and mechanical properties, the optimum soaking time was determined to be 6 h at 680 ~C during subcritical annealing to obtain preferable cold heading. In addition, the carbide particles gradually coarsened when the soaking time was extended from 2 to 8 h. A formula was presented to quantitatively characterize the progress of Ostwald ripening of the carbide particles during the subcritical annealing of SCM435 steel, and the relative error was less than 8.02%.展开更多
Euphausia pacific is an important source of natural astaxanthin. Studies were carried out to assess the extractability of astaxanthin from E. pacific using subcritical 1, 1, 1,2-tetrafluoroethane （R134a）. To examine...Euphausia pacific is an important source of natural astaxanthin. Studies were carried out to assess the extractability of astaxanthin from E. pacific using subcritical 1, 1, 1,2-tetrafluoroethane （R134a）. To examine the effects of multiple process variables on the extraction yield, astaxanthin was extracted under various conditions of pressure （30-150bar）, temperature （303-343 K）, time （10-50rain）, flow rate （2-10gmin-1）, moisture content （5.5%-63.61%）, and particle size （0.25-0.109mm）. The results showed that the extraction yield increased with temperature, pressure, time and flow rate, but decreased with moisture content and particle size. A maximum yield of 87.74% was obtained under conditions of 100bar, 333K, and 30min with a flow rate of 6gmin-1 and a moisture content of 5.5%. The substantial astaxanthin yield obtained under low-pressure conditions demonstrates that subcritical R134a is a good alternative to CO2 for extraction of astaxanthin from E. pacific.展开更多
Subcritical and supercritical water gasification of petroleum coke and asphaltene was performed at variable temperatures(350–650°C),feed concentrations(15–30 wt%)and reaction times(15–60 min).Nickel-impregnate...Subcritical and supercritical water gasification of petroleum coke and asphaltene was performed at variable temperatures(350–650°C),feed concentrations(15–30 wt%)and reaction times(15–60 min).Nickel-impregnated activated carbon(Ni/AC)was synthesized as a catalyst for enhancing syngas yields at optimal gasification conditions(650°C,15 wt%and 60 min).Structural chemistry of precursors and chars developed at different gasification temperatures was studied using physicochemical and synchrotronbased approaches such as carbon–hydrogen–nitrogen–sulfur(CHNS)analysis,thermogravimetric and differential thermogravimetric analysis(TGA/DTA),scanning electron microscopy(SEM),Fourier-Transform Infrared spectroscopy(FTIR),Raman spectroscopy,X-ray diffraction(XRD)and X-ray absorption spectroscopy(XAS).Asphaltene testified to be a better precursor for catalytic hydrothermal gasification leading to 11.97 mmol/g of total gas yield compared to petroleum coke(8.04 mmol/g).In particular,supercritical water gasification using 5 wt%Ni/AC at 650°C with 15 wt%feed concentration for 60 min resulted in 4.17 and 2.98 mmol/g of H_2from asphaltene and petroleum coke,respectively.Under the same conditions,the respective CH_4yields from catalytic gasification of asphaltene and petroleum coke were 2.54and 1.07 mmol/g.Nonetheless,asphaltene also seemed to an attractive feedstock for the production of highly aromatic chars through hydrothermal gasification.展开更多
The subcritical crack growth and fracture toughness in peridotite, lherzolite and amphibolite were investigated with double torsion test. The results show that water-rock interaction has a significant influence on sub...The subcritical crack growth and fracture toughness in peridotite, lherzolite and amphibolite were investigated with double torsion test. The results show that water-rock interaction has a significant influence on subcritical crack growth. With water-rock interaction, the crack velocity increases, while the stress intensity factor declines, which illustrates that water-rock interaction can decrease the strength of rocks and accelerate the subcritical crack growth. Based on Charlse theory and Hilling & Charlse theory, the test data were analyzed by regression and the correlation coefficients were all higher than 0.7, which shows the correlation is significant. This illustrates that both theories can explain the results of tests very well. Therefore, it is believed that the subcritical crack growth attributes to the breaking of chemical bond, which is caused by the combined effect of the tensile stress and the chemical reaction between the material at crack tip and the corrosive agent. Meanwhile, water-rock interaction has a vital effect on fracture toughness. The fracture toughness of samples under atmospheric environment is higher than that of samples immersed in water. And water-rock interaction has larger influence on fracture toughness in amphibolite than that in peridotite and lherzolite.展开更多
Starting from nonlinear equations on the F-plane containing frictional dissipation under the Boussinesq approximation, a new kind of generalized energy is proposed as the Lyapunov function, and averages are taken as a...Starting from nonlinear equations on the F-plane containing frictional dissipation under the Boussinesq approximation, a new kind of generalized energy is proposed as the Lyapunov function, and averages are taken as any functions of (x, z) instead of the commonly-used means of bilinear functions of (x, z), thereby resulting in a new criterion of generalized nonlinear symmetric stability. It shows that not only must the dissipative coefficient be greater than a certain critical value but the initial disturbance amplitude must be synchronously smaller than another marginal value as well. It follows that the latter imposes a crucial constraint on the former, thus leading to the fact that when the amplitude is bigger compared to another critical value, generalized nonlinear subcritical symmetrical instability may occur. The new criterion contributes greatly to the improvement of the previous results of its kind.展开更多
The effect of subcritical annealing temperature on microstructure and mechanical properties of SCM435 steel was investigated through changing the heating and soaking temperature as 660 °C, 680 °C, 700 °...The effect of subcritical annealing temperature on microstructure and mechanical properties of SCM435 steel was investigated through changing the heating and soaking temperature as 660 °C, 680 °C, 700 °C, 720 °C and 745 °C. The microstructure and mechanical properties of intercritically annealed specimens were analyzed. With increasing the subcritical annealing temperature from 660 °C to 720 °C, the spheroidization ratio gradually increased, and the mechanical properties, formability and Vickers hardness were improved. According to the comprehensive comparison of mechanical properties and formability, the subcritical process at soaking temperature of 680-720 °C could achieve similar annealing effect as that of intercritical process. Therefore, the subcritical annealing temperature could be set as 700 °C in practice, with the Ac1 temperature fluctuation within ±20 °C, and the applicability and stability of subcritical annealing were guaranteed in industrial application. The plant results of the cold heading showed that the subcritical annealing could replace original intercritical annealing successfully with significantly saving time and energy.展开更多
Subcritical crack growth of double torsion specimens made of marble was studied using Instron1342 type electro hydraulic servo test machine. The relations of the mode-I stress intensity factor KI versus the subcritica...Subcritical crack growth of double torsion specimens made of marble was studied using Instron1342 type electro hydraulic servo test machine. The relations of the mode-I stress intensity factor KI versus the subcritical crack growth velocity V and the fracture toughness KIC were obtained by the double torsion constant displacement load relaxation method. The behavior of subcritical crack growth was analyzed. The results show that lgKI-lgV relations of marble measured by this method accord with linear rule, i.e. the relations between subcritical crack growth velocity V and stress intensity factor KI have a power law, which is in good agreement with Charles theory. The testing results provide a basis for time-dependency of rock engineering stability.展开更多
The Hopf bifurcations of an airfoil flutter system with a cubic nonlinearity are investigated, with the flow speed as the bifurcation parameter. The center manifold theory and complex normal form method are Used to ob...The Hopf bifurcations of an airfoil flutter system with a cubic nonlinearity are investigated, with the flow speed as the bifurcation parameter. The center manifold theory and complex normal form method are Used to obtain the bifurcation equation. Interestingly, for a certain linear pitching stiffness the Hopf bifurcation is both supercritical and subcritical. It is found, mathematically, this is caused by the fact that one coefficient in the bifurcation equation does not contain the first power of the bifurcation parameter. The solutions of the bifurcation equation are validated by the equivalent linearization method and incremental harmonic balance method.展开更多
We analyze the exponential decay property of solutions of the semilinear wave equation in bounded domain Ω of R^N with a damping term which is effective on the exterior of a ball and boundary conditions of the Cauchy...We analyze the exponential decay property of solutions of the semilinear wave equation in bounded domain Ω of R^N with a damping term which is effective on the exterior of a ball and boundary conditions of the Cauchy-Ventcel type. Under suitable and natural assumptions on the nonlinearity, we prove that the exponential decay holds locally uniformly for finite energy solutions provided the nonlinearity is subcritical at infinity. Subcriticality means, roughly speaking, that the nonlinearity grows at infinity at most as a power p 〈 5. The results obtained in R^3 and RN by B. Dehman, G. Lebeau and E. Zuazua on the inequalities of the classical energy （which estimate the total energy of solutions in terms of the energy localized in the exterior of a ball） and on Strichartz＇s estimates, allow us to give an application to the stabilization controllability of the semilinear wave equation in a bounded domain of R^N with a subcritical nonlinearity on the domain and its boundary, and conditions on the boundary of Cauchy-Ventcel type.展开更多
Flow around an oscillating cylinder in a subcritical region are numerically studied with a lattice Boltzmann method(LBM). The effects of the Reynolds number,oscillation amplitude and frequency on the vortex wake modes...Flow around an oscillating cylinder in a subcritical region are numerically studied with a lattice Boltzmann method(LBM). The effects of the Reynolds number,oscillation amplitude and frequency on the vortex wake modes and hydrodynamics forces on the cylinder surface are systematically investigated. Special attention is paid to the phenomenon of resonance induced by the cylinder oscillation. The results demonstrate that vortex shedding can be excited extensively under subcritical conditions, and the response region of vibration frequency broadens with increasing Reynolds number and oscillation amplitude. Two distinct types of vortex shedding regimes are observed. The first type of vortex shedding regime(VSR I) is excited at low frequencies close to the intrinsic frequency of flow, and the second type of vortex shedding regime(VSR II)occurs at high frequencies with the Reynolds number close to the critical value. In the VSR I, a pair of alternately rotating vortices are shed in the wake per oscillation cycle,and lock-in/synchronization occurs, while in the VSR II, two alternately rotating vortices are shed for several oscillation cycles, and the vortex shedding frequency is close to that of a stationary cylinder under the critical condition. The excitation mechanisms of the two types of vortex shedding modes are analyzed separately.展开更多
The scattering process, which means the redistribution of energy fluy in modenumber space, is analyzed for internal waves propagating from the abyssal ocean onto a subcritical strait slope and then a shelf region. In ...The scattering process, which means the redistribution of energy fluy in modenumber space, is analyzed for internal waves propagating from the abyssal ocean onto a subcritical strait slope and then a shelf region. In light of Wunsch＇s work, the waves are analytically expressed as superimposition of eigensolutions distribution of energy flux in the shelf region： one is the ratio of water depth in and the other is the ratio of the slope of the internal tide rays to the topographic energy flux distribution： the energy flux is focused around one modenumber or case, the range of modenumbers where energy flux is distributed is narrow. Two parameters have evident effects on the the shelf region to that in the abyssal ocean slope. Generally, there are two patterns of focused around two modenumbers. In any case, the range of modenumbers where energy flux is distributed is narrow.展开更多
基金supported by the Strategic Priority Research Program of The Chinese Academy of Sciences(No.XDA21010202)
文摘The accelerator-driven subcritical system (ADS) with a hard neutron energy spectrum was used to study transmutation of minor actinides (MAs). The aim of the study was to improve the efficiency of MA transmutation while ensuring that variations in the effective multiplication factor (keff) remained within safe margins during reactor operation. All calculations were completed using code COUPLE3.0. The subcritical reactor was operated at a thermal power level of 800 MW, and a mixture of mononitrides of MAs and plutonium (Pu) was used as fuel. Zirconium nitride (ZrN) was used as an inert matrix in the fuel elements. The initial mass composition in terms of weight percentages in the heavy metal component (IHM) was 30.6% Pu/IHM and 69.4% MA/IHM. To verify the feasibility of this MA loading scheme, variations in keff, the amplification factor of the core, maximum power density and the content of MAs and Pu were calculated over six refueling cycles. Each cycle was of 600 days duration, and therefore, there were 3600 effective full power days. Results demonstrated that the effective transmutation support ratio of MAs was approximately 28, and the ADS was able to efficiently transmute MAs. The changes in other physical parameters were also within their normal ranges.It is concluded that the proposed MA transmutation scheme for an ADS core is reasonable.
基金financial support from the National Natural Science Foundation of China(No.52074349)China Scholarship Council(No.202206370108)the Hunan Provincial Innovation Foundation for Postgraduate(No.CX20230193).
文摘Subcritical crack growth(SCG)in fluid-rock interactions plays a crucial role in understanding crustal deformation and fracture network development.Using a double-torsion technique,the subcritical crack growth and fracture characteristics of Zhangzhou granite were investigated under fluids with different pH values.Subcritical crack growth index(SCI)was reduced in both acidic and alkaline fluids compared with the neutral environment,with reduction percentages of 9.8%e31.9%under acidic environment(pH=1-5)and 8.3%e17.5%under alkaline environment(pH=10-14),respectively.In contrast,the weakening effect of fluid pH values on critical stress intensity was less than that of SCI.Scanning electron microscopy(SEM)results showed that grain boundaries were prone to dissolution compared to the basal surface,proving that subcritical cracks preferentially propagate along the grain boundaries.Fracture toughness was insensitive to fluid pH values in the short term but sensitive to solution salinity.Considering mineral compositions and contents,a rock dissolution rate was defined,and a SCI prediction model was proposed,which was demonstrated to be capable of estimating variations in SCI under various fluid environments for different rock types and could provide valuable insights for engineering applications and environmental assessments.
文摘This study examines the nonlinear behaviors of a clamped-clamped porous pipe made of a functionally graded material(FGM)that conveys fluids and is equipped with a retaining clip,focusing on primary resonance and subcritical dynamics.The nonlinear governing equations for the FGM pipe are derived by the extended Hamilton's principle,and subsequently discretized through the application of the Galerkin method.The direct method of multi-scales is then used to solve the derived equations.A thorough analysis of various parameters,including the clip stiffness,the power-law index,the porosity,and the clip location,is conducted to gain a comprehensive understanding of the system's nonlinear dynamics.Through the analysis of the first natural frequency,the study highlights the influence of the flow velocity and the clip stiffness,while the comparisons with metallic pipes emphasize the role of FGM composition.The examination of the forced response curves reveals saddle-node bifurcations and their dependence on parameters such as the detuning parameter and the power-law index,offering valuable insights into the system's nonlinear resonant behavior.Furthermore,the frequency-response curves illustrate the hardening nonlinearities influenced by factors such as the porosity and the clip stiffness,revealing nuanced effects on the system response and resonance characteristics.This comprehensive analysis enhances the understanding of nonlinear behaviors in FGM porous pipes with a retaining clip,providing key insights for practical engineering applications in system design and optimization.
基金supported by the Chinese TMSR Strategic Pioneer Science and Technology Project(No.XDA02010000)the Frontier Science Key Program of the Chinese Academy of Sciences(No.QYZDY-SSW-JSC016)
文摘Accelerator-driven systems based on molten salt fuel have several unique advantages and features for advanced nuclear fuel utilization.The aim of this work was to study the Th-U breeding capability in such systems,known as‘‘accelerator-driven subcritical molten salt reactors’’(ADS–MSRs).Breeding capacities including conversion ratio and net^(233)U production for various subcriticalities and different minor actinides(MA)loadings were analyzed for an ADS–MSR.The results show that the subcriticality of the core has a considerable effect on the Th-U breeding.A high subcriticality is favorable to improving the conversion ratio,increasing the net^(233)U production,and reducing the doubling time.Specifically,the doubling time for k_(eff)of 0.99 is larger than 80 years,while the counterpart for k_(eff)of 0.93 is only approximately22 years.Nevertheless,in an ADS–MSR with a high initial MA loading,MA results in a non-negligible^(233)U depletion in the first two decades,while increasing the net^(233)U production compared to reactors without MA loading.During the 50 years of operation,for the subcritical reactor(k_(eff)0:97)with MA fraction increasing from 1 to 14%,the net^(233)U production increases from 3.94 to 8.24 t.
基金supported by the ‘‘Strategic Priority Research Program’’ of the Chinese Academy of Sciences(No.XDA03030102)
文摘The study of accelerator-driven subcritical reactor systems(ADSs) has been an important research topic in the field of nuclear energy for years. The main code applied in ADS research is MCNPX, which was developed by Los Alamos National Laboratory. We studied the application of the open-source Monte Carlo codes FLUKA and OpenMC to a coupled ADS calculation. The FLUKA code was used to simulate the reaction of highenergy protons with the nucleus of the target material in the ADS, which produces spallation neutrons. Information on the spallation neutrons, such as their energy, position,direction, and weight, can be recorded by a user-defined routine called FLUSCW provided by FLUKA. Then, the information was stored in an external neutron source file in HDF5 format by using a conversion code, as required by the OpenMC calculation. Finally, the fixed-source calculation function of OpenMC was applied to simulate the transport of spallation neutrons and obtain the distribution of the neutron flux in the core region. In the coupled calculation, the high-energy cross-section library JENDL4.0/HE in ACE format produced by NJOY2016 was applied in the OpenMC transport simulation. The OECD–ADS benchmark problem was calculated, and the results were compared with those obtained using MCNPX. It was found that the flux calculations performed by FLUKA–OpenMC and MCNPX were in agreement, so the coupling calculation method for ADS is reasonable and feasible.
文摘Effect of cryogenic treatment on the microstructure, hardening behavior and abrasion resistance of 14Cr2Mn2V high chromium cast iron （HCCI） subjected to subcritical treatment was investigated. The results show that cryogenic treatment after subcritical treatment can obviously improve the hardness and abrasion resistance of HCCI because abundant retained austenite is transformed into martensite and fine secondary carbides E（Fe, Cr）23 C6 ] precipitate. The amount of martensite and precipitated secondary carbide in HCCI experiencing subcritical treatment followed by cryogenic treatment was more than that experiencing the subcritical treatment followed by air cooling. When the abrasion resistance of HCCI reaches the maximum, its microstructure contains about 15 % retained austenite. Cryogenic treatment can further reduce the austenite content but the retained austenite cannot be transformed in to martensite completely.
基金Supported by the National Natural Science Foundation of China （50578091） and Shanghai Leading Academic Discipline Project （T-105）.
文摘The hydrolysis technology and reaction kinetics for amino acids production from fish proteins in subcritical water reactor without catalysts were investigated in a reactor with volume of 400 ml under the conditions of reaction temperature from 180-320℃, pressure from 5-26 MPa, and time from 5-60 rain. The quality and quantity of amino acids in hydrolysate were determined by bioLiquid chromatography, and 17 kinds of amino acids were obtained. For the important 8 amino acids, the experiments were conducted to examine the effects of reaction temperature, pressure and time on amino acids yield. The optimum conditions for high yield are obtained from the experimental results. It is found that the nitrogen and carbon dioxide atmosphere should be used for leucine, isoleucine and histidine production while the air atmosphere might be used for other amino acids. The reaction time of 30 rain and the experimental temperature of 220℃, 240℃ and 260℃ were adopted for reaction kinetic research. The total yield of amino acids versus reaction time have been examined experimentally. According to these experimental data and under the condition of water excess, the macroscopic reaction kinetic equation of fish proteins hydrolysis was obtained with the hydrolysis reaction order of 1.615 and the rate constants being 0.0017, 0.0045 and 0.0097 at 220℃, 240℃ and 260℃ respectively. The activation energy is 145.1 kJ·mol^- 1.
文摘Effects of reaction parameter on yield of benzaldehyde produced from toluene oxidization using hydrogen peroxide in subcritical water are investigated. The experimental results show that if the molar ratio of hydrogen peroxide to toluene is controlled within a reasonable range, the by-products may be neglected. The optimum technology of toluene oxidization to benzaldehyde is reaction time 60 min, reaction temperature 350℃, molar ratio of hydrogen peroxide to toluene 3.5. The yield of benzaldehyde can reach 17.2 % under the optimum condition. Research results of chemical reaction kinetics show that the consecutive reaction consists of two first-order reaction, and activation energy of these two reactions are 89 kJ·mol^-1 and 76 kJ·mol^-1 respectively,
基金the National Nature Science Foundation of China under contract No. 40876015the National High Technology Research and Development Program of China (863 Program) under contract No. 2008AA09A402
文摘Diapycnal mixing plays an important role in the ocean circulation.Internal waves are a kind of bridge relating the diapycnal mixing to external sources of mechanical energy.Difficulty in obtaining eigen solutions of internal waves over curved topography is a limitation for further theoretical study on the generation problem and scattering process.In this study,a kind of transform method is put forward to derive the eigen solutions of internal waves over subcritical topography in twodimensional and linear framework.The transform converts the curved topography in physical space to flat bottom in transform space while the governing equation of internal waves is still hyperbolic if proper transform function is selected.Thus,one can obtain eigen solutions of internal waves in the transform space.Several examples of transform functions,which convert the linear slope,the convex slope,and the concave slope to flat bottom,and the corresponding eigen solutions are illustrated.A method,using a polynomial to approximate the transform function and least squares method to estimate the undetermined coefficients in the polynomial,is introduced to calculate the approximate expression of the transform function for the given subcritical topography.
文摘The Ostwald ripening of carbide particles occurs during the process of subcritical annealing in SCM435 steel, and the degree of ripening influences the microstructure and mechanical properties of the steel. The effects of Ostwald ripening were studied by simulating different soaking time at 680 ~C using SCM435 steel. The spheroidized specimens were analysed by conducting microstructure and mechanical tests. After increasing the soaking time from 2 to 6 h at 680 ~C during subcritical annealing, the number of carbide particles and the spheroidization ratio increased gradually, and the formability was improved. When the soaking time ranged from 6 to 8 h, the spheroidization ratio was similar; however, the number of carbide particles decreased, and the formability gradually worsened. Therefore, by comprehensively comparing the microstructures and mechanical properties, the optimum soaking time was determined to be 6 h at 680 ~C during subcritical annealing to obtain preferable cold heading. In addition, the carbide particles gradually coarsened when the soaking time was extended from 2 to 8 h. A formula was presented to quantitatively characterize the progress of Ostwald ripening of the carbide particles during the subcritical annealing of SCM435 steel, and the relative error was less than 8.02%.
基金supported by the National Natural Science Foundation of China (No.31071541)
文摘Euphausia pacific is an important source of natural astaxanthin. Studies were carried out to assess the extractability of astaxanthin from E. pacific using subcritical 1, 1, 1,2-tetrafluoroethane （R134a）. To examine the effects of multiple process variables on the extraction yield, astaxanthin was extracted under various conditions of pressure （30-150bar）, temperature （303-343 K）, time （10-50rain）, flow rate （2-10gmin-1）, moisture content （5.5%-63.61%）, and particle size （0.25-0.109mm）. The results showed that the extraction yield increased with temperature, pressure, time and flow rate, but decreased with moisture content and particle size. A maximum yield of 87.74% was obtained under conditions of 100bar, 333K, and 30min with a flow rate of 6gmin-1 and a moisture content of 5.5%. The substantial astaxanthin yield obtained under low-pressure conditions demonstrates that subcritical R134a is a good alternative to CO2 for extraction of astaxanthin from E. pacific.
基金the Natural Sciences and Engineering Research Council of Canada (NSERC)Canada Research Chair program for funding this bioenergy research
文摘Subcritical and supercritical water gasification of petroleum coke and asphaltene was performed at variable temperatures(350–650°C),feed concentrations(15–30 wt%)and reaction times(15–60 min).Nickel-impregnated activated carbon(Ni/AC)was synthesized as a catalyst for enhancing syngas yields at optimal gasification conditions(650°C,15 wt%and 60 min).Structural chemistry of precursors and chars developed at different gasification temperatures was studied using physicochemical and synchrotronbased approaches such as carbon–hydrogen–nitrogen–sulfur(CHNS)analysis,thermogravimetric and differential thermogravimetric analysis(TGA/DTA),scanning electron microscopy(SEM),Fourier-Transform Infrared spectroscopy(FTIR),Raman spectroscopy,X-ray diffraction(XRD)and X-ray absorption spectroscopy(XAS).Asphaltene testified to be a better precursor for catalytic hydrothermal gasification leading to 11.97 mmol/g of total gas yield compared to petroleum coke(8.04 mmol/g).In particular,supercritical water gasification using 5 wt%Ni/AC at 650°C with 15 wt%feed concentration for 60 min resulted in 4.17 and 2.98 mmol/g of H_2from asphaltene and petroleum coke,respectively.Under the same conditions,the respective CH_4yields from catalytic gasification of asphaltene and petroleum coke were 2.54and 1.07 mmol/g.Nonetheless,asphaltene also seemed to an attractive feedstock for the production of highly aromatic chars through hydrothermal gasification.
基金Project(51374246,51474249)supported by the National Natural Science Foundation of ChinaProject(2013FJ6002)supported by the Science-Technology Project of Science-Technology Department of Hunan Province,China
文摘The subcritical crack growth and fracture toughness in peridotite, lherzolite and amphibolite were investigated with double torsion test. The results show that water-rock interaction has a significant influence on subcritical crack growth. With water-rock interaction, the crack velocity increases, while the stress intensity factor declines, which illustrates that water-rock interaction can decrease the strength of rocks and accelerate the subcritical crack growth. Based on Charlse theory and Hilling & Charlse theory, the test data were analyzed by regression and the correlation coefficients were all higher than 0.7, which shows the correlation is significant. This illustrates that both theories can explain the results of tests very well. Therefore, it is believed that the subcritical crack growth attributes to the breaking of chemical bond, which is caused by the combined effect of the tensile stress and the chemical reaction between the material at crack tip and the corrosive agent. Meanwhile, water-rock interaction has a vital effect on fracture toughness. The fracture toughness of samples under atmospheric environment is higher than that of samples immersed in water. And water-rock interaction has larger influence on fracture toughness in amphibolite than that in peridotite and lherzolite.
文摘Starting from nonlinear equations on the F-plane containing frictional dissipation under the Boussinesq approximation, a new kind of generalized energy is proposed as the Lyapunov function, and averages are taken as any functions of (x, z) instead of the commonly-used means of bilinear functions of (x, z), thereby resulting in a new criterion of generalized nonlinear symmetric stability. It shows that not only must the dissipative coefficient be greater than a certain critical value but the initial disturbance amplitude must be synchronously smaller than another marginal value as well. It follows that the latter imposes a crucial constraint on the former, thus leading to the fact that when the amplitude is bigger compared to another critical value, generalized nonlinear subcritical symmetrical instability may occur. The new criterion contributes greatly to the improvement of the previous results of its kind.
基金Item Sponsored by National Natural Science Foundation of China(51474058)Fundamental Research Funds for the Central Universities of China(N130402017)
文摘The effect of subcritical annealing temperature on microstructure and mechanical properties of SCM435 steel was investigated through changing the heating and soaking temperature as 660 °C, 680 °C, 700 °C, 720 °C and 745 °C. The microstructure and mechanical properties of intercritically annealed specimens were analyzed. With increasing the subcritical annealing temperature from 660 °C to 720 °C, the spheroidization ratio gradually increased, and the mechanical properties, formability and Vickers hardness were improved. According to the comprehensive comparison of mechanical properties and formability, the subcritical process at soaking temperature of 680-720 °C could achieve similar annealing effect as that of intercritical process. Therefore, the subcritical annealing temperature could be set as 700 °C in practice, with the Ac1 temperature fluctuation within ±20 °C, and the applicability and stability of subcritical annealing were guaranteed in industrial application. The plant results of the cold heading showed that the subcritical annealing could replace original intercritical annealing successfully with significantly saving time and energy.
基金Supported by the National Nature Science Foundation of China(50274074, 50490274) Innovation Research Project for PhD Candidate of CSU(030608)
文摘Subcritical crack growth of double torsion specimens made of marble was studied using Instron1342 type electro hydraulic servo test machine. The relations of the mode-I stress intensity factor KI versus the subcritical crack growth velocity V and the fracture toughness KIC were obtained by the double torsion constant displacement load relaxation method. The behavior of subcritical crack growth was analyzed. The results show that lgKI-lgV relations of marble measured by this method accord with linear rule, i.e. the relations between subcritical crack growth velocity V and stress intensity factor KI have a power law, which is in good agreement with Charles theory. The testing results provide a basis for time-dependency of rock engineering stability.
基金Project supported by the National Natural Science Foundation of China (No.10772202)the Doctoral Foundation of Ministry of Education of China (No.20050558032)the Natural Science Foundation of Guangdong Province (Nos.07003680 and 05003295)
文摘The Hopf bifurcations of an airfoil flutter system with a cubic nonlinearity are investigated, with the flow speed as the bifurcation parameter. The center manifold theory and complex normal form method are Used to obtain the bifurcation equation. Interestingly, for a certain linear pitching stiffness the Hopf bifurcation is both supercritical and subcritical. It is found, mathematically, this is caused by the fact that one coefficient in the bifurcation equation does not contain the first power of the bifurcation parameter. The solutions of the bifurcation equation are validated by the equivalent linearization method and incremental harmonic balance method.
文摘We analyze the exponential decay property of solutions of the semilinear wave equation in bounded domain Ω of R^N with a damping term which is effective on the exterior of a ball and boundary conditions of the Cauchy-Ventcel type. Under suitable and natural assumptions on the nonlinearity, we prove that the exponential decay holds locally uniformly for finite energy solutions provided the nonlinearity is subcritical at infinity. Subcriticality means, roughly speaking, that the nonlinearity grows at infinity at most as a power p 〈 5. The results obtained in R^3 and RN by B. Dehman, G. Lebeau and E. Zuazua on the inequalities of the classical energy （which estimate the total energy of solutions in terms of the energy localized in the exterior of a ball） and on Strichartz＇s estimates, allow us to give an application to the stabilization controllability of the semilinear wave equation in a bounded domain of R^N with a subcritical nonlinearity on the domain and its boundary, and conditions on the boundary of Cauchy-Ventcel type.
基金Project supported by the National Natural Science Foundation of China(No.11402129)the Zhejiang Provincial Natural Science Foundation of China(No.LY17A020002)
文摘Flow around an oscillating cylinder in a subcritical region are numerically studied with a lattice Boltzmann method(LBM). The effects of the Reynolds number,oscillation amplitude and frequency on the vortex wake modes and hydrodynamics forces on the cylinder surface are systematically investigated. Special attention is paid to the phenomenon of resonance induced by the cylinder oscillation. The results demonstrate that vortex shedding can be excited extensively under subcritical conditions, and the response region of vibration frequency broadens with increasing Reynolds number and oscillation amplitude. Two distinct types of vortex shedding regimes are observed. The first type of vortex shedding regime(VSR I) is excited at low frequencies close to the intrinsic frequency of flow, and the second type of vortex shedding regime(VSR II)occurs at high frequencies with the Reynolds number close to the critical value. In the VSR I, a pair of alternately rotating vortices are shed in the wake per oscillation cycle,and lock-in/synchronization occurs, while in the VSR II, two alternately rotating vortices are shed for several oscillation cycles, and the vortex shedding frequency is close to that of a stationary cylinder under the critical condition. The excitation mechanisms of the two types of vortex shedding modes are analyzed separately.
基金This study was financially supported by the National Nature Science Foundation of China(Grant No.40406008)the Foundation for Open Proiects of the Key Lab of Physical Oceanography,Ministry of Education,China(Grant No.200309).
文摘The scattering process, which means the redistribution of energy fluy in modenumber space, is analyzed for internal waves propagating from the abyssal ocean onto a subcritical strait slope and then a shelf region. In light of Wunsch＇s work, the waves are analytically expressed as superimposition of eigensolutions distribution of energy flux in the shelf region： one is the ratio of water depth in and the other is the ratio of the slope of the internal tide rays to the topographic energy flux distribution： the energy flux is focused around one modenumber or case, the range of modenumbers where energy flux is distributed is narrow. Two parameters have evident effects on the the shelf region to that in the abyssal ocean slope. Generally, there are two patterns of focused around two modenumbers. In any case, the range of modenumbers where energy flux is distributed is narrow.
