The purpose is to accurately predict the performance of foil bearing and achieve accurate results in the design of foil bearing structure.A new type of foil bearing with surface microstructure is used as experimental ...The purpose is to accurately predict the performance of foil bearing and achieve accurate results in the design of foil bearing structure.A new type of foil bearing with surface microstructure is used as experimental material.First,the lubrication mechanism of elastic foil gas bearing is analyzed.Then,the numerical solution process of the static bearing capacity and friction torque is analyzed,including the discretization of the governing equation of rarefied gas pressure based on the non-dimensional modified Reynolds equation and the over relaxation iteration method,the grid planning within the calculation range,the static solution of boundary parameters and static solution of the numerical process.Finally,the solution program is analyzed.The experimental data in National Aeronautics and Space Administration(NASA)public literature are compared with the simulation results of this exploration,so as to judge the accuracy of the calculation process.The results show that under the same static load,the difference between the minimum film thickness calculated and the test results is not obvious;when the rotor speed of the bearing is 60000 r/min,the influence of the boundary slip effect increases with the increase of the micro groove depth on the flat foil surface;when the eccentricity or the micro groove depth of the bearing increases,the bearing capacity will be strengthened.When the eccentricity is 6µm and 14µm,the viscous friction torque of the new foil bearing increases significantly with the increase of the depth of the foil micro groove,but when the eccentricity is 22µm,the viscous friction torque does not change with the change of the depth of the foil micro groove.It shows that the bearing capacity and performance of foil bearing are improved.展开更多
For the large sparse block two-by-two real nonsingular matrices, we establish a general framework of structured preconditioners through matrix transformation and matrix approximations. For the specific versions such a...For the large sparse block two-by-two real nonsingular matrices, we establish a general framework of structured preconditioners through matrix transformation and matrix approximations. For the specific versions such as modified block Jacobi-type, modified block Gauss-Seidel-type, and modified block unsymmetric (symmetric) Gauss-Seidel-type preconditioners, we precisely describe their concrete expressions and deliberately analyze eigenvalue distributions and positive definiteness of the preconditioned matrices. Also, we show that when these structured preconditioners are employed to precondition the Krylov subspace methods such as GMRES and restarted GMRES, fast and effective iteration solvers can be obtained for the large sparse systems of linear equations with block two-by-two coefficient matrices. In particular, these structured preconditioners can lead to high-quality preconditioning matrices for some typical matrices from the real-world applications.展开更多
The Judd-Ofelt theoretic transition intensity parameters A（tp）k of luminescence of rare-earth ions in solids are important for the quantitative analysis of luminescence.It is very difficult to determine them with em...The Judd-Ofelt theoretic transition intensity parameters A（tp）k of luminescence of rare-earth ions in solids are important for the quantitative analysis of luminescence.It is very difficult to determine them with emission or absorption spectra for a long time.A ＂full profile fitting＂ method to obtain A（tp）k in solids with its emission spectrum is proposed,in which the contribution of a radiative transition to the emission spectrum is expressed as the product of transition probability,line profile function,instrument measurement constant and transition center frequency or wavelength,and the whole experimental emission spectrum is the sum of all transitions.In this way,the emission spectrum is expressed as a function with the independent variables intensity parameters A（tp）k,full width at half maximum（FWHM） of profile functions,instrument measurement constant,wavelength,and the Huang-Rhys factor S if the lattice vibronic peaks in the emission spectrum should be considered.The ratios of the experimental to the calculated energy lifetimes are incorporated into the fitting function to remove the arbitrariness during fitting A（tp）k and other parameters.Employing this method obviates measurement of the absolute emission spectrum intensity.It also eliminates dependence upon the number of emission transition peaks.Every experiment point in emission spectra,which usually have at least hundreds of data points,is the function with variables A（tp）k and other parameters,so it is usually viable to determine A（tp）k and other parameters using a large number of experimental values.We applied this method to determine twenty-five A（tp）k of Yb（3＋） in GdTaO4.The calculated and experiment energy lifetimes,experimental and calculated emission spectrum are very consistent,indicating that it is viable to obtain the transition intensity parameters of rare-earth ions in solids by a full profile fitting to the ions＇ emission spectrum.The calculated emission cross sections of Yb（3＋）：GdTaO4 also indicate that the F-L formula gives larger values in the wavelength range with reabsorption.展开更多
In the sense of the nonlinear multisplitting and based on the principle of suffi-ciently using the delayed information, we propose models of asynchronous parallelaccelerated overrelaxation iteration methods for solvin...In the sense of the nonlinear multisplitting and based on the principle of suffi-ciently using the delayed information, we propose models of asynchronous parallelaccelerated overrelaxation iteration methods for solving large scale system of non-linear equations. Under proper conditions, we set up the local convergence theoriesof these new method models.展开更多
文摘The purpose is to accurately predict the performance of foil bearing and achieve accurate results in the design of foil bearing structure.A new type of foil bearing with surface microstructure is used as experimental material.First,the lubrication mechanism of elastic foil gas bearing is analyzed.Then,the numerical solution process of the static bearing capacity and friction torque is analyzed,including the discretization of the governing equation of rarefied gas pressure based on the non-dimensional modified Reynolds equation and the over relaxation iteration method,the grid planning within the calculation range,the static solution of boundary parameters and static solution of the numerical process.Finally,the solution program is analyzed.The experimental data in National Aeronautics and Space Administration(NASA)public literature are compared with the simulation results of this exploration,so as to judge the accuracy of the calculation process.The results show that under the same static load,the difference between the minimum film thickness calculated and the test results is not obvious;when the rotor speed of the bearing is 60000 r/min,the influence of the boundary slip effect increases with the increase of the micro groove depth on the flat foil surface;when the eccentricity or the micro groove depth of the bearing increases,the bearing capacity will be strengthened.When the eccentricity is 6µm and 14µm,the viscous friction torque of the new foil bearing increases significantly with the increase of the depth of the foil micro groove,but when the eccentricity is 22µm,the viscous friction torque does not change with the change of the depth of the foil micro groove.It shows that the bearing capacity and performance of foil bearing are improved.
文摘For the large sparse block two-by-two real nonsingular matrices, we establish a general framework of structured preconditioners through matrix transformation and matrix approximations. For the specific versions such as modified block Jacobi-type, modified block Gauss-Seidel-type, and modified block unsymmetric (symmetric) Gauss-Seidel-type preconditioners, we precisely describe their concrete expressions and deliberately analyze eigenvalue distributions and positive definiteness of the preconditioned matrices. Also, we show that when these structured preconditioners are employed to precondition the Krylov subspace methods such as GMRES and restarted GMRES, fast and effective iteration solvers can be obtained for the large sparse systems of linear equations with block two-by-two coefficient matrices. In particular, these structured preconditioners can lead to high-quality preconditioning matrices for some typical matrices from the real-world applications.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51172236,51502292,51272254,51102239,61205173,and 61405206)
文摘The Judd-Ofelt theoretic transition intensity parameters A（tp）k of luminescence of rare-earth ions in solids are important for the quantitative analysis of luminescence.It is very difficult to determine them with emission or absorption spectra for a long time.A ＂full profile fitting＂ method to obtain A（tp）k in solids with its emission spectrum is proposed,in which the contribution of a radiative transition to the emission spectrum is expressed as the product of transition probability,line profile function,instrument measurement constant and transition center frequency or wavelength,and the whole experimental emission spectrum is the sum of all transitions.In this way,the emission spectrum is expressed as a function with the independent variables intensity parameters A（tp）k,full width at half maximum（FWHM） of profile functions,instrument measurement constant,wavelength,and the Huang-Rhys factor S if the lattice vibronic peaks in the emission spectrum should be considered.The ratios of the experimental to the calculated energy lifetimes are incorporated into the fitting function to remove the arbitrariness during fitting A（tp）k and other parameters.Employing this method obviates measurement of the absolute emission spectrum intensity.It also eliminates dependence upon the number of emission transition peaks.Every experiment point in emission spectra,which usually have at least hundreds of data points,is the function with variables A（tp）k and other parameters,so it is usually viable to determine A（tp）k and other parameters using a large number of experimental values.We applied this method to determine twenty-five A（tp）k of Yb（3＋） in GdTaO4.The calculated and experiment energy lifetimes,experimental and calculated emission spectrum are very consistent,indicating that it is viable to obtain the transition intensity parameters of rare-earth ions in solids by a full profile fitting to the ions＇ emission spectrum.The calculated emission cross sections of Yb（3＋）：GdTaO4 also indicate that the F-L formula gives larger values in the wavelength range with reabsorption.
文摘In the sense of the nonlinear multisplitting and based on the principle of suffi-ciently using the delayed information, we propose models of asynchronous parallelaccelerated overrelaxation iteration methods for solving large scale system of non-linear equations. Under proper conditions, we set up the local convergence theoriesof these new method models.
