76 results about "Periodic boundary conditions" patented technology

A noise prediction scheme provides a method of predicting an output noise variance resulting from a spatial filtering transformation. For a given input image signal with a known input noise variance, a periodic model is developed. The periodic model defines periodic boundary conditions for the input image signal based on the principal that the input image signal is repeated in each direction. In this manner, pixel values are defined about either side of the input image signal boundaries in either one, two, or three dimensions. A spatial filtering transformation includes convoluting the input image signal with an impulse response of a filter. Autocavariances at different points in time or lags of the input image signal are also determined. The number of autocovariances is determined by the nature of the spatial filtering transformation. The noise prediction scheme predicts an output noise variance resulting from the spatial filtering transformation based on the input noise variance, the autocovariances, and the periodic boundary conditions of the input image signal.

The invention relates to a method for predicting residual stiffness of a two-dimensional braided ceramic matrix composite material after oxidation. The stiffness refers to elastic deformation resistance ability of the material under stress. By analyzing the stiffness of each component of the material, stress and strain distribution in the material can be determined. Therefore, the invention provides the method capable of accurately predicting the residual stiffness of the two-dimensional braided ceramic matrix composite material after oxidation. A kinetic model considering fiber oxidation is proposed, and based on this, a microscale model considering fiber oxidation and a mesoscale model of the two-dimensional braided ceramic matrix composite material are established. With the adoption of a finite element method, the residual stiffness of the material after oxidation is calculated by applying a periodic boundary condition. According to the method, the residual stiffness of the material in different oxidation temperature intervals at different oxidation time can be accurately predicted and does not need to be tested by a large amount of manpower and material resources through tests, so that a large amount of test costs are reduced.

The invention provides a method for generating a random structure of a continuous fiber composite material and predicting the elastic performance of the continuous fiber composite material. The method comprises the following steps: generating a fiber model by a particle swarm algorithm, and optimizing the fiber model according to fiber jumping treatment to obtain particle space random distribution information for generating a three-phase RVE finite element model; and performing finite element simulation operation on the three-phase RVE finite element model to obtain a prediction result. Based on a representative volume element generation strategy of the particle swarm algorithm, the distance among fibers is controlled by the particle swarm algorithm in the process of generating the representative volume element, the requirement for the material volume percentage is fulfilled while fiber random distribution is ensured; and based on efficient generation of the representative volume unit and a homogenization theory, an elasticity prediction finite element model is established, a periodic boundary condition is applied, and the elasticity performance prediction result of the material can be obtained by microscomic finite element simulation, so that the efficiency of elasticity performance prediction is improved.

The invention relates to a finite element simulation method capable of removing a microwave tube high-frequency circuit in a pseudo-DC mode, comprising the flowing steps: (A) using a zero electric displacement vector as an electric field constraint equation and acquiring an integrated form of the electric field constraint equation according to an boundary value problem of an electromagnetic field in a microwave tube high-frequency circuit and acquiring a functional equation of the boundary value problem of the electromagnetic field through a standard variation principle of a finite element method; and (B) necessarily ensuring the match between grids on a main surface and grids on a secondary surface on a peripheral boundary when solving a solution domain and considering a pseudo-periodic boundary condition by adopting a dissection solution domain of tetrahedral grids. The invention has the advantages that the finite element simulation method can greatly improve the accuracy, the efficiency and the robustness of microwave tube high-frequency system simulation.

The invention provides a multi-dimensional predicting method for strength of a braided ceramic base composite material. Firstly a parameterization method is used for establishing a braided ceramic base composite material single-cell model which comprises yarns and a matrix, and then period grid dividing is performed. Afterwards a mesomechanics method is used for simulating the mechanics behavior of the yarn unit. Furthermore a strain conversion matrix is used for converting a yarn element stiffness matrix from a local coordinate system to an integral coordinate system. Finally through applyingan increment type periodic boundary condition, a micro-stress and a strain field of a single cell are calculated. A volume averaging method is used for obtaining a microscopic stress and strain of the braided ceramic base composite material. If a failure unit band which penetrates through the single cell is formed, failure of the braided ceramic base composite material is determined, and the single-cell average stress is the strength of the braided ceramic base composite material. According to the multi-dimensional predicting method, the multidimensional analysis method in which macrography and mesography are combined is utilized. The strength of the braided ceramic base composite material can be accurately predicted without dependence to a large number of experiments with time consumption and high cost.

The invention discloses a method for comparison test of thermal performance of two walls and a test device. The test device comprises a test frame, two walls with different properties, temperature sensors, heat flow sensors and a data collecting and recording terminal. The method comprises the steps of collecting parameters of internal temperature distribution and surface heat flow transfer and the like under same heat transfer boundary conditions, of the two walls with different properties in the test frame, by utilizing the temperature sensors and the heat flow sensors; and carrying out comparative analysis on difference between the two walls on the aspects of the attenuation and the delay of temperature waves, heat transfer coefficient thermal performance parameters according to test data, wherein by applying the alternating temperature waves, specific values of the attenuation coefficients and the delay time of the two test walls can also be obtained respectively under periodic boundary conditions. The method disclosed by the invention has the advantages that not only can the advantages and the disadvantages of the thermal performance of the two walls be directly compared, butalso the test error can be reduced and the accuracy of the comparative analysis is improved. The device has the advantages of being simple in structure, low in manufacturing cost and convenient to install.

The invention provides a one-dimensional photonic crystal beam structure band gap designing method based on a wavelet finite element model. The wavelet finite element model uses the section B sample wavelet to be combined with a finite element method, a BSWI scaling function is used for replacing the polynomial interpolation of the traditional finite element, and the unit cell technology and periodic boundary condition PBCs are combined to build a real symmetrical feature value problem about the one-dimensional photonic crystal dispersing structure, so the band gap feature of the photonic crystal is obtained by calculating. The wavelet finite element model of the one-dimensional photonic crystal beam structure band gap calculation is capable of absorbing the advantages of the wavelet multi-scale approach feature and the complex solution domain of the finite element method, and obtaining a numerical calculation model with high precision and rapid convergence. The provided wavelet finite element model of the one-dimensional photonic crystal beam structure band gap design has the advantages of high precision and rapid convergence, and is suitable for the one-dimensional photonic crystal beam structure band gap design.

The invention provides an image denoising method based on high-order overlapping group sparse total variation, and provides an overlapping group sparse total variation image recovery method based on high-order regularization term constraint on the basis of a traditional first-order overlapping group sparse total variation technology. According to the first-order overlapping combination technology,a total variation gradient of each conventional pixel is popularized into a combination gradient, so that the difference between a smooth region and an edge region is improved, and a high-order regular term can more effectively alleviate a'step effect 'from second-order or higher-order gradient information, so that the protection on the edge of the image is improved. In order to improve the operation speed of image restoration, transverse and longitudinal differential matrix operation of an image is modeled as convolution operation, periodic boundary conditions are combined, so that two-dimensional fast Fourier transform is skillfully applied to an image restoration problem, and point multiplication operation on a frequency domain is used for replacing large matrix operation on an airspace.

The invention discloses a value calculating method of a thermal residual stress of a fiber reinforced composite material under a low temperature. The method comprises the following steps of a, based on fiber random distribution, constructing a representative volume element (RVE) of a composite material; b, dividing a network for the composite material and acquiring a finite element model requiredby calculation; c, endowing the finite element model to thermal/mechanical performance parameters of a fiber and a matrix material which are related to a temperature; d, adding a periodic boundary condition for the finite element model; and e, applying a temperature load to the finite element model and calculating and acquiring the thermal residual stress. By using the method, operation is simpleand prediction precision is high; the method can play an important role in predicting the low temperature residual stress of the composite material so as to lay the foundation for the application of the composite material in a low temperature field.

The invention discloses a two-dimensional photonic crystal plate structure band gap design method based on a wavelet finite element model. The wavelet finite element model combines interval B-spline wavelets and a finite element method, uses a BSWI scaling function to replace the polynomial interpolation of a traditional finite element and combines the unit cell technology and periodic boundary conditions PBCs to build the real symmetric eigenvalue problem of a two-dimensional photonic crystal discrete structure so as to calculate to obtain the band gap features of photonic crystals. The wavelet finite element model for calculating the two-dimensional photonic crystal plate structure band gap has the advantages of capability of processing complex solution domains and wavelet multi-dimensional approximation properties of the finite element method and can obtain the numerical calculation model high in precision and fast in convergence. The wavelet finite element model for designing the two-dimensional photonic crystal plate structure band gap is high in calculation precision, fast in convergence and suitable for the designing of the two-dimensional photonic crystal plate structure band gap.

The invention discloses a method for analyzing microscomic mechanical damage evolution of a fan blade composite material. Parametric modeling of the RVE structure model of the representative volume unit is achieved, the accuracy of damage initiation and crack generation of the described composite material component phase and the accuracy of the expansion evolution process are ensured, and for theboundary condition of the RVE model, an Abaqus-Python interface is utilized, periodic boundary conditions of the RVE model are quickly and smoothly applied, and a reasonable microscopic field quantityis obtained; according to the invention, isotropic damage of the matrix is considered; a single damage variable influencing the material rigidity is used; an interface phase is introduced into microscopic damage analysis of a composite material, a damage model is compiled into a UMAT material subprogram in combination with a subprogram interface of Abaqus finite element software, and simulation verification is carried out on the damage process of the blade material under the transverse stretching effect in Abaqus/Standard. The trend and expansion condition of microscopical volume unit interface cracks under the action of transverse tensile load and the influence of periodic temperature on the mechanical response are simulated.

The invention belongs to the field of electromagnetic wave absorption and radiation control, and in particular relates to a design method of a terahertz broadband absorbing metamaterial. According to the effective medium theory, and using CST microwave studio to obtain S parameters through frequency domain simulation, the periodic unit structure is at x Both the and y directions are periodically distributed, and are set as periodic boundary conditions. Combining the parameters S11 and S21 obtained by scanning, the impedance value is calculated. By changing the period of the unit structure and the size of the metal thin film and dielectric material, the corresponding absorption frequency is adjusted, and multiple metal thin films and dielectric materials are cross-stacked in one unit period, so that the absorption lines corresponding to different resonant circular frustums are superimposed. The invention can effectively broaden the absorption spectrum of the terahertz frequency band, so that the frequency band with an absorption rate exceeding 90% can be widened, and meanwhile, a certain high relative absorption bandwidth can be guaranteed. And the first 9 absorption peaks are caused by the interior of the unit structure, so they are not affected by the period.

The invention discloses a seven point frequency domain finite difference method for analyzing periodic inhomogeneous dielectric waveguide characteristic modes. The seven point frequency domain finite difference method for analyzing the periodic inhomogeneous dielectric waveguide characteristic modes mainly includes steps: firstly, performing finite difference mesh dissection, enabling an interface of inhomogeneous dielectric to coincide with a dissection unit, and using a computational node as a dissection unit peak; then, converting a field equation of an electromagnetic field real frequency domain in the inhomogeneous dielectric into a field equation of a complex frequency domain by using periodic boundary conditions and an equivalent resonant cavity theory; achieving dispersion for the field equation of the inhomogeneous dielectric by using tangential continuity boundary conditions of a field on eight dissection unit interfaces adjacent to the computational node and using seven computational node interpolation values adjacent to the computational node; obtaining frequency and field distribution of the characteristic modes by using a characteristic value decomposition technology through the dispersed field equation; establishing a function relationship between a propagation constant of each waveguide mode and working frequency, and thereby guiding design of a periodic inhomogeneous dielectric waveguide. The seven point frequency domain finite difference method for analyzing the periodic inhomogeneous dielectric waveguide characteristic modes solves the problem that uneven dielectric distribution in the propagation direction can not be achieved in the prior art.

The invention discloses a method and device for calculating the shielding effectiveness of an electromagnetic shielding net and a storage medium, and the method comprises the steps: obtaining a distribution model diagram of the electromagnetic shielding net with periodic distribution characteristics and uniform plane electromagnetic waves, and obtaining subunits of the electromagnetic shielding net; establishing a geometric model containing continuous periodic boundary conditions according to the subunits; dividing the geometric model into an electromagnetic shielding net space, an external space and a shielded space; placing the subunits in an electromagnetic shielding net space, placing the uniform planar electromagnetic waves in an external space, and presetting an observation point ina shielded space; setting simulation model parameters according to the geometric model and the electromagnetic shielding net to obtain a simulation model; performing numerical calculation on the simulation model to obtain the electric field intensity at the observation point; and obtaining the shielding effectiveness of the electromagnetic shielding net according to a shielding effectiveness calculation formula. The shielding effectiveness of the electromagnetic shielding net with the periodic distribution characteristic and any shape can be calculated, and the calculation result is more accurate.

The invention relates to a method for multi-scale detection of a composite material liquid storage container. The steps are: obtaining the mesoscopic geometric shape of the material through optical equipment, using image processing technology to extract the mesoscopic geometric parameters of the material; The three-dimensional reconstruction method is used to establish the material unit cell, and the comprehensive performance parameters of the material are predicted by loading the periodic boundary conditions; the composite material liquid storage container model is established by using the material comprehensive performance parameters and the design size of the liquid storage container. The fluid-solid coupling is realized in the form of a function, and the safety detection of the collision impact of the liquid storage container is carried out with the numerical reproduction of the airdrop test; for the damaged area of ​​the liquid storage container, the microscopic damage behavior of the material is detected through the unit cell model, and the macroscopic damage behavior of the composite material is obtained. performance parameters. The invention solves the performance detection problem of the composite material liquid storage container, greatly shortens the equipment development time, and reduces the randomness of experiments and capital investment.

The invention belongs to the technical field of quantum image processing and relates to a quantum image convolution method. The method includes steps: S1, changing transverse or vertical coordinates of a pixel point of an original image by adoption of a coordination transformation mode and periodic boundary conditions to obtain information of the pixel point in neighborhood pixel points; S2, multiplying the neighborhood pixel points with corresponding weights on a template to obtain corresponding weight products, and adding all weight products to obtain convolution of the pixel point; S3, repeatedly executing the step S1-S2 on each pixel point of the image to obtain convolution results of any templates and images. By a quantum adder and a quantum multiplier, convolution of any templates and images on a quantum computer is realized, and the quantum image convolution method is greatly superior to a classical algorithm.

The invention discloses a rapid optimization design method and system based on a cylindrical surface conformal array, and belongs to the technical field of microwaves, and the method comprises the following steps: S1, setting modeling conditions; S2, selecting the number of optimization units; S3, optimizing the model by using an algorithm. According to the method, the cylinder array model is built by combining the periodic boundary condition and PML. The minimum number of units needed for optimization is found by utilizing the mutual coupling relation of the circumference of the cylinder, andthen optimization is carried out through algorithms such as heredity and the like. The cylinder array is modeled in a mode of combining the periodic boundary condition and the PML. The complexity ofthe model can be greatly reduced, the modeling efficiency is effectively improved. Mutual coupling strength relationship between the antenna units is utilized. The minimum number of units is selectedto optimize the central active standing wave. The time required by simulation can be greatly reduced, optimization design can be conveniently carried out on the antenna through algorithms such as heredity, and the method is worthy of being popularized and used.

The invention discloses an active brightness enhancement film, a preparation method thereof and a method for analyzing the polarization of the active brightness enhancement film based on FDTD. The active brightness enhancement film comprises at least one layer of quantum dot doped polymer film and at least one layer of metal nanorod containing polymer film, wherein metal nanorods in the metal nanorod containing polymer film are uniform in orientation and are periodically arranged. The brightness enhancement film is unique in structure, efficient red and green fluorescence emitted by quantum dots can be obtained, and high-efficiency polarized light in a light source wave band can also be obtained. The active brightness enhancement film is economical in cost and excellent in performance, and the market monopoly formed by dual brightness enhancement films (DBEF) of 3M radicals is broken through. The invention also provides the method for analyzing the polarization of the active brightness enhancement film based on FDTD, and 3D-FDTD periodic boundary conditions are used, so that a great deal of computing time is reduced, and the method is an effective tool applicable for analyzing polarization behaviors of the nanorods.

The invention discloses a method for generating a geometric model of a two-dimensional high-volume-fraction earth-rock mixed material, which comprises the following steps of: firstly, generating randomly distributed particles in any shape according to a grading curve; performing Minkowski sum operation on the particles, and controlling the minimum gap between the adjacent particles; achieving transition from particles to clusters by an overlapped discrete element cluster method, and randomly placing the particles in a certain area; assigning a linear contact model, performing DEM simulation, separating overlapped clusters, and recording initial positions, displacement and rotation of the clusters; and finally, reconstructing the model based on the displacement and rotation information. The theoretical maximum volume fraction of any particle shape is easy to obtain, meanwhile, the boundary distribution problem of the particles and the contact problem between the particles are solved, in addition, the periodic boundary condition in the DEM provides a simple implementation method for the periodic microstructure, the generated model better conforms to the actual situation. Reliability of a subsequent numerical method test research result can be improved, and the method has relatively high application significance.

The invention belongs to the technical field of numerical calculation of surface acoustic wave filters, and particularly relates to a frequency response characteristic analysis method of a surface acoustic wave resonator based on a dimensionality reduction PDE model. The method comprises the steps of: obtaining the structural data of a surface acoustic wave resonator; inputting the data into a dimension reduction PDF model to obtain a partial differential equation set representing the surface acoustic wave resonator; solving the partial differential equation set by adopting a finite element method to obtain a system matrix representing the surface acoustic wave resonator; adopting a finite element degree-of-freedom compression method and an order reduction technology to eliminate the degree-of-freedom needing no attention on the system matrix, and adopting periodic boundary conditions to eliminate the degree-of-freedom of left and right boundaries to obtain a system matrix equation after the degree-of-freedom is eliminated; solving the system matrix equation to obtain frequency response characteristics of the surface acoustic wave resonator. According to the method, irrelevant degree-of-freedom are eliminated by adopting the finite element degree-of-freedom compression method and the order reduction technology, and a uniform residual sound field can be realized in a directivity area.

The invention discloses a method for simulating linear polymer crystallization. The method comprises the following steps of building a polymer model, simulating crystallization, building a polymer coarse-grained model, and setting particle position, particle initial velocity, bond length and bond angle; setting a corresponding force field for the polymer model, i.e. adopting LJ-96 potential for intermolecular forces, and adopting corresponding energy potential for bond length and bond angle; initially setting corresponding periodic boundary conditions for the model; sequentially performing down balance when T* is equal to 0.1, temperature raising NPT movement from T* which is equal to 0.1 to T* which is equal to 1.6, NPT balance movement when T* is equal to 1.6, temperature reducing NPT movement from T* which is equal to 1.6 to T* which is equal to 0.4 under the experiment temperature, and NPT balance movement when T* is equal to 0.4 on the model. According to the computer simulation method provided by the invention, the defect of the traditional observation experiment method is overcome; integral and real-time observation can be performed, and the result shows that computer simulated data can be well identical to the traditional experiment data.