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371 results about "Analytical expressions" patented technology

Analytic expression. An analytic expression (or expression in analytic form) is a mathematical expression constructed using well-known operations that lend themselves readily to calculation.

Life evaluation method for modular multilevel converter

The invention discloses a life evaluation method for a modular multilevel converter (MMC). The life evaluation method comprises the following steps: reading year-round temperature data of a running natural environment of the MMC and power data input into the MMC; performing analytic calculation on the average value and the effective value of the current of sub-modules IGBT and Diode of the MMC; calculating the average loss power Ploss,T and Ploss,D of the sub-modules IGBT and Diode of the MMC within the fundamental frequency period; calculating the average temperature rise Tja of a semiconductor device within the working frequency period by use of a Forster network model to obtain the average junction temperature value Tj of IGBT modules (IGBT modules, IGBTs, including IGBT and Diode); modifying fitting calculation of loss of the IGBTs according to the average junction temperature of the IGBTs; calculating the extreme values of the function temperature within the working frequency and counting the year-round fundamental frequency junction temperature cycle; counting fluctuation information of the year-round low-frequency junction temperature; and calculating the failure number Nf of the fundamental frequency and the low frequency of the semi-conductor device by use of a Bayerer life model, and obtaining the life of the MMC in combination with operation conditions. The life evaluation method can reliably forecast the life of the MMC, can effectively improve the forecasting calculation speed through obtaining an analytical expression of both current and the junction temperature, and has the characteristics of project operational capability and the like.
Owner:ELECTRIC POWER RESEARCH INSTITUTE, CHINA SOUTHERN POWER GRID CO LTD +1

Five-axis side milling machining process parameter design method

InactiveCN102129232AAccurate transient cutting thicknessImprove accuracyNumerical controlNumerical controlAnalytical expressions
The invention discloses a five-axis side milling machining process parameter design method, belongs to the technology of numerical control (NC) machining, and solves the problem that real machining conditions cannot be reflected in cutting force calculation in the conventional process parameter design method. The method comprises the following steps of: tool path planning, cutting force calculation and process parameter optimization; in the tool path planning step, an NC code is generated by using computer-aided manufacturing (CAM) software; in the cutting force calculation step, first, a continuous tool path is generated from the NC code; then, a cutting thickness is obtained; and finally, the cutting force is calculated according to the cutting thickness; and in the process parameter optimization step, whether the calculated cutting force is not greater than a design threshold is judged; if the calculated cutting force is not greater than the design threshold, the NC code, the cutting depth and a feed rate are taken as input parameters; and otherwise, an NC code is regenerated. In the method, the real machining conditions are reflected by utilizing a tool enveloping surface analytical expression and the obtained transient cutting thickness is more accurate, so that the accuracy of the calculation of the cutting thickness and the cutting force is improved, and reliable assurance is provided for precisely and efficiently machining a spatial curved surface.
Owner:HUAZHONG UNIV OF SCI & TECH

Method for actually compensating for geometrical errors of five-axis numerical control tooth manufacturing machine tool through inverse kinematics

The invention provides a method for actually compensating for geometrical errors of a five-axis numerical control tooth manufacturing machine tool through the inverse kinematics. The method includes the steps of building a space geometrical error model containing position unrelated errors and position related errors on the basis of a homogeneous coordinate transformational matrix, and deducing a processing code analytical expression containing the geometrical errors from the space geometrical error model according to the characteristics of the homogeneous coordinate transformational matrix. Theoretical cutter location data is modified by 12 pose deviations (6 static pose deviations and 6 movement pose deviations) of a cutter relative to a workpiece. The geometrical errors of the machine tool can be compensated for by substituting the position unrelated errors, the position related errors and the modified cutter location data into the processing code analytical expression for compensating for the geometrical errors of the machine tool, and meanwhile the12 pose deviations of the cutter relative to the workpiece are modified. The error compensation method is simple in compensation process, easy to understand, small in calculation amount, high in compensation efficiency and wide in application range, and the basic compensation concept of the method is suitable for numerical control machine tools of various types.
Owner:NANJING GONGDA CNC TECH

Avoidance manoeuvre generator for an aircraft

A method for automatically determining an avoidance maneuver in an automatic collision avoidance system of an aircraft. A maximum kinematic acceleration envelope is determined by determining a multitude of avoidance maneuver angle kinematic acceleration pairs in a kinematic acceleration plane, and interpolating gaps between points, thus creating a curve. The curve is called maximum kinematic acceleration envelope. The curve may also be approximated by an analytical expression. An adjusted kinematic acceleration envelope is formed in the plane by forming a new envelope. The new envelope at each point laying closer to or at the same distance from an origin as the points of the maximum kinematic acceleration envelope and such that there is only one value of the kinematic acceleration a for a given avoidance maneuver angle. An avoidance maneuver angle is received for which a suitable bank angle and a suitable normal load is to be determined. Determining The magnitude of the kinematic acceleration a corresponding to the adjusted kinematic acceleration envelope for the avoidance maneuver angle is determined by reading the envelope curve, or if the curve is an analytical expression, calculating the curve by using the analytical expression. The normal load is determined based on the kinematic acceleration, and the avoidance maneuver angle. The bank angle is determined based on the kinematic acceleration and the avoidance maneuver angle.
Owner:SAAB AB

Method for predicting milling force of five-axis numerical control side milling

The invention provides a method for predicting milling force of five-axis numerical control side milling. The method comprises the steps that firstly, the current cutter spacing cutter-workpiece meshing area is acquired based on the distance field method, points and normal directions on a cutting edge of the current cutter spacing are converted to a previous cutter spacing cutter coordinate system, the analytical expression of a non-transformation cuttings thickness is obtained according to the line and face intersection method, and milling force coefficients are acquired through three-axis single-tooth milling experiment calibration; secondly, the cutter is dispersed into a plurality of slice infinitesimals in the axial direction, and the tangential milling force, the radial milling force and the axial milling force of the slice infinitesimals are obtained through calculation according to cutter geometrical parameter information, cutter-workpiece meshing area information, non-transformation cutting thicknesses calculated value and the milling force coefficients; lastly, the force coordinates are converted into the X-axis direction, the Y-axis direction and the Z-axis direction, and integration is carried out on the slice infinitesimals in the axial direction to obtain the five-axis side milling force predicting value at current time. By means of the method, the accuracy and efficiency of prediction and calculation on the milling force of five-axis side milling are improved.
Owner:SHANGHAI JIAO TONG UNIV

Self-adapting wave form retrieval method through utilization of zero offset vertical seismic profile (VSP) data to estimate speed and Q value

The invention discloses a self-adapting wave form retrieval method through utilization of zero offset vertical seismic profile (VSP) data to estimate speed and Q value. The method includes a first step of selecting undisturbed a segment of a first-motion wave in a self-adapting mode to the maximum extent according to the signal to noise ratio of the actual VSP data and the degree of a direct wave disturbed by an upward traveling wave, and fully utilizing effective information to construct an objective function, a second step of improving the sensitiveness of the objective function to changes of the Q value through proper construction of a data weighting matrix according to the feature that the Q value is more difficult to estimate than other parameters; a third step of adopting a recently developmental self-adapting multiplication regularization method to improve the ill-conditional problem of nonlinear inversion, and limiting the value range of the unknown parameters through nonlinear transformation, and a fourth step of inferring analytical expressions of elements of a jacobian matrix so as to decrease the calculated amount of inverse problems. Compared with a spectrum ratio method and a wavelet envelope peak value instantaneous frequency method, the method is relatively smaller in influence of the upward traveling wave, stronger in anti-noise performance, and higher in accuracy of inverse parameters.
Owner:XI AN JIAOTONG UNIV

Fracture-cavity reservoir inter-well communication passage and flow parameter characterization method

InactiveCN105117511AEnabling Quantitative Computational CharacterizationIn line with the real situationSpecial data processing applicationsConcentration curveMathematical model
The present invention relates to the technical field of reservoir description in oil field development, in particular to a fracture-cavity inter-well communication passage and flow parameter characterization method. The method comprises the following steps of: (A) establishing an analytical expression of describing a fracture-cavity reservoir inter-well flow rule; (B) establishing a tracing production concentration curve fitting mathematical model; (C) performing curve fitting model solution; and according to principles of the three steps, compiling fracture-cavity reservoir tracing curve fitting software, performing fitting on a theoretical tracing curve and an actually measured tracing curve by a method of adjusting a parameter on a software interface, and simultaneously carrying out calculation to obtain mass mik, a flow velocity vik, an orifice area Aik and a flow duct length lik of a fracture-cavity injection tracer so as to implement characterization on a communication passage and a flow parameter. According to the present invention, an established model of describing the flow rule of the fracture-cavity reservoir tracer further accords with the true situations; quantitative calculation characterization on the fracture-cavity reservoir inter-well communication passage and the flow parameter is implemented; and in the fitting process, automatic fitting of a computer and parameter regulation of a worker are combined.
Owner:SOUTHWEST PETROLEUM UNIV

Online prediction method for remaining life of electromechanical equipment under situation of two-stage degradation

The invention discloses an online prediction method for the remaining life of electromechanical equipment under the situation of two-stage degradation. The online prediction method can be applied to online service life prediction and health management of mechanical equipment and electric and electronic devices. The method comprises the steps that a Wiener process model serves as a basic degradation model of an object, and a degradation drifting coefficient is expanded into a state and described with a closed oblique Wiener process. A new algorithm is proposed to overcome prediction deviation caused by the Markovian feature of a common Wiener process. For state estimation in the online prediction stage, an iteration filter algorithm is proposed to obtain an analytical expression of updated states. On parameter estimation, a two-stage parameter estimation algorithm is proposed. An analytical expression related to remaining life prediction results is obtained by using updated states and parameters. The model proposed in the method better conforms to the general degradation rules, more accurate online remaining life prediction results can be obtained, and great significance is achieved on fault prediction and health management in engineering.
Owner:ZHEJIANG UNIV +1

Method and system for planning escape route for spacecraft

The invention discloses a method and a system for planning an escape route for a spacecraft. The method comprises steps of: 1) constructing a Hamilton function and a terminal constraint function of differential game based on a near circle deviation equation; 2) solving a co-state equation of the differential game to obtain an evolutionary formula for co-state quantity analysis; 3) solving an optimal control equation of the differential game to obtain an analytical expression of optimal control quantity; 4) solving a cross-section condition of the differential game to obtain terminal values ofHamilton quantity and co-state quantity; 5) solving a nonlinear equation set iteratively to obtain a saddle point of the differential game; and 6) planning the escape route for the spacecraft according to the saddle point of the differential game. According to the method and the system for planning the escape route for the spacecraft, the saddle point of the differential game of chase and escape in the spacecraft can be quickly solved, and by an optimal control law of the chase and escape corresponding to the saddle point, space threat can be evaded and a game route can be planned for the spacecraft. Therefore, the method and the system have the advantages of being correct and reasonable in design, fast in calculation, good in applicability to actual tasks, and the like.
Owner:NAT UNIV OF DEFENSE TECH

Method and device for judging stability of grid-connected sub-synchronous oscillation of double-fed induction generator

The invention relates to a method and device for judging the stability of grid-connected sub-synchronous oscillation of a double-fed induction generator. The method comprises the steps of setting positive sequence harmonic voltage and positive sequence harmonic current of a stator of the double-fed induction generator according to stator phase-a voltage, stator phase-a current and rotor phase-a current of the double-fed induction generator; determining an output voltage expression of a current regulation link according to the positive sequence harmonic voltage and the positive sequence harmonic current; establishing a stator-side impedance analytical expression of the double-fed induction generator according to the positive sequence harmonic voltage, the positive sequence harmonic currentand the output voltage expression so as to obtain double-fed induction generator-side impedance characteristics; building a grid-side impedance model so as to obtain grid-side impedance characteristics; establishing a characteristic function equation of the double-fed induction generator-side impedance characteristics and the grid-side impedance characteristics; and solving the characteristic function equation so as to quantitatively judge the oscillation frequency and damping level of the double-fed induction generator. The oscillation frequency and damping level of can be quantitatively judged according to the method and device.
Owner:STATE GRID LIAONING ELECTRIC POWER RES INST +2
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