Since Thermal error in precision CNC machine tools cannot be ignored, it is essential to construct a simple and effective thermal error compensation mathematical model. In this paper, three modeling methods are introduced in detail. The first is multiple linear regression model; the second is congruence model, which combines multiple linear regression model with AR model of its residual error; and the third is autoregressive distributed lag model(ADL), which is compared and analyzed. Multiple linear regression analysis is used most commonly in thermal error compensation, since it is a simple and quick modeling method. But thermal error is nonlinear and interactive, so it is difficult to model a precise least squares model of thermal error. The congruence model and autoregressive distributed lag model belong to time series analysis method which has the advantage of establishing a precise mathematical model. The distinctions between the two models are that: the congruence model divides the parameter into two parts to estimate them respectively, but autoregressive distributed lag model estimates parameter uniformly, so congruence model is less accurate than autoregressive distributed lag model in modeling. This paper, based upon an actual example, concludes that autoregressive distributed lag model for thermal error of precision CNC machine tools is a good way to improve modeling accuracy.
The transport-reaction process characteristics during product layer formation in flue gas desulfurization was studied theoretically and experimentally.The transport-reaction process could be described by Thiele number incorporating the influences of chemical reaction resistance and diffusion resistance.It was found that the conversion rate at the end of the process decreased with increasing Thiele number.The conversion rate increased with increasing temperature and porosity, and also depended upon pore geometry and distribution.
The static corrosion tests and the dynamic simulative tests show that the complex formula YSW-120 has a good corrosion inhibition effect in high hard recirculating cooling water,in which concentration of Ca2+ can be as high as 2000 mg/L,hardness can reach 3000 mg/L,by adding acid.
Based on the analysis for the bauxite resources and existing grade composite ore of two main bauxite producing area in domestic,this article introduces the distribution and exploitation of bauxite resources in China and puts forward the critical situation that the existing resources mainly are diafpore with low grade composite,difficult process,high energy consumption,advising the possibility to utilize the overseas bauxite and alternative sources.
Residual statics corrections can be formulated as a linear inverse problem. Usually, solving this problem involves a large ill-posed matrix inverse calculation. Therefore, a fast algorithm that can handle the ill-posed problem is needed in practice. In this paper, the least-squares QR factorization (LSQR), based on Lanczos and QR factorization, is presented. This method works on rectangular matrix and is a rapidly converging and stable algorithm for the ill-posed problem.
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