Dynamic Matrices

C. R. Cutier and B. L. Ramaker, "Dynamic Matrix Control A Computer Control Algorithm," Proceedings of Joint Auto. Control Conference, Paper... 

A. M. Morshedi, C. R. Cutier, and T. A. Skrovanek, "Optimal Solution of Dynamic Matrix Control with Linear Programming Techniques,"... 

The current widespread interest in MFC techniques was initiated by pioneering research performed by two industrial groups in the 1970s. Shell Oil (Houston, TX) reported their Dynamic Matrix Control (DMC) approach in 1979, while a similar technique, marketed as IDCOM, was published by a small French company, ADERSA, in 1978. Since then, there have been over one thousand applications of these and related MFC techniques in oil refineries and petrochemical plants around the world. Thus, MFC has had a substantial impact and is currently the method of choice for difficult multivariable control problems in these industries. However, relatively few applications have been reported in other process industries, even though MFC is a veiy general approach that is not limited to a particular industiy. 

One important class of nonlinear programming techniques is called quadratic programming (QP), where the objective function is quadratic and the constraints are hnear. While the solution is iterative, it can be obtained qmckly as in linear programming. This is the basis for the newest type of constrained multivariable control algorithms called model predic tive control. The dominant method used in the refining industiy utilizes the solution of a QP and is called dynamic matrix con-... 

In order to determine the phonon dispersion of CuZn and FeaNi we made use of an expanded tight binding theory from Varma and Weber . In the framework of a second order perturbation theory the dynamical matrix splits in two parts. The short range part can be treated by a force constant model, while the T>2 arising from second order perturbation theory is given by... 

Frequencies m and polarisation vectors are determined by the diago-nalisation of the dynamical matrix... 

The sum is called the partially Fourier transformed dynamical matrix, which depends only on Q, and For each wave vector Q the normal mode frequencies of the crystal can be found by setting the secular determinant equal to zero ... 

Due to the hermitian character of the dynamical matrix, the eigenvalues are real and the eigenvector satisfies the orthonormality and closure conditions. The coupling coefficients are given by... 

Finally, a brief discussion is given of a new type of control algorithm called dynamic matrix control. This is a time-domain method that uses a model of the process to calculate future changes in the manipulated variable such that an objective function is minimized. It is basically a least-squares solution. 

There is one method that is based on a time-domain model. It was developed at Shell Oil Company (C, R. Cutler and B. L. Kamaker, Dynamic Matrix Control A Computer Control Algorithm, paper presented at the 86th National AlChE Meeting, 1979) and is called dynamic matrix control (DMC). Several other methods have also been proposed ihat are quite similar. The basic idea is to use a time-domain step-response model of the process to calculate the future changes in the manipulated variable that will minimize some performance index. Much of the explanation of DMC given in this section follows the development presented by C. C. Yu in his Ph.D. thesis (Lehigh University, 1987). 

Dynamic matrix control uses time-domain step-response models (called convolution models). As sketched in Fig. 8.18, the response (x) of a process to a unit step change in the input (Ami = ) made at time equal zero can be described by the values of x at discrete points in time (the fc, s shown on the figure). At r nTJ, the value of X is h r,. If Affii is not equal to one, the value of x at f = n7 is b j Aibi, The complete response can be described using a finite number (NP) values of b coefficients. NP is typically chosen such that the response has reached 90 to 95 percent of its final value. 

Calculate the JVC values of the future changes in the manipulated variables from Eq. (8.37) using the dynamic matrix 4 given in Eq. (8.28),... 

Undoubtedly the most popular multivariable controller is the multivariable extension of dynamic matrix control. We developed DMC for a SISO loop in Chap. 8. The procedure was a fairly direct least-squares computational one that solved for the future values of the manipulated variable such that some performance index was rninirnized. 

Morshedi, A. M., Universal dynamic matrix control, Chemical Process Control Conf. Ill (Morari and McAvoy, eds.). CACHE Corp., 1986, p. 547. 

The system comprised of equations 3.62 and 3.63 has solutions only when the determinant of coefficients and 2 (secular determinant) is zero. The coefficient matrix, or dynamic matrix, is... 

The elements of D represent the sum over all unit cells of the interaction between a pair of atoms. D has 3n x 3n elements for a specific q and j, though the numerical value of the elements will rapidly decrease as pairs of atoms at greater distances are considered. Its eigenvectors, labeled e ( fcq), where k is the branch index, represent the directions and relative size of the displacements of the atoms for each of the normal modes of the crystal. Eigenvector ejj Icq) is a column matrix with three rows for each of the n atoms in the unit cell. Because the dynamical matrix is Hermitian, the eigenvectors obey the orthonormality condition... 

For a molecular crystal, the internal modes tend to be q independent and thus appear as horizontal lines in Fig. 2.1 n is then equal to the number of molecules M in the cell, leading to a considerable simplification. The resulting dynamical matrix has 6M x 6M elements, considering both translational and rotational motions, and atom-atom potential functions may be used for its evaluation. Dispersion curves obtained in this manner for anthracene and naphthalene, are illustrated in Fig. 2.2. 

The dynamic matrix L can be obtained by the full matrix analysis, solving eq. (8) [42-47] ... 

The left and right eigenvectors are equal only when the populations at all spin sites are the same. As a result of the invariance of modal matrices to matrix functions, the dynamic matrix L can be written as... 

Thus, full matrix analysis comprises calculation of eigenvectors and eigenvalues of the dynamic matrix over the eigenvectors and eigenvalues of the normalized spectral matrix A(rni)A(0) . Then,... 

Equation (27) expresses an error in the dynamic matrix element Lij obtained from full matrix analysis if the error in peak volumes is Aa [50]. It also assumes that volume errors are equal for all peaks and are uncorrelated Aa is volume error normalized to the volume of a single spin at Tm = 0. Modem computer programs (Matlab, Mathematica, Mapple) can calculate the dynamic matrix from eq. (11) directly. 

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