Potential of minicomputer-array processor system for nonlinear finite-element analysis

A study is made of the potential of using a minicomputer-array processor system for efficient solution of large-scale nonlinear finite-element problems. A PRIME 750 is used as the host computer, and a software simulator residing on the PRIME is employed to assess the performance of the Floating Point Systems AP-120B array processor. Major hardware characteristics of the system such as virtual memory, parallel and pipeline processing are reviewed and the interplay between various hardware components is examined. Effective use of the minicomputer-array processor system for nonlinear analysis requires the following: (a) proper selection of the computational procedure and the capability to vectorize the numerical algorithms; (b) reduction of I/O operations; and (c) overlapping host and array-processor operations. A detailed discussion is given of techniques to accomplish each of these tasks. Two benchmark problems with 1715 and 3230 degrees of freedom, respectively, are selected to measure the anticipated gain in speed obtained by using the proposed algorithms on the array processor. Results of the study of the two benchmarks indicate that these two problems would run faster on a PRIME 750 coupled with the AP-120B than on the PRIME 750 alone. The 1715 degree-of-freedom problem would run about five times faster, and the 3230 degree-of-freedom problem would run about ten times faster. New advances in array-processor hardware are outlined, and possible improvements in the computational algorithms are discussed. The combination of the two can significantly enhance the effectiveness of the minicomputer-array processor system for large-scale nonlinear analysis.     

Minimum sensitivity pole placer

A method is presented for designing a constant-gain state feedback controller for assigning the closed-loop poles of a linear time-invariant multivariable system to desired locations which at the same time minimizes the sensitivity of these poles to variation in the parameters of the plant. The design procedure is illustrated by examples.     

Spectral analysis of a sampling optical time-domain reflectometer

A spectral analysis is presented for the backscatter signal of optical time-domain reflectometers (OTDR). Periodic spatial fluctuations in the fiber attenuation produce modulation sidebands in the frequency spectrum of the backscatter signal. Applying the sampling technique to OTDR leads to a considerable improvement of the signal-to-noise ratio (S/N) due to spectrum compression, as a tradeoff with the measurement time. It gives a performance equivalent to digital averaging. Design examples are given at wavelengths of 0.85, 1.3, and 1.55 μm. A practical setup of a sampling OTDR is described     

Analysis of self-dual excited synchronous machine. I. Developmentof the general mathematical model and steady-state performanceexperimental verification

The use of the dual excitation system for improving the overall performance of a self-excited synchronous machines is considered, along with the replacement of the compound transformer and rectifier bridge by a potential transformer and thyristor bridge for the self-excitation system. The output DC voltage of the bridge is controlled over a wide range by an automatic feedback control circuit to vary the firing angle of the thyristors in such a way that the terminal voltage is sustained at a constant value. The mathematical models for two distinctive alternatives of the excitation system are derived. The mathematical model thus derived is suitable for transient, dynamic as well as steady-state analysis. However it should be modified to investigate the steady-state and dynamic performance. Exact steady-state operating points are achieved by solving the steady-state equations obtained from the general model. Charts describing the performance of the self-dual excited synchronous machine under steady-state operation for the two alternatives of the excitation system have been calculated at different values of the power factor, i.e., the turns ratio of the transformer and the ratio of field currents. The experimental results obtained on a 7.6 kVA induction machine converted to a d-q synchronous machine confirm the validity and accuracy of the analysis and mathematical models developed     

Inhibition of the corrosion of steel by acid dihydrazides

The corrosion inhibitory properties of homologous series of acid dihydrazides were studied. Gasometry, potentiodynamic polarization and impedance measurements were recorded for mild steel specimens immersed in 1.0 M H₂SO₄ or a mixture of 1.0 M H₂SO₄ + 1.0 M Na₂SO₄ having the same ionic strength with a pH range from zero to 7. Effect of presence of different concentrations of oxalic, malonic, succinic or pimelic dihydrazide on the corrosion rate of steel in the above solutions were investigated. The results indicated that the protection efficiency of the acid dihydrazides increased with the increase of the number of the methylene groups in the acid dihydrazide molecule. The results are discussed on the basis of the change of each, of the electron density of the donating atoms, of the inhibitor molecules, and the orientation of the inhibitor at the metal surface with the molecular structure of the inhibitor.     

Probabilistic Studies of Generation Capacity (Part I)

A simplified model is constructed and analyzed to determine the power flow through channels of finite capacity when the supply and demand at the separate nodes are probabilistic. The supplies are generators of different sizes scattered throughout the system; their outages are treated as independent random events. Failure to meet demand is due to forced outages of generators and to inadequate transmission facilities. The model divides an interconnected power system into subsystems and tie lines. It calculates the cost of unsatisfied demand and sudden supply interruption. The difference between generation and demand in the different subsystems is correlated, and this has an effect on the interconnection and reserve requirements. A cost analysis is carried out to obtain the optimum allocation of generators in the model.     

Scaling and Roundoff in Fixed-Point Implementation of Control Algorithms

The analysis and design of digital controllers on microprocessors using fixed-point arithmetic have been considered. Three scaling techniques are applied to the design of digital controllers in such a way as to avoid overflow and to optimize the signal-to-roundoff noise ratio. Both the scaler and the multivariable cases are treated. Statistical estimates of the steady-state roundoff and quantization errors are derived.     

Activation of low dose silicon implants in GaAs by multiply scanned electron beams

Low dose implants of Si+ into semi-insulating GaAs have been annealed with the multiply scanned electron beam processing system. The activation of ions was about 55%, with a high peak concentration and a carrier mobility of 3800 cm2/Vs. The samples were unencapsulated and showed no surface degradation after annealing.     

Sufficient conditions for controllability of a class of distributed parameter systems

In the paper we present certain results on the question of controllability for (i) linear evolution equations (parabolic and hyperbolic) with distributed controls and (ii) a class of linear parabolic equations with boundary controls.     

Block-oriented programmable design with switching networkinterconnect

A block-oriented programmable design with switching network interconnect is proposed for fast turn-around, low manufacturing cost, and layout-independent high-speed systems. We introduce the architecture and investigate the constraints and properties originated from the architecture. We show that routability is the most crucial concern for a successful design, and propose objective functions as well as algorithms for switching network optimization. The mapping for the circuits is performed by partitioning, placement, and routing using a maximum matching method. The integration of the whole system demonstrates excellent results in terms of circuit usage