DEMCMC-GPU: An Efficient Multi-Objective Optimization Method with GPU Acceleration on the Fermi Architecture

In this paper, we present an efficient method implemented on Graphics Processing Unit (GPU), DEMCMC-GPU, for multi-objective continuous optimization problems. The DEMCMC-GPU kernel is the DEMCMC algorithm, which combines the attractive features of Differential Evolution (DE) and Markov Chain Monte Carlo (MCMC) to evolve a population of Markov chains toward a diversified set of solutions at the Pareto optimal front in the multi-objective search space. With parallel evolution of a population of Markov chains, the DEMCMC algorithm is a natural fit for the GPU architecture. The implementation of DEMCMC-GPU on the pre-Fermi architecture can lead to a ^~25 speedup on a set of multi-objective benchmark function problems, compare to the CPU-only implementation of DEMCMC. By taking advantage of new cache mechanism in the emerging NVIDIA Fermi GPU architecture, efficient sorting algorithm on GPU, and efficient parallel pseudorandom number generators, the speedup of DEMCMC-GPU can be aggressively improved to ^~100.     

Microscale materials testing using MEMS actuators

Small size scale and high resolutions in force and displacement measurements make MEMS actuators appropriate for micromechanical testing. In this paper, for the first time, we present methodologies for uniaxial tensile and cantilever bending testing of both micrometer- and submicrometer-scale freestanding specimens using MEMS actuators. We also introduce dry fabrication processes for the specimens. The methodologies allow freestanding single or multilayered thin-film specimens to be fabricated separately from the MEMS actuators. For the uniaxial tension test, tensile forces are applied by lateral comb drive actuators capable of generating a total load of 383 μN at 40 V with resolutions on the order of 3 nN. A similar actuator is used in the bending test, with load resolution of 58 nN and spring constant of 0.78 N/m. The tensile testing methodology is demonstrated with the testing of a 110-nm-thick freestanding aluminum specimen. The cantilever bending experiment is performed on a 100-nm-thick aluminum specimen. The experimental setups can be mounted in a SEM (and also in a TEM after modifications for tensile testing) for in situ observation of materials behavior under different environmental conditions. Remarkable strengthening is observed in all the specimens tested compared to their bulk counterparts in both tensile and bending experiments. Experimental results highlight the potential of MEMS actuators as a new tool for materials research     

On-line tuning strategy for model predictive controllers

This paper presents an intuitive on-line tuning strategy for linear model predictive control (MPC) algorithms. The tuning strategy is based on the linear approximation between the closed-loop predicted output and the MPC tuning parameters. By direct utilization of the sensitivity expressions for the closed-loop response with respect to the MPC tuning parameters, new values of the tuning parameters can be found to steer the MPC feedback response inside predefined time-domain performance specifications. Hence, the algorithm is cast as a simple constrained least squares optimization problem which has a straightforward solution. The simplicity of this strategy makes it more practical for on-line implementation. Effectiveness of the proposed strategy is tested on two simulated examples. One is a linear model for a three-product distillation column and the second is a non-linear model for a CSTR. The effectiveness of the proposed tuning method is compared to an exiting offline tuning method and showed superior performance.     

The effect of axisymmetric two-dimensional magnetic field on the configuration of vacuum-arc plasma

An experimental investigation is made of the effect of axisymmetric two-dimensional magnetic field on the forming of plasma and on the configuration of cathode spots in a vacuum-arc discharge. It is demonstrated that a magnetic field with a transverse (relative to the discharge axis) component has a significant effect on the shape of plasma column and on the rate of expansion of the cathode spot region. In a magnetic field, arc plasma has the form of truncated cone expanding toward the anode. The cathode spots take up a part of the cathode area which decreases with increasing magnetic field. Arguments are given in support of the assumption that the arrangement of cathode spots and the form of arc plasma are defined by the minimum principle similar to the Steinbeck principle. In so doing, the displacement of spots is caused by their emergence in a new region corresponding to a lower arc voltage. Also discussed is the mechanism associated with retrograde motion of cathode spot in view of the effect of azimuthal magnetic field on the axial component of current and of the effect of axial magnetic field on the azimuthal component of current.     

Sol–gel preparation of boron-containing cordierite Mg2(Al4−xBx)Si5O18 and its crystallization

Five cordierite-based powders were investigated regarding their thermal and crystallization behaviors. The powders were obtained from amorphous gels having nominal compositions of 2Mg : xAl : (4 − x)B : 5Si where x = 4 down to 0. Thermal gravimetry analysis of the dry gels showed some absorbed water and decomposition of organic ligands in addition to network condensation. Gradual substitution of B for Al in the dried gel powders showed a new band in their infrared spectra corresponding to triangular BO₃, whereas the bands corresponding to Al vanished. This also showed a noticeable effect on the crystallization trends, type and stability of cordierite. Cordierite crystallized in samples of B/Al ratio up to 1 while protoenstatite predominated in samples of higher B/Al ratios. In addition, some silica minerals, with little amorphous phase, were formed. Incorporation of boron and increase in temperature enhanced the transformation of γ cordierite to its form.     

Failure analysis of superheater tube supports of the primary reformer in a fertilizer factory

A failure analysis of superheater tube supports of the primary reformer in a local fertilizer factory is presented. A number of tube supports failed at approximately half of their designed service life. Following the failure, the factory was visited, and relevant information and samples were collected. The samples were investigated in the laboratory by chemical analysis, macro- and microhardness measurements, macro-and micrometallographic examinations, and X-ray diffractometry. The analysis showed the supports were fabricated from HH-type heat-resisting alloy and that the failure mode was high-temperature creep. The microstructure of the alloy showed the presence of massive intergranular as well as intragranular σ-phase and intragranular needle-shaped M₂₃C₆ carbides. It was also concluded from the formation of massive σ-phase in the tube that the failure was hastened because the supports were operating at approximately 800 °C. The alloy composition led to the formation of σ-phase under the operating conditions of the reformer, and the use of an alloy with a higher concentration of austenite-stabilizing element(s) could have avoided the failure.     

An efficient and robust integration technique for applied random vibration analysis

The mode-based finite element formulation of the equations of motion is usually adopted for linear random vibration analysis (RVA). In general, the RVA of large systems requires a large number of numerical integrations which is very time-consuming for a reasonable level of desired accuracy. Moreover, conventional numerical integration methods may fail to converge when the integrands are highly oscillatory due to slow propagation velocities. In this paper, a robust general-purpose RVA integration technique which can overcome these drawbacks is presented. Multi-point base and nodal excitations including wave passage effect and frequency-independent spatial correlation can be taken into account in the analysis. The proposed technique is based on the closed-form solutions for polynomial-type power spectral density functions and has been verified to be efficient and accurate for many engineering problems. This paper describes the implementation details, presents two examples taken from engineering applications and demonstrates the dramatic time-saving in the computation compared to numerical integration solutions. Response statistics, such as standard deviation of structural responses, are computed and displayed over the entire structures for these examples.     

An exact solution for the bending of thin rectangular plates with uniform, linear, and quadratic thickness variations

In this paper, the analysis of the titled problem is based on classical thin-plate theory, and its numerical solution is carried out by using the small parameter method and Lévy-type approach. The thin rectangular plate considered herein is simply supported on two opposite edges. The boundary conditions at the other two edges may be quite general, and between these two edges the plate may have varying thickness. Closed-form solutions have been developed for the static response of isotropic rectangular plates with non-uniform thickness variation and subjected to arbitrary loading. The accuracy of the present model is demonstrated via problems for which the exact solutions and numerical results are available, and results are also compared with those obtained by using the finite-difference method.