1,463 research outputs found
Large scale optimization of transonic axial compressor rotor blades
[First Paragraphs]
In the present work the Multipoint Approximation Method (MAM) by Toropov et al. (1993) has been applied to
the shape optimization of an existing transonic compressor rotor (NASA rotor 37) as a benchmark case.
Simulations were performed using the Rolls-Royce plc. PADRAM-HYDRA system (Shahpar and Lapworth 2003,
Lapworth and Shahpar 2004) that includes the parameterization of the blade shape, meshing, CFD analysis, postprocessing,
and objective/constraints evaluation. The parameterization approach adopted in this system is very
flexible but can result in a large scale optimization problem.
For this pilot study, a relatively coarse mesh has been used including around 470,000 nodes. The
parameterization was done using 5 engineering blade parameters like axial movement of sections along the engine
axis in mm (XCEN), circumferential movements of sections in degrees (DELT), solid body rotation of sections in
degrees (SKEW), and leading/trailing edge recambering (LEM0/TEMO) in degrees. The design variables were
specified using 6 control points at 0 % (hub), 20%, 40%, 60%, 80%, and 100% (tip) along the span. Thus the total
number of independent design variables N was 30. B-spline interpolation was used through the control points to
generate smooth design perturbations in the radial direction
Additive SMILES-Based Carcinogenicity Models: Probabilistic Principles in the Search for Robust Predictions
Optimal descriptors calculated with the simplified molecular input line entry system (SMILES) have been utilized in modeling of carcinogenicity as continuous values (logTD50). These descriptors can be calculated using correlation weights of SMILES attributes calculated by the Monte Carlo method. A considerable subset of these attributes includes rare attributes. The use of these rare attributes can lead to overtraining. One can avoid the influence of the rare attributes if their correlation weights are fixed to zero. A function, limS, has been defined to identify rare attributes. The limS defines the minimum number of occurrences in the set of structures of the training (subtraining) set, to accept attributes as usable. If an attribute is present less than limS, it is considered “rare”, and thus not used. Two systems of building up models were examined: 1. classic training-test system; 2. balance of correlations for the subtraining and calibration sets (together, they are the original training set: the function of the calibration set is imitation of a preliminary test set). Three random splits into subtraining, calibration, and test sets were analysed. Comparison of abovementioned systems has shown that balance of correlations gives more robust prediction of the carcinogenicity for all three splits (split 1: rtest2=0.7514, stest=0.684; split 2: rtest2=0.7998, stest=0.600; split 3: rtest2=0.7192, stest=0.728)
Aerodynamic shape optimization of a low drag fairing for small livestock trailers
Small livestock trailers are commonly used to transport animals from farms to market
within the United Kingdom. Due to the bluff nature of these vehicles there is great potential
for reducing drag with a simple add-on fairing. This paper explores the feasibility of
combining high-fidelity aerodynamic analysis, accurate metamodeling, and efficient
optimization techniques to find an optimum fairing geometry which reduces drag, without
significantly impairing internal ventilation. Airflow simulations were carried out using
Computational Fluid Dynamics (CFD) to assess the performance of each fairing based on
three design variables. A Moving Least Squares (MLS) metamodel was built on a fifty-point
Optimal Latin Hypercube (OLH) Design of Experiments (DoE), where each point
represented a different geometry configuration. Traditional optimization techniques were
employed on the metamodel until an optimum geometrical configuration was found. This
optimum design was tested using CFD and it matched closely to the metamodel prediction.
Further, the drag reduction was measured at 14.4% on the trailer and 6.6% for the
combined truck and trailer
Implementation of Discrete Capability into the enhanced Multipoint Approximation Method for solving mixed integer-continuous optimization problems
Multipoint approximation method (MAM) focuses on the development of metamodels for the objective and constraint functions in solving a mid-range optimization problem within a trust region. To develop an optimization technique applicable to mixed integer-continuous design optimization problems in which the objective and constraint functions are computationally expensive and could be impossible to evaluate at some combinations of design variables, a simple and efficient algorithm, coordinate search, is implemented in the MAM. This discrete optimization capability is examined by the well established benchmark problem and its effectiveness is also evaluated as the discreteness interval for discrete design variables is increased from 0.2 to 1. Furthermore, an application to the optimization of a lattice composite fuselage structure where one of design variables (number of helical ribs) is integer is also presented to demonstrate the efficiency of this capability
Implementation of a Heuristic Method of Decomposition of Partial Boolean Functions
An original heuristic algorithm of sequential two-block decomposition of partial Boolean functions is
researched. The key combinatorial task is considered: finding of suitable partition on the set of arguments, i. e.
such one, on which the function is separable. The search for suitable partition is essentially accelerated by
preliminary detection of its traces. Within the framework of the experimental system the efficiency of the algorithm
is evaluated, the boundaries of its practical application are determined
Magnetic field induced transition in a wide parabolic well superimposed with superlattice
We study a parabolic quantum wells (PQW) with
square superlattice. The magnetotransport in PQW with
intentionally disordered short-period superlattice reveals a surprising
transition from electrons distribution over whole parabolic well to
independent-layer states with unequal density. The transition occurs in the
perpendicular magnetic field at Landau filling factor and is
signaled by the appearance of the strong and developing fractional quantum Hall
(FQH) states and by the enhanced slope of the Hall resistance. We attribute the
transition to the possible electron localization in the x-y plane inside the
lateral wells, and formation of the FQH states in the central well of the
superlattice, driven by electron-electron interaction.Comment: 5 pages, 4 figure
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