111 research outputs found
Hybridization of multi-objective deterministic particle swarm with derivative-free local searches
The paper presents a multi-objective derivative-free and deterministic global/local hybrid algorithm for the efficient and effective solution of simulation-based design optimization (SBDO) problems. The objective is to show how the hybridization of two multi-objective derivative-free global and local algorithms achieves better performance than the separate use of the two algorithms in solving specific SBDO problems for hull-form design. The proposed method belongs to the class of memetic algorithms, where the global exploration capability of multi-objective deterministic particle swarm optimization is enriched by exploiting the local search accuracy of a derivative-free multi-objective line-search method. To the authors best knowledge, studies are still limited on memetic, multi-objective, deterministic, derivative-free, and evolutionary algorithms for an effective and efficient solution of SBDO for hull-form design. The proposed formulation manages global and local searches based on the hypervolume metric. The hybridization scheme uses two parameters to control the local search activation and the number of function calls used by the local algorithm. The most promising values of these parameters were identified using forty analytical tests representative of the SBDO problem of interest. The resulting hybrid algorithm was finally applied to two SBDO problems for hull-form design. For both analytical tests and SBDO problems, the hybrid method achieves better performance than its global and local counterparts
Are random coefficients needed in particle swarm optimization for simulation-based ship design?
Simulation-based design optimization (SBDO) methods integrate computer simu-
lations, design modification tools, and optimization algorithms. In hydrodynamic applications,
often objective functions are computationally expensive and likely noisy, their
derivatives are not directly provided, and the existence of local minima cannot be
excluded a priori, which motivates the use of derivative-free global optimization
algorithms. This type of algorithms (such as Particle Swarm Optimization, PSO) usually follow
a stochastic formulation, requiring computationally expensive numerical experiments in order to
provide statistically significant re- sults. The objective of the present work is to investigate
the effects of using (versus suppressing) random coefficients in PSO for ship hydrodynamics
SBDO. A comparison is shown of 1,000 random PSO to deterministic PSO (DPSO) using 12
well-known scalable test problems, with dimensionality ranging from two to fifty. A total of
588 test functions is considered and more than 500,000 optimization runs are performed and
evaluated. The results are discussed based on the probability of success of random PSO
versus DPSO. Finally, a comparison of random PSO to DPSO is shown for the hull-form
optimization of the DTMB 5415 model. In summary, test functions show the robustness of DPSO, which
outperforms random PSO with odds of 30/1
for low-dimensional problems (indicatively N ≤ 30) and 5/1 for high-dimensional problems
(N > 30). The hull-form SBDO (N = 11) shows how DPSO outperforms PSO with odds of
20/1. The use of DPSO in the SBDO context is therefore advised, especially if computationally
expensive analyses are involved in the optimization
Hull-form optimization of a luxury yacht under deterministic and stochastic operating conditions via global derivative-free algorithms
Simulation-based design optimization (SBDO) techniques are used in the shape
design of complex engineering systems. SBDO methods integrate an optimization algorithm,
a tool for the design modification, and analysis tools. In the context of ship/ocean
applica- tions the objective function is often noisy, its derivatives are not directly
provided and local minima cannot be excluded, therefore global derivative-free algorithms
are widely used. The objective of this work is to investigate the efficiency of three global
deterministic derivative-free optimization algorithms for the deterministic and stochastic
hull-form optimization of a luxury yacht. Particle Swarm Optimization (DPSO), Dolphin Pod
Optimization (DPO), and DIviding RECTangles (DIRECT) are applied to reduce the total resistance
over a variety of conditions. The approach includes a comparison of the performances of the
optimization algorithms, based on deterministic results for two separate operating conditions.
DPSO is identified as the most promising optimization algorithm and is used for the robust
design optimization (RDO) per- formed considering a stochastic variation of the cruise
speed with uniform distribution within a speed range from 8 to 16 kn. The resistance
curve of deterministic and robust solutions is finally presented
Mission-based hull-form and propeller optimization of a transom stern destroyer for best performance in the sea environment
An overview is presented of the activities conducted within the NATO STO Task
Group AVT-204 to “Assess the Ability to Optimize Hull Forms of Sea Vehicles for the Best Per-
formance in a Sea Environment.” The objective is the development of a greater understanding of
the potential and limitations of the hydrodynamic optimization tools. These include
low- and high-fidelity solvers, automatic shape modification methods, and multi-objective optimiza-
tion algorithms, and are limited here to a deterministic application. The approach
includes simulation-based design optimization methods from different research teams.
Analysis tools include potential flow and Reynolds-averaged Navier-Stokes equation solvers.
Design modifica- tion tools include global modification functions, control point based methods, and
parametric modelling by hull sections and basic curves. Optimization algorithms include particle
swarm optimization, sequential quadratic programming, genetic and evolutionary algorithms. The ap-
plication is the hull-form and propeller optimization of the DTMB 5415 model for significant
conditions, based on actual missions at sea
Multi-objective hull-form optimization of a swath configuration via design-space dimensionality reduction, multi-fidelity metamodels, and swarm intelligence
A multi-objective simulation-based design optimization (SBDO) is presented for the
resistance reduction and displacement increase of a small water-plane area twin hull (SWATH).
The geometry is realized as a parametric model with the CAESESQR software, using 27 design
parameters. Sobol sampling is used to realize design variations of the original
geometry and provide data to the design-space dimensionality reduction method by
Karhunen-Lo`eve expan- sion. The hydrodynamic performance is evaluated with the potential
flow code WARP, which is used to train a multi-fidelity metamodel through an adaptive
sampling procedure based on prediction uncertainty. Two fidelity levels are used varying the
computational grid. Finally, the SWATH is optimized by a multi-objective deterministic version of
the particle swarm optimiza- tion algorithm. The current SBDO procedure allows for the reduction
of the design parameters from 27 to 4, resolving more than the 95% of the original geometric
variability. The metamodel is trained by 117 coarse-grid and 27 fine-grid simulations. Finally,
significant improvements are identified by the multi-objective algorithm, for both the total
resistance and the displacement
Dense conjugate initialization for deterministic PSO in applications: ORTHOinit+
This paper describes a class of novel initializations in Deterministic Particle Swarm Optimization (DPSO) for approximately solving costly unconstrained global optimization problems. The initializations are based on choosing specific dense initial positions and velocities for particles. These choices tend to induce in some sense orthogonality of particles’ trajectories, in the early iterations, in order to better explore the search space. Our proposal is inspired by both a theoretical analysis on a reformulation of PSO iteration, and by possible limits of the proposals reported in Campana et al. (2010); Campana et al. (2013). We explicitly show that, in comparison with other initializations from the literature, our initializations tend to scatter PSO particles, at least in the first iterations. The latter goal is obtained by imposing that the initial choice of particles’ position/velocity satisfies specific conjugacy conditions, with respect to a matrix depending on the parameters of PSO. In particular, by an appropriate condition on particles’ velocities, our initializations also resemble and partially extend a general paradigm in the literature of exact methods for derivative-free optimization. Moreover, we propose dense initializations for DPSO, so that the final approximate global solution obtained is possibly not too sparse, which might cause troubles in some applications. Numerical results, on both Portfolio Selection and Computational Fluid Dynamics problems, validate our theory and prove the effectiveness of our proposal, which applies also in case different neighborhood topologies are adopted in DPSO
On the use of Synchronous and Asynchronous Single-objective Deterministic Particle Swarm Optimization in Ship Design Problems
A guideline for an effective and efficient use of a deterministic variant of the Particle Swarm Optimization (PSO) algorithm is presented and discussed, assuming limited computational
resources. PSO was introduced in Kennedy and Eberhart (1995) and successfully applied in many fields of engineering optimization for its ease of use. Its performance depends on three main characteristics: the number of swarm particles used, their initialization in terms of initial location and speed, and the set of coefficients defining the behavior of the swarm. Original PSO makes use of random coefficients to sustain the variety of the swarm dynamics, and requires extensive
numerical campaigns to achieve statistically convergent results. Such an approach can be too expensive in industrial applications, especially when CFD simulations are used, and for this reason, efficient deterministic approaches have been developed (Campana et al. 2009).
Additionally, the availability of parallel architectures has offered the opportunity to develop and compare synchronous and asynchronous implementation of PSO. The objective of present work is the identification of the most promising implementation for deterministic PSO. A parametric
analysis is conducted using 60 analytical test functions and three different performance criteria, varying the number of particles, the initialization of the swarm, and the set of coefficients.
The most promising PSO setup is applied to a ship design optimization problem, namely the high-speed Delft catamaran advancing in calm water at fixed speed, using a potential-flow
code
Optimized DBD plasma actuator system for the suppression of flow separation over a NACA0012 profile
We address the problem of controlling the unsteady flow separation over an aerofoil,
using plasma actuators. Despite the complexity of the dynamics of interest, we show
how the problem of controlling flow separation can be formulated as a simple output
regulation problem, so that a simple control strategy may be used. Different
configurations are tested, in order to identify optimal positions of the actuator/sensor
pairs along the aerofoil, as well as the corresponding references for the available
real-time velocity measurements. A multi- objective deterministic particle swarm optimization
algorithm is applied to identify the set of non dominated configurations considering as objectives
the time-averaged input signal and the drag- to-lift ratio. Accurate numerical simulations of
incompressible flows around a NACA0012 profile at Reynolds Re = 20, 000 and angle of attack
15â—¦ illustrate the effectiveness of the proposed approach, in the presence of complex
nonlinear dynamics, which are neglected in the control design. Fast flow reattachment is
achieved, along with both stabilisation and increase/reduction of the lift/drag, respectively.
A major advantage of the presented method is that the chosen
controlled outputs can be easily measured in realistic applications
A Hybrid Computational Intelligence based Technique for Automatic Cryptanalysis of Playfair Ciphers
The Playfair cipher is a symmetric key cryptosystem-based on encryption of digrams of letters. The cipher shows higher cryptanalytic complexity compared to mono-alphabetic cipher due to the use of 625 different letter-digrams in encryption instead of 26 letters from Roman alphabets. Population-based techniques like Genetic algorithm (GA) and Swarm intelligence (SI) are more suitable compared to the Brute force approach for cryptanalysis of cipher because of specific and unique structure of its Key Table. This work is an attempt to automate the process of cryptanalysis using hybrid computational intelligence. Multiple particle swarm optimization (MPSO) and GA-based hybrid technique (MPSO-GA) have been proposed and applied in solving Playfair ciphers. The authors have attempted to find the solution key applied in generating Playfair crypts by using the proposed hybrid technique to reduce the exhaustive search space. As per the computed results of the MPSO-GA technique, correct solution was obtained for the Playfair ciphers of 100 to 200 letters length. The proposed technique provided better results compared to either GA or PSO-based technique. Furthermore, the technique was also able to recover partial English text message for short Playfair ciphers of 80 to 120 characters length
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