2008 SEP 15 - (VerticalNews.com) -- "Optimal sensor placement technique plays a key role in structural health monitoring of spatial lattice structures. This paper considers the problem of locating sensors oil a spatial lattice structure with the aim of maximizing the d ata information so that structural dynamic behavior can be fully characterized," investigators in Harbin, People's Republic of China report.

  "Based on the criterion of optimal sensor placement for modal test, an improved genetic algorithm is introduced to find the optimal placement of sensors. The modal strain energy (MSE) and the modal assurance criterion (MAC) have been taken as the fitness function, respectively, so that three placement designs were produced. The decimal two-dimension array coding method instead of binary coding method is proposed to code the solution. Forced mutation operator is introduced when the identical genes appear via the crossover procedure. A computational simulation of a 12-bay plain truss model has been implemented to demonstrate the feasibility of the three optimal algorithms above. The obtained optimal sensor placements using the improved genetic algorithm are compared with those gained by exiting genetic algorithm using the binary coding method. Further the comparison criterion based oil the mean square error between the finite element method (FEM) mode shapes and the Guyan expansion mode shapes identified by data-driven stochastic subspace identification (SSI-DATA) method are employed to demonstrate the advantage of the different fitness function. The results showed that some innovations in genetic algorithm proposed ill this paper can enlarge the genes storage and improve the convergence of the algorithm," wrote W. Liu and colleagues ...read more

  2008 APR 28 - (VerticalNews.com) -- According to a study from Iran, "In this paper, suppression of the dynamic response of tall buildings, supported on elastomeric bearings with both linear and nonlinear behaviors, is studied. The isolated building is modeled as a shear-type structure having one lateral degree of freedom at each story level."

  "The elastic supports are modeled as an additional degree of freedom having three unknown parameters: mass, stiffness, and damping ratio. The main objective of the paper is to find the optimal values of the parameters of the base isolation system, using genetic algorithms (GAs), to simultaneously minimize the displacement of the building's top story and that of the base isolation system. In order to simultaneously minimize the objective functions, a fast and elitist non-dominated sorting genetic algorithm (NSGA-II) approach is used to find a set of Pareto-optimal solutions. The optimal values of the parameters of the base isolators, namely: their mass, stiffness, and damping ratio are evaluated using the GAs by taking into account the nonlinearity of the isolator bearings to minimize the objective functions. Moreover, in order to solve the undesirable horizontal displacement of the lead-rubber bearings, a new method called the ''independent story'' (IS) system is proposed in this investigation. This system works as a big tuned mass damper (TMD) system, without using any additional damping or stiffness devices except those of the structure itself. Either one full story of the building or even a part of one story can be considered the IS system. For a numerical example, a ten-story building located in Mashhad, Iran is chosen," wrote S. Pourzeynali and colleagues, University of Guilan ...read more

  2008 APR 14 - (VerticalNews.com) -- "Zhang and Chen [The boundary point method for the calculation of exterior acoustic radiation problem, Journal of Sound and Vibration 228 (1999) 761-772] proposed a boundary point method (BPM) for exterior acoustic problems. The idea is similar to the CHUNKY CHIEF by Wu [A weighted residual formulation for the CHIEF method in acoustic, Journal of Acoustical Society of America 90 (1991) 1608-1614], but Chunky CHIEF provides constraints using null-field equations while the BPM used the CHUNKY BLOCK singularity outside the domain," researchers in Taiwan report ...read more