40,818 research outputs found
Roots' like Natural Behavior Applied to Guidance Algorithms for Space Exploration Missions
No full textPaper IAC-10-C.2.3.
A Comparison Between Frequency and Time Domain approaches for Determining a Structural Damage Using the Adjoint Method
No full text
Damage assessment of large space structures through the variational approach
No full textThe present investigation is focused on the solution of a dynamic inverse problem which is concerned with the assessment of damage in large space structures by means of measured vibration data. This inverse problem has been presented as an optimization problem and has been solved through the use of the Conjugate Gradient method with the Adjoint Equation also called Variational Approach. When a high number of damage elements is to be individualized and these elements are also severely damaged, it is shown that the use of an additional method is necessary in order to provide a better initial guess for the conjugate gradient method. A stochastic method, represented by the Genetic Algorithm Method, has been chosen because it provides robust search in complex spaces and also reduces the chance of converging to local optima. The application of this hybrid approach showed that better results can be achieved, although the computational time for the application here analyzed could increase. The damage estimation has been evaluated using noiseless and noisy synthetic experimental data, and the reported results are concerned with a space truss structure
A hybrid multilevel approach for aeroelastic optimization of composite wing-box
No full textThe main problem in a multidisciplinary aircraft design is usually the development of an efficient method to integrate structures or structural properties, which can be considered both as “global” and “local” design variables. This paper describes an integrated aerodynamic / dynamic / structural optimization proce-dure for a composite wing-box design. The procedure combines an aeroelastic optimization of a composite wing based on a general purpose optimizer such as the Sequential Quadratic Programming (SQP) and a com- posite optimization using Genetic Algorithm (GA). Both the optimizations are implemented through a hy- brid multilevel decomposition technique
A Comparison Between Frequency and Time Domain Approaches for Determining a Structural Damage Using the Adjoint Method
No full textThe present investigation is focused on the solution of a dynamic inverse problem which is concerned with the
assessment of damage in structures by means of measured vibration data. Considerable research and effort over
the last few decades has taken place in the field of damage detection and damage classification in structures,
generating a variety of experimental, numerical and analytical techniques [1, 2].
The inverse problem solution is generally unstable, therefore small perturbations in the input data, like random
errors inherent to the measurements used in the analysis, can cause large oscillations on the solution. In order
to overcame this difficulty a sort of methods have been propose by using regularization techniques coupled with
both deterministic and stochastic approaches. An example of deterministic approach is the conjugate gradient
method with the use of the adjoint equation whereas the genetic algorithm method belongs to the class of the
stochastic approaches. Both techniques have already been used successfully in inverse heat conduction problems
[3].
In this work the inverse vibration problem, i.e. the ill-posed problem, is presented as a well-posed functional
form, whose solution is obtained through the use of a hybrid approach which employs the genetic algorithm
method coupled with the conjugate gradient method with the adjoint equation, also called variational approach.
In addition, two different methodologies have been compared, the one based on frequency domain approach and
the other one based on time domain approach. In the first case it has been assumed that the experimental data
available are the eigenfrequencies and eigenmodes of the structure, whereas in the second one measurements
of displacements of the structure have been assumed as the data available for the analysis. In both cases the
damage estimation has been evaluated using noiseless and noisy synthetic experimental data. The idea of this
work is to analyze and compare the results obtained with the two formulations (i.e. the time-domain and the
frequency-domain formulation) making it possible a better understanding of the inverse method here adopted
and its ability to find, locate and quantify a damage in a structure
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