Janis Auzins

Surrogate models for optimum design of stiffened composite shells

An optimization procedure is developed for the design of composite stiffened shells subjected to buckling and post-buckling constraints. The optimization method is based on building surrogate models employing the experimental design and response surface methodology. A combined data set consisting of test results of stiffened shells and numerical data obtained by finite element simulation is used for building the surrogate models. These models are used for sensitivity analysis, evaluation of the weight saving parameters and for design optimization of stiffened composite panels under axial compression loading. It was shown that employing the surrogate models satisfactory accuracy can be achieved to describe the post-buckling behavior of the stiffened panels and to use these models in design optimization.

Response surface method for solution of structural identification problems

The article is focused on the application of the Response surface method for the solution of structural identification problems. The approximating functions are obtained from the data of numerical experiments, which is performed in the sample points of experimental design. A Minimal mean squared distance Latin hypercube design is used in the present article. A local approximation method is employed for building the response surfaces. An example of the application of the response surface method and experimental design for the identification of elastic properties of a laminated composite material is discussed. The five elastic constants of carbon/epoxy laminate are determined employing experimentally measured eigenfrequencies of composite plates. The identification functional represents discrepancy between experimentally measured and numerically calculated frequencies, which are dependent on the variables to be identified. The identified elastic constants have been compared with the values obtained from an independent static test. A good agreement of the results is observed.

Identification of Elastic Properties of Composite Laminates

This article is focused on application of the response surface method (RSM) for solution of structural identification problems. The approximating functions are obtained from the data of deterministic numerical experiment. The numerical experiment is performed in the sample points of experiment design. A minimal mean squared distance Latin hypercube (MMSDLH) design is used in the present paper. For building the response surfaces, a local approximation method is employed. An example of application of the response surface method and experiment design for identification of elastic properties of laminated composite material is discussed. Elastic properties of carbon/epoxy laminate are determined employing the experimentally measured eigenfrequencies of composite plates. The identification functional represents differences between experimentally measured and numerically calculated frequencies, which are dependent on variables to be identified. The identification parameters are five elastic constants of material. The elastic constants identified from vibration test have been compared with the values obtained from independent static test. Good agreement of the results is observed.

METAMODELING METHODOLOGY FOR POSTBUCKLING SIMULATION OF DAMAGED COMPOSITE STIFFENED STRUCTURES WITH PHYSICAL VALIDATION

A metamodeling methodology has been proposed for postbuckling simulation of stiffened composite structures with integrated degradation scenarios. The presence of artificial damage in between the outer skin and stiffeners has been simulated as softening of the material properties in predetermined regions in the structure. The proposed methodology for the fast design procedure of axially or torsionally loaded stiffened composite structures is based on response surface methodology (RSM) and design and analysis of computer experiments (DACE). Numerical analyses have been parametrically sampled by means of ANSYS/LS-DYNA probabilistic design toolbox extracting the load-shortening response curves in the preselected domain of interest. These response curves have been simplified using piece-wise linear approximation identifying the buckling and postbuckling stiffness ratios along with the values of the skin and the stiffener buckling loads. Three stiffened panel designs and a closed box structure with preselected damage scenarios have been elaborated and validated with the tests performed within the COCOMAT project. The resulting design procedure provides a time effective design tool for preliminary study and for elaboration of the optimum design guidelines of composite stiffened structures with material degradation restraints.

Material degradation assessment for stiffened composite shells using metamodelling approach.

The intense interest coming from the aerospace industry indicates the need of safe exploitation of composite materials in stiffened shell structures. Since stiffened shells are far most consumed structural component, it is important to study the behaviour of material degradation to evaluate the safe design guidelines. Moreover, current numerical procedures cannot simulate the collapse of stiffened shells with sufficient reliability and efficiency, leading to over-conservative designs. One can assume that great potential exist for future increase of effectiveness of stiffened composite structures by allowing of post-buckling of skin to occur during the exploitation [1].

Shape Optimization of Mechanical Components for Measurement Systems

For the topology and shape optimization of structures, the different realizations of homogenization method are widely used (Arora, 2004; Bendsoe & Sigmund, 2003). This method is highly effective for shell constructions and allows implementing topometry and topography, sizing and shape as well as freeform optimization (Vanderplaats, 2004). However, it is a very time consuming procedure because the number of design parameters can reach a million and more. There is the possibility of taking into account some technological factors, nevertheless, in the case of bulky bodies it frequently produces shapes that are difficult to manufacture. As shown in work (Mullerschon et al., 2010), the Hybrid Cellular Automata method does not allow parallelization of computations and PBS queuing system has been used. At the same time the following resource saving approach (Janushevskis et al., 2010; Janushevskis & Melnikovs, 2010) can be used for shape optimization which includes the following steps: 1) Planning the position of control points of NURBS (see, for example, Saxena & Sahay, 2005) for obtaining a smooth shape. 2) Building geometrical models using CAD software in conformity with design of experiment. 3) Calculation of responses for a complete FEM model using CAE software. 4) Building metamodels (surrogate models) for responses on the basis of computer experiment. 5) Using metamodels for shape optimization. 6) Validating the optimal design using CAE software for the complete FEM model.

Metamodel-Based Analysis of Cross-Flow-Induced Vibrations

This work presents the study of numerical modelling of the fluid flow and circular cylinder interaction to investigate the cross-flow induced vibrations in the rod bundle. It is assumed that failure due to flow-induced vibrations of the rod can be described by the reduction of the rod mass, the rod support stiffness or damping coefficient. The metamodel-based approach is applied to investigate the main trends of the system’s characteristic behaviour related to the variations of the chosen parameters. The two-dimensional Finite Volume models have been developed using open-source software to get a mapping of input and output variables for the metamodel. The impact of assumed failure parameters (the mass, the stiffness and the damping) on the vibration amplitude and frequency of the oscillating rod is analysed.

Metamodeling for the Identification of Composite Material Properties

The problem of identification of elastic properties E=·E x,·E y,·E xy,μ× of composite structural elements from vibration tests is considered. The metamodels built on basis of FEM computer experiments and natural measurements of eigenfrequencies are used for the identification [1], [2]. Two methods are compared. First - the minimization of the discrepancy between calculated and measured frequencies. The numerical frequencies are calculated by finite element model using numerical experiment - a set of trial values for the unknown material parameters. The numerical frequencies are compared with the measured frequencies, and material properties are found by minimizing the relative discrepancy

Surrogate modeling in design optimization of stiffened composite shells

\mathop {\min }\limits_E \sum\limits_{i = 1}^m {\left( {\frac{{f_i^{\exp } - f_i^{calc} }} {{f_i^{\exp } }}} \right)} ^2