Facta Universitatis, Series: Mechanical Engineering

15-25

Authors: Björn Nutti, Dragan Marinković

The paper presents a highly efficient way of simulating the dynamic behavior of deformable objects by means of the finite element method (FEM) with computations performed on Graphics Processing Units (GPU). The presented implementation reduces bottlenecks related to memory accesses by grouping the necessary data per node pairs, in contrast to the classical way done per element. This strategy reduces the memory access patterns that are not suitable for the GPU memory architecture. Furthermore, the presented implementation takes advantage of the underlying sparse-block-matrix structure, and it has been demonstrated how to avoid potential bottlenecks in the algorithm. To achieve plausible deformational behavior for large local rotations, the objects are modeled by means of a simplified co-rotational FEM formulation.

37-50

Authors: Humberto Peredo Fuentes, Manfred Zehn

The Craig-Bampton model order reduction (CBMOR) method based on the Rayleigh-Ritz approach is applied to dynamic behavior simulation of a composite structure in order to verify the method's feasibility and accuracy. The principle of this method is to represent a coupled component model based on the mass, damping and stiffness matrices. The methodology consists of a finite element model based on the classical laminate theory (CLT), a design of experiment to improve the modal assurance criteria (MAC) and experimental results in order to validate the reduced model based on CBMOR method and substructures (super-elements). Experimental modal analysis has been performed using a scanner laser Doppler vibrometer (SLDV) in order to assess the quality of the finite element models. The MAC and cross orthogonality MAC (XOR) values are computed to verify the eigenfrequencies and eigenvectors. This approach demonstrates the feasibility of using CBMOR for composite structures. The example is prepared and solved with MSC/NASTRAN SOL103. The design of experiments (DOE) method has been applied in order to identify the critical parameters and thus obtain high MAC values.

61 - 72

Authors: Jovan Pavlović, Miomir Jovanović, Andrija Milojević

This paper defines a program realization for finding the optimal geometry of a planar Z-mechanism. The paper shows the mathematical procedure for defining the objective function, the constraint function and the search fields which are used for solving the optimization problem. Starting from the solutions in practice, a numerical example is given to determine an optimum design with four optimization parameters. All the optimization parameters are geometric on the mechanism for defining the bucket position. The problem is solved by two different numerical methods - the method of formal search of hyperspace (passive scanning method) and the approximate method of Sequential Quadratic Programming - SQP (applying the function fminmax of the Matlab optimization toolbox). The verification is performed with animation using software for geometric modeling. The results are graphically illustrated.

85 - 94

Authors: Milena Todorović, Dragoljub Živković, Marko Mančić, Dragan Milčić

The most commonly used central units in the district heating system are most certainly hot water boilers. Experience in exploitation as well as their former development have given rise to new demands and possibilities of using hot water boilers for achieving a more efficient utilization of fuel. Yet, the current trend is not only for an efficient operation in terms of energy efficiency of primary fuel, but it also comprises many strict requirements when it comes to a cost-effective, reliable and safe operation. A mathematical - empirical model of the hot water boiler during the start-up process is presented in this paper. The dynamic behavior of the object will be discussed in the start-up regime because it represents one of the most critical transient regimes during the operation.