Contents of Journal of Mechanical Engineering 58, 5 (2007) 




LEHUGEUR, B., GILLIÉRON, P., LOC TA-PHUOC: Characterization and 
control of longitudinal vortices over a dihedral bluff body: 
Numerical approach                                                      249

ĎURIŠ, R., MURÍN, J.,KUTIŠ, V.: Nonlinear composite truss finite 
element with varying stiffness                                          273

SWORNOWSKI, P.: The coordinate measuring machine software as 
a potential source of errors                                            298

Abstracts



Characterization and control of longitudinal vortices over a dihedral bluff body: Numerical approach

BENJAMIN LEHUGEUR, PATRICK GILLIÉRON, LOC TA-PHUOC

A longitudinal vortex emanating from the front pillar of a simplified dihedral geometry is analysed by numerical simulations. The objective is to develop and validate flow control techniques able to act on the dynamics of such vortices in order to reduce aerodynamic drag of automotive vehicle. Numerical simulations are conducted according to a computation code based on the Lattice Boltzmann Method. The findings highlight the sudden and spontaneous disintegration of the vortex referred to vortex breakdown, which is characterized by the appearance of a recirculation zone in the vortex core. Open loop control is then applied by continuous blowing or suction on the edge of the front pillars. The results reveal that suction-type control tends to delay the breakdown of the vortex while blowing-type control triggers the onset of vortex breakdown upstream compared to the uncontrolled case. Aerodynamic drag reductions of close to 40 % are obtained with suction-type control.

Nonlinear composite truss finite element with varying stiffness on steering effort

RASTISLAV ĎURIŠ, JUSTÍN MURÍN, VLADIMÍR KUTIŠ

This paper deals with a new truss element with varying stiffness intended to geometric and physically nonlinear analysis of composite or functionally graded materials (FGM's) structures. The varying stiffness considers longitudinal variation of cross-sectional area and material properties, like elasticity modulus, yield stress and elasto-plastic modulus. These variations could be caused by nonhomogeneous temperature field or by varying volume fractions of composite components. Stiffness matrices of the finite element are derived using full nonlinear non-incremental Lagrangian formulation without any linearization. Effective longitudinal material properties are calculated with the extended mixture rule. Two cases were solved to verify the established relations. Bilinear elasto-plastic material response was considered. Accuracy and effectiveness of the new proposed finite truss element are compared and discussed.

The coordinate measuring machine software as a potential source of errors

PAWEŁ SWORNOWSKI

Coordinate measuring technique has become the key element in automated quality control. A system based on the coordinate measuring machine should be treated as a single element made up of a geometrical-mechanical block and an electronic block. Both blocks distinctly influence the measurement results. However, the calculating algorithms applied are of particular significance. Relatively large measurement errors may occur due to the application of some algorithms currently used. The coordinates of points belonging to particular geometrical elements are entered into the computer working with the CMM. The computer and software are treated as a "black box". The final results show only the errors generated by the computer and its software (without CMM). The same test is used in 14 cases.