S e lf-E x c ite d V ib ra tio n s and D a m p in g in C irc u la to ry S y ste m sSelf-excited vibrations in mechanical engineering systems are in general unwanted and sometimes dangerous. There are many systems exhibiting self-excited vibrations which up to this day cannot be completely avoided, such as brake squeal, the galloping vibra tions of overhead transmission lines, the ground resonance in helicopters and others. These systems have in common that in the linearized equations of motion the self excitation terms are given by nonconservative, circulatory forces. It has been well known for some time, that such systems are very sensitive to damping. Recently, several new the orems concerning the effect of damping on the stability and on the self-excited vibrations were proved by some of the authors. The present paper discusses these new mathematical results for practical mechanical engineering systems. It turns out that the structure of the damping matrix is of utmost importance, and the common assumption, namely, represent ing the damping matrix as a linear combination of the mass and the stiffness matrices, may give completely misleading results for the problem of instability and the onset of self-excited vibrations. The authors give some indications on improving the description of the damping matrix in the linearized problems, in order to enhance the modeling of the self-excited vibrations. The improved models should lead to a better understanding of these unwanted phenomena and possibly also to designs oriented toward their avoidance.
The manufacturing process of paper machines consists of several steps to produce high quality papers. This is done by sequentially lined‐up machines including the head box, the drying sections, the finishing part and the wrapping systems. In the finishing part, the rollers of the paper calender compress the fibrous material involving viscoelastic and plastic deformations. Modern calenders are composed of several roller pairs, each consisting of a soft and a hard roller. The homogenization of the paper density and the refinement of the paper surface is achieved by the compression in the roller pairs. While very high values for the plastic strain occur in the first roller pair, the plastification decreases for the subsequent pairs. Therefore, the force distribution and the occurring vibrations can deviate significantly between the roller pairs. Two main vibration problems are observed in paper calenders caused by the contact and the orthotropic behavior of the paper: wear‐induced corrugation on the surface of the soft rollers and sudden instabilities going along with high vibration amplitudes. In this paper the main focus is placed on a simplified modeling of the paper plastification during the calendering process. The restoring forces are non‐smooth due to the plasticity and additional considerations have to be included for the derivation of the stability problem.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.