The analysis of the ventricle assist device controlled rotor dynamics

The analysis of dynamics of rotor-driven artificial ventricle (VAD) was conducted in the work. A comparison of two types of control is given: a linear-quadratic (LC) optimization and PID-regulator. It was shown that LC – control allows the pump rotor positioning with an accuracy of 0.2 mm at speeds ranging from 5,000 to 12,000 rev/min

On parametric oscillations of pendular and rotor systems

Different kind of parametrical phenomena in vibrating systems are presented. Nonlinear properties of rotating and pendulum dynamical systems give some interesting industrial applications. The purpose of this paper is to show the possibility to generalize the models and to find a similarity of certain physical presentations and possible analysis. The effects of non-uniform rotation of unbalanced rotor, synchronization of multiples pendulums with common vibrating base, stabilization of vertical column, auto parametrical damper etc. are included in consideratio

Small and large wetland fragments are equally suited breeding sites for a ground-nesting passerine

Large habitat fragments are generally thought to host more species and to offer more diverse and/or better quality habitats than small fragments. However, the importance of small fragments for population dynamics in general and for reproductive performance in particular is highly controversial. Using an information-theoretic approach, we examined reproductive performance and probability of local recruitment of color-banded reed buntings Emberiza schoeniclus in relation to the size of 18 wetland fragments in northeastern Switzerland over 4years. We also investigated if reproductive performance and recruitment probability were density-dependent. None of the four measures of reproductive performance (laying date, nest failure probability, fledgling production per territory, fledgling condition) nor recruitment probability were found to be related to wetland fragment size. In terms of fledgling production, however, fragment size interacted with year, indicating that small fragments were better reproductive grounds in some years than large fragments. Reproductive performance and recruitment probability were not density-dependent. Our results suggest that small fragments are equally suited as breeding grounds for the reed bunting as large fragments and should therefore be managed to provide a habitat for this and other specialists occurring in the same habitat. Moreover, large fragments may represent sinks in specific years because a substantial percentage of all breeding pairs in our study area breed in large fragments, and reproductive failure in these fragments due to the regularly occurring floods may have a much stronger impact on regional population dynamics than comparable events in small fragment

Influence of flank face on the condition of chatter self-excitation during turning

This paper addresses a modelling approach for cutting tool and workpiece material interaction with ploughing taken into account. In the proposed model the distributed contact on the flank face is replaced by a concentrated additional cutting edge characterised by two physical parameters and bringing about a new delay term into the dynamical system. It is shown that under monoharmonic excitation of the tool on the direction orthogonal to the cutting velocity, it is possible to isolate the effect of the flank face and observe experimentally its parameters. The influence of the ploughing on the instability boundaries of continuous cutting is investigated. An analytical expression is obtained for the effective linear damping coefficient due to ploughing and depending on the cutting velocit

Analytical approach of turning thin-walled tubular parts. Stability analysis of regenerative chatter

The purpose of this work is to develop a mathematical model of the dynamics of turning a thin-walled cylindrical shell. It is then possible to obtain estimates of the boundaries of stability of the continuous cutting process. The model is constructed using the theory of shells with application of Galerkin’s method in conjunction with the expansion of the field of displacement in beam and trigonometric functions. On the basis of the developed model, an algorithm designed for constructing boundaries of stability of turning of the thin-walled cylindrical parts is presented

Parametric synthesis of rod spatial vibroisolation system under arbitrarily directed external disturbance

A mathematical model of flexible-rod spatial vibroisolating suspension, describing the motion of protected object, is considered. An algorithm is proposed for solving the problem of spatial displacement of the object under the action of static forces applied in an arbitrary direction. The coefficients of stiffness matrix of the suspension are determined depending on the position of static equilibrium. It is demonstrated that, depending on the requirements by varying geometrical parameters of the rods, different dynamic properties of the suspension may be obtained

Multi-cutter turning process stability analysis

This work displays results of a modelling-based investigation a process of multi-cutter turning process focusing on the stability of nominal steady-state case. The modelling is based on the new surface formation equations, on the equations of motion and on a rational fraction cutting law. The influence of the parameters of the system on the stability of the steady cut is analyzed

Dynamic stability of a flexible rod under parametric excitation

A homogeneous rod with a constant cross section, vertically mounted and cantilevered, is considered. At the unstrained state, the rod’s axis is straight. It is supposed lateral stiffness is that the rod buckles in static conditions only under gravity and its axis bends. Flexural oscillations of the rod when its base vibrates vertically are investigated. Stabilization circumstances of the rod axis rectilinearity depending on excitation parameters, internal and external damping, and rod flexibility are determined