Displacement Control of Nonlinear Pin-Jointed Assemblies Based on Force Method and Optimization

The accuracy of two-tool machining on automatic lathes is analyzed. Full-factor models of distortions and scattering fields of the performed dimensions, taking into account the flexibility of the technological system on six degrees of freedom, i. e. angular displacements in the technological system, were used in the research. Possibilities of design and control of two-tool adjustment are considered. Keywords turning processing, cutting mode, two-tool setup, full-factor model, accuracy, angular displacement, control, calculation [email protected]

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Experimental Methods for Measuring the Viscous Friction Coefficient in Hydraulic Spool Valves

Sustainability ◽

10.3390/su13137174 ◽

2021 ◽

Vol 13 (13) ◽

pp. 7174

Author(s):

Massimo Rundo ◽

Paolo Casoli ◽

Antonio Lettini

Keyword(s):

Friction Coefficient ◽

Viscous Friction ◽

Experimental Tests ◽

Experimental Methods ◽

Displacement Transducer ◽

A Posteriori ◽

Displacement Control ◽

Spool Valves ◽

The University ◽

Good Agreement

In hydraulic components, nonlinearities are responsible for critical behaviors that make it difficult to realize a reliable mathematical model for numerical simulation. With particular reference to hydraulic spool valves, the viscous friction coefficient between the sliding and the fixed body is an unknown parameter that is normally set a posteriori in order to obtain a good agreement with the experimental data. In this paper, two different methodologies to characterize experimentally the viscous friction coefficient in a hydraulic component with spool are presented. The two approaches are significantly different and are both based on experimental tests; they were developed in two distinct laboratories in different periods of time and applied to the same flow compensator of a pump displacement control. One of the procedures was carried out at the Fluid Power Research Laboratory of the Politecnico di Torino, while the other approach was developed at the University of Parma. Both the proposed methods reached similar outcomes; moreover, neither method requires the installation of a spool displacement transducer that can significantly affect the results.

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Robust force and displacement control of an active landing gear for vibration reduction at touchdown and during taxiing

SN Applied Sciences ◽

10.1007/s42452-021-04320-1 ◽

2021 ◽

Vol 3 (4) ◽

Author(s):

Mehran Pirooz ◽

Seyed Hossein Mirmahdi ◽

Ahmad Reza Khoogar

Keyword(s):

Control System ◽

Force Control ◽

Direct Method ◽

Landing Gear ◽

Gear System ◽

Displacement Control ◽

Robust Nonlinear Control ◽

Control Loops ◽

Tire Force ◽

The Mathematical Model

AbstractIn this paper, a new approach is proposed to control the dynamic response of a landing gear system subjected to runway force, both on heavy landing conditions and at the taxiing process. The mathematical model of the system is used in a way that covers nonlinear dynamics characteristics of landing gear and nonlinear/nonaffine property of the external actuator. The operation of the landing gear system and its components are described briefly. The desired control system includes two different interior loops for displacement and force control. The inner loop determines the actuator force and the outer loop performs the displacement control. A lumped uncertainty is considered in both displacement and force control loops that represent uncertainties including parametric errors, measurement noises, unmodeled dynamics, disturbance due to runway excitation, and other disturbances. The direct method of Lyapunov is utilized for asymptotic stability analysis of the robust nonlinear control system (RNCS). This system is simulated in MATLAB software and the performance of the proposed controller is analyzed exactly. Besides, the results are compared with a passive system and conventional PID control. The comparison indicates that RNCS works better and more precisely. This method can reduce vibrations at touchdown and taxiing and effectively overcome uncertainty and provide well aircraft handling by decreasing the changes in tire force.

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Application of Hyperelastic Nodal Force Method to Evaluation of Aortic Valve Cusps Coaptation: Thin Shell vs. Membrane Formulations

Mathematics ◽

10.3390/math9121450 ◽

2021 ◽

Vol 9 (12) ◽

pp. 1450

Author(s):

Yuri Vassilevski ◽

Alexey Liogky ◽

Victoria Salamatova

Keyword(s):

Aortic Valve ◽

Finite Elements ◽

Shell Model ◽

Thin Shell ◽

Aortic Valves ◽

Shear Moduli ◽

Force Method ◽

Elastic Potentials ◽

Shell Analysis ◽

First Time

Coaptation characteristics are crucial in an assessment of the competence of reconstructed aortic valves. Shell or membrane formulations can be used to model the valve cusps coaptation. In this paper we compare both formulations in terms of their coaptation characteristics for the first time. Our numerical thin shell model is based on a combination of the hyperelastic nodal forces method and the rotation-free finite elements. The shell model is verified on several popular benchmarks for thin-shell analysis. The relative error with respect to reference solutions does not exceed 1–2%. We apply our numerical shell and membrane formulations to model the closure of an idealized aortic valve varying hyperelasticity models and their shear moduli. The coaptation characteristics become almost insensitive to elastic potentials and sensitive to bending stiffness, which reduces the coaptation zone.

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