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This disturbance rejection feature allows users to treat the considered system with a simpler model insofar as the negative effects of modeling uncertainty are compensated in real time. As a result, the operator does not need a precise analytical description of the base system; one can model the unknown parts of the dynamics as internal ...
The structure’s unknown displacements and forces can then be determined by solving this equation. The direct stiffness method forms the basis for most commercial and free source finite element software. The direct stiffness method originated in the field of aerospace. Researchers looked at various approaches for analysis of complex airplane ...
A linear constant coefficient system is stiff if all of its eigenvalues have negative real part and the stiffness ratio is large. Stiffness occurs when stability requirements, rather than those of accuracy, constrain the step length. Stiffness occurs when some components of the solution decay much more rapidly than others. [3]
The stiffness does not only depend on the static stability term , it also contains a term which effectively determines the angle of attack due to the body rotation. The distance of the center of lift, including this term, ahead of the centre of gravity is called the maneuver margin .
disturbance rejection (such as hills in a cruise control) guaranteed performance even with model uncertainties, when the model structure does not match perfectly the real process and the model parameters are not exact; unstable processes can be stabilized; reduced sensitivity to parameter variations; improved reference tracking performance
Stiffness depends upon material properties and geometry. The stiffness of a structural element of a given material is the product of the material's Young's modulus and the element's second moment of area. Stiffness is measured in force per unit length (newtons per millimetre or N/mm), and is equivalent to the 'force constant' in Hooke's Law.
Otherwise methods such as virtual work, direct integration, Castigliano's method, Macaulay's method or the direct stiffness method are used. The deflection of beam elements is usually calculated on the basis of the Euler–Bernoulli beam equation while that of a plate or shell element is calculated using plate or shell theory.
ISO 10846-4:2003 Part 4: Dynamic stiffness of elements other than resilient supports for translatory motion; ISO 10846-5:2008 Part 5: Driving point method for determination of the low-frequency transfer stiffness of resilient supports for translatory motion