Monoharmonic approach to investigation of the vibrations and self‐heating of thin‐wall inelastic members

An approximate formulation is given to a dynamic coupled thermo‐mechanical problem for physically nonlinear inelastic thin‐walled structural elements within the framework of a geometrically linear theory and the Kirchhoff‐Love hypotheses. A simplified model is used to describe the vibrations and dissipative heating of inhomogeneous physically non‐linear bodies under harmonic loading. Unsteady vibration self‐heating problem is solved. The dissipative function obtained from the solution for steady‐state vibrations is used to simulate internal heat sources. For the partial case of forced vibrations of a beam, the amplitude‐frequency characteristics of the field quantities are studied within a wide frequency range. The temperature characteristics for the first and second resonance modes are compared. Santrauka Naudojant geometrinio tiesiškumo ir Kirchhofo ir Love hipotezes, pateikiama apytikslė jungtinė dinamikos ir disipacinės šilumos uždavinio formuluotė fiziškai netiesiniams konstrukciniams elementams. Apytikslis modelis taikomas harmonine apkrova veikiamo nehomogeninio fiziškai netiesinio kūno svyravimams ir išskiriamai šilumai aprašyti. Sprendžiamas neharmoninių svyravimų disipacinės šilumos uždavinys. Pasitelkus harmoninių svyravimų uždavinį, gaunama disipacijos funkcija, kuri naudojama vidinės šilumos šaltiniams modeliuoti. Esant priverstiniams sijos svyravimams, plačiai nagrinėjamos amplitudės ir dažnio charakteristikos. Lyginamos temperatūros charakteristikos, atitinkančios pirmojo ir antrojo rezonanso formas. First Published Online: 14 Oct 2010 Reikšminiai žodžiai: plonasienė konstrukcija, jungtinis temperatūrinis ir mechaninis uždavinys, disipacinė šiluma, monoharmoninė aproksimacija

Development of a method for assessment and forecasting of the radio electronic environment

Decision making support systems (DSS) are actively used in all spheres of human life. The system of the electronic environment analysis is not an exception. However, there are a number of problems in the analysis of the electronic environment, for example: the signals are analyzed in a complex electronic environment against the background of intentional and natural interference. Input signals do not match the standards, and their interpretation depends on the experience of the operator (expert), the completeness of additional information on a particular task (uncertainty condition). The best solution in this situation is found in the integration with the data of the information system analysis of the electronic environment, artificial neural networks and fuzzy cognitive models. Their advantages are also the ability to work in real time and quick adaptation to specific situations. The article develops a method for assessing and forecasting the electronic environment. Improving the efficiency of evaluation information processing is achieved through the use of evolving neuro-fuzzy artificial neural networks; learning not only the synaptic weights of the artificial neural network, the type and parameters of the membership function. The efficiency of information processing is also achieved through training in the architecture of artificial neural networks; taking into account the type of uncertainty of the information that has to be assessed; synthesis of rational structure of fuzzy cognitive model. It reduces the computational complexity of decision-making; has no accumulation of learning error of artificial neural networks as a result of processing the information coming to the input of artificial neural networks. The example of assessing the state of the electronic environment showed an increase in the efficiency of assessment at the level of 15–25 % on the efficiency of information processin

Finite element analysis of wind turbine blade vibrations

The article is devoted to the practical problem of computer simulation of the dynamic behaviour of horizontal axis wind turbine composite rotor blades. This type of wind turbine is the dominant design in modern wind farms, and as such its dynamics and strength characteristics should be carefully studied. For this purpose, in this paper the mechanical model of a rotor blade with a composite skin possessing a stiffener was developed and implemented as a finite element model in ABAQUS. On the basis of this computer model, modal analysis of turbine blade vibrations was performed and benchmark cases for the dynamic response were investigated. The response of the system subjected to a uniform underneath pressure was studied, and the root reaction force and blade tip displacement time histories were obtained from the numerical calculations conducted

Approximate mode-based simulation of composite wind turbine blade vibrations using a simplified beam model

It is well-known that lower modes of vibration are responsible for a high percentage of the dynamic response. In this paper, the task of simulation of the dynamic response of the composite wind turbine blade on the basis numerical realisation of a developed low dimensional beam type model is considered. From the governing system of differential-algebraic equation of the simplified beam type model of the blade, and using the mode superposition approximation, the system of linear ordinary differential equations with respect to the coefficient functions of the modal representation was obtained. The developed program codes allow to simulate low frequency bending vibrations of wind turbine blades under different steady-state and transient loadings. The comparison of the simulation results obtained by the proposed simplified blade model with the results of the direct Finite Element Method (FEM) simulation shows their close agreement, which confirms the adequacy of the developed model and its mode-based approximation to the level of the requirements necessary in engineering practice. The presented approach to the creating low-dimensional simplified models of slender structures can therefore be useful in different fields of aerospace, civil, mechanical, and transport engineering

Dynamics of Pulse-Loaded Circular Föppl-von Kármán Thin Plates-Analytical and Numerical Studies

Materials such as modern armour steel, benefit from appreciably high elastic energy storage capacity prior to failure. Such a capacity contributes to absorption of the impulse generated during an extreme pulse pressure loading event such as a localised blast. As the plate deforms within the bounds of the elastic region without plastic dissipation, the probability of catastrophic failure is mitigated while large deformations compared to conventional metallic panels are encountered. No studies have proposed, to date, a closed-form solution for nonlinear elastic response of thin circular plates subject to localised pulse loads. The present work aims at deducing, from the minimization of the F ̈oppl-von K ́arm ́an (FVK) energy functional, explicit solutions for the response of dynamically (pulse) loaded thin clamped circular plates undergoing large deformations. The solutions were derived from a presumed kinematically admissible displacement field together with an associated stress tensor potential as an infinite polynomial series, which was truncated into a multiplicative decomposition of tem-poral parts and spatial parts, representative of a Multiple Degrees-of-Freedom (MDOF’s) system. In the case of static loading, using the Frobenius method, an exact recursive solution to each mode of defamation was obtained. In the event of dynamic loading, useful expressions for stress tensor components were delineated, corresponding to a multimode multiplicative product, and a series of coupled Ordinary Differential Equations (ODE’s) were derived, using the Ritz-Galerkin variational method. The explicit solutions were sought using the Poincar ́e-Lindstedt (PL) perturbation method. The closed-form solutions obtained were corroborated with FE results including the Fluid-Structure Interaction (FSI) effects and showed convergence when the first few modes were considered. The influence of higher modes, however, on the peak deformation was negligible and the solution with 3 DOF’s conveniently estimated the blast response to a satis-factory level of precision. The influence of element type on the response was also examined and discussed in the context of the problem