Analytical and fem studies on buckling of sandwich beams

The paper is devoted to the analytical and numerical studies of buckling of the three-layer beams with core from aluminium foam. Mechanical properties of this core are variable on vertical direction. Young’s modulus is the highest in the middle of the core. There are two schemes of displacement of faces and core of the beam: a broken line hypothesis and a nonlinear hypothesis. The mathematical models for both types of displacement are presented. The equations of equilibrium are written using the principle of stationary of total potential energy. Numerical analysis of sandwich beam is conducted in ANSYS environment. Finite elements analysis has been performed using a linear buckling model. The analysis is carried out for constant and variable Young’s modulus of the core of the beam. Modelling of variable Young’s modulus is difficult. To solve this problem the core is divided into several layers. Each layer is modelled with different mechanical properties. The load is applied symmetric to the faces. The values of the critical load obtained by the analytical and numerical (FEM) methods are compared

Energy transmissibility of biodynamical structure of the human body exposed on whole-body vibration

Badania przepływu energii w biodynamicznej strukturze ciała ludzkiego w pozycji siedzącej przy pobudzeniu do kinematycznych drgań siedziska umożliwiły zdefiniowanie i obliczenie wartości energetycznej transmitancji w funkcji częstotliwości pasma normowego oraz wartości transmitancji dla wszystkich punktów redukcji modelu dynamicznego badanej struktury. Transmitancja wykazała pasma częstotliwości i miejsca wzmocnienia oraz redukcji przepływu energii.Investigations of energy flow in biodynamical structure of the human body in sitting position during kinematical excitation of seat allows defining and calculating values of energy transmissibility as a function of the frequency standard band and points of reduction of the dynamical model of studied structure. Transmissibility has shown bands of frequencies and points of amplification and reduction of energy flow

Examples of regularization for tasks of determining moisture diffusivity and mass surface emission of wood

W pracy rozważa się sposób wyznaczania współczynnika dyfuzji wilgoci i przejmowania masy drewna na podstawie pomiarów masy całkowitej próbek rejestrowanych w procesie niestacjonarnej sorpcji, gdzie oszacowania parametrów materiałowych dokonuje się na drodze minimalizacji sumy błędów kwadratowych pomiędzy wynikami pomiaru i obliczeń modelowych. W [9,12] pokazano, że szczególnie w przypadku wyrażenia współczynnika dyfuzji, jako nieliniowej funkcji zależnej od wilgotności materiału lub wystąpienia względnie dużych wartości współczynnika przejmowania masy w procesie dyfuzji zachodzącym wzdłuż włókien drewna, w zagadnieniach tego typu jednoznaczne określenie globalnego minimum funkcji celu może stać się bardzo utrudnione. W niniejszej pracy, jako sposób, który pozwala na skuteczną regularyzację omawianego, współczynnikowego zadania odwrotnego, wykorzystano metody Tichonowa i L-curve. Rozważania zilustrowano przykładami pomiarów prowadzonych na próbkach z drewna sosnowego, dębowego i lipowego, w przypadku, których, dzięki zastosowanemu podejściu, otrzymano znaczną poprawę jakości wyników.In the paper, a method for determining the moisture diffusion coefficient and mass surface emission coefficient of wood is considered which employs measurements of total mass of samples recorded in a non-stationary sorption process where the estimation of the material parameters is realized by minimizing the sum of square errors between the measurement results and adopted calculation model. It was shown in [9,12] that in problems of this type, especially in the case of the expression of diffusion coefficient as a nonlinear function dependent on the moisture content or of a relatively large mass surface emission coefficient when diffusion process taking place along the wood fibres, unambiguous definition of the global minimum of the objective function can be very difficult. In this paper, as a way that allows for the effective regularization of this parametric inverse problem, Tikhonov method and L-curve method are used. The considerations are illustrated with examples of measurements conducted on the samples of pine, oak, and linden wood where, thanks to the used approach, one significantly improved quality of results

Model tests of fast units on the open waters of Jeziorak Lake

Paper presents model tests of fast units carried out in the years 1956-2000 in the Experimental Centre of the Gdansk University of Technology Shipbuilding Institute on Jeziorak Lake. The experimental tests included single- and twin-hull hydrofoils, amphibian hovercraft, side-wall hovercraft and also speedboats and SWATH type catamarans. The aim of those tests was to acquire data for developing the design and safety criteria as well as computer programs for predicting the hydrodynamic properties of fast units. The gathered experimental material was used in the theoretical studies, publications and conference papers

Experimental and numerical buoyancy analysis of tracked military vehicle

The paper presents experimental validation of numerical flow analysis around tracked amphibious military vehicle. The aim of the study was to validate the simulation results and visualize the flow around optimized geometry To perform numerical simulations, a Computational Fluid Dynamics code FLUENT was used. The software is dedicated to model flow, turbulence, heat transfer, and reactions. The area was divided into two domains – air and water. During the simulation, water was moving with speed specified in standardization. However the numerical techniques are constantly developed and improved there is still a strong need for verification especially in buoyancy analysis and water performance evaluation. Results showed quite good agreement with literature after some modifications of the model. Then the flow was numerically visualized. That allowed in-depth analysis of the flow around each of vehicle's parts and some major and minor modifications were proposed. Modified geometry was analyzed and obtained results will be compared with previous ones. Additional stability and manoeuvrability tests were conducted. The results will be used to modify the geometry of vehicle and conduct experimental tests to verify the numerical code performance and check the actual change in vehicle's water performance. Future work will also consider propeller influence on results

The predictions of resistance and propulsion for 4 types of ships

In this paper the predictions of resistance and propulsion for 4 types of ships: container carrier, oil product tanker, ro-ro vessel and river-sea vessel included in the EUREKA "Baltecologicalship" project E!2772 are presented. All the above ships were designed by the SINUS Enterprise Ltd. The scope of the research covers: experimental measurement of ship resistance in calm water, determination of resistance increment in irregular waves and computational powering prediction for POD propulsors. The experiments were conducted in the Laboratory of the Department of Underwater Technology, Hydromechanics and Design of Ships, Faculty of Ocean Engineering and Ship Technology, Gdansk University of Technology