Analysis of fluid-structure interaction in a double tank

Predmet magistrskega dela je interakcija med tekočino in trdnino v poenostavljenem modelu rezervoarja valjaste oblike, ki ga je na sredi delila pregrada na dve enako veliki polovici. Vsaka polovica je bila polovično napolnjena z vodo. Za celoten sistem se je določilo lastne frekvence in oblike nihanja. Te so bile določene na podlagi lastnih frekvenc in oblik nihanja praznega rezervoarja, lastnih frekvenc in hitrostnih potencialov tekočine v togem rezervoarju ter hitrostnih potencialov tekočine delno napolnjenega elastičnega rezervoarja. Elastičnost rezervoarja ni imela velikega vpliva na lastne frekvence tekočine in se niso dosti spremenile, lastne frekvence delno napolnjenega rezervoarja pa so se zmanjšale v primerjavi s praznim rezervoarjem, spremenile so se tudi lastne oblike nihanja sten. Obnašanje tekočine v rezervoarju pod vplivom vibracij se je simuliralo s programskim paketom ANSYS CFX, uporabljen je bil homogeni večfazni model. Ustreznost numeričnega modela se je preverilo z rezultati eksperimenta, ki je bil objavljen v literaturi. V primerjavi z eksperimentom se je trenutek maksimalnega tlaka, kot posledica pljuska tekočine ob steno, zelo dobro ujemal, oblika proste površine tekočine je malo odstopala, maksimalen tlak pa je bil višji. Pri dvojnem rezervoarju se je preverilo obnašanje tekočine pod vplivom nihanja sten v skladu s prej izračunano 5. lastno frekvenco in pripadajočo obliko. Pri tej obliki je nihala pregrada, tako da se je pojavilo gibanje proste površine le v zgornji polovici rezervoarja. Voda je prevladujoče nihala z obliko, ki so jo sestavljale prve štiri lastne oblike gibanja vode v togem rezervoarju in s frekvenco enako vzbujevalni. Oblike nihajočih prostih površin se niso tako dobro ujemale z izračunano, kakor so se frekvence, in sicer je pri simulaciji prevladovala prva namesto druge in tretje lastne oblike gibanja vode v togem rezervoarju, kakor je bilo izračunano.In this thesis a study of fluid-structure interaction in a double tank has been performed. The tank has been compartmented into two equally sized compartments. Each compartment has been half full, filled with water. Natural frequencies and mode shapes of partially fluid-filled tank have been determined from natural frequencies and mode shapes of the empty tank, velocity potentials of fluid-filled tank for each of the empty tank mode and sloshing velocity potentials and frequencies of water in the rigid tank. The elasticity of the tank has had little influence on the water sloshing, so the calculated natural frequencies of water sloshing have been almost unchanged. On the other side, the natural frequencies of the tank have been reduced in comparison with the empty tank and also mode shapes have been changed. The software package ANSYS CFX has simulated water behaviour under the influence of the vibrations and the homogeneous multiphase model has been used. The numerical model has been validated by a published benchmark test case. In comparison with the benchmark test, the moment of peak pressure has had a very good agreement with it, the shape of free surface has been slightly different and the peak pressure has been higher. After that, simulation with the double tank has been done. Here the walls have been vibrating with the 5th previously calculated natural frequency and a mode shape. In this mode, the compartment dividing wall has been vibrating and consequently sloshing has appeared in the upper compartment only. Water has been dominantly sloshing with the mode shape consisting out of the first four natural mode shapes of water in the rigid tank and with the frequency equal to the driving frequency. The mode shape of water has not been in such a good agreement with the calculated one, namely the first natural mode shape of water has dominated instead of the second and third, as calculated