مدل‌سازي عددي نيروهاي وارده از طرف امواج بلند (سونامي) بر موج‌شكن‌هاي كيسوني

Numerical Simulation of Long Waves (Tsunami) Forces on Caisson Breakwaters

در اين پژوهش، نيروهاي وارده از طرف امواج بلند (سونامي) بر موج‌شكن‌هاي كيسوني با كمك شبيه‌سازي عددي مورد مطالعه قرار گرفته است. نتايج صحت‌سنجي نشان مي‌دهد كه مدل‌عددي مورد استفاده، دقت خوبي براي مدل‌سازي نيروهاي وارده بر موج‌شكن‌هاي‌كيسوني از طرف امواج بلند دارد. در ادامه، فرمول تجربي براي محاسبه‌ي نيرو معرفي شده است. نتايج نشان مي‌دهد فشار نقطه‌‌يي وارد بر سازه علاوه بر ارتفاع موج، با عمق آب نيز مرتبط است. همچنين با جابه‌جايي سازه به سمت ساحل، مقدار نيروهاي وارده در ابتدا كاهش مي‌يابد؛ ولي در ادامه با تغيير فرم موج، نيرو افزايش مي‌يابد و در نهايت پس از شكست موج، نيرو با شيب تندي كاهش مي‌يابد. در پايان، بررسي‌هاي انجام‌شده نشان مي‌دهند كه در حالت شكست موج بر روي بدنه‌ي موج‌شكن، نيروهايي تا حدود 6 برابر نيروي امواج ناشكنا بر موج‌شكن وارد شده است.

In this research, long wave (tsunami) forces on caisson breakwaters have been investigated using numerical modeling. Verifications of the simulation results using experimental data, analytical formula and empirical formula show that numerical model is capable of modeling the aforesaid problem with enough accuracy. Several numerical simulations have been performed in the framework of this thesis to study different parameters affecting the forces induced by long waves on caisson breakwaters. An empirical equation has been introduced to estimate non-breaking long wave forces on caisson breakwaters. Results indicate that the force is a function of water depth and wave period in addition to wave amplitude. By moving the breakwater towards the shoreline, first, the force decreases, then, the force increases, by changing the shape of the wave, and, finally, the force significantly decreases after wave breaking. Results suggest that the wave action time on the breakwater shortens by decreasing water depth. Results show that the amount of exerted force by long wave, in our investigated model, is around 3.5 times more than the amount of force by short wave. Moreover, vertical distribution of long wave forces on the structure is more uniform than that for short waves. By increasing the seabed slope, wave amplitude and speed of horizontal orbitals in the wave crest significantly increase, which further increases wave forces on the structure. Results show that in a sloping bed, by increasing water depth, the effect of changes in bed slope on the amount of wave force is insignificant. Therefore, for relatively deep water, the seabed slope can be overlooked and then the force can be calculated using the formula for flat seabeds. The results also show that unlike the previous formula, the pressure unbreaking waves at the still water level is also influenced by water depth. Based on our results, breaking waves exert forces up to six times more compared to non-breaking waves.