مطالعه آزمايشگاهي رفتار هيدروالاستيك سازه هاي شناور بسيار بزرگ پيوسته و چند جزيي با اتصال مفصلي در برابر امواج

An experimental study on the hydroelastic behavior of continuous and multi component very large floating structures with hinge connection against waves

رفتار هيدروالاستيك نقش موثري در طراحي و ساخت سازه هاي شناور بسيار بزرگ دارد. معمولا اين سازه ها به صورت اجزاي جدا از هم بيرون از دريا ساخته مي شوند و با اتصال صلب در محل نصب به يكديگر متصل مي‌شوند. راه هاي مختلفي براي كاهش جابه‌جايي و تنش در اثر برخورد موج به سازه وجود دارد؛ اتصال اجزا سازه به يكديگر با اتصالات مفصلي يكي از راه‌هاي كاهش پاسخ هيدروالاستيك است. در اين مقاله رفتار هيدروالاستيك سازه ي يكپارچه، سازه هاي متشكل از دو و سه بخش به صورت آزمايشگاهي با يكديگر مقايسه شده‌اند. مدل آزمايشگاهي از جنس آلومينيوم با طول، عرض و ارتفاع به‌ترتيب 2، 55/0، 04/0 متر ساخته شد. اتصال بين بخش ها به صورت مفصل مدل شد. در يك مخزن توليد موج، كرنش‌ها و جابه‌جايي قايم مدل آزمايشگاهي در نقاط مختلف آن اندازه‌گيري شده است. موج‌هاي ايجاد شده، منظم و داراي دوره تناوب 67/0، 80/0، 91/0، 01/1 و 10/1 ثانيه بوده‌اند. مقايسه نتايج نشان مي‌دهد كه در هر يك از مدل‌ها، جابه‌جايي در امواج با طول بلندتر بيشتر است. همچنين تنش‌ در مدل‌هاي داراي اتصال، نسبت به مدل پيوسته، كاهش چشم‌گيري داشته و مقدار آن تقريبا نصف شده است. در امواج با دوره تناوب 67/0 و 80/0 ثانيه، مدل سه جزيي و در سه موج ديگر، مدل يكپارچه داراي جابه‌جايي كمتري بوده است. در مورد سه موج آخر (موج‌هاي با طول بلند) مي‌توان گفت در صورتي‌كه جابه‌جايي سازه‌ در حد مجاز باشد؛ براي كاهش تنش، بهتر است از اتصال در سازه استفاده شود.

Very large floating structures (VLFSs) have attracted the attention of many researchers and engineers working in the offshore and marine industry. They have proposed VLFSs for various applications such as floating airports, bridges, breakwaters, piers and docks, fuel storage facilities, emergency bases, entertainment facilities, recreation parks, mobile offshore military bases, and even for habitation. Hydroelastic behavior plays a significant role in designing and constructing very large floating structures. There are different ways to reduce structure displacement and its stress due to wave. These structures are usually made separately out of the sea, and then components are connected to each other with rigid connection in installation location. Connecting components with joint connections to each other is one way to reduce the hydroelastic response. In this paper, the hydroelastic behavior of continuous structures is compared experimentally with structures composed of two and three sections. In order to simulate the hydroelastic behaviors of floating structure, the applied floating structure was 300 meters in height, 60 meters in width and its bending rigidity was equal to 4.77×1011 N.m2. Experimental model of aluminum was fabricated with length, width and height of 2, 0.55 and 0.04 meters respectively. polyethylene was used beneath aluminum plate in order to provide floating. The first model had no connection in its length; it was continuous. In the second model which consisted of two sections with 1 meter in length, there was a joint connection as a cross line in the middle of it. The third model consisted of three sections is made up by attaching three aluminum plates 67 centimeters in length which were connected together by hinges. In a wave generated tank of Graduate University of Advanced Technology laboratory with 16 meters in length and 1 meter in width and height, strain and vertical displacement measured at different points of experimental model. 5 regular waves’ periods of 0.67, 0.80, 0.91, 1.01 and 1.10 seconds were created. water depth was 70 centimeter. Comparison of the results shows that in all three models, the displacement in long waves is more than other waves. Also, in the models with hinge connection compared to the continuous model, the stress has been significantly reduced and its value has almost halved. At the first wave whose period is 0.67 second, the maximum stress is almost equal in the models with connections; so the models with three components reflected better performance regarding displacement and bending in comparison with other models. Due to the second wave (with periods of 0.8) displacement in the model with three components was less than the others, but the stress of this model was more than the model with two components. In such a case, in structure designing regarding the ratio of wave length to structure length, the more significant factor (displacement or stress) for the project must be preferred. In the last three waves (waves with longer length) the continuous model had less displacement. On the other hand, in this model which had no connections, the stress was more than the other cases. Therefore, a parameter which may offer both advantages canʹt be recommended. Since bending moment difference in the continuous model is twice more than the models with joint connections, if the structure displacement be within permissible limit of the project, using joint connection would be economical in designing.