مدل‌سازي بارهاي ضربه‌يي انفجاري موثر بر عرشه‌ي شناورها و تحليل پاسخ محلي سازه‌يي در مقابل آن‌ها

MODELLING OF BLAST WAVE LOADS IMPOSED ON SHIP DECKS AND THEIR LOCAL STRUCTURAL RESPONSE

در اين نوشتار چگونگي مدل‌سازي بارهاي انفجاري منتجه از شليك تسليحات عرشه‌ي شناورها مورد مطالعه قرار گرفته است. در آغاز با بهبود يك روش مدل‌سازي موجود، تخميني بهتر از توزيع بارهاي ضربه‌يي ناشي از شليك تسليحات عرشه ارايه مي‌شود. سپس صحت نتايج حاصل از كاربرد مدل بهبود‌يافته، با استفاده از نتايج آزمايشگاهي موجود ارزيابي مي‌شود. آنگاه، ضمن تخمين توزيع بارهاي ضربه‌يي انفجاري موثر بر عرشه يك شناور آلومينيمي تخمين، پاسخ محلي سازه‌ي عرشه به اين نوع بارها مورد مطالعه قرار مي‌گيرد. مشاهده مي‌شود كه ورق‌ها در ميانه‌ي مرزهاي خود مستعد تسليم‌شدن هستند و با افزايش فركانس شليك در معرض افزايش ارتعاشات قرار مي‌گيرند. در فركانسي خاص از شليك (حدود نصف فركانس طبيعي سازه)، بحراني‌ترين حالت براي ورق اتفاق مي‌افتد.

In this paper, a method for modelling blast loads, induced as a result of firing guns installed on ship decks, and also their local structural response have been studied. First, it is attempted to give a better estimation of the distribution of the impulsive loads induced through firing deck guns, by improving an existing modelling method based on a scaling approach. Formulation of a free field muzzle blast wave using Friedlander waveform is discussed. The values of the parameters involved in the Friedlander waveform function, including the pick incident overpressure, blast arrival time and phase duration, are then expanded in detail. The formulation is further extended for far fields. The developed formulations are implemented in a computer code, enabling the user to obtain the distributions of pick incident overpressure, blast arrival time and phase duration for different locations lying on the surface of the structure under consideration. The outputs of the computer code are available in either graphical or tabular formats. The developed code, in combination with a finite element code, may be used for structural assessment of blast loaded structures. Then, the accuracy of the developed algorithm is evaluated against experimental data for a stiffened steel plate subjected to lateral blast loads. The values of maximum deflections obtained numerically and experimentally for the stiffened plate are compared against each other. It is revealed that the developed algorithm is capable of performing useful analyses for modelling blast loads and investigating their effect on structures. In the next step, using the expanded modelling procedure, the distribution of blast wave loads affecting the deck of an aluminium boat is estimated and, then, the local structural response of the deck structure to such loads is studied applying a non-linear finite element method. The analyses performed are of a non-linear transient dynamic type, and the effects of structural damping, and also heat affected zones due to welding, are considered in them.