Underwater Shock
Be prepared for a serious challenge
The threat posed by underwater explosions is still one of the most challenging design parameters for navy vessels. Numerical shock simulation is an inexpensive way to achieve sufficient shock strength, allowing easy comparison of different design variants.
Shock knowledge is of crucial importance in the design of naval ships; different topics have to be addressed. At first it must be demonstrated that the hull has sufficient strength to withstand underwater explosions (UNDEX) of defined intensity. Secondly, flooding of the vessel must be ruled out, i.e. it has to be shown that shell structures, directly exposed to the underwater pressure wave, will not collapse. Thirdly, it must be proven that hull appendages like rudders and shaft brackets remain operational after the shock. The same is true for machinery and equipment necessary to fulfil the vessel's mission.
Finally, it has to be demonstrated that the crew will not be seriously insured, either by the extreme accelerations or by being hit by equipment parts becoming loose. Naturally, a variety of methods and calculations is applied to perform such different kinds of computations. GL offers services tailored to the needs of ship yards, supply industries, navy or governmental bodies.
Global Shock Analysis
Global Shock Analyses require an interdisciplinary know-how on hydro-dynamics and structural mechanics. GL offers identification of eventual problem areas at an early design stage, development support of new and unique designs, determination of individual Shock Response Spectra (SRS) by considering the specific ship design. This may lead to more realistic shock loads apart from standardized rule loads. Several naval authorities require underwater shock simulations for the global hull girder during the design process. Specific software is needed for the related time domain simulation of the dynamic pressure loads, e.g. to account for the load effects resulting from the shock wave, local and bulk cavitation effects and the pulsation of the gas bubble.
The applied fluid-structure-interaction code enables to achieve the computational efficiency required to solve shock problems to an acceptable degree of accuracy at reasonable cost. A Global Shock Analysis will show whether the structural concept of your vessel is able to withstand a pre-defined shock factor and which modifications are required to fulfill the specified levels. Individual Shock Response Spectra (SRS) can be obtained, which are valid for the actual position of the respective machine or equipment in the hull.
Local Shock Analysis
In case of an underwater explosion the equipment on board a navy vessel is exposed to shock loads via its foundations in the form of accelerations, displacements and velocities. GL supports to identify shock resistant designs. GL offers optimisation of the supporting machinery and outfitting component structure, evaluation of the chosen shock mountings effectiveness and proof, that the shock resistance of structures, machinery and equipment are according to relevant standards.
For hull outfitting components installed on naval vessels and their supporting structures sufficient shock resistance against impulsive loads must be proved. The same is true for hull appendages like rudders and shaft brackets, which have to remain operational after an underwater explosion. It also has to be demonstrated that the crew will not be insured by being hit by equipment parts becoming loose. Naturally, a variety of methods and calculations is applied to solve such different kinds of problems. Almost for all calculations the finite element method is used. In addition to using Shock Response Spectra, the analysis can be carried out by employing a structural analysis in the time domain. The deflection and acceleration of outfitting components under shock load as well as the stress distribution and stress concentration of the local structure can be predicted. The results are compared to the target values and it is discussed whether design modifications are advisable.
Contact: shock@gl-group.com
