Frequency Domain Seakeeping Computation (IR_SPEED)

IR_SPEED is a frequency domain seakeeping program based on the 3D Green Function Method (GFM). Its primary purpose is to assess ship motions and calculate the Response Amplitude Operator (RAO) in the presence of moderate forward speed conditions. The program utilizes the zero-speed Green function to determine the oscillating velocity potential and incorporates forward speed corrections, akin to strip theory. By implementing these forward speed corrections, the equation of motion is appropriately adjusted, resulting in modifications to the added mass, damping, and excitation terms. This comprehensive approach allows for a thorough evaluation of ship responses and loads, accounting for the influence of forward speed on the vessel's behaviour.

IR_SPEED is utilized for the computation of linear ship motions, accelerations, global loads, and dynamic hull pressure. These computed ship responses are then combined with environmental data to accurately estimate both the long-term and short-term seakeeping characteristics of the ship. In the analysis processes, this tool plays a pivotal role in deriving Equivalent Design Waves (EDW) for conducting the Direct Strength Analysis (DSA) of Ships. Additionally, it is also utilized to compute the linear wave loads for the direct application on Finite Element (FE) model of the ship. This step enables the assessment of structural responses to predict the potential fatigue damage using Spectral method and Residual Fatigue Life under various conditions.

• Ship motions and load RAOs at forward speed
• Dynamic hull pressure RAOs at the centroid of the panel
• Global hull shear forces and bending moments
• Added wave resistance amplitude operator
• Added mass and damping as a function of wave frequency
• Active fin control to stabilize the ship motion

Figure: Real and Imaginary dynamic hull pressure for a given wave frequency