# Study on Oscillatory and Undulatory Motion of Robotic Fish
## 3 Results and Discussion  
### Robotic Fish with Different Base Dimension  
The 3D model is meticulously crafted and edited with the assistance of Rhino 6 software (as shown in Figure 8). This software not only facilitates the construction of intricate models but also offers convenient accessibility to the body plan, making it exceptionally well-suited for manufacturing applications. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Properties** & **Condition** & **Value** \\ \hline Inlet & Prescribed velocity & 1–4 m/s \\ Outlet & Prescribed pressure & Gauge pressure \\ Fish surface & Prescribed velocity & \\ Wall & No slip and smooth wall & \\ Overset region & Inner interior & \\ Background region & Outer interior & \\ Density of water & - & 999.7 kg/m\({}^{3}\) \\ Kinematic viscosity & - & \(1.3084\times 10^{-6}\) m\({}^{2}\)/s \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Parameter conditions used in the simulations. Figure 6: Meshes created in the studied domain. Figure 7: Physical specifications of the domain with the boundary conditions. The entire calculation is performed with dimensionless parameters. Implementation of the dimensionless model is shown in Figures 9 and 10. Expressing the body's meridian section equation in coordinates \((X,\ Y)\) using a polynomial for the sectional-area curve [23] is shown as  
\[\pi Y^{2}=A_{1}X+A_{2}X^{2}+\ldots+A_{n}X^{n} \tag{14}\]  
The function f(\(x\)) is of degree six, while the function f(\(y\)) is of degree two:  
\[y^{2}=a_{1}x+a_{2}x^{2}+\ldots+a_{n}x^{n} \tag{15}\]  
The dimensionless combinations of the primary geometric quantities are as follows:  
\[x=\frac{X}{L},y=\frac{Y}{d};m=\frac{x_{m}}{L};\ r_{o}=\frac{R_{o}L}{d^{2}};\ r_{t}=\frac{R_{t}L}{d^{2}} \tag{16}\]  
Table 2 is used to explain the notation in Equations (14). The model utilized in this research study is derived from approximate specifications representing an adult shark. It  
Figure 8: Shape of the fish. Figure 10: Nondimensional representation of a sectional–area curve. Figure 9: Principal dimensions of a body of revolution. is important to note that this model is primarily designed for conducting computational fluid dynamic (CFD) simulations rather than resembling a robotic fish. Consequently, various details typically associated with a robotic fish, such as joints, connections, and openings, have intentionally been omitted from the design. This streamlined and simplified approach ensures that the model serves its primary purpose of facilitating CFD simulations effectively, allowing for a focused and comprehensive analysis of fluid dynamics and related phenomena without unnecessary complexities (as shown in Figure 11). To perform this simulation, the initial step involves creating a 3D model of the object or structure for which drag force calculations are required. This model should include all relevant surfaces and boundary conditions necessary for the simulation. Once the model is prepared, Ansys Fluent is used to set up the simulation project. This involves specifying the flow conditions, initial pressures, and boundary conditions. Turbulence model k-epsilon is chosen to accurately capture turbulent effects. Within the simulation setup, the drag force calculation feature is enabled. Once all parameters are configured, the simulation is executed. Ansys Fluent utilizes the provided information about the flow and object geometry to calculate the drag force based on the Navier-Stokes equations and relevant experimental or computational data. Upon completion of the simulation, the results are available for analysis within Ansys Fluent, displaying the magnitude and direction of the calculated drag force. These results are invaluable for optimizing designs, assessing performance, and making informed decisions in engineering and design processes. The flow velocity across the range of 1 to 4 m/s exhibits an interesting trend in the context of drag coefficient calculations.