# Numerical Simulation of the Force Acting on the Riser by Two Internal Solitary Waves
###### Abstract
For seasonal water layers, the load imposed on the riser by the inner solitary wave depends mainly on the variation in the water layer [29]. Numerical simulation has been used to investigate the interaction between internal solitary waves and transverse and extended cylindrical structures [30]. In another study, Open FOAM was used to numerically simulate the interaction between internal solitary waves in three cylinders and characterize the effect on the impact coefficient [31]. One study analyzing the stress at different sections of the riser under the action of the internal solitary wave using PIV technology found the variation trends for Cd and Cm hydrodynamic coefficients, where Cd decreases with an increasing Reynolds number, and Cm does not have a significant trend with an increasing Reynolds number [32]. The flow evolution of a cylinder with a single groove is also a focus of study. Different grooving angles have a significant effect on the fluid separation in the boundary layer, and the Strohal number (ST) reaches a maximum when the grooving angle \(\theta=90\) degrees [33; 34]. In addition, numerous studies have investigated internal solitary waves and offshore structures. Large gravity density stratified tanks have been used to analyze the interaction between an internal solitary wave and a tension leg platform and its load characteristics. Studies have found that the drag force coefficient in the Morison formula is in a power function relationship with the KC number [35; 36]. One study established a time-domain numerical model to calculate the action of internal solitary waves on offshore structures and structural motion response [37]. The reaction force caused by mooring lines was analyzed using the conduit theory, while the motion equation for offshore structures was solved in time-domain by the fourth-order Runge-Kutta method. Another study constructed an internal solitary wave propagation model in a continuous density stratified ocean and simulated a numerical flume with a submerged dike [38; 39]. One study experimentally investigated the effect of the splitter plate perpendicular to the waveform on the interaction between internal solitary wave and riser [40]. Semi-submersible platforms have also been used to simulate the nonlinear interaction between ISW and semi-submersible platforms. Studies have shown that the stress is mainly composed of wave pressure difference forces, viscous pressure difference forces, and frictional force [41]. [PERSON] conducted a numerical simulation on the interaction between an internal solitary wave and a floating tunnel. This research shows that changing the tunnel section shape can effectively reduce the vertical force and floating weight ratio [42]. Most studies have focused on the numerical simulation of a single internal solitary wave opposite a pipe. As a complex ocean phenomenon, the occurrence of internal solitary waves is often accompanied by many other phenomena. To address the current gaps in research, this paper numerically simulates the interaction between the symmetric and asymmetric internal solitary waves and the riser. Complex waveform changes and flow fields around the neutral and the force on the riser during relative motion are also explored and discussed.