In the modern engineering world, shell-like and conical panel structures play a crucial role. These structures are used across various industries, from aerospace to civil and mechanical engineering. Although frequently relied upon, these structures face significant challenges from a dynamic phenomenon known as flutter. Flutter is an instability that can threaten the structural integrity when the structure operates at high speeds. Among various types of structures, conical shells are less studied compared to cylindrical shells, and this research aims to fill that knowledge gap.

Research on flutter in conical shells began with early efforts by Bismarck-Nasr and Costa Savio in 1979, and Sunder et al. in 1983. These works identified the challenges and fundamentals of the flutter phenomenon, although a full understanding of the aeroelastic stability of conical shells was not entirely revealed at that time. This research provided an important initial framework for further studies but was not comprehensive enough to explain all aspects of flutter in conical shells, especially in the context of using modern composite materials.

Research conducted by Mahmoudkhani et al. and Sabri et al. in 2010 expanded the understanding of aeroelastic stability by focusing on various parameters and conditions affecting flutter. Nevertheless, despite many studies on cylindrical shells, conical shells, particularly those using advanced composite materials like fibers and graphene nanoplatelets (GNP), still require more in-depth research to explore existing potentials and challenges.

Based on previous research, several researchers from various institutional backgrounds collaborated to investigate the secrets of flutter. They include Prof. Mahyuddin K.M. Nasution (Universitas Sumatera Utara, Indonesia), Rahmad Syah and Dadan Ramdan (Universitas Medan Area, Indonesia), Hassan Afshari and Hossein Amirabadi (Islamic Azad University, Iran), Mahmoud M. Selim (Prince Sattam bin Abdulaziz University, Saudi Arabia), Afrasyab Khan (Suez University, Egypt), Md Lutfor Rahman and Mohd Sani Sarjadi (Universiti Malaysia Sabah, Malaysia), and Chia-Hung Su (University of Technology, Taiwan).

To analyze the flutter phenomenon in conical shells, Prof. Mahyuddin and the team used the First-Order Shear Deformation Theory (FSDT) as the basis for modeling. This theory allows researchers to account for deformations due to significant shear forces in thin structures. Aerodynamic pressure is then calculated using linear piston theory, which considers the interaction between airflow and the shell structure. "This theory is important because it provides insight into how airflow affects the shell, especially at high speeds where aerodynamic effects become more complex," said Prof. Mahyuddin.

The effective mechanical properties of the composite material used in the conical shell are calculated using several methods, including the rule of mixtures, Halpin-Tsai model, and micromechanics relations. The rule of mixtures helps determine the average properties of the composite material based on the proportion of each component, while the Halpin-Tsai model is used to estimate the effective elastic modulus. Micromechanical relations are used to calculate the shear modulus and density of materials consisting of various phases. This approach allows researchers to understand how different material components interact and affect the overall properties of the conical shell.

"In the calculation of mechanical properties, the Poisson ratio and density of the GNP-reinforced matrix are calculated based on the volume fraction of each component. The Poisson ratio measures how much the material expands or contracts laterally when deformed. Density, on the other hand, affects the total weight of the structure. The effective elastic modulus for the GNP-reinforced polymer matrix is estimated using the Halpin-Tsai model, which allows researchers to accurately calculate the material's strength and stiffness," added Prof. Mahyuddin.

Additionally, the shear modulus and density of the three-phase material are calculated using micromechanical relations. The shear modulus is a measure of the material's resistance to shear deformation, while density affects the mass and weight distribution of the structure. These calculations are crucial for understanding how the shell structure behaves under various load conditions and aerodynamic forces.

For flutter analysis, the natural frequencies and mode shapes of the conical shell are obtained using the Differential Quadrature Method (DQM). This method allows researchers to calculate how the structure vibrates at different frequencies and modes. The influence of various parameters, including geometric characteristics, boundary conditions, the number of circumferential waves, as well as the weight fractions of GNP and fibers, is explored to determine flutter boundaries. Prof. Mahyuddin emphasizes that these parameters affect how the conical shell behaves and how stable it is when operating at high speeds.

The results of this research show that increasing the weight fraction of fibers and GNP significantly enhances the aeroelastic stability and natural frequency of layered conical shells. This means that by adding more fibers and graphene nanoplatelets to the structure, the conical shell can become more stable and better withstand vibrations at supersonic speeds. This research provides an in-depth analysis of supersonic flutter characteristics in layered conical shells made from polymer composites, GNP, and fibers.

A better understanding of this structural behavior opens new opportunities for practical applications in high-tech design and development. For instance, more stable conical shells can be applied in high-speed aircraft, spacecraft, and other structures requiring vibration resistance and stability at high speeds. With this research, we can design more effective and reliable structures, leveraging modern composite materials to enhance performance and safety.

This research also highlights the importance of a multidisciplinary approach in understanding and addressing complex technical issues. "By combining mathematical theory, material experiments, and computational simulations, researchers can uncover new insights that improve the design and performance of conical shell structures. This not only enhances technical knowledge but also paves the way for innovations in various industrial applications," concluded Prof. Mahyuddin.