In recent years, the rapid development of the battery energy storage industry has led to widespread applications of energy storage battery cabins, which play a critical role in power system operations, such as peak shaving, frequency regulation in power plants, black start capabilities, and serving as mobile power sources. The energy storage battery cabin under investigation is a novel structure based on standard designs, specifically engineered for housing and transporting energy storage systems. It can be deployed at generation sites, transmission and distribution points, and user ends to expand grid capacity, improve power quality, and enhance reliability for critical loads. Currently, lithium-based energy storage systems in cabin configurations are favored for their high capacity, integration, mobility, adaptability, and scalability, making them indispensable in renewable energy generation, user-side applications, and grid-side operations. As a key component of energy storage systems, the structural reliability and safety of these cabins are paramount, necessitating thorough assessments to ensure performance under various conditions, including marine transportation.
Marine transportation poses significant challenges due to harsh environmental conditions, such as waves and winds, which can induce dynamic loads on the cabin structure. During ocean voyages, ships may experience rolling motions up to 20 degrees, leading to accelerations that stress the internal components, particularly the connections between liquid-cooled battery boxes and guide rails. These connections are identified as potential weak points, where structural failures could occur, risking the integrity of the energy storage cells. In this study, we address these issues through finite element analysis (FEA) using ANSYS Workbench, focusing on the strength evaluation and optimization of the cabin under extreme marine conditions. Our approach involves modeling the cabin structure, applying relevant loads, and designing reinforcement strategies to enhance safety and reliability.
The energy storage battery cabin examined here is a standard 20-foot liquid-cooled unit with external dimensions of 6,058 mm in length, 2,438 mm in width, and 2,896 mm in height, and a total mass of approximately 32 metric tons. It houses multiple systems, including battery packs, battery management systems (BMS), power distribution, liquid cooling thermal management, condensation prevention, fire protection, and environmental control. The main frame is constructed from high-weathering steel, with a corrugated roof panel reinforced with stiffeners, and rectangular tubes used for base beams and top cross-members, forming an integrated welded steel structure. Internally, the cabin contains nine battery racks, each welded to the bottom cross-beams and equipped with nine layers of guide rails. These rails hold eight liquid-cooled battery boxes and one high-voltage box per rack, secured via Z-shaped brackets that connect the energy storage cells to the rails. Limiting components are installed on the left, right, and rear sides of the rails to restrict movement of the battery boxes.
To perform the finite element analysis, we simplified the complex 3D model of the energy storage battery cabin to reduce computational effort while maintaining accuracy. Using SpaceClaim software, we removed minor features such as small holes, fillets, and chamfers, and retained only two battery racks along with the main cabin frame. Gaps between components were filled, and surfaces were repaired to ensure a clean, interference-free model. The masses of the battery boxes and other equipment were represented as point masses applied at their respective centers of gravity in the FEA model. This simplification allowed for efficient simulation without compromising the integrity of the structural analysis.
The material properties assigned to the cabin components are critical for accurate simulations. The primary structural elements are made of steel, while rubber pads are used at the rail limiting points to absorb shocks and vibrations. The properties are summarized in Table 1.
| Material | Density (kg/m³) | Elastic Modulus (MPa) | Poisson’s Ratio |
|---|---|---|---|
| Steel | 7,850 | 206,000 | 0.3 |
| Rubber | 1,200 | 5 | 0.495 |
Mesh generation is a crucial step in FEA, as it affects solution accuracy, convergence, and computational time. We employed an intelligent meshing algorithm in Workbench, with refined elements in regions of high stress gradients, such as the connections between the energy storage cells and guide rails. The resulting mesh consisted of 1,325,902 elements and 2,746,012 nodes, ensuring a balance between precision and efficiency. The mesh quality was verified to avoid distortions, with element sizes adjusted based on sensitivity studies. Contact definitions were established to simulate the welded and bolted connections within the cabin. All interfaces were modeled as bonded contacts, representing the integrated nature of the structure. This approach ensures that loads are properly transferred between components, mimicking real-world behavior.
The marine transportation conditions were derived from operational data for routes from Shanghai to Guyana, considering both normal and extreme scenarios. In normal sea states, wave heights average 2–4 meters, with wind speeds of 10–20 m/s, resulting in ship rolling angles of up to 20 degrees. This induces accelerations in the transverse (0.12g), vertical (1g), and longitudinal (0.01–0.03g) directions. However, during extreme weather events like typhoons, accelerations can increase significantly, with transverse accelerations reaching 0.5g, vertical accelerations up to 1.5g, and longitudinal accelerations of 2 m/s², while the rolling angle remains at 20 degrees. For this study, we focused on the extreme typhoon scenario as the critical case for strength evaluation. The accelerations are summarized in Table 2.
| Direction | Acceleration |
|---|---|
| Transverse | 0.5g (4.905 m/s²) |
| Vertical | 1.5g (14.715 m/s²) |
| Longitudinal | 2 m/s² |
To apply these loads, we defined a local coordinate system tilted at 20 degrees to represent the ship’s inclination. Accelerations were applied in this local system, while gravitational acceleration (9.81 m/s²) was applied in the global vertical direction. The base of the cabin was fully constrained to simulate fixation to the ship’s deck. The governing equations for stress and deformation in the FEA are based on the principles of linear elasticity, where the stress tensor $\sigma$ is related to the strain tensor $\epsilon$ via Hooke’s law: $$\sigma = C \epsilon,$$ where $C$ is the stiffness matrix. For von Mises stress, used to assess yield criteria, the formula is: $$\sigma_v = \sqrt{\frac{(\sigma_1 – \sigma_2)^2 + (\sigma_2 – \sigma_3)^2 + (\sigma_3 – \sigma_1)^2}{2}},$$ where $\sigma_1$, $\sigma_2$, and $\sigma_3$ are the principal stresses. Deformation is calculated from the displacement field $u$, satisfying the equilibrium equation: $$\nabla \cdot \sigma + f = 0,$$ where $f$ represents body forces, including those from accelerations.
The initial simulation results under extreme conditions revealed significant structural weaknesses. The maximum deformation was 46 mm, occurring in the cabin frame, while the maximum von Mises stress of 4,511.8 MPa was localized at the connection between the Z-shaped brackets and guide rails for the energy storage cells. This stress far exceeds the yield strength of steel (235 MPa), indicating potential failure at these points. The high stress concentrations suggest that the existing design is inadequate for marine transportation, as it could lead to bracket fracture and dislodgement of battery boxes, compromising the safety of the energy storage cells. Further analysis showed that stress gradients were steepest near the connections, emphasizing the need for reinforcement to distribute loads more evenly.
To address these issues, we designed a reinforcement structure consisting of a rectangular tube array installed in the gaps between the liquid-cooled battery boxes and the door frame. This array includes vertical rectangular tubes connected to all Z-shaped brackets and battery boxes within each rack, linked by horizontal stiffeners to form a rigid framework. Rubber cushion pads are attached to the tubes to fill voids and absorb impacts, thereby restricting outward movement of the energy storage cells during accelerations. The reinforcement acts to transfer loads from the battery boxes to the door panel and main frame, reducing stress concentrations at the original weak points. The design is lightweight and minimally invasive, ensuring it does not interfere with the cabin’s internal layout or functionality.
We then performed a second FEA on the optimized model under the same extreme conditions. The results demonstrated a remarkable improvement: the maximum deformation decreased to 1.95 mm, well below the allowable limit of 12 mm (calculated as L/500, where L is the cabin length of 6,058 mm). The maximum von Mises stress was reduced to 243 MPa, with only isolated stress concentration points that can be disregarded in practice. The majority of the structure exhibited stresses below the allowable value of 213 MPa, derived from the yield strength divided by a safety factor of 1.1 (i.e., 235 MPa / 1.1). This confirms that the reinforced design meets strength requirements for marine transportation. The deformation and stress distributions are more uniform, indicating effective load redistribution. A comparison of key parameters before and after optimization is provided in Table 3.
| Parameter | Initial Model | Optimized Model | Allowable Value |
|---|---|---|---|
| Max Deformation (mm) | 46 | 1.95 | 12 |
| Max von Mises Stress (MPa) | 4,511.8 | 243 | 213 |
| Critical Locations | Z-bracket and rail connections | Isolated points | N/A |
The optimization not only enhances the strength but also improves the overall safety and reliability of the energy storage battery cabin. By integrating the rectangular tube array, we effectively mitigate the risks associated with marine transportation, ensuring that the energy storage cells remain secure under dynamic loads. This approach leverages finite element analysis as a predictive tool, allowing for proactive design improvements without costly physical prototypes. The methodology can be extended to other components of energy storage systems, such as thermal management units or battery enclosures, to further optimize performance in harsh environments.
In conclusion, this study successfully identifies and resolves structural weaknesses in energy storage battery cabins for marine transportation through finite element analysis and targeted reinforcement. The initial model revealed critical stress concentrations at the connections between energy storage cells and guide rails, which were alleviated by a rectangular tube array design. Simulation results confirm that the optimized cabin withstands extreme accelerations and rolling motions, with deformations and stresses within safe limits. This work provides a robust framework for assessing and enhancing the structural integrity of energy storage systems, contributing to safer and more reliable operations in global energy applications. Future research could explore dynamic analyses, material innovations, or real-time monitoring to further advance the design of energy storage cells and their enclosures.