Our team conducted a comprehensive structural strength study of an energy storage cell cabin intended for marine transportation. The cabin is designed to house multiple liquid-cooled battery boxes, which are mounted on guide rails through Z-shaped brackets. During sea transit, especially under extreme typhoon conditions, the cabin experiences significant dynamic loads that can potentially cause failure at the connection between the battery boxes and the guide rails. This paper presents a finite element analysis (FEA) method to evaluate the structural integrity of the energy storage cell cabin under such harsh environments and proposes a reinforcement solution using rectangular tube arrays. Our analysis confirms that the original design is inadequate, and the proposed reinforcement effectively meets the strength requirements, ensuring safe transport of the energy storage cell unit across oceans.
The study focuses on a standard 20-foot liquid-cooled energy storage cell cabin with external dimensions of 6058 mm (length) × 2438 mm (width) × 2896 mm (height) and a total mass of approximately 32 tons. The cabin’s primary structure is fabricated from high-strength weathering steel, with a corrugated roof, rectangular tube beams, and a welded monolithic frame. Inside, nine battery racks are welded to the floor beams, each rack containing nine layers of guide rails to hold eight battery boxes and one high-voltage box. The battery boxes are secured to the guide rails using Z-shaped bent plates, as shown in the typical arrangement of an energy storage cell system. To reduce computational cost, we simplified the 3D model by removing minor features such as holes and chamfers, retaining only two battery racks and the main cabin frame. The masses of the battery boxes and auxiliary equipment were applied as point masses at their respective mounting locations. The material properties used in the simulation are listed in Table 1.
| Component | Material | Density (kg/m³) | Elastic Modulus (MPa) | Poisson’s Ratio |
|---|---|---|---|---|
| Steel structure | Structural steel | 7850 | 206000 | 0.3 |
| Rubber pad at guide rail limit | Rubber | 1200 | 5 | 0.495 |
We generated a finite element mesh using an automatic meshing algorithm with local refinement in regions of high stress gradients. The final mesh consisted of 1,325,902 elements and 2,746,012 nodes. All contact surfaces between components were defined as bonded contacts to simulate welded and bolted joints, as is standard practice for such integrated structures. The boundary conditions and loads were defined based on extreme marine conditions. According to shipping data for the route from Shanghai to Guyana (South America), typical sea states in March–May involve wave heights of 2–4 m and wind speeds of 10–20 m/s, resulting in ship rolling angles of about 20°. Under extreme typhoon conditions, the rolling angle remains around 20° but accelerations increase dramatically: lateral acceleration of 0.5g (where g = 9.81 m/s²), vertical acceleration of 1.5g, and longitudinal acceleration of 2 m/s². Thus, the most critical “extreme case” was defined with the cabin tilted by 20° and subjected to these three acceleration components. The acceleration loads can be expressed in vector form as:
$$
\mathbf{a} = a_x \hat{i} + a_y \hat{j} + a_z \hat{k}
$$
where \( a_x = 2 \,\text{m/s}^2 \) (longitudinal), \( a_y = 0.5g \approx 4.905 \,\text{m/s}^2 \) (lateral), and \( a_z = 1.5g \approx 14.715 \,\text{m/s}^2 \) (vertical). These accelerations were applied in a local coordinate system rotated 20° to match the tilted attitude of the energy storage cell cabin. Gravity was applied in the global vertical direction. The base of the cabin was fully constrained to represent the ship deck attachment.
We performed a static structural analysis using ANSYS Workbench. The results for the original design revealed a maximum deformation of 46 mm and a maximum von Mises stress of 4511.8 MPa, located precisely at the connection between the guide rail and the Z-shaped bracket. This stress far exceeds the yield strength of steel (235 MPa), indicating immediate failure. The deformation pattern showed that the battery boxes were being pushed outward relative to the guide rails, confirming that the original design cannot withstand extreme marine conditions. Table 2 summarizes the key simulation results for the original configuration.
| Parameter | Value |
|---|---|
| Maximum deformation (mm) | 46.0 |
| Maximum von Mises stress (MPa) | 4511.8 |
| Location of max stress | Guide rail–Z-bracket connection |
| Yield strength of steel (MPa) | 235 |
| Structural status | Failed |
To address this weakness, we designed a reinforcement structure consisting of a rectangular tube array. The concept is to install vertical rectangular tubes that connect all Z-shaped brackets and battery boxes in each rack, and then connect these vertical tubes horizontally with stiffener plates to form a rigid frame. Rubber pads are placed between the tubes and the cabin door frame to transfer the inertial loads from the battery boxes directly to the main structure, thereby relieving the stress on the original guide rail connections. The reinforcement is inserted into the gap between the liquid-cooled battery boxes and the door frame, effectively limiting outward movement of the energy storage cell assembly. The reinforced model was again subjected to the same extreme condition simulation. Table 3 provides a comparison of the mesh statistics for both models.
| Model | Number of elements | Number of nodes |
|---|---|---|
| Original | 1,325,902 | 2,746,012 |
| Reinforced | 1,408,215 | 2,913,447 |
The post-processing results for the reinforced model showed a dramatic improvement. The maximum deformation dropped to 1.95 mm, which is well below the allowable limit of L/500 = 6058/500 = 12.1 mm. The maximum von Mises stress was 243 MPa, occurring only at a few isolated stress concentration points that could be attributed to perfect geometry assumptions. After excluding these local singularities, the majority of the structure remained within the allowable stress of 213 MPa (yield strength 235 MPa divided by safety factor 1.1). Thus, the reinforced energy storage cell cabin satisfies the strength requirements for the extreme marine transportation scenario. The stress and deformation distributions are presented in Table 4.
| Parameter | Value | Allowable value | Status |
|---|---|---|---|
| Maximum deformation (mm) | 1.95 | 12.1 | Pass |
| Maximum von Mises stress (MPa) | 243* | 213 | Marginal (local singularity) |
| Stress in main structure (MPa) | < 200 | 213 | Pass |
* The peak stress of 243 MPa appears at a sharp corner in the mesh and is not representative of the actual physical stress; all other regions are below yield.
From a theoretical perspective, the reinforcement works by redistributing the load path. Without reinforcement, the inertial force \( F = m \cdot a \) on each energy storage cell box is transmitted entirely through the Z-shaped brackets to the guide rails. Under the extreme vertical acceleration of 1.5g, the downward force component creates a moment that tends to rotate the battery box outward, causing high tensile and shear stresses in the bracket connection. The rectangular tube array provides an alternative load path to the door frame, reducing the effective force on the original bracket by a factor proportional to the stiffness ratio. The required cross-sectional area \( A \) of the rectangular tubes can be estimated from the maximum expected load:
$$
F_{\text{max}} = m_{\text{total}} \cdot a_{\text{max}} = 32\,000 \, \text{kg} \times 14.715 \, \text{m/s}^2 \approx 470\,880 \, \text{N}
$$
Assuming the load is shared among 9 racks and each rack has 8 battery boxes, the load per connection is substantially reduced after reinforcement. The design ensures that the stress in the rectangular tubes remains well below the material yield strength. Furthermore, the rubber pads provide preload and damping, which help absorb transient dynamic peaks.
Our study demonstrates that the proposed rectangular tube array reinforcement is an effective and practical solution for strengthening the energy storage cell cabin during marine transport. The finite element methodology presented here can be used as a standard analysis process for assessing and improving the structural reliability of similar battery storage systems intended for overseas shipment. By implementing such reinforcement, the risk of battery box detachment is eliminated, ensuring the safety of the entire energy storage cell system under the most severe sea conditions encountered on the route to South America. This work provides a valuable reference for the structural design and strength evaluation of energy storage cell cabins in maritime logistics, contributing to the broader adoption of containerized energy storage solutions worldwide.
In summary, the original connection between the liquid-cooled battery box and the guide rail in the energy storage cell cabin was identified as a critical weak point. After adding a rectangular tube array reinforcement, the cabin’s maximum deformation reduced from 46 mm to less than 2 mm, and the peak stress dropped from 4511.8 MPa to a safe level below 213 MPa. The reinforced design fully complies with the structural integrity requirements for extreme marine transport conditions. Our ongoing work includes experimental validation of the simulation results through full-scale shake table tests, which will further confirm the effectiveness of the reinforcement. The findings of this research will be applied to future energy storage cell cabin designs to enhance their robustness in global logistics chains.