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Optimal design for composite high-pressure hydrogen storage tank

Updated: Nov 6, 2022

Contents

Overview

The article covers the design of composite vessels from the physical and mechanical aspects. The design heavily relies on the properties of materials to the geometry. The design cycle of hydrogen tanks begins with general characteristics, such as the tank capacity, working pressure, material attributes, and safety factors. followed by dome design and fiber placement orientation. The same finite element technique has been widely used to predict the failure properties and strengths of composites based on different failure modalities. The ultimate goal of all of these techniques is to arrive at a reliable burst pressure. ensuring the design conforms to the local authorities' standard, the burst pressure design has to be optimized for safety and reliability. The article leaves on a positive note by talking about the prospect of h2 vessels.


What is the design optimization of H2 tanks?

The design of the composite vessel relates the physical and mechanical properties of materials to the geometry. Essentially, two main works are required for the design: one is the prediction of burst pressure and another is the optimization. The burst pressure denotes the limited load-carrying ability of the composite vessel. Since the failure mechanisms of composites are complicated from the view of composite micromechanics, including the matrix cracking, fiber/matrix debonding, and fiber breakage as well as their interactions. The optimization attempts to improve the weight, strength, reliability, and lifetime of the composite vessel by designing the wound angles and thickness.

Design and Analysis Methodology

A complete design cycle of a composite hydrogen tank is illustrated in the Figure below. The design cycle of hydrogen tanks begins with step no. 1, which defines the project's general characteristics, such as the tank capacity, working pressure, material attributes, and safety factors. The designer can use this information to compute other parameters that are required for the tank geometry definition, such as the cylinder radius, boss radius, and tank length.


Design of Dome Profile

The dome shape of composite tanks has a significant impact on their mechanical performance. The isotensoidal dome geometry, which is based on geodesic winding trajectories, is a common dome geometry. Parameters defined in step no. 1, such as the tank capacity, working pressure, and material characteristics, were the input parameters for the dome profile equations


Dome design: (a) schematic representation of dome; (b) isotensoid dome contour generated with numerical integration.
Dome design: (a) schematic representation of dome; (b) isotensoid dome contour generated with numerical integration.

The optimum dome shapes can be approximated as quasi-elliptic curves. The most important design parameter would be the depth of the elliptical dome. When the dome depths are between 0.6 and 0.775, designed domes present a stronger structure and greater internal volume.


Finite Element Analysis of Hydrogen Tanks

The analytical design solution of composite hydrogen tanks is based on broad assumptions about load and boundary conditions and does not account for stiffness discontinuities near the polar boss. The finite element analysis (FEA) must be used to correctly model these and other effects in order to accurately predict the behavior of filament wound pressure vessels. Most filament wound pressure vessels exhibit first-order non-linear geometry effects, which can only be captured via the FEA.


The accuracy of the numerical analysis is mainly dependent upon the modeling technique and analysis conditions. The table below summarizes some approaches developed in the literature.




Modeling of Winding Layers

Composite tanks are wound using a combination of the alternate hoop and helical windings, whose main features are summarized in the table below. An alternate helical/hoop winding scheme is used to remove the excess resin and to obtain the target fiber volume fraction during the winding process.

Winding Type

Feature

Hoop winding

- Filaments are placed nearly perpendicular to the mandrel axis (α ≈ 90◦).

- Usually used with other strategies to resist circumferential stresses.

- Creates high consolidation pressure.

- Generally applied only to cylindrical sections.

- Placed at high speeds.

- Used to describe geodesics, non-geodesics and combinations thereof.

Low helical winding

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