## 2 Contribution Rate Modeling Framework  
### Analysis of the Causes and Threats  
An analysis of the causes and threats of submarines' ELF magnetic fields is crucial for research. Analyzing the causes of these magnetic fields provides a comprehensive understanding of their origins and composition. This understanding is vital for establishing a model. It is also essential for designing evaluation methods. ELF magnetic fields are particularly significant in the submarine domain, as they can be utilized for target detection and communication. Naval electromagnetic stealth refers to the use of specific designs, materials, and technical means to reduce the detectability of ships across the electromagnetic spectrum, which includes radio waves, microwaves, infrared, visible light, etc. This reduction in detectability aims to decrease the likelihood of ships being detected by enemy electromagnetic detection equipment, such as radar, infrared detectors, and photonic systems. The objective of this technology is to enhance the survivability and concealment of ships on the battlefield by minimizing their electromagnetic signal characteristics. The ELF magnetic fields generated by submarines during navigation can reveal their position. This poses a threat to their safety. In the current maritime battlefield, submarines face magnetic stealth threats. These threats are influenced by various causative magnetic fields. Firstly, the magnetic fields generated by the electronic equipment, power systems, and communication systems of submarines can produce detectable magnetic signals. The equipment's magnetic fields mainly comprise two forms: first, the submarine's internal electrical system and powered equipment often have multiple grounding points, with resistances and poor grounding creating potential differences that result in leakage currents radiating magnetic fields through the hull; second, high-power equipment inside the submarine radiates magnetic waves, which propagate into the seawater. The submarine equipment's magnetic fields are predominantly composed of extremely-low-frequency components, with frequencies related to equipment rotational speed. Changes in the magnetic field are related to equipment power and load, and the distribution of the magnetic field is closely related to the equipment's position, with varying trends in different positions, exhibiting complex spatial distribution characteristics. The intensity of the equipment magnetic field is dependent on the equipment power, load, and distance. Secondly, the rotation of the propeller causes periodic changes in the shaft system contact resistance, leading to corresponding periodic pulsations in the corrosion and anti-corrosion currents in the seawater. Naval corrosion is the process of gradual damage or destruction of a ship's metal structures due to chemical or electrochemical reactions in seawater, atmospheric conditions, or other corrosive environments. This process typically manifests as oxidation, dissolution, or loss of metal, leading to decreased structural integrity and impaired functionality of the ship, and potentially causing safety incidents. Anti-corrosion currents are direct currents applied to the metal structures of a ship from an external power source to prevent or slow down the corrosion process. These currents are used in cathodic protection systems, where the metal structure becomes the cathode in an electrolytic solution, thereby reducing the corrosion rate of the metal. The application of anti-corrosion currents can be achieved through methods such as sacrificial anode or impressed current systems, and it represents a crucial technical means to protect the metal structures of ships from corrosion damage. This results in the generation of ELF alternating shaft frequency magnetic fields [19]. The movement of the submarine causes changes in the shaft frequency electric field. As the submarine's speed or rotational speed increases,the intensity of the shaft frequency electric field also increases accordingly.