1. Key: U-locks are generally equipped with keys, which can easily open the lock core.

2. Use password: Some U-locks are equipped with digital password locks. Enter the correct password to open the lock cylinder.

3. Use key card: Some high-end U locks are equipped with key cards, which are similar to credit card-sized cards and can easily open the lock core.

4. Use the master key: Some low-end U locks can use the master key to open the lock core, but this method is not recommended because it is easy to be used by thieves.

5. Use tools: If the lock core is damaged or the key is lost, you can use a professional unlocking tool to open the lock core. However, this method requires professional skills and tools, and it is not recommended to try it yourself.