I'm going to have to knuckle down to some serious study.

我得开始认认真真地学习了。

《牛津词典》

He managed to knuckle down to his lessons long enough to pass his examination.

他在离考试还有足够长时间的时候就开始认真学习，从而通过了考试。

youdao

As for Ronaldinho's fitness, if he doesn't move I am sure that he will knuckle down and train hard to get back to his previous levels.

鉴于罗纳尔迪尼奥的健康状况，如果他不转会，我确定他能够一扫阴霾并且努力训练找回自己的最佳状态。

youdao

And Russell told any cricketers who are feeling the wearying effects of their commitment to T20 cricket to knuckle down to the busy schedule.

BBC: Players 'do not enjoy' Twenty20

We've got to knuckle down, work hard and keep working at the shape.

BBC: Holmes hoping for Salisbury run

When he is over the euphoria of this innings he will have to knuckle down a bit, and he can do that without losing his natural flair.

BBC: Jonathan Agnew column