According to new legal docs, obtained by TMZ ... model Ashley Morgan Smithline claims the shock rocker began contacting her in 2010 via social media and told her he wanted to cast her in an upcoming film project ... and developed an obsession, calling her "the perfect girl for him."

She claims he flew her to L.A. in Nov. 2010, and asked her to move into his apartment ... which she did, and she says they began a consensual sexual relationship.

However, Smithline alleges days after moving in with Manson, she "awoke from unconsciousness with her ankles and wrists tied together behind her back and [Manson] sexually penetrating her." She claims she told him no multiple times but he told her to shut up, and squeezed her ribs so hard it caused injuries ... along with injuries to her vagina.

According to the docs ... she was sexually assaulted by Manson again the same month, after he choked her and forced her on a bed. Smithline claims he "grabbed a knife next to the bed and began cutting [her] shoulder, inner arm, and stomach." She says she went into shock, and still has scars from the cuts.

On another occasion, she claims he broke her nose during forced sex.

Smithline claims they continued dating until January 2013. She says Manson frequently threatened her life, kept her confined to a dark space, physically abused her, called her anti-Semitic names and implemented torture tactics to maintain control over her.

Along with sexual assault and sexual battery, she's suing for intentional infliction of emotional distress and false imprisonment.

As we've reported ... Manson has also been recently sued for sexual assault by "Game of Thrones" actress Esme Bianco, his former assistant Ashley Walters, and an unnamed accuser.

A spokesperson for Manson tells TMZ, "We strongly deny Ms. Smithline’s claims. There are so many falsehoods within her claims that we wouldn’t know where to begin to answer them. This relationship, to the limited extent it was a relationship, lasted less than a week in 2010."