Houdini vat in unreal engine shading error

i have made an fluid simulation in houdini and export to unreal ,in went find in playing back animation ,but when i look closer ,the model shows some weird triangle shading ,i was though it might be normal errow ,but when i push the color map render out from houdini ,the color information in color map also messup by the triangle ,is there any one ever meet this propblem!