Kirxgof tenglamalari
Suyuqlik dinamikasida, Gustav Kirchhoff nomi bilan atalgan Kirchhoff tenglamalari, ideal suyuqlikdagi qattiq jismning harakatini tasvirlaydi. d d t ∂ T ∂ ω → = ∂ T ∂ ω → × ω → + ∂ T ∂ v → × v → + Q → h + Q → , d d t ∂ T ∂ v → = ∂ T ∂ v → × ω → + F → h + F → , T = 1 2 ( ω → T I ~ ω → + m v 2 ) Q → h = − ∫ p x → × n ^ d σ , F → h = − ∫ p n ^ d σ {\displaystyle {\begin{aligned}{d \over {dt}}{{\partial T} \over {\partial {\vec {\omega }}}}&={{\partial T} \over {\partial {\vec {\omega }}}}\times {\vec {\omega }}+{{\partial T} \over {\partial {\vec {v}}}}\times {\vec {v}}+{\vec {Q}}_{h}+{\vec {Q}},\\[10pt]{d \over {dt}}{{\partial T} \over {\partial {\vec {v}}}}&={{\partial T} \over {\partial {\vec {v}}}}\times {\vec {\omega }}+{\vec {F}}_{h}+{\vec {F}},\\[10pt]T&={1 \over 2}\left({\vec {\omega }}^{T}{\tilde {I}}{\vec {\omega }}+mv^{2}\right)\\[10pt]{\vec {Q}}_{h}&=-\int p{\vec {x}}\times {\hat {n}}\,d\sigma ,\\[10pt]{\vec {F}}_{h}&=-\int p{\hat {n}}\,d\sigma \end{aligned}}} bu yerda ω → {\displaystyle {\vec {\omega }}} va v → {\displaystyle {\vec {v}}} x → {\displaystyle {\vec {x}}} , mos ravishda; I ~ {\displaystyle {\tilde {I}}} inersiya tensor momenti, m {\displaystyle m} tananing massasi; n ^ {\displaystyle {\hat {n}}} nuqtadagi jismning sirtiga normal birlikdir x → {\displaystyle {\vec {x}}}  ; p {\displaystyle p} bu nuqtada bosim; Q → h {\displaystyle {\vec {Q}}_{h}} va F → h {\displaystyle {\vec {F}}_{h}} mos ravishda jismga taʼsir qiluvchi gidrodinamik moment va kuch; Q → {\displaystyle {\vec {Q}}} va F → {\displaystyle {\vec {F}}} jismga taʼsir etuvchi boshqa barcha moment va kuchlarni ham xuddi shunday bildiring. Integratsiya jismning sirtining suyuqlik bilan taʼsirlangan qismida amalga oshiriladi. Agar tana butunlay suvga botgan boʻlsa, jism cheksiz katta hajmdagi aylanadigan, siqilmaydigan, oʻzgarmas suyuqlikda, yaʼni cheksiz dam olishda boʻlsa, u holda vektorlar. Q → h {\displaystyle {\vec {Q}}_{h}} va F → h {\displaystyle {\vec {F}}_{h}} aniq integratsiya orqali topish mumkin va tananing dinamikasi Kirchhoff — Klebsh tenglamalari bilan tavsiflanadi: d d t ∂ L ∂ ω → = ∂ L ∂ ω → × ω → + ∂ L ∂ v → × v → , d d t ∂ L ∂ v → = ∂ L ∂ v → × ω → , {\displaystyle {d \over {dt}}{{\partial L} \over {\partial {\vec {\omega }}}}={{\partial L} \over {\partial {\vec {\omega }}}}\times {\vec {\omega }}+{{\partial L} \over {\partial {\vec {v}}}}\times {\vec {v}},\quad {d \over {dt}}{{\partial L} \over {\partial {\vec {v}}}}={{\partial L} \over {\partial {\vec {v}}}}\times {\vec {\omega }},} L ( ω → , v → ) = 1 2 ( A ω → , ω → ) + ( B ω → , v → ) + 1 2 ( C v → , v → ) + ( k → , ω → ) + ( l → , v → ) . {\displaystyle L({\vec {\omega }},{\vec {v}})={1 \over 2}(A{\vec {\omega }},{\vec {\omega }})+(B{\vec {\omega }},{\vec {v}})+{1 \over 2}(C{\vec {v}},{\vec {v}})+({\vec {k}},{\vec {\omega }})+({\vec {l}},{\vec {v}}).} Ularning birinchi integrallari oʻqiladi J 0 = ( ∂ L ∂ ω → , ω → ) + ( ∂ L ∂ v → , v → ) − L , J 1 = ( ∂ L ∂ ω → , ∂ L ∂ v → ) , J 2 = ( ∂ L ∂ v → , ∂ L ∂ v → ) . {\displaystyle J_{0}=\left({{\partial L} \over {\partial {\vec {\omega }}}},{\vec {\omega }}\right)+\left({{\partial L} \over {\partial {\vec {v}}}},{\vec {v}}\right)-L,\quad J_{1}=\left({{\partial L} \over {\partial {\vec {\omega }}}},{{\partial L} \over {\partial {\vec {v}}}}\right),\quad J_{2}=\left({{\partial L} \over {\partial {\vec {v}}}},{{\partial L} \over {\partial {\vec {v}}}}\right).} Keyingi integratsiya pozitsiya va tezliklar uchun aniq ifodalarni ishlab chiqaradi.