充液航天器质量特性计算方法研究

充液航天器的质量特性对飞行动力学建模和控制设计有着重要影响。质量特性测量装置通常只能测出干重状态下航天器的质量特性，而充液状态下的航天器质量特性只能靠计算给出，其中如何计及各贮箱内液体的惯性张量是此类工程计算的难点。首先采用势流理论推导了任意形状贮箱内液体质量特性的一般表达式，包括全充液情况和部分充液情况，其中对部分充液情况考虑了自由液面小幅晃动的影响；然后采用三维有限元方法建立了液体质量特性的数值计算方法，并通过一个验证算例确认了该计算方法的有效性；最后应用该方法计算了一个充液航天器的质量特性，并研究了不同的液体处理方法对计算结果的影响。研究表明，工程上通常采用的“固化液体”处理方法所计算出来的转动惯量明显偏大，而所提出的计算方法具有更好的理论正确性和工程适用性。

Computational methods of mass properties for liquid-filled spacecraft

Mass properties of liquid-filled spacecraft are important for flight dynamics modeling and control design. However, measuring devices for mass properties are usually applicable to measure the spacecraft mass properties of dry weight only. Mass properties of liquid-filled spacecraft can only be obtained by computational methods. How to take into account the inertial tensor of liquid in each tank is the difficult point in such engineering computation. Theoretical expressions for mass properties of liquid in an arbitrary shaped tank were derived in a general sense. The derivation was conducted for a fully filled liquid tank with no free liquid surface and a partially filled liquid tank with a free sloshing liquid surface of small amplitude respectively. A numerical method for computing the mass properties of liquid was proposed using 3D finite elements. As a verification example, the numerical solutions and the analytical solutions of mass properties of the liquid in a rectangular tank were compared, which confirmed the accuracy of the proposed method. As an application research, mass properties of a liquid-filled spacecraft were computed using different computational methods. Studies show that the traditional computational method which solidifies the liquid obtains obviously larger moments of inertia, while the proposed method is more correct in theory and more applicable in engineering.