## 1 Introduction  
Truss-like structures are widely used in the practical engineering field, such as spacecraft [1], ships and underwater vehicles [2], and civil engineering [3], because of their high stiffness-to-weight ratio. Due to the higher configuration flexibility of truss structures, the wave propagation characteristics of truss structures are complex. Hence, there is inevitably a strong demand to establish an accurate prediction method, especially in mid- and high-frequency ranges, and analyze the vibration power flow transfer paths of the complex truss structure. Based on the above background, numerous studies have been carried out on the dynamics of truss structures, such as the differential transfer method [4], Rayleigh-Ritz method [5; 6], transfer matrix method [7; 8; 9], dynamic stiffness method [10; 11], and so on. [PERSON] [12] investigated the free vibration and vibration response of the space frame system under an external random load. They also developed a novel third-order shear deformation beam theory to simulate the static bending and free vibration responses of piezoelectric nanobeams [13]. [PERSON] [14] and [PERSON] [15] used a two-node beam element and finite element to analyze the static bend of FGM beam. [PERSON] [16; 17] used the finite element to solve the temperature, displacement, radial stress and hoop stress of a cylinder with thermal conductivity and cavity. [PERSON] [18] established a mathematical model and finite element implementation of heat transfer and mechanics of soils with phase change. Because most truss structures are arranged periodically in two or three dimensions, bandgap characteristics and wave propagation analysis of truss structures were studied by many researchers [19; 20; 21]. [PERSON] [22] analyzed the bandgap characteristics of the flexural wave of a two-dimensional periodic frame structure with a multi-material composite and local resonance by the spectral element method. [PERSON] [23] and [PERSON] [24; 25] also used the spectral element method to study the vibration band gap characteristics of periodic rigid-frame structures. [PERSON] [26] combined periodic structure theory and the finite element method to study free wave propagation and forced response in periodic truss beams with and without material periodicity. Band gaps were found to match well with the attenuation frequency ranges of the forced response. From the above, many works have been paid to the attention of band gaps, and litter works are focused on the vibration power flow analysis of truss structure, which can also be viewed as the wave propagation analysis point. The analysis of power flow in a vibration structure has been recognized as an important tool for controlling vibrations [27; 28]. [PERSON] et al. [29] presented a general power flow analysis of simple and complex rod/beam systems based on the concepts of the subsystem structural dynamics method. The results show that the power flow in each rod may be larger than the input power of excitation due to resonance. [PERSON] [30] based their work upon the transfer matrix of a single bay of the structure to investigate wave propagation, power flow, and resonance in a periodic truss beam. [PERSON] [31] investigated the power flow in two- and three-dimensional frames using a wave scattering approach, including axial, torsional, and flexural wave modes. They pointed out that the convenient FEM software can also be used to calculate the power flow, but a large number of elements are required at mid and high frequencies. Developing a fast and accurate calculation method for the power flow of a truss structure is also the purpose of this paper. The impedance synthesis method (ISM) is one kind of substructure method [32], which uses the interface force balance and geometrical compatibility to establish the whole dynamic model. It can be used for fluid-filled pipe systems [33; 34], pipe-plate coupled structures [35], and so on.