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With the help of theoretical analysis and numerical simulation, the modal parameters of the two-dimensionally low-order beam elements and high-order beam elements based on the absolute nodal coordinate formulation were studied. The analytical solution of the first-order thickness natural frequency of low-order and high-order beam elements considering the Poisson effect was derived. Based on the generalized characteristic equation, four natural frequencies and natural modes of bending, axial, shear and thickness of the shear beam element based on the absolute nodal coordinate formulation were obtained. Taking a simply supported beam structure as an example, the effects of the polynomial displacement field of the shear beam element on the four natural frequencies and natural modes of bending, axial, shear and thickness were analyzed. The results show that the polynomial displacement field of the shear beam element needs to introduce both the horizontal and vertical high-order terms x~2 and y~2. They mainly affect the bending and axial modal parameters, but have little effect on the shear and thickness modal parameters, and first-order thickness natural frequencies of the lower-order and higher-order beam elements is relatively close to the derived analytical solutions of first-order thickness natural frequencies.

In order to explore the application of the flexible multi-body systems with large deformation containing the nonlinearity of hyperelastic materials in engineering practice, the high-order beam elements and hyperelastic material constitutive models were studied for large deformation rubber beamsbased on the absolute nodal coordinate formulation ( ANCF) . The elastic force models of Neo-Hookean,Mooney-Rivlin and Yeoh, and their motion differential equations of three incompressible hyperelastic rubber beams were established by using the displacement mode of two-dimensional high-order ANCF beam element. Through the static and dynamic large deformation examples, the simulation results were compared with transverse low-order ANCF beam element and ABAQUS software. The results show that the incompressible hyperelastic constitutive model Yeoh and high-order ANCF beam elements are suitable for the dynamic analysis of large deformation rubber beams, and the polynomial displacement mode of element, the types of generalized coordinates of element nodes and the degrees of freedom of element have a great influence on the calculation efficiency of large deformation rubber beams. [ABSTRACT FROM AUTHOR]

Objective: To isolate bacteria from Nansha area of South China sea,, Methods: Sediment samples of 22 sites were used. Bacterial isolation was conducted on plates of marine medium, followed by 16S rRNA identification and phylogenetic analysis., Results: In total 349 bacteria were obtained, belonging to 87 species. Analyses of 16S rRNA sequence showed that Bacillus and other spore-forming bacteria occupied the majority of isolates in 10 sites. Bacillus was the most abundant bacterium and of high diversity; with 34 species and 8 possible novel species. Halobacillus also occurred frequently while other spore-forming bacteria including Brevibacillus, Paenibacillus, Pontibacillus and Thalassobacillus were also found, but less occurred in this area. In addition to these low-G+C-content bacteria, gamma-Proteobacteria were the second subgroup of high occurrence, among which Pseudomonas, Marinobacter and Alcanivorax were relatively abundant. Generally, isolates of 750-2000 m deep mainly consist of low-G+C-content bacteria, while mainly composed of gamma-Proteobacteria when the depth is over 2000 m., Conclusion: Marine sediments of South China Sea are rich in spore-forming bacteria, which deserve further study and exploitation.