The isolation and control of the vibration of structures under fixed rotating machineries is an important issue. While the vibration in vertical direction is extensively studied, the horizontal vibration is paid little attention. This paper investigates the dynamic behavior of a single-story frame structure under the action of a rotating machinery. The relation between the amplitude of the horizontal/vertical displacement and the natural frequency of the structure, the location and the operating frequency of the machinery is analyzed in detail. The results show that the amplitude of the horizontal vibration can be larger than that in the vertical direction under certain circumstances, which should be taken seriously in design.
Cables are widely used as tension structure members in engineering as they are light, flexible and of high strength. On one hand, the external excitations induce cable's complex dynamic responses with large amplitudes, which might cause structure's failure. On the other hand, the cable structure is a typical nonlinear system with both quadratic and cubic nonlinearities, which means extensive nonlinear dynamic behaviors. Therefore, the cable dynamics is an interesting research issue in both engineering and applied mechanics, and our knowledge about the cable dynamics is much enriched in the past few decades. This paper reviews the progress of cable dynamics, including cable's dynamic models, internally resonant dynamics, moving support induced cable dynamics, and complex excitation induced cable dynamics. And we also discuss the limitations of the present cable dynamics.
By comparing the characteristics of the frozen soil and the unfrozen soil, it is shown that the strength of the frozen soil is much stronger than that of the unfrozen soil, which increases the difficulty of the frozen soil excavation, as an issue in front of engineering operations in cold regions. There are several methods for the frozen soil excavation and the practicability and the feasibility of the methods are reviewed in this paper. It is shown that the mechanical method used to excavate the frozen soil is extremely effective. Secondly, the difficulty of the frozen soil excavation is related to the physic-mechanical properties of the frozen soil. In the process of excavation, the fracture mechanics and the damage mechanics of the frozen soil are more involved. This paper gives a brief overview of the dynamics of the permafrost to indicate the main factors that affect the mechanical properties of the frozen soil and the features of the damaged frozen soil, to help the permafrost mechanical excavation. A review of the previous experimental researches aims to help the studies of the permafrost cutting and impact performance, and a few suggestions are made for the further study of the frozen soil excavation.
The contact process during a passive dynamic walking is studied experimetally, then the influences of the contact process on the passive waling stability are analyzed. The simulation method is used for comparison, and the simulation results are consistent with the testing results.
This paper presents an experimental study of the solid-water two-phase flow with different solid grain size distributions and flow velocities. First, the controlling parameters are obtained through the dimensional analysis, then a two phase flow is created by using glass beads(grain size:0.25 mm-2.0mm) and sands(d10=0:044 mm), respectively. The effects of the Reynolds number Re(640-3300) and the solid grain size are investigated. The results show that for the glass bead bed of mean grain sizes, the height of the bed in the tube increases linearly with the Reynolds number. For the sands of a wide particle gradation range, the small grains are flushed out of the tube and the residue mass decreases with the Reynolds number exponentially. The results might help the evaluation of the elevation of the soils containing the gas hydrate under the seafloor.
In this paper, the load capabilities of undamaged, damaged and double-sided scarf patch repaired foam-core sandwich structures are tested through the four-point-bending test. The test results show that the specimen will not fail at the repaired zone but at the loading position far away from the repaired zone. The maximum load applicable for the repaired structure is lower than that for the undamaged structure. Possible reasons and solutions for these problems are discussed in this paper. The simulation of the structure before and after being repaired by the finite element method(FEM) analysis shows that the analysis results agree well with the test results.
Although an indentation does not induce apparent cracking in ductile materials, the degradation of the elastic stiffness of ductile metals does occur in micro-/macro-indentation tests. After comparing the degradation predicted based on extended damaged-plasticity models with that measured by experimental testing, it is found that the softening due to the distortion of the existing voids is not enough to cause a notable degradation of elasticity. It is suggested that an independent damage-nucleation mechanism due to the shear deformation may be in operation. Although attractive in practical applications for its nondestructive nature, the damage-based indentation technique for estimating the fracture properties of ductile materials needs further investigations.
Catastrophic ruptures of the prestressed concrete cylinder pipe(prestressed concrete cylinder pipe, PCCP) due to corrosion of pre-stressed steel wires after cracking are very common. A new structural form of the PCCP with corrosion-resistant plastic coated steel liner(prestressed concrete cylinder pipe with plastic, PCCP-P) is proposed. A mechanical model based on the elastic plane strain theory for axisymmetric multilayer cylinders is established, with the radial pressure due to the pre-stressing at an intermediate radial position being taken into consideration. The mortar coating is not involved in the load bearing during construction, and the modulus of elasticity of the concrete varies during the precast stage and the operation stage, therefore, the analysis of the stress distribution in different layers is divided into several stages. The solutions obtained are consistent with the results of the finite element analysis. These study results can be used for analysis, especially in the design of the PCCP-P and the PCCP.
This paper analyzes the shear lag effect of box girder bridge based on the stiffened plate theory, and establishes the bar simulation method to study the shear lag effect of single box double cell box girder. A stiffener area formula and the shear lag differential equation are derived for the single box double cell box girder, based on a comparison of examples of the organic glass single box double cell box girder model for the shear lag effect in the numerical solution of plate and shell, and in the analysis of the experimental solutions and analytical solutions. The reliability and the accuracy of the bar simulation method in the study of shear lag effect of single box double cell box girder are verified.
This paper focuses on studying the relation between the Mei symmetry and the Noether symmetry, which takes the Lagrange system as an example. Based on the variational problem for Lagrangians under action of infinitesimal generator vectors, the Euler-Lagrange equations for the variational problem are established. The Noether symmetry for the variational problem is studied and corresponding conserved quantity is given. The studies show that the Euler-Lagrange equations and the Noether identity and the Noether conserved quantity of the variational problem are exactly the same with the criterion equation and structural equation and the conserved quantity for Mei symmetry of classical Lagrange system. In the end of the paper, we take the well-known Emden equation as example to illustrate the application of the results.