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The temperature is a critical factor that determines the unfrozen water content and ice content in the frozen soil. In view of mechanical properties of the frozen soil depend on the volume of components of the four-phase systems, thus the temperature has a significant impact on the mechanical behaviors and deformation properties. The thermal state of the embankment in permafrost regions has a significant seasonal difference, then the seismic performance of the embankment alters with the season. In addition, the seismic performance is highly influenced by the properties of the earthquake motion, especially the seismic intensity. Combining these factors, a numerical simulation was conducted in this study. In this study, taking a typical section of Qinghai-Tibet Railway as an example, a numerical case study on the seismic behavior of embankment was carried out using the dynamic explicit FEM code ABAQUS/Explicit. The El Centro excitation with different intensities was performed in numerical analysis and two distinct thermal states of the embankment in extreme cold and warm days were considered as well. The seismic behaviors of the embankment, including the acceleration responses, the strain response, and the displacement response, were studied effectively. This paper proposes approaches and methods to study the seismic failure mechanism of the infrastructures, and the results can serve as a scientific basis for resisting earthquakes and preventing disasters in cold regions. [ABSTRACT FROM AUTHOR]

The thermal insulation effect of snow on the active layer thickness of permafrost cannot be ignored. Under the dual influence of snow cover and roadbed construction, this paper studies the influence of snow cover on the temperature field and permafrost upper limit under the permafrost roadbed in the alpine mountains. Through the application of PDE module in Comsol software, the hydrothermal coupling analysis of roadbed is carried out by means of numerical analysis. The results show that the permafrost degradation is accelerated by the snow on the subgrade surface, the temperature increases significantly, the thickness of the active layer increases, and the permafrost upper limit moves downward. With the increase of seasonal snow thickness, the permafrost temperature under the subgrade increases, the low-temperature permafrost under the subgrade has the risk of changing to high-temperature permafrost. The melting groove is formed under the subgrade on the right side, and with the increase of snow thickness, the area of the melting groove expands and develops towards the center of the subgrade. Permafrost upper limit on the left and right shoulder is lower than that on the right shoulder, and snow cover has a greater impact on permafrost upper limit on the right shoulder. [ABSTRACT FROM AUTHOR]

Because thermowells are prone to fatigue damage in petroleum cracking gas pipelines, in this paper, the LES method is used to simulate the flow around thermowells through two-way thermal-fluid-solid coupling, the internal causes of thermowell damage are explored, and measures for improving the thermowell safety are proposed. According to this study, when high-speed, high-temperature gas passes the thermocouple bushing, the main factors affecting the structural safety of the thermocouple bushing are the alternating stress caused by the vortex falling off, the thermal stress cycle due to the temperature gradient, and the pressure gradient impacted by the gas. Furthermore, this paper proposes improving the thermowell safety by installing the interference devices and optimizing the installation angle. The improvement measures were studied by conducting a two-way thermal fluid-structure coupling simulation. The results of this study show that after installing the interference device and optimizing the installation angle the displacement deformation of the thermowell and the equivalent stress is reduced by 57.2% and 72.1%, respectively, which indicates the safety improvement of the thermowell structure and the effectiveness of the method. The research contents of this paper can provide guidance for the installation and use of thermocouple bushing. [ABSTRACT FROM AUTHOR]

A brand-new rubber cushion is proposed in this paper, which is installed between hinged floating modules in order to reduce the relative motion of the pitch; meanwhile, the cushion can be used as a fender for anti-impact in the docking process. Using the linear wave potential method, the structural dynamic model is formulated where the equivalent stiffness matrix for the rubber cushion is obtained by an integrating method employing linear assumption in addition to considering the heterogeneity of rubber. A numerical analysis is presented for a two-module semisubmersible floating structure. The hydrodynamic responses and connector loads of the floating structures with a rubber cushion are analyzed by using the frequency domain approach in both regular and irregular waves. The topological design and stiffness parameter selection of the rubber cushion is studied. This work may provide a new idea for suppressing the pitch motion of multiple hinged floating structures. [ABSTRACT FROM AUTHOR]

Collision on reinforced concrete (RC) piers by moving vessels or vehicles is a significant issue. This paper presents the static and impact behavior of RC piers with different hollow ratios. Three specimens were statically tested to obtain the load-displacement response. Low-velocity collision on eleven RC piers was conducted under the same velocity of 2.42 m/s. The damage process, failure mode, and force response were comprehensively analyzed. The experimental results indicate that the hollow ratio plays a significant role in the failure mode and ultimate load of RC piers under static and impact loadings. For RC piers with a hollow ratio of 0 and 0.4, the global failure dominated the damage process. However, failure of piers with a hollow ratio of 0.6 was governed by the local damage near the loading point. The static load capacities of the RC piers with a hollow ratio of 0.4 and 0.6 were 1.27% and 60.5% smaller than that of the solid pier, respectively. RC piers with a higher hollow ratio or lighter drop weight suffer smaller peak impact force. The increase of the longitudinal reinforcements leads to a promotion of the peak and mean impact force. Furthermore, the numerically predicted failure modes and impact load response show satisfactory agreement with the experimental results. [ABSTRACT FROM AUTHOR]

The main purpose of this paper is to investigate the qualitative effects of external excitation and friction factor on the response of permanent magnet synchronous motor (PMSM) system. Three different modes of bursting oscillations are found. In particular, the introduction of friction function changes the governing equations from a smooth type to a nonsmooth (Filippov) type in which the special sliding motion is observed. The mechanism, attractor structure, vector field structure, and analytic bifurcation conditions of bursting oscillation and sliding motion are discussed in detail. The validity of theoretical results obtained is verified by numerical simulations and analysis. [ABSTRACT FROM AUTHOR]

To analyze heat effect in deep metal mines, it is crucial to understand the temperature field distribution around the mine tunnel. In this paper, a numerical model of the random mineral composition of the rock body is established based on finite element software to analyze the influence of the internal composition of the surrounding rock on the temperature field, and a numerical simulation model based on COMSOL finite element software is established based on the two heat exchange modes of heat conduction and heat convection in the surrounding rock. The results show that the numerical simulation results of a typical numerical simulation model using a single material are lower than the real situation; increasing the tunnel length does not increase the heat exchange efficiency between the rock wall and the air; increasing the wind velocity has a limited impact on the temperature field; the wind temperature more directly affects the mining surface; and the effect of wet air on the temperature field of the surrounding rock has a more substantial variation. [ABSTRACT FROM AUTHOR]

With the increasing depth of coal mining and expanding mining scale, the rocks surrounding deep roadways are in a complex mechanical condition of frequent dynamic disturbance. The heterogeneity has an important influence on rock mass failure under dynamic loads. Therefore, it is necessary to study the deformation and failure of heterogeneous roadway under dynamic load. In this paper, the effect of heterogeneity on stability of roadway under static and different dynamic loads is studied. According to the results, the effect of rock mass heterogeneity on the deformation and failure of surrounding rock varies with different degrees of heterogeneity. Under static loading conditions, the stability of roadway is negatively correlated with the degree of heterogeneity of the rock mass. Under dynamic loading conditions, the change of heterogeneity degree has significant influence on the stability of surrounding rock. With the increase in dynamic load strength, the change in variation difference in the average value of roof sag, stress distribution, and plastic zone caused by variations in heterogeneity will increase. This study contributes to understanding the deformation and failure characteristics of heterogeneous roadways under dynamic loads and can be used to analyze heterogeneous roadways under dynamic loads. [ABSTRACT FROM AUTHOR]

The numerical tools can be used to facilitate the design of the railway pantograph-catenary system. The validation of the current numerical results is mostly performed at a speed slower than 350 km/h. This paper aims at the validation and analysis of the numerical results at a super-high-speed. The catenary model is constructed based on a nonlinear finite element approach employing the absolute nodal coordinate formulation. A multibody dynamics model is adopted to represent the pantograph. The measurement data are collected by an inspection vehicle equipped with an instrumented pantograph operating at 378 km/h in Chengdu-Chongqing high-speed line. Comparing the numerical simulation and the field test shows that the present pantograph-catenary model can provide reliable numerical results at 378 km/h. The numerical analysis of pantograph-catenary interaction at super-high-speed shows that the trailing pantograph performance does not comply with the assessment standard at 378 km/h. The adjustment of double-pantograph interval and messenger wire tension can effectively improve the trailing pantograph performance. [ABSTRACT FROM AUTHOR]

Regarding the vib-acoustic performance of internal coupled structures, basically all relevant studies have been confined to the classic form of connections. In this investigation, the boundary and internal elastic constraint matrices of the coupled structure are established, the vibration and sound calculation model of the coupled structure is then established, and numerical analysis is performed to show the effect of constraint stiffness on the vibration and acoustical performance of a coupled plate-cylindrical shell system. The results show that impedance matching between the structures is improved with the increase of the elastic connection stiffness, which is conducive to the vibration energy propagation. Moreover, the supporting coupling stiffness between elastic coupled structures plays an important role in vibration energy transfers. [ABSTRACT FROM AUTHOR]

Mechanical power loss in pneumatic hammers comes from the friction between parts in relative motion, and wear is among the failure mechanisms of the top hammer. Therefore, it is important for high performance and a longer service life of pneumatic hammers to reduce the friction force between parts in relative motion. This study presented a novel approach to quantitatively determine the friction force and consider it in the simulation model of pneumatic hammer. First, the friction force between piston and cylinder in a small pneumatic hammer was measured using an experimental setup at different inlet pressures. We could find from the experimental result that the friction force was about 0.8 N under the horizontal installation when there was no pressure supply, but it increased significantly, was 20 times greater than that without pressure supply, due to aerodynamic action by compressed air leaked from the annular gaps between the cylindrical matching surfaces of the components. In addition, it increased from 10.27 to 16.7 N due to an increase in inlet pressure and mechanical power loss in the pneumatic hammer that was about 10% of impact energy. Then, numerical analysis for a small pneumatic hammer performance was performed by a model considered the friction force using AMESim software. Finally, it can be seen from the simulation results that the proposed approach could significantly reduce the error between the simulated and the measured values for the impact energy because of ignoring the friction force. This approach will be used to predict service life of piston and find a low friction piston of pneumatic hammer in practical engineering. [ABSTRACT FROM AUTHOR]

A model of a segmented electrode multilayer cantilever piezoelectric actuator was established to predict its actuation performance, and then, theoretical and numerical analyses of the strain nodes were performed based on normalized deflection and strain distributions. The segmented electrodes instead of the continuous electrodes are applied in a multilayer cantilever piezoelectric actuator which can avoid the modal displacement offsets at the high vibration modes, thereby enhancing the tip deflection. The theoretical analysis and simulation results show that the tip deflection of the segmented electrode at the second mode was almost 100% larger than that of the continuous electrode. At the second mode, the maximum error between the theoretical calculation value of the tip deflection and the simulation result is 6.8%. It is because the segmented electrode is optimally designed at the strain node, which avoids the modal displacement offsets of a multilayer cantilever piezoelectric actuator at the high vibration modes; meanwhile, the theoretical results are closer to the FEM simulation results. It reveals that the tip deflection of a multilayer cantilever piezoelectric actuator can be precisely estimated by the proposed model. This research can provide some useful guidance improving the actuation performance and optimizing the design of a multilayer cantilever piezoelectric actuator. [ABSTRACT FROM AUTHOR]

In order to further reveal the influence mechanism of borehole water content on anchoring force in soft surrounding rock, three different research methods are used. Firstly, through theoretical analysis, it reveals that borehole water content will affect the cohesion of anchoring agent and then leads to the decrease of anchoring force. Secondly, through experimental analysis and numerical simulation of the influence of different boreholes water content on the anchoring force, it indicates that the borehole water content has a weakening effect on the mechanics characteristics of bolts significantly. When the borehole water content is less than 15 mL, the influence of borehole water content on anchoring force is weak for a given borehole length. When the borehole water content is greater than 15 mL, the anchoring force decreases greatly with the increase of borehole water content for a given borehole length and the decline of anchorage force is more than 30%. At the same time, through the experimental analysis, it reveals that the failure type of bolt in weak surrounding rock is the typical failure of anchorage force where the fracture goes far into the surrounding rock. Thus, in practical operation, reasonably controlling the borehole water content (rate) within the critical value can improve the bolt support effect and reduce the support cost. [ABSTRACT FROM AUTHOR]

The investigation aims to propose a refined model to analyze the parametric resonance under multicable systems such as cable-stayed bridges. Considering the interaction between the adjacent beam portions, the shear difference is applied to modify the vibration equations derived from the multi-degree-of-freedom stiffness method. Furthermore, the difference method is adopted to make the equations more accessible for numerical analysis. The comparison results indicate that the refined model exhibits the key character of parametric resonance and also further verified the simulation methods. The consequences show that the cable will resonate at the fundamental frequency under the support excitation. In particular, when resonance occurs, most of the energy in the subsystem is transferred to the cable, resulting in the resonance amplitude of the beam portion being weakened to some certain extent. Moreover, the global resonance will have a sufficient excitation on the local resonance only when the resonance condition is satisfied. [ABSTRACT FROM AUTHOR]

Based on a lumped parameter model with two degrees of freedom, the periodic response of the coupled axial-torsional nonlinear vibration of drill strings is studied by HB-AFT (harmonic balance and alternating frequency/time domain) method and numerical simulations. The amplitude-frequency characteristic curves of axial relative displacement and torsional relative angular velocity are given to reveal the mechanism of bit bounce and stick-slip motion. The stability of periodic response is analyzed by Floquet theory, and the boundary conditions of bifurcation of periodic response are given when parameters such as nominal drilling pressure, angular velocity of turntable, and formation stiffness are varied. The results show that the amplitude of the periodic response of the system precipitates a spontaneous jump and Hopf bifurcation may occur when the angular velocity of the turntable is varied. The variation of parameters may lead to the complex dynamic behavior of the system, such as period-doubling motion, quasiperiodic motion, and chaos. Bit bounce and stick-slip phenomenon can be effectively suppressed by varying the angular velocity of turntable and nominal drilling pressure. [ABSTRACT FROM AUTHOR]

Particle dampers are devices used to control the vibration of mechanical systems. In this research, prototypes of rotary elastomer particle dampers are experimentally tested considering gap and no gap between shaft and cylinder. There is a gap between the rotor and cylinder in the gap model; particles can move from one chamber to another. There is no space for the particles to move from one chamber to another in the no-gap model. Elastomer particles are soft, and they have different behavior from hard (metallic) particles. Experiments on rotary elastomer particle dampers considering the gap between rotor and cylinder helped investigate the effects of the change in packing fraction, rotational speed, size of elastomers, and the gap between the rotor and the damper body. A numerical simulation approach based on the discrete element analysis method is used to perform a quantitative and qualitative analysis of the rotary elastomer particle damper. The simulation results are in great agreement with the experiment results. It is observed that packing fraction, rotational speed, size of elastomer particles, and the gap between rotor and cylinder play a vital role in producing higher damper torque. [ABSTRACT FROM AUTHOR]

The rock burst caused by geological structures is abrupt and destructive, and the special structure of a graben fault decides the uniqueness of mine ground pressure in the mining process. By simplifying the graben fault structure, the evolution law of roof stress during the recovery process was studied based on the theory of the elastic shear beam. The change laws of stress field and displacement nearby the fault during the advancement process of the working face were explored through a numerical simulation, and the instability mechanism and laws of rock strata nearby this graben fault were revealed. This study will be of great significance for preventing and controlling the rock burst in the graben fault. [ABSTRACT FROM AUTHOR]

It is important to guarantee the safety of adjacent underground structures during the foundation pit blasting excavation of modern city construction. The blasting excavation construction of a large, deep foundation pit near an existing metro station of Guangzhou Metro Line 3 is used as the example in this study. Based on blasting vibration field test results, the influence of blasting dynamic load on the lining of an adjacent metro tunnel is numerically analyzed in simulation using Fast Lagrangian Analysis of Continua 3D (FLAC3D), and the relationships between the blasting vibration velocity and stress and the displacement of the metro tunnel lining are obtained. The results show that the stress of lining structure is within the allowable range under the experimental blasting conditions, the lining displacement increases linearly with the applied dynamic vibration velocity, and the vertical displacement of the lining is more obviously affected than the horizontal displacement by the dynamic load. This study can be used as a basis for the control of blasting vibration in a complex urban environment. Its practical application shows that the proposed blasting plan and parameters are reasonable and effective. [ABSTRACT FROM AUTHOR]