scholarly journals Mechanical Characteristics of Ballast Bed under Dynamic Stabilization Operation Based on Discrete Element and Experimental Approaches

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Lihua Wang ◽  
Zemin Zhao ◽  
Jiongli Wang ◽  
Xianzeng Li ◽  
Yayu Huang ◽  
...  
Keyword(s):  
Mechanical Characteristics ◽  
Simulation Analysis ◽  
Excitation Frequency ◽  
Three Dimensional ◽  
Element Model ◽  
Discrete Element ◽  
Stable Operation ◽  
Simulation Test ◽  
Lateral Resistance ◽  
Experimental Approaches

To study the mechanical characteristics of ballasted bed under dynamic stability, a three-dimensional discrete element model of ballasted bed with 1000 mm × 700 mm × 550 mm is established based on the discrete element method. Meanwhile, a simulation test bench with the same size is built for simulation analysis and experimental research. The variation law and trend of settlement, lateral resistance, and compactness of ballasted bed under different excitation frequencies are analyzed comprehensively. The results show that when the excitation frequency is constant, the lateral resistance of sleeper, the settlement of sleeper, and the compactness of track bed under sleeper increase first and then tend to be stable. With the increase in horizontal excitation frequency, lateral resistance of ballast bed, sleeper settlement, and compactness first increase and then decrease after stable operation. The values of these parameters are maximized when the excitation frequency is 36 Hz which is the relative optimal horizontal excitation frequency of this model.

Reduced Rough-Surface Parametrization for Use With the Discrete-Element Model

2009 ◽  
Vol 131 (2) ◽  
Author(s):  
Stephen T. McClain ◽  
Jason M. Brown
Keyword(s):  
Heat Transfer ◽  
Rough Surface ◽  
Surface Characterization ◽  
Rough Surfaces ◽  
Roughness Element ◽  
Three Dimensional ◽  
Element Model ◽  
Discrete Element ◽  
Diameter Distribution ◽  
Discrete Element Model

The discrete-element model for flows over rough surfaces was recently modified to predict drag and heat transfer for flow over randomly rough surfaces. However, the current form of the discrete-element model requires a blockage fraction and a roughness-element diameter distribution as a function of height to predict the drag and heat transfer of flow over a randomly rough surface. The requirement for a roughness-element diameter distribution at each height from the reference elevation has hindered the usefulness of the discrete-element model and inhibited its incorporation into a computational fluid dynamics (CFD) solver. To incorporate the discrete-element model into a CFD solver and to enable the discrete-element model to become a more useful engineering tool, the randomly rough surface characterization must be simplified. Methods for determining characteristic diameters for drag and heat transfer using complete three-dimensional surface measurements are presented. Drag and heat transfer predictions made using the model simplifications are compared to predictions made using the complete surface characterization and to experimental measurements for two randomly rough surfaces. Methods to use statistical surface information, as opposed to the complete three-dimensional surface measurements, to evaluate the characteristic dimensions of the roughness are also explored.

scholarly journals Ballast bed resistance characteristics based on discrete-element modeling

2018 ◽  
Vol 10 (6) ◽  
pp. 168781401878146 ◽  
Author(s):  
Zhiping Zeng ◽  
Shanyi Song ◽  
Weidong Wang ◽  
Haijian Yan ◽  
Guoshu Wang ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Discrete Element ◽  
Discrete Element Modeling ◽  
Slope Gradient ◽  
Three Dimensional Model ◽  
Lateral Resistance ◽  
In Situ Experiments ◽  
Distribution Limits ◽  
Longitudinal Resistance

In this study, in situ experiments were conducted to study the changing characteristics of the lateral and longitudinal resistance of a ballast bed, and a three-dimensional model for the ballast bed and sleeper was constructed based on the discrete-element method. The effects of the lateral and longitudinal resistance of the ballast bed, such as gravel ballast grading, sleeper depth, the angle of the shoulder slope, and ballast bed shoulder width, among others, were studied. The results suggest that (1) the lateral and longitudinal resistance of the ballast bed increases with the widening of ballast grading, and within the size distribution limits, the resistance of the ballast bed satisfies the specification; (2) the lateral and longitudinal resistance of ballast bed increases with an increase in the sleeper depth and the resistance of ballast bed satisfies the specifications for sleeper depth greater than 150 mm; (3) the lateral resistance of the ballast bed increases with a decrease in the angle of the shoulder slope, whereas the longitudinal resistance remains unchanged and the resistance of the ballast bed satisfies the specifications for slope gradient of 1:1.75 or less; and finally, (4) the lateral resistance of the ballast bed increases with the widening of the ballast bed shoulder, whereas the longitudinal resistance remains unchanged, and the resistance of ballast bed satisfies the specifications when the shoulder width is greater than 400 mm.

scholarly journals Analysis of Contact Mechanical Characteristics of Flexible Parts in Harmonic Gear Reducer

2021 ◽  
Vol 2021 ◽  
pp. 1-17
Author(s):  
Fanjie Li ◽  
Xiaopeng Li ◽  
Yajing Guo ◽  
Dongyang Shang
Keyword(s):  
Mechanical Characteristics ◽  
Angular Displacement ◽  
Excitation Frequency ◽  
Element Model ◽  
Industrial Robots ◽  
Axial Distance ◽  
Axial Vibration ◽  
Cylinder Length ◽  
Flexible Parts ◽  
Contact Mechanical

Harmonic gear reducer is widely used in industrial robots, aerospace, optics, and other high-end fields. The failure of harmonic gear reducer is mainly caused by the damage of flexible bearing and flexspline of thin-walled vulnerable components. To study the contact mechanical characteristics of flexible components such as flexible bearing and flexspline in harmonic gear reducer, the contact mechanical model of flexible bearing, vibration differential equation of flexspline, and finite element model of each component in harmonic gear reducer were established. Based on the established model of harmonic gear reducer, the influence of the length of flexspline cylinder and the thickness of cylinder bottom on the stress of flexspline is discussed, respectively, and the motion characteristics of flexible bearing are studied. At the same time, the spatial distribution of the displacement of the flexspline and the axial vibration response of the flexspline are studied. The correctness of the model established in this paper is verified by experiments. The results show that the increase of cylinder length can improve the stress of flexspline in harmonic gear reducer; the wall thickness of cylinder bottom mainly affects the stress at the bottom of flexspline but has little effect on the stress of gear ring and smooth cylinder. Along the axis direction of the flexspline, the radial displacement, circumferential displacement, and angular displacement increase linearly with the increase of the axial distance between the cylinder and the bottom. When the excitation frequency is high, the vibration mode of flexspline shell is mainly axial vibration. The research results will provide a theoretical reference for the optimal design of harmonic gear reducer and improving the service life of flexible parts.

Reduced Rough-Surface Parameterization for Use With the Discrete-Element Model

2007 ◽  
Author(s):  
Stephen T. McClain ◽  
Jason M. Brown
Keyword(s):  
Heat Transfer ◽  
Rough Surface ◽  
Surface Characterization ◽  
Rough Surfaces ◽  
Roughness Element ◽  
Three Dimensional ◽  
Element Model ◽  
Discrete Element ◽  
Diameter Distribution ◽  
Discrete Element Model

The discrete-element model for flows over rough surfaces was recently modified to predict drag and heat transfer for flow over randomly-rough surfaces. However, the current form of the discrete-element model requires a blockage fraction and a roughness-element diameter distribution as a function of height to predict the drag and heat transfer of flow over a randomly-rough surface. The requirement for a roughness element-diameter distribution at each height from the reference elevation has hindered the usefulness of the discrete-element model and inhibited its incorporation into a computational fluid dynamics (CFD) solver. To incorporate the discrete-element model into a CFD solver and to enable the discrete-element model to become a more useful engineering tool, the randomly-rough surface characterization must be simplified. Methods for determining characteristic diameters for drag and heat transfer using complete three-dimensional surface measurements are presented. Drag and heat transfer predictions made using the model simplifications are compared to predictions made using the complete surface characterization and to experimental measurements for two randomly-rough surfaces. Methods to use statistical surface information, as opposed to the complete three-dimensional surface measurements, to evaluate the characteristic dimensions of the roughness are also explored.

scholarly journals Calculation of Reasonable Tension Value for Longitudinal Connecting Reinforcement of CRTSII Slab Ballastless Track

2018 ◽  
Vol 8 (11) ◽  
pp. 2139 ◽  
Author(s):  
Long Chen ◽  
Jinjie Chen ◽  
Jianxi Wang
Keyword(s):  
Prestressed Concrete ◽  
Crack Width ◽  
Mechanical Characteristics ◽  
Tensile Force ◽  
Three Dimensional ◽  
Element Model ◽  
Railway Track ◽  
Tension Force ◽  
Original Design ◽  
Ballastless Track

There is confusion in the original design concept for the tensioning of longitudinally connected reinforcement of the CRTSII (China Railway Track System) slab ballastless track. In order to clarify the effect of tension value of longitudinal reinforcement on the mechanical characteristics of the ballastless track, a three-dimensional finite element model, considering the nonlinear interaction between the track slab and cement-emulsified asphalt (CA) mortar of the CRTSII slab ballastless track, was established. The mechanical characteristics of the track structure under longitudinal tension load and temperature gradient load of the longitudinal joint were calculated. A method of applying prestress to post-pouring concrete was proposed according to the concept of prestress loss of pretensioning prestressed concrete, a reasonable tensile force value was proposed after the crack width, and the reinforcement stress of the ballastless track in the operation stage was checked and calculated according to the concrete design principle. When the tension force is greater than 300 kN, it is harmful to the bonding between the slab and mortar layer, which is prone to interlayer damage. In order to add prestress to concrete with wide joints to ensure the longitudinal stability of the ballastless track, and that the reinforcement stress and crack width meet design requirements, it is suggested that the tension force value should be 230 kN. Further, the temperature difference between reinforcement and concrete should be 30 °C before the initial curdle of wide joint concrete.

The Application of Moldflow in Injection Mold Design of Mobile Phone Cover

2011 ◽  
Vol 228-229 ◽  
pp. 542-547
Author(s):  
Wen Jian Zhang ◽  
Qi Zhang
Keyword(s):  
Mobile Phone ◽  
Simulation Analysis ◽  
Three Dimensional ◽  
Element Model ◽  
Mold Design ◽  
Injection Mold ◽  
Three Dimensional Model ◽  
Molding Process ◽  
Injection Mold Design ◽  
Cae Technology

Based the CAE technology, the paper introduced the application of Moldflow Insight in injection mold design of mobile phone cover. First, we must preprocess the finite element model, including importing three-dimensional model, meshing, and process setting. And then, we can use preliminary simulation analysis to determine the number and location of the gate. Finally to filling, cooling, packing and warpage analysis for part which can help us to find the causes from warpage generated. By optimizing the molding process parameters, adjusting the dwell pressure and the dwell time we can get less warpage, which can meet the precision demand of parts, consequently, the result can provide gist for the mold designers to design and for the injection molding technologist to process parameter adjustment.

Finite Element Analysis of Resisting Explosive Loading for Mine Escape Capsule

2012 ◽  
Vol 446-449 ◽  
pp. 2206-2209
Author(s):  
Jin Long Wang
Keyword(s):  
Finite Element ◽  
Shock Waves ◽  
Simulation Analysis ◽  
Three Dimensional ◽  
Element Model ◽  
Explosive Loading ◽  
Element Analysis ◽  
Dimensional Finite Element ◽  
Simulation Results ◽  
Three Dimensional Finite Element

Three-dimensional finite element model of the mine escape capsule is established. With the different values of explosion shock waves, simulation analysis of the entry locker is performed by using ABAQUS. The simulation results indicate that the mine escape capsule is safe and available if the surge pressure of shock waves is less than 3.5Mpa.

Evaluation of Thermal Performance for Vacuum Glazing by Using Three-Dimensional Finite Element Model

2011 ◽  
Vol 492 ◽  
pp. 328-332 ◽  
Author(s):  
Zhi Ming Han ◽  
Yi Wang Bao ◽  
Wei Dong Wu ◽  
Zheng Quan Liu ◽  
Xiao Gen Liu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Simulation Analysis ◽  
Three Dimensional ◽  
Central Area ◽  
Element Model ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Vacuum Glazing ◽  
Three Dimensional Finite Element

Simulation analysis of thermal performance for vacuum glazing was conducted in this paper. The heat conduction through the support pillars and edge seal and the radiation between two glass sheets were considered. The heat conductance of residual gas in vacuum gap was ignored for a low pressure of less than 0.1Pa. Two pieces of vacuum glazing with sizes of 0.3 × 0.3 m and 1.0 × 1.0 m were simulated. In order to check the accuracy of simulations with specified mesh number, the thermal performance of a small central area (4mm×4mm) with a single pillar in the center was simulated using a graded mesh of 41×41×5 nodes. The heat transfer coefficients of this unit obtained from simulation and analytic prediction were 2.194Wm-2K-1and 2.257Wm-2K-1respectively, with a deviation of 2.79%. The three dimensional (3D) isotherms and two dimensional (2D) isotherms on the cold and hot surfaces of the specimens were also presented. For a validity of simulated results, a guarded hot box calorimeter was used to determine the experimental thermal performance of 1.0m×1.0m vacuum glazing. The overall heat transfer coefficients obtained from experiment and simulation were 2.55Wm-2K-1 and 2.47Wm-2K-1respectively, with a deviation of 3.14%.

Numerical Simulation Analysis of Deformation in TIG Welding of I-Steel

2011 ◽  
Vol 189-193 ◽  
pp. 2196-2199
Author(s):  
Ling Li Meng ◽  
Yan Qun Huang ◽  
Ming Liu
Keyword(s):  
Finite Element ◽  
Simulation Analysis ◽  
Three Dimensional ◽  
Element Model ◽  
Welding Parameters ◽  
Gas Tungsten Arc ◽  
Dimensional Finite Element ◽  
Welding Sequences ◽  
Set Up ◽  
Three Dimensional Finite Element

Since it is inconsistent and uncontrollable in the experiment, any variance in specimen dimensions, welding parameters and testing conditions will influence the consistency of testing results to some extent. In this paper, the Finite Element Method(FEM) is employed to solve this problem. A three-dimensional finite element model is established to simulate the deformation of I-steel during gas tungsten arc welding (TIG) with FEM software, which is set up to analysis the deformation of I-steel with different welding sequences.

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