Applied Mechanics and Materials Vols. 105-107

Abstract: With the aiming of mathematically modeling dynamic behavior in latitudinal and vertical movements of the 6-axle locomotive, this paper introduces the Kalker’s Wheel-Rail Rolling Contact Theories and their implementation in multibody codes. This paper also highlights methodology for solving inhomogeneous linear second-order differential equations with MATLAB computer software aided. The calculation has reported that the dynamic behaviors of Diesel-Electric 6-axle locomotive are significantly demonstrated. The calculation has reported that the dynamic behaviors of Diesel-Electric 6-axle locomotive are significantly demonstrated the requirements on Rolling stock Dynamic behaviors of Vietnam Railways.

Abstract: The TDS changed the drive mode and established a simple, flexible multi-body drill string system. The system consists of a derrick, a hoisting system, TDS, and a drill string system, and is inserted into a long, narrow borehole. The drill string then interacts with mud, the borehole wall, and the bottom hole, which generates resonance and increases the risk of drilling accidents. Natural frequency, which is related to the structure of the drill string, determines critical speed. In a vertical well, the transverse, torsional, and longitudinal fluid–structure interaction vibrations of the flexible multi-body drill string system within 1,700 m was analysed using the ANSYS. The natural frequency and the associated critical speed for different bottomhole assemblies (BHAs) were obtained. Results show that reasonably selecting the TDS rotation speed and optimizing BHA offer practical engineering applications for increasing drilling speed, reducing drilling accidents, and improving economic returns.

Abstract: The FE model of a combined gantry milling machine was constructed. The joint stiffness of bolt fastening, ball screw, and roller guideway were calculated. The static analysis, modal analysis and harmonic analysis of the whole machine were carried out. The results indicated that the static stiffness and minimum dynamic stiffness of the spindle could satisfy the accuracy requirements of milling, but the stiffness of the X-axis feed system was comparatively low, while the stiffness of the rest and the cross-beam could be relatively abundant. The result of “considering joint stiffness” modal analysis was more accurate than “unconsidering joint stiffness”, especially the 5th-order natural frequency had a difference of up to 52.2%. The harmonic analysis result showed that the response amplitude of the spindle center was comparatively large in three directions when the 1st-order and the 17th-order natural frequency were working, so the frequencies should be avoided while working.

Abstract: A new method based on surface integral is presented in the research of mechanical mechanism of spheres penetrating gelatin. On the assumption that each wetted area element is applied with dynamic force perpendicular to the surface, frictional force parallel to the surface and material resistance which is a constant, the resultant force applied on spheres was integrated containing three unknown coefficients. Transparent gelatin was used in the experiments and steel spheres were fired at speed around 800m/s. High speed cameras got the position data of the penetrating spheres. The uncertain coefficients in the movement equations were determined with these data. The equations were solved in analytical forms. Experiments show that the coefficients are constant for spheres with different radiuses. Calculation results demonstrate that the mechanical model is good to predict the movement of spheres in gelatin.

Abstract: A dynamic model of semi-vehicle under acceleration/braking condition based on air suspension was established. By applying wheelbase preview control to forecast the road surface roughness at the front wheel, the optimal controller based on wheelbase preview control theory was designed. Then the dynamic model was simulating with the MATLAB. The results show that both optimal control and optimal control with wheelbase preview can effectively reduce vibration of acceleration/braking system, which make an improvement in the vehicle’s ride comfort and handing stability. Finally, a controller based on wheelbase preview of air active suspension acceleration/braking system was designed, and then simulation was analyzed with white noise input. Centric acceleration, pitch angular acceleration and rear tire dynamic load of the back section were reduced significantly proving pre-wheelbase control can further improve the performance of the vehicle potentially, especially having an effect on decreasing the vibration of rear suppression.

Abstract: Servo system is a very important part of Remote Control Weapon Station , its accuracy has considerable impact on the performance of armament system. This article analysis the stucture compositon of the machine gun RCWS servo system, and elevating servo system is simplified and model is assumed. Virtual prototype model is built using Admas though adding constraints and loads; Elevating servo system model is built using Admas and Matlab/Simulink; Simulation analysis for tracing precision is conducted in the process of firing, tracing precision error and maximam removing velocity are got ,and that meet the general requirements of system design ,which verify the credibility of the model. This model has remarkable thoery and pratical meaning in the study of RCWS servo system design.

Abstract: Abstract. In order to improve the convergence of nonlinear simulation of wind pressure on buildings by turbulence theory pattern, QSMA technique is proposed based on full implicit marching-on in time method in CFX. During marching-on in time, the unit time step and non-convergence tolerance test are employed to approximate the steady state solution in this technique. Comparing with the traditional method, the proposed technique can reduce the restriction for time step and requirement for the target tolerance significantly. It is mathematically proved that the time discretization scheme is stable and the error transfer tends to zero with QSMA technique. Through numerical analysis for flow around Marakami 3D cubic, the research result indicates that solution accuracy and time consumption of QSMA are consistent with traditional steady state method, but the convergence is better.

Abstract: According to the statistics and analysis of the situation that administrative decrees reference technical standard, this paper find that there are several conclusive interactive relations between these two terms. Paper simulate the inner mechanism of the relationship between technical standard and administrative decree in the way of system dynamics and identify the key factors which has great impact on the correlation, point that there are three associated states of "strong, weak, zero" between technical standard and administrative decree and give the way of how to define them. Finally it makes a conclusion in the paper that we should construct an appropriate correlation depending on their needs.

Abstract: Dynamic equations of viscoelastic bodies with fractional constitutive are derived base on the principle of virtual work and the theory of continuum mechanics. The three-dimensional fractional derivative viscoelastic constitutive model is implemented into the flexible multibody system (FMBS), using the 3D solid element based on the absolute nodal coordinate formulation (ANCF), which can exactly describe the geometric nonlinearities due to large rotation and large deformation. The BDF time integration scheme in conjunction with the Grünwald approximation of fractional derivative and the Newton-Raphson algorithm are used to solve the equations of motion. Several numerical examples are presented to demonstrate the use of the modeling procedure presented in this investigation and the effects of parameters in the fractional derivative model.

Abstract: This paper first derives the accurate computational formula of guidance electromagnetic force, when guidance magnet has the movement of the lateral excursion and yawing relative to the curved guideway. Firstly, the gap distribution characteristics between the guidance magnet and the curved guideway have been analyzed and simplified. Secondly, the theoretical formula of electro- magnetic force for singled magnetic pole has been derived by the air-gap magnetic permeance and flux tube methods. Then, the numerical calculations have been done by Ansoft Maxwell, and according to the numerical results, the theoretical formula has been modified accurately. Finally, the formulas of electromagnetic resultant force and resultant moment for guidance magnet have been represented, and the variation curves of electromagnetic force changing with maglev line indicate that gap changes caused by curved guideway should not be neglected. The formulas acquired in this paper are in favor of dynamics modeling and controller design for guidance system, and analyzing the running states of magnet and the curved form of guideway influencing on guidance system.