Journal of Engineering and Thermal Sciences
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Uncertainty representation and quantification for a nonlinear rotor/stator system with mixed uncertainties
Get PDFA rotor-to-stator coupled system usually exhibits complicated dynamic behaviors due to its nonlinear nature. Moreover, the inherent uncertainty (aleatory uncertainty) and many undetermined factors either brought by manufacturing process or due to the lack of knowledge (epistemic uncertainty) make the analysis of system response a challenging task. Existing studies on rotor uncertainties are mostly focused on the stochastic variables, yet pay less attention to other forms of uncertain variables such as intervals. However, some physical parameters (e.g. friction coefficient) can be hardly assigned one specific probability distribution and often available in interval forms. To deal with this, the concept of likelihood is extended from classical discrete point value to interval variable in the presence of mixed uncertainties. A likelihood-based approach is carried out for the mixed uncertainties representation and quantification. In addition, a new single loop sampling algorithm is developed to reduce the computation cost. This framework could be applied in the field of industry manufacturing and mounting, especially take effect in risk assessment and product maintaining. A series of numerical cases are demonstrated for validation and comparison
Determining coupling dynamic stiffness of structural connection by tested FRFs
Get PDFIdentifying coupling dynamic stiffness of structural connection is often needed in substructural dynamic analysis. To overcome the faultiness of conventional approaches existed, five indirect schemes of inverse substructuring analysis by using tested frequency response functions (FRFs) are provided. And the first indirect scheme is verified by three mass-rubber models constructed as two-level substructures with mono-coupling, bi-coupling and tri-coupling connection. Compared to existing direct scheme of inverse substructuring analysis, it shows better performance with acceptable precision of determining the stiffness
Research on vehicle handling inverse dynamics based on optimal control while encountering emergency collision avoidance
Get PDFVehicle driving safety is the urgent key problem to be solved of vehicle independent development while encountering emergency collision avoidance with high speed. And it is also the premise and one of the necessary conditions of vehicle active safety. A new technique for vehicle handling inverse dynamics which can evaluate the emergency collision avoidance performance is proposed. Firstly, the steering angle input of 3-DOF vehicle mode is established. The steering angle input imposed by driver is the control variable, and accurately tracking the expected path was the control object. The optimal control problem can be converted into a nonlinear programming problem while using the state variables conversion, which was solved by the sequential quadratic programming (SQP) algorithm. The results show that vehicle can well track the expected path in high speed
Equilibrium forms branching of a nanolayers system
Get PDFIn this work we analyze equilibrium forms branching of three parallel conductive micro/nanolayers which can be used as a sensor of internal or external mechanical and electrical parameters such as conductivity, tension force or gap between layers. Alteration of physical parameters can lead to symmetry breaking, i.e. asymmetrical deflection of outermost layers and nonzero deflection of middle, initially neutral layer. By slow current intensity variation in one of outermost layers, initial symmetry of the system can be achieved, thus determining the parameters alteration which had occurred
Automatic system for measuring shifts and deformation of dental prostheses
Get PDFThe paper presented a multi-purpose system for testing of dental prostheses within the static and kinematic conditions as well as the conditions of its stability quick analysis. The common goal of prosthetics specialists is to define biomechanical criteria shaping the restorations to protect the existing state of the biological substrate [1]. In prosthesis biomechanics, the gingival soft tissue, as substances with heterogeneous properties, are difficult to individual assessment of the value, direction and duration of the occlusion forces transmitted by the prosthesis in the life cycle [2]. More predictable are static or kinematic behaviors, reflecting the mechanical states of prosthesis design with designed shape and material properties which are possible to determine. However, static measurements of dentures do not reflect their work in natural conditions [3], and can only designate the values of selected parameters (deflection, stress) during the reference of constant load values. The article presents the author’s research stand for kinematic loads testing, which are similar to natural ones during shredding of food. The results of stress and strain of denture prosthesis, identified during laboratory tests, will be used to verify the mathematical models of dentures during kinematic forces
Nonlinear dynamic characteristic of the spindle-cutter system
Get PDFA nonlinear dynamic model of spindle-cutter coupling system under cutting force, which takes into account the cutter stiffness and the nonlinearity of bearing clearance, is established. Analysis of the cross-section of a two-flute end mill is conducted to determine cutter stiffness. Then, the calculated cutter stiffness is introduced into the nonlinear dynamic model of coupling system. In the modeling of cutting force, the cutting width takes into account the cutter tip displacement. Moreover, nonlinear dynamic characteristics of spindle-cutter coupling system are studied and the effects of bearing clearance on the response of cutter tip are discussed as well, considering unbalanced force. The numerical results show that the bearing clearance strongly affects the equilibrium position. With different values of bearing clearance and rotation speed, the responses of cutter tip exhibit periodic, quasi-periodic and chaotic characteristics. Dynamic characteristics of spindle-cutter system depends on the bearing clearance and rotation speed. The proper bearing clearance and rotation speed should be chosen to ensure a stable cutting and high cutting rate according to the bifurcation diagram. The response of the cutter tip is a quasi-periodic motion when the cutting force is considered. The time-domain response of cutter tip predicted by nonlinear dynamic analysis can provide the basis for machining error prediction
Experimental research and numerical simulation on vibration characteristics of a rectangular plate structure in fast time-varying thermal environments
Get PDFPlate attitude control structures such as rudders and vertical tails of high-speed aircraft are faced with the compound effect of fast time-varying thermal environments and vibration during the high maneuvering flight. In this paper, a thermal/vibration test system was established by combining a transient aerodynamic heating simulation system with a vibration test system. A rectangular plate structure made of nickel-based stainless steel was tested at different heating rates and its modal frequencies in fast time-varying thermal environments were obtained. Numerical calculation was performed accordingly. The calculated results coincide well with the experimental results, verifying the credibility and effectiveness of the experimental methods. The research results can provide an important test method and reference basis for the dynamic performance analysis and safety design for the plate-like structures of high-speed aircraft in fast time-varying thermal environments
Dynamic response and dangerous point stress analysis of gear transmission system
Get PDFGear transmission is the principal power transmission mode of many machine, the reliability of transmission system has important influence on the accomplishment of daily task. This paper made a gear transmission system as the research object, we build the two-stage gear transmission system model and calculate its dynamic response in theory. Then, we study the mesh stiffness of gear concerning the variation of the mesh position from the gear transmission system. On the basis of these work, we establish the gear system’s finite element simulation model considering the tooth contact of internal gear system. After the simulation, we had get the contact response and the time history of some important area’s equivalent stress. Through these work, we can study the contact stress of the two-stage gear system in theory method and finite element simulation method, which has a guiding significance on the optimum structural design of two-stage transmission gear system
Nonlinear vibration of rested Euler-Bernoulli beams on linear elastic foundation using Hamiltonian approach
Get PDFIn this paper, nonlinear vibration of Euler-Bernoulli beams resting on linear elastic foundation and subjected to the axial loads are studied analytically. Hamiltonian approach is new kind of analytical approaches are used to achieve the nonlinear frequency of the problem. The nonlinear vibration equation is also solved numerically using Runge-Kutta 4th technique. Comparison of Hamiltonian approach (HA) with Runge-Kutta 4th leads to highly accurate solutions using Hamiltonian approach
Study of fuzzy control for cab’s isolation system of heavy truck
Get PDFHeavy truck cabin ride comfort is studied, the evaluation method of the root-mean-square (r.m.s) acceleration of the vertical driver’s seat, the cab pitch and roll of heavy truck is presented, the random road roughness model is used for excitation. In this paper, a 3-D dynamic model with 13 DOF is established. Fuzzy logic controller is applied to control the cab’s isolation system of heavy truck, and the program is developed based on Matlab/Simulink software to simulate and calculate the r.m.s acceleration of the vertical driver’s seat, the cab pitch angle and roll angle under different road surface conditions. The obtained results showed that the semi-active cab’s isolation system is compared with the passive cab’s isolation system can reduce vibration and improve heavy truck ride comfort. Especially, on the ISO level B road at vehicle speed of 72 km/h, the r.m.s acceleration of the vertical driver's seat, cab pitch and roll angle are greatly reduced by 36.5 %, 10.8 % and 25 % respectively