The check of compliance with legislative requirements for vibration protection of operators is carried out at the stage of certification testing of new and upgrading products. At this stage, the further development is associated with high time and material costs. The article substantiates the possibility of use of a calculation and experimental method which allows to determine at the development stage the level and frequency content of potentially dangerous sources of vibration; to develop a computer model for the system «excitation source - frame - cab - antivibration seat - operator»; to make out proposals to comply with legislative requirements by means of parametric forecasting. As an example, the problem of vibration in the low frequency range of 2-14 Hz is considered. This vibration is the result of the process of rolling of track rollers on track chain that lies on the yieldable soil foundation. According to biomedical research, the resonance frequencies of critical parts of human body are in this low frequency range, which is displayed in sanitary norms. Based on the analysis of field test results, the kinematic impact of track rollers on tractor frame is represented as stationary narrow-band random processes. Mathematical model of the system is described by a set of differential equations with random input processes. The methods of statistical dynamics are used to implement the model. The simulation results are presented as a set of transfer functions. They represent the distribution of resonance frequencies of angular and heave oscillations of the separate system elements and the spectral density functions. These results allow to obtain the quantitative estimations in the form of mean-square values of the output processes. The use of this approach allows to solve the problems of vibration protection of operator at the stages of design and testing of prototypes of road-building machinery. It is achieved by tuning-out of the system «track assembly - frame - cab - antivibration seat» from resonance phenomena and by introducing some design solutions.
The article presents the results of a study aimed at creating a mathematical model of thermodynamic processes in the intake manifold of a forced diesel engine, taking into account the features of simultaneous injection of fuel and water into the collector. In the course of the study, the tasks of developing a mathematical model were solved, it was implemented in the existing software for component simulation “Internal combustion engine research and development” (ICE RnD), created using the Modelica language, and verification was undertaken using the results of bench tests of diesel engines with injection fuel and water into the intake manifold. The mathematical model is based on a system of equations for the energy and mass balances of gases and includes detailed mathematical submodels of the processes of simultaneous evaporation of fuel and water in the intake manifold; it takes into account the effect of the evaporation of fuel and water on the parameters of the gas state in the intake manifold; it takes into account the influence of the state parameters of the working fluid in the intake manifold on the physical characteristics of fuel and water; it meets the principles of component modeling, since it does not contain parameters that are not related to the simulated component; it describes the process of simultaneous transfer of vapors and non-evaporated liquids between components; and it does not include empirical relationships requiring data on the dynamics of fuel evaporation under reference conditions. According to the results of a full-scale experiment, the adequacy of the mathematical model developed was confirmed. This model can be used to determine the rational design parameters of the fuel and water injection system, the adjusting parameters of the forced diesel engine that provide the required power, and economic indicators, taking into account the limitations on the magnitude of the mechanical and thermal loads of its parts.
Results of experimental investigation of operational loading and tension of load-carrying system of a crawler bulldozer and ripper aggregate are given. A mathematical model is suggested, requirements are substantiated.
Reliability of results of computer simulation depends on the accuracy of specified dynamic characteristics of the elements of oscillating system. In this connection, identification of model parameters and verifying of its adequacy are of major importance. Bench tests of new elements of vibration protection of T-11 tractor cab and seat involving the hydropneumatic way of vibration damping were conducted. The equipment of test bench conforms with loading scheme of investigated elements and reproduces the cab and seat working conditions identical to these of tractor operation, in particular the impact of given random process and shock loading. The information-measuring unit provides the registration and processing of experimental data. Bench tests allowed to reveal the fundamental features of the dynamic characteristics of shock absorbing elements, determine the numerical values of parameters contained in them and substantiate a number of assumptions inherent in the mathematical model. Adequacy check of the model was made by comparing the simulation results with field tests of T-11 tractor. The layout of acceleration sensors at various points of the tractor allowed to describe quite adequately the overall picture of vibration loading of the system of «caterpillar truck - frame - cab - seat», and to reveal a number of regularities that correct the model and perform a comparison of simulation results and field tests. The laboratory tests of vibration protection elements for operator workplace increased the accuracy of simulation results. Field tests allowed to confirm the adequacy of calculation model. The possibility of substitution of the field tests for laboratory ones in case of determining a number of certification characteristics of vibration protection systems is substantiated.
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