On problem of calculating longitudinal vibrations of piston engine crankshaft

One of the initial stages of calculating the crankshaft longitudinal vibrations is developing an oscillatory system model, which includes the determination of longitudinal pliability (rigidity) of elastic sections. If it is impossible to determine the pliability experimental, the empiric formulas or the final element method (FEM) are used. There are given the values of crank longitudinal pliability of the crankshafts of different marine engine types found by using the formulas of L. Gugliemotti – R. Machciotta, P. Draminsky, E. Y. Gorbunov, S. F. Dorey, N. S. Skorchev, V. S. Stoyanov, etc. It is shown that the calculation results obtained from these formulas for the same engine significantly differ; therefore, the choice of one or another empirical formula for practical calculations is difficult. The preference of using FEM for determining the longitudinal (axial) compliance of cranks and other areas with complex geometric shapes has been proven. The possibility of its application is also shown to determine the longitudinal disturbing force as the reaction of the crankshaft support against the action of the radial force exerted to the connecting rod journal. It is proposed to use, along with empirical formulas, regression equations connecting the longitudinal compliance of the cranks with a significantly larger number of their design dimensions.

NUMERICAL SIMULATION OF AERODYNAMIC STABILITY OF LONG-SPAN BRIDGES

Statement of the problem. The aim of the work is to simulate the resonant vibrations of the continuous beam span of the bridge in the direction perpendicular to the wind flow by the finite element method. The article deals with a non-standard situation that arose on May 20, 2010 on the bridge over the Volga River in the city of Volgograd.Results. As a result, an effective algorithm for calculating the aerodynamic stability of large-span bridge structures was developed using one of the most widespread software systems in Russia and neighboring countries - "Lira-SAPR". Recommendations for the selection and modeling of dampers are given. Conclusions. The developed algorithm makes it possible to numerically describe the disturbing force of periodic breakdown of wind flow vortices, which causes resonant oscillations of bridge spans, to apply this force to the design model in Lira-SAPR, and to obtain parameters that make it possible to assess the stress-strain state of the system during oscillations and to select the optimal characteristics of the damping devices.

Random oscillations of nonlinear systems with distributed Parameter

The article analyzes random vibrations of nonlinear mechanical systems with distributed parameters. The motion of such systems is described by nonlinear partial differential equations with corresponding initial and boundary conditions. In our case, the system as a whole is limited, so any motion can be considered as the sum of the natural oscillations of the system, i.e. in the form of an expansion of the boundary value problem in terms of own functions. The use of the theory of random processes in the calculation of mechanical systems is a prerequisite for the creation of sound design methods and the creation of effective vibration protection devices, these methods allow us to investigate dynamic processes, to determine the probabilistic characteristics of displacements of points of the system and their first two derivatives. In the work established these conditions are met, they provide effective vibration protection of the system under study with wide changes in the pass band of the frequencies of the random vibration effect, and the frequency of the disturbing force is much greater than the natural frequency of the system as a whole, in addition, with an increase in the damping capacity of the elastic-damping link of the system, the intensity of the random process significantly decreases, which in turn leads to a sharp decrease in the dynamic coefficient of the system.

Study of a Stripper Header for Grain Harvesting as a Vibrating System

Introduction. Grain losses caused by stripping defects are the main problem to be solved in designing a stripper header. To reduce these losses, a design of a stripper header with a vibration drive is proposed. This device combines the processes of stripping grain crops and the vibration effect of the stripping fingers upon the ears of plants. The most important stage of the mathematical description of these processes is composing the differential equation of the stripping fingers motion. Materials and Methods. A computational-graphic diagram of an oscillatory system with one degree of freedom is proposed. To compose the differential equation of the stripping fingers motion, a method based on the application of the Lagrange equation was used. The oscillations of the system under studying arise from the motion of a point in the system according to a given law. The problem of kinematic excitation is reduced to the problem of force perturbation. This stage of the study was carried out without taking into account the resistance forces. Results. An equation for motion of stripping fingers making vibrational reciprocating movements is obtained. It is proposed to select the elastic element in the design scheme and consider a more general case of the stripping fingers movement. In this case, the movement of the stripping fingers is considered to be difficult. A characteristic feature of the mathematical description is the presence of a generalized force of potential forces. The differential equation of motion of a comb in the presence of an elastic element and the solution of this equation are composed. Discussion and Conclusion. Forced oscillations of a system without resistance, excited by a harmonic disturbing force, are harmonic oscillations with constant amplitude. On close values of the angular frequency of vibration of the drive output link and the root of the ratio of the stiffness coefficient of the elastic element to the stripping fingers mass, the case of resonance takes place. The system parameters must be selected so as to avoid this negative phenomenon.

ESTIMATION OF THE INFLUENCE OF CONSTRUCTIVE FEATURES AND PARAMETERS OF THE VEHICLE ON THE DYNAMICS OF THE WORKING PROCESS BY LOAD UNDER MINE DETONATION

Approaches of mathematical modeling and calculation results for the loading of vehicle structural elements are presented (using the example of typical design solutions of modern armored personnel carriers). The mathematical model takes into account the peculiarities of the working process of loading during detonation on a mine underneath the front wheel in the direction of movement. The peculiarity lies in taking into account the simultaneous action of excess gas pressure on the wheel and the bottom of the machine body. The influence of the main parameters of the research object in terms of geometry, stiffness, damping, mass and weight is taken into account. The main nonlinearities of elastic damping connections of structural elements (wheels with the machine body and with the supporting surface) are also taken into account. The calculations were made by the numerical Runge - Kutta method with a variable step. With the help of the original program, calculations were carried out and a comprehensive quantitative assessment of the features of the working process of loading during blasting was obtained. The complexity of the assessment consists in a quantitative assessment of the effect of an external force factor, both separately (applied only to the wheel or only to the bottom) and together (excess pressure acts both on the wheel and on the bottom). It has been established that there is a shift in the peak values of the force on the vehicle body during suspension breakdown and accelerations on the vehicle body in the driver's seat and directly on the driver. The reason for the shift of 0.019 sec is the transformation of the force flow on the way from the wheel to the body of the machine during detonation. The magnitude of changes in the parameters of the power flow depends mainly on the value of the given parameters of the wheel suspension (mass, stiffness, damping) and the parameters of the impulse disturbing force factor applied to the wheel. At the same time, the disturbing force factors applied to the wheel and to the body of the machine during blasting differ significantly in magnitude and duration of action. The force factor applied to the wheel is 5.06 times greater than the force factor applied to the body, and the action time is 9.7 times less. It has been established that, taking into account the simultaneous action of excess gas pressure on both the wheel and the bottom of the car body, the driver's acceleration rate from suspension breakdown is 6.33 times greater than the fraction from the gas action on the bottom.

Dynamics of the movement of the ripping tool for surface tillage

The study aims to analyze the stability of the movement of the ripper tool for surface tillage. The basic principles and methods of classical mechanics, mathematical analysis, and statistics were used in this study. The dynamics of the movement of a ripper tool for surface tillage are considered, depending on the forces acting on it and its design parameters. A computational dynamic model is developed, and an equation describing the angular oscillations of the longitudinal links of the parallelogram ripper mechanism is obtained. It is established that the uniformity of the depth of the cultivator depends on the amplitude and frequency changes of the components of the disturbing force, physical and mechanical properties of the soil, the moment of inertia of the Ripper, the length of the longitudinal links parallelogram mechanism, the forces of the pre-tension pressure springs, and its stiffness. It is established that the required uniformity of the depth of tillage can be achieved by selecting the pre-tension force of the pressure spring and its rigidity. Theoretical and experimental studies have established that the required uniformity of the processing depth with minimal energy consumption of the soil is provided with a pre-tension force of the pressure spring of the ripper attachment mechanism of 350 n, spring stiffness of 40 n / cm, and a speed of 2.0 m/s.

AUTONOMOUS CORRECTION OF A SINGLE-CHANNEL INERTIAL CONTROL SYSTEM

The problem of algorithmic design of the system of inertial control of a moving object is considered, in which the compensation of number errors caused by errors of accelerometers without external sources of information about the navigation elements of the object is carried out. The principle of solving the problem is demonstrated on the model of a single-channel positional inertial control system. Algorithms of instantaneous a posteriori estimation of calculated variables are investigated, which allow to obtain estimates that are invariant to measurement errors, and to correct the inertial control channel without an external positioning system. For the operating conditions of the system, under which the values of measurement errors and the disturbing force are represented by random numbers that preserve constant values over the observation interval, estimates of the calculated variables corresponding to almost complete compensation of the calculation errors are obtained.

Active change in the state of self-oscillations in machines and mechanisms in a system with various types of nonlinearities of an arbitrary structure under the action of a impulse or harmonic disturbing force

The method of actively changing the state of self-oscillations in machines and mechanisms in a system with various types of nonlinearities of an arbitrary structure under the action of external periodic perturbations was proposed. The differential equations of the method take into account two types of external force periodic disturbances: impulse and harmonic.