A Nonlinear Model and Parameter Identification Method for Rubber Isolators under Shock Excitation in Underwater Vehicles

Rubber isolators are usually used to protect high-precision equipment of autonomous underwater vehicles (AUVs), avoiding damage from overlarge dynamic excitation. Considering the nonlinear properties of the rubber material, the nonlinear behavior of rubber isolators under shock exaltation is hard to be predict accurately without the available modal and accurate parameters. In view of this, the present study proposes a nonlinear model and parameter identification method of rubber isolators to present their transient responses under shock excitation. First, a nonlinear model of rubber isolators is introduced for simulating their amplitude and frequency-dependent deformation under shock excitation. A corresponding dynamic equation of the isolation system is proposed and analytically solved by the Newmark method and the Newton-arithmetic mean method. Secondly, a multilayer feed-forward neural network (MFFNN) is constructed with the current model to search the parameters, in which the differences between the estimated and tested responses are minimized. The sine-sweep and drop test are planned with MFFNN to build the parameter identification process of rubber isolators. Then, a T-shaped isolator composed of high-damping silicon rubber is selected as a sample, and its parameters were determined by the current identification process. The transient responses of the isolation system are reconstructed by the current mode with the identified parameter, which show good agreement with measured responses. The accuracy of the proposed model and parameter identification method is proved. Finally, the errors between the reconstructed responses and tested responses are analyzed, and the main mode of energy attenuation in the rubber isolator is discussed in order to provide an inside view of the current model.

Investigating the transverse motion of a pneumatic shock exciter using two different anvil mounting configurations

This paper describes novel design changes to the accelerometer mounting support of a commercial pneumatic shock exciter, with the aim of reducing the transverse motion the accelerometer is subjected to during shock excitation. The author describes the mounting support supplied by the manufacturer, the design changes made and the measurement data to compare the transfer motions recorded using two different mounting designs.

STUDY OF THE APERIODIC REGIME DURING THE TRANSIENT PROCESS IN AN OSCILLATING CIRCUIT IN ORDER TO CONVERT THE ENERGY OF AN ELECTRIC CURRENT INTO THE HEAT OF A JOULE

Purpose. Research initiated by revealing the paradox of disturbed energy balance based on the position of the virial theorem and studying examples of the Van de Graaf generator, a capacitor containing a ferroelectric, and a heat pump capable of providing an energy conversion factor greater than 100%, as well as an idealized theoretical known as the Maxwell demon, showed the possibility of increasing the efficiency of converting current energy into Joule heat. Methodology. The results are verified by comparing the relative efficiency of the conversion of current energy into heat in the oscillatory, critical and aperiodic modes of the transient process in a series oscillating circuit. Mathematical modeling in a wide range of parameter changes has shown the advantage of using the aperiodic transient mode of a series oscillating circuit to convert current energy into heat, compared to the power supply of an electric heating system, which is based on the established method. Experimental tests of the experimental sample fully confirm the qualitative results of mathematical modeling. Results. An achievable limit level of conversion efficiency in the active resistance of energy accumulated by inductance and capacitance according to the virial theorem is established. Originality. For the first time, the application of the aperiodic transient mode in a series oscillatory circuit is proposed in order to convert the energy of current to Joule heat. Practical value. As a practical result, a method of converting current energy into pulse energy has been developed, which implements the algorithm of simultaneous energy accumulation by inductance and capacitance, and its simultaneous conversion in a series oscillating circuit, for which a patent has been obtained. Possibilities of application of the developed method for the purpose of induction heating of metals by Foucault currents as replacement of a method of shock excitation of fluctuations are studied. To this end, the conductivity of metals, which causes the flow of Foucault currents, should be considered as the introduction of equivalent active resistance in the oscillating circuit. The introduction of the method will not require changes in the process equipment, except for the power supply scheme, and should eliminate the fundamental disadvantage of the method of shock excitation of powerful oscillations, which is low efficiency.

Research of the echo-impulse method of control of drilled pieces (non-destructive control)

The results of field and computational experimental studies of the pulse echo method are presented. Typical reflectograms of bored piles are presented. The factors that complicate the interpretation of control data are noted. An analysis of the formation of the fronts of an acoustic pulse during its shock excitation is presented. Estimates of the influence of reinforcement on the estimates of the propagation velocity of an acoustic pulse are given.

An Experimental Study on Dynamic Model Groove Under Shock Excitation

Introduction: Variation laws of dynamic response and settlement deformation at different depths of soil roadbed were investigated and summarized in this study through a simulation test with a dynamic model groove in soft clay foundation of low road embankment. Materials and Methods: In this test, the traffic load was simulated by single-point and double-point shock excitation. Besides, loading frequency, intensity and duration were adjusted by a single variable control method. Research results show that peak values of soil pressure and pore water pressure decrease with the increase of buried depth, but they are unrelated to loading intensity and frequency. Conclusion: Nevertheless, settlement deformation does not increase linearly with the increase of frequency or time difference. The accumulative settlement at a depth varies as the loading time increases.

First NIR interferometrically resolved high-order Brackett and forbidden Fe lines of a B[e] star: V921 Sco

ABSTRACT We present near-infrared interferometric AMBER observations of the B[e] binary V921 Sco at low (R ∼ 30) and medium spectral resolution (R∼ 1500) in the K and H bands. Low spectral resolution AMBER data were used to estimate the position of the companion V921 Sco B and confirmed a clockwise movement on sky with respect to the primary of 33° between 2008 and 2012. Our observations resolve for the first time higher order Brackett lines (Br6–Br12). The modelling of the different line transitions revealed a decrease in the size of the line-emitting regions from Br3 to Br12. We are able to reproduce this decrease with a simple radiative transfer model of an equatorial disc in local thermodynamic equilibrium. In addition to the Brackett series, we also resolve permitted and forbidden Fe line emission. Our modelling shows that these lines originate from ∼2 au from the star, corresponding roughly to the measured dust sublimation region. This might indicate that the forbidden line emission arises from shock excitation at the base of a disc wind.

A Reduced-Order Model for Loosening of Bolted Joints Subjected to Axial Shock Excitation

Maintaining preload in bolted joints is critical for the safe and efficient operation of nearly all built-up structures. Dynamic loss of preload during operation occurs when sufficient shear force is applied to the joint such that slip is induced in at least the threads if not the entire bolt. Such shear forces are often realized when the joint is subjected to sustained vibrations, resulting in loosening over relatively long periods of time, or extreme shock loading where loosening occurs over fractions of a second. Modeling of joint loosening often focuses on complex analytical approaches or high-fidelity simulations using finite element models. While such approaches may succeed for a single bolt, they are unfeasible for use in simulations of entire built-up structures, which may possess dozens to thousands of joints. Thus, there is a need for reduced-order models (ROMs) that capture the dominant governing physics, but at drastically lower computational costs. This research introduces a phenomenological ROM for loosening in bolted joints subjected to axial shock excitation. The model introduces a mathematical relationship between the stiffness of the joint and torque of the fastener and treats the torque as a dynamic internal variable governed by a first-order, ordinary differential equation. The proposed ROM is presented then applied to an experimental study of a split-Hopkinson pressure bar with a threaded joint subjected to extreme shock loading. The results demonstrate that the proposed ROM is able to reproduce the dominant effects of loosening in bolted joints subjected to axial shock excitation.