Self-Excited Acoustical Measurement System for Rock Mass Stress Mapping

This paper presents the results of a preliminary study of a self-excited acoustical system (SAS) for nondestructive testing (NDT). The SAS system was used for mine excavation stresses examination. The principle of operation of the SAS system based on the elastoacoustical effect is presented. A numerical analysis of the excavation was carried out considering the stress factor. An equivalent model based on a two-degree-of-freedom system with a delay has been developed. This model allowed to determine the relation which relates the frequency of the self-excited system to the stress level in the studied ceiling section. This relationship is defined by the elastoacoustic coefficient. The test details for anchorages in laboratory conditions and Wieliczka Salt Mine were presented. This research details of a method for creating actual stress maps in the ceiling of a mine excavation. The results confirmed the possibility of using the new measurement system to monitor the state of stresses in the rock mass.

Non-Destructive Acoustical Rock Bolt Testing System with Intelligent Filtering in Salt Mine ‘Wieliczka’

This article presents the application of a self-excited acoustic SAS system for non-destructive testing (NDT) for roof-bolt housings in laboratory and real mine conditions. The proposed system with a filtering mechanism was applied to the J64-27 composite anchors. The conducted tests allowed successful confirmation of the usefulness of the system in the detection of rod defects, damage of the mechanism coupling the anchor to the rock mass and testing of the stress state of the anchor itself. The proposed filtering system allowed eliminating the effect of jump change of frequency in the limit cycle of self-excited system. The proposed method is a novel solution for safety diagnostics of bolt housings in mining applications.

Study of N-doping in (Bi2MoO6, MoO3)/SnOx:N photocatalys in the degradation of RhB using visible light

Novel composites operating in visible light (VL) energy are an important issue in photon excited system. The (Bi2MoO6, MoO3)/SnO[Formula: see text]:N composite photocatalysts were prepared by the one-step spray pyrolysis method. The effect of N-doping in SnO[Formula: see text] layer with controlled N/Sn ratio in precursor to the photocatalystic ability of the composite was studied. The photocatalytic ability of the composites was evaluated by photodegradation of Rhodamine B (RhB) under visible-light emitting diode illumination. The composites were characterized by film optical absorption analysis, X-ray diffraction and scanning electron microscopy. Film with suitable N-doping shows the improved visible-light photocatalytic ability with rate constant 0.019 min[Formula: see text]. With the electrical property of SnO[Formula: see text]:N films and the scavenger analysis of the composites, the photocatalytic mechanism was discussed.

Development and control of an active torsional vibration damper for vehicle powertrains

Due to environmental pollution concerns, emission regulations on internal combustion engines (ICEs) have been tightening and the importance of fuel efficiency has become pronounced. Thereupon, downsizing, downspeeding, turbo supercharging, and cylinder deactivation techniques have been implemented in designing modern ICEs. Despite their considerable benefits, these methods result in boosted torsional oscillations necessitating new vibration isolation technologies due to the limited performance of passive torsional vibration dampers. In addition, trade-offs are indispensable in the passive damper system designs since different engine operating points demand different values of oscillation attenuation parameters. Thus, this study was initiated to develop a novel active torsional vibration damper (ATVD) to attenuate the torsional vibrations of all engine operating points without making any trade-off and to open up a new comfort zone for the development of modern ICEs. Proposed ATVD is essentially a parametrically excited system that adjusts the stiffness rate, damping rate, and moment of inertia in accordance with a fuzzy logic control (FLC) law to maximize engine-borne torsional vibration attenuation capability. The ATVD performance is evaluated in a co-simulation environment by using a driving cycle with six engine operating points and its advantages over conventional passive dampers are demonstrated.

Forced-self-excited System of Iced Transmission Lines under Planar Harmonic Excitations

This paper is concerned with the analysis of the self-excited vibrations and forced vibrations of the iced transmission lines. By introducing the external excitation load, the effect of dynamic wind on the nonlinear vibration equations of motion is reflected by vertical aerodynamic force. The approximate analytical solution of the non-resonance, and the amplitude frequency response relation of the principal resonance of the forced self-excited system are obtained by using the multiple scale method. With the increase in excitation amplitude, the nonlinearity of the system is enhanced, and the forced-self-excited system experiences three vibration stages (self-excited vibration, the superposition form of self-excited vibration and forced vibration, forced vibration controlled by nonlinear damping). Among them, the accuracy of the approximate analytical solution decreases with the increase of the nonlinear strength. And the excitation amplitude is greater than the critical value, the quenching phenomenon appear in the forced-self-excited system, and the discriminant formula is derived in this paper. In addition, the frequency of excitation term determines the vibration form of the system. The principal resonance, super-harmonic resonance and sub-harmonic resonance of the forced-self-excited system are analyzed by using different excitation frequencies. Compared with the principal resonance and the harmonic resonance, the meaningful transition from periodic response to quasi periodic response is easy to appear with the condition of the 1/3-order sub-harmonic and the 3-order super-harmonic. The conclusions would be helpful to the practical engineering of the iced transmission lines. More important, as a combination of Duffing equation and Rayleigh equation, the forced-self-excited system also has high theoretical research value.

Planar Nonlinear Galloping of Iced Transmission Lines under Forced Self-Excitation Conditions

In order to study the influence of dynamic wind on the nonlinear galloping characteristics of iced transmission lines, an external excitation load is added to the governing equation of iced transmission lines under the condition of stable wind, and a new forced self-excited system has been established. The frequency-amplitude relationship of the forced self-excited system under weak excitation and strong excitation is obtained by using the multiple-scale method. The principal resonances and superharmonic and subharmonic resonances of the forced self-excited system have also been analyzed. The results show that, in the forced self-excited system under strong excitation, when the excitation frequency is close to the integral and fractional times of the natural frequency, it is easier to produce 1/2-order subharmonic resonance, 2-order superharmonic resonance, and 3-order superharmonic resonance. In addition, numerical techniques provide bifurcation diagrams of different control parameters, which are able to highlight the effects of the simultaneous presence of the sources of excitation. When the control parameters (wind velocity, excitation amplitude, tuning parameter, tension, and Young’s modulus) change, the response amplitudes of the principal resonance and harmonic resonance will have multivalues, jump phenomenon, and hardening behavior. The control parameters can be used as a reference for engineering design. More importantly, as a combination of the Duffing equation and the Rayleigh equation, the forced self-excited system also has high theoretical research value.