Physical tenderization technologies for beef have been of particular interest to the meat industry. Here a novel tenderization technology by mechanical resonance vibration was proposed. The ...fundamental natural frequency (NFf) of the yak longissimus thoracis et lumborum (LTL) was obtained through a hammer impacting on the muscle, and was reported to be 24.89 Hz. The tensile stress and Warner–Bratzler shear force of the yak meat were decreased by using the obtained NFf as the frequency of resonance vibration (RV), and only linear elastic deformation was found in stress-strain behavior of the vibrated meat. The variation of mechanical properties in post-rigor meat is responsible for the disappearance of the M-bands, shortening of the A-bands, and lengthening change in I-bands, rather than of the sarcomere length. The research demonstrated that RV treatment resulted in the M-band disappearance, the extensively detachment of endomysium from the myofibers, and the destruction of the linkages between α-actinin and thin filaments as well as other linkages.
•The natural frequency of yak meat was accurately determined by hammer excitation.•The effect of the components of yak meat on mechanical properties was revealed.•The myofibril detached and the collagen fibers decomposed by resonance vibration.•Resonance vibration resulted in the disappearance of M-bands in sarcomeres.
Aerodynamic loading is one of the most dominating environmental excitations of Floating Wind Turbines (FWTs) and plays an important role in the FWT dynamics. In this study, we developed a model ...Spar-type FWT and then constructed a dedicated experiment apparatus to reveal the aerodynamic loading effects. As for the floater motion, the wind loading serves as an external exciting force, as well as potential damping source and equivalent added mass item. To take all these roles into account, we proposed a concept of aerodynamic loading effect. The presence of aerodynamic loading effect is validated by free decay tests and white noise wave tests. Results show that the aerodynamic loading effect alters the natural frequencies and damping ratios of the FWT system. We suggest the FWT designers refer to the altered natural frequencies when designing the floater and the FWT controllers. We experimentally observed that the increased aerodynamic loading seems to suppress the pitch resonance vibration while amplifies the resonance vibration at surge frequency. Besides, the nacelle motions, blade loads, and the tower dynamics, are all significantly impacted by the aerodynamic loading effect. The presented results are potentially helpful for optimizing FWTs and developing advanced FWT controllers.
•Aerodynamic loading effect is addressed to depict the impact of wind loads on FWT dynamics.•An experimental apparatus is developed to reveal FWT dynamics under aerodynamic loading effect.•Floater natural frequencies are altered by aerodynamic loading effect.•FWT design and controller development should incorporate aerodynamic loading effect.
The tower is an essential supporting structure for a Floating Wind Turbine (FWT). Due to the complexities of system structure and the environmental excitations, FWT towers present rather complicated ...loading characteristics, potentially threat the system reliability. This paper aims to reveal the FWT tower dynamics in wind-wave-current environments with a dedicated experimental apparatus. A new strategy is proposed to design the FWT structure. Then, extensive tests are conducted with different offshore environments and varying rotor operating conditions. Results show that the FWT tower loading presents complicated dynamic characteristics. The frequency response mainly consists of three parts: the low-frequency component associated with floater oscillations and wind excitations, the wave-frequency component induced by the linear wave loads, and the high-frequency component resulted from the rotor-nacelle assembly (RNA) operating and vibrations. The low- and wave-frequency responses increase with the wave height, while the high-frequency response amplifies with the aerodynamic loads. Vibrations transmit between the upper RNA and the lower floating platform through the tower structure, smearing the system stability and increasing the structure fatigue damages. Optimizations should be proposed to improve the FWT tower performance to suppress or isolate these unexpected vibrations.
•A novel FWT tower design strategy is proposed.•An experimental apparatus is developed to study the FWT tower dynamics in wind-wave conditions.•The tower loading can be clearly divided into the low-frequency, wave-frequency and high-frequency responses, which are caused by different excitations.•The tower structure can serve as a filter to isolate the vibration transmission between the turbine and the floater.
This study investigated an energy-efficient harvesting method to collect microalgae of Chlorella Vulgaris (C. vulgaris). The method proposed in the current study was a combination of a resonance ...vibration submerged membrane (RVSM) system and centrifugation. The result showed that the RVSM system was able to concentrate the C. vulgaris solution by 17 times (0.61 g·L−1 to 10.4 g·L−1) without chemical cleaning during filtration with intermittent relaxation (i.e., filtration for 9 min and relaxation for 1 min) at a flux of 40 LMH (L·m−2·h−1) until the transmembrane pressure (TMP) reached 70 kPa. In addition, extracellular polymeric substances such as polysaccharides and protein were found mainly responsible for membrane fouling during the operation of concentrating C. vulgaris solution. Integrating the RVSM system with the centrifugation process required the total specific energy consumption of 0.56 kWh·m−3 (0.09 kWh·m−3 for the RVSM and 0.47 kWh·m−3 for the centrifugation). This study demonstrated the combination of the RVSM system and centrifugation to be a feasible C. vulgaris harvesting method by showing lower energy consumption than other conventional processes.
•Resonance vibration submerged membrane (RVSM) had a low membrane fouling.•RVSM system showed twice as high as the critical flux of 45 LMH.•RVSM system concentrated the C. vulgaris solution by 17 times.•Combining the RVSM system and centrifugation consumed the energy of 0.56 kWh·m−3.
•A non-resonance method using MRE isolator is proposed to suppress TBM's vibration.•The resonance of the TBM can be avoided by controlling its natural frequency.•The improved vibration control ...performance of the TBM with MRE isolator is verified.
Tunnel boring machines (TBM) are efficient tunnel excavation equipment, and the number of TBM in many countries is increasing rapidly. TBM works in a harsh geological environment and long-term vibration will cause tremendous damages, including loosening the pipeline and damaging the mechanical system on the main frame of TBM. In this paper, a variable stiffness magnetorheological elastomer (MRE) isolator is installed under the main frame in order to control its resonance frequency to avoid the vibration resonance to reduce the high-level vibration of TBM, this is called non-resonance control approach. A multi-degree-of-freedom dynamics model of the TBM is established as the first step. The performance of the MRE isolator on vibration control of TBM is numerically evaluated. Then a scaled TBM is built for experimental evaluation and a laminated MRE isolator is designed, prototyped according to the requirement of the scaled TBM; its properties are tested by a shaking table, including its current-dependency, frequency-dependency, and amplitude-dependency features. In the end, the MRE is installed on the scaled TBM platform to evaluate its vibration reduction effectiveness. The experimental test results demonstrate that the displacement amplitude of the TBM vibration could be reduced by up to 20.18% and 14.52% under harmonic sweep excitation and nonsynchronous excitation, respectively.
Sonic vibration sampling technology is widely used due to its high sample fidelity, low disturbance to the stratum and environmental protection. The influence of the diameter variation of sonic drill ...string caused by the sampling tube on the axial vibration of the system is still unclear, which restricts the improvement of coring efficiency. In this study, an axial vibration model of a sonic drilling string with a sampling tool is established, which takes into account the section variation. Adopting numerical simulations, the influence of the drill string on the vibration characteristics of the system, the relationship between the excitation and the amplitude of the sampling bit, and the effect of the cross-sectional area on the bearing capacity of the drill string with the sampling tube are obtained. With the longer the sampling tube and the thicker the wall thickness, the lower the inherent frequency and the higher the bearing capacity. The results show that the discontinuity of the drill string section caused by the sampling tube inevitably affects the natural frequency and response of the drill string system. The model can provide a theoretical basis for the research of sonic vibration sampling engineering. Properly balancing parameters can improve drilling and sampling performance.
Focus on fatigue fracture of shearer cutting gearbox housing（ SCGH）,the fatigue failure mechanism of（ SCGH）is investigated considering both high frequency internal excitation caused by gear meshing ...and low frequency external excitation caused by coal cutting. Force analysis is proposed to obtain the region of stress concentration and stress values are calculated by finite element analysis. Torque caused by gear meshing Mp and eccentric L0 is firstly considered in mechanical model and the influence of them on strain amplitude is analyzed. Local resonance characteristics are analyzed based on vibration signals of shearer cutting experiment. Power spectral density（ PSD） analysis is used to obtain local resonance frequencies and they were checked to be natural frequencies of SCGH. Based on strain modal analysis,the region of strain concentration of modal shape and stress concentration are compared. The results show that: Region of local resonance modal shape strain concentration is similar to that of stress conce
The longitudinal fluctuating forces of a propeller are a major cause of sound radiation of an underwater vehicle in the low frequency range. A hydraulic leveraged dynamic anti-resonance vibration ...isolator (HLVI) is proposed to attenuate the longitudinal vibration of a shaft system transmitted to the hull. The semi-analytical model of the shafting system with and without the isolator is set up by employing the frequency response synthesis method, in which the elasticity of the foundation is taken into consideration. Compared to the traditional isolation scheme and DVA, the proposed control scheme will not change the longitudinal effective stiffness and needs a small mass to attenuate the longitudinal vibration of the shafting system. A parametric study was conducted to investigate the key parameters of the isolator and their impact on its isolation performance. An experimental apparatus is set up to validate the isolation scheme. The acceleration frequency response results of the shafting system under axial excitation with both the frequency sweep method and discrete sinusoidal frequencies are presented and discussed. The results indicate that the proposed method is capable of attenuating the corresponding longitudinal vibration of the shafting system.
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