Load identification in one dimensional structure based on hybrid finite element method

The new hybrid elements are proposed by combing modified Hermitian wavelet elements with ANASYS elements. Then hybrid elements are substituted into finite element formulations to solve the load identification. Transfer matrix can be constructed by using the inverse Newmark algorithm and hybrid finite element method. Loads can obtain through the responses and the transfer matrix. Load identification law was studied under different excitation cases in rod and Timoshenko beam. Regularization method is adopted to solve ill-posed inverse problem of load identification. Compared with ANSYS results, hybrid elements and HCSWI elements can accurately identify the applied load. Numerical results show that the algorithm of hybrid elements is effective. The accuracy of hybrid elements and HCSWI elements can be verified by comparing the load identification result of ANASYS elements with the experiment data. Hermitian wavelet finite element methods have high accuracy advantage but it is difficult to apply the engineering practice. In practical engineering, complex structure can be analyzed by using the hybrid finite element methods which can be obtained the high accuracy in the crucial component.     

Adaptive fuzzy sliding mode control for coordinated longitudinal and lateral motions of multiple autonomous vehicles in a platoon

In this paper, the platoon control problem of autonomous vehicles in highway is studied. Since the autonomous vehicles have the characteristics of nonlinearities, external disturbances and strong coupling, a novel adaptive fuzzy sliding coordinated control system is constructed to supervise the longitudinal and lateral motions of autonomous vehicles, in which the fuzzy system is employed to approximate the unknown nonlinear functions. Due to the low sensitivity to disturbances and plant parameter variations, the proposed control approach is an efficient way to handle with the complex dynamic plants operating under un-certainty conditions. The asymptotic stability of adaptive coordinated platoon close-loop control system is verified based on the Lyapunov stability theory. The results indicate that the presented adaptive coordinated platoon control approach can accurately achieve the tracking performance and ensures the stability and riding comfort of autonomous vehicles in a platoon. Finally, simulation test is exploited to demonstrate the effectiveness of the proposed control approach.     

Bimodal plate structures induced by pulsed laser in duplex-phase Zr alloy

A duplex-phase Zr-2.5Nb alloy was treated by pulsed laser, followed by careful microstructural characterization using field emission gun scanning electron microscope and attached electron backscatter diffraction. Beneath the modification zones with common uniform α-plate structures(UPS), a layer of unreported bimodal α-plate structures(BPS) featured by coarse(submicron)plates forming multiple cores surrounded by dense fine(nanoscale) plates was found. Presence of such BPS is attributed to non-equilibrium thermodynamic conditions induced by the pulsed laser treatments. Limited diffusion of Nb due to the short pulse during laser heating allows β phases with distinctly different Nb contents to be presented: Nb-enriched prior β films and Nb-depleted β phases, transforming into the fine and the coarse plates during cooling, respectively. Orientation analyses show that both types of plates in the BPS are aroused essentially from a single β orientation, suggesting epitaxial growth of the Nb-depletedβ phases from the preexisting β films.     

Indoor and outdoor particle concentration distributions of a typical meeting room during haze and clear-sky days

Air quality has increasingly been a great concern all over the world, and the good command of indoor and outdoor air qualities is of benefit to the air pollution alleviation by various measures. In this work, the indoor and outdoor particle concentration distributions of a typical meeting room during the haze and clear-sky days were measured. The results show that the mass concentrations of the indoor and outdoor PM₁, PM_2.5, PM10 in heavy haze days are 114±1.8, 135.5±3.2, 161.7±12.8 μg/m³ and 146.4±8.4, 192.3±10.2, 431.4±34.8 μg/m³ respectively, corresponding to 39.3±1.5, 58.5±2.5, 127.9±10.5 μg/m³ and 54.5±4.0, 77.8±6.0, 173.4±21.6 μg/m³ in clear-sky days. Both in the haze and clear-sky days, the number distribution of particles reaches its peak value at the diameter of 0.25 μm, but the particle number concentration in the haze day is two times greater than the clear-sky day. The indoor particle concentration is not uniform with the peak value at the corner, which can be effectively alleviated by the air cleaner. The in-situ measurements of particle concentrations in a meeting room are helpful for the indoor air quality control.     

Optimization of uncertain acoustic metamaterial with Helmholtz resonators based on interval model

Uncertainties existing in the acoustic metamaterial may strongly affect its unusual properties. Aiming at this actuality, the interval model is introduced to treat with uncertainties existing in the acoustic metamaterial with Helmholtz resonators. Frequency intervals in which the sound intensity transmission coefficients are certainly less than the required value and the effective bulk moduli are certainly negative are defined as conservative approximations. Frequency intervals in which the sound intensity transmission coefficients may be less than the required value and the effective bulk moduli may be negative are defined as unsafe approximations. The proportion of the conservative approximation and the unsafe approximation is defined as an approximate precision. Based on the quantification of uncertainties of the sound intensity transmission coefficients and the negative effective bulk moduli, an optimization model for the interval acoustic metamaterial with Helmholtz resonators is constructed. Numerical results showed that even suffering from effects of interval parameters, unusual properties of the optimized acoustic metamaterial (such as the bandgap of the sound transmission and the negative effective bulk modulus) could be improved.     

Ultralow frequency wave characteristics extracted from particle data: Application of IGSO observations

Interaction between ultralow frequency (ULF) waves and charged particles plays an important role in the acceleration of particles in the Van Allen radiation belts. The strong wave-particle interaction predicts an energy-dependent observational signature of particle flux variations during different stages of the ULF wave evolution. In this paper, we find that the energetic particle data newly available from an IGSO spacecraft are quite consistent with theoretical predictions, which enables the application of a best-fit procedure to quantitatively extract key parameters of the ULF waves from the particle data. The general agreement between observations and the best-fit results validates the scenario of wave-particle drift resonance within the entire ULF life span, and provides a new technique to understand the ULF wave characteristics in the absence of electromagnetic field data. We also examine the minor differences between observations and the best-fit results, and propose that the differences may result from a longitudinal dependence of the ULF wave power to be considered in a future study.     

Power recovery method for testing the efficiency of the ECD of an integrated generation unit for offshore wind power and ocean wave energy

Offshore wind power and ocean wave energy are clean, renewable and rich resources. The integrated generation unit for the two kinds of energy is introduced. The energy conversion device (ECD) is utilized to convert the mechanical energy absorbed from the wind power and wave energy into the hydraulic energy, the conversion efficiency of which is significant. In this paper, a power recovery method for testing the efficiency of the ECD is proposed. A simulation desktop is developed to validate the proposed method. The efficiency of the ECD is influenced by the hydraulic cylinders and the mechanical transmission. Here, the static efficiency of the hydraulic cylinders of the ECD is tested first. The results show that the static mechanical efficiency is about 95% and that the volumetric efficiency is over 99%. To test the effects induced by the mechanical transmission of the ECD, each hydraulic cylinder of the ECD is substituted with two springs. Then the power loss of the ECDM under different rotational speeds is obtained. Finally, a test platform is built and the efficiency of the ECD under different rotational speeds and pressures is obtained. The results show that the efficiency is about 80%.     

The numerical investigation of flow and heat transfer characteristics of flow past a slit-cylinder

The flow and heat transfer characteristics, including transition critical Reynolds number from two-dimensional to three-dimensional, the influence of slit-cylinder geometric parameter on Strouhal number, Nusselt number and forces acting on the slit-cylinder are numerically investigated. It’s found that transition critical Reynolds number from two-dimensional (flow wake deforms in two directions) to three-dimensional (flow wake deforms in three directions) increases with the augment of the slit width ratio in the range of present considered Reynolds number. The present results indicate that the three-dimensional vortex structures resulting from the deformation of the vortex shedding have significant effects on flow and heat transfer features such as Strouhal number, Nusselt number and forces acting on the cylinders with different ratios of slit width. It’s observed that the drag and lift coefficients reduce as the increase of slit width ratio, and vortex shedding is effectively suppressed by the slits. Moreover, the comprehensive heat transfer performance of the cylinder with the slits is significantly improved with the increase of the slit width ratio.     

Finite element analysis for inclined wellbore stability of transversely iso-tropic rock with HMCD coupling based on weak plane strength criterion

The finite element analysis (FEA) technology by hydraulic-mechanical-chemical-damage (HMCD) coupling is proposed in this paper for inclined wellbore stability analysis of water-sensitive and laminated rock, developed basing on the recently established FEA technology for transversely isotropic rock with hydraulic-mechanical-damage (HMD) coupling. The chemical activity of the drilling fluid is considered as phenomenological hydration behavior, the moisture content and parameters of rock considering hydration could be determined with time. The finite element (FE) solutions of numerical wellbore model considering the chemical activity of drilling fluid, damage tensor calculation and weak plane strength criterion for transversely isotropic rock are developed for researching the wellbore failure characteristics and computing the time-dependent collapse and fracture pressure of laminated rock as shale reservoirs. A three-dimensional FE model and elastic solid deformation and seepage flow coupled equations are developed, and the damage tensor calculation technology for transversely isotropic rock are realized by introducing effect of the hydration and the stress state under the current load. The proposed method utilizing weak plane strength criterion fully reflects the strength parameters in rock matrix and weak plane. To the end, an effective and reliable numerically three-step FEA strategy is well established for wellbore stability analysis. Numerical examples are given to show that the proposed method can establish efficient and applicable FE model and be suitable for analyzing the timedependent solutions of pore pressure and stresses, and the evolution region considering the hydration surrounding wellbore, furthermore to compute the collapse cycling time and the safe mud weight for collapse and fracture pressure of transversely isotropic rock.     

Investigation on the cleaning of KDP ultra-precision surface polished with micro water dissolution machining principle

A potassium dihydrogen phosphate (KDP) optical crystal was machined to an ultra-precision surface with water-in-oil (W/O) micro emulsion polishing fluid. The micro water dissolution principle utilized in the machining process is discussed, its planarization mechanism is illustrated, and an ultra-precision polished surface with 2.205 nm RMS roughness is obtained. However, a substantial quantity of residual contamination remained on the polished surface after machining. This can seriously impact the optical performance of the crystal, and so it must be removed. Fourier transform infrared (FTIR) spectroscopy was used to conduct an investigation into the composition of the surface residue, and the results showed that the residue was comprised of organic chemicals with hydrocarbon chains and aromatic ether, i.e., mostly the polishing fluid. The cleaning method and the principle on which the KDP ultra precision surface investigation is based are discussed in detail, and the cleaning experiments with selected KDP-compatible organic solvents were then performed. FTIR transmittance spectra measurement and microscopic observations were employed to assess the effects of the cleaning process on the surface of the KDP crystal. The results showed that toluene cleaning achieved the most desirable results. This cleaning method produced a surface roughness of 1.826 nm RMS, which allows the KDP crystal to be applied to subsequent engineering applications.