| 1. |
- Liang, S. D., et al.
(författare)
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An experimental study on pile scour mitigating measures under waves and currents
- 2015
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Ingår i: Science China Technological Sciences. - : Springer Science and Business Media LLC. - 1674-7321 .- 1869-1900. ; 58:6, s. 1031-1045
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Tidskriftsartikel (refereegranskat)abstract
- An experimental study has been carried out to investigate effects of four flow-altering scour countermeasures placed around a foundation pile under currents only as well as under coexisting waves and currents. The countermeasures are sacrificial piles, downstream bed sill, sleeve and slot in the pile. Their arrangements follow the suggested optimal configurations, with some of them slightly modified. In terms of the evolution of scour depth and bed topography around the pile, the scour countermeasures are evaluated, subjected to steady currents with or without irregular waves. A comparison between maximum scour depth with the countermeasures and one without the countermeasures demonstrates the efficiency of countermeasures. All the tested scour measures reduce the scour depth by 17.6%–42.6% under the action of currents only and 5.8%–24.0% under the combined action of both currents and waves. The results also show that it takes a shorter time for the scour depth to reach its equilibrium with the measures under either coexisting currents and waves or currents only than ones without the measures.
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| 2. |
- PengLi, Dong, et al.
(författare)
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Conductivity properties of beta-SiAlON ceramics
- 2012
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Ingår i: Science China Technological Sciences. - : Springer Science and Business Media LLC. - 1674-7321 .- 1869-1900. ; 55:9, s. 2409-2415
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Tidskriftsartikel (refereegranskat)abstract
- The thermal diffusivity and heat capacity of beta-SiAlON ceramics with different Z values (0.6, 1.5, 3.0) were measured by laser flash technique and differential scanning calorimetry (DSC), respectively. The thermal conductivity of beta-SiAlON was calculated from thermal diffusivity, heat capacity and density and it decreased and then kept almost constant with increasing of temperature. Two different models representing effective thermal conductivity were established and the various parameters of these models were simulated based on the results from the present work. The fitted regression lines were in good agreement with the experimental values.
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| 3. |
- QingMiao, Hu, et al.
(författare)
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Composition dependent elastic modulus and phase stability of Ni2MnGa based ferromagnetic shape memory alloys
- 2012
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Ingår i: SCI CHINA TECHNOL SC. - : Springer Science and Business Media LLC. - 1674-7321 .- 1869-1900. ; 55:2, s. 295-305
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Tidskriftsartikel (refereegranskat)abstract
- Ni2MnGa based ferromagnetic alloys are ideal candidates for applications such as actuators, magnetic refrigerators or magnetostrictive transducers due to their attractive properties such as magnetic field induced shape memory effect and large magnetocaloric effect. The properties of these alloys (e.g., the martensitic transformation temperature T (M) ) sensitively depend on the composition. Understanding the composition dependence of these properties so as to design the alloy as desired is one of the main research topics in this area. In recent years, we have investigated the composition dependent elastic modulus and phase stability of Ni2MnGa-based alloys by using a first-principles method, in hope of clarifying their connection to the properties of these alloys. In this article, we review the main results of our investigations. We show that the tetragonal shear modulus C' is a better predictor of the composition dependent T (M) than the number of valence electrons per atom (e/a) since the general T (M) similar to C' correlation works for some of the alloys for which the T (M) similar to e/a correlation fails, although there exist several cases for which both the general T (M) similar to C' and T (M)similar to e/a correlations break down. Employing the experimentally determined modulation function, the complex 5-layer modulated (5M) structure of the martensite of Ni2MnGa and the Al-doping effect on it are studied. We find that the shuffle and shear of the 5M structure are linearly coupled. The relative stability of the austenite and the martensites is examined by comparing their total energies. The non-modulated martensite beta aEuro(3)aEuro(2) with the tetragonality of the unit cell c/a > 1 is shown to be globally stable whereas the 5M martensite with c/a < 1 is metastable. The critical Al atomic fraction over which the martensitic transformation between the 5M martensite and austenite cannot occur is predicted to be 0.26, in reasonable agreement with experimental findings.
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| 4. |
- Wang, Yifan, et al.
(författare)
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Time delay recursive neural network-based direct adaptive control for a piezo-actuated stage
- 2023
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Ingår i: Science China Technological Sciences. - 1869-1900 .- 1674-7321. ; 66:5, s. 1397-1407
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Tidskriftsartikel (refereegranskat)abstract
- Piezo-actuated stage is a core component in micro-nano manufacturing field. However, the inherent nonlinearity, such as rate-dependent hysteresis, in the piezo-actuated stage severely impacts its tracking accuracy. This study proposes a direct adaptive control (DAC) method to realize high precision tracking. The proposed controller is designed by a time delay recursive neural network. Compared with those existing DAC methods designed under the general Lipschitz condition, the proposed control method can be easily generalized to the actual systems, which have hysteresis behavior. Then, a hopfield neural network (HNN) estimator is proposed to adjust the parameters of the proposed controller online. Meanwhile, a modular model consisting of linear submodel, hysteresis submodel, and lumped uncertainties is established based on the HNN estimator to describe the piezo-actuated stage in this study. Thus, the performance of the HNN estimator can be exhibited visually through the modeling results. The proposed control method eradicates the adverse effects on the control performance arising from the inaccuracy in establishing the offline model and improves the capability to suppress the influence of hysteresis on the tracking accuracy of piezo-actuated stage in comparison with the conventional DAC methods. The stability of the control system is studied. Finally, a series of comparison experiments with a dual neural networks-based data driven adaptive controller are carried out to demonstrate the superiority of the proposed controller.
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| 5. |
- XiaoTeng, Ma, et al.
(författare)
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Transient heat transfer analysis in packed beds : Entropy generation model and multi-objective optimization
- 2019
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Ingår i: SCIENCE CHINA-TECHNOLOGICAL SCIENCES. - : SCIENCE PRESS. - 1674-7321 .- 1869-1900. ; 62:11, s. 1999-2008
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Tidskriftsartikel (refereegranskat)abstract
- Due to the important role of the unsteady heat transfer process of packed beds in industrial production, the construction of the transient heat transfer model is of great significance for the operation and optimization. The present study performs a transient thermal analysis of packed bed, in which the convective heat transfer and conductive thermal resistance within the particles are considered simultaneously. A mathematical model is established of the total entropy generations (0-t) contributed by viscous dissipation and heat transfer; the influence of particle diameter, air flow rate, and pressure drop, is then investigated. Because of the time cost, these results present some different trends from the steady-state process. Furthermore, for a laboratory heat transfer system, with the aid of the genetic algorithm we adopt a multi-objective genetic algorithm model and modified expressions of the entropy generations are set as objective functions. Finally, optimal operational and structural parameters are obtained for different fan power settings. When the fan power is 300 W, the optimal particle diameter and inlet wind speed are 14 mm and 2.4 m/s, respectively. The results also suggest that the time cost is reduced with increasing fan power consumption.
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| 6. |
- Xie, Rui Li, et al.
(författare)
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Mirror-assisted multi-view high-speed digital image correlation for dual-surface dynamic deformation measurement
- 2023
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Ingår i: Science China Technological Sciences. - : Science Press. - 1674-7321 .- 1869-1900. ; 66:3, s. 807-820
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Tidskriftsartikel (refereegranskat)abstract
- Based on the recently proposed mirror-assisted multi-view digital image correlation (MV-DIC), we establish a cost-effective and easy-to-implement mirror-assisted multi-view high-speed digital image correlation (MVHS-DIC) method and explore its applications for dual-surface full-field dynamic deformation measurement. In contrast to the general requirement of four expensive high-speed cameras for dual-surface dynamic deformation field measurement, the established mirror-assisted MVHS-DIC halves the cost by involving only two synchronized high-speed cameras and two planar mirrors. The two synchronized high-speed cameras can dynamically measure the front and rear surfaces of a sheet sample simultaneously through the reflection of the two mirrors. The results on the two surfaces are then transformed into the same coordinate system, leading to the required dual-surface 3D dynamical deformation fields. The effectiveness and accuracy of the established system are validated through modal tests of a cantilever aluminum sheet. The vibration measurement of a drum and dual-surface transient deformation measurement of a smartphone in the drop-collision process further prove its practicability. Benefiting from the attractive advantages of multi-view dynamic deformation measurement in a cost-efficient way, the established mirror-assisted MVHS-DIC is expected to encourage more comprehensive dynamic mechanical behavior characterization of regular-sized materials and structures in vibration and impact engineering fields.
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