1.

2018-11-23

Meshfree modeling of a fluid-particle two-phase flow with an improved SPH method

Z. L. Zhang, K. Walayat, J. Z. Chang, M. B. Liu

Abstract:

Fluid-particle two-phase flows are very complex and quite challenging to numerically simulate due to the complex and constantly moving fluid-particle interface. Recent developments in meshfree and particle methods provide alternatives in modeling fluid flows with moving boundaries. In this paper, a modified smoothed particle hydrodynamics (SPH) method is developed to simulate particle sedimentation (two-dimensional) in Newtonian fluids. The modified SPH includes an enhanced particle approximation scheme, an effective solid boundary treatment algorithm, the artificial stress model, and a turbulence model. By decoupling a field variable and its derivatives in a finite particle method, a decoupled finite particle method is presented, which balances accuracy, efficiency, and stability in SPH simulations without the necessity of solving redundant and challenging corrective matrix equations. A coupled dynamic solid boundary treatment is developed to improve the accuracy near the fixed and moving solid boundaries. The artificial stress term is added into the SPH equations of motion to remove the possible tensile instability phenomenon. The large eddy simulation model is incorporated into the SPH to describe the turbulence effects at high Reynolds numbers. Four different particle sedimentation tests are conducted using the modified SPH along with the finite element fictitious boundary method. It is demonstrated that the improved SPH method can achieve much better results than the conventional SPH while showing a good comparison with the results from the finite element fictitious boundary method and from other sources.

Reference:

Zhang, Z. L., et al. "Meshfree modeling of a fluid‐particle two‐phase flow with an improved SPH method." International Journal for Numerical Methods in Engineering 116.8 (2018): 530-569.

2.

2018-11-01

Experimental study on transient response of the fiber optic seismic accelerometer

Yi, D; Liu, F; He, XG; Zhang, M

Abstract:

Transient response accuracy of the fiber optic seismic accelerometer influences greatly the seismic reservoir monitoring in the smart oilfield fields. This study demonstrates the transient response analysis of an optimized fiber optic seismic accelerometer, and the effects of damping on the transient response are experimentally verified. The silicone oil is injected into the accelerometer structure to increase the damping, and an additional elastic rubber ring is used to provide an adjustable damping. The experimental results show that the injected silicone oil increases obviously the stamper damping, and the variations of torsional moment also modify slightly the damping of the accelerometer. The increase of the damping avoids the oscillation tailing phenomenon, and therefore largely improves the transient response, which is confirmed by the commercial piezoelectric accelerometer. This study can be used to modify the measurement error and improve the accuracy of the seismic reservoir monitoring in the smart oilfield applications.

Reference:

Duo, Yi, et al. "Experimental study on transient response of the fiber optic seismic accelerometer." Optical Fiber Technology 45 (2018): 58-63.

3.

2018-10-18

超疏水小球低速入水空泡研究1)

黄超 翁翕 刘谋斌

Abstract:

物体入水问题是一类复杂的流固耦合问题，具有广泛的工程应用背景。物体在跨越自由液面入水的过程中，在一定的条件下，物体入水时会向水中卷入空气形成空泡，空泡的运动还可能形成指向物体的射流，从而对物体的受力及其运动过程产生影响。超疏水表面能够在物体入水过程中形成多尺度流固耦合作用，进而影响物体的运动和宏观流动现象。而对于小尺度的小球低速入水问题，表面和界面力往往起主导作用。为了在更广的参数空间获得超疏水小球入水空泡类型和小球的运动特性，采用高速摄影实验方法，研究了半径0.175 mm~10 mm的超疏水小球低速入水及空泡动力学行为，获得了小球漂浮振荡、准静态空泡、浅闭合空泡、深闭合空泡和表面闭合空泡5种类型的动力学行为，探讨了这些运动行为与韦伯数We和邦德数Bo之间的关系，并推导了小球漂浮振荡与下沉现象的无量纲关系。研究结果表明：超疏水小球的入水及空泡动力学行为主要与韦伯数We和邦德数Bo有关。在邦德数Bo<O(10-1)范围内，表面张力对流动的影响显著，随着韦伯数We的增加，小球入水及空泡动力学行为依次经历漂浮振荡、准静态闭合、浅闭合、深闭合和表面闭合；在邦德数O(10-1)<Bo<O(1)范围内，漂浮振荡现象不再发生；当邦德数Bo>O(1)后，浅闭合现象也不再发生；小球漂浮振荡与下沉现象的临界关系可以用相似律关系描述。

Reference:

Huang Chao, Wen Xi and Liu Moubin. Study on low-speed water entry of super-hydrophobic small spheres. Chinese Journal of Theoretical and Applied Mechanics, 2019, 51（1）

4.

2018-10-16

油气储层长石矿物表面水滴接触角

邓亚骏 徐蕾 卢海龙 王昊 师永民

Abstract:

润湿性是油气储层岩石的一个重要特性,但由于组成储层孔隙的矿物成分多样且颗粒多在微米尺度,准确评价某一矿物的润湿性是一个难题.长石是砂岩储层的重要组成矿物,然而关于长石润湿性的研究却很少.本文利用原子力显微镜测量了微米级水滴在储层岩石钾长石和钠长石表面的接触角.结果表明,水-钾/钠长石接触角并不是一个定值,而是分布一定范围,这可能与晶体表面粗糙与非均质、晶面不同有关.相比于以前研究中用间接方法计算得出的水-长石接触角,本研究在实际储层长石矿物表面直接测量的接触角具有更好的代表性.就平均接触角而言,水-钾/钠长石的接触角均小于相同条件下测得的水-石英接触角,从而说明在用接触角法评价人造砂岩岩心的润湿性时,应综合考虑长石、石英对润湿性的影响。

Reference:

Deng Y J, Xu L, Lu H L, et al. The contact angle of water on feldspar in a reservoir rock (in Chinese). Chin Sci Bull, 2018, 63: 3137–3145, doi: 10.1360/N972018-00120

5.

2018-10-01

Coupled microbial bloom and oxygenation decline recorded by magnetofossils during the Palaeocene-Eocene Thermal Maximum

Chang, L., R. J. Harrison, F. Zeng, T.，Berndt, A. P. Roberts, D. Heslop, X. Zhao

Abstract:

Understanding marine environmental change and associated biological turnover across the Palaeocene-Eocene Thermal Maximum(PETM; -56 Ma)-themost pronounced Cenozoic short-term global warming event-is important because of the potential role of the ocean in atmospheric CO2 drawdown, yet proxies for tracing marine productivity and oxygenation across the PETM are limited and results remain controversial. Here we show that a high-resolution record of South Atlantic Ocean bottom water oxygenation can be extracted from exceptionally preserved magnetofossils-the bioinorganic magnetite nanocrystals produced b ymagnetotactic bacteria (MTB) using a new multiscale environmental magnetic approach. Our results suggest that a transient MTB bloom occurred due to increased nutrient supply. Bottom water oxygenation decreased gradually from the onset to the peak PETM. These observations provide a record of microbial response to the PETM and establish the value of magnetofossils as palaeo environmental indicators.

Reference:

Chang, L., R. J. Harrison, F. Zeng, T. Berndt, A. P. Roberts, D. Heslop, X. Zhao, (2018). Coupled microbial bloom and oxygenation decline recorded by magnetofossils during the Palaeocene-Eocene Thermal Maximum, Nature Communications, 4007, DOI: 10.1038/s41467-018-06472-y.

6.

2018-09-05:

Comparing the Hydrological Responses of Conceptual and Process-Based Models with Varying Rain Gauge Density and Distribution

Zhaokai Yin, Weihong Liao, Xiaohui Lei, Hao Wang and Ruojia Wang

Abstract:

Precipitation provides the most crucial input for hydrological modeling. However, rain gauge networks, the most common precipitation measurement mechanisms, are sometimes sparse and inadequately distributed in practice, resulting in an imperfect representation of rainfall spatial variability. The objective of this study is to analyze the sensitivity of different model structures to the different density and distribution of rain gauges and evaluate their reliability and robustness. Based on a rain gauge network of 20 gauges in the Jinjiang River Basin, south-eastern China, this study compared the performance of two conceptual models (the hydrologic model (HYMOD) and Xinanjiang) and one process-based distributed model (the water and energy transfer between soil, plants and atmosphere model (WetSpa)) with different rain gauge distributions. The results show that the average accuracy for the three models is generally stable as the number of rain gauges decreases but is sensitive to changes in the network distribution. HYMOD has the highest calibration uncertainty, followed by Xinanjiang and WetSpa. Differing model responses are consistent with changes in network distribution, while calibration uncertainties are more related to model structures.

Reference:

Yin, Zhaokai, et al. "Comparing the Hydrological Responses of Conceptual and Process-Based Models with Varying Rain Gauge Density and Distribution." Sustainability 10.9 (2018): 3209.

7.

2018-08-15

Acousto-Optic Modulation Induced Noises on Heterodyne-Interrogated Interferometric Fiber-Optic Sensors

Liu, F; Gu, LJ; Xie, SR; He, XG; Yi, D; Zhang, M; Tao, QC

Abstract:

Acousto-optic modulator (AOM) is a key component in heterodyne-interrogated interferometric fiber-optic sensors. Here, we analyze in detail the effect of AOM on the noise floor of interferometric fiber-optic sensors with heterodyne detection. Besides the well-known phase noises caused by the AOM driver, the intensity noise induced by the relative diffraction efficiency fluctuation (RDEF) of AOM is considered and for the first time studied in detail. The power spectrum density of the intensity noise is found 0.8-0.9 times of the "switching noise," which is defined as the sum of RDEF and relative intensity noise of the laser. The switching noise varies with the driving power of AOM and can be reduced by setting the driving power close to its saturation point. Experimentally, we achieved similar to 5-dB suppression of the switching noise and similar to 2-dB reduction of the overall noise floor. By working at the optimal driving power, together with reducing the AOM-induced phase noise to -130 dB level at the frequency offset twice of the heterodyne frequency, the overall noise floor of the sensor can be optimized to about -101 dB, i.e., the order of 10 mu rad/root Hz.

Reference:

Liu, F.; Gu, L. J.; Xie, S. R.; He, X. G.; Yi, D.; Zhang, M.; Tao, Q. C., Acousto-Optic Modulation Induced Noises on Heterodyne-Interrogated Interferometric Fiber-Optic Sensors.J. Lightwave Technol. 2018,36 (16), 3465-3471.

8.

2018-08-01

Three-Dimensional Modeling of a Fin-Actuated Robotic Fish With Multimodal Swimming

Wang, W; Dai, X; Li, L; Gheneti, BH; Ding, Y; Yu, JZ ; Xie, GM

Abstract:

Dynamical model is always an important factor in controller design for robots. Existing models of robotic fish typically incorporate only planar motion, rarely considering spatial motion. This paper formulates a complete three-dimensional (3-D) dynamic model for the robotic fish actuated by pectoral and caudal fins, in which the fluid forces mainly contain quasi-steady lift and drag, gravity and buoyancy, and waterjet strike force. The critical lift and drag of flapping fins are derived with an explicit 3-D angle of attack. Taking a bioinspired central pattern generator as the system actuation, our model can produce multi-modal maneuvers, including forward/backward swimming, turning, and ascending/descending, as well as complicated motions, such as rolling and spiraling. Motions simulated in a 3-D environment are experimentally validated with a free-swimming robotic fish. Furthermore, systematic comparisons between simulations and experiments are conducted over a wide range of the control parameter space for beating frequency, amplitude, and offset. The overall results demonstrate the effectiveness and the versatility of the developed 3-D dynamic model in the prediction of the robot trajectory, velocity, and attitude.

Reference:

Wang, Wei, et al. "Three-Dimensional Modeling of a Fin-Actuated Robotic Fish With Multimodal Swimming." IEEE/ASME Transactions on Mechatronics 23.4 (2018): 1641-1652.

9.

2018-07-27

Brasilianoids A–F, New Meroterpenoids From the Sponge-Associated Fungus Penicillium brasilianum

Jianping Zhang, Bochuan Yuan, Dong Liu, Shuang Gao, Peter Proksch, and Wenhan Lin

Abstract:

3,5-Dimethylorsellinic acid (DMOA) derived meroterpenoids comprise an unique class of natural products with diverse scaffolds and with a broad spectrum of bioactivities. Bioinformatics analysis of the gene clusters in association with the qRT-PCR detection of the amplification of two key genes led to speculate that the sponge associated fungus Penicillium brasilianum WZXY-m122-9 is a potential producer of meroterpenoids. Chromatographic separation of the EtOAc extract of this fungal strain on a large-scale fermentation resulted in the isolation of six new DMOA-related meroterpenoids with trivial names of brasilianoids A-F (1-6), together with preaustinoid D and preaustinoid A2. The structures were determined by extensive analyses of spectroscopic data, including the X-ray diffraction and the ECD data for configurational assignment. Brasilianoids A and F showed an unprecedented skeleton with a gamma-lactone in ring A, while brasilianoids B-C featured a 7/6/6/5/5 pentacyclic ring system finding in nature for the first time. The biosynthetic relationship among the isolated compounds was postulated. Compound 1 significantly stimulated the expression of filaggrin and caspase-14 in HaCaT cells in dose-dependent manner, while compounds 2 and 3 showed moderate inhibition against NO production in LPS-induced RAW 264.7 macrophages.

Reference:

Zhang J, Yuan B, Liu D, et al. Brasilianoids A–F, New Meroterpenoids From the Sponge-Associated Fungus Penicillium brasilianum[J]. Frontiers in Chemistry, 2018, 6.

10.

2018-07-18

Palaeoclimate constraints on the impact of 2 degrees C anthropogenic warming and beyond (vol 11, pg 474, 2018).

liping Zhou, et al.

Abstract:

Over the past 3.5 million years, there have been several intervals when climate conditions were warmer than during the pre-industrial Holocene. Although past intervals of warming were forced differently than future anthropogenic change, such periods can provide insights into potential future climate impacts and ecosystem feedbacks, especially over centennial-to-millennial timescales that are often not covered by climate model simulations. Our observation-based synthesis of the understanding of past intervals with temperatures within the range of projected future warming suggests that there is a low risk of runaway greenhouse gas feedbacks for global warming of no more than 2 °C. However, substantial regional environmental impacts can occur. A global average warming of 1–2 °C with strong polar amplification has, in the past, been accompanied by significant shifts in climate zones and the spatial distribution of land and ocean ecosystems. Sustained warming at this level has also led to substantial reductions of the Greenland and Antarctic ice sheets, with sea-level increases of at least several metres on millennial timescales. Comparison of palaeo observations with climate model results suggests that, due to the lack of certain feedback processes, model-based climate projections may underestimate long-term warming in response to future radiative forcing by as much as a factor of two, and thus may also underestimate centennial-to-millennial-scale sea-level rise.

Reference:

Fischer, Hubertus, et al. "Palaeoclimate constraints on the impact of 2 C anthropogenic warming and beyond." Nature geoscience (2018): 1.

11.

2018-07-15

Self-Referenced Accelerometer Array Multiplexed on a Single Fiber Using a Dual-Pulse Heterodyne Phase-Sensitive OTDR

Xiangge He, Min Zhang, Shangran Xie, Fei Liu, Lijuan Gu, and Duo Yi

Abstract:

We report a new type of multiplexed fiber-optic accelerometer array based on a dual-heterodyne-pulse phase-sensitive OTDR technique. This scheme significantly simplifies the structure of fiber accelerometer and can greatly benefit its practical applications. The sensitivity model for the new type accelerometer based on the Rayleigh backscattering is developed for the first time, which shows a great difference from the transmission-type interferometric accelerometer. On a single piece of telecommunication fiber, we demonstrate the multiplexing of three accelerometers separated by 20 m, each with a measured sensitivity of∼36 rad/g that agrees well with the theoretical analysis. The connecting fiber between accelerometers simultaneously acts as a distributed acoustic sensor, which under proper vibration isolation can be used as a self-reference to suppress system noises. We show that the common-mode noises of the sensor can be suppressed by 35 dB at a frequency of 100 Hz without using additional reference interferometers.

Reference:

He X, Zhang M, Xie S, et al. Self-Referenced Accelerometer Array Multiplexed on a Single Fiber Using a Dual-Pulse Heterodyne Phase-Sensitive OTDR[J]. Journal of Lightwave Technology, 2018, 36(14): 2973-2979.

12.

2018-07-04

Long-term viability of carbon sequestration in deep-sea sediments

Yihua Teng, and Dongxiao Zhang

Abstract:

Sequestration of carbon dioxide in deep-sea sediments has been proposed for the long-term storage of anthropogenic CO2 that can take advantage of the current offshore infrastructure. It benefits from the negative buoyancy effect and hydrate formation under conditions of high pressure and low temperature. However, the multiphysics process of injection and postinjection fate of CO2 and the feasibility of subseabed disposal of CO2 under different geological and operational conditions have not been well studied. With a detailed study of the coupled processes, we investigate whether storing CO2 into deep-sea sediments is viable, efficient, and secure over the long term. We also study the evolution of multiphase and multicomponent flow and the impact of hydrate formation on storage efficiency. The results show that low buoyancy and high viscosity slow down the ascending plume and the forming of the hydrate cap effectively reduces permeability and finally becomes an impermeable seal, thus limiting the movement of CO2 toward the seafloor. We identify different flow patterns at varied time scales by analyzing the mass distribution of CO2 in different phases over time. We observe the formation of a fluid inclusion, which mainly consists of liquid CO2 and is encapsulated by an impermeable hydrate film in the diffusion-dominated stage. The trapped liquid CO2 and CO2 hydrate finally dissolve into the pore water through diffusion of the CO2 component, resulting in permanent storage. We perform sensitivity analyses on storage efficiency under variable geological and operational conditions. We find that under a deep-sea setting, CO2 sequestration in intact marine sediments is generally safe and permanent.

Reference:

Teng Y, Zhang D. Long-term viability of carbon sequestration in deep-sea sediments[J]. Science advances, 2018, 4(7): eaao6588.

13.

2018-07-01

Versiquinazolines L-Q, new polycyclic alkaloids from the marine-derived fungus Aspergillus versicolor

Cheng, ZB; Liu, D; Cheng, W; Proksch, P; Lin, WH

Abstract:

Further chemical examination of a coral-associated fungus Aspergillus versicolor LZD-14-1 by the PHLC-DAD detection resulted in the isolation of six new polycyclic alkaloids, namely versiquinazolines L-Q (1-6). Their structures were determined by extensive analyses of spectroscopic data, including quantum ECD calculation and X-ray single crystal diffraction for the assignment of absolute configurations. Versiquinazoline L bearing a d-Ala residue and versiquinazoline M containing an l-serine residue are rarely found in the fumiquinazoline-type alkaloids, while versiquinazoline P displayed an unusual scaffold with a spiro--lactone. Versiquinazolines P and Q exhibited significant inhibition against thioredoxin reductase (TrxR) with IC50 values of 13.6 +/- 0.6 and 12.2 +/- 0.7 M, which showed higher activity than the positive control curcumin (IC50 = 25 M). The weak cytotoxicity and potent inhibition toward TrxR suggested that versiquinazolines P and Q are potential for microenvironmental regulation of tumor progression and metastasis.

Reference:

Cheng, Zhongbin, et al. "Versiquinazolines L–Q, new polycyclic alkaloids from the marine-derived fungus Aspergillus versicolor." RSC Advances 8.55 (2018): 31427-31439.

14.

2018-07-01

Geochemical characteristics of iron in sediments from the Sea of Marmara

Yang, HL; Lu, HL; Ruffine, L

Abstract:

Two similar to 1000 cm long sediment cores were recovered from the Sea of Marmara, one with the occurrence of gas hydrates in the Western High, and the other without hydrates in the Cinarcik Basin. Differences in mineralogical and chemical compositions have been identified between the two sediment cores. Based on the results of the mineralogical and geochemical analyses, the main sources of the sediments are quite similar for both investigated areas, but the authigenic components are different, particularly iron sulfides and carbonates. Authigenic Fe(II) carbonate are much higher in Core MRS-CS-05 in the Western High, while crystalline Fe(III) phases are more abundant in Core MRS-CS-16 in the Cinarcik Basin. Notably, the enrichments of greigite (Fe3S4), a metastable ferromagnetic iron sulfide mineral and intermediate polysulfide, as well as iron carbonates are identified at 400 cmbsf with the maximum iron content in Core MRS-CS-05. These indicate the presence of a more reducing and acidic environment in the Western High, mainly due to higher organic matter content and seepage of heavy hydrocarbons in the sediments.

Reference:

15.

2018-06-21

Asynchronous distributed event-triggered circle formation of multi-agent systems

Wen, Jiayan; Wang, Chen; Xie, Guangming

Abstract:

This paper proposes distributed event-triggered algorithmic solutions to circle formation problems of first-order multi-agent systems, where the communication topology of networks is described by weight-unbalanced, strongly connected digraph. In particular, the controller updates and communications between neighboring agents considered here are event-triggered, depending on the specified threshold of a certain measurement error by contrast with the norm of a function with state-dependent. Sufficient conditions on both uniform and arbitrary circle formation are derived under which the resulting asynchronous network executions converge to some equilibrium point. Furthermore, we show that the Zeno behavior can be avoided under the proposed control laws. Numerical simulation results are given to illustrate the effectiveness of the proposed methods.

Reference:

Wen J, Wang C, Xie G. Asynchronous distributed event-triggered circle formation of multi-agent systems[J]. Neurocomputing, 2018, 295: 118-126.

16.

2018-06-11

Self-suppression of common-mode noises of the different fiber optic interferometric accelerometers

Yi Duo; He Xiangge; Liu Fei; Gu Lijuan; Zhang Min; Qiu Xiaokang; Ye Han

Abstract:

This study proposes two new fiber optic interferometric accelerometers with the utilization of the push-pull structure, one is based on the principle of triple low-reflectivity fiber Bragg gratings, and the other is based on the 1x3 unbalanced Michelson interferometer. The proposed accelerometers are capable of suppressing the common-mode noises (CMNs) by themselves without additional reference accelerometers, and therefore reducing the volume and the cost of the sensing system. Besides, the accelerometers can also suppress the sensor noises caused by the environment, and therefore show better CMNs suppression effect than the traditional method of using the reference accelerometer. The two accelerometers are experimentally verified and show respectively an improvement of 33 dB and 28 dB in CMNs suppression at 100 Hz. Both presented fiber optic accelerometers show huge advantages for the large-scale quasi-distributed oil and gas reservoir monitoring applications. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement.

Reference:

Duo Y, Xiangge H, Fei L, et al. Self-suppression of common-mode noises of the different fiber optic interferometric accelerometers[J]. Optics Express, 2018, 26(12): 15384-15397.

17.

2018-06-08

Two-scalar turbulent Rayleigh-Benard convection: numerical simulations and unifyingtheory.

Yang, YT; Verzicco, R; Lohse, D

Abstract:

We conduct direct numerical simulations for turbulent Rayleigh-Benard (RB) convection, driven simultaneously by two scalar components (say, temperature and concentration) with different molecular diffusivities, and measure the respective fluxes and the Reynolds number. To account for the results, we generalize the Grossmann-Lohse theory for traditional RB convection (Grossmann & Lohse, J. Fluid Mech., vol. 407, 2000, pp. 27-56; Phys. Rev. Lett., vol. 86 (15), 2001, pp. 3316-3319; Stevens etal., J. Fluid Mech., vol. 730, 2013, pp. 295-308) to this two-scalar turbulent convection. Our numerical results suggest that the generalized theory can successfully capture the overall trends for the fluxes of two scalars and the Reynolds number without introducing any new free parameters. In fact, for most of the parameter space explored here, the theory can even predict the absolute values of the fluxes and the Reynolds number with good accuracy. The current study extends the generality of the Grossmann-Lohse theory in the area of buoyancy-driven convection flows.

Reference:

Yang, Y.; Verzicco, R.; Lohse, D., Two-scalar turbulent Rayleigh-Benard convection: numerical simulations and unifyingtheory. Journal of Fluid Mechanics 2018, 848, 648-659.

18.

2018-04-15

Precession and atmospheric CO2modulated variability of sea ice in the central Okhotsk Sea since 130,000 years ago

Liping Zhou, et al.

Abstract:

Recent reduction in high-latitude sea ice extent demonstrates that sea ice is highly sensitive to external and internal radiative forcings. In order to better understand sea ice system responses to external orbital forcing and internal oscillations on orbital timescales, here we reconstruct changes in sea ice extent and summer sea surface temperature (SSST) over the past 130,000 yrs in the central Okhotsk Sea. We applied novel organic geochemical proxies of sea ice (IP25), SSST (TEXL86) and open water marine productivity (a tri-unsaturated highly branched isoprenoid and biogenic opal) to marine sediment core MD01-2414 (53°11.77′N, 149°34.80′E, water depth 1123 m). To complement the proxy data, we also carried out transient Earth system model simulations and sensitivity tests to identify contributions of different climatic forcing factors. Our results show that the central Okhotsk Sea was ice-free during Marine Isotope Stage (MIS) 5e and the early-mid Holocene, but experienced variable sea ice cover during MIS 2–4, consistent with intervals of relatively high and low SSST, respectively. Our data also show that the sea ice extent was governed by precession-dominated insolation changes during intervals of atmospheric CO2 concentrations ranging from 190 to 260 ppm. However, the proxy record and the model simulation data show that the central Okhotsk Sea was near ice-free regardless of insolation forcing throughout the penultimate interglacial, and during the Holocene, when atmospheric CO2 was above∼260 ppm. Past sea ice conditions in the central Okhotsk Sea were therefore strongly modulated by both orbital-driven insolation and CO2-induced radiative forcing during the past glacial/interglacial cycle.

Reference:

Lo L, Belt S T, Lattaud J, et al. Precession and atmospheric CO 2 modulated variability of sea ice in the central Okhotsk Sea since 130,000 years ago[J]. Earth and Planetary Science Letters, 2018, 488: 36-45.

19.

2018-03-15

海洋保护区管理与保护成效评估的方法与进展

宋瑞玲 姚锦仙 吴恺悦 张晓川 吕植 朱争光 殷丽洁

Abstract:

全球物种多样性的持续下降使得生物多样性保护面临巨大挑战,海洋生物多样性的保护任务尤其艰巨。海洋保护区是保护生物多样性的有效方式之一,如何对其成效进行评估是当前研究热点。然而,目前针对海洋保护区的评估体系较少,而且评估指标多侧重于管理成效。近年来随着全球生物多样性监测网络和数据库的建立,以及多种新技术(如遥感、声呐系统、卫星追踪、基因组学等)在海洋生物多样性监测中的应用,使得从生态系统到基因水平的多层次连续监测成为可能。基于此,建议未来我国海洋保护区成效评估应在充分利用新技术方法的基础上,加强长期科学监测,建立并完善生物多样性监测数据库和信息共享机制,发展跨学科的综合保护成效评估体系,加强基于生物多样性监测的保护成效评估。

Reference:

宋瑞玲, 姚锦仙, 吴恺悦, 等. 海洋保护区管理与保护成效评估的方法与进展[J]. 生物多样性, 2018, 26(3): 286-294.

20.

2018-03-07

Numerical simulation of water entry with improved SPH method

J. R. Shao, Y. Yang, H. F. Gong, M. B. Liu

Abstract:

Water entry problems are very common in engineering and sciences. When objects move with relatively high speed, bubble cavities will be generated, and the behavior of moving objects will also be affected conversely. In this paper, the water entry problems are studied using smoothed particle hydrodynamics (SPH) method, which has special advantages in modeling free surfaces, moving interfaces. First, an improved fluid–solid interface treatment algorithm is presented, whose effectiveness is validated by a water entry of a buoyant cylinder. Then the water entry with different velocities and directions are researched. It is found that the velocities and angles of the moving objects will affect the movement of the object greatly, and the SPH model can give optimal predication of these corresponding conditions.

Reference:

J. R. Shao, Y. Yang, H. F. Gong, M. B. Liu (2018) Numerical simulation of water entry with improved SPH method. Int. Journal of Computational Methods. 10.1142/S0219876218460040.

21.

2018-02-23

Direct measurement of the contact angle of water droplet on quartz in a reservoir rock with atomic force microscopy

Deng, Yajun; Xu, Lei; Lu, Hailong; Wang, Hao; Shi, Yongmin

Abstract:

The wettability of a reservoir rock is an important property affecting the states of fluids in pores that are constructed with minerals of various types. However, the mineral grains are usually micro-sized so that the traditional optical contact angle method is hard to be applied to study their wettabilities. Although some measurements have been carried out for the contact angles of liquids on mineral surfaces, those previous studies were mainly on flat artificial mineral surfaces. To understand the wettabilities of water on rough natural mineral surfaces, the contact angles of micro-sized water droplets on relatively rough quartz surfaces in a natural sand rock were measured with an atomic force microscopy (AFM). The results obtained show that the droplets were asymmetrical so that the contact angles, which were around 27.8–50.3°, were different along the triple-phase contact lines, probably due to surface roughness, heterogeneity, atomic arrangement, etc. As compared with previous studies, surface pretreatment and droplet size were regarded as the two key factors that caused the substantial difference in contact angles of water on quartz between the current and previous researches, which might imply that the present results could better describe the wettability of a natural reservoir rock.

Reference:

Deng Y, Xu L, Lu H, et al. Direct measurement of the contact angle of water droplet on quartz in a reservoir rock with atomic force microscopy[J]. Chemical Engineering Science, 2018, 177: 445-454.

22.

2018-02-19

Ultra-narrow photonic nanojets through a glass cuboid embedded in a dielectric cylinder

Jianming Yang, Patrice Twardowski, Philippe Gérard, Yi Duo, Joël Fontaine, and Sylvain Lecler

Abstract:

A glass cuboid, embedded inside a dielectric cylinder is studied when illuminated with a monochromatic plane wave. A photonic nanojet (PNJ) with a full-width at half-maximum (FWHM) waist of around 0.25λ0 is obtained outside the external surface of the cuboid. The influence of the parameters of a square section cuboid is studied. Three particular phenomena can be obtained and are discussed: an ultra-narrow PNJ on the external surface of the cuboid, a long photonic jet and the excitation of whispering gallery modes (WGMs). A parametric study, over the width and the height of a rectangular section cuboid, shows that these parameters can be used to control the photonic jet properties. We also study several other geometries of the insert, which shows that the key parameter is the refractive index of the inserted material. Finally, we show that by changing the incident angle we can obtain a curved photonic jet.

Reference:

Yang J, Twardowski P, Gérard P, et al. Ultra-narrow photonic nanojets through a glass cuboid embedded in a dielectric cylinder[J]. Optics express, 2018, 26(4): 3723-3731.

23.

2018-02-08

Greatly enhanced anticorrosion of Cu by commensurate graphene coating

Xiaozhi Xu; Ding Yi; Zhichang Wang; Jiachen Yu; Zhihong Zhang; Ruixi Qiao; Zhanghao Sun; Zonghai Hu Peng Gao; Hailin Peng; Zhongfan Liu; Dapeng Yu; Enge Wang; Ying Jiang; Feng Ding; Kaihui Liu

Abstract:

Metal corrosion is a long‐lasting problem in history and ultrahigh anticorrosion is one ultimate pursuit in the metal‐related industry. Graphene, in principle, can be a revolutionary material for anticorrosion due to its excellent impermeability to any molecule or ion (except for protons). However, in real applications, it is found that the metallic graphene forms an electrochemical circuit with the protected metals to accelerate the corrosion once the corrosive fluids leaks into the interface. Therefore, whether graphene can be used as an excellent anticorrosion material is under intense debate now. Here, graphene‐coated Cu is employed to investigate the facet‐dependent anticorrosion of metals. It is demonstrated that as‐grown graphene can protect Cu(111) surface from oxidation in humid air lasting for more than 2.5 years, in sharp contrast with the accelerated oxidation of graphene‐coated Cu(100) surface. Further atomic‐scale characterization and ab initio calculations reveal that the strong interfacial coupling of the commensurate graphene/Cu(111) prevents H2O diffusion into the graphene/Cu(111) interface, but the one‐dimensional wrinkles formed in the incommensurate graphene on Cu(100) can facilitate the H2O diffusion at the interface. This study resolves the contradiction on the anticorrosion capacity of graphene and opens a new opportunity for ultrahigh metal anticorrosion through commensurate graphene coating.

Reference:

Xu X, Yi D, Wang Z, et al. Greatly enhanced anticorrosion of Cu by commensurate graphene coating[J]. Advanced Materials, 2018, 30(6): 1702944.

24.

2018-02-08

Artificial lateral line based local sensing between two adjacent robotic fish

Xingwen Zheng, Chen Wang, Ruifeng Fan and Guangming Xie

Abstract:

The lateral line system (LLS) is a mechanoreceptive organ system with which fish and aquatic amphibians can effectively sense the surrounding flow field. The reverse Kármán vortex street (KVS), known to be a typical thrust-producing wake, is commonly observed in fish-like locomotion and is known to be generated by fish's tails. The vortex street generally reflects the motion information of the fish. A fish can use LLS to detect such vortex streets generated by its neighboring fish, thus sensing its own state and the states of its neighbors in a school of fish. Inspired by this typical biological phenomenon, we design a robotic fish with an onboard artificial lateral line system (ALLS) composed of pressure sensor arrays and use it to detect the reverse KVS-like vortex wake generated by its adjacent robotic fish. Specifically, the vortex wake results in hydrodynamic pressure variations (HPVs) in the flow field. By measuring the HPV using the ALLS and extracting meaningful information from the pressure sensor readings, the oscillating frequency/amplitude/offset of the adjacent robotic fish, the relative vertical distance and the relative yaw/pitch/roll angle between the robotic fish and its neighbor are sensed efficiently. This work investigates the hydrodynamic characteristics of the reverse KVS-like vortex wake using an ALLS. Furthermore, this work demonstrates the effectiveness and practicability of an artificial lateral line in local sensing for adjacent underwater robots, indicating the potential to improve close-range interaction and cooperation within a group of underwater vehicles through the application of ALLSs in the near future.

Reference:

Zheng X, Wang C, Fan R, et al. Artificial lateral line based local sensing between two adjacent robotic fish[J]. Bioinspiration & biomimetics, 2017, 13(1): 016002.