基于广义接触模型的离散元方法及其对船体冰载荷的分析

冰载荷是影响船舶结构安全的主要环境载荷,因而确定破冰船的冰载荷特征可用于船体结构设计及船舶安全预警分析。海冰作为典型的脆性材料,可采用单元间具有黏结失效效应的离散元方法模拟其破碎行为。为有效地模拟海冰破碎的渐进过程,采用由局部黏结点组成黏结单元的广义接触模型。为分析该模型中直接决定黏结单元失效的强度参数的影响,采用海冰单轴压缩和三点弯曲试验数值模拟进行分析。通过模型试验确定了失效模型中法向黏结强度、切向黏结强度和Mohr-Coulomb准则中的接触摩擦系数的影响。将该数值模型应用于极地科学考察船"雪龙号"的平整冰区冰载荷分析中,并与船舶整体冰阻力经验公式进行了对比验证。     

基于广义可加模型探讨大亚湾初级生产力月变化及其与环境因子的关系

In this study, the horizontal and vertical distribution of primary production(PP) and its monthly variations were described based on field data collected from the Daya Bay in January–December of 2016. The relationships between PP and environmental factors were analyzed using a general additive model(GAM). Significant seasonal differences were observed in the horizontal distribution of PP, while vertical distribution showed a relatively consistent unimodal pattern. The monthly average PP(calculated by carbon) ranged from 48.03 to 390.56 mg/(m~2·h),with an annual average of 182.77 mg/(m~2·h). The highest PP was observed in May and the lowest in November.Additionally, the overall trend in PP was springsummerwinterautumn, and spring PP was approximately three times that of autumn PP. GAM analysis revealed that temperature, bottom salinity, phytoplankton, and photosynthetically active radiation(PAR) had no significant relationships with PP, while longitude, depth, surface salinity, chlorophyll a(Chl a) and transparency were significantly correlated with PP. Overall, the results presented herein indicate that monsoonal changes and terrestrial and offshore water systems have crucial effects on environmental factors that are associated with PP changes.     

赋双平滑参数的广义补偿最小二乘估计

基于补偿最小二乘法思想,研究推导了半参数模型解算的极小化过程中,在残差和补偿项均赋予平滑参数的广义补偿最小二乘估计解的形式及其均方误差计算公式;模拟算例表明:在这种规则下,不仅可以克服病态性对半参数模型解的影响,而且也可以正确分离系统误差。新规则下,要求赋予的两个平滑参数之和等于1,各平滑参数严格限定在区间(0,1],从而使平滑参数的选择范围得到大幅缩小,为本法的应用提供了有利条件。     

Radiation energy flux of Dirac field of static spherically symmetric black holes

By the statistical entropy of the Dirac field of the static spherically symmetric black hole, the result is obtained that the radiation energy flux of the black hole is proportional to the quartic of the temperature of its event horizon. That is, the thermal radiation of the black hole always satisfies the generalised Stenfan--Boltzmann law. The derived generalised Stenfan--Boltzmann coefficient is no longer a constant. When the cut-off distance and the thin film thickness are both fixed, it is a proportional coefficient related to the space--time metric near the event horizon and the average radial effusion velocity of the radiation particles from the thin film. Finally, the radiation energy fluxes and the radiation powers of the Schwarzschild black hole and the Reissner--Nordstrõm black hole are derived, separately.     

包围有暗能量黑洞的Hawking辐射修正

运用由Banerjee和Majhi所发展的非半经典近似的Hamiliton-Jacobi方法,计算了被暗能量包围的黑洞温度和熵,得到了修正后的温度和熵.在修正后的熵中,面积定理包含面积对数修正和面积幂的倒数.     

Massive particle radiation from Gibbons-Maeda black hole

This paper investigated the massive particle radiation from Gibbons--Maeda black hole by using a semi-classical method. The calculations showed that, if the self-gravitation of the radiated particle is taken into account, the radiation spectrum deviates from exact black body spectrum and the rate of tunneling equals precisely the exponent of the difference of the black hole entropies before and after emission. The conclusion supports the viewpoint of information conservation.     

Spectral modification and geographic redistribution of the semi-diurnal internal tide

A realistic-geometry global baroclinic tidal model forced with a single tidal constituent $(M_2)$ is used to investigate the generation of the internal tide and the associated radiated baroclinic energy flux. The model internal wave spectrum is populated at discrete frequency multiples $(1/2\text{,}1\text{,}3/2\text{,}2\text{,}5/2\text{,}\dots )$ of $M_2$. The $1/2M_2$ subharmonic is particularly energetic at its turning latitude of $\pm 28.8°$. Poleward only integer superharmonics of $M_2$ are significantly excited. The subharmonic turning latitude (SHTL) disturbance has high vertical wavenumber and shear, provided that internal tide energy level exceeds a threshold value. Under these circumstances, Richardson numbers smaller than 1/4 occur in the upper few hundred meters in both the realistic-geometry model and in a complimentary idealized geometry two-dimensional (2D) model. In the 2D model, the disturbance enables Richardson number dependent diapycnal entrainment to effect a modification of the stratification of the upper 400 m of the ocean, and poleward cross-SHTL energy flux falls to 10% of its pre-instability value due to energy transfer to the non-propagating (i.e., inertial) subharmonic. Realistic-geometry simulations suggest a more modest 40% decrease in net flux, although the strongest beams are almost entirely shut down. The predicted energy flux-convergence implies a thermocline dissipation rate in the 28.5–30.0°N latitude band of $5\times {10}^{-9}\text{W}{\text{kg}}^{-1}$, with an associated diapycnal diffusivity of ${10}^{-4}{\text{m}}^2{\text{s}}^{-1}$. North of Hawaii the implied regional dissipation rate reaches $4\times {10}^{-8}\text{W}{\text{kg}}^{-1}$ with an associated thermocline diffusivity of $8\times {10}^{-4}{\text{m}}^2{\text{s}}^{-1}$. Investigations of subgridscale parameterization and resolution sensitivity suggest that the basic character and magnitude of the predictions are robust to details of the numerical solutions. The present results are taken as further evidence that an increase in shear-driven turbulent mixing in the upper ocean is predicted at special latitudes. It is suggested that the search should be directed to regions where intense low-mode internal tide beams cross their subharmonic turning latitude.     

水温和余氯对黑棘鲷仔鱼存活的影响

采用静水试验法, 模拟研究了电厂温排水排放导致的海水升温和余氯残留对黑棘鲷(Acanthopagrus schlegelii)存活的影响。试验水温设4 个梯度: 18、22、26、30℃, 余氯设6 个浓度水平:0.025、0.05、0.1、0.2、0.4、0.8 mg/L, 同时以过滤海水为对照组, 每一个水温条件下的余氯浓度均设3 个平行样本, 取黑棘鲷初孵仔鱼进行试验, 试验共进行96 h 观测。试验结果表明, 当水温升高至30℃时, 对仔鱼的存活会产生显著性影响, 24 h 的死亡率为23.4%, 48 h 的死亡率骤升至98%, 而18、22、26℃ 3 组96 h 时死亡率均未超过10%。24 h 时4 种水温条件下余氯对黑棘鲷仔鱼的LC50 值分别为0.816、0.460、0.433、0.319 mg/L, 可见水温升高会增强余氯对仔鱼的致死效应, 而随着时间延长, 余氯对仔鱼的LC50 值进一步降低, 至96 h, 其值分别为0.242、0.211、0.140、<0.025 mg/L。广义相加模型分析结果显示, 水温由26℃升至30℃时, 或当余氯浓度高于0.2 mg/L 时, 或曝露时间超过48 h, 均会对黑棘鲷初孵仔鱼产生明显致死效应, 双因素方差分析结果显示, 水温、余氯、曝露时间对仔鱼死亡率具有显著性影响(P< 0.05), 且水温-余氯、水温-曝露时间之间具有显著性交互作用(P< 0.05)。     

南海混合层近惯性能通量的时空变化

On the basis of the QSCAT/NCEP blended wind data and simple ocean data assimilation(SODA), the wind-induced near-inertial energy flux(NIEF) in the mixed layer of the South China Sea(SCS) is estimated by a slab model, and the model results are verified by observational data near the Xisha Islands in the SCS. Then, the spatial and temporal variations of the NIEF in the SCS are analyzed. It is found that, the monthly mean NIEF exhibits obvious spatial and temporal variabilities, i.e., it is large west of Luzon Island all the year, east of the Indo-China Peninsula all the year except in spring, and in the northern SCS from May to September. The large monthly mean NIEF in the first two zones may be affected by the large local wind stress curl whilst that in the last zone is probably due to the shallow mixed layer depth. Moreover, the monthly mean NIEF is relatively large in summer and autumn due to the passage of typhoons. The spatial mean NIEF in the mixed layer of the SCS is estimated to be about 1.25 m W/m2 and the total wind energy input from wind is approximately 4.4 GW. Furthermore, the interannual variability of the spatial monthly mean NIEF and the Ni?o3.4 index are negatively correlated.     

The influence of main ecological and environmental factors on the energy budget of Schlegel''s black rockfish Sebastes schlegeli

In the Maidao Ecological Laboratory of the Huanghai Sea Fisheries Research Institute in 1998 ~ 2000, the continuous flow-through method was adopted to determine the energy budget components and models of Schlegel＇ s black rockfish under different ecological and environmental factors, such as temperature, food species, body mass and feeding level, etc. The body mass of test fish ranged from 21.2 to 224.5 g. The specific growth rate tended to invert ＂U＂ change with temperature increase. The ecological conversion efficiency showed the same trend as temperature and feeding level rise. Only the specific growth rate tended to decelerate the increment with the rise of feeding level. From the above quantitative relationships, the maximum and optimal growth temper- atures could be obtained as 17.5 and 16.2 ℃, and the maintenance feeding rate and optimum feeding rate as 0.8% and 4. 1% of the body mass. The specific growth rate and ecological conversion coefficient showed a decelerating decrease trend with body mass increment. The small-sized fish food was more advantageous to the feeding level increase in comparison with the small-sized shrimp food, which led to the increase of growth, metabolism and excretion, but had no significant influence on the ecological conversion coefficient. All of temperature, feeding level, body mass and food species can obviously change the energy budget models. The assigning rate of growth energy tended to change along the invert ＂U＂ curve with the increase of temperature and feeding level, and decrease with the body mass increase, but the assigning rates of metabolism energy and excretion energy were quite reverse. These relationships could be quantitatively described as quadratic or power function curve. If the above relationships proved true to other marine fish, the establishment of energy budget model of the same fish under different conditions can be largely simplified.