Robust control based on feedback linearization for roll stabilizing of autonomous underwater vehicle under wave disturbances

In the case of Autonomous Underwater Vehicle(AUV) navigating with low speed near water surface,a new method for design of roll motion controller is proposed in order to restrain wave disturbance effectively and improve roll stabilizing performance.Robust control is applied,which is based on uncertain nonlinear horizontal motion model of AUV and the principle of zero speed fin stabilizer.Feedback linearization approach is used to transform the complex nonlinear system into a comparatively simple linear system.For parameter uncertainty of motion model,the controller is designed with mixed-sensitivity method based on H-infinity robust control theory.Simulation results show better robustness improved by this control method for roll stabilizing of AUV navigating near water surface.     

Parametric vibration of submerged floating tunnel tether under random excitation

For the study of the parametric vibration response of submerged floating tunnel tether under random excitation,a nonlinear random parametric vibration equation of coupled tether and tube of submerged floating tunnel is set up.Subsequently,vibration response of tether in the tether-tube system is analyzed by Monte Carlo method.It may be concluded that when the tube is subjected to zero-mean Gaussian white noise random excitation,the displacement and velocity root mean square responses of tether reach the peak if the circular frequency of tube doubles that of tether;the displacement and velocity root mean square responses of tether increase as the random excitation root mean square increases;owing to the damping force of water,the displacement and velocity root mean square responses of tether decrease rapidly compared with tether in air;increasing the damping of the tether or tube reduces the displacement and velocity root mean square responses of tether;the large-amplitude vibration of tether may be avoided by locating dampers on the tether or tube.     

A precise bathymetric map of the world’s deepest seafloor,Challenger Deep in the Mariana Trench

Data from three bathymetric surveys by R/V Kairei using a 12-kHz multibeam echosounder and differential GPS were used to create an improved topographic model of the Challenger Deep in the southwestern part of the Mariana Trench, which is known as the deepest seafloor in the world. The strike of most of the elongated structures related to plate bending accompanied by subduction of the Pacific plate is N70°E and is not parallel to the trench axis. The bending-related structures were formed by reactivation of seafloor spreading fabric. Challenger Deep consists of three en echelon depressions along the trench axis, each of which is 6–10 km long, about 2 km wide, and deeper than 10,850 m. The eastern depression is the deepest, with a depth of 10,920 ± 5 m.     

Study on scattering wave force of horizontal and vertical plate type breakwaters

The interaction between wave and horizontal and vertical plates is investigated by the boundary element method,and the relations of wave exciting force with plate thickness,submergence and length are obtained.It is found that:1) The efficient wave exciting force exists while plate submergence is less than 0.5 m,and the plate is very thin with order O(0.005 m).2) The maximum heave wave exciting force exists,and it is the main factor for surface and submerged horizontal plate while the roll force can be ignored.3) The maximum sway wave exciting force exists,it is the main factor for surface or submerged vertical plate,and the roll force is about 20 times of horizontal plate.     

Linkage between winter air temperature over the subtropical Western Pacific and the ice extent anomaly in the Sea of Okhotsk

This study deals with the correlation between ice extent in the Sea of Okhotsk and the interannual variability of winter (December–February) air temperature over the subtropical Western Pacific from 1979 to 2008. The analysis indicates that the increase in sea ice extent coincides not only with cooling over the Sea of Okhotsk and the adjacent area, but also with significant warming over the subtropical Western Pacific that extends from the surface to the middle troposphere. This meridional dipole pattern of tropospheric temperature anomalies (cooling in the high latitudes and warming in the low latitudes) primarily results from dynamical processes driven by the large-scale atmospheric circulation change. A heat budget diagnosis reveals that when ice extent in the Sea of Okhotsk increases by one standard deviation, the tropospheric air temperature over the subtropical Western Pacific rises by about 0.25°C. It also suggests that the adiabatic heating and stationary eddy heat flux convergence may be the most important factors, which account for 30 and 15% of the warming, respectively. In addition, these two factors also coordinate to result in significant cooling over the Sea of Okhotsk and the adjacent regions.     

Development and application of an operational tide and storm surge prediction model for the seas around Taiwan

Storm surges are abnormal rises in sea level along coastal areas and are mainly formed by strong wind and atmospheric depressions.When storm surges coincide with high tide,coastal flooding can occur.Creating storm surge prediction systems has been an important and operational task worldwide.This study developed a coupled tide and storm surge numerical model of the seas around Taiwan for operational purposes at the Central Weather Bureau.The model was calibrated and verified by using tidal records from seas around Taiwan.Model skill was assessed based on measured records,and the results are presented in details.At 3-minute resolution,tides were generally well predicted,with the root mean-square errors of less than 0.11 m and an overall correlation of more than 0.9.Storms(winds and depressions) were introduced into the model forcing by using the parameter typhoon model.Five typical typhoons that threatened Taiwan were simulated for assessment.The surges were well predicted compared with the records.     

Phytoplankton productivity in the western subarctic gyre of the North Pacific in early summer 2006

We deployed a profiling buoy system incorporating a fast repetition rate fluorometer in the western subarctic Pacific and carried out time-series observations of phytoplankton productivity from 9 June to 15 July 2006. The chlorophyll a (Chl a) biomass integrated over the euphotic layer was as high as 45–50 mg Chl a m⁻² in the middle of June and remained in the 30–40 mg Chl a m⁻² range during the rest of observation period; day-to-day variation in Chl a biomass was relatively small. The daily net primary productivity integrated over the euphotic layer ranged from 144 to 919 mg C m⁻² day⁻¹ and varied greatly, depending more on insolation rather than Chl a biomass. In addition, we found that part of primary production was exported to a 150-m depth within 2 days, indicating that the variations in primary productivity quickly influenced the organic carbon flux from the upper ocean. Our results suggest that the short-term variability in primary productivity is one of the key factors controlling the carbon cycle in the surface ocean in the western subarctic Pacific.     

Secondary production of the eusirid amphipod <Emphasis Type="Italic">Pontogeneia rostrata</Emphasis> Gurjanova, 1938 (Crustacea: Peracarida) on a sandy shore in Korea

The secondary production of the eusirid amphipod Pontogeneia rostrata Gurjanova, 1938, was examined on a sandy shore in Korea. Secondary production was estimated using a size-frequency method. The biomass structure of P. rostrata included one peak in spring, with maximum biomass occurring in April. The annual secondary production of this species was 0.57 g DW m⁻² yr⁻¹ with an annual P/B ratio of 6.97. Secondary production of P. rostrata fell within the range observed for other amphipods on intertidal sandy shores, although the production/biomass (P/B) ratio was higher than those recorded previously from the sampling site and from other tidal and estuary areas, as the number of generations increases the P/B ratio. The results showing high abundance and P/B ratios suggest that P. rostrata plays an important role in the sandy shore ecosystem as a trophic link between primary producers and higher consumers.     

季节内SST和混合层深度变化的模式研究

用Niiler—Kraus类型的混合层积分模式,对TOGA—COARE强化观测期间由《实验3号》科学考察船观测资料得到的混合层深度和SST在季节内时间尺度的变化进行了模式研究。指出:1.混合层耗散参数与较长时间尺度过程风应力的变化存在着比较好的对应关系;2.模式可以较好的对风场和热通量场在季节内时间尺度的变化作出响应,模拟出季节内时间尺度SST的变化;3.Niiler,-Kraus模式在考虑耗散作用后,可用于海洋季节内时间尺度变化的模式研究。