ROV attitude control based on multi-motor cooperative propulsion北大核心CSCD

[目的]为了提高遥控水下航行器(ROV)在复杂水下环境中的姿态控制性能,开展多电机协同推进的ROV姿态控制研究。[方法]首先,针对多电机系统的结构和算法,分别提出一种基于PID速度补偿器的偏差耦合结构和一种新型非奇异终端滑模控制(SMC)算法,并设计一种新颖的基于多电机协同推进的ROV姿态控制方法;然后,建立ROV的运动学和动力学模型,开展推进器组推力建模分析、解耦简化ROV动力学模型研究;最后,设计一种ROV滑模姿态控制器。[结果]仿真结果表明,所提的结构和算法可提高多电机系统的抗干扰性、同步性和快速响应能力,进而提高ROV姿态控制系统的稳定性与鲁棒性。[结论]所提方法可为ROV姿态控制提供一种新的可用方案。     

Biochemical composition of marine sediment from the eastern Weddell Sea (Antarctica): High nutritive value in a high benthic-biomass environment

Within the SCAR's international EASIZ programme, as part of the benthic–pelagic coupling experiment, grain size and organic matter contents in marine surface sediment were measured. Samples were taken during the austral autumn of 2000 from 3 regions in the eastern Weddell Sea: Kapp Norvegia, Four Seasons Bank, and Austasen.In general, sediments were fine sand with a grain size fraction < 200 μm representing more than 40% of the total weight. The sediments from Four Seasons Bank (64 to 107 m depth) were coarser than those from Austasen and Kapp Norvegia (209 to 480 m depth), presumably due to winnowing of fine sediment at shallow depths. Organic carbon (OC) content ranged from 0.25% to 1.2% and constituted 10% to 97% of the total carbon. The samples from Kapp Norvegia presented the highest OC values. Overall, protein (PRT), lipid (LPD), and carbohydrate (CHO) contents were similar to those in sediment from cold regions (e.g., the North Atlantic and the Ross Sea) but higher than those in sediment from other Antarctic and more septentrional regions (e.g., the Ross Sea and the Mediterranean). The difference within the Antarctic is explained through the local conditions in Terra Nova Bay and Kapp Norvegia. In the Antarctic, PRT and LPD carbon were the main contributors to the biopolymeric carbon (BPC). In the eastern Weddell Sea shelf, the BPC accounted for more than 90% of the OC in most of the samples. More than 82% of the total PRT, LPD, and CHO were present in the fraction < 200 μm. This work remarks the existence of sediments with a high nutritional value persistent several weeks after the spring–summer pulse of fresh organic matter. It is also highlighted the high potential availability of these sediments (due to its grain size) for the benthic communities inhabiting this high-latitude continental shelf.     

Using a random displacement model to simulate turbulent particle motion in a baroclinic frontal zone: A new implementation scheme and model performance tests

Numerical artifacts can limit accurate simulation of turbulent particle motion when Lagrangian particle-tracking models are implemented in hydrodynamic models with stratified conditions like fronts. Yet, modeling of individual particle motion in frontal regions is critical for understanding sediment dynamics as well as the transport and retention of planktonic organisms. The objective of this research was to develop a numerical technique to accurately simulate turbulent particle motions in a particle-tracking model embedded within a hydrodynamic model of a frontal zone. A new interpolation scheme, the ‘water column profile’ scheme, was developed and used to implement a random displacement model for turbulent particle motions. A new interpolation scheme was necessary because linear interpolation schemes caused artificial aggregation of particles where abrupt changes in vertical diffusivity occurred. The new ‘water column profile’ scheme was used to fit a continuous function (a tension spline) to a smoothed profile of vertical diffusivities at the x–y particle location. The new implementation scheme was checked for artifacts and compared with a standard random walk model using (1) Well Mixed Condition tests, and (2) dye-release experiments. The Well Mixed Condition tests confirmed that the use of the ‘water column profile’ interpolation scheme for implementing the random displacement model significantly reduced numerical artifacts. In dye-release experiments, high concentrations of Eulerian tracer and Lagrangian particles were released at the same location up-estuary of the salt front and tracked for 4 days. After small differences in initial dispersal rates, tracer and particle distributions remained highly correlated (r = 0.84 to 0.99) when a random displacement model was implemented in the particle-tracking model. In contrast, correlation coefficients were substantially lower (r = 0.07 to 0.58) when a random walk model was implemented. In general, model performance tests indicated that the ‘water column interpolation’ scheme was an effective technique for implementing a random displacement model within a hydrodynamic model, and both could be used to accurately simulate diffusion in a highly baroclinic frontal region. The new implementation scheme has the potential to be a useful tool for investigating the influence of hydrodynamic variability on the transport of sediment particles and planktonic organisms in frontal zones.     

Egg production and associated losses of carbon, nitrogen and fatty acids from maternal biomass in Calanus finmarchicus before the spring bloom

We present concurrent data on ingestion, egg production and the loss of maternal biomass in pre-spring bloom female Calanus finmarchicus incubated under conditions representative of those in situ in the North Atlantic. A balanced metabolic budget was constructed and used to examine the relative importance of ingestion and biomass for fuelling egg production during the incubations. Ingested carbon was not sufficient to meet the observed demands for egg production. More than 80% of the carbon utilised by the females was instead derived from their biomass. Fatty acid analysis demonstrated that the storage reserves, 20:1 (n−9) and 22:1 (n−11), were virtually absent before experimentation began, and therefore could not have been used to supply the carbon required for egg production during the incubations. The C:N mass-specific ratio of the biomass utilised was 4.1, suggesting that the females had instead catabolised protein in order to meet their metabolic demands. These results suggest that C. finmarchicus adopts a sacrificial reproductive strategy when food availability is low.     

Coastal Tourist Interest in Value-Added,Aquaculture-Based,Culinary Tourism Opportunities

Despite increasing focus on sustainable aquaculture investment in the U.S. coastal zones, the aquaculture industry continues to face skepticism among consumers due to perceived negative environmental impacts, and health and food safety concerns. Partnering with culinary tourism and local food promotion efforts has potential for improving public outreach about the benefits of aquaculture, especially in coastal destinations where sustainable marine aquaculture and tourism are both occurring. Culinary tourism implies that local foods reflect the local livelihood and culture, and may be important to the tourist's experience. Aquaculture is becoming increasingly valuable to coastal destinations for assuring the steady availability of local seafood to meet demand and retaining commercial fisheries as a means to differentiate themselves to tourists. This study examined the role of subjective knowledge and attitude about aquaculture, and their effect on intention to participate in value-added culinary aquaculture tourism experiences. The study found that tourists' subjective knowledge and attitude about aquaculture influenced intentions to participate in culinary aquaculture tourism. In order for farmers or tour operators to be successful in diversifying with value-added culinary aquaculture, attention needs to be paid to educating consumers, which may be possible through strategic partnerships with tourism organizations, chefs, and restaurants.     

Development of Green-Naghdi models with a wave-absorbing beach for nonlinear, irregular wave propagation

Two-dimensional and three-dimensional Green-Naghdi (GN) models equipped with a numerical wave-absorbing beach have been developed to simulate nonlinear, regular, and irregular wave propagation. The numerical beach is introduced near the downstream boundary to absorb outgoing waves. An appropriate amount of numerical damping and an appropriate length of numerical beach are investigated using numerical experiments. The results show that the GN models with a numerical beach work very well in simulating wave propagation in water in a small computational domain.     

Widening the Panama Canal and U.S. ports: historical and economic impact analyses

ABSTRACT

The economic history of the U.S. illustrates how the role of many cities has been changed by being seaports or located on navigable rivers or lakes. Based on the widening of the Panama Canal in 2016, the West Coast ports that include the west coast seaports of California, Oregon, and Washington were expected to become less important, while the freight shares of the East Coast and Gulf ports would increase. By how much it has been not easy to measure or predict so far, but this study attempted to define some of the key parameters in the measurement. As well as several relevant background topics, both the demand- and supply-side versions of the National Interstate Economic Model, have been applied for the measurement of economic impacts. U.S. port authorities and policy makers at the local and national levels who respond and develop plans for coping with the new realities of the Panama Canal are able to understand the extent to which changes in shippers’ and land-mode transporters’ behaviors would undermine the logistics and the costs of their activities. Therefore, this study is important for a diverse spectrum of port development strategies in the U.S. to respond to the Canal expansion.     

China shipbuilding management challenges in the 1980s

Since the economic reforms in the late 1970s, the shipbuilding industry in China has enjoyed rapid growth. Over the past two decades, many new building contracts have been won and successfully completed. However, some shipyards have also suffered great losses. Basing on their experience in Southern China, the authors examine some of the major challenges that Chinese shipbuilders faced during this transitional period, when the industry ventured into the international market. These challenges are broadly categorized into two areas: (i) external factors, such as inflation and infrastructural support that the shipbuilder had no control over, and (ii) shipbuilding management, which the shipbuilder had to master in order to gain competitive advantage. Suggestions on how these problems could be tackled are discussed.     

Characteristics and calculation method of sound radiation of cylindrical shell with porous sound-absorbing material under acoustic excitation北大核心CSCD

［Objective］This paper aims to study the characteristics and calculation method of the vibration and sound radiation of single ring-stiffened cylindrical shells with porous fiber composite materials installed in the inner wall under acoustic excitation. ［Method ］ Based on the equivalent fluid theory model of Johnson–Champoux–Allard (JCA) and the transfer matrix of the multilayer medium, a theoretical formula of the sound absorption coefficient of multilayer sound absorption structures is derived. The three methods for calculating the vibration and sound radiation of a single ring-stiffened cylindrical shell with porous fiber materials under acoustic excitation, namely acoustic solid modeling of porous media, finite element model combined with theoretical formula and imposition of impedance boundary on sound absorption coefficient, are then verified and compared. Finally, the influences of sound-absorbing material's thickness, backed-air gap, static flow resistance, and material arrangement order on the acoustic absorption performance of the cylindrical shell are investigated. ［Results］The results show that laying porous fiber composite materials on the cylindrical shell internally can reduce the vibration and acoustic radiation of cylindrical shell structure. The sound absorption coefficient curve can quickly and effectively predict the resulting trend of the vibration and sound radiation of the cylindrical shell. ［Conclusion］The acoustic absorption performance of sound absorption structures can be effectively improved through the rational design of their properties and arrangement order of the sound-absorbing materials in order to achieve the purpose of vibration and noise reduction. © 2023 Chinese Journal of Ship Research. All rights reserved.