涡街提频振荡水柱驱动压电发电理论分析

海洋波浪能频率低(0.3~1Hz),海浪进入振荡水柱气室压缩空气形成高速气流。在高速气流通道内放置绕流圆柱钝体,采用卡门涡街效应提高波浪能振荡水柱采集气室气压激振频率,实现高频驱动压电发电,提高海洋能量转换效率。推导波浪进入气室形成振荡的水气动力转换理论,计算了气室初级压强和流速。分析了低频高压气流经钝体形成卡门涡街高频涡流激振提频过程,计算出气压作用于钹型压电发电结构输出的电量。研究气体流速、钝体等系统参数与输出能量的关系。计算结果表明,周期为0.65~1.1s的海浪进入气室经提频作用于钹型压电发电结构,稳定输出电能可达70~80mW,为新型波浪能采集技术提供了理论基础。

Advances in Nitrogen Denitrification and N_2O Emission in Agro-ecosystem

Nitrification and denitrification are two key links of nitrogen flow cycle in soil.N2O and N2,generated from biochemical process of nitrogen,can cause not only the nitrogen losses and reduction of nitrogen use efficiency,but also the boosted concentration of greenhouse gases,severely endangering the environment.Accordingly,nitrification-denitrification has been more and more concerned from whether an agricultural view,or an environmental one.Referring to the related literatures published at home and abroad in recent years,we overviewed the denitrification-caused N loss and N2O emission in various agro-ecosystems,and based on which we put forward countermeasures to reduce the denitrification-caused N loss and N2O emission and its research prospects in the future.

Responses of Hydrological Processes to Climate Change in the Zhujiang River Basin in the 21st Century

In this study, discharge at the outlet of Xijiang River, the biggest sub-basin of the Zhujiang River, was simulated and projected from 1961 to 2099 using the hydrological model HBV-D. The model uses precipitation and temperature data from CISRO/MK3 5, MPI/ECHAM5, and NCAR/CCSM3 under three greenhouse gas emission scenarios (SRES A2, A1B, B1). The results in water resources and flood frequency suggest that annual precipitation and annual runoff would increase after 2050 relative to the reference period of 1961-1990. In addition, increasing trends have been projected in area averaged monthly precipitation and runoff from May to October, while decreasing trends in those from December to February. More often and larger floods would occur in future. Potential increase in runoff during the low-flow season could ease the pressure of water demand until 2030, but the increase in runoff in the high-flow season, with more often and larger floods, more pressure on flood control after 2050 is expected.

Numerical Analysis of Influencing Factors on Temperature Field and Airflow Distribution of the Displacement Ventilation System

Indoor air quality and thermal comfort are important features of indoor environment. In this paper, a numerical simulation based on the k-ε model of CFD is used to analyze factors such as loading, exterior-protected construction, blowing-in rate that play an important role in the temperature field and airflow field of the displacement ventilation system. Exterior-protected construction has little influence on indoor temperature distribution of displacement ventilation systems and the influence is limited only in a small area near the external wall when the indoor heat source is the main cooling load.The height of a room has little influence on indoor temperature field, and the temperature gradient of active region is basically unchanged. In the system combined with a displacement ventilation system and a cooling system, the height also has little influence. When the cooling load is high,the indoor heat source creates a strong convective plume, which will make the average indoor air age lower, the ventilation efficiency higher and the elimination of pollutant easier. Air supply rate plays an important role in displacement ventilation systems. The increase of air supply rate that can be realized by increasing the air supply velocity and enlarging the area of air inlet will increase the mass capability of the system and diminish the vertical temperature gradient. From the comparison between simulations and experiments, it is concluded that this simulation are creditable.

Impact of Climate Change and Deforestation on Stream Discharge and Sediment Yield in Phu Luong Watershed, Viet Nam

The purpose of this paper is to apply ＂Soil and Water Assessment Tool （SWAT）＂ model to assess the impacts of climate change and deforestation on stream discharge and sediment yield from Phu Luong watershed in Northern Viet Nam. Among the three climate change scenarios B 1, B2, and A2, representing low, medium, and high levels of greenhouse gas emission, respectively were set up for Viet Nam, the B2 scenario was selected for this study. Two land use scenarios （S1-2030 and $2-2050） were formulated combination with climate change in WSAT simulation. In B2 climate change scenario, mean temperature increases 0.7℃（2030） and 1.3 ℃ （2050）; annual rainfall increases 2.1% （2030） and 3.80% （2050） respect to baseline scenario. The results show that the stream discharge is likely to increase in the future during the wet season with increasing threats of sedimentation.

Coupled simulation of BES-CFD and performance assessment of energy recovery ventilation system for office model

Thermal comfort and indoor air quality as well as the energy efficiency have been recognized as essential parts of sustainable building assessment. This work aims to analyze the energy conservation of the heat recovery ventilator and to investigate the effect of the air supply arrangement. Three types of mixing ventilation are chosen for the analysis of coupling ANSYS/FLUENT （a computational fluid dynamics （CFD） program） with TRNSYS （a building energy simulation （BES） software）. The adoption of mutual complementary boundary conditions for CFD and BES provides more accurate and complete information of indoor air distribution and thermal performance in buildings. A typical office-space situated in a middle storey is chosen for the analysis. The office-space is equipped with air-conditioners on the ceiling. A heat recovery ventilation system directly supplies flesh air to the office space. Its thermal performance and indoor air distribution predicted by the coupled method are compared under three types of ventilation system. When the supply and return openings for ventilation are arranged on the ceiling, there is no critical difference between the predictions of the coupled method and BES on the energy consumption of HVAC because PID control is adopted for the supply air temperature of the occupied zone. On the other hand, approximately 21% discrepancy for the heat recovery estimation in the maximum between the simulated results of coupled method and BES-only can be obviously found in the floor air supply ventilation case. The discrepancy emphasizes the necessity of coupling CFD with BES when vertical air temperature gradient exists. Our future target is to estimate the optimum design of heat recovery ventilation system to control CO2 concentration by adjusting flow rate of flesh air.

Simulation Nutrient Load under Climate Change Condition and Deforestation Scenarios in Phu Luong Watershed, Viet Nam

The purpose of this paper is to apply ＂Soil and Water Assessment Tool （SWAT）＂ model to simulate the impacts of climate change and deforestation on nutrient （nitrogen and phosphorus） yield from Phu Luong watershed in Northern Viet Nam. Among the three climate change scenarios B1, B2 and A2, which represented low, medium, and high levels of greenhouse gas emission respectively, were set up for Viet Nam. The B2 scenario was selected for this study. Two land use scenarios （SI-2030 and S2-2050 which converted 4.43%. and 13.40% forest-mixed land into agricultural land, respectively） were formulated by combination with climatic change in SWAT simulation. In B2 climate change scenario, mean temperature increases 0.7 ℃ （2030） and 1.3 ℃（2050）; annual rainfall increases 2.1% （2030） and 3.80% （2050） with respect to baseline scenario. The results showed that monthly Nash-Sutcliffe coefficient of Efficiency （NSE） ranged from 0.81 to 0.96 and percent bias （PB1AS） ranged from -7.88 to 9.38. Additionally, SWAT simulation results also showed that climate change and deforestation caused significant percentage of changes in total N and P loads within Phu Luong watershed.

Eutrophication of Aquatic Ecosystems： A Viewpoint on the Environmental Impact of Climate Change

Environmental concerns associated with nutrient-oriented eutrophication phenomenon have become a serious issue and a major cause of water quality deficiency nowadays. This necessitated eutrophication to occupy a front seat in research accompanied with climate change. Climate change has revealed to be a key player and a main contributor in the occurrence of such phenomenon. This paper discusses the ever-growing concern about eutrophication as a cause of climate change. Climate change affects storms intensity, changing the precipitation regime and increasing temperature. These effects increase the nutrient loading diffusion and cause excessive nutrients accompanied with storm water runoff, domestic wastewaters, and agricultural discharges to pour into water bodies. Eutrophication conversely contributes in the global wanning by releasing greenhouse gases from deoxygenated waters and sediments. Some control and mitigation measures are needed to fight climate change and achieve desired water quality goals. These measures include mitigation of climate change causes, enhancement of natural ecohydrological processes, application of proper integrated water resource management and participation of communities and governments.

Developing More Effective Enhanced Biochar Fertilisers for Improvement of Pepper Yield and Quality

Utilization of biochar at high application rates can increase soil C and crop yields, decrease greenhouse gas emissions and reduce nutrient run-off from soils. However, the high application rate of 10 t ha-1 may not return a profit to the farmer due to the high cost of biochar. In this study biochar was modified through pre-treating the biomass and post-treating with phosphoric acid, minerals and different chemical fertilisers to study the effects of two new enhanced biochar fertilisers on the yield and quality of green pepper in a field experiment with 5 fertilisation treatments and 3 replications. The two new biochar fertilisers significantly （P 〈 0.05） increased the yield of green pepper （11.33-11.47 t ha-l）, compared with the conventional chemical fertiliser （9.72 t ha-l）. The biochar fertiliser treatments improved the vitamin C content of green pepper from 236.99 to 278.28 mg kg-1, and also significantly （P 〈 0.05） reduced the nitrate content from 132.32 to 101.92 mg kg-1, compared with chemical fertiliser. This study indicated that, compared to the use of conventional chemical fertiliser, all of the biochar fertiliser treatments could significantly improve the yield and quality of green pepper.

Diurnal Variations of Greenhouse Gas Fluxes from Mixed Broad-leaved and Coniferous Forest Soil in Dinghushan

The subtropical mixed broad-leaved and coniferous forest, a typical successional monsoon forest, is one of the major forests in the subtropics of China. Therefore, it is very important to estimate the fluxes of the greenhouse gases from the forest soil in order to evaluate the impact of subtropical forests on the greenhouse gas emissions or absorptions. This study investigated the diurnal variations of fluxes of three greenhouse gases （CO 2 , CH 4 , and N 2 O） from a mixed broad-leaved and coniferous forest soil. A static chamber-gas chromatograph technique was used to measure the fluxes of three greenhouse gases. By using the improved gas chromatography sampling system, the fluxes were analyzed with a single injection. In order to find out the effects of litter and seedling on the emissions or absorptions of these greenhouse gases, three treatments were set in the field:（1）bare soil surface （litter was removed previously）; （3） litter + soil; （3） seedling + litter + soil. The experimental results demonstrated that the forest soil was a source of CO 2 , N 2 O and a weak sink of CH 4 .The daily fluxes of CO 2 , CH 4 , and N 2 O from the soil surface were in the range of 488.99700.57, 0.0490.108 and –0.025 –0.053 mg/（m 2 ·h ）, respectively. CO 2 from the litter decomposition accounted for about 1/3 of the total CO 2 emission from the soil surface, while the litter and seedling had no significant effect on the fluxes of CH 4 and N 2 O. The fluxes of CO 2 and N 2 O measured at 9:00 11:00 a.m. were significantly different from their daily averages. Therefore, caution must be taken if the CO 2 and N 2 O fluxes measured within 9:0011:00 a.m. are used for extrapolation.