Search

Pollution resulting from increased human activities is threatening the drinking water quality in China. Lushui Reservoir was selected as a typical example to represent polluted drinking water sources with rapid social economic development. This study analyzed the pollution load of Lushui Reservoir from rural areas by estimating the chemical oxygen demand (COD), ammonia nitrogen, total nitrogen and total phosphorus contributed by domestic sewage, agricultural activity, livestock breeding and aquaculture activity. Results show that the annual chemical oxygen demand, ammonia nitrogen, total nitrogen and total phosphorus loads in Lushui Reservoir were 180.44, 22.99, 33.15, and 3.99 t, respectively. The highest contribution to pollution load in all four aspects is domestic sewage, which was 89%, 96%, 82%, and 79%, respectively. Therefore, policies for sustainable development in the region should be directed primarily towards a reduction of domestic pollution.

Master's thesis in Offshore structural engineering Pipelines in a subsea environment are exposed to a very complex system of hydrodynamic reaction. The on-bottom stability has long been a important study for offshore practice. The soil types, wave conditions as well as the structure itself are considered to be the main focus of the on-bottom stability analysis for a subsea pipeline. The objective of this thesis is to study the on-bottom stability in a series of complex environmental conditions through the dynamic analysis, as well as the generalized stability method and absolute lateral static stability method. The effect of different parameters regarding stability is investigated through the sensitivity analysis. Models will be built using PONDUS, a software developed by MARINTEK for the dynamic on-bottom stability analysis. The linear wave theory, the JONSWAP spectrum and the energy-based soil model will be considered for irregular waves and soil-pipe interactions respectively. Based on the different case set-ups, the results will be compared and discussions will be made on the methodology of pipeline stability analysis, considering the sensitive variables as follows. Both regular waves and irregular waves have been studied in the past. Behaviours of the pipe in irregular waves are studied further in this thesis based on the previous research. Important development patterns and characteristic values such as displacement, forces and velocity will be compared between cases with regular and irregular waves. The mechanisms are further discussed based on simulation results. Same values taken for the wave height and wave period of regular waves, the significant wave height and the peak wave period of irregular waves. Results indicate that the maximum wave-induced water particle velocity is larger in irregular waves. It suggests that when considering the environmental condition, 10-year return currents and 100-year return irregular waves is the most critical load combination. These recommendations are important to obtain a more realistic and reliable model among all the cases in the present study for the on-bottom stability analysis. Furthermore, the stair-like development pattern of dynamic displacement is quite distinguishable when the pipeline is exposed to underwater environment with irregular waves. The pipe-soil interaction is also investigated in this thesis. Past studies took only one single type of soil for the investigation of pipe-soil interactions. However, the seabed soil condition is actually more complicated in reality, considering that pipes run a very long distance and will pass several areas of different soil types. Three typical values of the friction coefficient are applied for the pipe-clay model and pipe-sand model respectively. The maximum displacement seems to decrease as the friction coefficient increases for both the pipe-sand model and the pipe-clay model. The friction coefficient and the relative velocity between the pipe and the water particles, and the penetration will interact with each other. While for the pipe-sand model, the different friction coefficients do not seem to affect the displacement in the same way as it is for the pipe-clay model. This is likely due to the varying residual force that interacts differently and further leads to a different interaction between the soil resistance force, the relative penetration and the displacement. It appears that the displacement and friction coefficient does not interact with each other in any explicit pattern. But in general, the penetration and accumulated displacement tends to grow larger as the friction coefficient decreases. [...]