S. Neelamani

TECHNICAL FEASIBILITY ANALYSIS OF SUBMARINE PIPELINES FOR INTAKE OF SEA WATER WITH HIGH TOTAL SUSPENDED SEDIMENT LOADS

ABSTRACT Submarine pipeline is used as a seawater intake system since it is cost effective compared to canal and jetty type intake structures. Open channel type intakes attract large deposition of sediments and hence periodic maintenance dredging is essential. Jetty type seawater intake is generally expensive. Much coastal water around the world hold high concentration of Total Suspended Sediments (TSS) like the coastal waters of Sabiya area, Kuwait in the north western part of Arabian Gulf. The existing seawater intake channel of a power plant is attracting significant settlement of TSS. Maintenance dredging of about 400,000 m25/year is carried out. It is proposed to increase the seawater intake for a proposed 2050 MW additional power plant and hence further increase in the TSS settlement is anticipated, if the present sea water intake system is used. Alternative type of seawater intake system, which can reduce the TSS is explored. Feasibility study is carried out to reduce the sediment entry into the power plant utility. The TSS levels were assessed, and its variations with respect to tidal phase, water depth and elevation along the depth are assessed. The settling velocity of the sediments is assessed. A sea water intake system is designed and the modality of taking water from the inlet and the configurations of the settling tanks are provided. It is advisable to draw water closer to the free water surface using a vertically moving intake well. It is found that the TSS level reduces 40% to 60% when the ambient flow velocity of sea water is minimum. Hence it is beneficial to avoid taking seawater when the sediment carrying capacity of the seawater is high during high currents. This study will be useful for feasibility design of submarine pipeline type intake for similar locations around the world.

Effect of Offhsore Low-Crested Barrier in Reduction of Wave Pressures on Caissons

Wave pressures on vertical structure defenced by a low-crested rubble mound breakwater were investigated. A series of physical model tests were carried out in a wave flume to examine the performance of the defence structure in reducing the wave pressures over the seawall/caisson. The influence of the pool length and relative submergence depths on wave pressures was also investigated. Influence of the pool length on reduction of pressure ratios is observed to be small for two ranges studied. Average shoreward pressure ratio is more for relative barrier height, h/d=0.83 for the pool lengths chosen in the experimental investigation.

Slamming Forces due to Random Waves on Horizontal Circular Members in Intertidal Zone

Wave forces acting on slender cylinders are normally estimated using Morison equation. When a structural member is near the free water surface, it experiences the slamming force. Wave slamming on horizontal members of any ocean structure is crucial to its design. API Recommended Practice 2A-WSD (2000) recommends slamming coefficient C S equal to π for circular cross sectional members near the still water level. The horizontal cylinders in the inter tidal zone for Port craft jetties are subjected not only to slamming force in the vertical direction and horizontal direction but also berthing force in the horizontal direction. If two cylinders are kept in close spacing, then the load on each member will be different compared to force on a single member kept alone. In this paper, the results of investigations of the effect of tidal variation on slamming forces are reported. The comparison of single circular member and twin circular members with c/c spacing varying from two to four times the diameter of cylindrical member in random waves is also included in this paper. The slamming coefficient is found to be not a constant value and it varies with respect to the spacing between the cylinder and free water surface, the incident wave height and wave period.

PERFORMANCE OF AN OFFSHORE LOW-CRESTED BREAKWATER AS A REHABILITATION STRUCTURE

ABSTRACT Low-crested offshore rubble mound breakwaters (LCB) are gaining more popularity as a potential coastal protection structures, where a moderate transmission is allowed with significant energy dissipation. This paper presents results obtained from a physical model study to understand the transmission and reflection characteristics of LCB as a defence structure in front of a vertical seawall. The paper mainly focuses on the influence of crest level of LCB in reducing the water surface elevations between two structures and on reflection characteristics of the combined system. In this study, five different relative crest heights (h/d) are used keeping the water depth constant and varying the breakwater height. The results of this investigation can be used in the design of seawalls with less overtopping or for preventing the heavy overtopping on existing seawalls from severe storms. This type of protection can also be used as a rehabilitation measure in situations wherein it is required to reduce the w...