Measuring the effects of cutter suction dredge operating parameters on minor losses due to fixed screens installed at the suction inlet
Lewis, Joshua Mark
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One of the most efficient and versatile types of modern dredges is the cutter suction dredge. Specific regulations mandate the placement of screens over the suction mouth during dredging operations to prevent ordnance, wildlife, and other debris from entering the system; however, these screens change the operational capability of the dredge in the form of an additional minor loss. The goal of this experiment was to determine the effects of different dredge operating parameters – cutter head speed, ladder arm swing speed, flow rate, and screen opening area ratio – on a screen’s calculated minor loss coefficient (or k-value). The Haynes Coastal Engineering Laboratory and Center for Dredging Studies at Texas A&M University houses a model cutter suction dredge that is used to test various parameters associated with hydraulic dredging. Testing consisted of 121 test dredge runs, which included water-only runs and slurry runs, at three flow rates, three swing speeds, three cutter head speeds, and three screen configurations. Minor loss coefficients were calculated for each test run and qualitatively and quantitatively analyzed. The results showed that neither cutter head speed nor swing speed had a significant, direct correlation with the screen’s minor loss in the range of selected parameters; however, they did have an indirect effect on k-value through an increased specific gravity in the slurry. The screen opening area ratio (B) showed a direct correlation with the screen’s k-value and was quantified for water tests and sand tests in the form of an empirical equation which can be applied to both model and prototype cutter suction dredges. The k-values for different screen opening shapes showed an upward or downward shift in the overall k-value curves, indicating the possibility of inherent efficiencies for differently-shaped openings. Qualitative observations of the Haynes Laboratory model dredge included sediment spillage at high cutter head speeds and a sand bulldozer effect at low cutter head speeds. Future testing should focus on a wider range of cutter head speeds and swing speeds to determine if any correlation exists beyond the ranges tested in this experiment. Additional testing of screens with more B- values and different screen opening shapes would increase the resolution and precision of the proposed k-value prediction equations.
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