Browsing by Subject "dredging"
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Item Comparison of Experimental and Theoretical Forces on a Model Dredge Cutterhead(2011-02-22) Permenter, RustyDredging is a critical part of maintaining the nation?s ports and harbors that play a major role in international trade. The design of dredge equipment requires knowledge of the forces expected on an average dredge. For a cutter suction dredge one of the largest forces is applied on the cutter head. To determine the design criteria for a given cutter suction dredge the forces on the cutter head must be known. Forces on a 33 cm (13 inch) model cutter head have been measured using a model cutter suction dredge 10.2 cm ( (4 inch)) suction and 3 inch (7.6 cm) discharge) in the Haynes Coastal Engineering Laboratory. The experimental results are compared to the results of a previously developed theory for estimating cutterhead forces. A MATLAB program is written and used to solve the theoretical equations. The sediment used in the study had a d50 of 0.27 mm and an angle of internal friction of 21.6?. The sediment is contained in the deep sediment pit 7.6 m (25 ft long), 3.7 m wide(12 ft ) and 1.5 m deep(5 ft) in the dredge/tow tank that is 45.7 m long(150 ft), 3.7 m wide(12 ft), and 3.0 m deep(10 ft). The objectives of the study are to calculate the forces using existing theory and MATLAB program and compare the theoretical results to those measured in the laboratory. The effects of the depth of cut, direction of swing, and cutter rpm on the forces acting on the cutter head are evaluated. The forces on the cutterhead are determined through the use of a set of six load cells rated at 13.3 kN (3000 lb). The load cell measurements allow direct calculation of the forces on the cutter head through the use of static equilibrium equations with the assumption of a constant swing speed. Once the forces are determined the results can be scaled to fit an actual dredge and then be applied in the determination of dredge design characteristics. The study shows the ability of the theory to determine the forces within an order or magnitude. The theoretical forces allow design of a cutter using a factor of safety. The variability of the forces in the laboratory study shows the assumption that the cutting forces are generally steady is not always valid.Item Experimental Measurement of a Model Pipeline Dredge Entrance Loss Coefficient and Modification of a Spreadsheet for Estimating Model Dredge Performance(2014-04-17) Girani, JosephCutter suction dredges are used in a multitude of scenarios, as they are mobile and efficient. One such situation includes dredge sites where debris could be present. In a location with the possibility of debris impeding the cutter suction dredge centrifugal pump, often a screen is placed over the suction line entrance. Although this prevents the inflow of large debris, it increases the entrance loss of the system. The objective of the study is to determine the minor loss coefficient of the Center for Dredging Studies? model cutter suction dredge. Testing was completed over the spectrum of specific gravities (SG) and flow rates achievable in the laboratory. The results show that the minor loss coefficient of the screen is a function of specific gravity and velocity, and varies between approximately 1.4 and 2.4 for the model laboratory dredge. Above the critical velocity the loss coefficient increases nearly linearly with specific gravity, if velocity is held constant. Similarly, if specific gravity is held constant the losses increase linearly with velocity. Additionally, as specific gravity is increased, the screen losses become a weaker function of velocity. Higher losses were observed at large specific gravities, as the flow rate decreased below the critical flow rate of the system. The production losses associated with the screen for the model cutter suction dredge were calculated using the pump characteristic curves. They showed variations between 2.4% and 3.4%, presenting larger production losses at higher pump speeds. An additional aspect of the study concerned comparing the experimental data with that of a widely accepted theoretical method. A previously existing spreadsheet from the Center for Dredging Studies (CDS) was modified to accommodate the minor loss values of the screen, along with the characteristics of the model laboratory dredge and intake losses. The spreadsheet outputs the predicted head loss of the system according to the flow rate and specific gravity, which was compared to the experimental head loss of the study. The theoretical methods matched the experimental results more closely at higher flow rates, achieving approximately 5.7% (no screen) and 6.9% (screen) average error for the suction line at a flow rate of 25.2 L/sec (400 GPM) and 9.4% in the discharge line at a flow rate of 18.9 L/sec (300 GPM). The modified spreadsheet allows the user to input whether or not the screen is present and predict pump performance at a specified specific gravity for a range of flow rates.Item Near-Field Sediment Resuspension Measurement and Modeling for Cutter Suction Dredging Operations(2011-02-22) Henriksen, John ChristopherThe sediment resuspension and turbidity created during dredging operations is both an economical and environmental issue. The movement of sediment plumes created from dredging operations has been predicted with numerical modeling, however, these far-field models need a ?source term? or near-field model as input. Although data from field tests have been used to create near-field models that predict the amount of material suspended in the water column, these results are skewed due to limitations such as non-uniform sediment distributions, water currents, and water quality issues. Laboratory investigations have obtained data for turbidity during dredging operations, but these results do not take advantage of the most contemporary testing methods. The purpose of this dissertation is to provide an estimation of turbidity created during a cutter suction dredging operation. This estimation was facilited by the development of resuspension measurement and data acquisition techniques in a laboratory setting. Near-field turbidity measurements around the cutter head were measured in the Haynes Coastal Engineering Laboratory at Texas A&M University. The laboratory contains a dredge/tow tank that is ideal for conducting dredging research. A dredge carriage is located in the dredge/tow tank and is composed of a carriage, cradle, and ladder. Acoustic Doppler Velocimetry (ADV) and Optical Backscatter Sensor (OBS) measurements were taken at specific points around the cutter head. The variables of suction flow rate, cutter speed, and the thickness of cut were investigated to understand their specific effect on turbidity generation and turbulence production around the cutter head. A near-field advection diffusion model was created to predict resuspension of sediment from a cutter suction dredge. The model incorporates the laboratory data to determine the velocity field as well as the turbulent diffusion. The model is validated with laboratory testing as well as field data. Conclusions from this research demonstrate undercutting consistently produced larger point specific turbidity maximum than overcutting in the laboratory testing. An increase in suction flow rate was shown to increase production and decrease turbidity around the cutter head. In general, an increase in cutter speed led to an increase in turbidity. The thickness of cut produced less resuspension for a full cut versus a partial cut. Data for a ?shallow cut? also produced less turbidity generation than partial cuts. The numerical model was compared to all laboratory testing cases as well as the Calumet Harbor and New Bedford cutter resuspension data and produced suitable MRA values for all tests. The numerical model produced higher point specific regions of turbidity for undercutting but produced larger mean values of turbidity for overcutting.