13.42 Design Principles of Ocean Vehicles. Lab #2: SHIP RESPONSE IN HEAD SEAS Date issued: April 22, 2003 Date Due: May 6, 2003 This laboratory is designed to illustrate how to predict the seakeeping response in heave and pitch of a full scale vessel using model testing methods in the MIT towing tank. MODEL INFORMATION: At the tow tank, you will be measuring the resistance of a 100:1 scale USS Arleigh Burke class DDG (destroyer, guided missile) model. The primary characteristics of the DDG 51 follow. The model tested will be without a sonar dome. LPP 466.0 ft T 20.69 ft B 58.98 ft CP 0.625 CX 0.830 Cb 0.519 Cwp 0.789 ∆ 8240 LTsw Sws 29,754 ft2The lab will be held at the MIT Towing Tank, located in Building 48 Room 015 (48-015) in the Parsons Laboratory at 15 Vassar Street. Use the entrance at the far end (the corner of Vassar and Main) and go down to the basement, past the bicycle rack, and knock on the door. You may be requested to help in the running of the towing tank equipment during the lab. The lab is controlled from 3 computers. Here is an outline of the equipment and use procedure. Software The tow tank laboratory uses Daisylab for data acquisition, and Matlab for post-processing. The data acquisition file from the measurement instrumentation is out.i32, a daisylab formatted file which holds the result from each model test run. This file is over-written each time, so make sure you complete all of the steps below before starting the proceeding run. Carriage The carriage is operated from a computer for test runs. The power will be on and the computer set up and ready. You just need to set the desired speed, and make sure the model is at the far end of the tank before starting a run. Limit switches are activated at the far end of the tank, when the model is in position prior to a run, and at the near end, to shut off the carriage at the end of the run. The model is returned to the far end slowly in preparation for the next run. Data Collection and Analysis Daisylab and Matlab have been set up to collect and analyze the raw data from the model test. Start Daisylab approximately 10 seconds before starting the carriage by pushing the play button on the Daisylab screen. Push the stop button after the model has stopped at the end of the run. Eaach group should collect their data into their groups directory. The data is initially stored in i32 format. These files (initially out.i32) should be saved after each run to a name designated by the group (newfilename.i32). These files can be read into MATLAB with parsedl2.m. From here you will be responsible for processing your data, as a team or individually, and writing individual lab reports. Lab Procedure:Two cases of the model in head seas will be investigated. First for zero forward speed and second for a set towing speed. Things to do: 1) Measure the location of the model with respect to the upstream wave probe. 2) Check with the lab TA to assure the potentiometers for heave and pitch and also the wave probes have been calibrated. Be sure to obtain a copy of the calibration data. 3) Collect data in pitch and heave for monochromatic incoming waves with a fixed amplitude (the TA will give you an appropriate wave amplitude) and increasing wave frequency for two cases: a. Uship = 0 b. Uship = 0.5 m/s 4) Collect data in pitch and heave for incoming waves with a Bretschneider wave spectrum for the same speeds used in part 3 (U = 0 & 0.5 m/s). 5) If time permits, pick an additional speed or see the effects of the ship being towed in stern seas (following procedure for part 3). 6) Process data & write report. Lab Write-Up For this report, follow basic technical report or journal paper format, with embedded figures, which are properly non-dimensionalized where appropriate. Include references, error analysis, setup and any conclusions. In the body of the report discuss the following: 1) Plot heave and pitch response of the model normalized by the appropriate wave properties as a function of frequency. How do you estimate this response to change for a full scale ship? With change in wave amplitude? 2) Discuss the ship behavior as a function of frequency: is there a frequency range for which this ship’s response seems excessive? (ie someone on board might get seasick? Or cargo might shift?) 3) From your data can you determine the cancellation frequency for heave and pitch? How do you estimate this will change for the full scale ship? 4) How do these plots and the cancellation frequency change with forward towing speed & encounter frequency?5) Determine the phase shift between the heave motion and the wave surface elevation at the ship model for at least three wave frequencies at U=0 with monochromatic head seas. Does this value change with frequency? Is this to be expected? 6) For the Bretschneider waves, plot the incoming wave spectrum and measured heave and pitch spectrums. How do the motion spectrums change with forward speed? Do you see any effects that might indicate that the system is not an LTI system? 7) Considering all of this data, how would you go about using this model data to design a full scale vessel? 8) Is there anything else you would be interested in measuring? 9) In your discussions, consider possible sources of error, discuss setup and calibration and any underlying theory that might be useful for explaining your