Java程序辅导
C C++ Java Python Processing编程在线培训 程序编写 软件开发 视频讲解
C C++ Java Python Processing编程在线培训 程序编写 软件开发 视频讲解
Oceanography Lab Waves Waves are characterized by their wavelength, L (distance between adjacent crests, or troughs), height, H (vertical distance between a crest and trough), and their period, T (time between two successive crests, or troughs). The amplitude is ½ the wave height. Waves are grouped into categories depending on the depth of water relative to the wavelength. This is because in deep-water the wave does not “feel” the bottom, while in shallow water it does. Deep-water waves occur when the water depth is deeper than ½ the wavelength (D > L/2). Shallow-water waves occur in water depths less than 1/20 the wavelength (D < L/20). At intermediate depths the waves are transitional. Wave motion is orbital, not forward as you might think. Use the computer model of linear wave kinematics ( http://www.coastal.udel.edu/faculty/rad/ ) to investigate waves orbital motion. Do this as suggested in the model: As an example, you might compare the case: wave height = 2 m, period = 6 sec, depth = 10 m to the case of longer waves, by changing the period to 12 sec. Note that the horizontal velocities under the second wave are almost constant with depth as compared to the shorter period wave. Then you might try changing the period to 2 secs. For each of these scenarios write down the parameters (make sure to write down units too) and note your observations 1) Height _2 m____ Observations: Period _2 sec__ Depth _10 m___ Length ________ Umax ________ Vmax ________ 2) Height __2 m___ Observations: Period __6 sec__ Depth __10m___ Length ________ Umax ________ Vmax ________ 3) Height ___2 m__ Observations: Period __12 sec Depth ___10 m_ Length ________ Umax ________ Vmax ________ From the examples above you have seen that orbitals change as one goes from deep-water to shallow-water. Other things change as well as a wave “shoals”. Listen to the description by Ernest Knowles at NC State http://www4.ncsu.edu/eos/users/c/ceknowle/public/lesson07/part3.html For deep-water, the wavelength is: L g T L m s T= = 2 1562 2 2pi or . where g is gravitational acceleration (9.8 m/s2). The speed at which the waveform travels is called Celerity, C. In deep-water the celerity is: C L T g T or C L T g L= = = = 2 2 2 2 2pi pi C T or C L= =156 1562. . In shallow water, friction of the waves on the bottom can cause resuspension of sediments, and sediment transport. Transport is related to particle size and current speed. An important thing to find out then is speed at the bottom, u_b. You also know that waves have a lot of energy associated with them. We can actually calculate the energy. E is the energy content per meter (N-m/m2) of wave surface, while E_f is the flux (that is movement ) of this energy per meter (Watts/m) of crest length. You will investigate the change of wave characteristics using the Wave Calculator (http://www.coastal.udel.edu/faculty/rad/). The subscripts D and S stand for deep-water and shallow-water, respectively. First lets look at what happens at different wave heights, while keeping T, Angle and Depth the same. You will need to calculate deep-water values according to the formulas above. HD T Angl Depth CD CS LD LS HS u_b E E_f 1 5 0 4 3 5 0 4 6 5 0 4 4) What trends do you see? Repeat the above with a wave angle of 10 degrees. HD T Angl Depth CD CS LD LS HS u_b E E_f 1 5 10 4 3 5 10 4 6 5 10 4 5) What trends do you see? How does angle influence the results? 6) What do you think might be the importance of E and E_f? Waves can only get so steep, before the cohesion of water fails and the waves break. Steepness S H L = = At a ratio of height to length of 1:7 they start to break. 7) For the three different waves above, what is the steepness for both the deep- and shallow- water (Remember to use the appropriate H). HD 1 3 6 SD SS Next lets vary the Period, while keeping H, Angle and Depth the same H D T Angl Depth CD CS LD LS HS u_b E E_f 1 2 0 4 1 6 0 4 1 12 0 4 8) What trends do you see? 9) Do the problem near the bottom of the Wave Calculator page. Now that you have some experience playing with waves, go to the exercise on traveling wavesuperposition http://webphysics.davidson.edu/physletprob/ncssm/waves/wavesintro.htm. As we all now, waves can be added together. If the wave forms are in phase (peaks match up) they will add together to make a larger wave. In the figure on the left the top two waves are added together to make the bottom wave which has higher peaks. In the figure on the right, the waves are out of phase and cancel one another to produce a straight line. If the waves are traveling, they may add up to a standing wave, one where the peak and trough oscillate in place instead of moving in some direction. Do the problems on the web site relating to superposition. 9. 10. Why must the two waves have the same speed? (Think in terms of what influences wave speed in the medium.) 11. Stop the top wave and measure its wavelength in units of divisions along the horizontal axis. Sketch the wave, showing the two points between which you measured the wavelength. 12. Now measure the period of the top wave in time units. Describe your method for doing this. 13. Calculate the speed of the top wave. Show your work. For exercise two of the superposition, answer the following: 14 Click on the Forward tab to start the waves moving. The amplitudes and wavelengths are both in the ratio 2:1. Why must the frequencies be in the ratio 1:2? 15. Try changing the frequency of g(x,t) to 3. What else must you change? 16. Keeping f(x,t) the same, make all necessary changes to g(x,t) in order that the superposition of the two waves will be a standing wave. Once you have a standing wave, list all the parameters selected for each wave. 17. Make a change to the frequency of f(x,t). What change must you make to the frequency of g(x,t) in order to restore a standing wave? 18. If you have time, work with the wave equations directly. Try changing a constant to see how that changes the corresponding wave. Can you figure out what each constant in the equation represents? Waves are now measured routinely by buoys and by satellite. Go to this commercial satellite page http://oceanweather.com/data/ which carries wave heights around the world. 19. Look at the forecast of global wave heights.What are some of the current highest waves? How might this kind of service be useful? 20. The significant wave height is the height at which the highest one third of the waves occur..make a sketch showing where the largest wave heights are occurring. On the sketch note the highest significant wave heights 21. Go to the maps for the US Northeast. What are the current highest significant wave heights? 22. Where are they? 22. Next, look at the Marine observations. The symbols (wind barbs) indicate both the wind speed in knots (nautical mile per hour) and the wind direction (from which the wind is coming from). Each flag on a wind barb indicates 50 knots, each long whisker is 10 knots, and each short whisker is 5 knots. To get the wind speed, just add up the flags and segments. Are there any relationships between the winds and the waves? 23. What do the iso-lines represent? 24. What is their relationship to the wind? 25. Set the Java loop in motion and describe the progression you see The numbers show the wave height and period at buoys. Compare the wave heights measured at buoys to the predicted significant wave heights you looked at above 26. Is there a difference? Why do you think this is? 27. Click on “observation table” and look at the wave heights and periods. What are some of the largest wave heights you can find in the table? Birdies located (click on the buoy name)? Record the data in the table. Height Period Location You will next look at some ways near you and me. Use ImageJ. to look at the file coast1.jpg. This is a mosaic of aerial photographs from the Maine office of GIS ( http://megisims.state.me.us/website/orthomap/viewer.htm ). ( http://apollo.ogis.state.me.us/ ). It will be working with two seems from these images one north of the jetty is the other off Biddeford beach. 28. Open coast3.jpg in ImageJ. You will need to calibrate the scale for the image. Zoom in on Bridge Road (Hwy 208) where it intersects with Mile Stretch Road and Fortunes Rocks Road. At the end of the parking lot opposite the dredging that is a dirt lot changing to pavement of the driveway to a house. You’ll also notice the white line for the stop sign at the end of Bridge Road. The distance between the line and the and of the driveway is 80 m. Click on the straight line segment tool, and run a line from the white stop line to the edge of the driveway. Click Analyze, choose Set Scale. It should have filled in the number of pixels along the line, enter 80 for the known distance, and change the units to meters.. Then click OK to get back to the image. 29. Zoom out so you can see the whole image. You notice that there are big swells coming in. Measure the distance between crests in six different places, starting offshore and ending up next to the beach. Draw a line between two crests then click Analyze and select Measure. The last column should be your distance in meters. 1. _____________ What trend can you see in the wavelength? Why is this? 2. _____________ 3. _____________ 4. _____________ 5. _____________ 6. _____________ 30. Notice that there are at least two other sets of ways besides the big swell. Measure five wavelengths for each of these and calculate the average wavelength. Also note what direction they are coming from (North is up). a. _______ ________ _________ __________ ________ Avg ______ Dir ______ b. _______ ________ _________ __________ ________ Avg ______ Dir ______ 31. Loaded image coast4.jpg. This is a Mathematica chart of the area, the depths are a meters. The parking lot is at the edge between the green and brown areas near the stream. Determine whether the waves are deep water or shallow waterways and state why. Type Why Swell _____________ ________________________________________________ 1. _____________ ________________________________________________ b. _____________ ________________________________________________ 32. What is the period of these waves? Period Units Swell ____________ ______ a. ____________ ______ b. ____________ ______ Interestingly, race can also occur in sand (called sand ripples were sand ways). Load image coast2.jpg. Go through the process as above to set the scale. For a known distance, the pond at fairy beach is 330 m long from the sand beach at the north and to the pointy tip at the South. 33. Measure five or six crest to crest distances for the sand waves, which are clearly visible in the water just off the beach. Also measure five or six crest to crest distances for this well. Sand _______ ________ _________ __________ ________ ______ Avg _______ Swell _______ ________ _________ __________ ________ ______ Avg _______ Is there any relation between wavelengths of the sand in the water? Explain. something else to note are the slick areas in this image. These are the result of Langmuir circulation – parallel vortices of water caused by the wind. Seiches are phenomena seen in lakes and basins. They are standing waves often set up by winds or tides. Standing waves have nodes, where the surface remains relatively constant, and antinodes, where the surface rises in falls to form the crests and troughs. Use the Seiche Calculator ( http://www.coastal.udel.edu/faculty/rad/ ) to investigate standing waves. Read the description provided on the web site. 34. In the opening screen the basin length is 100 m, depth 5 m, and modes 3. What do modes correspond to physically? (Hint: try changing modes to 1, 2, 3, and 4, and observe what changes.) 35. How do the particle motions (white lines) differ from those of traveling waves? 36. How does the modal number relate to wavelength? 37. Describe what happens to particle motions as you make the water deeper. Waves can occur wherever there is an interface, air-water, air-earth and even water-water or air-air, when there are two different densities. The latter is a case for internal waves which can travel along a thermocline or pycnocline. This Cornell Univ. site http://ceeserver.cee.cornell.edu/pjl2/research_web/iw/internal.htm has some good illustrations and descriptions. Another illustration of internal waves is at UNC-Wilmington http://www.uncwil.edu/nurc/aquarius/2001/6_2001/iwaves.htm. There is also a good page for waves in general (wind waves, seiches) with some good illustrations of internal waves created by Prof. Tomczak http://www.es.flinders.edu.au/~mattom/IntroOc/notes/lecture10.html. Finally, Peter Franks’ Site at Scripps http://spiff.ucsd.edu/iwave.html shows how these waves can influence the distribution of organisms. In the tank provided, make a two layered system by using fresh and salt water. Use a dye to color one of the layers. Then raise up one end and quickly lower it to generate waves. 38. Measure the wavelength and period for the surface waves and the internal waves. Discuss your observations. Wavelength Period Surface Deep 39. Think about the various waves you have examined in this lab. In this last experiment, what kind(s) of wave(s) did you generate. Explain. Web sites http://www.coastal.udel.edu/faculty/rad/ http://www4.ncsu.edu/eos/users/c/ceknowle/public/lesson07/part3.html http://webphysics.davidson.edu/physletprob/ncssm/waves/wavesintro.htm http://www.satobsys.co.uk/WWWaves/Free.html http://www.oceanweather.com/data/ http://ndbc.noaa.gov/Maps/Northeast.shtml http://ceeserver.cee.cornell.edu/pjl2/research_web/iw/internal.htm http://www.es.flinders.edu.au/~mattom/IntroOc/notes/lecture10.html http://spiff.ucsd.edu/iwave.html http://www.uncwil.edu/nurc/aquarius/2001/6_2001/iwaves.htm