Monograph records
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A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenThu, 30 Nov 2023 18:25:30 +0000Wave-induced oscillations of small moored vessels
https://resolver.caltech.edu/CaltechKHR:KH-R-10
Authors: Raichlen, Fredric
Year: 2004
DOI: 10.7907/Z9Z899CQ
The general objective of this research is to investigate the motion of small boats moored to fixed or floating platforms in a standing wave environment. The study is directed toward an understanding of the problems of mooring small craft in marinas and toward providing information that will assist in the planning and operation of marinas.
This report deals with the first phase of the experimental study concerning the surge motions of a simply moored body in a standing wave system. The body is a rectangular parallelpiped moored to a fixed support by means of a linear spring.
In general it can be stated that the inviscid theory proposed by Wilson (5) and Kilner (7) adequately describes the surge motion of this body for standing waves ranging from shallow-water to deep-water waves and for ratios of body length to wave length from 0.1 to 1.5. Agreement between the experimental data and the theoretical response curves is better for certain ranges of the ratio of the natural period of the body to the wave period than for others. This is attributed to the effect of wave generation by the body on its motion. The response curves become more selective with respect to frequency as the distance of the body from a reflecting surface increases. Therefore, coupling this with viscous effects it is possible to reduce the effect of resonance considerably simply by choosing the proper body location in its standing wave environment for a particular natural frequency.
The coefficient of virtual mass of the body in surge (ratio of width to length, 1:4) determined from simple free oscillations was found to correlate best with the ratio of draft to beam. For a variation of draft to beam from 0.25 to 0.95 the coefficient of virtual mass varied from approximately 1.1 to 1.25.
This study emphasizes the need for more field information on the characteristics of small craft, such as the elastic characteristics of the mooring system, natural frequencies of moored boats, and the relative importance of viscous effects upon boat motions.https://authors.library.caltech.edu/records/2pwh0-30s03Wave induced oscillations in harbors with connected basins
https://resolver.caltech.edu/CaltechKHR:KH-R-26
Authors: Lee, Jiin-Jen; Raichlen, Frederic
Year: 2009
DOI: 10.7907/Z9SJ1HH5
A linear, inviscid theory, termed the coupled basins theory, has been developed to analyze the response to periodic incident waves of an arbitrary shape harbor containing several interconnected basins. The region of consideration is divided into an open-sea region and several inner-basin regions (the number depending on the harbor geometry). The solution in each region is formulated as an integral equation in terms of the normal velocity at the entrance and/or at the common boundaries between regions. An approximate method is used to solve the integral equation by converting it to a matrix equation. The initially unknown boundary condition at the entrance is determined by matching the wave amplitudes and their normal derivatives at the harbor entrance and at all the common boundaries. The solution for the response and the amplitude distribution within the complete harbor can then be obtained.
It has been found that the coupled-basins theory gives results which agree well with experiments both for an irregular shape harbor as well as for a harbor composed of two connected circular basins. Various aspects of the response of harbors composed of several types of circular connected basins as well as circular harbors with rectangular entrance channels have been investigated. It is found that to a first approximation the response of a coupled harbor system can be constructed by superposing the response of the individual harbors
Certain aspects of the effect of viscous dissipation on harbor resonance are discussed. Some attention is given to problems of scaling model results to the prototype harbor.https://authors.library.caltech.edu/records/wdpek-mtd07Motions of small boats moored in standing waves
https://resolver.caltech.edu/CaltechKHR:KH-R-17
Authors: Raichlen, Frederic
Year: 2009
DOI: 10.7907/Z90C4SQF
This study was conducted to determine the dynamic characteristics of small boats moored with non-linear-elastic lines in an asymmetrical manner. The motions being considered are surge motions where the moored boat is allowed to move either in the direction of the bow or the stern, but not in other coordinate directions.
An analytical model is proposed where the small boat is simulated by a block-body which is moored asymmetrically to a fixed dock. A method is developed from which the non-linear restoring forces and the dynamic response of the boat in surge can be obtained. The restoring force which is associated with the boat displacement is defined by the material, condition, and dimensions of the lines and the mooring geometry. From those results, an approximation to the restoring force is made so that a closed solution to the problem is possible. The periods of free oscillation determined by this method are compared to the results of some experiments conducted on a 26-foot boat with a displaced weight of approximately 7000 lbs. The experiments were performed using this small boat moored under different conditions: all lines taut, 4 inches slack in all lines, and 8 inches slack in all lines. These results compared favorably with the analytical results.
The response of seven small boats of various displaced weights were determined analytically to evaluate the range of important wave periods for this sample. The mooring dimensions of these boats were measured in situ and the theoretical approach developed was applied. The results indicate, for the samples considered, that the important range of periods of forced oscillation for excessive motions of these boats in surge was less than 10 secs. If stiff mooring systems had been employed for all of these boats the important wave period range for these motions could probably be reduced further. Due to the different mooring systems used, the response curves for some of the small boats were highly asymmetrical indicating the possibility of much greater motions in one direction than in another under the action of a periodic symmetrical force.
A limited series of experiments were conducted to determine the effect of the proximity of flotation chambers which are used on some floating slips on the response of the moored boat. It was found that these chambers, as simulated in the laboratory, did not have a significant effect on the dynamic characteristics of the moored boat. However, they did act as floating breakwaters thereby reducing the transmitted wave energy.https://authors.library.caltech.edu/records/dkepq-d8k40Laboratory design-studies of the effect of waves on a proposed island site for a combined nuclear power and desalting plant
https://resolver.caltech.edu/CaltechKHR:KH-R-14
Authors: Vanoni, Vito; Raichlen, Frederic
Year: 2010
DOI: 10.7907/Z9BC3WG8
There were four major objectives to this investigation: 1) the determination of the degree of stability of the island face when constructed of armor units of various weights; 2) the run-up for a two-dimensional wave system impinging on the island face; 3) the run-up envelope on the four sides of the island in a three-dimensional model; and 4) the wave patterns caused by the effect of the island on its wave environment. Models having three different length scales were tested in the wave tank (1:50, 1:45, and 1:40) and these models are referred to as the two-dimensional models. One model was tested in the wave basin at an undistorted scale of 1:150 and it is referred to in this report as the three-dimensional model.
The first two-dimensional model was built to a scale of 1:50 and essentially corresponded to the original design proposed by Omar Lillevang, Consulting Engineer to the Bechtel Corporation. The prototype tribar weight, equivalent to the model tribar used, was 18.9 tons. This structure was stable; however, it was overtopped by waves. With an increase in the crest elevation from +30 ft. to +40 ft. some overtopping was still experienced.
The second model was built at an increased scale, 1:40. At the same time the composite slope which existed in the original design was changed so that the island face had a continuous slope of 3 horizontal to 1 vertical with the crest of the defense at elevation +40 ft. This particular model scale was chosen so that, according to the literature, the tribars would be at a condition of incipient failure for high waves. Since the same armor units were used in this model as were used in the 1:50 scale model, the increase in model scale reduced the equivalent weight of the tribars to 9.7 tons and the maximum weight of the armor rock "B" from 10 tons to 5.1 tons. The prototype structure which corresponds to this model was found to be unstable, as expected. It was observed in testing that a critical feature of the construction which contributes to the stability of the structure is the degree to which the cap-rock section is interlocked with the tribar section. The modification made to the slope of the island face and the increased crest elevation eliminated the problem of overtopping, and the maximum run-up for a 14-sec. wave was to elevation +38 ft.
Since the model having a 1:40 length scale was unstable and that with a scale of 1:50 was stable, a third model was constructed with a model scale between these two values, a scale of 1:45. The equivalent prototype tribar weight and the maximum weight of the "B" rock for this third model, still using the same model armor units, were increased to 13.8 tons and 7.3 tons respectively by this change. The slope of the wave defense and the crest elevation were the same for this structure as they were in the 1:40 scale model, i. e., a continuous slope of the island face of 3 horizontal to 1 vertical and a crest elevation of +40 ft. This model was satisfactory both with respect to stability and to run-up. Run-up measurements were made for waves of various heights at wave periods of 16 sec., 14 sec., and 12 sec. The maximum run-up was to elevations +39 ft., +35 ft., and +31 ft. respectively for these three wave periods.
The three-dimensional model of the ocean bottom and the island was built to an undistorted scale of 1:150 with the island constructed the same as the 1:45 scale two-dimensional model. In these tests in the large wave basin the wave direction was varied as well as the wave period and wave height. The run-up envelopes obtained showed that, for comparable wave heights, the worst condition of run-up was for normally incident waves impinging on the seaward face of the island. The run-up measured for the normally incident direction was usually approximately 10% less than the run-up in the two-dimensional model for the same wave periods and wave heights. For the case of oblique wave incidence the maximum run-up was at the island corner first attacked by the wave with the run-up decreasing with distance from this corner, and this run-up was comparable to the maximum run-up experienced at normal wave incidence. However, the maximum average run up for the oblique case was significantly less than that experienced in the case of normal wave incidence. The run-up on the shoreward face of the island for all wave directions was of the order of 1/10th of that experienced on the seaward face.
Detailed observations of the wave pattern in the lee of the island indicated that there were regions near the beach where the currents were in a direction opposite to the observed general current. From overhead photographs it was found that generally this occurred in regions where the waves which diffract from around the sides of the island intersect. Measurements were made of the maximum elevation of the water surface in the region of the causeway for the case of oblique wave incidence.https://authors.library.caltech.edu/records/94ttz-apt73Sediment Management for Southern California Mountains, Coastal Plains, and Shoreline
https://resolver.caltech.edu/CaltechAUTHORS:20140624-133116283
Authors: Brooks, Norman; Brown, William; Cass, Glen; Durkan, Ray; Eagleson, Peter; Goring, Derek; Hashimoto, Lewis; Koh, Robert C. Y.; Lewis, Tracy; List, E. John; McMurry, Pamela; McMurry, Peter; Raichlen, Fredric; Sharp, Robert; Sung, Windsor; Taylor, Brent; Van Ingen, Katherine; Vanoni, Vito
Year: 2014
During 1976, with financial support from Los Angeles County, U. S.
Geological Survey, and discretionary funding provided by a grant from the
Ford Foundation, substantial progress was made at EQL and SPL in achieving
the objectives in the initial Planning and Assessment Phase of the CIT/SIO Sediment Management Project. The current timetable for completion of
this phase is June 1978.
This report briefly describes the project activities during the
year including general administration, special activities, and technical
work; and is submitted in accordance with the letter of agreement between
Los Angeles County and Caltech dated 1 April 1976.https://authors.library.caltech.edu/records/jn7z9-pbc38Sediment Management for Southern California Mountains, Coastal Plains, and Shoreline
https://resolver.caltech.edu/CaltechAUTHORS:20140624-145908791
Authors: Brooks, Norman; Brown, William M.; Cass, Glen; Durkan, Ray; Eagleson, Peter; Goring, Derek; Hashimoto, Lewis; Koh, Robert C. Y.; Lewis, Tracy; List, E. John; McMurry, Pamela; McMurry, Peter; Raichlen, Fredric; Sharp, Robert; Sung, Windsor; Taylor, Brent; Van Ingen, Katherine; Vanoni, Vito
Year: 2014
During FY77, with financial support from Los Angeles County,
U. S. Geological Survey, Orange County, U. S. Army Corps of Engineers,
and discretionary funding provided by a grant from the Ford Foundation,
substantial progress was made at EQL and SPL in achieving the objectives
of the initial Planning and Assessment Phase of the CIT/SIO
Sediment Management Project. The current timetable for completion
of this phase is June 1978.
This report briefly describes the project status including
general administration, special activities, and technical work.https://authors.library.caltech.edu/records/kbhcd-ye713