|Publication number||USH2195 H1|
|Application number||US 10/657,486|
|Publication date||Jul 3, 2007|
|Filing date||Sep 8, 2003|
|Priority date||Sep 8, 2003|
|Also published as||US20050052453|
|Publication number||10657486, 657486, US H2195 H1, US H2195H1, US-H1-H2195, USH2195 H1, USH2195H1|
|Inventors||Carl L. Sisemore|
|Original Assignee||The United States Of America As Represented By The Secretary Of The Navy|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (7), Non-Patent Citations (1), Referenced by (3), Classifications (5), Legal Events (1)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present invention relates to enhanced methods for modeling shipboard systems and equipment and more particularly to such a system that involves melding the beam and slice methods of such modeling to obtain more accurate predictive models of these systems and their elements.
There are three predominant methods used for the modeling of ships. First a detailed section of a ship can be represented. In this method, essentially, a “slice” out of the ship is modeled in detail and loads and boundary conditions are applied to the ship structure and/or keel surrounding this detailed section of the ship. The primary disadvantage of this method is that the entire ship is not represented in one activation of the model. Therefore, gross ship motions cannot be represented and the ship-wide mass and stiffness are not accounted for. This can lead to incorrect representations in the frequency spectrum.
The second modeling method represents the ship as a beam. This method works fairly well in obtaining gross motions since most ships are significantly longer than they are wide, and thus resemble a beam from a mathematical standpoint. The advantages of this method are that gross ship motions are represented quite well and the ship's actual mass and stiffness can be accounted for leading to good representations in the frequency spectrum. The primary disadvantage of this method is that fine details of the ship cannot be represented. Thus, internal ship spaces and equipment cannot be represented. The way that the beam model is connected to the ship's hull is through a series of stiff connections from the hull to the main beam model of the ship. This series of stiff connections or webs is used to transfer the applied loads from the hull representation to the beam model. This web technique is a fairly typical approach for transferring hull loads to the beam model. Additionally, since the desire has been to represent the internal ship spaces and equipment, the beam method is not sufficient and the ship section does not provide the appropriate ship motions to the modeling and simulation.
The final approach has been to extend the detailed “slice” of the ship to the entire ship, essentially creating a ship model with every ship space contained in the model. This has the significant disadvantage of resulting in mathematical models that cannot be solved on most currently commonly available computer systems. Other disadvantages are the significant amounts of time that are required to build the mathematical model and the fact that shipboard frequencies tend to be “under predicted” using this method.
It is therefore an object of the present invention to provide a ship modeling method that provides good representation of both the structure of the ship and its contained internal spaces and equipment in the frequency spectrum.
It is another object of the present invention to provide such a system that can be efficiently run on most conventional modeling computers in a reasonable amount of time.
According to the present invention, the beam method and the “slice” method for ship modeling are melded. The method uses a detailed ship model in the ship section immediately surrounding the system or equipment under study and a beam model for the portions of the ship away from the detailed ship section. This combined method has the advantage of providing a detailed section of the ship in the area of interest which allows for good system and equipment level modeling and a course beam model of the ship everywhere else which, in turn, allows for the ship's mass and stiffness and hence frequency spectrum to be accurately represented.
Similar attempts have been made in the past to incorporate a detailed ship section in a course beam model of a ship, but these attempts have been quite unsuccessful. The methodology with which the coarse beam ship model is connected to the detailed ship section forms the essence of the present invention.
In the past when connecting a course model to a detailed model a system of rigid or nearly rigid beams was used to connect a point on the coarse model to the face of the detailed section. For ship models of the type under discussion herein, this would be repeated twice, once for the ship section ahead of the detailed section and a second time for the ship section aft of the detailed section. The difficulty is that when this is done, it does not appear to provide an accurate model of the ship's overall behavior. It results in a model where both coarse models behave appropriately and the detailed section behaves quite poorly.
To correct this problem of connecting the coarse ship to the detailed section, the two coarse sections of the ship are connected to each other by a continuous beam model of the ship. Thus, the beam model of the ship is continuous along the entire length of the ship and, in fact, passes through the detailed “slice” section of the ship. This is entirely possible from a mathematical standpoint since beams can easily pass through plates and bulkheads in the mathematical representation of the model and techniques for such incorporation or “melding” are well known to those skilled in the modeling arts. This has a very significant advantage of having the entire ship behave like a continuous ship. Thus, the whole ship will heave and roll as it should under various kinds of sea and battle loads, specifically in high stress situations such as near miss shock.
The detailed portions of the ship can be “dropped”, i.e. inserted or positioned, into the coarse model as such techniques are well known to the skilled artisan familiar with the art of ship and similar modeling techniques. The bulkheads and ship structure surrounding the area of interest are built up from the bull of the coarse model. One of the fundamental differences between this modeling process and those of the prior art is that the beam representing the stiffness of the ship is allowed to pass through the detailed section and the stiff web structure used to connect the beam to the hull is continued throughout the detailed sections. This has the effect of forcing the structure in the volume of the detailed model to behave as part of the overall structure.
There are, of course, some mildly detrimental side effects to this technique. What this technique does is to sacrifice some degree of accuracy in the geometric representation of the ship sections in favor of imposing the correct physical motions on the ship sections. These mild deficiencies are a relatively trivial price to pay for the advantage of actually being able to solve the problem as opposed to the current trend which is to have models that are highly geometrically accurate, but either will not solve on current computer systems or give incorrect results when they do solve.
Referring now to
Referring now to
In the practice of the modeling method described herein, the following describes the process steps utilized to obtained the desired results:
The advantage of this modeling technique is that it actually works and yields results that correlate well to test data. This is in contrast to the ship models using a combination of coarse and detailed sections that have been described above and which in practice do not produce correlatable results. The other principle advantage of this technique is that it allows for smaller models to represent shipboard systems. This in turn allows the models to be solved efficiently using commonly available computing resources. This is in sharp contrast to models being developed in other arenas where an excessive level of detail across the entire ship is attempted to be modeled in a single operation. These highly detailed models are often so large that they cannot be solved on even the largest computer systems currently available.
The novel feature of this modeling method is that ability to successfully integrate the coarse and detailed models so as to yield a model that is both accurate and solvable. It accomplishes this result by effectively overlaying a detailed ship section or “slice” model 18 and a coarse model 10 of the entire ship while correctly imposing the motions of the coarse model 10 on the structure of the detailed or “slice” sections 18.
As the invention as been described, it will be apparent to those skilled in the art that the same may be varied in many ways without departing from the spirit and scope of the invention. Any and all such modifications are intended to be included within the scope of the appended claims.
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|Citing Patent||Filing date||Publication date||Applicant||Title|
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|International Classification||G06T17/00, G06T17/10|
|Sep 8, 2003||AS||Assignment|
Owner name: UNITED STATES OF AMERICA AS REPRESENTED BY THE SEC
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:SISEMORE, CARL L.;REEL/FRAME:014478/0701
Effective date: 20030908