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  1. 3 points
    DrD

    What Makes A Ship Move?

    Mechanics Corner A Journal of Applied Mechanics and Mathematics by DrD, #47 What Makes a Ship Move? One of the problems that often confronts engineers is the description of large, interconnected systems. Engineers tend to specialize, so that one is very knowledgeable on gears, another knows bearings, a third knows pumps, but none of them are comfortable with the whole system. In the automotive context, this is often expressed as, "How does the engine cause the car to move forward?" On the one hand, most engineers can describe the process in words, but they are far less quick to talk about equations for the whole system. Here, I will address a similar modeling question in the marine context, "What makes a ship move?" WhatMakesAShipMove.pdf
  2. 2 points
    DrD

    What Makes A Ship Move?

    What has happened? Is the sky falling? This is unprecedented!! A well thought out response to one of my posts! I am simply stunned!!! Thank you, HKS! This is the first time I have ever seen such a good response to a post. You asked about learning whole system level modeling. I suggest that you might simply want to pick some everyday systems and try to model them. A car or motorcycle is an obvious choice, but there are others such as a railroad train (starting/stopping/running down the track), a rolling mill (if you are familiar with how such systems are built), a diesel engine driven generator starting a pump motor load, or perhaps a soda bottle filling machine. At the time I first wrote this article, some 15 years ago, I was working for the US Navy in a propulsion engineering group. Most of the engineers around me were EEs, because we were looking at electric drive for ships. I found that most of them did not know much about motors, much less the rest of the system. Their knowledge was largely limited to power electronics for speed control of electric motors. They has no idea how that related to ship motion. DrD
  3. 1 point
    HKS

    What Makes A Ship Move?

    DrD, first, I want to apologize for the lack of response my colleagues and I have shown to your great content, is just a sad behavior of recent generations, to show indifference even to things that interest us. One can argue that in a greater extent is due to the massive distractions we are exposed (primarily social media) in current times and I don't see a practical solution to that problem in the near future. In any case, I'm not better than anyone in that regard, just happened that I don't want to continue wasting time in trivial things and that's the reason why I decided to take the time to respond to your post this Sunday. Second, I thank you, all of your posted content is enriching, especially from a professional growth point of view. I will do as you say, starting with the modeling of simple everyday systems while I develop my analytical skills. If it isn't a burden I will be pleased if you can review the models I'll do. I don't want you to waste time so I will take the time to produce something worth reviewing. Lastly, I can relate to your experience with the team of EEs and I could not agree more. Two years ago I was looking for design a centrifugal separator but I didn't want to use a motor and multiplier (neither gear or pulley) but directly design (and build) an electric motor capable of high rpm (I know that they already exist but I was looking for built it specifically for the work at hand), so I seek for an EE to help me and to my surprise he just relates to a lecture where they "learn" the principles of electric motor design and that was the limit of his help. Certainly, I could have done that by myself in the library. It appears that specialization along with a lack of knowledge in the basics and the general perspective of things is not exclusive to mechanical engineering. I only remain to say that I just want to be a better engineer and your content help me (and others that are silent) in that direction. Best Regards, HKS.
  4. 1 point
    HKS

    What Makes A Ship Move?

    I agree that the description of large interconnected systems is difficult for most of us. In my opinion, this lack of skill responds to two main factors: First, the mechanical engineering curriculum usually devotes more time to the teaching and evaluation of very specific topics and less time to the analysis of large interconnected systems. Second, the industry, for the most part, demands specialized personnel either to solve problems or to make small improvements in subsystems in order to obtain a small but continuous improvement that allows them to remain competitive at the lowest possible cost. Regarding the issue of education, I do not have any complaints, after all, whoever wants to learn has all the resources and tools at their disposal to do so. Similarly, regarding the behavior of the industry, I do not complain, it is a behavior that responds to more factors (economic, social and political) which I do not intend to mention here. It is known that one can succeed in the exercise of the profession in different ways and one of them is to become an expert in a specific area. So if the educational system, neither the industry nor the economic incentive are of interest for the analysis of large interconnected systems, I suppose that only people who have a desire to understand and describe these systems will do so. I believe that we all have the ability to describe those systems and if so, we would surely notice an incredible advance in the technological development since great advances are a consequence not of the improvement of very specific things but of the proposition of new approaches for the solution of a problem. The main idea that I take away after reading your article is to try to describe through equations a complete system and in doing so identify which areas I lack knowledge or skill. One point that caught my attention is the fact that all the thrust generated by the turbine reaches a single point (the seat of the thrust bearing) that although it was obvious I had not stopped to think about it and its importance in the structural design of the ship's hull. Finally, I have a question, if one wanted to develop the ability to describe systems at that level, is it enough to take systems at random and try to describe them with equations or are there books that teach methods of analyzing those systems that would be worth studying? If so, I would appreciate a recommendation. Best regards, HKS.
  5. 1 point
    Maybe that might work. Measure the thermal loss in watts for your particular time interval in which your cooling unit has to operate. Multiply that thermal/ power loss by the time interval to calculate energy/ enthalpy mostly measured in Joules or BTU.


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