So, you can find out how much time the fore peak comes out, of course, slamming is a phenomena that is connected to the impact.
(Refer Slide Time: 15:28)
What happened is that, sometimes it turns out that that the ships fore peak comes out like that and it when it comes down, it hits here and if you actually take a point here and make a pressure, you’ll see that pressure is going like that like that, suddenly goes up very high.
When it hits here, it becomes very high. This is called as slamming and people, specially the society people wants to know slamming pressure.
Now, or you want to find out probability of slamming, how much you know or what kind of time it will slam.
Now, you see the chance is that the bow will emerge, as I said you can find out by again finding out the chances of this point coming out of water exactly same way.
But, for slamming, there is you know, people have given many speculations slamming occurrence. It turns out, (( )) see every time it hits, may not slam, you say normally that the see this is coming down with the velocity and this particular water also coming up with the velocity.
So, the relative velocity of impact, the relative velocity by which it is entering water, say, I call it v r, you know, of the bow point of this some point, if this is exceeding some some value, people say that slamming has occurred.
So, in other words you actually introduce a criteria that you say that I will tell slam has occurred, provided the rate at which it is meeting this surface, the relative velocity of that particular point exceeds some (( )) values, something like say, point 3 g or some some numbers is there. ok?
Let us just take the principle of it. Essentially it is found out that it is connected to the rate at which, see, after all the ship is coming down slowly. It see Think think of this, the ship has come out of the water fine.
So, you can tell, it has the bow has emerged, but when its coming down, its coming down very slowly. As it comes down very slowly, all though it is coming down, it may not give that pressure.
So, slamming normally is, you can imagine initiatively it is related to how fast it is coming down. You now, If you take a stone and throw like that, it gives much more impact. If we just drop, it will be much smaller.
So, you know it is connected to velocity. So, in here, the criteria that is derived is that, what is the I mean, rather, I will say other way around.
If this point is the relative velocity of that point with respect to the water surface, or you may say that the relative velocity of this point at which it is entering water exceeds or is more than some number, then you will call that it has got it has got slamming.
Now again that you can find out, because, you know now velocity, see, I know the distance. So, I know this point’s location. So, I know the relative distance of r, you know of this point particular p, which will be of course, the z of the point p minus xi at the point p, the wave height sea.
I can find out the relative displacement of that, just like I had done before; which is the z value of the point p minus the wave height. Then if I do a dot, I will get the velocity of that that also.
So, I know again exactly the same way the velocity distribution of that point. I will know that by I can draw the spectrum again, I can have an RAO of that velocity.
See, these are all Responses. Case number 1, I did Bow Bow Motion displacement 2. I did relative Bow Motion. Now, I am doing, say relative bottom motion of the bottom point.
Now, I am doing relative velocity of the bottom point. So, I say now. So, I know how much the relative velocity; how it occurs. So, I know this is my relative velocity, this is s relative velocity spectrum.
From there again, I will find out what is the chance that it has exceeded. So much so, Then I say that, it is, you know slamming percent is so much. In fact, again, everything I can find out, I can tell slamming would occur once in so many cycles.
See, I can find out what is called a, you know, average period. Then I find out that it occurs at every, say hundred second; now average be at 10 seconds. So, I will tell that every 10 cycle, that 10 times it it it slams. People like to know that you know severity of slams. This is a subjective decision, there is no objective.
You are sitting on a ship, you find that it is banging. banging You have to quantify that. There is no hard and first quantifications.
So, you tell in terms of some kind of statistical term, you say it is bad, it is bad for you, but not bad for you. So, you say I will tell that if it is more than this, is bad like that, there are some criteria. So, here you’ll say that if you say you know velocity is more than this, it is the slamming.
Similarly, once you know, now now you define slamming, to. so and so. Then you can find out the chance of slamming, number of times it slams in 1 hour. Normally, people like to know this, actually how, what is the number of times it may slam in 1 hour.
See, you can find that out also. Because, if you know it slams once in hundred seconds, then in thirty 6 hundreds, thirty 6 time it will slam.
So, all this you can find out. this we I am not going through that the typical way of deriving. But you can find out this again. Derive this much same way, I will have to go little quickly, slamming is gone.
(Refer Slide Time: 20:40)
Then propeller emergence; some time you want to do the same thing, that propeller is coming out of water. Again, you will say that propeller location, the centre plane of propeller, you define and find out relative motion. What is the chance of this coming out of water?
See again, here you take this particular propeller point, this point as p. Find out what is the chance that it comes out of water. Same thing, there is no difference.
Then some people will want to know this is propeller. You can relate this propeller emergence with with propulsive performance, because, you can now tell that if it emerges more than this thing, my first I get is so much.
So, you can relate, you can say that, look since my propeller emerges so many times, and if every time it emerges, my thrust goes down. So, my there is a reduction of thrust.
So, you can relate that to, you can say that I am going to get average sets in a sea state 5. I am going to get 20 percent this thrust.
So, you can find out how much time the fore peak comes out, of course, slamming is a phenomena that is connected to the impact.(Refer Slide Time: 15:28)What happened is that, sometimes it turns out that that the ships fore peak comes out like that and it when it comes down, it hits here and if you actually take a point here and make a pressure, you’ll see that pressure is going like that like that, suddenly goes up very high.When it hits here, it becomes very high. This is called as slamming and people, specially the society people wants to know slamming pressure.Now, or you want to find out probability of slamming, how much you know or what kind of time it will slam.Now, you see the chance is that the bow will emerge, as I said you can find out by again finding out the chances of this point coming out of water exactly same way.But, for slamming, there is you know, people have given many speculations slamming occurrence. It turns out, (( )) see every time it hits, may not slam, you say normally that the see this is coming down with the velocity and this particular water also coming up with the velocity.So, the relative velocity of impact, the relative velocity by which it is entering water, say, I call it v r, you know, of the bow point of this some point, if this is exceeding some some value, people say that slamming has occurred.So, in other words you actually introduce a criteria that you say that I will tell slam has occurred, provided the rate at which it is meeting this surface, the relative velocity of that particular point exceeds some (( )) values, something like say, point 3 g or some some numbers is there. ok?Let us just take the principle of it. Essentially it is found out that it is connected to the rate at which, see, after all the ship is coming down slowly. It see Think think of this, the ship has come out of the water fine.So, you can tell, it has the bow has emerged, but when its coming down, its coming down very slowly. As it comes down very slowly, all though it is coming down, it may not give that pressure.So, slamming normally is, you can imagine initiatively it is related to how fast it is coming down. You now, If you take a stone and throw like that, it gives much more impact. If we just drop, it will be much smaller.So, you know it is connected to velocity. So, in here, the criteria that is derived is that, what is the I mean, rather, I will say other way around.If this point is the relative velocity of that point with respect to the water surface, or you may say that the relative velocity of this point at which it is entering water exceeds or is more than some number, then you will call that it has got it has got slamming.Now again that you can find out, because, you know now velocity, see, I know the distance. So, I know this point’s location. So, I know the relative distance of r, you know of this point particular p, which will be of course, the z of the point p minus xi at the point p, the wave height sea.I can find out the relative displacement of that, just like I had done before; which is the z value of the point p minus the wave height. Then if I do a dot, I will get the velocity of that that also.So, I know again exactly the same way the velocity distribution of that point. I will know that by I can draw the spectrum again, I can have an RAO of that velocity.See, these are all Responses. Case number 1, I did Bow Bow Motion displacement 2. I did relative Bow Motion. Now, I am doing, say relative bottom motion of the bottom point.Now, I am doing relative velocity of the bottom point. So, I say now. So, I know how much the relative velocity; how it occurs. So, I know this is my relative velocity, this is s relative velocity spectrum.From there again, I will find out what is the chance that it has exceeded. So much so, Then I say that, it is, you know slamming percent is so much. In fact, again, everything I can find out, I can tell slamming would occur once in so many cycles.See, I can find out what is called a, you know, average period. Then I find out that it occurs at every, say hundred second; now average be at 10 seconds. So, I will tell that every 10 cycle, that 10 times it it it slams. People like to know that you know severity of slams. This is a subjective decision, there is no objective.You are sitting on a ship, you find that it is banging. banging You have to quantify that. There is no hard and first quantifications.So, you tell in terms of some kind of statistical term, you say it is bad, it is bad for you, but not bad for you. So, you say I will tell that if it is more than this, is bad like that, there are some criteria. So, here you’ll say that if you say you know velocity is more than this, it is the slamming.Similarly, once you know, now now you define slamming, to. so and so. Then you can find out the chance of slamming, number of times it slams in 1 hour. Normally, people like to know this, actually how, what is the number of times it may slam in 1 hour.See, you can find that out also. Because, if you know it slams once in hundred seconds, then in thirty 6 hundreds, thirty 6 time it will slam.So, all this you can find out. this we I am not going through that the typical way of deriving. But you can find out this again. Derive this much same way, I will have to go little quickly, slamming is gone.(Refer Slide Time: 20:40)Then propeller emergence; some time you want to do the same thing, that propeller is coming out of water. Again, you will say that propeller location, the centre plane of propeller, you define and find out relative motion. What is the chance of this coming out of water?See again, here you take this particular propeller point, this point as p. Find out what is the chance that it comes out of water. Same thing, there is no difference.Then some people will want to know this is propeller. You can relate this propeller emergence with with propulsive performance, because, you can now tell that if it emerges more than this thing, my first I get is so much.So, you can relate, you can say that, look since my propeller emerges so many times, and if every time it emerges, my thrust goes down. So, my there is a reduction of thrust.So, you can relate that to, you can say that I am going to get average sets in a sea state 5. I am going to get 20 percent this thrust.
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