# Презентация на тему: PRACTICAL LOOK TO DYNAMIC STABILITY

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## Первый слайд презентации: PRACTICAL LOOK TO DYNAMIC STABILITY

What means under “Dynamic stability” Two practical ways “how to do” table for to build diagram of Dynamic stability Which data we can get from our beautiful pictures 1

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## Слайд 2: Dynamic stability

Sometimes happens vessel floats it smooth water and then unforeseen appears squally wind or big swell and vessel get a dynamic inclination, may be for a short time, but more exceeding then inclination which could appear during static action of same moment. Let’s imagine that our vessel is upright and then unpredictable to she attached some moment under force of which vessel start heel with acceleration so as on initial period other moment which try to return vessel to initial position will be much slower. After vessel reach certain position when heeling moment will be equal to moment trying to return vessel to initial position ( Righting moment ) and acceleration will be maximum, vessel continue to heel, but already she’s acceleration will be much less. That means that moment trying to return vessel to initial position “ Righting moment” getting more then “Heeling moment”. At certain moment acceleration of vessel becomes “0”, heeling angle reach its maximum (Angle of dynamic heel) and vessel stuck in this position. After this vessel return to its initial position. Under dynamic moment called “ Heeling moment ” we use maximum attached to vessel moment which she can keep without collapse. 2

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## Слайд 3: Dynamic stability

Under dynamic stability means ability of vessel to withstand dynamic impact of heeling moment. The relative measure of dynamic stability is dynamic stability arm. Lets build a diagram looks like transverse static stability, but on axis of ordinates Y we apply “Righting moments” which we calculate with simple formula Righting moment = GZ x Displacement Please see next page. We expect that due to some external force vessel heels to 30 deg Dynamical stability determined by area under the curve of righting moments from “0” up to the heel concerned (our case 30 deg) eg it is SUM of forces (righting moments) from “0” to “30” deg in our case. 3

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## Слайд 4: Dynamic stability

For to build DYNAMIC STABILITY diagram we will use formula Righting moment = GZ x Displacement 10 20 3 0 4 0 5 0 6 0 7 0 8 0 1000 2 000 3000 4000 5000 6000 7000 8000 0 Righting moments Heel deg 4

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## Слайд 5: Dynamic stability

Just to remind you what is GZ please see picture below G B1 Z Weight force 5

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## Слайд 6: Dynamic stability

In practice usually used not diagram which we build before for dynamic stability, but we build diagram of dynamic stability basing on diagram of transverse static stability. ϴ GZ (from static transverse stability) SUM of GZ for different ϴ GZ dynamic 0 GZ 0 Ʃ = 0 0 10 GZ 10 Ʃ 10 = GZ 10 0.0873 X Ʃ 10 20 GZ 20 Ʃ 20 = 2 X GZ 10 + GZ 20 0.0873 X Ʃ 20 30 GZ 30 Ʃ30 = 2GZ10 + 2GZ20 + GZ30 0.0873 X Ʃ 30 40 GZ 40 Ʃ40 = 2GZ10 + 2GZ20 + 2GZ30 + GZ40 0.0873 X Ʃ 40 50 GZ 50 Ʃ50 = 2GZ10 + 2GZ20 + 2GZ30 + 2GZ40 + GZ50 0.0873 X Ʃ 50 60 GZ 60 Ʃ60 = 2GZ10 + 2GZ20 + 2GZ30 + 2GZ40 + 2GZ50 + GZ60 0.0873 X Ʃ 60 70 GZ 70 Ʃ70 = 2GZ10 + 2GZ20 + 2GZ30 + 2GZ40 + 2GZ50 + 2GZ60 + GZ70 0.0873 X Ʃ 70 80 GZ 80 Ʃ80 = 2GZ10 + 2GZ20 + 2GZ30 + 2GZ40 + 2GZ50 + 2GZ60 + 2GZ70 + GZ80 0.0873 X Ʃ 80 90 GZ 90 Ʃ90 = 2GZ10 + 2GZ20 + 2GZ30 + 2GZ40 + 2GZ50 + 2GZ60 + 2GZ70 + 2GZ80 + GZ90 0.0873 X Ʃ 90 6

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## Слайд 7: Dynamic stability

Other possible way for calculations (with digits) Check Ʃ 10= 0+0+0.16=0.16 GZdin10 = 0.16 x 0.0872 = 0.01 Ʃ 20 = 0.16+0.16+0.28= 0.6 GZdin20 = 0.6 x 0.0872 = 0.05 Ʃ 30 = 0.6+0.28+0.48 =1.36 GZdin30 = 1.36 x 0.0872 =0.12 and so on…. ϴ 0 10 20 30 40 50 60 70 80 GZ static Ʃ 0 0.16 0.28 0.48 0.47 0.3 0.21 0.1 -0.10 0 0.16 0.60 1.36 2.31 3.08 3.59 3.9 3.9 GZdin =0.0872 x Ʃ 0 0.01 0.05 0.12 0.2 0.27 0.31 0.34 3.9 7

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## Слайд 8: Dynamic stability

After completion of above table (one of shown before for your choice) we build dynamic stability diagram. GZdin 1 rad = 57.3 grad C D A E B ϴ ϴ dyn GZ max allowable ϴ of max heeling Maximum lever GZ point D 8

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## Слайд 9: Dynamic stability

After all this beautiful tables and pictures certainly appears question what we can do with it ? Please see page 8 For to find Heeling moment during which vessel will not collapse. Measure 1 rad eg 57.3 deg on axis of inclination ϴ From point 57.3 deg draw vertical line Draw tangent line touching dynamic stability curve from centre of coordinates Point in position where crossing your tangent line and vertical line from 1 rad give you lever GZ at which vessel collapse. Heeling moment at which vessel collapse could be found as GZ x weigh of vessel Point C give you limit of dynamic ϴ 9

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## Слайд 10: Dynamic stability

When we build diagram of dynamic stability we expect dynamic heeling moment as permanent for different angles of inclination then it’s work Will be in linear dependency from inclination and could be presented as a strait line passing through center of coordinates. For to build it we install vertical line from point 1 rad =57,3 deg and mark on it given GZ (point E) Strait line passing through center of coordinates and point E will be graph of work of Heeling moment related to force of weight of vessel. This strait line cross diagram of dynamic stability in 2 points “A” and “B”. Perpendicular from “A” to axis ϴ give you angle ϴ din in which work of Heeling moment and Upright moment will be equal. Point “B” has no practical use. If line NOT CROSS diagram of dynamic stability that means that VESSEL COLLAPSE. 10

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## Последний слайд презентации: PRACTICAL LOOK TO DYNAMIC STABILITY: After word

Here I am not talk about how to use Transverse static stability diagram for to solve questions of Dynamic stability. Everything step by step and preferably attached to practice then will be more easy to understand “for what?” I’ll be thankful to professionals who give me some feedback with own opinion about my articles. You can use my e-mail windy2000@mail.ru Or say something below my videos on You tube https:// www.youtube.com/channel/UCanTqwk9ER1uSuSofigUARQ Or https:// vk.com/id340694957 11

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