Ship Structure Calculation with Python
The longitudinal strength of a series of 60 ships, whose main dimensions were determined, was examined. Here, the stress conditions in the case of the ship’s trochoidal wave crest and trough are examined. Calculations are made for 100 posts.
Calculations:
The Bonjean Cross Sectional Area curves of the ship were not drawn but the equations were formed. The ship loading distribution was prepared. The maximum shear force for the region where the shear force is maximum and the resultant stresses at the side 1 meter below the deck were calculated.
Calm Water Calculations:
Steel boat weights at the time of floating on Wave Hill and Calm Water were calculated by Prohaska method. In the Prohaska Method, the ship is divided into three equal parts. The stern is defined as the A section, the middle section as the B section and the fore section as C section.
While the ship is floating in calm water, the total load must be equal to the total load on the loaded waterline, but as a result of the calculations, the residual moment on this ship is calculated. Residual moment in the ship makes the ship trim at an angle. This trim, which was unintentional on the ship, was made desired by the Calm Water Trim Correction. In Calm Water Trim Correction, the ship’s longitudinal center of gravity (LCG) and the ship’s longitudinal volume center (LCB) have been brought to the same point.
For Calm Water operations, load values are taken as negative and buoyancy values as positive.Shear Force and Moment values as a result of calculations:
As seen in the graph, maximum values are observed at two points. These points are defined as critical points. As can be seen in the graphic, there are breaks at some points. The reason for the occurrence of this image is a situation originating from the points where the shear force is maximum.
Calculations for the Wave Hill:
The Prohaska method was used in calculations for the Wave Hill, as in Calm Water. In these calculations, some first and last values in the Lifting Force values are calculated as negative. The reason for this calculation is that the contoured curves do not overlap at the head and stern. Therefore, these negative values are accepted as zero.
As can be seen in the graph, maximum values were calculated at two different points and these points are critical points. As can be seen in the graph, the moments at the top of the wave are close to the mastorium. It takes minimum values in fore and aft sections.
At the top of the wave, the stress graph on the deck of the ship can be seen in the graph, and there are breaks at two points. These breaks were caused by the critical points of the cutting forces.
Calculations for Wave Pit:
Volume Ratio method was preferred instead of Prohaska method used for Wave Crest and Calm Water calculations in the wave trough. While the results of the operation in the Wave Hill and Calm Water values were calculated below the desired margin of error, the results of the calculations made with Prohaska in the Wave Trough were incorrect. Therefore, the load distributions were calculated using the Volume Ratio method and the proceedings were continued.
Calculation results made with this method are below the desired margin of error. The maximum wave height is equalized with the height of the ship deck so that the wave height does not exceed the deck of the ship.
And here is the stress of Wave Pit Situation.
Result:
Considering the calculations, results and graphics in three cases, the ship’s sinking status is out of question. Because the maximum shear force and moment values did not even reach the yield limit 235 MPa. Shipbuilding steel has a rupture limit after the yield limit. The calculated results did not even approach the yield point. On the other hand, we can come to such an opinion because we only consider the steel hull weight of the ship when making calculations. Values to be added or subtracted to the ship and not considered will affect this result.
Fatigue Condition:
S-N curve curve can be considered to examine the fatigue condition of the ship. Stress below half of the yield limit causes infinite life. For the stresses above this limit, according to the stress result calculated from the curve, it looks at the graph where it intersects with the curve and gives an idea about how long it will get tired after being exposed to the wave crest and wave trough.
Other Admissions:
The minimum cross section modulus was calculated according to German Loyd and was calculated as 4.71 m3.
It has been calculated in relation to the mid-section modulus with moment of inertia for Mastori and found to be 20.47 m4. The max distance of the neutral axis used in the calculations to the deck was calculated as 4.35 meters.
While calculating the stress 1 meter below the deck, that area was accepted as the transverse bulkhead and calculations were made.
While calculating the minimum cross section modulus, CRS and CRW coefficients are taken as 1 for unlimited service. The material factor is taken as 1.
All calculations are made with Python. Graphics are only example and ship values getting for example graphics.
