登录查看更多内容

How do you measure and calculate LCG accurately for complex hull shapes and structures?

由人工智能和领英社区提供技术支持

How do you measure and calculate LCG accurately for complex hull shapes and structures? LCG, or longitudinal center of gravity, is a crucial parameter for naval architects, as it affects the stability, trim, and resistance of a vessel. In this article, you will learn how to determine and estimate LCG for different types of hulls and superstructures, using various methods and tools.

本文章的要点总结

Numerical methods for complex shapes:

Use Simpson's or trapezoidal rules to divide the hull into sections. Calculate each section's area and centroid, then sum their moments to estimate the LCG accurately.### *Software tools for precision:Leverage tools like AutoCAD or Maxsurf to create 3D models and simulate weight distribution. These tools provide detailed reports and graphs, enhancing your LCG calculations.

本摘要由 AI 和以下专家提供支持

1 What is LCG and why is it important?

LCG is the distance from a reference point, usually the aft perpendicular, to the center of gravity of the whole vessel, including the hull, the cargo, the fuel, the equipment, and the superstructure. LCG determines how the vessel balances along its longitudinal axis, and how it reacts to external forces, such as waves, wind, and propulsion. A vessel with a large LCG will tend to have a large trim angle, which means it will be tilted forward or backward. This can reduce the efficiency and performance of the vessel, as well as increase the risk of capsizing or flooding.

添加您的观点

Alejandro Lagunas

Port Captain, Merchant Maritime Deck Officer, Captain A-II/2, Marine Operation. Master in Operation Logistics and Management , Industrial Engineer.
举报内容
La estructura de la nave en su desplazamiento en rosca en base a cálculos posee un centro de gravedad, vertical, transversal y longitudinal. Este ultimo es un punto que representa la distribución de todos los pesos a lo largo de la nave, los cuales son enormemente influenciados por la distribución de la carga y el lastre. Entonces el LCG es un punto que representa la distribución longitudinal de los pesos resultante. Cabe mencionar que cada uno de los pesos de la nave tienen su propio Lcg, y no tiene su resultante una injerencia directa con el asiento, sino más bien dependerá de cómo interactúa con respecto a la ubicación del centro de boyantes.

已翻译

赞

2 How to measure LCG for simple hull shapes?

For simple hull shapes, such as prisms, cylinders, or cones, you can measure LCG by applying the principle of moments. This means that the sum of the moments of each part of the vessel around the reference point must be equal to zero. A moment is the product of the weight of a part and its distance from the reference point. For example, if you have a rectangular prism hull with a uniform density, you can calculate its LCG by dividing its length by two. If you have a cylindrical hull with a uniform density, you can calculate its LCG by multiplying its length by 0.5 minus 0.125 times the ratio of its diameter to its length.

添加您的观点

3 How to estimate LCG for complex hull shapes?

For complex hull shapes, such as those with curves, bulges, or cutouts, you can estimate LCG by using numerical methods, such as Simpson's rules or trapezoidal rules. These methods involve dividing the hull into small sections, calculating the area and the centroid of each section, and then summing up the moments of each section around the reference point. The centroid is the point where the section would balance if it were cut out and placed on a pivot. The area and the centroid of each section can be obtained by using geometric formulas, or by using software tools, such as CAD or Excel.

添加您的观点

Peter Dandy

M.Eng C.Eng FRINA
举报内容
It's important to remember that numerical methods such as Simpson's rules and trapezoidal rules work for calculating volumes and their centroids as opposed to weight and weight centroid. Therefore, to use these methods, one must have a good understanding of any density differences in certain sections, e.g. extra frames/stiffeners, thicker plate etc at different sections. A spreadsheet based weight summation where frames, plates, decks, equipment etc are itemised along with their centroids is a better approach, with increasing level of granularity as the design progresses.

已翻译

赞

4 How to calculate LCG for superstructures and other components?

To calculate LCG for superstructures and other components, such as masts, funnels, cranes, or containers, you need to know their weight and their location on the vessel. You can obtain their weight from the manufacturer's specifications, or by using empirical formulas based on their dimensions and material. You can obtain their location by measuring their distance from the reference point, or by using a coordinate system that aligns with the vessel's axes. Once you have the weight and the location of each component, you can calculate their moments around the reference point, and then add them to the moments of the hull.

添加您的观点

Alejandro Lagunas

Port Captain, Merchant Maritime Deck Officer, Captain A-II/2, Marine Operation. Master in Operation Logistics and Management , Industrial Engineer.
举报内容
Convengamos que las estructuras fijas de la nave que pertenecen a su desplazamiento en rosca previo a la botadura, cuentan con la debida identificación en sus tres dimensiones del centro de gravedad. Si por algún motivo, el armador decide alterar la superestructura del buque, el arquitecto Naval deberá previamente estimar la ubicación del centro de gravedad de la nave, en base a cálculos, y corroborarlo posteriormente mediante experimento de inclinación para determinar su ubicación vertical. Longitudinalmente también posible la ubicación del centro de gravedad de manera experimental, podemos calcular mediante la lectura de calados el cambio de asiento que produjo la instalación de este nueva parte fijo de la nave

已翻译

赞

5 How to check and adjust LCG?

Once you have calculated LCG for the whole vessel, you need to check and adjust it to ensure that it meets the design requirements and the operational conditions. You can check LCG by comparing it with the longitudinal center of buoyancy (LCB), which is the center of gravity of the displaced water. The difference between LCG and LCB is called the longitudinal metacentric height (LM), which is a measure of the longitudinal stability of the vessel. A positive LM means that the vessel is stable, while a negative LM means that the vessel is unstable. You can adjust LCG by shifting or adding weight to different parts of the vessel, such as ballast tanks, fuel tanks, or cargo spaces. You can also adjust LCG by modifying the hull shape or the superstructure design.

添加您的观点

Capt. Amarinder Singh Brar, LLM, AFNI
举报内容
Another example of ‘power of AI’ Difference between LCG & LCB will cause a change in trim. The vessel will trim itself until LCB and LCG are vertically above each other to attain equilibrium. Therefore ‘LM’, a term I’ve never heard before in naval architecture or ship stability, as discussed above will always be zero. What the article wants to talk is about VCG~VCB which, when considered with another parameter called BM, will eventually yield GM. Positive values are good, zero is ‘mmm it depends where you are’ and negative values will demand lifeboats in water. Even within positive GM, too little or too large are not good. GM is used by mariners as a measure of stability during cargo ops, port departure, enroute and upon arrival port.

已翻译

赞
Peter Dandy

M.Eng C.Eng FRINA
举报内容
As written, this is incorrect. The positions of the vessel's centre of buoyancy and centre of gravity are just two points in space. These two points can be described in the longitudinal, vertical and transverse axes. If the two points have a different longitudinal value, when you float the ship, it will take up a trim angle, which moves the LCB and settles when they LCB and LCG are equal.

已翻译

赞
Alejandro Lagunas

Port Captain, Merchant Maritime Deck Officer, Captain A-II/2, Marine Operation. Master in Operation Logistics and Management , Industrial Engineer.
举报内容
La verdad es que no estoy muy de acuerdo con lo anterior descrito, porque se ajusta más bien a la definición de la ubicación del centro de gravedad vertical con respecto al Metacentro. Simplemente el centro de gravedad longitudinal se determina en base a cálculos , que, en su mayoría de las veces se realiza por medio de cálculos de momentos con respecto a un punto en particular que podría ser el centro de Eslora de la nave o la perpendicular de popa.

已翻译

赞

6 How to use software tools for LCG calculation?

There are many software tools available for naval architects that can help them with LCG calculation, such as AutoCAD, Rhino, Maxsurf, Orca3D, or ShipConstructor. These tools can create 3D models of the vessel, calculate the hydrostatic properties, such as displacement, LCB, and LM, and simulate the effects of weight distribution, loading conditions, and environmental factors on LCG. These tools can also generate reports, graphs, and drawings that can facilitate the communication and documentation of LCG calculation.

添加您的观点

William George

Marine Educator, Consultant and Expert Witness at William E. George and Associates, LLC
举报内容
Assuming the hydrostatic are calculated for the draft and zero Trim: Trim x MTC = Trim Moment Trim Moment / Displacement = TRIM ARM TRIM ARM = LCB - LCG LCG = LCB + or - TRIM ARM LCG will always be toward the deeper draft.

已翻译

赞
Peter Dandy

M.Eng C.Eng FRINA
(已编辑)
举报内容
2. Longitudinal stability is the ability for the vessel to return to level trim (assuming LCG and LCB are the same) after some external load is removed, e.g. from wind or waves. This ability is partially affected by the height difference between the COB and COG, usually described as BG, but mainly affected by the vessel's waterplane area and its longitudinal distribution

已翻译

赞

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?

添加您的观点

Naval Architecture

+ 关注

给文章评分

我们借助人工智能创建了此文章。您认为这篇文章怎么样？

很棒不太好

举报此文章

查看全部

How do you measure and calculate LCG accurately for complex hull shapes and structures?

1

2

3

4

5

6

7

1 What is LCG and why is it important?

2 How to measure LCG for simple hull shapes?

3 How to estimate LCG for complex hull shapes?

4 How to calculate LCG for superstructures and other components?

5 How to check and adjust LCG?

6 How to use software tools for LCG calculation?

7 Here’s what else to consider

Naval Architecture

给文章评分

感谢您的反馈

更多Naval Architecture相关文章

更多相关阅读内容