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Anonymous users2024-02-07When the ship floats in still water, it is subjected to two forces, one is the gravity caused by the weight of the ship itself and the items and personnel it carries, and the direction is vertically downward, and its point of action is called the center of gravity, and the other is the buoyancy formed by the water pressure outside the ship, which is vertically upward, which is equal to the weight of the same volume of water discharged by the ship, and is called the displacement.
Its point of action is located in the center of the drainage volume and is called the center of buoyancy.
The equilibrium floating state of the ship can be divided into normal floating state, trim state, horizontal roll state, and arbitrary state. In order to ensure the safety of the ship, the ship must have a certain reserve buoyancy (also called reserved buoyancy). Reserve buoyancy refers to the buoyancy generated by the watertight space between the ship's main deck below and the waterline.
The positive floating state refers to the situation in which the drafts of the nose, stern, and left and right sides of the ship are equal. Trim refers to a situation in which the left and right drafts are equal but the head and tail drafts are unequal. The bow draft is greater than the stern draft is called the first tilt, and the stern draft is greater than the bow draft is called the tail tilt. to keep the propellers.
A certain water depth, improve the efficiency of the propeller, a voyage of unloaded ships should have a certain amount of tail roll.
The pitch state refers to the situation that the bow and tail drafts are equal but the left and right drafts are not equal, and the nose is not allowed to appear during the voyage. An arbitrary state is one in which there is both a horizontal and a vertical and horizontal tilt.
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Anonymous users2024-02-06Float principle and state.
The boat is subjected to two forces while floating in still water. One is the gravity caused by the weight of the ship itself, the items and people it carries, and the direction is vertically downward, and its point of action is called the center of gravity; One is the buoyancy formed by the water pressure outside the ship, which is vertically upward, which is equal to the weight of the same volume of water discharged by the ship, and weighs the displacement.
Its point of action is located in the center of the drainage volume and is called the center of buoyancy.
The conditions for the equilibrium of the boat on the water are that gravity is equal to buoyancy, and the center of gravity and center of buoyancy are on the same plumb line. If the center of buoyancy and center of gravity of the boat are not on the same plumb line, the boat will tilt, changing the shape of the displacement volume and the position of the center of buoyancy until the center of buoyancy is readjusted to the same plumb line as the center of gravity to equilibrium.
There are four types of floating states of the ship: positive floating, horizontal tilting, trimming and arbitrary tilting. If the longitudinal coordinates and transverse coordinates of the center of gravity of the ship correspond to the longitudinal coordinates and transverse coordinates of the center of buoyancy, the ship is in a state of positive floating, and the bow and stern of the ship and the draft of the starboard and starboard sides are equal, otherwise there will be any tilt of the ship, trim or both.
Generally, the design of the ship is required to maintain positive floating, or slightly tail roll. In the operation of the ship, the cargo stowage calculation should be carried out, and the loading weight and the position of the center of gravity should be controlled to obtain a good floating state.
Static stability.
A floating object is stable if it tends to return to an equilibrium position after a small displacement. For example, a floating object will generally have vertical stability, and if the object is gently pushed downward, it will create a greater buoyant force, which will push the object back into place in the case of an imbalance in gravity.
Rotational stability is very important for pontoons. Given a small angular displacement, the ship may return to its original position (stable), move away from its original position (unstable), or remain in its original position (neutral).
Rotational stability depends on the relative lines of action of the forces acting on the object. The upward buoyancy force on an object acts through the center of buoyancy, which is the center of mass of the fluid displacement volume.
The gravitational force acting on an object acts through its center of gravity. If the center of gravity is lower than the center of buoyancy, then the buoyant object will be stable because any angular displacement will produce a "righting moment".
The stability of a buoyant object on the surface of the water is complex, and the center of gravity may remain stable even if it is above the center of buoyancy, provided that when disturbed from the equilibrium position, the center of buoyancy moves further to the same side and the center of gravity moves, thus providing a positive righting moment. If this happens, then the floating object is said to have a positive centering height.
This situation usually applies to a range of yalt, beyond which the center of buoyancy does not move enough to provide a positive righting moment, and the object becomes unstable. During a dip disturbance, it is possible to change from positive to negative and vice versa more than once, and many shapes are stable in more than one position.
The above content refers to Encyclopedia - Ship Buoyancy.
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