The magnitude of the centrifugal force during the circulation of the vessel depends. Circulation is usually divided into three periods: maneuverable, evolutionary and steady. Diameter of circulation described by the aft end

If the rudder blade is removed from the centerline plane (DP) of the vessel, then the vessel will move along a curved trajectory. This trajectory, described by the ship's center of gravity, is called circulation.

There are four periods of circulation: preliminary, maneuvering, evolutionary and steady circulation.

The preliminary period is the time from the moment the command is given to the helmsman until the rudder begins to shift.

Maneuvering period is the time from the moment the rudder begins to shift until the moment it ends.

The evolutionary period is the time from the moment the steering wheel is finished shifting until the moment when the elements of movement take on a stable character.

The period of steady circulation is from the moment the ship's center of gravity moves along a closed curve.

In the initial, evolutionary period of circulation, a hydrodynamic force acts on the rudder blade, removed from the DP, one of the components of which is directed perpendicular to the DP, and causes ship drift. Under the action of the propeller stop and lateral force, the ship moves forward and shifts in the direction opposite to the rudder. Therefore, along with drift, a reverse displacement of the vessel occurs in the direction opposite to the turn. The circulation trajectory is distorted at the first moment. The reverse displacement decreases as the centrifugal force of inertia increases, applied to the center of gravity of the vessel and directed towards outside turn. The reverse displacement takes the vessel outside the circulation. And although it does not exceed half the width of the vessel, it must be taken into account, especially when sharp turns in narrowness.

During the period of steady circulation, the moments of forces acting on the rudder and hull of the ship are balanced and the ship moves in a circle. Violation of the ship's motion parameters can occur when the rudder angle, ship speed, or under the influence of external forces change.

The main elements of a vessel's circulation are diameter and period. The circulation diameter characterizes the maneuverability of the vessel. There are tactical circulation diameter Dt and steady circulation diameter Dc (Fig. 163).

Tactical circulation diameter Dt - this is the distance between the initial course of the ship and after its turn by 180 ° and is 4-6 lengths of sea transport ships.

Diameter of steady circulation Dc - This is the diameter of the circle along which the ship's center of gravity moves during steady circulation.

The tactical circulation diameter is approximately 10% larger than the steady circulation diameter.

The circulation diameter depends on many factors: length, width, draft, loading, vessel speed, trim, roll, side and angle of laying, number of propellers and rudders, etc.

When circulating. The vessel's DP does not coincide with the tangent to the curvilinear trajectory of the center of gravity. As a result, a drift angle R is formed. The bow of the vessel moves inside the circulation curve, and the stern moves outward. As the speed increases, the drift angle increases, and vice versa. Due to the presence of a drift angle, a vessel in circulation occupies a strip of water larger than its size. This must be taken into account by navigators when maneuvering and passing in cramped navigation conditions.

The next element characterizing the maneuverability of the vessel is circulation period. This is the time it takes for the ship to turn 360°. It depends on the speed of the vessel and the rudder angle. With increasing speed and rudder angle, the circulation period decreases. When the rudder is shifted, the ship initially rolls in the direction of the turn. It disappears at the beginning of the movement in the circulation and with further movement the ship begins to roll in the opposite direction of the turn. This is explained by the fact that initially a heeling moment acts on the ship M"cr, arising from force R - water pressure on the rudder blade and force R lateral resistance (Fig. 164). As the vessel turns further, the centrifugal force of inertia begins to act on it TO, applied to the center of gravity of the vessel (G) and directed to the outer side of the turn, and the lateral resistance force R. These two forces form a moment M"cr, significantly larger than M"cr, which heels the ship on the side opposite to the shifted rudder (the opposite side of the turn). The above explanation is simplified. In reality, the distribution of forces during a turn is more complex.

Action of forces on circulation

Definition of Circulation Elements

Determination of circulation elements can be done in many ways: using radar, phase RNS, floating objects, on alignments, by two horizontal angles, by bearing and vertical angle, etc.

Circulation elements are determined empirically for the main modes of the main engine (full, medium, small, smallest), when turning through the port and starboard sides, in ballast and in full load.

The agility of a vessel means its ability to change the direction of movement under the influence of the rudder (controls) and move along a trajectory of a given curvature. The movement of a vessel with the rudder shifted along a curved path is called circulation. (Different points of the ship’s hull during circulation move along different trajectories, therefore, unless specifically stated, the ship’s trajectory means the trajectory of its CG.)

With such a movement, the bow of the vessel (Fig. 1) is directed into the circulation, and the angle a 0 between the tangent to the CG trajectory and the center plane (DP) is called drift angle on circulation.

The center of curvature of this section of the trajectory is called the center of circulation (CC), and the distance from the CC to the CG (point O) - circulation radius.

In Fig. 1 it can be seen that different points along the length of the vessel move along trajectories with different radii of curvature with a common center of gravity and have different drift angles. For a point located at the aft end, the radius of circulation and the drift angle are maximum. On DP the vessel has a special point - turning pole(PP), for which the drift angle is equal to zero, The position of the PP, determined by the perpendicular lowered from the CC to the DP, is shifted from the CG along the DP to the bow by approximately 0.4 of the ship’s length; The magnitude of this displacement varies within small limits on different vessels. For points on the DP located on opposite sides of the PP, the drift angles have opposite signs. The angular velocity of the vessel during circulation first quickly increases, reaches a maximum, and then, as the point of application of force Y o shifts towards the stern, decreases slightly. When the moments of forces P y and Y o balance each other, the angular velocity acquires a steady-state value.

The vessel's circulation is divided into three periods: maneuvering, equal to the time of shifting the rudder; evolutionary - from the moment the rudder is shifted until the moment when the linear and angular velocities of the vessel acquire steady-state values; steady - from the end of the evolutionary period until the steering wheel remains in the shifted position. The elements characterizing a typical circulation are (Fig. 2):

-extension l 1- the distance by which the ship’s center of gravity moves in the direction of the initial course from the moment the rudder is shifted until the course changes by 90°;

- forward displacement l 2- the distance from the line of the original course to the ship’s center of gravity at the moment when its course changed by 90°;



-reverse bias l 3- the distance by which, under the influence of the lateral force of the rudder, the ship’s center of gravity shifts from the original course line to the side, opposite direction turning;

-tactical circulation diameter D T- the shortest distance between the vessel’s DP at the beginning of the turn and its position at the moment of the course change by 180°;

- diameter of steady circulation D mouth- the distance between the positions of the vessel's DP for two successive courses, differing by 180°, with steady motion.

It is impossible to define a clear boundary between the evolutionary period and the established circulation, since the change in the elements of movement fades out gradually. Conventionally, we can assume that after a rotation of 160-180°, the movement acquires a character close to the steady state. Thus, practical maneuvering of the vessel always occurs under unsteady conditions.

It is more convenient to express circulation elements during maneuvering in dimensionless form - in body lengths:

in this form it is easier to compare the agility of different vessels. The smaller the dimensionless value, the better the agility.

The circulation elements of a conventional transport vessel for a given rudder angle are practically independent of the initial speed at steady state engine operation. However, if you increase the propeller speed when shifting the rudder, the ship will make a sharper turn. , than with an unchangeable mode of the main engine (MA).

Attached are two drawings.

The change in engine load during ship acceleration can be illustrated in Fig. 2.19. In an installation with direct transmission to a fixed pitch propeller, in the absence of release clutches, during engine start-up, the propeller simultaneously begins to rotate. At the first moment, the ship's speed is close to zero, so the load on the diesel engine will vary according to mooring screw characteristic until it intersects with the engine regulatory characteristic (section 1-2), corresponding to a certain position of the control lever of the all-mode regulator. Further, as the speed of the vessel increases, the load decreases according to the regulatory characteristic of the engine (section 2-3). At point 3 the ship finishes accelerating to a speed determined screw characteristic II. Further acceleration until the required speed of the vessel is achieved is carried out according to the screw characteristic (sections 3-5 ÷ 13-14). For this purpose, the control handle of the all-mode regulator is installed in a number of intermediate positions corresponding to the regulatory characteristics of the engine. Typically, at each intermediate position of the engine's regulatory characteristic, a delay is made necessary to achieve the appropriate speed of the vessel and to establish the thermal state of the engine. The shaded areas correspond to the engine work required additionally to accelerate the ship. Stepwise acceleration of the vessel allows for less engine work and eliminates the possibility of engine overload.

Rice. 2.19. Change in engine load during ship acceleration

In cases of emergency acceleration of the vessel, the control handle of the all-mode governor, after starting the engine, is immediately moved from the position to the position corresponding to the nominal crankshaft rotation speed. Rail fuel pump The high pressure valve is moved by the regulator to the position corresponding to the maximum fuel supply. This leads to the fact that the change in effective power and crankshaft rotation speed during the acceleration period occurs along a steeper screw characteristic (in Fig. 2.19 - along the characteristic corresponding to the relative speed of the vessel = 0.4). At point 15 the engine reaches the external nominal speed characteristic of the engine. With further acceleration of the vessel, the load on the engine will change according to the external nominal speed characteristic of the engine (section 15-14). Point 14 characterizes the load on the engine at the end of the ship's acceleration.

In Fig. Figure 2.19 shows the dynamics of changes in the load on the engine during the acceleration of the vessel under the assumption that in one case (with slow acceleration of the vessel) the loads will be mainly determined by the position of the screw characteristic, and with rapid acceleration of the vessel the engine will reach the external nominal speed characteristic. In this case, the engine is overloaded in terms of effective torque.

Above, we considered the acceleration mode in the presence of a fixed propeller. An installation with a propeller propeller ensures a faster acceleration of the vessel due to the possibility of fully using the effective power of the engines and obtaining higher traction characteristics of the vessel.

The operating conditions of the engine during ship acceleration depend on the method of controlling the fuel supply and on the law of movement of the engine controls.

Change in load on engines during vessel circulation. According to the nature of the impact of the load on the main engines, the entire circulation maneuver of the vessel should be divided into sections of entry and exit from the circulation and a section of movement with a constant circulation radius. In the first two sections, the engines operate in unsteady modes caused by changes in the ship's speed, drift angle, and rudder angle. While maintaining the circulation radius, the engines operate in steady-state modes, which are different, however, from those that occurred during the ship's forward course. During circulation, the vessel moves not only along the radius, but also with drift; its speed drops at the same speed of rotation of the propeller shaft, propellers operate in an oblique water flow, and their efficiency decreases. In this regard, the load on the engine increases. The increase in engine load depends on the speed, the shape of the ship's hull, the design of the rudders and the angle of their shift.

The curvilinear trajectory of movement of the center of gravity G when the steering wheel is shifted to a certain angle and held in this position is called circulation

There are 4 circulation periods:

  1. Preliminary period- time from the moment the command is given to the helmsman until the rudder begins to shift.
  2. Maneuvering circulation period- determined by the beginning and end of the rudder shift. those. coincides in time with the duration of the rudder shift.
  3. Evolutionary period of circulation- begins from the moment the steering is completed and ends when the elements of movement take on a steady character.
  4. Steady circulation period- begins from the moment the center of gravity moves along a closed straight line, with the steering wheel in a constant position.

Elements of the vessel's movement on the circulation: dt - tactical diameter of the circulation; Dc is the diameter of the established circulation; l 1 - extension - the distance between the positions of the vessel’s center of gravity at the initial moment of circulation and after a turn of 90°: l 2 - reverse displacement; l 3 - forward displacement - the distance from the line of the initial course to the center of gravity of the vessel after a turn of 90°. B-drift angle

In the initial, evolutionary period of circulation, a hydrodynamic force acts on the rudder blade, removed from the DP, one of the components of which is directed perpendicular to the DP, and causes the ship to drift. Under the action of the propeller stop and lateral force, the ship moves forward and shifts in the direction opposite to the rudder. Therefore, along with drift, a reverse displacement of the vessel occurs in the direction opposite to the turn. The circulation trajectory is distorted at the first moment. The reverse displacement decreases as the centrifugal force of inertia increases, applied to the center of gravity of the vessel and directed to the outer side of the turn. The reverse displacement takes the vessel outside the circulation. And although it does not exceed half the width of the vessel, it must be taken into account, especially when making sharp turns in narrow areas.

During the period of steady circulation, the moments of forces acting on the rudder and hull of the ship are balanced and the ship moves in a circle. Violation of the ship's motion parameters can occur when the rudder angle, ship speed, or under the influence of external forces change.

The main elements of a vessel's circulation are diameter and period. The circulation diameter characterizes the maneuverability of the vessel. There are tactical circulation diameter Dt and steady circulation diameter Dc.

Tactical circulation diameter Dt is the distance between the initial course of the vessel and after its turn by 180 ° and is 4-6 lengths of sea transport ships.

The diameter of the steady circulation Dc is the diameter of the circle along which the center of gravity of the vessel moves during steady circulation. The tactical circulation diameter is approximately 10% larger than the steady circulation diameter.

The circulation diameter depends on many factors: length, width, draft, loading, vessel speed, trim, roll, side and angle of laying, number of propellers and rudders, etc.

When circulating. The vessel's DP does not coincide with the tangent to the curvilinear trajectory of the center of gravity. As a result, a drift angle R is formed. The bow of the vessel moves inside the circulation curve, and the stern moves outward. As the speed increases, the drift angle increases, and vice versa. Due to the presence of a drift angle, a vessel in circulation occupies a strip of water larger than its size. This must be taken into account by navigators when maneuvering and passing in cramped navigation conditions.

The next element characterizing the maneuverability of the vessel is the circulation period. This is the time it takes for the ship to turn 360°. It depends on the speed of the vessel and the rudder angle. With increasing speed and rudder angle, the circulation period decreases. When the rudder is shifted, the ship initially rolls in the direction of the turn. It disappears at the beginning of the movement in the circulation and with further movement the ship begins to roll in the opposite direction of the turn. This is explained by the fact that at first the ship is affected by a heeling moment M"cr, arising from the force P - the water pressure on the rudder blade and the force R of lateral resistance. With further rotation of the ship, the centrifugal force of inertia K applied to the center of gravity of the ship begins to act on it. G) and directed to the outer side of the turn, and the lateral resistance force R. These two forces form a moment M"cr, significantly greater than M"cr, which heels the ship on the side opposite to the shifted rudder (the opposite side of the turn).

 

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