Calculation of circulation elements. Circulation of the ship, its periods and elements General provisions of the course work

The curvilinear trajectory described by the center of gravity of the ship when the rudder is shifted to a certain angle and then held in this position is called circulation.

There are three periods of circulation: maneuvering, evolutionary and the period of steady circulation. Maneuvering circulation period is determined by the beginning and end of the rudder shift, i.e. coincides in time with the duration of the rudder shift. During this period, the ship continues to move almost straight. Evolutionary period of circulation begins from the moment the rudder is shifted and ends when the elements of movement take on a steady character, i.e. will stop changing over time. The period of steady circulation begins from the end of the evolutionary period and lasts as long as the ship's rudder is in the reversed position.

The trajectory of the curvilinear movement of the vessel’s center of gravity, i.e. its circulation is characterized by the following elements:

Diameter of steady circulation (D c)- the diameter of the circle described by the ship during the steady period of circulation, which begins after the ship turns 90-180°; Tactical circulation diameter (D t)- the shortest distance between the position of the ship's centreline at the beginning of the turn and after changing the initial course by 180°. Extension l 1 the distance by which the ship's center of gravity shifts in the direction of the original course from the point at which the circulation begins to the point corresponding to a change in the ship's course by 90°. Forward displacement l 2- the distance from the initial course of the ship to the point of the center of gravity at the moment the ship turns 90°. Reverse bias l 3- the greatest distance by which the ship’s center of gravity shifts from the original course line in the direction opposite to the turn.

Circulation characteristics also include: the period of steady circulation T - the time the vessel turns 360°; angular speed of rotation of the vessel in steady circulation ω = 2π / T.

Steps to prepare the steering gear before leaving the vessel at sea

Gyrocompass directions. Gyrocompass correction

Gyrocompass meridian - the direction in which the main axis of the gyrocompass is installed

Gyrocompass heading is the direction of the ship's centerline plane, measured by the horizontal angle between the northern part of the gyrocompass meridian and the bow of the ship's centerline plane.

Gyrocompass bearing is the direction to a landmark, measured by the horizontal angle between the northern part of the gyrocompass meridian and the bearing line.

Reverse gyrocompass bearing is the direction opposite to the direction towards the object.

Gyrocompass correction is the angle in the plane of the true horizon between the true and gyrocompass meridians.

Types of ship motion. Elements of pitching

The rocking of the ship- oscillatory movements that a ship makes around its equilibrium position. There are three types of ship motion: a) vertical- vibrations of the vessel in the vertical plane in the form of periodic translational movements; b) onboard(or lateral) - oscillations of the ship in the plane of the frames in the form of angular movements; V) keel(or longitudinal) rolling - vibrations of the vessel in the center plane, also in the form of angular movements. When a ship is sailing on a rough water surface, all three types of motion often occur simultaneously or in various combinations.

Two types of oscillations of a ship when pitching: free(on still water), which occur by inertia after the cessation of the forces that caused them, and forced, which are caused by external periodically applied forces, for example, sea waves.

Pitching elements:

Amplitude of pitching (a) - the greatest deviation of the ship from its original position, measured in degrees. Pitching range(b) - the sum of two successive amplitudes (the inclination of the vessel on both sides).

Rolling period (in)- the time between two successive inclinations or the time during which the ship completes a complete cycle of oscillations, returning to the position at which the countdown began.

28 (10.1) Name the features of the steering control modes: “simple”, “following”, “automatic”

To quantify circulation, geometric and time-velocity characteristics are used.

Geometric characteristics include the following quantities:

1. Steady circulation diameter – D c = 2R c.

The diameter of the steady circulation is the diameter of the trajectory of the central circulation. vessel at a steady circulation period.

For a comparative assessment of the agility of different vessels, the value D c(or R c) are usually expressed in terms of ship hull lengths L. This ratio is called the main measure of the ship’s turning ability and this value is the relative circulation diameter ( D DOT).

For inland navigation vessels D DOT lies within the range of 2.5 3.5.

2. Tactical circulation diameter D T- the distance between the centerline of the ship on a straight course and its position when turning 180 o.

D T = (6.5)

Where L– length of the vessel, m;

T– vessel draft, m;

S R- rudder area, m2;

To OP– experimental coefficient.

usually the value D T = (0,9 – 1,2)D c.

Rice. 6.3 Vessel circulation pattern

3. Extension l 1– The distance by which the ship’s center of gravity shifts in the direction of the initial course from the point at which the circulation begins to the point corresponding to a change in the ship’s course by 90 o. For various vessels l 1 fluctuates within l 1 = (0,6 -1,5)D C.

4. Forward displacement l 2– the shortest distance from the line of the ship’s initial course to the point at which the center of gravity (CG) coincides at the moment the course changes by 90 o; usually l 2 = (0,25 -0,50)D c.

5. Reverse bias l 3– the greatest distance by which the center of gravity shifts. the vessel in the direction opposite to the direction of turn; usually l 3 = (0,01 – 0,1)D c.

Speed-time characteristics include:

1. Circulation period TC- time of turning the vessel by 360 o.

2. Linear speed of movement of C.T. vessel on steady circulation – V c.

3. Angular speed of rotation of the vessel on steady circulation ω.

The drift angle of the vessel in circulation is determined by the C.T. stern and bow respectively β C , β K And β C. .

The assessment of the vessel's reaction to the steering gear shift is determined by the response coefficient k review, which is expressed by the time ratio t o from the beginning of the shift of the ship's steering gear to the required amount of shift, to the time the ship begins to turn.

To review = (6.7)

For single vessels, this coefficient, as a rule, tends to unity, and for pushed convoys it is significantly less, since pushed convoys, after the end of the control shift, continue to move on the same course for some time.

The width of the navigation channel required for movement is determined by the circulation parameters along the stern end of ships and convoys, since the stern end of the vessel moves along a curve of a larger radius than its center of gravity.

In accordance with (Fig. 6.4) the elements of the trajectory of movement of the stern end of the vessel in circulation, it is advisable to evaluate the maximum reverse displacement of the stern end. Largest diameter called the stern circulation diameter, will characterize the circulation movement of the extreme point of the stern end of the vessel. The circulation diameter at the stern of the vessel will be

D K = D C + L P sinβ (6.8)

Where L R – distance from C.T. of the vessel to the point of application of forces Р Р (to the stern).

Knowing the magnitude D K, the navigator can estimate the size of the water area required for the turnover.

Fig.6.4. Changing the drift angle along the length of the vessel and the radius of circulation.

In table 6.1. Data on the relative radii of the steady circulation of some inland navigation vessels are presented.

Table 6.1.

6.2.3 Heel of the ship during circulation.

During the circulation process, the ship becomes heeled (Fig. 6.5). The magnitude and side of the heel angle depend on what period of circulation the ship is in. In the maneuvering period of circulation, under the influence of the steering force (R Y), the roll is directed towards the side on which shifted steering wheel. During the evolutionary period, the ship first straightens as a result of the action of the righting moment of stability, and then acquires a maximum dynamic roll outward circulation, as the centripetal force begins to act. After one or two oscillations, by the beginning of the period of steady circulation the ship acquires static roll directed outward circulation, which can be determined by the formula of G.A. Firsov

θ o max = 1.4 (6.9)

Where θ o max– maximum value of the roll angle at steady circulation;

V o– speed of the vessel on a straight course, m/sec;

Z D– ordinate of the vessel’s center of gravity relative to the main plane, m;

h- initial metacentric height of the vessel, m;

T And L– draft and length of the vessel, m.

Metocentric height ( h) – the distance between the meteorological center and the center of gravity (CG) of the vessel

Metocentre ( M) – the point of intersection of the resultant forces of water pressure with the DP.

The most dangerous roll occurs when circling at full speed, when the rudder is on the side.

The dynamic roll in the evolutionary period of circulation can exceed the roll in the steady period by more than 2 times.

For ships with low stability, the heel during circulation at full speed can reach 12 - 15 degrees. On passenger ships, a heel in circulation of more than 7 o is not desirable, and more than 12 o is considered unacceptable.

To reduce the angle of roll of the vessel during circulation, it is necessary to reduce the speed before entering circulation. The limits for changing the speed of the vessel before entering the circulation can be determined by the navigator from the Stability Information available on the vessel.

Fig.6.5 Roll of the ship during circulation.

Failure to take these factors into account can lead to tragic consequences and disasters. An example is the disaster of the motor ship "Bulgaria", which occurred on the Kuibyshev Reservoir.

The motor ship "Bulgaria", cruising along the route Kazan - Bolgar - Kazan, sank on July 10, 2011 in the Volga near the village of Syukeevo, Kamsko-Ustinsky district of Tatarstan.

According to the Rostransnadzor report, “at about 12:25 on July 10, the ship was hit by a strong gust of wind from the port side, and a heavy downpour and thunderstorm began. At this moment, the D/E "Bulgaria" entered the left turn. It should be noted that when the rudders are shifted to the left, all ships acquire an additional dynamic roll to starboard.

As a result, the roll angle was 9 degrees. “With such a list, the starboard portholes entered the water, as a result of which about 50 tons of sea water entered the ship’s compartments in 1 minute through the open portholes. To reduce the area exposed to the wind on the port side, the captain decided to head into the wind. To do this, the rudders were placed 15 to the left.” As a result, the list increased and the total amount of water entering the vessel compartment reached 125 tons per minute. After this, all the portholes and part of the main deck on the starboard side sank into the water. Over the last 5-7 seconds, there was a sharp increase in the list from 15 to 20 degrees, as a result of which the ship capsized to starboard and sank.

The commission concluded that one of the causes of the accident was the fact that the left turn maneuver was carried out without taking into account the stability of the vessel, which already had a list of 4 degrees to starboard; an additional roll to starboard caused by centrifugal force during circulation to the left; a strong wind blowing on the left side and a large sail of the ship.

Changing the speed of the vessel during circulation can be achieved by regulating the operating mode of ship propulsors by reducing the speed of rotation of the propulsion unit before circulation and during circulation, as well as by operating the propulsors in different directions - “against each other” (which is possible with a multi-shaft installation on a ship).

Reducing the speed of the vessel before circulation causes a decrease in circulation extension l 1 and its tactical diameter D T, which is clearly illustrated (Fig. 6.6).

Fig.6.6. Circulation of a motor ship at different initial speeds.

After the ship has entered a steady circulation, to increase the intensity of the turn, the rotation speed of the propulsors can be increased, which will not significantly change the geometric characteristics of the circulation.

A significant reduction in the required water area for circulation can be achieved by using a maneuver called “stationary rotation”. In this case, the vessel is stopped before starting the maneuver, the rudders are shifted to the maximum angle of the corresponding side and the propellers are given full speed in forward motion. The vessel immediately enters circulation, the dimensions of which are smaller than when moving at low speed, and the maneuver time is reduced.

The circulation diameter is influenced by:

a) rudder blade area; the larger it is, the smaller the circulation diameter.

To increase the steering area, several rudders are installed, active steering wheels and steering attachments are used.

b) distribution of cargo on the ship; if the loads are concentrated in the middle part of the vessel, then it turns faster, with a smaller circulation diameter, and if at the ends, it turns more slowly, with a larger circulation diameter;

c) in relation to the length of the vessel to its width; the larger the ratio, the larger the circulation diameter;

d) area of ​​the immersed part of the diametrical plane; the larger it is, the larger the circulation diameter;

e) trim of the ship; when trimmed to the bow, the ship has slightly better maneuverability than when trimmed to the stern.

As a conclusion, we can say that when sailing along the GDP, the ship constantly moves along curved trajectories and makes a large number of circulations. Therefore, knowledge of circulation elements is of great importance to ensure the safety of ships.

To judge the turning ability of a vessel, circulation is usually analyzed as the simplest type of curvilinear motion of a vessel.

The circulation of a vessel is its movement with the control element deflected at a constant angle, as well as the trajectory described by the center of gravity of the vessel.

In terms of time, the circulation movement of the vessel is divided into three periods:

1. Maneuvering period - during this period the control is shifted to a given angle; with further movement, the shift angle remains unchanged. During the maneuvering period, single vessels are just beginning to turn, while pushed convoys often continue to move in a straight line.

2. The evolutionary period (evolution) begins from the moment the control is transferred and continues until the moment when all parameters are established and the center of gravity of the vessel or convoy begins to describe a trajectory in the form of a circle.

3. The steady-state circulation period begins from the end of the evolutionary period and continues as long as the angle of shift of the ship's control remains constant.

The trajectory of the vessel in the third period of circulation is usually called steady circulation. A distinctive feature of the established circulation is the constancy of the movement characteristics and their small dependence on the initial conditions.

The diagram shows the following circulation characteristics used to quantify it:

− diameter of the established circulation along the CG of the vessel or train;

− diameter of the established circulation along the stern of the vessel or convoy;

− tactical circulation diameter (the distance between the ship’s DP on a straight course and after turning it by 180°);

− circulation advance (step) (displacement of the vessel’s CG in the direction of the initial straight-line motion until the vessel turns 90°);

− direct displacement of the vessel in circulation (distance from the line of the initial straight course to the CG of the vessel turned 90°);

− reverse displacement of the vessel during circulation (the greatest distance by which the vessel’s CG shifts in the direction opposite to the rudder shift);

− the ship's drift angle during the circulation (the angle between the vessel's DP and the speed vector during the circulation);

− pole of the ship’s turn (the point on the ship’s DP or its extension at which = 0).

In general, the picture of the vessel’s movement by circulation periods comes down to the following. If on a ship moving in a straight line, the controls are shifted to a certain angle, then a hydrodynamic force arises on the rudders or rotary nozzles, one of the components of which will be directed normally to the centerline plane of the ship (lateral force).

Under the influence of lateral force, the vessel shifts in the direction opposite to the direction of the control shift. A reverse displacement of the vessel occurs, the greatest value of which will be observed at the stern perpendicular point. The reverse displacement of the vessel leads to the appearance of a drift angle, and the flow, which initially ran along the center plane, begins to flow onto the side opposite to the direction of the control shift. This leads to the formation of a lateral hydrodynamic force on the ship’s hull, directed towards the repositioning of the controls and applied, as a rule, to the bow from the ship’s CG.

Under the influence of moments from lateral forces on the controls and the hull, the vessel rotates around a vertical axis in the direction of the shifted control. The centrifugal force of inertia arising in this case is balanced by the lateral steering and hull forces, and the moment of these forces is balanced by the moment of inertia forces.

During the evolutionary period, an intensive increase in the drift angle is observed, which leads to a decrease in the angle of attack of the steering wheel or rotary nozzle and a corresponding decrease in the magnitude of the steering force. Simultaneously with the increase in the drift angle, the force acting on the hull increases, and the point of its application gradually shifts towards the stern. During the same period, an increase in the angular speed of rotation and a decrease in the radius of curvature of the trajectory are observed, which, despite the decrease in the linear speed of movement, causes an increase in the centrifugal force of inertia.

Steady circulation occurs when the forces and moments acting on the controls, the ship's hull, as well as inertial forces and moments are balanced and cease to change over time. This determines the stabilization of the vessel’s motion parameters, which take constant values ​​at an angle of rotation from the initial course line of 90÷130° for single vessels and 60÷80° for pushed convoys.

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. The high pressure fuel pump rack 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 rated 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.

Vessel circulation.

Circulation and its periods.

Circulation is the process of changing the kinematic parameters of a vessel moving rectilinearly and uniformly in response to a stepwise shift of the rudder, starting from the moment it was set for testing. Trajectory, which the ship's CM describes in this process is also called circulation.

The circulation movement in time is usually divided into three periods: maneuverable, evolutionary (transitional), established. Before defining these periods, let us clarify what is meant by the steady curvilinear motion of the vessel.

Steady linear motion The movement of a vessel is called its movement in one course at a constant speed.

Steady rotational motion represents the rotation of the vessel relative to the CM with a constant angular velocity.

The curvilinear movement of the vessel consists of translational and rotational. Under steady curvilinear movement refers to the movement of a vessel in which, over time, the angular and linear velocity of the vessel's CM does not change either in magnitude or direction relative to the axes rigidly connected to the vessel. Thus, the steady curvilinear motion of the vessel is characterized by a constant angular velocity , drift angle and ground speed vessel.

In the process of circulation motion, the linear speed of the vessel takes the longest to reach a steady value. At the final stage, the approach of the linear speed of the vessel to the steady value is monotonous and slow. For large-tonnage vessels in circulation, the linear speed can reach a constant value after turning through an angle greater than 270°. In addition, in a steady circulation, the ship may experience small fluctuations in the drift angle and angular velocity. Therefore, the question arises from what point in time the vessel’s circling motion is considered steady.

Based on the boundary between evolutionary and steady-state movement accepted in the theory of automatic control, we can assume that the circulation movement of the vessel is established, when current values , , begin to differ from their established values
less than 3-5%.

Due to the fact that the drift angle on the circulation is not measured, and the linear speed of the vessel is measured with a large error, the moment after which the change in course becomes almost uniform is usually taken as the beginning of the steady circulation period. For medium-tonnage vessels, this moment occurs after the vessel has turned approximately 130°. However, studies show that during circulation motion the angular velocity is established faster than And . The drift angle and especially the linear speed of the vessel reach 3-5% closer to their steady values ​​later.

Now we can give definitions of circulation periods.

Maneuvering period (
) - the period of shifting the rudder from zero to the selected value, starting from the moment the steering device is assigned to work out the selected value.

Evolutionary period ( ) - the time interval from the moment the rudder is shifted until the moment when the curvilinear movement of the vessel becomes steady.

The steady-state period begins from the end of the second period and continues as long as the steering wheel remains in the specified position.

To evaluate and compare the controllability of ships, they are used circulation under reference conditions. The beginning of the circulation corresponds to the moment the rudder is set, and the end corresponds to the moment the vessel's DP rotates through an angle of 360°. The trajectory of such circulation is shown schematically in Fig. 3.1

Fig. 3.1 Vessel circulation diagram.

Circulation parameters.

When considering circulation, its main and additional elements are distinguished.

The following circulation parameters are the main ones.

Steady circulation diameter - the distance between the positions of the ship's DP on opposite courses during steady circulation movement, usually between the DP at the moment of a 180° turn and the DP at the moment of a 360° turn

Tactical circulation diameter - the distance between the line of the initial course and the ship’s DP after turning it by 180. Tactical diameter can be (0.9-1.2)

Extension - the distance between the positions of the ship's CM at the moment the rudder begins to shift and at the moment after turning the DP by 90, measured in the direction of the initial course. Approximately

Forward offset - the distance from the initial course line to the center of gravity of the ship, turned 90°. It is about
.

Reverse bias - the greatest deviation of the ship's center of gravity from the initial course line in the direction opposite to the rudder shift. The reverse bias is small and amounts to
.

Drift angle - the angle between the DP and the ship's speed vector.

Circulation period - the time interval from the moment the rudder begins to shift until the ship turns 360°.

Of the additional circulation parameters, the most important from the point of view of ensuring maneuvering safety are.

Half-width of sweep strip - the distance from the circulation trajectory at which the points of the body most distant from it are located during circulation;

Distance - the distance from the position of the ship's center of gravity at the initial moment of circulation to the point at which the ship's hull leaves the line of the initial course;

Maximum extension of vessel tip - the greatest distance along the initial course from the position of the ship’s center of gravity at the initial moment of circulation to the extreme tip of the ship during the maneuver (can be determined similarly maximum center of mass extension vessel, simply called maximum extension);

Maximum forward displacement of the tip of the vessel - the largest lateral deviation from the initial course line to the extreme tip of the vessel during circulation (can be determined similarly maximum forward displacement of the center of mass a vessel simply called maximum forward displacement).

The main parameter of the vessel's turning ability, the diameter of the steady circulation , depends little on the speed of the vessel before the start of the maneuver. This fact has been confirmed by numerous field tests. However, the extension of the vessel does not have this property and depends on the initial speed of the vessel. When circulating at low speed, the extension is about 10-5-20% less than the extension at full speed. Therefore, in a limited water area in the absence of wind, before making a turn at a large angle, it is advisable to slow down.