A fast calculation method for power reserve margin of ship main engine

Abstract

The present invention discloses a method for quickly calculating the power reserve margin of a ship main engine, comprising the following steps: defining the physical concept of the power reserve margin of the main engine; deriving the formula of the standard power output curve of the main engine; constructing the relationship between the X-axis amount of the propeller light turn margin curve and the X-axis amount of the main engine standard output power curve according to the definition of the propeller light turn margin and deriving the formula of the propeller light turn margin curve; constructing the relationship between the X-axis amount of the ship bollard tension curve and the X-axis amount of the propeller light turn margin curve according to the definition of the ship bollard tension and deriving the formula of the ship bollard tension curve; substituting the ship bollard tension curve formula into the power reserve margin calculation formula within the main engine speed restricted zone, and deriving the rapid calculation formula of the power reserve margin within the main engine speed restricted zone. The present invention provides a method for calculating the power reserve margin of the main engine from a quantitative perspective, thereby ensuring the safety and stability of the ship.

Description

Technical Field

[0001] The invention relates to the field of ship main engine power calculation, and in particular to a method for quickly calculating the power reserve margin of a ship main engine. Background Art

[0002] Affected by factors such as global warming and resource crisis, the International Maritime Organization (IMO) launched the Ship Energy Efficiency Design Index (EEDI). The implementation of this law has had a profound impact on the selection of ship main engines. Shipyards have chosen to reduce the power of the main engine to meet the EEDI requirements. When the main engine is used at reduced power, a series of problems have arisen, such as the ship passing through the speed restricted area for too long.

[0003] At present, the research on the problem of ships taking too long to pass through the speed restricted zone is still in the exploratory stage, and there is no clear parameter definition and corresponding calculation method. When a ship needs to pass through the speed restricted zone quickly or in severe sea conditions, if the main engine does not have enough power reserve, it will increase the time it takes to pass through the speed restricted zone and reduce the ship's control performance, posing a great safety hazard to the ship's operation. Summary of the invention

[0004] In view of the above problems, the present invention provides a calculation method for quickly calculating the power reserve margin of the main engine. By defining the power reserve margin in the speed forbidden zone and taking into account the propeller light rotation margin, the ship's bollard tension and the basic parameters of the main engine, the power reserve margin of the ship in the speed forbidden zone is calculated and derived, thereby ensuring the safety and stability of the ship.

[0005] In order to achieve the above object, the present invention provides a method for quickly calculating the power reserve margin of a ship main engine, the steps of which include:

[0006] S1: The power reserve margin in the ship speed restricted zone is defined as: the difference between the maximum output torque of the main engine and the ship resistance at the large end of the ship speed restricted zone / ship resistance. The calculation formula of the power reserve margin in the ship speed restricted zone is:

[0007] y PM =100%*(y L -y B ) / y B

[0008] In the formula, y L The maximum output torque of the main engine, which represents the Y-axis value of the main engine limited power output curve in actual calculation; PM y is the power reserve margin of the main engine in the speed restricted zone; B is the ship resistance, which represents the Y-axis value of the ship's mooring tension curve in actual calculations;

[0009] S2: The formula of the main engine standard power output curve is derived according to the relationship between the ship main engine power and the rotation speed. The formula of the main engine standard power output curve is:

[0010]

[0011] In the formula, y s is the Y-axis value of the host standard power output curve, y s =G m / G1, where G m is the rated power of the host, G1 is the instantaneous power of the host; x s is the X-axis value of the host standard power output curve, x s =z m / z1, where z m is the rated speed of the main engine, z1 is the instantaneous speed of the main engine;

[0012] S3: According to the definition of propeller light rotation margin, the relationship between the X-axis value of the propeller light rotation margin curve and the X-axis value of the main engine standard output power curve is constructed as follows:

[0013] x p =x s / (1+P)

[0014] In the formula, x p is the X-axis value of the propeller light turn margin curve, and P is the propeller light turn margin percentage;

[0015] S4: The formula for deriving the propeller light turn margin curve is:

[0016]

[0017] In the formula, y p It is the Y-axis value of the propeller light rotation margin curve;

[0018] S5: According to the definition of ship bollard tension, the relationship between the X-axis value of the ship bollard tension curve and the X-axis value of the propeller light rotation margin curve is constructed as follows:

[0019] x B =x p / (1-B)

[0020] In the formula, x B is the X-axis value of the ship's mooring pile tension curve, and B is the percentage of the ship's mooring pile tension coefficient;

[0021] S6: The formula for deriving the ship mooring pile tension curve is:

[0022]

[0023] In the formula, y B Y-axis value of the ship's mooring tension curve;

[0024] S7: Substitute the ship bollard tension curve formula into the main engine speed restricted zone power reserve margin calculation formula, and derive the main engine speed restricted zone power reserve margin quick calculation formula:

[0025]

[0026] In a preferred embodiment, the host limiting power output curve formula is obtained by polynomial fitting, and the specific formula of the polynomial is:

[0027]

[0028] In the formula, a, b, c, d, and e are the coefficients of each monomial respectively.

[0029] In a preferred embodiment, the relationship between the power and rotation speed of the ship's main engine is:

[0030] G=C*z 3

[0031] In the formula, G is the main engine power, C is a constant, and z is the main engine speed.

[0032] The beneficial effects of the present invention are as follows: the present invention can calculate the power reserve margin within the main engine speed restricted zone when only the propeller light rotation margin, the ship bollard tension and the ship speed restricted zone are known, thereby simplifying the calculation steps, providing a theoretical basis for the main engine selection, propeller design, shaft system design, etc. in the design stage, and laying a solid foundation for the safe and stable operation of the ship. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic flow chart of a method for calculating the power reserve margin of a main engine in a speed restricted zone of the present invention;

[0034] Figure 2 It is a schematic diagram of relevant curves of the host power reserve margin rapid calculation method of the present invention. DETAILED DESCRIPTION Specific embodiment:

[0036] In the ship design stage, the present invention can obtain the main engine standard power speed curve and the main engine power speed limit curve according to the basic parameters of the main engine, and then derive the ship mooring pile tension curve through the propeller light rotation margin and the setting parameters of the ship mooring pile tension. Through the definition of the power reserve margin in the speed restricted zone, the power reserve margin of the ship in the speed restricted zone is calculated and analyzed, and a calculation method for the main engine power reserve margin is given from a quantitative perspective. Figure 1 As shown, the present invention provides a method for quickly calculating the power reserve margin of a ship main engine, and the specific steps are as follows:

[0037] 1. Definition and formula of power reserve margin in the restricted speed zone of ship main engine

[0038] (1) Generally speaking, the greater the value of the main engine output torque is greater than the ship's resistance, the greater the power reserve margin of the ship, and the better the acceleration performance of the ship; the better the acceleration performance of the ship, the shorter the time it takes to pass through the speed restricted zone.

[0039] Based on the specific relationship between the host's limited power output curve and the host's standard power output curve, the larger the X-axis value, the smaller the difference between the two, and the lower the host's power reserve margin. Therefore, it is safer to choose the larger end of the speed restricted zone with a higher safety margin, that is, the minimum reserve margin in the speed restricted zone.

[0040] Based on this analysis, the definitions are as follows.

[0041] (2) Definition of power reserve margin in the ship speed restricted zone: at the large end of the ship speed restricted zone, the difference between the maximum output torque of the main engine and the ship resistance / ship resistance.

[0042] (3) In actual calculation, the maximum output torque of the main engine is the point corresponding to the main engine limit power output curve, and the ship resistance is the point corresponding to the ship mooring tension curve. Based on this, the theoretical formula for calculating the main engine power reserve margin in the ship speed restricted zone is derived: PM =100%*(y L -y B ) / y B , where y PM y is the power reserve margin of the main engine in the speed restricted zone; L The Y axis value of the host power output curve; B It is the Y-axis value of the ship’s mooring tension curve.

[0043] (4) After the above basic formula is defined, the following content will complete the formula derivation based on the actual meaning of each parameter and the existing theoretical formula, so that it has the conditions for practical application.

[0044] 2. Formula for the ratio of host standard output power to host speed ratio

[0045] (5) The relationship between the ship's main engine power and speed is: G = C*z 3 , where G is the main engine power; z is the main engine speed; C is a constant.

[0046] (6) According to the above formula, Where G m is the rated power of the host; G1 is the instantaneous power of the host; z m is the rated speed of the main engine; z1 is the instantaneous speed of the main engine; C is a constant.

[0047] (7) Based on the above formula, it can be deduced that: Assume that the host rated power / host instantaneous power = y, that is, G m / G1=y; At the same time, assuming that the rated speed of the main engine / the instantaneous speed of the main engine = x, that is, z m / z1=x; then we can deduce that y=x 3 , that is, the main engine power ratio and the main engine speed ratio have a cubic relationship.

[0048] (8) After the above three steps of derivation, the formula of the host standard power output curve is obtained, that is, the relationship between the host standard output power ratio and the host speed ratio, y s =x s 3 .

[0049] 3. Relationship between the ship's mooring pile tension curve and the main engine's standard output power

[0050] (9) Derivation of the X-axis value of the propeller light rotation margin curve: Based on the definition of the propeller light rotation margin, the relationship between the X-axis value of the propeller light rotation margin curve and the X-axis value of the main engine standard output power curve can be derived as follows:

[0051] x p =x s / (1+P)

[0052] Where x p is the X-axis value of the propeller light rotation margin curve, x s is the X-axis value of the main engine standard power output curve, and P is the propeller light rotation margin percentage.

[0053] (10) Derivation of propeller light rotation margin curve: Based on y p =x p 3 ,y s =x s 3 , x p =x s / (1+P), we can deduce:

[0054]

[0055] y in the formula p is the Y-axis value of the propeller light rotation margin curve, y s is the Y-axis value of the main engine standard output power curve. So far, the relationship between the Y-axis value of the propeller light rotation margin curve and the X-axis value of the main engine standard output power curve is derived.

[0056] (11) Derivation of the X-axis value of the bollard tension curve: Based on the definition of the bollard tension curve, the relationship between the X-axis value of the bollard tension curve and the X-axis value of the propeller light rotation margin curve can be derived as follows:

[0057] xB =x p / (1-B)

[0058] Where x B is the X-axis value of the ship's mooring pile tension curve, and B is the percentage of the ship's mooring pile tension coefficient.

[0059] (12) Derivation of ship mooring pile tension curve: According to y B =x B 3 ,y p =x p 3 , x B =x p / (1-B), we can deduce:

[0060]

[0061] y in the formula B is the Y-axis value of the ship mooring pile tension curve. So far, the relationship between the Y-axis value of the ship mooring pile tension curve and the X-axis value of the propeller light turn margin curve is derived.

[0062] (13) After the above four steps of derivation, the relationship between the Y-axis value of the ship's mooring force curve and the X-axis value of the main engine standard output power curve is obtained, that is, x p =x s / (1+P), and the relationship between a series of formulas is derived:

[0063]

[0064] 4. Host power limit output curve formula

[0065] (14) The host power output limit curve is usually determined by the host manufacturer based on the host's own performance and the load bearing capacity of each component.

[0066] (15) The host limited power output curve is greater than the host standard power output curve and there is a certain relationship, usually a polynomial The host power output limit curve can be fitted completely, where y L The Y axis value of the host power output curve, x s It is the X-axis quantity of the host standard output power curve, and a, b, c, d, and e are constants.

[0067] (16) In actual calculations, the host power output limit curve is usually very simple. Here, for the convenience of subsequent derivation, it is simplified to y L =cx s 2 If the curve is other formula, it can be derived similarly using the following method.

[0068] 5. Calculation formula for power reserve margin within the restricted area of ​​main engine speed

[0069] (17) According to the derivation in step (3), the power reserve margin y PM =100%*(y L -y B ) / y B , according to the above derivation and simplification, y L =cx s 2 , From this, we can derive the quick calculation formula for the power reserve margin in the host speed restricted area:

[0070] y PM =100%*(c*(1+P) 3 *(1-B) 3 / x s -1)

[0071] (18) In the formula, P is the propeller light rotation margin percentage, B is the ship's mooring tension coefficient percentage, and x s is the X-axis value of the host standard power output curve, that is, the ratio of the large-end speed in the speed restricted zone to the rated speed of the host, and c is the constant in step (14).

[0072] like Figure 1 , 2 As shown, the specific embodiment of the calculation method is:

[0073] (1) Define the physical concept of host power reserve margin and then list the basic calculation formula of power reserve margin;

[0074] (2) Based on the basic parameters of the host, draw a curve y showing the host speed and the percentage of the host standard power in the software. s According to the propeller's light rotation margin P and the main engine's standard power output curve, a curve of propeller speed and main engine power percentage is drawn, namely the propeller light rotation margin curve y P ;

[0075] (3) Based on the ship's mooring pile tension B and the propeller's light turn margin curve, draw a curve of the ship's mooring pile tension and the percentage of the main engine power, i.e., the ship's mooring pile tension curve;

[0076] (4) Using the basic parameters of the host, a curve of the host speed and the host limit power percentage is drawn in the software, i.e., the host limit power output curve;

[0077] (5) Use the formula to derive or software to fit the ship mooring pile tension curve y B And host limit power output curve y LThe relevant formula of

[0078] (6) The obtained bollard tension and limiting power curve formulas are substituted into the basic formula of the power reserve margin, and a power reserve margin calculation formula that is only related to the propeller light rotation margin, bollard tension and the large end of the speed restricted zone is derived, thus obtaining a set of efficient and accurate calculation methods.

[0079] More specifically, the calculation process with specific values ​​is:

[0080] (1) Calculation formula for power reserve margin within the engine speed restricted zone: Based on the above content, the formula is y PM =100%*(c*(1+P) 3 *(1-B) 3 / x s -1);

[0081] (2) The meaning of each letter in the formula and the assumed parameters are as follows:

[0082] a) Power reserve margin within the main engine speed restricted area: y PM ; b) Assume that the large end of the speed restricted zone accounts for 54.1% of the rated speed of the main engine, that is, the X-axis value of the main engine standard power output curve: x s =0.541; c) Assuming the host limits the power output curve That is, the constant of the main engine power limit output curve formula: c = 1.032; d) Assuming the propeller light rotation margin percentage: P = 5.6%; e) Assuming the ship bollard tension coefficient percentage: B = 17.5%;

[0083] (3) Calculation results of the embodiment of the invention

[0084] y PM =100%*(c*(1+P) 3 *(1-B) 3 / x s -1)=100%*(1.032*(1+5.6%) 3 *(1-17.5%) 3 / 0.54-1)=26.1%

[0085] The above results show that when the larger end of the ship speed forbidden zone is at 54.1% of the rated power, the propeller light rotation margin is 5.6%, and the ship bollard tension coefficient is 17.5%, the power reserve margin in the main engine speed forbidden zone is 26.1%.

[0086] The present invention discloses a method for quickly calculating the power reserve margin of a ship's main engine, which provides a method for calculating the power reserve margin of the main engine from a quantitative perspective. It provides a theoretical basis for the main engine selection, propeller design, shaft system design, etc. in the initial design stage of the ship, ensuring that the ship has sufficient power reserve margin to quickly pass through the speed restricted zone, laying a solid foundation for the safe and stable operation of the ship.

[0087] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for quickly calculating the power reserve margin of a ship main engine, characterized in that: The steps include: S1: The power reserve margin in the ship speed restricted zone is defined as: the difference between the maximum output torque of the main engine and the ship resistance at the large end of the ship speed restricted zone / ship resistance. The calculation formula of the power reserve margin in the ship speed restricted zone is: and PM =100%*(and L -and B ) / and B In the formula, y L The maximum output torque of the main engine, which represents the Y-axis value of the main engine limited power output curve in actual calculation; PM y is the power reserve margin of the main engine in the speed restricted zone; B is the ship resistance, which represents the Y-axis value of the ship's mooring tension curve in actual calculations; S2: The formula of the main engine standard power output curve is derived according to the relationship between the ship main engine power and the rotation speed. The formula of the main engine standard power output curve is: In the formula, y s is the Y-axis value of the host standard power output curve, y s =G m / G1, where G m is the rated power of the host, G1 is the instantaneous power of the host; x s is the X-axis value of the host standard power output curve, x s =z m / z1, where z m is the rated speed of the main engine, z1 is the instantaneous speed of the main engine; S3: According to the definition of propeller light rotation margin, the relationship between the X-axis value of the propeller light rotation margin curve and the X-axis value of the main engine standard output power curve is constructed as follows: x p =x s / (1+P) In the formula, x p is the X-axis value of the propeller light turn margin curve, and P is the propeller light turn margin percentage; S4: The formula for deriving the propeller light turn margin curve is: In the formula, y p It is the Y-axis value of the propeller light rotation margin curve; S5: According to the definition of ship bollard tension, the relationship between the X-axis value of the ship bollard tension curve and the X-axis value of the propeller light rotation margin curve is constructed as follows: x B =x p / (1-B) In the formula, x B is the X-axis value of the ship's mooring pile tension curve, and B is the percentage of the ship's mooring pile tension coefficient; S6: The formula for deriving the ship mooring pile tension curve is: In the formula, y B Y-axis value of the ship's mooring tension curve; S7: Substitute the ship bollard tension curve formula into the ship speed restricted zone power reserve margin calculation formula, and derive the rapid calculation formula of the main engine speed restricted zone power reserve margin:

2. According to claim 1, the method for quickly calculating the power reserve margin of a ship main engine is characterized in that: The host power output limiting curve formula is obtained by polynomial fitting, and the specific formula of the polynomial is: In the formula, a, b, c, d, and e are the coefficients of each monomial respectively.

3. The method for quickly calculating the power reserve margin of a ship main engine according to claim 1 is characterized in that: The relationship between the ship's main engine power and speed is: G=C*z 3 In the formula, G is the main engine power, C is a constant, and z is the main engine speed.

4. According to claim 3, the method for quickly calculating the power reserve margin of a ship main engine is characterized in that: The relationship between the ship's main engine power and speed is: Where G m is the rated power of the host; G1 is the instantaneous power of the host; z m is the rated speed of the host; z1 is the instantaneous speed of the host.

5. According to claim 2, the method for quickly calculating the power reserve margin of a ship main engine is characterized in that: The host limiting power output curve formula is: y L =cx s 2 。 6. The method for quickly calculating the power reserve margin of a ship main engine according to claim 5 is characterized in that: c＝1.032，

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