Equivalent layer ice conversion method of snow in continuous icebreaking resistance of icebreaker

Abstract

The invention discloses an equivalent layer ice conversion method for snow in continuous icebreaking resistance of an icebreaker, which comprises the following steps of: dividing the icebreaking resistance into collision resistance, bending failure resistance and immersion resistance, and respectively determining a conversion relation between the actual layer thickness of the snow and the layer thickness of the snow equivalent to ice when the collision resistance, the bending failure resistance and the immersion resistance are calculated; the ice breaking resistance of the snow is calculated according to a calculation formula of the ice breaking resistance of the ice, and the layer thickness of the ice in the calculation formula of the ice breaking resistance of the ice is equal to the layer thickness of the snow equivalent to ice. The ice breaking resistance estimation result obtained by the method is more accurate.

Description

Technical Field

[0001] The invention relates to the technical field of ships, and in particular to a method for converting the equivalent layer of ice of snow in the continuous icebreaking resistance of an icebreaker. Background Art

[0002] The polar regions are rich in resources, and polar routes can greatly shorten the journey from Asia to Europe, so economic activities in the polar regions are becoming more frequent. Whether it is an icebreaker or a ship that can sail autonomously in the polar regions, it needs to have a certain icebreaking capability. The prediction of icebreaking resistance is one of the key technologies in the design of polar ships, which determines the line shape of the ship and the selection of the main engine power. The current resistance estimation methods include empirical formulas and numerical simulations, and the evaluation object is the icebreaking resistance performance of the ship in the ice layer state. In addition to the ice layer, the actual polar channel state also has snow on the ice layer. The physical properties of snow are different from those of ice, and the resistance form brought to the ship during the icebreaking process is also different. Since the physical properties of snow are difficult to construct in numerical simulation, the current common practice internationally is to simplify the snow model, equating the specified thickness of snow to a certain thickness of ice layer, and then numerically simulate or convert the single ice layer mode using empirical formulas. This approach greatly simplifies the evaluation process, but there are problems with accuracy. The composition of the resistance of the ice layer to the ship in the typical icebreaking process can be mainly divided into four parts: collision resistance, ice layer bending damage resistance, ice layer potential energy reduction resistance, and friction resistance between the ice layer and the hull. Among these four parts, the bending damage strength of snow is much smaller than that of ice layer, but the friction coefficient of snow is greater than that of ice layer. Snow will melt in water, but ice will still bring relatively large friction resistance to the hull in water. Therefore, the different physical properties of snow and ice lead to the fact that the resistance brought by snow to the ship during the icebreaking process is completely different from that of ice. If the thickness of snow is simply equivalent to the thickness of ice, the principle of evaluation is flawed and the accuracy of the result cannot be guaranteed.

[0003] With more and more ships sailing in polar regions, the assessment of polar ships' icebreaking resistance is becoming more and more important. Currently, the more common assessment techniques are empirical formula methods and numerical simulation methods. Among them, the empirical formula assessment method uses a more commonly used method, which divides the icebreaking resistance into three parts: impact resistance, ice bending damage resistance, and immersion resistance (including changes in ice potential energy and friction resistance between the ice and the hull). The empirical formula assessment only includes the thickness of the ice layer, not the thickness of the snow. It is common in polar regions that the upper part of the ice layer is covered with a certain thickness of snow. Therefore, this empirical formula has certain limitations in use. In order to solve the problem of evaluating the resistance brought by snow to ships, the International Towing Tank Conference (ITTC) gave the concept of equivalent ice thickness, that is, snow is equivalent to a certain thickness of ice layer for resistance assessment, h′ i =h i +k e *h SN , where h i is the thickness of the ice, h SN is the thickness of snow, k e Empirical coefficient, h′ i is the equivalent total ice thickness taking into account the snow thickness.

[0004] For k e Some international scholars have given their own methods for estimating the value of e The value range is 0.5~1.5. Some scholars have suggested a value of 1 / 3, and some believe that if the snow is new, the value should be 0.

[0005] Some people also think that if the density of snow is 400kg / m 3 , the density of ice is 920kg / m 3 , then k e The value of is approximately 1.83.

[0006] Some scholars have also given the following calculation method: e =0.284+0.575*10 -3 SWB -0.164 h I -0.048V, where V is the ship speed, S WB is the wet bottom area.

[0007] In summary, the estimated thickness of snow equivalent ice is in a relatively large range, ranging from about 1 / 3 to about 1.8. If the thickness of the snow is taken as 0.3 meters, the equivalent ice thickness can be from 0.1 meters to 0.5 meters. The span is relatively large, which is not conducive to estimating icebreaking resistance. If the equivalent ice thickness of snow is too small, it may lead to insufficient icebreaking ability. If it is too large, it may cause the configuration of installed power to be too large, resulting in an increase in initial investment or waste of host power.

[0008] The existing snow equivalent ice thickness estimation method has the following disadvantages:

[0009] Most equivalent conversion formulas are relatively simple, and do not reflect the composition mechanism of snow or ice in icebreaking resistance, nor do they reflect the differences in physical and mechanical properties between snow and ice. In addition, the numerical differences between different estimation methods are relatively large. Such input conditions overestimate the icebreaking resistance. According to the snow thickness of 0.3 meters, the equivalent ice thickness can range from 0.1 meters to 0.5 meters. If the ice thickness of 2.0 meters is added, the ice thickness used to calculate the icebreaking resistance can range from 2.1 meters to 2.5 meters, and the total ice thickness differs by nearly 20%. According to the components of icebreaking resistance, the relationship between different resistance parts and ice thickness is different. According to the empirical formula, the relationship between the impact ice load part of icebreaking resistance and ice thickness is a square relationship, the resistance part caused by the bending damage of ice layer and ice thickness is a 1.5-power relationship, and the friction resistance part and ice thickness are linear. Therefore, a 20% difference in ice thickness may result in a difference of more than 20% in the total resistance value estimate. Such a fluctuation is unbearable for ship design and may lead to major changes in ship type plans. Summary of the invention

[0010] The technical problem to be solved by the present invention is to overcome the above-mentioned defects in the prior art and provide a method for converting the equivalent layer of ice of snow in the continuous icebreaking resistance of an icebreaker.

[0011] The present invention solves the above technical problems through the following technical solutions:

[0012] A method for converting the equivalent layer of ice of snow in the continuous icebreaking resistance of an icebreaker, comprising:

[0013] The ice breaking resistance is divided into collision resistance, bending damage resistance and immersion resistance, and the conversion relationship between the actual thickness of snow and the thickness of snow equivalent to ice is determined respectively when calculating the collision resistance, bending damage resistance and immersion resistance;

[0014] The ice-breaking resistance of snow is calculated using the calculation formula of the ice-breaking resistance of ice, wherein the layer thickness of ice in the calculation formula of the ice-breaking resistance of ice is equal to the layer thickness of snow equivalent to ice.

[0015] Furthermore, when calculating the impact resistance, the actual thickness of the snow layer H SN The thickness of the ice layer equivalent to snow is H′ ICE The relationship between them is: ICE =k c *H SN ;

[0016] Among them, k c is the collision resistance equivalent coefficient, k=σ SN / σ ICE ; Among them, σ ICE is the bending failure strength of ice, σ SN The bending strength of snow.

[0017] Furthermore, in the snow breaking resistance, the collision resistance R C The calculation formula is:

[0018]

[0019] Among them, σ0 is the bending failure strength of ice, μ is the friction coefficient of ice, is the bow column inclination angle, α is the waterline angle, H1=H′ ICE .

[0020] Furthermore, when calculating the bending failure resistance, the actual thickness of the snow layer H SN The thickness of the ice layer equivalent to snow is H″ ICE The relationship between them is: H″ ICE =k b *H SN ;

[0021] Among them, k b is the equivalent coefficient of bending failure resistance; k=σ SN / σ ICE ; Among them, σ ICE is the bending failure strength of ice, σ SN The bending strength of snow.

[0022] Furthermore, among the resistances to breaking ice of snow, the bending resistance R b The calculation formula is:

[0023]

[0024] Among them, σ0 is the bending failure strength of ice, μ is the friction coefficient of ice, is the bow column inclination angle, α is the waterline angle, H2=H″ ICE ; B is the width of the ship at the waterline;

[0025] m=E / (12*(1-v 2 )*g*ρ sea ;

[0026] Where E is Young's modulus, v is Poisson's ratio, g is the acceleration due to gravity, ρ sea is the density of sea water.

[0027] Furthermore, when calculating the immersion resistance, the actual thickness of the snow layer H SN Thickness of the layer equivalent to snow and ice H″′ ICE The relationship between them is: H″′ ICE =k s *H SN ;

[0028] Among them, k s is the equivalent coefficient of immersion resistance;

[0029] k s =(ρ sea -ρ snow ) / (ρ sea -ρ ice );

[0030] Among them, ρ sea is the density of seawater, ρ snow is the density of snow, ρ ice is the density of ice.

[0031] Furthermore, in the snow breaking resistance, the immersion resistance R s The calculation formula is:

[0032]

[0033] Among them, δ ρ is the density difference between water and ice; g is the acceleration due to gravity;

[0034] H3=H″′ ICE ;

[0035] T is the draft of the ship; B is the width of the ship at the waterline; μ is the friction coefficient of ice; A μ A is the flat bottom area of ​​the ship; f is the bow area; is the bow column inclination angle, α is the waterline angle,

[0036] The beneficial effects of the present invention are as follows: the present invention provides snow equivalent ice thickness conversion methods for different ice-breaking resistance parts, according to their ice-breaking mechanisms, and with reference to the physical properties of ice and snow; the equivalent ice thickness estimation methods provided by the present invention for different ice-breaking mechanisms are more accurate than specifying a calculated value of the equivalent ice thickness of snow, and the ice-breaking resistance estimation result obtained by estimating the equivalent ice thickness of snow using the present invention is more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of the main features of the hull of a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0038] A preferred embodiment is given below, and the present invention is described more clearly and completely in conjunction with the accompanying drawings.

[0039] A method for converting the equivalent layer of ice of snow in the continuous icebreaking resistance of an icebreaker, comprising:

[0040] The ice breaking resistance is divided into collision resistance, bending damage resistance and immersion resistance, and the conversion relationship between the actual thickness of snow and the thickness of snow equivalent to ice is determined respectively when calculating the collision resistance, bending damage resistance and immersion resistance;

[0041] The ice-breaking resistance of snow is calculated using the calculation formula of the ice-breaking resistance of ice, wherein the layer thickness of ice in the calculation formula of the ice-breaking resistance of ice is equal to the layer thickness of snow equivalent to ice.

[0042] In this method, the icebreaking resistance is divided into collision resistance, bending damage resistance and immersion resistance, and the calculation is divided into three parts.

[0043] Part 1: When calculating the impact resistance, the actual thickness of the snow layer H SN The thickness of the ice layer equivalent to snow is H′ ICE The relationship between them is: ICE =k c *H SN ;

[0044] Among them, k c is the collision resistance equivalent coefficient, k=σ SN / σ ICE ; Among them, σ ICE is the bending failure strength of ice, σ SN The bending strength of snow.

[0045] Among the resistances of snow breaking ice, the collision resistance R C The calculation formula is:

[0046]

[0047] Among them, σ0 is the bending failure strength of ice, μ is the friction coefficient of ice, is the bow column inclination angle, α is the waterline angle, H1=H′ ICE .

[0048] Head column inclination and the waterline angle α, such as Figure 1 shown.

[0049] Figure 1 Where T is the draft of the ship, L is the length of the ship at the waterline, and B is the width of the ship at the waterline.

[0050] Part 2: When calculating the bending failure resistance, the actual thickness of the snow layer H SN The thickness of the ice layer equivalent to snow is H″ ICE The relationship between them is: H″ ICE =k b *H SN ;

[0051] Among them, k b is the equivalent coefficient of bending failure resistance; k=σ SN / σ ICE ; Among them, σ ICE is the bending failure strength of ice, σ SN The bending strength of snow.

[0052] Among the resistances to breaking ice of snow, the bending resistance R b The calculation formula is:

[0053]

[0054] Among them, σ0 is the bending failure strength of ice, μ is the friction coefficient of ice, is the bow column inclination angle, α is the waterline angle, H2=H″ ICE ; B is the width of the ship at the waterline;

[0055] m=E / (12*(1-v 2 )*g*ρ sea ;

[0056] Where E is Young's modulus, v is Poisson's ratio, g is the acceleration due to gravity, ρ sea is the density of sea water.

[0057] Part 3: When calculating the immersion resistance, the actual thickness of the snow layer H SN Thickness of the layer equivalent to snow and ice H″′ ICE The relationship between them is: ICE =k s *H SN ;

[0058] Among them, k s is the equivalent coefficient of immersion resistance;

[0059] k s =(ρ sea -ρ snow ) / (ρ sea –ρ ice );

[0060] Among them, ρ sea is the density of seawater, ρ snow is the density of snow, ρ ice is the density of ice.

[0061] Among the resistances to breaking ice of snow, the immersion resistance R s The calculation formula is:

[0062]

[0063] Among them, δ ρ is the density difference between water and ice; g is the acceleration due to gravity;

[0064] H3=H″′ ICE ;

[0065] T is the draft of the ship; B is the width of the ship at the waterline; μ is the friction coefficient of ice; A μ A is the flat bottom area of ​​the ship; f is the bow area; is the bow column inclination angle, α is the waterline angle,

[0066] Figure 1 The above parameters are shown in FIG.

[0067] The present invention is based on the ice breaking mechanism and the composition of its resistance, and the collision resistance R C , bending failure resistance R b , immersion resistance R S The equivalent ice thickness is given respectively.

[0068] The present invention innovates the equivalent ice thickness method of snow in ice breaking resistance estimation:

[0069] 1. According to the morphological characteristics of ice breaking, the ice breaking resistance is divided into impact resistance, bending damage resistance and immersion resistance, and the equivalent ice thickness conversion methods of snow are given respectively.

[0070] 2. In the calculations related to the hull line characteristic values, an exhaustive calculation was performed based on the mainstream characteristic value range of the icebreaker line, and an average value was given based on the results with a smaller fluctuation range, thus realizing a unified calculation method for equivalent ice thickness under different hull line characteristic values, which simplified the calculation while ensuring the conversion accuracy.

[0071] 3. The conversion method allows users to customize the bending failure strength of the ice layer. Because the bending failure strength of the current year ice and the multi-year ice is quite different, the conversion result of the equivalent ice thickness of snow is guaranteed to be consistent with the actual use conditions, ensuring the accuracy of the resistance estimation.

[0072] The present invention has the following advantages:

[0073] 1. According to the different ice-breaking resistance parts, based on their ice-breaking mechanisms and referring to the physical properties of ice and snow, the equivalent ice thickness conversion methods of snow are given respectively.

[0074] 2. The equivalent ice thickness estimation method given for different ice-breaking mechanisms is more accurate than specifying a calculated value of equivalent ice thickness of snow. The ice-breaking resistance estimation result obtained by estimating the equivalent ice thickness of snow using the present invention is more accurate.

[0075] Although the specific embodiments of the present invention are described above, it should be understood by those skilled in the art that this is only for illustration and the protection scope of the present invention is defined by the appended claims. Those skilled in the art may make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but these changes and modifications all fall within the protection scope of the present invention.

Claims

1. A method for calculating the equivalent layer of ice in the continuous icebreaking resistance of an icebreaker, characterized in that: It includes: The ice breaking resistance is divided into collision resistance, bending damage resistance and immersion resistance, and the conversion relationship between the actual thickness of snow and the thickness of snow equivalent to ice is determined respectively when calculating the collision resistance, bending damage resistance and immersion resistance; The ice-breaking resistance of snow is calculated using the calculation formula of the ice-breaking resistance of ice, wherein the layer thickness of ice in the calculation formula of the ice-breaking resistance of ice is equal to the layer thickness of snow equivalent to ice.

2. The equivalent layer ice conversion method of snow in the continuous icebreaking resistance of icebreakers according to claim 1 is characterized in that: When calculating the impact resistance, the actual thickness of the snow layer H SN The thickness of the ice layer equivalent to snow is H′ ICE The relationship between them is: ICE =k c *H SN ; Among them, k c is the collision resistance equivalent coefficient, k=σ SN / σ ICE ; Among them, σ ICE is the bending failure strength of ice, σ SN The bending strength of snow.

3. The equivalent layer ice conversion method of snow in the continuous icebreaking resistance of icebreakers according to claim 1 is characterized in that: Among the resistances of snow breaking ice, the collision resistance R C The calculation formula is: Among them, σ0 is the bending failure strength of ice, μ is the friction coefficient of ice, is the bow column inclination angle, α is the waterline angle, H1=H′ ICE .

4. The method for calculating equivalent layer of ice of snow in continuous icebreaking resistance of icebreaker according to claim 1, characterized in that: When calculating the bending failure resistance, the actual thickness of the snow layer H SN The thickness of the ice layer equivalent to snow is H″ ICE The relationship between them is: H″ ICE =k b *H SN ; Among them, k b is the equivalent coefficient of bending failure resistance; k=σ SN / σ ICE ; Among them, σ ICE is the bending failure strength of ice, σ SN The bending strength of snow.

5. The method for calculating equivalent layer of ice of snow in continuous icebreaking resistance of icebreaker according to claim 4, characterized in that: Among the resistances to breaking ice of snow, the bending resistance R b The calculation formula is: Among them, σ0 is the bending failure strength of ice, μ is the friction coefficient of ice, is the bow column inclination angle, α is the waterline angle, H2=H″ ICE ; B is the width of the ship at the waterline; m=E / (12*(1-v 2 )*g*r sea ; Where E is Young's modulus, v is Poisson's ratio, g is the acceleration due to gravity, ρ sea is the density of sea water.

6. The equivalent layer ice conversion method of snow in the continuous icebreaking resistance of icebreakers according to claim 1 is characterized in that: When calculating the immersion resistance, the actual thickness of the snow layer H SN Thickness of the layer equivalent to snow and ice H″′ ICE The relationship between them is: ICE =k s *H SN ; Among them, k s is the equivalent coefficient of immersion resistance; k s =(ρ sea -r snow ) / (ρ sea -r ice ); Among them, ρ sea is the density of seawater, ρ snow is the density of snow, ρ ice is the density of ice.

7. The method for calculating equivalent layer of ice of snow in the continuous icebreaking resistance of icebreakers according to claim 6, characterized in that: Among the resistances to breaking ice of snow, the immersion resistance R s The calculation formula is: Among them, δ ρ is the density difference between water and ice; g is the acceleration due to gravity; H3=H″′ ICE ; T is the draft of the ship; B is the width of the ship at the waterline; μ is the friction coefficient of ice; A μ A is the flat bottom area of ​​the ship; f is the bow area; is the bow column inclination angle, α is the waterline angle,

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