Method for generating virtual ice flake channels and apparatus for generating virtual ice flake channels

Abstract

The present invention provides a method for generating virtual ice fragment channels and a device for generating virtual ice fragment channels that can improve the reproducibility of ice fragment channels in computational space. [Solution] The method for generating a virtual ice floe channel is a method for generating a virtual ice floe channel in a computational space through which a ship navigates, and involves generating a virtual container 4 in the computational space that reproduces the shape of the bottom surface of the ice floe channel, filling the virtual container 4 with virtual particles 5 in an amount equivalent to the ice floe in the ice floe channel, placing a virtual lid 6 on the top surface of the virtual container 4 filled with virtual particles 5, adjusting the position of the virtual particles 5 in the space surrounded by the virtual container 4 and the virtual lid 6, and then removing the virtual container 4 and the virtual lid 6 to generate a virtual ice floe channel 1 with the virtual particles 5.

Description

[Technical Field]

[0001] The present invention relates to a method for generating a virtual ice flake channel and a virtual ice flake channel generating apparatus, and more particularly to a method for generating a virtual ice flake channel and a virtual ice flake channel generating apparatus suitable for computational space simulations used when navigating a channel covered with small ice flakes called a Brash Ice Channel (BIC) at a predetermined speed. [Background technology]

[0002] Ships operating in ice-covered waters are broadly classified into two types: "icebreakers that are capable of navigating through ice under their own power and possess icebreaking capabilities" and "ice-strengthened ships that can withstand drift ice and ice broken by icebreakers and navigate through it." A representative set of rules for the latter type of ice-strengthened ship is the Finnish-Swedish Ice Class Rules (FSICR), established by the Finnish and Swedish governments (Non-Patent Document 1), which are widely applied, especially to the development of merchant ships that navigate in ice-covered waters.

[0003] FSICR requires that a ship be able to navigate at a speed of 5 knots through a waterway covered with small ice floes called a Brash Ice Channel (BIC) as part of its propulsion performance requirements. FSICR has established a simplified formula to estimate the resistance necessary to prove propulsion performance in a BIC, but this formula tends to overestimate resistance as the size of the ship increases. Therefore, resistance estimation and propulsion performance evaluation through BIC sea trials (BIC tests) conducted using model ships in ice-filled tanks have become the mainstream method. However, recreating a BIC in an ice-filled tank takes a lot of time, and the number of trials is limited, making it difficult to confirm propulsion performance in a BIC before the final stages of ship design development.

[0004] In recent years, research has been conducted on numerical calculations as an alternative to ice-sea tank tests for estimating resistance in BIC (Block In-Cold Ice). Examples include calculations using physical-based modeling as described in Non-Patent Documents 2 and 3, and calculations using the discrete element method as described in Non-Patent Document 4. In all of these studies, each ice segment is treated as an independent entity, and the phenomenon is reproduced by calculating the contact between each segment. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Finnish Transport and Communications Agency: Ice Class Regulations and the Application Thereof, TRAFICOM / 68863 / 03.04.01.00 / 2021. [Non-Patent Document 2] Yoshihisa Konno, Kazuhiro Yoshimoto: Development of a resistance evaluation method for brush ice channel navigating vessels based on physical modeling, Transactions of the Japan Society of Naval Architects and Ocean Engineers, Vol. 10, pp. 49-56, 2009. [Non-Patent Document 3] Taiki Tokudome, Yuya Yoshida, and Akihisa Konno: Fluid Force Modeling Affecting on Ice Piece for Ship Navigation in Broken Ice Fields, Proceedings of the 26th International Conference on Port and Ocean Engineering under Arctic Conditions, 2021. [Non-Patent Document 4] Wanzhen Luo, Dapeng Jiang, Tiecheng Wu, Chunyu Guo, Chao Wang, Rui Deng,and Saishuai Dai: Numerical simulation of an ice-strengthened bulk carrier in brash ice channel, Ocean Engineering, Vol. 196, 106830, 2020.

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, it is known that in the Brash Ice Channel (BIC), the thickness of the ice floes is thinner in the center of the waterway than at both ends. However, in conventional simulations, calculations considering such a thickness distribution of the ice floes have not been performed, and the calculations have been carried out with a uniform thickness. Therefore, there is a problem that the position where the ice floes contact the hull and the amount of ice floes are not accurately reproduced.

[0007] The present invention was devised in view of such problems, and an object thereof is to provide a method for generating a virtual ice floe waterway and a virtual ice floe waterway generation device that can improve the reproducibility in the calculation space of the ice floe waterway.

Means for Solving the Problems

[0008] According to the present invention, there is provided a method for generating a virtual ice floe waterway that generates an ice floe waterway in which a ship sails in a calculation space, comprising: generating a virtual container that reproduces the lower surface shape of the ice floe waterway in the calculation space; filling the virtual container with virtual particles corresponding to the amount of ice floes in the ice floe waterway; adjusting the positions of the virtual particles filled in the virtual container; and removing the virtual container to generate the virtual ice floe waterway by the virtual particles.

[0009] The method for generating the virtual ice floe waterway may adjust the positions of the virtual particles by swaying the virtual container in the width direction.

[0010] The method for generating the virtual ice floe waterway may press the upper surface of the virtual particles filled in the virtual container with a virtual lid before swaying the virtual container.

[0011] The virtual container may have inclined surfaces extending such that the central thickness of the cross-section of the ice floe waterway is smaller than the thickness at the cross-section ends, and both ends in the width direction contact the lower surface of virtual flat ice adjacent to the ice floe waterway.

[0012] Further, according to the present invention, there is provided a virtual ice floe waterway generation device for generating an ice floe waterway through which a ship sails in a calculation space, comprising a computer that processes operations in the calculation space, wherein the computer generates a virtual container that reproduces the lower surface shape of the ice floe waterway in the calculation space, fills the virtual container with virtual particles corresponding to the amount of ice floes in the ice floe waterway, adjusts the positions of the virtual particles filled in the virtual container, and removes the virtual container to generate the virtual ice floe waterway with the virtual particles.

[0013] The computer may adjust the positions of the virtual particles by swaying the virtual container in the width direction.

[0014] The computer may press the upper surface of the virtual particles filled in the virtual container with a virtual lid before swaying the virtual container.

[0015] The virtual container may be generated by the computer to have inclined surfaces extending such that the central thickness of the cross-section of the ice floe waterway is smaller than the thickness at the cross-section ends, and both ends in the width direction contact the lower surface of virtual flat ice adjacent to the ice floe waterway.

Advantages of the Invention

[0016] According to the virtual ice channel generation method and virtual ice channel generation apparatus of the present invention described above, the reproducibility of ice channels in computational space can be improved by reproducing ice channels having a cross-sectional shape in accordance with guidelines such as FSICR in computational space. [Brief explanation of the drawing]

[0017] [Figure 1] This figure shows the coordinate system for the BIC simulation. [Figure 2] This figure shows the ideal cross-sectional shape of BIC. [Figure 3] This is a conceptual diagram illustrating a method for generating a virtual ice channel according to one embodiment, where (A) shows a state in which a flat ice and a virtual container are placed in computational space, (B) shows a state in which a virtual lid is placed and the virtual container is moved, and (C) shows a state in which the virtual container and virtual lid are separated. [Figure 4] This is a cross-sectional view showing the shape of a virtual container, where (A) is this embodiment and (B) is a comparative example. [Figure 5] This is a screen transition diagram showing a method for generating virtual ice fragments in the computational space of a virtual ice fragment waterway generation apparatus according to one embodiment. [Figure 6] This is a conceptual diagram illustrating an example of a method for measuring cross-sectional thickness. [Figure 7] This figure shows an example of a test vessel type, with (A) being an overall perspective view and (B) showing the waterline shape of the bow. [Figure 8] This figure shows an example of a method for determining ice shard size. (A) is a log-normal distribution plot showing the analysis results of ice shard size in the BIC test, and (B) is a distribution plot of the determined ice shard size. [Figure 9] The cross-sectional shapes show virtual ice floe channels generated in computational space, with (A) representing this embodiment and (B) representing a comparative example. [Figure 10] Figure 9(A) shows the results of analyzing the thickness distribution of the virtual ice floe channel (in this embodiment), where (A) is at X=1m, (B) is at X=5m, (C) is at X=9m, and (D) is at X=13m. [Figure 11]Figure 9(B) shows the results of analyzing the thickness distribution of the virtual ice floe channel (comparative example), with (A) at X=1m, (B) at X=5m, (C) at X=9m, and (D) at X=13m. [Figure 12] This is an external view showing a virtual vessel navigating a virtual ice floe channel. [Figure 13] This figure shows the estimated resistance of a hypothetical vessel in a virtual ice floe channel, with (A) showing the resistance over time and (B) showing the estimated resistance against the average ice thickness of the BIC. [Modes for carrying out the invention]

[0018] Embodiments of the present invention will be described below with reference to Figures 1 to 13. Here, Figure 1 is a diagram showing the coordinate system for the BIC simulation. Figure 2 is a diagram showing the ideal cross-sectional shape of the BIC. In this specification, BIC is an abbreviation for Brash Ice Channel, and BIC means a channel covered with small ice fragments.

[0019] This embodiment aims to develop a numerical calculation method for estimating the resistance in a BIC (Bioelectric Insulator). The method uses the Discrete Element Method (DEM) to estimate the resistance in a BIC, and the results are compared with experimental results obtained in an ice-filled tank by the applicant (JMU).

[0020] Furthermore, the FSICR guidelines present an ideal cross-sectional shape for BICs, and JMU's ice-sea tank tests are conducted by reproducing that cross-sectional shape as closely as possible. In this embodiment, two types of BICs—one with the cross-sectional shape presented in the guidelines and another with a flat cross-sectional shape having an equivalent average thickness—are numerically reproduced, and the effect of the cross-sectional shape on the resistance within the BIC is investigated by estimating the resistance under each condition.

[0021] (Calculation method) In this embodiment, the resistance R experienced by a ship when navigating through the BIC (Battleship Intake Center) ch Resistance R from ice fragments in BIC iand the resistance R of water w is considered by dividing into ((Equation (1))). Here, the resistance of water is not considered, and the calculation is performed for the resistance R i received from ice pieces.

[0022]

Number

[0023] Since BIC is composed of small ice pieces densely packed, it can be considered as a granular material. Therefore, the ice pieces are replaced with spheres to reproduce the resistance test in BIC, and R i is estimated by calculating the movement of ice pieces using DEM. The coordinate system used in this calculation is shown in Fig. 1. Here, L ch is the length of BIC, B ch is the width of BIC, and point O is the origin of coordinates.

[0024] As shown in Fig. 1, BIC (virtual ice piece waterway 1) is generated in a space surrounded by level ice (virtual flat ice 2) on both sides and the tip part. The level ice (virtual flat ice 2) is a model of flat sea ice that has not undergone deformation (the part of sea ice without cracks in ice pieces). A rectangular three-axis coordinate system is used for the coordinate system. For example, the x-axis is set in the advancing direction of the virtual ship 3, the y-axis is in the ship width direction of the virtual ship 3 (the direction perpendicular to the x-axis in the horizontal plane), and the z-axis is in the vertical direction. Note that the upper part of Fig. 1 shows a plan view, and the lower part of Fig. 1 shows a side view.

[0025] (Calculation of ice piece movement) An open-source DEM calculation tool was used for resistance estimation. By sequentially calculating the equation of motion ((Equation (2))) considering the contact forces between "hull - ice" and "ice - ice" obtained by DEM, the fluid force and buoyancy acting on the ice pieces, the movement of the ice pieces and the resistance received by the hull were obtained. Here, ρ i is the density of ice, V i is the volume of the ice piece, a is the acceleration, F DEM is the contact force obtained by DEM, F w is the fluid force received by the ice piece, F buoy is the buoyancy acting on the ice piece.

[0026]

number

[0027] (Contact force according to DEM: F) DEM ) DEM (Digital Element Method) is a computational method that analyzes the overall mechanical behavior of granular materials by approximating the object as a collection of simple particles and calculating the interactions between those particles. Originally developed in the field of civil engineering to analyze the motion of soil, it is now widely used to analyze granular materials other than soil.

[0028] In this calculation, ice shards were replaced with spheres, and the contact force was calculated based on Hertz's model (Catherine O'Sullivan: Particulate Discrete Element Modelling: A Geomechanics Perspective, translated by Teruichi Suzuki, Morikita Publishing, 1st edition, 2014). Furthermore, since the ice shards replaced with spheres are more prone to rotation than actual ice shards, the rotation of the ice shards was suppressed by applying rolling resistance based on the Directional Constant Torque (CDT) model (Jun Ai, Jian-Fei Chen, J. Michael Rotter, and Jin Y. Ooi: Assessment of rolling resistance models in discrete element simulations, Powder Technology, Vol. 206, Issue 3, pp. 269-282, 2011).

[0029] (Fluid force acting on the ice shard: F) w ) The hydrodynamic force Fw acting on the ice fragments from the water as they move was calculated from equation (3). Here, ρ w v is the density of water. i r is the velocity of the ice shard, r is the radius of the ice shard, C w This is the coefficient of resistance.

[0030]

number

[0031] (Buoyancy acting on ice fragments: F) buoy ) Buoyancy F acting on the ice fragment buoy We obtained this from equation (4). Here, V w is the volume of water submerged in the ice shard, and g is the acceleration due to gravity.

[0032]

number

[0033] (Modeling of BIC) In this embodiment, in order to investigate the effect of cross-sectional shape on resistance in the BIC, the BIC was reproduced in computational space by performing operations that simulated the JMU BIC test method.

[0034] (BIC cross-sectional shape based on FSICR) Figure 2 shows the cross-sectional shape of the BIC based on the FSICR guidelines. Here, B wl is the width of the ship, H M H is the thickness at the center of the cross-section. M This varies depending on the target icebreaker class (Ice Class), and at actual ship scale, it is 1.0m for Ice Class IA, 0.8m for Ice Class IB, and 0.6m for Ice Class IC. Also, according to the FSICR guidelines, the ideal average thickness of BIC is H a This can be calculated using equation (5).

[0035]

number

[0036] (Initial placement of ice shards) In JMU's BIC test method, the cross-sectional shape shown in Figure 2 is reproduced by arranging ice pieces using a mold with a 2° incline. Here, a virtual ice piece channel 1, which is a BIC, was generated in computational space according to the following procedure.

[0037] Here, Figure 3 is a conceptual diagram showing a method for generating a virtual ice channel according to one embodiment, where (A) shows a state in which a flat ice and a virtual container are placed in the computational space, (B) shows a state in which a virtual lid is placed and the virtual container is moved, and (C) shows a state in which the virtual container and virtual lid are separated. In Figure 3(B), for the sake of explanation, the movement of the virtual lid 6 is illustrated with a gradient. Also, in Figure 3(C), for the sake of explanation, the movement of the virtual container 4 and virtual lid 6 is illustrated with a gradient.

[0038] (1) A virtual flat ice 2 and a mold (virtual container 4) that constitute a channel (waterway) are placed in the computational space (see Figure 3(A)).

[0039] (2) Fill the mold (virtual container 4) with ice fragments (virtual particles 5) and press down from above with a flat plate (virtual lid 6). At this time, the mold (virtual container 4) is moved from side to side in small increments to level the ice fragments (virtual particles 5) (see Figure 3(B)).

[0040] (3) Slowly separate the mold (virtual container 4) and the flat plate (virtual lid 6) (see Figure 3(C)).

[0041] Figure 4 shows the shape of the mold used in this study. Mold A was used to reproduce the cross-sectional shape shown in Figure 2, and Mold B represents the ideal average thickness H shown in equation (5). a This was used to reproduce a flat BIC having [a certain characteristic]. Specifically, Figure 4(A) shows the cross-sectional shape of the virtual container 4 used in this embodiment, and Figure 4(B) shows the cross-sectional shape of a comparative example. Both Mold A and B have a 30° incline at the edges so that the ice shards (virtual particles 5) do not collapse outwards when the mold (virtual container 4) is released. In this embodiment, the calculations using Mold A and B are designated as Case 1 and Case 2, respectively.

[0042] (Method for generating virtual ice channel in this embodiment) In short, the method for generating a virtual ice floe channel in this embodiment is a method for generating a virtual ice floe channel in computational space through which a ship navigates, and is characterized by generating a virtual container 4 in computational space that reproduces the shape of the bottom surface of the ice floe channel, filling the virtual container 4 with virtual particles 5 in an amount equivalent to the ice floe in the ice floe channel, placing a virtual lid 6 on the top surface of the virtual container 4 filled with virtual particles 5, adjusting the position of the virtual particles 5 in the space surrounded by the virtual container 4 and the virtual lid 6, and then removing the virtual container 4 and the virtual lid 6 to generate a virtual ice floe channel 1 with the virtual particles 5.

[0043] The process of generating the virtual container 4 is a process of generating a virtual container 4 that will serve as a receptacle for virtual particles 5 in order to generate the cross-sectional shape (cross-sectional thickness) of the ice fragment channel in accordance with the guidelines.

[0044] The step of filling with virtual particles 5 is the step of filling the virtual container 4 with virtual particles 5 that model ice fragments. At this time, in order to prevent the filled virtual particles 5 from escaping from the virtual container 4, a virtual cylindrical body 7 (see Figure 5) that models the planar shape of the ice fragment waterway may be generated above the virtual container 4.

[0045] The step of positioning the virtual lid 6 is a step of positioning the virtual particles 5 filled in the virtual container 4 so that they form a cross-sectional shape having a predetermined thickness. In this step, for example, the virtual lid 6 is generated above and away from the virtual container 4, and the virtual lid 6 is lowered to a predetermined position to create a state in which the virtual particles 5 are densely packed within the predetermined cross-sectional shape.

[0046] The step of adjusting the position of the virtual particles 5 is a step of stabilizing the position of the densely packed virtual particles 5. For example, the position of the virtual particles 5 is adjusted by shaking the virtual container 4 in the width direction while maintaining the position of the virtual lid 6. Other means may be used to adjust the position of the virtual particles 5 besides shaking the virtual container 4 in the width direction.

[0047] The step of removing the virtual container 4 and virtual lid 6 involves, after the virtual particles 5 have been adjusted in position and settled to a stable state, moving the virtual container 4 downwards and the virtual lid 6 upwards, slowly separating the virtual container 4 and virtual lid 6 from the virtual particles 5. When moving the virtual container 4 and virtual lid 6, it is preferable to adjust the speed so that the position of the virtual particles 5 does not easily collapse. After the virtual container 4 and virtual lid 6 have moved to a position where they do not affect the virtual particles 5, the virtual container 4 and virtual lid 6 are removed from the virtual space. At this time, the virtual cylinder 7 is also removed from the virtual space.

[0048] In this way, by gradually separating the virtual container 4 and virtual lid 6 from the virtual particle 5, it is possible to remove the virtual container 4 and virtual lid 6 while minimizing the fluctuation of the virtual particle 5, even if the virtual particle 5 was compressed by the virtual container 4 and virtual lid 6.

[0049] As shown in Figure 4(A), the virtual container 4 has a cross-sectional thickness H in the center of the ice flake channel. M Cross-sectional end thickness H E It may have a smaller inclined surface 8 that extends so that both ends in the width direction contact the lower surface of the level ice (virtual flat ice 2) adjacent to the ice flake channel. The inclined surface 8 has, for example, a 30° inclination with respect to the level ice (virtual flat ice 2). Note that the degree of inclination is merely an example and is not limited to the numerical value shown in the figure.

[0050] By forming this inclined surface 8, it is possible to suppress the displacement of the virtual particles 5 at both ends in the width direction when the virtual container 4 and virtual lid 6 are removed during the process of removing the virtual container 4 and virtual lid 6.

[0051] The method for generating virtual ice floe channels described above is performed by a computer. That is, a virtual ice floe channel generation device that generates ice floe channels through which ships navigate in a computational space is equipped with a computer that processes the calculations in the computational space described above. Here, Figure 5 is a screen transition diagram showing the method for generating virtual ice floe channels in the computational space of a virtual ice floe channel generation device according to one embodiment.

[0052] The upper part of Figure 5 shows the state in which virtual particles 5 are filled into the virtual container 4. The middle part of Figure 5 shows the state in which the virtual lid 6 is lowered and the virtual particles 5 are densely packed together. In this state, the virtual container 4 is shaken in the width direction to stabilize the virtual particles 5. The lower part of Figure 5 shows the state in the intermediate stage of separating the virtual container 4 and virtual lid 6 from the virtual particles 5.

[0053] In the embodiment described above, the upper surface of the virtual particles 5 filled in the virtual container 4 is held down by the virtual lid 6 before the virtual container 4 is shaken, but the virtual lid 6 may be omitted if necessary. For example, if the position of the virtual particles 5 can be adjusted simply by shaking the virtual particles 5 filled in the virtual container 4 in the width direction, the virtual lid 6 can be omitted. Also, the virtual cylinder 7 can be omitted if it is not needed.

[0054] (Cross-sectional measurement) To confirm the cross-sectional shape of the BIC, the cross-sectional thickness of the BIC was calculated at intervals of 2m in the x-axis direction and 0.2m in the y-axis direction, referring to the FSICR guidelines. Here, a cylinder extending in the z-axis direction centered on the x,y coordinates of the measurement point was considered, and the coordinates of the upper / lower ends of the ice fragments contained within that cylinder were defined as the upper / lower ends of the BIC (Figure 6). The gray cylinder in the figure indicates the analysis range at a certain measurement point, and the circles indicated by dashed lines indicate the ice fragments to be analyzed. Note that the upper part of Figure 6 is a plan view, and the lower part of Figure 6 is a side view.

[0055] Previous studies have shown that if the diameter of the cylinder in the analysis range is small, it may measure only the local thickness and fail to measure the thickness of the ice fragment group as a whole. On the other hand, if the diameter of the cylinder is too large, it may overestimate the cross-sectional thickness, so the diameter of the cylinder must be set to an appropriate size. Here, the maximum radius r of the ice fragments used when creating the BIC was used as the reference value for determining the diameter of the cylinder. max Using this, the diameter of the cylinder is 2r max That's what I decided.

[0056] (calculation conditions) Based on the propulsion performance requirements of FSICR, the resistance experienced when navigating through Ice Class IA equivalent BIC at a ship speed of V=5kt was estimated. In this embodiment, calculations were performed on the same scale (1 / 45) as the JMU ice tank test. The calculation conditions are shown in Table 1.

[0057] [Table 1]

[0058] (Test ship type) Two types of hull shapes with different bow shapes, a parabolic hull shape and an ellipse hull shape, were used as test hull types for the hypothetical vessel 3. The main specifications of both hull types are shown in Table 2, and the overall diagram of the test hull type and the waterline shape of the bow are shown in Figures 7(A) and 7(B), respectively. Here, L wl B is the length of the ship's shape at the waterline. wl d is the width of the hull at the waterline, and d is the draft.

[0059] Note that the left diagram in Figure 7(A) shows a parabolic hull shape, and the right diagram in Figure 7(A) shows an ellipse hull shape. A parabolic hull shape has a pointed bow, as shown by the solid line in Figure 7(B), while an ellipse hull shape has a rounded bow, as shown by the dotted line in Figure 7(B).

[0060] [Table 2]

[0061] (Ice shard size) Regarding the ice fragment size, an important parameter representing the properties of BIC, in this embodiment, the size was determined based on JMU's BIC test results. In JMU's BIC tests, flat ice with a thickness of approximately 10 mm is crushed to create ice fragments, resulting in variations in the shape and size of the ice fragments. To replace these ice fragments with spheres, the radius of a sphere with the same volume as the ice fragment was calculated and used as a representative value for the ice fragment size in the analysis.

[0062] The probability distribution of ice fragment sizes was analyzed for 7358 ice fragments randomly selected during the BIC test. The results are shown in Figure 8(A). The gray histogram represents the frequency distribution of ice fragment sizes, the gray solid line represents the cumulative relative frequency, and the black dashed line represents the cumulative relative frequency of the log-normal distribution calculated based on the mean and standard deviation of ice fragment sizes (Table 3). Results from known field tests suggest that the actual size of sea ice follows a log-normal distribution, and although the scale and ice fragment formation process differ, the distribution of ice fragment sizes in the BIC test is also considered to follow a log-normal distribution similar to that of sea ice. As confirmed from Figure 8(A), the log-normal distribution corresponds well to the experimental results, so we decided to use the log-normal distribution to determine the ice fragment size.

[0063] [Table 3]

[0064] In this embodiment, BIC was generated by mixing ice fragments of three different sizes. As shown in Figure 8(B), when the 5% at both ends of the probability density function are excluded as singular values, the minimum and maximum ice fragment sizes are 5.74 mm and 15.35 mm, respectively. This interval was divided into three equal parts, and three types of spherical ice fragments were used, with the expected value in each interval as the radius. The radii of the ice fragments and the mixing ratios are shown in Table 4.

[0065] [Table 4]

[0066] (Amount of ice) In this embodiment, in addition to variations in the size of the ice pieces, the arrangement of the ice pieces becomes irregular because a mold is used to arrange them. Since it is difficult to theoretically determine the amount of ice pieces needed to create a BIC of the planned thickness, the amount of ice pieces was adjusted through trial and error. The amount of ice pieces used for resistance estimation is shown in Table 5. Note that this amount of ice pieces corresponds to a void ratio of 0.3 in an ideal cross-sectional shape. Case 1 (Mold A) is the embodiment shown in Figure 4(A), and Case 2 (Mold B) is the comparative example shown in Figure 4(B).

[0067] [Table 5]

[0068] (Calculation parameters) Table 6 shows a list of the properties of ice and parameters such as the drag coefficient used in this study. Among these, the coefficient of restitution e and the rolling resistance coefficient μ are shown. r Regarding this, the resistance of the parabolic boat shape was adjusted through trial and error to match the experimental results. Also, the friction coefficient between the ice and the mold was set to 0.00 to allow the ice pieces to be arranged smoothly. In the table, Young's modulus (E), Poisson's ratio (ν), coefficient of restitution (e), and friction coefficient (μ) are used. k Density of water: ρ w Density of the ice: ρ i Rolling resistance coefficient: μ r Water resistance coefficient: C w , that is.

[0069] [Table 6]

[0070] (calculation result) BIC shape Figure 9 shows the BIC generated according to the procedure of this embodiment, and Figures 10 and 11 show the measured thickness distribution of the BIC. The average thickness H for Case 1 and 2 is also shown. a This is shown in Table 7. In Figures 10 and 11, the upper solid line represents the height of the constructed BIC above the water surface, the lower solid line represents the depth of the constructed BIC below the water surface, and the black dashed line represents the ideal cross-sectional shape based on the FSICR guidelines. From the calculation results, the average thickness H a The error was kept to less than 1%, and it was confirmed that the cross-sectional shape closely matched the shape indicated in the guidelines.

[0071] Figure 9(A) shows the cross-sectional shape of a virtual ice floe channel generated by this embodiment, and Figure 9(B) shows the cross-sectional shape of a comparative example generated by the same procedure. In addition, each figure in Figure 10 shows the thickness distribution of Case 1, with Figure 10(A) showing the thickness distribution at X=1m, Figure 10(B) showing the thickness distribution at X=5m, Figure 10(C) showing the thickness distribution at X=9m, and Figure 10(D) showing the thickness distribution at X=13m. In addition, each figure in Figure 11 shows the thickness distribution of Case 2, with Figure 11(A) showing the thickness distribution at X=1m, Figure 10(B) showing the thickness distribution at X=5m, Figure 10(C) showing the thickness distribution at X=9m, and Figure 10(D) showing the thickness distribution at X=13m.

[0072] [Table 7]

[0073] (Resistance in ice) Figure 12 shows the condition of the hull during ice resistance calculations, and the resistance R from ice fragments during BIC navigation obtained from the calculations. i The time series is shown in Figure 13(A). Figure 12 illustrates the case of a parabolic boat shape. Here, the horizontal axis of Figure 13(A) represents the time when the FP enters the BIC as 0.0 sec. Regardless of the boat shape or the cross-sectional shape of the BIC, the resistance increased up to 15.0 sec, and thereafter it became stable and uniform.

[0074] In Figure 13(A), the results for the parabolic hull shape are shown as the lower line, and the results for the ellipse hull shape are shown as the upper line. In the parabolic hull shape line, light gray represents Case 2 (comparative example), and dark gray represents Case 1 (this embodiment). Similarly, in the ellipse hull shape line, light gray represents Case 2 (comparative example), and dark gray represents Case 1 (this embodiment).

[0075] The hull is L wl From the point where it has advanced and completely penetrated BIC, further L wl The average resistance during the period of advancement (16.9 sec to 33.9 sec) was calculated and compared with the experimental results. The results are shown in Figure 13(B). The horizontal axis of the figure represents the average ice thickness H. a The vertical axis represents the resistance R from the ice. i The results for the parabolic boat shape are shown in black, and the results for the ellipse boat shape are shown in gray. Note that the experimental results are R i This was calculated by subtracting the resistance in the open channel from the total resistance experienced while towing through the BIC.

[0076] The calculation results for both hull types show trends and values ​​close to those of the experimental results, accurately reproducing the difference in resistance between the hull types. Furthermore, in both hull types, the resistance was greater in Case 2 than in Case 1. The change in resistance compared to the results of Case 1 was +5.2% for the parabolic hull type and +10.8% for the elliptical hull type, showing a larger difference for the elliptical hull type. This difference is consistent with the property that elliptical hull types are more susceptible to resistance than parabolic hull types.

[0077] According to the method and apparatus for generating the virtual ice flake channel 1 of this embodiment described above, it is possible to reproduce ice flake channels having a cross-sectional shape in accordance with guidelines such as FSICR in computational space, enabling simulations that are faithful to the planned conditions. In other words, the reproducibility of ice flake channels in computational space can be improved.

[0078] In the embodiments described above, a virtual ice floe channel 1 is generated in the computational space, and its effect is verified in the case of a simulation to estimate ice resistance when a ship navigates through an ice floe channel. However, the method for generating the virtual ice floe channel 1 and the apparatus for generating the virtual ice floe channel 1 according to this embodiment are not limited to use in simulations to estimate ice resistance. For example, this embodiment can be used in simulations and analyses that require the generation of a virtual ice floe channel 1, such as simulations of self-propelled tests in which a ship is sailed while rotating its propeller, or analysis of pressure distribution on the hull surface.

[0079] The present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention. [Explanation of Symbols]

[0080] 1. Virtual ice floe channel 2. Virtual flat ice 3. Virtual ship 4 Virtual containers 5 virtual particles 6 Virtual Lid 7 Virtual cylinder 8 Slope

Claims

1. A method for generating a virtual ice channel in computational space, which generates an ice channel through which ships navigate, A virtual container is generated in the aforementioned computational space that reproduces the shape of the lower surface of the ice flake channel. The virtual container is filled with virtual particles in an amount equivalent to the ice fragments in the ice fragment channel. Adjust the position of the virtual particles filled in the virtual container, The virtual container is removed and the virtual ice floe channel is generated by the virtual particles. A method for generating a virtual ice floe channel, characterized by the features described above.

2. A method for generating a virtual ice floe channel according to claim 1, wherein the position of the virtual particles is adjusted by shaking the virtual container in the width direction.

3. The method for generating a virtual ice flake channel according to claim 2, wherein the upper surface of the virtual particles filled in the virtual container is pressed down with a virtual lid before the virtual container is shaken.

4. The method for generating a virtual ice flake channel according to claim 1, wherein the virtual container has an inclined surface that extends so that the central cross-sectional thickness of the ice flake channel is smaller than the cross-sectional end thickness, and both ends in the width direction contact the lower surface of a virtual flat ice adjacent to the ice flake channel.

5. A virtual ice channel generation device that generates ice channel routes for ships in computational space, The computer comprises a computer that processes operations in the aforementioned computing space, The aforementioned computer, A virtual container is generated in the aforementioned computational space that reproduces the shape of the lower surface of the ice flake channel. The virtual container is filled with virtual particles in an amount equivalent to the ice fragments in the ice fragment channel. Adjust the position of the virtual particles filled in the virtual container, The virtual container is removed and the virtual ice floe channel is generated by the virtual particles. A device for generating virtual ice floe channels, characterized by the following features.

6. The virtual ice flake channel generating apparatus according to claim 5, wherein the computer adjusts the position of the virtual particles by shaking the virtual container in the width direction.

7. The virtual ice flake channel generating apparatus according to claim 6, wherein the computer presses down on the upper surface of the virtual particles filled in the virtual container with a virtual lid before shaking the virtual container.

8. The virtual ice flake channel generating apparatus according to claim 5, wherein the virtual container is generated by the computer such that the central cross-sectional thickness of the ice flake channel is smaller than the cross-sectional end thickness, and both ends in the width direction have inclined surfaces that extend to contact the lower surface of a virtual flat ice adjacent to the ice flake channel.

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