High-resolution rapid simulation method for coastal city flood disasters
Technical Field
The invention relates to the field of coastal disaster protection, in particular to a high-resolution rapid simulation method for coastal city flood disasters.
Background
Coastal cities are often affected by extreme disasters such as typhoons, storm surge, tsunamis and the like, which can cause casualties and property loss, and can also have profound effects on the ecological environment and social economic development of the cities.
With the continuous development of remote sensing and radar technology, high-resolution DEM (digital elevation model) data has gradually become an important tool for researching disaster prevention and reduction of coastal cities. DEM data may provide important information on coastlines, altitude and terrain, which is of great importance in predicting coastal city inundation. However, due to the limitation of calculation cost, the existing coast inundation model still adopts a medium-scale grid (hundred meters) for simulation, so that the landform features of streets, buildings and the like in the city are often ignored, and the simulation result is inaccurate. The influence of the distributed buildings in the city on the water flow is not negligible. The building occupies a certain volume of water and also has a blocking effect on the water flow, thereby affecting the speed and direction of the water flow. Therefore, how to fully consider the high-resolution landform influence and ensure the calculation efficiency during the coastal city flood forecast simulation is the technical problem mainly solved by the invention.
Disclosure of Invention
The invention provides a high-resolution rapid simulation method for coastal city flood disasters, which aims to solve the problem that the calculation efficiency is difficult to consider under the condition that the high-resolution landforms such as streets, buildings and the like are considered in the conventional coastal city flooding simulation technology.
In order to solve the problems, the invention provides the following technical scheme:
a high-resolution rapid simulation method for coastal city flood disasters comprises the following steps:
s1: determining a target area, and collecting water depth and urban DEM data of the target area;
s2: dividing grids for the data obtained in the step S1, constructing a coastal city flood two-dimensional model, and establishing boundary conditions and initial conditions;
s3: based on a two-dimensional shallow water equation, introducing a porosity concept, and constructing a mass conservation equation considering the volume of the water body occupied by the building;
s4: calculating the drag force of water flow in each grid to a building through building distribution and elevation data based on a two-dimensional shallow water equation, and constructing a momentum conservation equation considering the drag force;
s5: and carrying out numerical simulation on the flood arrival time, the submerged depth, the submerged range and the submerged duration of the target area based on the improved shallow water equation, and carrying out flood submerged risk prediction.
Preferably, the resolution of the urban DEM data in step S1 is guaranteed to be capable of characterizing detailed street and building landform information in the city.
Preferably, in step S3, the mass conservation equation considering the volume of the water body occupied by the building is:,
in the method, in the process of the invention,for porosity->For water level, P and Q are flow in x and y directions, respectively, and t is time;
the porosity of theIs defined as follows: each calculation grid comprises a plurality of elevation data points, if the land elevation is higher than the water level of the grid, the elevation data points are marked as a plurality of points, otherwise, the elevation data points are wet points, and the ratio of the number of the wet points to the total elevation data points is the porosity corresponding to the grid +.>。
Preferably, the momentum conservation equation considering the drag force described in step S4 is calculated as follows:
,
,
wherein H is the water depth,shear stress caused by viscosity of water body, +.>Is the friction stress of the bottom->Which is a drag force caused by the building.
Preferably, the drag force caused by the building is calculated as follows:
,
,
wherein the method comprises the steps ofIs the resistance coefficient of the structure->Representing the projected area of all buildings in x and y directions within a single grid, +.>Representing the size of the computational grid, +.>Represents the average height of all buildings within a single grid,/->Representing the water depth of this drag effect.
Preferably, the projection area of the building in x and y directions and the average height of the building are calculated as follows:
,
,
,
in the middle ofFor the number of buildings present in each grid, < > j->Representing the projected area of all buildings in x and y directions within a single grid, +.>Representing the ith buildingProjection area in x and y direction, +.>Coordinates of the location of the ith building, +.>For the height of the ith building, < +.>Representing the average height of all buildings within a single grid.
The beneficial effects of the invention are as follows: aiming at the problem that storm surge flood disaster simulation in coastal urban areas is difficult to achieve both simulation efficiency and simulation resolution, the invention provides a high-resolution rapid simulation method for coastal urban flood disasters by improving a traditional two-dimensional shallow water equation.
When the method is used for carrying out the submerged simulation of the coastal cities by adopting the medium-scale grids, the high-resolution topographic data can be fully utilized, and key indexes such as submerged water depth, submerged arrival time and the like of the coastal cities under extreme disasters such as storm surge and the like can be rapidly and accurately simulated.
According to the method, the influence of the building is considered, so that the flood process can be restored more truly, and rapid and reliable prediction and decision support are provided for coping with disasters such as storm surge and the like facing coastal cities, so that the accuracy of urban flood risk early warning is improved.
The influence of the building on the water body in the city is mainly divided into two parts, firstly, the building occupies a part of the water body volume, and secondly, the existence of the building has a blocking effect on the water flow.
The invention can provide flood risk assessment, early warning and decision support, and help plan urban flood control measures and cope with disasters such as storm surge and the like facing coastal cities.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required to be used in the embodiments or the description of the prior art will be briefly described below, and it is obvious that the drawings in the following description are only embodiments of the present invention, and that other drawings can be obtained according to the provided drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart of a high-resolution rapid simulation method of a coastal city flood disaster disclosed by the invention;
FIG. 2 is a water depth topography of an exemplary area, with the abscissa (X, Y) representing a two-dimensional planar space in meters (m), the abscissa representing the distance in the X direction in the two-dimensional plane, the ordinate representing altitude, the color bar representing the water depth value in meters (m); wherein (a) is a two-dimensional water depth map of the simulation area, a building distribution area is arranged in a black dotted line frame, and O1-O4 are observation point positions; (b) is a water depth profile of the simulation area.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Embodiment 1 the embodiment of the invention provides a high-resolution rapid simulation method of coastal city flood disasters, which comprises the following specific steps:
s1: determining a target area, and collecting water depth and urban DEM data of the target area:
the coastal city inundation simulation needs to acquire offshore water depth data and high-resolution land topography elevation data, and unifies the data to the same datum plane.
S2: and (3) meshing the data obtained in the step (S1), constructing a coastal city flood two-dimensional model, and establishing boundary conditions and initial conditions:
according to the water depth and the topographic data in the step S1, a calculation grid with proper size is established to cover the target area, and the calculation grid is required to be far larger than the resolution of the land topographic elevation data so as to ensure that a plurality of buildings exist in each calculation grid. An input condition of a water level-time sequence is set at an open boundary of the target area for simulating a scene in which tsunami occurs.
S3: based on a two-dimensional shallow water equation, introducing a porosity concept, constructing a mass conservation equation considering the water volume occupied by a building,
according to the high-resolution land topography elevation data in the step S1, each calculation grid comprises a plurality of elevation data points, if the land elevation is higher than the water level of the grid, the land elevation data are marked as dry points, otherwise, the land elevation data are wet points, and the ratio of the number of the wet points to the total elevation data points is the porosity corresponding to the gridThereby constructing an improved mass conservation equation as follows:
,
in the method, in the process of the invention,for porosity->For water level, P and Q are flow rates in the x and y directions, respectively, and t is time.
S4: based on the two-dimensional shallow water equation, calculating the drag force of the water flow in each grid to the building through the building distribution and elevation data, constructing a momentum conservation equation considering the drag force,
and calculating the drag force of the water flow in each grid to the building according to the related geometric parameters of the building, thereby constructing an improved momentum conservation equation, wherein the calculation formula is as follows:
,
,
wherein H is the water depth,shear stress caused by viscosity of water body, +.>Is the friction stress of the bottom->Which is a drag force caused by the building.
The drag force caused by the building is calculated as follows:
,
,
wherein the method comprises the steps ofIs the resistance coefficient of the structure->Representing the projected area of all buildings in x and y directions within a single grid, +.>Representing the size of the computational grid, +.>Represents the average height of all buildings within a single grid,/->Representing the water depth of this drag effect.
Based on the distribution of the buildings and the elevation data, the relevant geometrical parameters (projected area of the buildings in x and y directions, the number of buildings and the average height of the buildings within a single grid) are calculated as follows:
,
,
,
in the middle ofFor the number of buildings present in each grid, < > j->Representing the projected area of all buildings in x and y directions within a single grid, +.>Representing the projected area of the ith building in x and y directions,/for example>Coordinates of the location of the ith building, +.>For the height of the ith building, < +.>Representing the average height of all buildings within a single grid.
S5: based on an improved shallow water equation, carrying out numerical simulation on flood arrival time, submerged water depth, submerged range and submerged duration of a target area, and carrying out flood submerged risk prediction:
the model calculation can obtain the factors such as the water level, the flow rate and the like of the whole area, the matlab is adopted to process and draw the calculation result, and the matlab is combined with the GIS to draw the urban inundation disaster map, so that a powerful tool is provided for the coastal urban disaster early warning.
To verify the capability of the coastal city flood disaster simulation method of this embodiment, an idealized coastal city area is designed, the topography of which is shown in fig. 2 (a) and (b), wherein the city area is within the dashed line box. The input conditions and model settings of the model are shown in table 1.
In order to show the reliability of the coastal city flood disaster simulation technology provided by the invention, the simulation result of the embodiment is compared with the simulation result of the traditional two-dimensional shallow water equation, and the high-precision simulation result of the traditional two-dimensional shallow water equation is used as a reference. 4 observation points O1-O4 are selected at the front edge and the inside of the city, and the positions of the observation points, the historical maximum water level and the historical maximum flow rate during flood are shown in table 2.
As can be seen from Table 2, O1 and O2 are located at the front of the urban area, and the low-precision simulation using the conventional shallow water equation results in lower historic maximum water level and historic maximum flow rate, while the low-precision simulation using the improved shallow water equation results in a much closer relationship to the reference group. O3 and O4 are located in the urban area, the historical maximum water level and the historical maximum flow rate are nearly doubled by using the traditional shallow water equation for low-precision simulation, and the improved shallow water equation is used for low-precision simulation, so that results which are closer to those of the reference group can be obtained. The simulation scheme provided by the invention can provide more reliable flood level and flow rate prediction results whether the simulation scheme is positioned at the front edge of a city area or inside the city area.
To demonstrate the effectiveness of the coastal city flood disaster simulation technique of the present invention, the simulation required length of the present example was compared with the simulation required length of the conventional two-dimensional shallow water equation, as shown in table 3.
From Table 3, the high-resolution rapid simulation method for the coastal city flood disaster provided by the invention can be used for obviously shortening the simulation time. The method is of great importance to the coastal city for coping with flood disasters, and can provide reliable flood risk assessment, early warning and decision support in time.
Table 1 input conditions and model settings for models
Model arrangement
|
Calculating grid accuracy
|
Control equation
|
Input wave height
|
Analog duration
|
Model A (reference group)
|
High precision (10 m)
|
Traditional two-dimensional shallow water equation
|
6 m
|
1800 s
|
Model B
|
Low precision (100 m)
|
Traditional two-dimensional shallow water equation
|
6m
|
1800 s
|
Model C
|
Low precision (100 m)
|
The invention improves two-dimensional shallow water equation
|
6 m
|
1800 s |
TABLE 2 positions of observation points and historic maximum water level values and historic maximum flow velocity values thereof
|
Observation point position
|
Observation point location
Device for placing articles
|
Historical maximum water
Bit (m)
|
History maximization
Water level (m)
|
History maximization
Water level (m)
|
History maximization
Flow rate (m/s)
|
History maximization
Flow rate (m/s)
|
History maximization
Flow rate (m/s)
|
|
X(m)
|
Y(m)
|
Model A
|
Model B
|
Model C
|
Model A
|
Model B
|
Model C
|
O1
|
8000
|
2500
|
4.474
|
4.387
|
4.435
|
5.624
|
5.245
|
5.345
|
O2
|
10000
|
2500
|
6.442
|
4.818
|
5.368
|
6.221
|
5.240
|
6.571
|
O3
|
11500
|
2500
|
1.605
|
3.081
|
2.045
|
4.339
|
5.554
|
3.251
|
O4
|
12000
|
2500
|
1.351
|
2.637
|
1.556
|
2.597
|
4.361
|
2.017 |
Table 3 simulation of the desired length-to-length comparison
Model
|
Model A
|
Model B
|
Model C
|
Simulation of the required duration (seconds)
|
6400
|
442
|
508 |
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention, and are intended to be included within the scope of the appended claims and description.