Method for parameter design and numerical simulation of jet trencher nozzle

Abstract

The present disclosure provides a parameter design and numerical simulation method for jet trencher nozzle, comprising the following steps: S1. designing parameters of nozzle; S2. selecting the parameters of nozzle; S3. establishing a geometric model; S4. setting boundary conditions and delineating grids; S5. performing numerical simulation using Flow-3D; and S6. performing results processing and analysis. According to the present invention, the whole process of nozzle flushing and ground breaking can be simulated, the size of the cross-section of the flushing trench is measured, and by analyzing the obtained result, the reasonability of nozzle radius parameter design can be verified, and a certain reference is provided for design of inclination angle parameters.

Claims

1. A method for parameter design and numerical simulation of a jet trencher nozzle, comprising the following steps: Step S1, designing parameters of nozzle, wherein: at a distance of x from the jet trencher nozzle, according to an effective pressure calculation equation of jet flow: $\overline{F}=\frac{p{R}^2}{0.0127x^2},$  denying a relation between a nozzle radius and an inclination angle of β when the effective pressures of jet flow of an inclined nozzle and a vertical nozzle are equal at a same vertical distance: $R_i=\frac{1}{\cos \beta }{R}_v,$  R being a radius of the jet trencher nozzle, p being an outlet dynamic pressure of the jet trencher nozzle, R.sub.v being a radius of the vertical nozzle, R.sub.i being a radius of the inclined nozzle; Step S2, selecting parameters of the nozzle, wherein: according to the equation $R_i=\frac{1}{\cos \beta }{R}_v$  derived in Step S1, taking the radius R.sub.v of the vertical nozzle as a fixed value, and selecting different inclination angles β to obtain different radii R.sub.i of inclined nozzles; Step S3, establishing a geometric model, wherein: according to the nozzle parameters selected in Step S2, establishing a combination geometric model of the vertical nozzle and the inclined nozzle; Step S4, setting boundary conditions and delineating grids, wherein: importing the combination geometric model established in Step S3 into a software program, dividing a computational domain into an upper block and a lower block connected with each other from top to bottom, defining boundaries of the upper block and the lower block, and delineating grids on the computational domain and checking the quality of the grids; Step S5, performing numerical simulation, comprising: adding a sediment physical model and defining the sediment parameters, setting an initial condition, time step of the computational domain, a physical time and a maximum number of iterations; solving numerical values; and Step S6, performing results processing and analysis deriving a topographic surface file based on simulation results obtained in Step S5, processing the topographic surface file to obtain and analyze the geometric parameters of a flushing trench profile.

2. The method according to claim 1, wherein in Step S1, when outlets of the inclined nozzle and the vertical nozzle at the same vertical distance, the target distance x.sub.i of the inclined nozzle is $\frac{1}{\cos \beta }$ times of a strike distance x.sub.v of the vertical nozzle, that is $x_i=\frac{1}{\cos \beta }{x}_v,$ when the inclined nozzle and the vertical nozzle reach the same jet flow effective pressure at the same vertical distance, $R_i=\frac{1}{\cos \beta }{R}_v.$

3. The method according to claim 1, wherein Step S4 comprises: defining the boundaries around the upper block as X.sub.Max, X.sub.Min, Y.sub.Max, and Y.sub.Min, which are set as pressure outlet boundaries with a pressure value of 0; setting Z.sub.Max of the upper block as a pressure inlet boundary with a pressure value as a nozzle inlet pressure; setting Z.sub.min of the upper block as a default boundary, Z.sub.min of the upper block being connected to Z.sub.max of the lower block; defining the four boundaries of the lower block as X′.sub.Max, X′.sub.Min, Y′.sub.Max, and Y′.sub.Min, which are set as wall boundaries; setting Z′.sub.Min of the lower block as a wall boundary, Z′.sub.Min of the lower block being sediment; and setting Z′.sub.Max of the lower block as a default boundary, which is connected with the Z.sub.Min boundary of the upper block.

4. The method according to claim 1, wherein Step S5 comprises: calculating a sediment volume fraction by tracking a sediment concentration C.sub.s of the suspended sediment and a sediment concentration C.sub.p of a bed load using the sediment physical model; a total sediment volume fraction α.sub.s is the total volume fraction of suspended sediment and bed load in the grid, with an equation: ${\alpha }_s=\frac{C_s+C_p}{{\rho }_s}=1-{\alpha }_f,$ wherein α.sub.f of is a volume fraction of the fluid in a grid, ρ.sub.s is a sediment particle density, an expression for a volume fraction of the bed load is α.sub.s,p=C.sub.p/ρ.sub.s, an expression for a volume fraction of suspended sediment is α.sub.s,s=C.sub.s/ρ.sub.s, a critical sediment volume fraction is α.sub.cr, and the total volume fraction α.sub.s is smaller or equal to the critical sediment volume fraction α.sub.cr; the parameters need to be defined in the sediment physical model are: median particle size with the unit of m, sediment density with the unit of kg/m.sup.3, entrainment coefficient α.sub.i, bed load coefficient β.sub.i, angle of repose with the unit of °, and critical sediment volume fraction; and using a turbulence model: $\rho \frac{Dk}{Dt}=\frac{\partial }{\partial y}\left({\alpha }_k{\mu }_{\mathrm{eff}}\frac{\partial k}{\partial y}\right)+G_k+G_b-\rho \epsilon -Y_M,$ $\rho \frac{D\epsilon }{Dt}=\frac{\partial }{\partial y}\left({\alpha }_{\epsilon }{\mu }_{\mathrm{eff}}\frac{\partial \epsilon }{\partial y}\right)+C_{1\epsilon }\frac{\epsilon }{k}\left(G_k+C_{3\epsilon }{G}_b\right)-C_{2\epsilon }\rho \frac{{\epsilon }^2}{k}-R,$ wherein ρ is fluid density, t is time, k is turbulent kinetic energy, ε is turbulent dissipation rate; α.sub.k and α.sub.ε are inverses of the turbulent Prandtl number; μ.sub.eff, and R are corrected parameters, G.sub.k and G.sub.b are respectively laminar velocity gradient and turbulent kinetic energy caused by buoyancy, Y.sub.M is turbulent expansion contribution of compressible fluid, and C.sub.1ε, C.sub.2ε and C.sub.3ε are empirical constants.

5. The method according to claim 1, wherein Step S6 further comprises: verifying that the effective pressures acting on the sediment surface at the same vertical distance of the inclined nozzle and vertical nozzle are equal by analyzing a parameter of maximum trench depth; and summarizing an influence rule of nozzle angle size on the trench profile by analyzing a geometrical shape of the flushing trench profile.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In order to more clearly illustrate the embodiments of the present disclosure or the technical solutions in the prior art, the drawings required in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following descriptions are some embodiments of the present disclosure. For those of ordinary skilled in the art, other drawings can be obtained based on these drawings without inventive effort.

(2) FIG. 1 is a flow diagram of one of the parameter design and numerical simulation of jet trencher nozzle in the embodiment of the present disclosure.

(3) FIG. 2 is a front view of a geometric model for the combination of a vertical nozzle and an inclined nozzle in the embodiment of the present disclosure.

(4) FIG. 3 is a side view of a geometric model for the combination of a vertical nozzle and an inclined nozzle in the embodiment of the present disclosure.

(5) FIG. 4 is a schematic diagram of the delineation and boundary conditions of the computational domain block in the embodiment of the present disclosure; wherein, P represents pressure boundary, and W represents wall boundary.

(6) FIG. 5 is a schematic diagram of grid delineation of the computational domain in the embodiment of the present disclosure.

(7) FIG. 6 is a schematic diagram of a flushing trench profile when the radius of the vertical nozzle is 1 cm, the radius of the inclined nozzle is 1.41 cm, and the inclined angle is 45°.

(8) FIG. 7 is a schematic diagram of a flushing trench profile when the radius of the vertical nozzle is 1 cm, the radius of the inclined nozzle is 1.15 cm, and the inclined angle is 30°.

(9) FIG. 8 is a schematic diagram of a flushing trench profile scoured by jet flow when the radius of the vertical nozzle is 1 cm, the radius of the inclined nozzle is 1.04 cm, and the inclined angle is 15°.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(10) To make the objectives, technical solutions and advantages of the present disclosure clearer, a clear and complete description in the embodiments of the present disclosure may be given herein after in combination with the accompany drawings in the embodiment of the present disclosure. Obviously, the described embodiments are parts of the embodiments of the present disclosure, but not all of them. Based on the embodiments in the present disclosure, all other embodiments obtained by those of ordinary skilled in the art without inventive effort are within the scope of the present disclosure.

(11) As FIG. 1 shown, a method for parameter design and numerical simulation of jet trencher nozzle, including the following steps: S1. designing parameters of nozzle at a distance of x from the nozzle, according to an effective pressure calculation equation of jet flow:

(12) $\overline{F}=\frac{p{R}^2}{0\text{.0127}{x}^2},$  a relation between a nozzle radius and an inclination angle β is derived when the jet flow effective pressures of an inclined nozzle and a vertical nozzle are equal at the same vertical distance:

(13) 0$R_i=\frac{1}{\cos \beta }{R}_v,$  wherein, R is a radius of the nozzle, p is outlet dynamic pressure of the nozzle, R.sub.v is a radius of the vertical nozzle, and R.sub.i is a radius of the inclined nozzle; S2. selecting parameters of nozzle according to the equation of

(14) $R_i=\frac{1}{\cos \beta }{R}_v$  derived by step S1, the radius R.sub.v (1 cm in the embodiment) of the vertical nozzle was set as a fixed value, and different inclination angles β were selected of 15°, 30° and 45° respectively in the embodiment, different inclined nozzle radii R.sub.i of 1.04 cm, 1.15 cm and 1.41 cm were obtained respectively; S3. establishing a geometric model a geometric model was established by combining a vertical nozzle and an inclined nozzle; according to the nozzle parameters selected in step S2, Solidworks was used to establish a combination geometric model of the vertical nozzle and the inclined nozzle, included: a combination model of a vertical nozzle with a radius of 1 cm and an inclined nozzle with a radius of 1.04 cm and an inclination angle of 15° (as shown in FIG. 2 and FIG. 3), a combination model of a vertical nozzle with a radius of 1 cm and a inclined nozzle with a radius of 1.15 cm and an inclination angle of 30°, a combination model of a vertical nozzle with a radius of 1 cm and an inclined nozzle with a radius of 1.41 cm and an inclination angle of 45°, and the outlets of the vertical nozzle and the inclined nozzle were kept at the same vertical height and the contraction angles of the nozzles were same. S4. setting boundary conditions and delineating grids the combination geometric model of the nozzles established in step S3 was imported into Flow-3D software, the computational domain was divided into two blocks connected with each other from top to bottom, the boundaries of the two blocks were defined, and delineated grids on the computational domain and the quality of the grids was checked; S5. performing numerical simulation by using Flow-3D a sediment physical model was added and the sediment parameters were defined, an initial condition and time step of the computational domain were set, and the physical timescale and maximum number of iterations were calculated; and, numerical values were solved in Flow-3D; and S6. performing results processing and analysis the topographic surface file in Flow-3D calculation results in step S5 was derived, the topographic surface file was processed by Matlab, and the geometric parameters of the flushing trench profile were obtained and analyzed.

(15) The trench-shaped profile flushed out by the combination model of a vertical nozzle with a radius of 1 cm and an inclined nozzle with a radius of 1.41 cm and an inclination angle 45° is shown as FIG. 6; it can be seen that two trench were flushed out by the vertical nozzle and the inclined nozzle and the maximum trench depths of the scouring profile were almost equal, which indicates that the effective impact pressures by the jet flow from the two nozzle outlets acting on the sediment surface are also almost equal, reaching the design purpose of the nozzle radius; the obvious bulge in the middle of the two trenches indicates that the sediment accumulate in the trench and cannot be effectively flushed out, which is not in line with the ideal trench shape of actual operation requirements. The trench-shaped profile flushed out by the combination model of a vertical nozzle with a radius of 1 cm and a inclined nozzle with a radius of 1.15 cm and an inclination angle 30° is shown as FIG. 7; it can be seen that the vertical nozzle and the inclined nozzle flushed out nearly a common trench, the bottom of the trench has a large flat area, and the maximum trench depth of the flushing profile was 0.169 m, which indicates that the effective impact pressures by jet flow from the two nozzle outlets acting on the sediment bed are consistent; most of the sediment in the trench has been flushed out of the trench, and the diameter of the pit is wide, which can meet the requirements of trench shape in some actual seabed trenching work. The trench-shaped profile flushed out by the combination model of a vertical nozzle with a radius of 1 cm and a inclined nozzle with a radius of 1.04 cm and an inclination angle 15° is shown as FIG. 8; it can be seen that the vertical nozzle and the inclined nozzle flushed out the same trench with a maximum trench depth of 0.177 m, which indicates that the effective impact pressures by high pressure flow from the two nozzle outlets acting on the sandy surface are equal, the maximum diameter of the flushing profile is 1.57 m; the bottom area of the trench is flat without bulges, indicating that the sediment in the trench has been flushed out completely. It can be seen from the figures that the maximum trench depths flushed out by the vertical nozzle and the inclined nozzle are equal, which proves that the flow jet at the outlets of two nozzles (satisfying the relation of

(16) $R_i=\frac{1}{\cos \beta }{R}_v$
can reach the same effectively impact pressure at the same vertical height, showing that the design method is reasonable and feasible. When the nozzle length and the target distance are fixed, the possibility of two trenches will be flushed out with the increase of inclined angle of the nozzle is analyzed qualitatively.

(17) In step S1, due to the out lets of the inclined nozzle and the vertical nozzle at the same vertical heights, the target distance x.sub.i of the inclined nozzle is

(18) $\frac{1}{\cos \beta }$
times of the striking distance x.sub.v, that is

(19) $x_i=\frac{1}{\cos \beta }{x}_v,$
which is plugged into the jet flow effective pressure calculation equation; in order to use the same outlet dynamic pressure to make the inclined nozzle and vertical nozzle reach the same jet flow effective pressure at a same vertical distance, an equation is derived as:

(20) $R_i=\frac{1}{\cos \beta }{R}_v.$

(21) As shown in FIG. 4, in step S4, the boundaries around the upper block were defined as X.sub.Max, X.sub.Min, Y.sub.Max and Y.sub.Min, all of which were set as pressure outlet boundaries with a pressure value of 0, Z.sub.Max of the upper block was set as the pressure inlet boundary with a pressure value as a nozzle inlet pressure.

(22) Due to Z.sub.min of the upper block was connected to Z.sub.max of the lower block, Z.sub.min of the upper block was set as default boundary, so that the software will automatically connect to the Z.sub.Max of the block during initialization.

(23) The four boundaries of the lower block were defined as X′.sub.Max, X′.sub.Min, Y′.sub.Max and Y′.sub.Min, all of which were set as wall boundaries; due to Z′.sub.Min of the lower block is sediment, Z′.sub.Min was also set as wall boundary, and Z′.sub.Max of the lower block was set as default boundary, which was connected with the Z.sub.Min boundary of the upper block.

(24) As shown in FIG. 5, increasing the density of grids of the nozzles in two blocks and the grids in three directions of the flushing area, the grids of the remaining area was set sparsely, so as to control the grid quantity reasonably.

(25) In step S5, a sediment volume fraction was calculated by tracking a sediment concentration C.sub.s of the suspended sediment and a sediment concentration C.sub.p of the bed load using the sediment physical model; a total sediment volume fraction α.sub.s was total volume fraction of suspended sediment and bed load in the grid, with an equation:

(26) ${\alpha }_s=\frac{C_s+C_p}{{\rho }_s}=1-{\alpha }_f$ wherein, α.sub.f is a volume fraction of the fluid in a grid, ρ.sub.s is a sediment particle density, an expression for the volume fraction of the bed load is α.sub.s,p=C.sub.p/ρ.sub.s, an expression for the volume fraction of the suspended sediment is α.sub.s,s=C.sub.s/ρ.sub.s, a critical sediment volume fraction is α.sub.cr, and the total volume fraction α.sub.s is smaller or equal to the critical sediment volume fraction α.sub.cr, the parameters need to be defined in the sediment physical model are: a median particle size with the unit of m, a sediment density with the unit of kg/m.sup.3, an entrainment coefficient α.sub.i, a bed load coefficient β.sub.i, a angle of repose with the unit of °, and a critical sediment volume fraction; and the RNGk-ε model, which is applicable to calculate local flushing caused by water flow, was used in the Flow-3D as a turbulence model:

(27) $\rho \frac{Dk}{Dt}=\frac{\partial }{\partial y}\left({\alpha }_k{\mu }_{\mathrm{eff}}\frac{\partial k}{\partial y}\right)+G_k+G_b-\rho \epsilon -Y_M$$\rho \frac{D\epsilon }{Dt}=\frac{\partial }{\partial y}\left({\alpha }_{\epsilon }{\mu }_{\mathrm{eff}}\frac{\partial \epsilon }{\partial y}\right)+C_{1\epsilon }\frac{\epsilon }{k}\left(G_k+C_{3\epsilon }{G}_b\right)-C_{2\epsilon }\rho \frac{{\epsilon }^2}{k}-R$ wherein, ρ is a fluid density, t is time, k is a turbulent kinetic energy, ε is a turbulent dissipation rate; α.sub.k and α.sub.ε are inverses of the turbulent Prandtl number; μ.sub.eff and R are corrected parameters; G.sub.k and G.sub.b are respectively laminar velocity gradient and turbulent kinetic energy caused by buoyancy; Y.sub.M is turbulent expansion contribution of compressible fluid; C.sub.1ε, C.sub.2ε and C.sub.3ε are empirical constants.

(28) In step S6, the topographic surface file of the Flow-3D calculation results in step S5 was derived, the topographic surface file by Matlab was processed, and the geometric parameters of the trench profile flushed by jet flow was obtained and the trench profile flushed by jet flow was drawn.

(29) The parameter of maximum trench depth was analyzed to verify that the effective pressures acting on the sediment surface at the same vertical distance of the inclined nozzle and vertical nozzle are equal.

(30) The influence rule of nozzle angle size on the trench profile was summarized by analyzing the geometrical shape of the trench profile flushed by jet flow.

(31) Finally, it should be stated that the above embodiments are only used to illustrate the technical solutions of the present disclosure without limitation; and despite reference to the aforementioned embodiments to make a detailed description of the present disclosure, those of ordinary skilled in the art should understand: the described technical solutions in above various embodiments may be modified or the part of or all technical features may be equivalently substituted; while these modifications or substitutions do not make the essence of their corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present disclosure.