Quantitative design method for pressure steel branch pipe group

Abstract

The invention discloses a quantitative design method for a pressure steel bifurcated pipe group in the field of hydraulic engineering, which comprises the following steps of: firstly, formulating quantitative indexes, head loss and total weight of steel pipes of the steel bifurcated pipe group according to actual engineering conditions, and then completing preliminary design of a steel bifurcated pipe group structure according to the actual engineering conditions; the hydraulic calculation formula, the finite element fluid numerical calculation method and the model test are sequentially used for calculating and verifying the head loss of the steel bifurcated pipe group, finally, structural stress analysis and weight calculation are conducted on the steel bifurcated pipe group, and during the period, the index requirement is met by adjusting the structural design. According to the method, the design thought that the quantitative indexes are formulated firstly and then the structure is optimized according to the quantitative indexes is adopted, the steel bifurcated pipe structure is adjusted according to the steps that the head loss is met firstly, then the structural strength is met, and the structural weight is optimized in combination with a feedback mechanism, and optimal design of the head loss and the steel pipe weight is achieved; and the design efficiency and the structural performance of the steel branch pipe group are improved, and the engineering cost is reduced.

Description

Technical Field

[0001] The invention relates to the field of water conservancy projects, and in particular to a quantitative design method for a pressure steel bifurcated pipe group. Background Art

[0002] The design of the penstock pipe of a hydropower station is a key and important part of the design of the entire penstock. The design of penstock and bifurcated pipes includes structural stress analysis and head loss analysis. The traditional steel bifurcated pipe layout is simple. The design generally determines the inlet and outlet diameters of the steel bifurcated pipe from the empirical flow rate, selects a certain bifurcation angle, and then directly enters the structural design. There is no quantitative regulation for head loss, that is, the steel bifurcated pipe is designed from a single structural perspective. However, when there are many penstock pipes in a hydropower station, the head loss of the penstock and bifurcated pipe cannot be ignored. Therefore, from the perspective of layout, it is necessary to consider that the structural stress and head loss of the steel bifurcated pipe can meet the requirements, which requires a quantitative design of the steel bifurcated pipe group. How to ensure that the hydraulics of the penstock are optimal, the head loss is minimized, and at the same time, the penstock structure is best stressed and the steel consumption of the penstock is the most economical are two important assessment indicators for the design of the penstock.

[0003] In general, the head loss of a pressure steel bifurcated pipe group is inversely proportional to its weight. The head loss is a function of the diameter D, the roughness n, and the bifurcated pipe geometry S, i.e. H = n / D(S). That is, the greater the roughness, the greater the head loss, and the larger the steel pipe diameter, the smaller the head loss. At the same time, the bifurcated pipe geometry S is also an implicit function of the diameter. If the shape is good, the diameter can be reduced, and if the shape is not good, the diameter needs to be increased, which affects the weight accordingly.

[0004] The weight T of the steel bifurcated pipe group is directly proportional to the diameter D and the wall thickness t, that is, T = Dt. The head loss variable H and the weight variable T of the steel bifurcated pipe group have been given target values ​​at the beginning of the design, so the product K = H*T is a constant. When the design is completed, the K value is larger than the given value, indicating that H or T needs to be reduced, or both need to be adjusted. The design of the entire pipeline is based on the variables of H and T, and the two variables are inversely proportional. If you want to reduce H, the diameter D of the steel pipe must be increased, and the weight T will also increase. If you want to reduce T, the D(S) of the steel pipe needs to be reduced or the size S needs to be optimized so that the wall thickness can be reduced and the weight can be reduced, but H will increase. At present, the existing literature cannot provide good guidance on how to balance these two indicators. Summary of the invention

[0005] In order to overcome the above-mentioned deficiencies in the existing steel bifurcation pipe design based on general experience, the technical problem to be solved by the present invention is to provide a quantitative design method for pressure steel bifurcation pipe groups that can take into account both head loss and structural lightweight.

[0006] The technical solution adopted by the present invention to solve its technical problem is:

[0007] A quantitative design method for a pressure steel bifurcated pipe group comprises the following steps:

[0008] Step 1: Develop quantitative indicators for the steel bifurcated pipe group based on the actual project conditions, including the head loss H from the start to the end of the steel pipe and the total weight T of the steel pipe;

[0009] Step 2: Complete the preliminary design of the steel bifurcated pipe group structure according to the actual project situation;

[0010] Step 3: Calculate the head loss of the steel bifurcated pipe group using the hydraulic calculation formula. When the calculated head loss is less than H, proceed to step 4, otherwise return to step 2 to readjust the layout and structure of the steel bifurcated pipe group.

[0011] Step 4: Calculate the head loss of the pressure steel pipe using the finite element fluid numerical calculation method. When the calculated head loss is less than H, proceed to step 5, otherwise return to step 2 to readjust the layout and structure of the steel bifurcated pipe group;

[0012] Step 5: Use a model test to verify the head loss of the steel bifurcated pipe group structure. When the test head loss is less than H, proceed to step 6, otherwise return to step 2 to readjust the layout and structure of the steel bifurcated pipe group;

[0013] Step 6: Perform structural stress analysis on the steel bifurcated pipe group. If the requirements are met, calculate the total weight of the steel pipe according to the current steel pipe wall thickness. When the calculated weight is less than T, proceed to step 7, otherwise return to step 2 to readjust the layout and structure of the steel bifurcated pipe group; if the stress analysis does not meet the requirements, adjust the steel pipe wall thickness and re-analyze until the stress requirements are met;

[0014] Step 7: Manufacture and install the steel pipes, and measure the head loss on site after completion.

[0015] Furthermore, in step three, the local head loss at the fork pipe portion of the steel fork pipe is calculated in detail.

[0016] Furthermore, in step four, the finite element fluid numerical calculation method is used to simulate the various geometric mutations, bifurcation angles and local water flow patterns of the actual turning points of the steel bifurcation pipe group, and the parameter ranges of the bifurcation angles, transition cone angles and flow surface widths of the reinforcing beams of each bifurcation pipe are determined through multiple scheme comparisons, and the structure of the steel bifurcation pipe group is subsequently adjusted within this parameter range.

[0017] Furthermore, in step five, a physical model is established according to the parameter range determined in step four, the scale of the model to the actual project is 1:20, and the actual head loss is measured through a hydraulic model test.

[0018] Furthermore, in step six, when the structural force analysis meets the requirements but the weight does not meet the requirements, the wall thickness of the steel pipe can be gradually reduced. During this process, if both the force requirements and the weight requirements are met at the same time, proceed to step seven, otherwise return to step two to readjust the layout and structure of the steel branch pipe group.

[0019] The beneficial effects of the present invention are as follows: a design concept of first formulating quantitative indicators and then optimizing the structure according to the quantitative indicators is adopted, the arrangement and shape parameters of the bifurcated pipes are adjusted according to the steps of first satisfying the head loss, then satisfying the structural strength, and then optimizing the structural weight, and a feedback mechanism is combined to finally obtain a solution that can simultaneously satisfy the head loss and the weight of the steel pipes, thereby improving the design efficiency and structural performance of the steel bifurcated pipe group and reducing the engineering cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a design flow chart of the present invention. DETAILED DESCRIPTION

[0021] The present invention is further described below in conjunction with the accompanying drawings.

[0022] The invention provides a method for quantitatively designing a pressure steel bifurcated pipe group, comprising the following steps:

[0023] Step 1: Develop quantitative indicators for the steel bifurcated pipe group based on the actual project conditions, including the head loss H from the start to the end of the steel pipe and the total weight T of the steel pipe;

[0024] Step 2: Complete the preliminary design of the layout and structure of the steel bifurcated pipe group according to the actual project situation;

[0025] Step 3: Calculate the head loss of the steel bifurcated pipe group using the hydraulic calculation formula. When the calculated head loss is less than H, proceed to step 4, otherwise return to step 2 to readjust the layout and structure of the steel bifurcated pipe group.

[0026] Step 4: Calculate the head loss of the pressure steel pipe using the finite element fluid numerical calculation method. When the calculated head loss is less than H, proceed to step 5, otherwise return to step 2 to readjust the layout and structure of the steel bifurcated pipe group;

[0027] Step 5: Use a model test to verify the head loss of the steel bifurcated pipe group structure. When the test head loss is less than H, proceed to step 6, otherwise return to step 2 to readjust the layout and structure of the steel bifurcated pipe group;

[0028] Step 6: Perform structural stress analysis on the steel bifurcated pipe group. If the requirements are met, calculate the total weight of the steel pipe according to the current steel pipe wall thickness. When the calculated weight is less than T, proceed to step 7, otherwise return to step 2 to readjust the layout and structure of the steel bifurcated pipe group; if the stress analysis does not meet the requirements, adjust the steel pipe wall thickness and re-analyze until the stress requirements are met;

[0029] Step 7: Manufacture and install the steel pipes, and measure the head loss on site after completion.

[0030] Because the head loss directly affects the power generation performance of the power plant, the head loss is considered first during the design. In the preliminary design stage of the steel bifurcated pipe group, the maximum allowable head loss is calculated and determined according to the power generation output requirements of the power station. In the subsequent detailed design stage, this maximum head loss value is used as a quantitative indicator for the head loss control of the steel bifurcated pipe group. Among them, steps three, four and five are all analyzing the head loss, and the focus is on calculating the local head loss of the bifurcated pipe part of the steel bifurcated pipe. Because of the steel bifurcated pipe group, the local head loss of the bifurcated pipe accounts for the main proportion. Controlling the bifurcated pipe body shape and reducing this head as much as possible can easily meet the limit value requirements. The mechanical calculation in step three is mainly a rough judgment, because when there are many bifurcated pipes, the local mechanical calculation is more complicated and may not be accurate enough. Therefore, it is necessary to perform finite element analysis in step four. The finite element fluid numerical calculation method can fully simulate the various geometric mutations, bifurcation angles and actual turning local water flow patterns and head losses of the steel bifurcated pipe group. At the same time, this method can also be used for multi-scheme comparison and optimization. Find the key factors affecting the head loss, conduct a sensitivity analysis on the factors, and determine the appropriate parameters of the steel bifurcated pipe body, including the range of parameters such as the bifurcation angle, transition cone angle, and the width of the flow surface extending from the reinforcing beam. The structure of the steel bifurcated pipe group can be adjusted within this parameter range. Step five is mainly to conduct a practical verification of the theoretical analysis. According to the parameter range determined in step four, a physical model is established. The ratio of the physical model to the actual project can be set to 1:20, and then the actual head loss is measured through a hydraulic model test to verify whether the theoretical basis of the design is correct.

[0031] After meeting the head loss requirements, the mechanical analysis and weight calculation of the pressure steel pipe are carried out. In the preliminary design stage of the steel bifurcated pipe group, the maximum allowable weight of the steel bifurcated pipe group is calculated and determined according to the cost control and economic requirements of the power station construction. This maximum allowable weight is used as a quantitative indicator for the weight control of the steel bifurcated pipe group in the subsequent detailed design stage. For mechanical analysis, it can actually be carried out simultaneously in step 4, and the stress conditions of each part are determined by finite element analysis. Because in the initial preliminary design, the wall thickness of the steel pipe may be designed to be thinner or thicker, so in step 6, when the structural stress analysis meets the requirements and the weight does not meet the requirements, the wall thickness of the steel pipe can be gradually reduced. In this process, if the stress requirements and weight requirements are met at the same time, step 7 is performed, otherwise, return to step 2 to readjust the structure of the steel bifurcated pipe group; when the stress analysis does not meet the requirements, the wall thickness of the steel pipe is gradually increased. If the stress requirements and weight requirements are met at the same time, step 7 is performed, otherwise, return to step 2 to readjust the structure of the steel bifurcated pipe group. Ultimately, the optimization goal is achieved that the head loss and the total weight of the steel pipe are respectively less than the head loss H and the total weight T of the steel pipe set in step one.

[0032] The present invention will be further described below in conjunction with embodiments.

[0033] Taking a complex pressure steel bifurcated pipe group as an example, the quantitative design method of pressure steel bifurcated pipe group is elaborated in detail:

[0034] The two quantitative control indicators in the quantitative design method of steel bifurcated pipe groups are that the average head loss H of the three units from the starting point to the end point of the steel pipe does not exceed 2.893m, and the total weight T of the steel pipe from the starting point to the end point does not exceed 10017t.

[0035] The constraint index product of the steel bifurcated pipe group is HT=2.893*10017=28979.181 (mt).

[0036] first step:

[0037] The layout design of the steel bifurcated pipe group was carried out, and the head loss of the complex bifurcated pipe group was calculated using the empirical hydraulic calculation formula when determining the preliminary head loss. After calculation, the head loss of the pressure steel pipe is: H = 2.775m, which meets the limit value of 2.894m. At this time, the structural strength design is not carried out to determine the thickness of the steel pipe, and further analysis of the head loss is required;

[0038] Step 2:

[0039] The finite element fluid numerical calculation method is used to calculate the head loss of the pressure steel pipe, and the head loss H = 2.416m is further accurately calculated, which also meets the limit value requirements;

[0040] Step 3:

[0041] According to the bifurcation arrangement and shape parameters (bifurcation angle, transition cone angle, width of the inner extension flow surface of the reinforcing beam, etc.) determined in the second step, a 1:20 overall physical model of the steel bifurcation group was established by physical model test. Through hydraulic model test, the head loss of the bifurcation group was further understood. The head loss value of the bifurcation determined by this arrangement was H = 2.521m, which also met the limit value requirement.

[0042] Step 4:

[0043] After the above three steps are completed, it is necessary to analyze the structure of the steel bifurcated pipe group, determine the thickness t of each part of the steel bifurcated pipe group, and further calculate the weight of the entire steel bifurcated pipe group. The final weight of the steel bifurcated pipe group is T = 8500t, which meets the limit value of 10017t. If the wall thickness of the obtained steel bifurcated pipe group is too large and the weight exceeds 10017t, it is necessary to repeat the calculation and adjustment of the above three steps and redesign until both H and T meet the requirements.

[0044] Step 5:

[0045] When the power station is actually operating and generating electricity, the head loss is measured at the start and end of the penstock. If the head loss of the penstock meets the limit value of 2.894m, the requirements are met. The measured head loss is 1.635m, which meets the design requirements.

Claims

1. A quantitative design method for a pressure steel bifurcated pipe group, characterized in that: The following steps are involved: Step 1: Develop quantitative indicators for the steel bifurcated pipe group based on the actual project conditions, including the head loss H from the start to the end of the steel pipe and the total weight T of the steel pipe; Step 2: Complete the preliminary design of the layout and structure of the steel bifurcated pipe group according to the actual project situation; Step 3: Calculate the head loss of the steel bifurcated pipe group using the hydraulic calculation formula. When the calculated head loss is less than H, proceed to step 4, otherwise return to step 2 to readjust the layout and structure of the steel bifurcated pipe group. Step 4: Calculate the head loss of the pressure steel pipe using the finite element fluid numerical calculation method. When the calculated head loss is less than H, proceed to step 5, otherwise return to step 2 to readjust the layout and structure of the steel bifurcated pipe group; Step 5: Use a model test to verify the head loss of the steel bifurcated pipe group structure. When the test head loss is less than H, proceed to step 6, otherwise return to step 2 to readjust the layout and structure of the steel bifurcated pipe group; Step 6: Perform structural stress analysis on the steel bifurcated pipe group. If the requirements are met, calculate the total weight of the steel pipe according to the current steel pipe wall thickness. When the calculated weight is less than T, proceed to step 7, otherwise return to step 2 to readjust the layout and structure of the steel bifurcated pipe group; if the stress analysis does not meet the requirements, adjust the steel pipe wall thickness and re-analyze until the stress requirements are met; Step 7: Manufacture and install the steel pipes, and measure the head loss on site after completion.

2. A method for quantitatively designing a pressure steel bifurcated pipe group as claimed in claim 1, characterized in that: In step three, the focus is on calculating the local head loss at the fork pipe of the steel fork pipe.

3. A method for quantitatively designing a pressure steel bifurcated pipe group as claimed in claim 1, characterized in that: In step four, the finite element fluid numerical calculation method is used to simulate the geometric mutations, bifurcation angles and local water flow patterns of the actual turning points of the steel bifurcation pipe group, and the parameter ranges of the bifurcation angles, transition cone angles and flow surface widths of the reinforcing beams of each bifurcation pipe are determined through multiple scheme comparisons. The structure of the steel bifurcation pipe group is subsequently adjusted within this parameter range.

4. A method for quantitatively designing a pressure steel bifurcated pipe group as claimed in claim 3, characterized in that: In step five, a physical model is established according to the parameter range determined in step four. The scale of the model to the actual project is 1:20, and the actual head loss is measured through a hydraulic model test.

5. A method for quantitatively designing a pressure steel bifurcated pipe group as claimed in claim 1, characterized in that: In step six, when the structural force analysis meets the requirements but the weight does not meet the requirements, the wall thickness of the steel pipe can be gradually reduced. During this process, if both the force requirements and the weight requirements are met at the same time, proceed to step seven, otherwise return to step two to readjust the structure of the steel branch pipe group.

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