The Water Hammer Characteristics of Long-Distance Water Pipelines under Different Water Supply Modes

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The transient characteristics are analyzed for a gravity flow and pump-pressurization hydraulic systems with long-distance pipelines under different valve closing time conditions in the manuscript. Furthermore, the effects of interval time and closing time on transient pressure characteristics under the multiple valves closed sequentially are studied.

Suggestion:

(1) The research statuses of domestically and internationally including the characteristics of long-distance water transportation systems, hydraulic transients, calculation methods, and existing problems are not analyzed systematically.

(2) It can be preliminarily concluded from the model validation in 2.3 that the calculation results are based on the program written by yourselves, however, the discretization schemes for the governing equations are not provided in the manuscript.

(3) The full characteristics of a pump have a significant impact on the transient for a pump pressurized hydraulic system under the valve closing condition, however, the full characteristic curves and the motion equation of the pump are not given in the manuscript.

(4) The boundary conditions of the valves have a significant impact on the transient characteristics under the valve closing condition, which is not provided in the manuscript.

(5) During the transition process of a hydraulic system with a pump, the rotation speed change of the pump is important and affects the safe operation of the unit, which is not provided in the manuscript.

(6) In line 121, "H denotes the total hydraulic head;" should be “H denotes the piezometric head”.

(7) in Line 213, in "Figure 4. Pump Water Supply Characteristics ", the pump efficiency decreases with the increase of flow rate, especially, the pump efficiency reaches its maximum at the flow rate of 0, which is against the external characteristics of the pump, but the detailed explanation is not provided in the manuscript..

(8) From lines 236-240, it cannot be concluded that the upstream air valve utilization efficiency is higher than that of the downstream air valve. 

(9) The time step and wave speed for numerical calculation are not provided.

Comments on the Quality of English Language

The transient characteristics are analyzed for a gravity flow and pump-pressurization hydraulic systems with long-distance pipelines under different valve closing time conditions in the manuscript. Furthermore, the effects of interval time and closing time on transient pressure characteristics under the multiple valves closed sequentially are studied.

Suggestion:

(1) The research statuses of domestically and internationally including the characteristics of long-distance water transportation systems, hydraulic transients, calculation methods, and existing problems are not analyzed systematically.

(2) It can be preliminarily concluded from the model validation in 2.3 that the calculation results are based on the program written by yourselves, however, the discretization schemes for the governing equations are not provided in the manuscript.

(3) The full characteristics of a pump have a significant impact on the transient for a pump pressurized hydraulic system under the valve closing condition, however, the full characteristic curves and the motion equation of the pump are not given in the manuscript.

(4) The boundary conditions of the valves have a significant impact on the transient characteristics under the valve closing condition, which is not provided in the manuscript.

(5) During the transition process of a hydraulic system with a pump, the rotation speed change of the pump is important and affects the safe operation of the unit, which is not provided in the manuscript.

(6) In line 121, "H denotes the total hydraulic head;" should be “H denotes the piezometric head”.

(7) in Line 213, in "Figure 4. Pump Water Supply Characteristics ", the pump efficiency decreases with the increase of flow rate, especially, the pump efficiency reaches its maximum at the flow rate of 0, which is against the external characteristics of the pump, but the detailed explanation is not provided in the manuscript..

(8) From lines 236-240, it cannot be concluded that the upstream air valve utilization efficiency is higher than that of the downstream air valve. 

(9) The time step and wave speed for numerical calculation are not provided.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The article is very interesting and deals with topical issues in many parts of the world. It is also relevant from both a scientific and technical point of view. To enrich the article, consider including the following corrections:

- Introduction - the theses put forward are unreadable and even contradictory. What do the authors mean by simultaneous gravity and pumped flow?

- Mathematical Model - the analyzed pipeline is designed in a suboptimal way, a better solution would be to lay at least two pipelines connected to each other in such a way that it is possible to use the entire length or a fragment, for example, during a failure or damage - Missing evaluation of the existing situation.

- Simulation Results Analysis - the subsection "Analysis of Water Supply Modes for Water Conveyance Pipeline" the two initial paragraphs should probably be in Section 2.1 Water Conveyance Pipeline.

Lines 221-222: the statement " air valves need to be installed at higher positions to mitigate the adverse effects of water hammer during hydraulic transient processes" is obvious and adds nothing new.

- Discussion - most of the content is not a substantive discussion of the results but background information that should be found in the Introduction. Consequently, the chapter is quite poor and does not exhaust the issue.

- Conclusions - the conclusions concern: 1. confirms the impossibility of simultaneous gravity and forced pump operation, which is obvious. 2 and 3 confirm theses that were not clearly formulated before.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

I think, the section 2.2. Methods needs to be revised.

Item 2.2.1 is called Basic Equations of the Method of Characteristics. But the method of characteristic is the solving techniques, not the mathematical model.

Equations (1) and (2) are typical equations describing long pipelines. However, it seems to me that they are worth describing in more detail: what assumptions do they make, what simplifications are there? It would also be good to provide a reference to the work (for example, a textbook on hydraulics), where they are described in detail.

I would also like more details on how the characteristics method was implemented. Homemade code? Commercial software package? What discretization was used?

It is also worth inserting a reference where the equations (3-6) for subsonic and sonic gas outflow from a reservoir are taken from.

In line 146 the ideal gas equation is mentioned. Please explain how it is justified to use this equation (instead of more complex equations)?

 

Comments on the Quality of English Language

Lines 324-325: the two supply modes cannot simultaneously supply flow – I suggest to change this phrase, as it’s hard to understand it

Author Response

Please see the attachment.

Author Response File: Author Response.pdf