Accurately determining the resistance coefficient of a pipe network under operational conditions is a crucial step in constructing an accurate hydraulic model. In heating systems, the limited number of measurement points poses a challenge, as the identified resistance coefficient of each pipeline may be expected. A resistance coefficient identification scheme based on the Differential Evolution algorithm (DE) is proposed to address this. Through simulations of a real pipe network, it is observed that the resistance coefficients identified by DE exhibit an approximately normal distribution. Building upon this observation, the proposed scheme generates an optimal solution set through multiple runs of the DE. The final optimal solution is then deduced based on the characteristics of the normal distribution. An actual pipe network with 14 thermal inlets is employed to validate the scheme’s feasibility. It is found that the identification process can be terminated after 1088 runs of the DE. The absolute relative error between the calculated and observed flows remains below the impressive threshold of 1%. These results prove that the scheme can significantly improve the stability and uniqueness of the resistance coefficient identification results.
The hydraulic and thermal simulation methods of heating pipe networks are reviewed.The development process of steady-state hydraulic simula-tion solution,dynamic hydraulic simulation solution,steady-state thermal simulation solution,and dynamic thermal simulation solution is elaborated.The applica-tion and development trend of simulation in the back-ground of digital twins are analyzed.
The variation characteristics of daily natural gas supply are analyzed.The factors that affect the daily natural gas supply are selected.Through cor-relation analysis,it is determined that the main influen-cing factors of daily gas supply are:date type,daily minimum temperature,daily maximum temperature,daily average temperature,weather type,air quality in-dex,PM2.5 index,PM 10 index,daily average air pres-sure and daily average relative humidity.The variation law of daily natural gas supply under the influence of different influencing factors is discussed.The variation trend of daily gas supply is opposite to that of tempera-ture,and the daily gas supply is affected by tempera-ture in both sensitive and insensitive ranges.The influ-ence of daily average air pressure and daily average relative humidity on daily gas supply has a significant seasonal variation.The variation of daily gas supply is the same as that of daily average air pressure in spring and autumn,but it is opposite to that of daily average relative humidity in autumn and winter.The daily gas supply increases with the decrease in air quality.The daily gas supply has an increasing trend in snowy days,but a decreasing trend in blizzard days.The daily gas supply has a downward trend during statutory holidays,and the decrease increases with the extension of holiday time.
The characteristics of non-destructive testing technologies such as ultrasonic phased array,digital ray,ultrasonic guided wave and microwave,etc,as well as their application scenarios in urban gas pipe-lines are analyzed from the two perspectives of steel pipeline testing and PE pipeline testing.The testing effect of ultrasonic phased array and digital ray testing technology on PE electrofusion joints and heated-tool fusion joints is verified through experiments.The ultra-sonic phased array testing technology can be used for the detection of steel pipeline welds and PE pipeline electrofusion joints.It can effectively detect various de-fects in steel pipeline welds and PE pipeline electrofu-sion joints,and can detect metal and non-metallic in-clusion defects in PE pipeline heated-tool fusion joints.Digital ray testing technology can effectively detect va-rious defects in steel pipeline welds,as well as metal inclusion defects in PE pipeline electrofusion joints and heated-tool fusion joints.Ultrasonic guided wave tes-ting technology can quickly detect the defects of long distance steel pipelines,but it cannot effectively identi-fy defects in welds.Microwave technology can effec-tively detect defects such as incomplete fusion and in-clusions,etc,in PE heated-tool fusion joints,and the development of relevant standards will effectively pro-mote the use of microwave testing technology.
The determination of direct replace-ment parameters(replacement qualification standard,replacement pressure,replacement flow rate,replace-ment time and grounding resistance)is discussed.The selection of replacement release points is analyzed.The direct replacement process of urban natural gas pipe-lines(trunk pipeline,ring pipeline and branched pipe-line)is introduced.The safety precautions for direct replacement are summarized.
