何　靖,白　丹,郭　霖,王新端

(西安理工大學(xué) 水利水電學(xué)院,陜西 西安 710048)

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豎管灌水器入滲特性影響因素分析

何靖,白丹,郭霖,王新端

(西安理工大學(xué) 水利水電學(xué)院,陜西 西安 710048)

豎管灌水器是一種用于地下灌溉系統(tǒng)的新型灌水器,本文研究影響豎管灌水器入滲特性的四個(gè)因素:壓力水頭、豎管灌水器直徑、土壤初始含水率和土壤容重等,為了研究這些因素對(duì)粉質(zhì)壤土累積入滲量的影響程度,采用正交試驗(yàn)安排試驗(yàn)方案;而對(duì)于砂質(zhì)壤土主要研究壓力水頭和豎管灌水器直徑對(duì)累積入滲量的影響。根據(jù)豎管灌水器入滲試驗(yàn)結(jié)果,采用灰色關(guān)聯(lián)度分析對(duì)影響粉質(zhì)壤土累積入滲量的影響因素進(jìn)行關(guān)聯(lián)度計(jì)算,表明壓力水頭對(duì)入滲量的影響起主導(dǎo)作用,其次依次為豎管灌水器直徑、土壤初始含水率、土壤容重;砂質(zhì)壤土試驗(yàn)結(jié)果表明:壓力水頭和豎管灌水器直徑與累積入滲量呈正相關(guān)關(guān)系,但隨著壓力水頭和豎管灌水器直徑的增大,累積入滲量的增大幅度減小。這一研究結(jié)果對(duì)進(jìn)一步研究豎管灌水器入滲規(guī)律具有重要意義。

豎管灌水器; 累積入滲量; 壓力水頭; 豎管灌水器直徑; 灰色關(guān)聯(lián)度分析

地下灌溉技術(shù)具有節(jié)水、節(jié)能、投資小、灌水均勻及使用壽命長(zhǎng)等優(yōu)點(diǎn),依據(jù)灌水器的類型,地下灌溉可分為地下滴灌[1-5]、無壓灌溉[6-7]和負(fù)水頭灌溉[8-9]等。地下灌溉技術(shù)的入滲影響因素較多,現(xiàn)有的對(duì)灌水器水力參數(shù)的分析方法主要有基于計(jì)算流體動(dòng)力學(xué)CFD數(shù)值模擬分析[10-11]和基于流體力學(xué)的理論分析[12]、試驗(yàn)分析[13],這些分析方法都是基于現(xiàn)有的一些模型對(duì)灌水器水力參數(shù)的一種數(shù)值模擬計(jì)算。為了分析豎管灌水器入滲影響因素的主次順序,本文在室內(nèi)試驗(yàn)的基礎(chǔ)上,采用灰色關(guān)聯(lián)分析法分析了豎管灌水器入滲試驗(yàn)中幾種主要影響因素對(duì)累積入滲量的影響,并對(duì)這幾個(gè)影響因素進(jìn)行了主次排序,以確定豎管灌水器入滲的主要影響因素。對(duì)豎管灌水器的入滲規(guī)律的進(jìn)一步研究提供一定的理論基礎(chǔ)。

1　入滲試驗(yàn)

1.1豎管灌水器

豎管灌水器是一種新型地下灌溉灌水器,以該灌水器為核心的灌溉系統(tǒng)同現(xiàn)有的地下灌溉系統(tǒng)的唯一區(qū)別在于灌水器。豎管灌水器為長(zhǎng)度30 cm的PVC管,其上端與毛管相連,下端開敞與土壤接觸,形成一個(gè)圓形的水土接觸面。豎管灌水器如圖1所示。

1.毛管; 2.豎管灌水器; 3.豎管灌水器剖面圖1　豎管灌水器Fig.1　Schematic diagram of vertical tube emitter

1.2試驗(yàn)材料及方法

1.2.1試驗(yàn)材料及裝置

試驗(yàn)用土選用西安周邊的粉質(zhì)壤土及新疆的砂質(zhì)壤土。西安粉土的土壤顆粒粒徑小于0.001的含量為3.817%,小于0.002的含量為8.566%,小于0.005的含量為19.857%,小于0.01的含量為34.065%,小于0.1的含量占到總量的99.868%,小于0.2的含量為99.997%。新疆砂質(zhì)壤土的土壤顆粒粒徑小于0.001的含量0.63%,小于0.002的含量為1.46%,小于0.05的含量為30.47%,小于0.1的含量為61.23%,小于0.5的含量為94.87%。

試驗(yàn)裝置主要由馬氏瓶(長(zhǎng)×寬×高:7×6×60 cm)、試驗(yàn)土箱(四周為10 mm鋼化玻璃,底部為5 mm鋼板,尺寸:長(zhǎng)41 cm×寬31 cm×高55 cm)、高度可調(diào)鐵架及核心部件豎管灌水器(豎管直徑分別為4 mm、8 mm、12 mm)。試驗(yàn)裝置如圖2所示。

1.馬氏瓶; 2.固定夾; 3.進(jìn)氣閥; 4.出水口; 5.鐵架; 6.土箱;7.豎管灌水器圖2　試驗(yàn)裝置示意圖Fig.2　Schematic diagram of experimental equipment

1.2.2試驗(yàn)方法

本次室內(nèi)試驗(yàn)中,粉質(zhì)壤土主要考慮壓力水頭h、豎管灌水器的豎管直徑d、土壤初始含水率θ和土壤容重γ四個(gè)因素。試驗(yàn)過程中,豎管灌水器的出水口處埋深均為20 cm,每組試驗(yàn)的地觀測(cè)時(shí)間為420 min,進(jìn)行3次重復(fù)取其平均值進(jìn)行分析。根據(jù)正交試驗(yàn)設(shè)計(jì)表L9(34)設(shè)計(jì)試驗(yàn)方案(見表1)。

表1　試驗(yàn)方案

砂質(zhì)壤土主要考慮壓力水頭和豎管直徑對(duì)入滲的影響。壓力水頭取1.0 m、2.0 m、3.0 m,豎管直徑取4 mm、8 mm、12 mm,埋深20 cm,初始含水率10%,容重1.35 g/cm3進(jìn)行試驗(yàn)研究,記錄300 min,進(jìn)行3次重復(fù)取其平均值進(jìn)行分析。

2　試驗(yàn)結(jié)果與分析

2.1試驗(yàn)結(jié)果

根據(jù)表1的安排進(jìn)行試驗(yàn),獲得了在表中所述4個(gè)因素的影響下各組的累積入滲量隨時(shí)間的變化情況,如圖3(a)所示。砂質(zhì)壤土給出了2.0 m壓力水頭及豎管直徑8 mm下的試驗(yàn)結(jié)果,如圖3(b)、(c)所示。

圖3　累積入滲量與時(shí)間的關(guān)系Fig.3　The relationship between cumulative infiltration and time

2.2試驗(yàn)結(jié)果分析

2.2.1粉質(zhì)壤土結(jié)果分析

為了明確粉質(zhì)壤土入滲試驗(yàn)中4個(gè)因素對(duì)累積入滲量的影響程度,本文采用灰色關(guān)聯(lián)分析法對(duì)這一試驗(yàn)結(jié)果進(jìn)行了分析。

由于4個(gè)因素與累積入滲量的量綱不同,在分析之前首先需要進(jìn)行無量綱化處理。無量綱化處理有多種方法,如初值化、均值化等方法,本文采用均值化無量綱化處理。對(duì)各數(shù)列進(jìn)行無量綱化處理,所得結(jié)果如表2所示。其中I表示累積入滲量。

由于要考慮的是各因素對(duì)累積入滲量的影響,所以將累積入滲量作為參考數(shù)列,各因素?cái)?shù)列作為對(duì)比數(shù)列。

表2　均值化值

根據(jù)表2中的均值化數(shù)值,計(jì)算各比較數(shù)列同參考數(shù)列的絕對(duì)差。計(jì)算步驟如下。

試驗(yàn)1:

根據(jù)上述計(jì)算步驟,再分別計(jì)算出其余8組試驗(yàn)的絕對(duì)差,結(jié)果如表3所示。

由表3中可以獲得最大和最小絕對(duì)差值分別為:Δmax=0.938 7，Δmin=0.015 4。

表3　絕對(duì)差序列

由此可以計(jì)算各因素對(duì)累積入滲量的關(guān)聯(lián)系數(shù),在計(jì)算關(guān)聯(lián)系數(shù)時(shí),分辨系數(shù)ρ取值0.05[14-15]。計(jì)算步驟如下:

計(jì)算結(jié)果如表4所示。

表4　關(guān)聯(lián)系數(shù)值

從表4中,可以知道任意一組試驗(yàn)中任一因素對(duì)累積入滲量的關(guān)聯(lián)系數(shù),基于此,進(jìn)行關(guān)聯(lián)度r的計(jì)算。關(guān)聯(lián)度計(jì)算步驟如下:

對(duì)計(jì)算得到的4個(gè)關(guān)聯(lián)度數(shù)值按照大小進(jìn)行排序:r(01)>r(02)>r(03)>r(04),即:4個(gè)因素對(duì)累積入滲量的關(guān)聯(lián)度的排序?yàn)閴毫λ^h、豎管灌水器的豎管直徑d、土壤的初始含水率θ、土壤容重γ。由此可以看出:在多因素影響豎管灌水器入滲試驗(yàn)中,壓力水頭居于主導(dǎo)地位,對(duì)累積入滲量的變化影響最大;豎管灌水器的豎管直徑和土壤初始含水率對(duì)于累積入滲量的關(guān)聯(lián)度處在同一數(shù)值水平上,對(duì)累積入滲量起到次要的影響作用;土壤容重的影響程度居于末位。

2.2.2砂質(zhì)壤土結(jié)果分析

由圖3(b)中可以看出,在壓力水頭一定的條件下,隨著豎管直徑的增大累積入滲量也在增大。最大累積入滲量依次為2.24 L、2.69 L和3.06 L,4 mm管徑時(shí)的累積入滲量最小,12 mm時(shí)的累積入滲量最大,表明管徑對(duì)累積入滲量有一定的影響程度。經(jīng)過計(jì)算,12 mm管徑較之8 mm管徑的累積入滲量增大了13.8%,8 mm管徑較之4 mm管徑的累積入滲量增大了20.1%;累積入滲量呈現(xiàn)正相關(guān)關(guān)系,即隨管徑增大,累積入滲量增大。

由圖3(c)可以看出,在豎管直徑一定的條件下,壓力水頭對(duì)豎管地下灌溉土壤累積入滲量具有明顯的作用。土壤的累積入滲量隨著壓力水頭的增大而增大。在實(shí)際應(yīng)用中,可以根據(jù)不同作物的需水要求,選擇適宜的壓力水頭。開始灌水3 h后,壓力水頭3.0 m的豎管灌溉累積入滲量比2.0 m的大15.7%、8.2%和7.6%(管徑由小到大),壓力水頭2.0 m的比1.0 m的大71.4%、16.1%和10.0%,5 h后,依次為31.0%、6.3%和6.0%;4.3%、10.4%和10.4%;57.1%、15.2%和9.4%。從以上數(shù)據(jù)可以看出,隨入滲時(shí)間增加,壓力水頭對(duì)累積入滲量變化的影響程度減小。因?yàn)樵诠嗨跗?土壤含水率較低,土壤水分?jǐn)U散為非飽和入滲[16],灌溉水分入滲主要受土壤基質(zhì)勢(shì)的作用;隨著水分的不斷入滲,水土結(jié)合面周圍的土壤含水率逐漸增大,在水土結(jié)合面周圍形成一個(gè)土壤含水率趨于飽和[17]的飽和帶,在該過程中灌溉水受基質(zhì)勢(shì)和壓力勢(shì)的共同作用,基質(zhì)勢(shì)的作用逐漸減小,壓力勢(shì)的作用逐漸增大;當(dāng)土壤達(dá)到飽和含水率時(shí),基質(zhì)勢(shì)為零,此時(shí)灌溉水入滲主要受壓力勢(shì)的作用。

3　結(jié)　論

1) 粉質(zhì)壤土試驗(yàn)通過灰色關(guān)聯(lián)法分析,確定四種影響因素的影響程度大小順序?yàn)?壓力水頭、豎管直徑、土壤初始含水率、土壤容重;壓力水頭是影響豎管灌水器水分入滲的主要因素,豎管灌水器的豎管直徑和土壤初始含水率為次要因素,土壤容重居于末位。

2) 砂質(zhì)壤土試驗(yàn)得出:豎管直徑和壓力水頭均對(duì)累積入滲量呈現(xiàn)為正相關(guān)影響,但隨著時(shí)間的增加,影響程度逐漸減小。

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(責(zé)任編輯王緒迪，王衛(wèi)勛)

Study on influence factors of vertical tube emitter’s infiltration characteristics

HE Jing,BAI Dan,GUO Lin,WANG Xinduan

(School of Water Resources and Hydroelectric Engineering, Xi’an University of Technology, Xi’an 710048, China)

Vertical tube emitter is a new type emitter applied for sub-irrigation system, in order to analyze the importance for cumulative infiltration of silt loam by influence factors which including pressure head, diameter of vertical tube, initial soil moisture content and soil bulk density. So as to the laboratory test have the accuracy, universal and representativeness, the nine groups of the experimental schemes designed based on the orthogonal experimental design table L9(34). In addition, the experiment of effects on sandy loam cumulative infiltration with influence factors of pressure head and diameter of vertical tube carried out. A Mariotte bottle used to regulate the pressure head. The total infiltration time was 7h for every treatment of silt loam and 5h for sandy loam, and the interface-between soil and outlet of emitter—was buried 20cm for every test. According to the results of experiments for silt loam, used grey correlational analysis method to calculate incidence degree between influence factors and cumulative infiltration. The incidence degree pointed out that pressure head was the main influence factor and the order of factors with incidence degree was pressure head>diameter of vertical tube>initial soil moisture content>soil bulk density. The experimental results of sandy loam showed that pressure head and diameter of vertical tube had a positive effect on cumulative infiltration; with the increasing of pressure head and diameter of vertical tube the rangeability of cumulative infiltration decreases. This research has an important significance on further study on infiltration law of vertical tube emitter.

vertical tube emitter; cumulative infiltration; pressure head; diameter of vertical tube emitter; gray correlation analysis

10.19322/j.cnki.issn.1006-4710.2016.03.018

2015-12-04

國(guó)家自然科學(xué)基金資助項(xiàng)目(41571222,5129156);高等學(xué)校博士學(xué)科點(diǎn)專項(xiàng)科研基金聯(lián)合資助課題(20116118110010);陜西省農(nóng)業(yè)科技攻關(guān)項(xiàng)目(2010K02-08)

何靖,男,碩士生,研究方向?yàn)楣?jié)水灌溉理論與技術(shù)研究。E-mail:18700409806@163.com

白丹,男,博士,教授,博導(dǎo),研究方向?yàn)楣?jié)水灌溉理論與技術(shù)。E-mail:baidan@xaut.edu.cn

S275.4

A

1006-4710(2016)03-0354-05