本文選題：沿海防護林 + 水杉　； 參考：《中國林業(yè)科學研究院》2017年碩士論文

【摘要】：為了更好地客觀地闡明林帶的空氣動力學機理,提高林帶邊界層流數(shù)值模擬的精度。本研究以沿海水杉和楊樹防護林帶為研究對象,通過標準木解析,利用胸徑、樹高和冠層半徑等指標,構建了水杉、楊樹林帶的三維結(jié)構參數(shù)模型;利用林帶的三維結(jié)構參數(shù)模型計算了水杉、楊樹林帶的空氣動力學參數(shù),運用FLUENT軟件進行林帶風流場數(shù)值模擬,分析了不同林帶的防護效應特征;并且對林帶的密度調(diào)控和復層林構建兩種結(jié)構調(diào)控措施進行了模擬,探討了不同措施對林帶防護效應的影響,篩選合適的林帶結(jié)構,以期為沿海防護林帶規(guī)劃設計和經(jīng)營管理提供依據(jù)。研究結(jié)果表明:(1)水杉林帶的表面積密度變化范圍為0.0012~3.4857 m2·m-3,體積密度變化范圍為0.000002~0.012397 m3·m-3;楊樹林帶的表面積密度變化范圍為0.0070~7.9337m2·m-3,體積密度變化范圍為0.000008~0.008028m3·m-3。整體上,楊樹林帶的表面積密度和體積密度要大于水杉林帶。林帶結(jié)構在空間上有十分明顯的異質(zhì)性:樹干的直徑隨著高度的上升而降低,水杉、楊樹林帶樹干的表面積和體積也隨之下降。水杉、楊樹林帶的枝下高分別為4m和6m,林帶冠層以下形成了較大空隙。在林帶冠層,枝條的表面積和體積密度隨著高度先上升后下降。水杉枝條表面積和體積密度的峰值出現(xiàn)在冠層的中部,楊樹則出現(xiàn)在冠層中上部。水杉葉片和枝條的分布特征較為一致,表面積和體積密度峰值出現(xiàn)的位置和枝條大致相同,楊樹葉片則主要集中在冠層的上部。林帶內(nèi)各組分表面積和體積占總體的比例差異較大:水杉各組分表面積占總體比例為葉片(78.39%)枝條(16.04%)樹干(5.57%),楊樹為葉片(84.76%)枝條(12.13%)樹干(3.11%);水杉各組分體積占總體比例為樹干(75.28%)枝條(20.85%)葉片(3.87%),楊樹為樹干(67.81%)枝條(26.34%)葉片(5.85%)。水杉表面積體積比:葉片(20.23)枝條(0.77)樹干(0.07),楊樹表面積體積比:葉片(14.49)枝條(0.46)樹干(0.05)。(2)通過對比水杉和楊樹林帶的風流場數(shù)值模擬結(jié)果發(fā)現(xiàn),水杉和楊樹林帶前的氣流變化趨勢基本一致:氣流在林帶前4H-6H左右受到林帶的影響,速度開始輕微下降,運動到達林帶前2H位置,流速急劇下降。而林帶后,氣流變化趨勢差異較大。在近地面區(qū)域,由于林帶冠層有較大空隙,流速衰減幅度小于林帶冠層區(qū)域。同時由于冠層枝葉密度較大,林帶冠層氣流發(fā)生分離、下沉,近地面氣流受到擠壓,流在林帶后小范圍有一定回升,隨后受擠壓的氣流產(chǎn)生擴散,氣流速度再次下降,之后緩慢恢復。冠層氣流的衰減程度相對較大,但由于近地面氣流的擴散,冠層氣流與擴散的氣流產(chǎn)生動量交換,氣流速度在林后小范圍內(nèi)急劇上升,隨后平緩恢復。對比水杉和楊樹林帶,由于楊樹林帶的整體密度要高于水杉林帶,楊樹林帶各高度上的風速衰減和氣流恢復速度基本都低于水杉林帶,有效防護距離比水杉大12H以上。因此,本研究中楊樹林帶的防護效果要強于水杉林帶。(3)不同株行距的水杉和楊樹林帶數(shù)值模擬結(jié)果表明:在林帶前,氣流流速受林帶株行距的影響較小。在林帶后,氣流整體的變化趨勢基本相同:氣流的衰減幅度隨著株行距的縮小而增加。各個高度上,株行距3m×2m和2m×2m的水杉林帶與3m×3m的林帶相比有效防護距離提升了2H-4H,楊樹林帶則提升了4H-7H。但林帶株行距也不宜進一步縮小。對于水杉林帶,株行距為2m×2m時,近地面速度接近于0,株行距進一步縮小林后將產(chǎn)生回流。株行距2m×2m的楊樹林帶與3m×2m的相比,氣流回流范圍有一定的擴大,回流位置有少許下移。綜上,對于水杉林帶,株行距2m×2m時,林帶防護效應較好。但對于楊樹林帶,當防護目標高度較低時,株行距為2m×2m的防護效果較好,而當防護目標的高度較高時,林帶的株行距最好設置為為3m×2m。(4)本研究中,通過林帶下設置不同行數(shù)的灌木來模擬復層結(jié)構林帶的構建,模擬結(jié)果顯示:由于灌木的存在,林帶冠層以下的空隙降低,近地面氣流的衰減幅度明顯提高,林帶后氣流度的加速效應明顯降低;在林帶冠層,林帶冠層的氣流下沉現(xiàn)象減少,因此氣流速度的衰減幅度下降。但林后動量交換程度明顯減弱,林后0-5H的氣流恢復速度明顯減緩。在林帶較遠位置,各高度上的氣流速度差異逐漸變小,有效防護距離差異不大。在冠層的中上部,種植兩行灌木的林帶的有效防護距離反而下降。綜上,林下種植灌木可以有效地改善林帶近地面防護效應,但對于冠層中上部的氣流影響不明顯,甚至可能產(chǎn)生負面影響。
[Abstract]:In order to better and objectively clarify the aerodynamic mechanism of the forest belt and improve the precision of the numerical simulation of the boundary laminar flow in the forest belt. This study takes the coastal metasequoia and poplar shelterbelt as the research object. Through the standard wood analysis, the three-dimensional structural parameters model of the metasequoia and poplar belt is constructed by using the diameter of the breast, the height of the tree and the radius of the canopy. The aerodynamic parameters of the metasequoia and poplar belt were calculated with the three-dimensional structural parameter model. The FLUENT software was used to simulate the wind flow field of the forest belt, and the protective effects of different forest belts were analyzed. The density control of the forest belts and the construction of two kinds of structure control measures were simulated, and the different measures for forest belt prevention were discussed. In order to provide the basis for the planning and management of coastal shelterbelts, the results show that: (1) the range of surface area density of the Metasequoia forest belt is 0.0012~3.4857 M2 M-3, the range of volume density is 0.000002~ 0.012397 m3. M-3; the range of surface area density of the poplar belt is changed. The density and volume density of the poplar area is greater than that of the Metasequoia forest. The density and volume density of the poplar belt are larger than that of the Metasequoia forest zone. The structure of the forest belt is very heterogeneous in space: the diameter of the tree stem decreases with the height of the tree, and the surface area and volume of the tree trunk with the 0.0070~7.9337m2 and the poplar trees. The lower branch height of the metasequoia and poplar belt is 4m and 6m respectively. A larger gap is formed below the canopy of the forest belt. In the canopy of the forest, the surface area and volume density of the branches decrease with the height first. The peak of the surface area and volume density of the Metasequoia branches appears in the middle of the canopy, and the poplar tree appears in the upper part of the canopy. The distribution of slices and branches is the same. The position of the peak value of the surface area and volume density is roughly the same. The poplar leaves are mainly concentrated in the upper part of the canopy. The total proportion of each sub surface area and volume in the forest belt is larger: the total proportion of the Metasequoia Metasequoia is 78.39% branches (16.04%) tree trunk (5.). 57%) poplar trees (84.76%) branches (12.13%) tree trunk (3.11%); the total proportion of each component of the Metasequoia (75.28%) branches (20.85%) leaves (3.87%), poplar tree trunk (67.81%) branches (26.34%) leaves (5.85%). The surface area volume ratio of the Metasequoia (20.23) branches (0.77) tree trunk (0.07), poplar tree area volume ratio: leaf (14.49) branches) 6) tree trunk (0.05). (2) by comparing the numerical simulation results of the wind flow field in the metasequoia and poplar belt, it was found that the trend of the air flow in the front of the metasequoia and poplar forest was basically the same: the air flow was affected by the forest belt around 4H-6H before the forest belt, the velocity began to decrease slightly, the movement to the front of the Darin belt was 2H, and the flow velocity dropped sharply. In the near ground area, the flow velocity attenuation amplitude is less than that of the canopy area. At the same time, the flow velocity attenuation amplitude is less than that of the canopy area. At the same time, due to the large density of the canopy and leaf, the flow of the canopy in the forest belt is separated, sinking, the near ground air flow is squeezed, and the flow in the small range has a certain recovery after the forest belt, and then the compressed air produces diffusion and airflow. The velocity decreases again and then slowly recovers. The attenuation of the canopy flow is relatively large, but due to the diffusion of the near ground air flow, the air flow has a momentum exchange with the diffused airflow, and the velocity of the air flow rises sharply in the small range after the forest, and then slowly recovers. The overall density of the poplar belt is higher than the water. The attenuation of wind speed and the speed of air flow recovery at the height of the poplar belt are basically lower than that of the Metasequoia, and the effective protection distance is more than 12H of the metasequoia. Therefore, the protective effect of the poplar forest belt in this study is stronger than that of the Metasequoia forest zone. (3) the numerical simulation results of the metasequoia and poplar belt with different row spacing show that the flow velocity before the forest belt The influence of the line spacing was small. After the forest belt, the trend of the air flow was basically the same: the attenuation of air flow increased with the decrease of line spacing. At each height, the effective protection distance of 3M * 2M and 2m x 2m in each height was 2H-4H compared to the 3M * 3M forest belt, while the poplar belt raised the 4H-7H. but the forest belt line. When the distance of plant line is 2m x 2m, the near ground speed is close to 0, and the line distance of the plant line is more than that of 2m x 2m. Compared with 3M * 2m, the flow range of the air flow is enlarged and the reflux position is little moved down. To sum up, when the line distance of the Metasequoia forest is 2m x 2m The protective effect of the forest belt is better. But for the poplar belt, when the height of the protective target is low, the line spacing of 2m x 2m is better. When the height of the protective target is high, the line spacing of the forest belt is best set for the 3m x 2M. (4) study, and the construction of the complex structure forest belt is simulated by setting the shrubs with no number of peers under the forest belt. The simulated results show that the gap in the canopy below the canopy of the forest is reduced because of the existence of shrubs, the attenuation amplitude of the air flow near the ground is obviously increased, and the acceleration effect of the air flow is obviously reduced after the forest belt. The airflow recovery speed of 0-5H after forest was obviously slowed down. In the far position of the forest belt, the difference of air velocity in each height was gradually smaller and the difference of effective protection distance was not significant. In the middle and upper part of the canopy, the effective protection distance of planting two rows of shrubs was decreased. In conclusion, the planting shrubs under forest could effectively improve the protective effect of the forest belt near the ground. But there is no obvious or even negative effect on the airflow in the upper and middle parts of the canopy.
【學位授予單位】：中國林業(yè)科學研究院
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：S718.5

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