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In general, trapezoidal channels are used in irrigation and drainage networks. When installing a side weir on the side wall of a trapezoidal channel, as excess water reaches the side weir plane, additional flow from the crest of the side weir is driven into the side channel. The main aim of this study is to predict the discharge coefficient of rectangular side weirs located on trapezoidal channels using support vector machines (SVMs). Based on the effective parameters on the discharge coefficient of side weirs in trapezoidal channels, six different models (SVM 1–SVM 6) are introduced. According to the analysis results of SVM 1–SVM 6 models, the superior model is introduced as a function of the Froude number (Fr), ratio of side weir length to the bottom width of a trapezoidal channel (L/b), ratio of side weir length to the flow depth upstream of the weir (L/y1), side slope of the trapezoidal channel (m) and ratio of flow depth upstream of the weir to the trapezoidal channel bottom width (y1/b). Based on the simulation results, the superior model has a reasonable accuracy. For example, the root mean square error, mean absolute relative error and correlation coefficient (R2) values calculated for the superior training model are 0.0156, 0.0327 and 0.884, respectively. Furthermore, the ratio of side weir length to trapezoidal channel bottom width (L/b) is identified as the most effective input parameter for modeling discharge coefficient. Additionally, a matrix is presented for superior model to estimate discharge coefficient of the side weirs.

Printed circuit heat exchanger (PCHE) is a promising regenerative device in the sCO2 power cycle, with the advantages of a large specific surface area and compact structure. Its tiny and complex flow channel structure brings enhanced heat transfer performance, while increasing pressure drop losses. It is, thus, important to balance heat transfer and flow resistance performances with the consideration of sCO2 as the working agent. Herein, three-dimensional models are built with a full consideration of fluid flow and heat transfer fields. A trapezoidal channel is developed and its thermal–hydraulic performances are compared with the straight, the S-shape, and the zigzag structures. Nusselt numbers and the Fanning friction factors are analyzed with respect to the changes in Reynolds numbers and structure geometric parameters. A sandwiched structure that couples two hot channels with one cold channel is further designed to match the heat transfer capacity and the velocity of sCO2 flows between different sides. Through this novel design, we can reduce the pressure drop by 75% and increase the regenerative efficiency by 5%. This work can serve as a solid reference for the design and applications of PCHEs.

Hydraulic jump is of fast altering flow type, within which a critical flow transforms into a subcritical flow, and such alteration occurs within a relatively short path of the channel. In the present study, the impact of lateral angles of trapezoidal channel walls in the continuous form on the relative loss of hydraulic jump energy is investigated. For this purpose, the meta-heuristic harmony search algorithm is used for declaring the continuous lateral angles within the range of 45°–75°. With regard to the hydraulic definition for the hydraulic jump phenomenon, the harmony search algorithm, which is widely used for optimization and continuous problems, is considered as a simple concept of a useful algorithm. The results demonstrated the high efficiency of harmony search in the optimization of hydraulic problems. The highest value of jump energy loss up to 81% was recorded for the angle of 45°, implying the high efficiency of this section. As can be clearly seen in the results, the amount of destructive energy loss of hydraulic jump in the meta-heuristic algorithm is significantly higher than other previous methods.

Rough bed channels are one of the appurtenances used to dissipate the extra energy of the flow through hydraulic jump. The aim of this paper is to assess the effects of channel geometry and rough boundary conditions (i.e., rectangular, trapezoidal, and expanding channels with different rough elements) in predicting the hydraulic jump energy dissipation using support vector machine (SVM) as a meta-model approach. Using different experimental data series, different models were developed with and without considering dimensional analysis. The results approved capability of the SVM model in predicting the relative energy dissipation. It was found that the developed models for expanding channel with central sill performed more successfully and, for this case, superior performance was obtained for the model with parameters Fr1 and h1/B. Considering the rectangular and trapezoidal channels, the model with parameters Fr1, (h2−h1)/h1, W/Z led to better predictions. It was observed that between two types of strip and staggered rough elements, strip type led to more accurate results. The obtained results showed that the developed models for the case of simulation based on dimensional analysis yielded better predictions. The sensitivity analysis results showed that Froude number had the most significant impact on the modeling.

In this study, the main properties of the hydraulic jump in an asymmetric trapezoidal flume are analyzed experimentally, including the so-called sequent depths, characteristic lengths, and efficiency. In particular, an asymmetric trapezoidal flume with a length of 7 m and a width of 0.304 m is considered, with the bottom of the flume transversely inclined at an angle of m = 0.296 and vertical lateral sides. The corresponding inflow Froude number is allowed to range in the interval (1.40 < F1 < 6.11). The properties of this jump are compared to those of hydraulic jumps in channels with other types of cross-sections. A relationship for calculating hydraulic jump efficiency is proposed for the considered flume. For F1 > 5, the hydraulic jump is found to be more effective than that occurring in triangular and symmetric trapezoidal channels. Also, when mes > 8 and > 5, the hydraulic jump in the asymmetrical trapezoidal channel downstream of a parallelogram sluice gate is completely formed as opposed to the situation where a triangular sluice is considered.

In this study, the entropy concept is employed to estimate the shear stress distribution in a circular channel with flat bed and trapezoidal channel. Using the principle of maximum entropy, the shear stress distribution is derived by maximizing the Tsallis entropy by assuming averaged shear stress as a random variable. The derived shear stress equation can describe the variation of shear stress along the wetted perimeter of channel. The developed model of shear stress distribution is tested with some credible experimental data and is also compared with equations obtained by other researchers based on the Shannon entropy concept. The present model has shown good agreement with the observed data and performed better than the Shannon-based model in both cross-sections with better results of several computed quantitative criteria. The model precision in estimating shear stress in the trapezoidal channel with mean root mean square error (RMSE) of 0.0158 was higher than the circular channel with flat bed with RMSE of 0.0679.

【目的】针对缺乏渠表温度数据而难以准确分析渠道冻胀破坏的缺陷，提出一种考虑太阳辐射的温度边界条件。【方法】考虑太阳辐射的角度及效率对梯形渠道阴阳坡温度的影响，结合混凝土表面的增温计算方法建立了梯形渠道混凝土衬砌表面增温计算模型，将梯形渠道表面增温计算结果与当地日最低气温结合后的温度作为温度边界条件。利用有限元软件ABAQUS，以赵口引黄灌区梯形渠道为研究对象，对其温度、应力和变形场进行模拟分析，并对渠道阴坡坡脚处、距坡脚1/3处2种衬砌分缝优化方案进行分析。【结果】计算冻深和开裂位置与工程实际情况吻合较好，且渠道衬砌在距坡脚1/3处分缝防冻胀效果更好。【结论】基于此温度边界条件可较好模拟无渠表温度数据的梯形渠道冻胀破坏情况，模拟结果与工程实际吻合较好，可为梯形渠道防冻胀设计提供参考。

【目的】研究进水口数、梯形流道齿数、出水口数对单翼迷宫式滴灌带抗堵塞性能的影响。【方法】采用物理试验、数值模拟、建立线性数学模型等方法，设计9组工况进行数值模拟，研究额定流量为1.8 L/h的单翼迷宫式滴灌带的水沙两相流流场，以及滴灌带不同进出水口数、梯形流道齿数对流态指数、流量系数的影响。【结果】SST k-ω两方程低雷诺数紊流模型更加适用于单翼迷宫式滴灌带流场的数值模拟；从进水口到梯形流道再到出水口，泥沙颗粒质量浓度逐渐变小；滴灌带第5进水口为主要进水口，第3出水口为主要出水口；进水口数、梯形流道齿数、出水口数对流态指数影响极小，对流量系数的影响显著性排序为梯形流道齿数＞出水口数＞进水口数；构建了流量系数与三因素之间的多元线性模型，该模型决定系数为0.987，精度较好。【结论】在梯形迷宫流道尺寸相同时，梯形流道齿数越少流道内部流速越大，更有利于泥沙颗粒排出流道。构建的流量系数与三因素的公式可实现出水口位置精准灌溉植物，合理利用土地资源。

【目的】探究翼柱型量水槽在梯形渠道量水的适用性。【方法】对4种不同收缩比的翼柱型量水槽进行水力性能模型试验，并运用Fluent 17.1软件对其中2种收缩比的量水槽进行了数值模拟。通过对上游水位、流量和收缩比等进行分析，拟合得到了量水槽流量公式，并从测流精度、佛汝德数、临界淹没度以及水头损失等方面对其量水性能进行了分析。【结果】翼柱型量水槽在梯形渠道量水性能优良，水位-流量相关度极好，R2可达0.997 1以上，拟合的流量公式简明易用，测流平均误差为2.41%，上游佛汝德数均小于0.4，临界淹没度达0.85以上，通过数值模拟对量水槽水面线和流量进行误差分析，将实测值与模拟值进行比较，二者平均误差分别为3.80%和3.72%，与试验结果高度吻合，模拟结果准确可靠。【结论】翼柱型量水槽可用于梯形渠道量水，且量水精度满足明渠测流规范相关要求。Fluent软件可用于翼柱型量水槽数值模拟。

Flow‐channel design plays a decisive role in the performance and water management of large‐scale proton exchange membrane (PEM) fuel cells (PEMFCs), especially for parallel flow fields (FFs) that feature low pressure drop but are prone to flow maldistribution. In this study, a three‐dimensional (3D) multiphase CFD model is developed to systematically investigate the effects of cathode flow‐channel cross‐sectional geometry on mass transport and electrochemical performance in a large‐area parallel‐flow PEMFC. Square, trapezoidal, and inverted‐trapezoidal channel cross‐sections are comparatively analyzed under identical structural parameters and operating conditions. The results show that the trapezoidal channel achieves the highest current density and power density by enhancing near‐gas diffusion layer (GDL) gas velocity and under‐rib convection, thereby improving oxygen transport and reaction uniformity, albeit with a higher liquid‐water saturation and potential flooding risk. In contrast, the inverted‐trapezoidal channel exhibits the lowest pressure drop and liquid‐water saturation due to its larger effective flow area but suffers from reduced reaction intensity and inferior overall performance. The square channel presents intermediate behavior. Temperature distributions remain highly uniform for all configurations, indicating a limited influence of channel cross‐section on thermal behavior. These results provide useful guidance for the engineering design of channel cross‐sections in large‐scale PEMFCs under different design priorities.