52 research outputs found
Investigation of flow through the two-stage orifice
No full textIn the field of engineering, understanding the flow characteristics of an orifice is key to accurately controlling pressure or flow; however, the transitional flow characteristics of the two-stage orifice has not been studied. The value of the discharge coefficient parameterizing the two-stage orifice flow equation is primarily based on that of the single classic orifice; however, this assumption leads to significant errors, because of the different numbers in the sudden contraction structure. Through theoretical derivation, the flow equations difference between the two-stage orifice and single classic orifice was compared and analyzed. Combing theoretical analysis, Computational Fluid Dynamics (CFD) simulation and experimental measurement, the transitional flow characteristics of the two-stage orifice were investigated using mineral oil. The comparison results of the three parts are essentially consistent. In this paper, the discharge coefficient and the pressure drop over the two-stage orifice were primarily focused on Reynolds numbers between 900 and 1700. In comparison with the single orifice, the results show that under the same dimensions (d = 3 mm), the discharge coefficient of the two-stage orifice is greater, and the transitional flow state of the two-stage orifice is different from that of the single orifice. Additionally, the pressure drop of the two-stage orifice is less than that of the single orifice under the same volume flow rate. The prestage cylindrical hole slows the changing trend of the flow field parameters, and the second-stage orifice with smaller diameter is mainly responsible for the pressure loss. The current research provides important support for accurate pressure and flow control of the two-stage orifice, and the role of the prestage cylindrical hole can also be a good reference in the structure design of micro-orifices
Case History on Prevention of the Landslide at Luoyiqi by Means of Rigid Frame Retaining Structure
No full textThis paper presents a new special type of retaining structure which prevents the large-scale landslide. It is named the rigid frame retaining structure. The author in this paper proposed a new computation method, i.e., analysis of the rigid frame within elastic foundation. The new formulations have been performed according to E. Ninkler\u27s theory and the difference principle and with the help of fundamental knowledge of strength of material and matrix algebra. The descriptions of the design and construction of the rigid frame retaining structure were given
BIOMECHANICAL ALTERATION OF CORNEAL MORPHOLOGY AFTER CORNEAL REFRACTIVE THERAPY
No full textI hereby declare that I am the sole author of this thesis. This is a true copy of the thesis, including any required final revisions, as accepted by my examiners. I understand that my thesis may be made electronically available to the public. ii Purpose: Although orthokeratology (non-surgical corneal reshaping, Corneal Refractive Therapy, CRT ® ) has been used for almost a half century, contemporary CRT’s outcomes and mechanisms still require investigation. A series of studies was designed to examine different aspects of non-surgical corneal reshaping for myopic and hyperopic corrections, including the efficacy and stability of this procedure, the effect of the lens material characteristics (Dk/t), and the corneal or superficial structural change (e.g. corneal/epithelial thickness) in corneal reshaping. Methods: Details are in the following summary Table A-1. Results: In the CRT1 study, after one night of CRT ® for myopia, the central cornea flattened and the mid-periphery steepened, and myopia reduced. In the CRTH study, after one night o
Deformation Compensation of Ram Components of Super-heavy-duty CNC Floor Type Boring and Milling Machine
No full textAbstractRam is a very important component of super-heavy-duty computer numerical control (CNC) floor type boring-milling machine, and deformation of ram is a significant source causing errors in machining process. To compensate the deformation error of super-heavy-duty CNC floor type boring-milling machine, based on force analysis theory, the law and compensation measures of deformation of ram are researched. Based on the principle of torque (force) balance of the ram components, the formulas of compensation forces and compensation torques are derived, the relations between compensation forces (compensation torques) and the stroke distance of the ram are given. According to theoretical analysis results and the structural characteristics of super-heavy-duty CNC floor type boring and milling machine of TK6932, rods compensation, hydrostatic pressure compensation and wire rope compensation measures are taken to compensate the deformation error of ram. The experiments and computer simulation results show that the straightness of the ram at its overhanging end meets the national machinery industry standards
Automobile-Demand Forecasting Based on Trend Extrapolation and Causality Analysis
No full textAccurate automobile-demand forecasting can provide effective guidance for automobile-manufacturing enterprises in terms of production planning and supply planning. However, automobile sales volume is affected by historical sales volume and other external factors, and it shows strong non-stationarity, nonlinearity, autocorrelation and other complex characteristics. It is difficult to accurately forecast sales volume using traditional models. To solve this problem, a forecasting model combining trend extrapolation and causality analysis is proposed and derived from the historical predictors of sales volume and the influence of external factors. In the trend-extrapolation model, the historical predictors of sales series was captured based on the Seasonal Autoregressive Integrated Moving Average (SARIMA) and Polynomial Regression (PR); then, Empirical Mode Decomposition (EMD), a stationarity-test algorithm, and an autocorrelation-test algorithm were introduced to reconstruct the sales sequence into stationary components with strong seasonality and trend components, which reduced the influences of non-stationarity and nonlinearity on the modeling. In the causality-analysis submodel, 31-dimensional feature data were extracted from influencing factors, such as date, macroeconomy, and promotion activities, and a Gradient-Boosting Decision Tree (GBDT) was used to establish the mapping between influencing factors and future sales because of its excellent ability to fit nonlinear relationships. Finally, the forecasting performance of three combination strategies, namely the boosting series, stacking parallel and weighted-average parallel strategies, were tested. Comparative experiments on three groups of sales data showed that the weighted-average parallel combination strategy had the best performance, with loss reductions of 16.81% and 4.68% for data from the number-one brand, 25.60% and 2.79% for data from the number-two brand, and 46.26% and 14.37% for data from the number-three brand compared with the other combination strategies. Other ablation studies and comparative experiments with six basic models proved the effectiveness and superiority of the proposed model
The Tabu_Genetic Algorithm: A Novel Method for Hyper-Parameter Optimization of Learning Algorithms
No full textMachine learning algorithms have been widely used to deal with a variety of practical problems such as computer vision and speech processing. But the performance of machine learning algorithms is primarily affected by their hyper-parameters, as without good hyper-parameter values the performance of these algorithms will be very poor. Unfortunately, for complex machine learning models like deep neural networks, it is very difficult to determine their hyper-parameters. Therefore, it is of great significance to develop an efficient algorithm for hyper-parameter automatic optimization. In this paper, a novel hyper-parameter optimization methodology is presented to combine the advantages of a Genetic Algorithm and Tabu Search to achieve the efficient search for hyper-parameters of learning algorithms. This method is defined as the Tabu_Genetic Algorithm. In order to verify the performance of the proposed algorithm, two sets of contrast experiments are conducted. The Tabu_Genetic Algorithm and other four methods are simultaneously used to search for good values of hyper-parameters of deep convolutional neural networks. Experimental results show that, compared to Random Search and Bayesian optimization methods, the proposed Tabu_Genetic Algorithm finds a better model in less time. Whether in a low-dimensional or high-dimensional space, the Tabu_Genetic Algorithm has better search capabilities as an effective method for finding the hyper-parameters of learning algorithms. The presented method in this paper provides a new solution for solving the hyper-parameters optimization problem of complex machine learning models, which will provide machine learning algorithms with better performance when solving practical problems
Debris flow hazard analysis before and after improvement of Hanjia gully control engineering at the source area of the Fujiang River
No full textObjective Debris flow from the Hanjia gully develops on the left bank of the source area of the Fujiang River, Fenghe Village, Xiaohe Town, Songpan County, China. In recent years, debris flows have occurred frequently, and the largest debris flow occurred in August 2022, which seriously threatened the lives and properties of villagers in the Hanjia gully. Existing prevention and control engineering methods have decreased in effectiveness or even become ineffective. Currently, researchers have set a variety of extreme rainfall conditions and used FLO-2D to analyze the hazards of debris flow, based on which the governance effect of debris flow prevention and control engineering can be evaluated. However, there are few reports on how to improve the prevention and control engineering and evaluate the effect of the improved prevention and control engineering when the existing prevention and control engineering is ineffective. Methods To reduce damage to the Hanjia gully, the characteristics as well as prevention and control status of the debris flow in/from this gully were determined using remote sensing interpretation, field investigation, and FLO-2D numerical simulation; subsequently, improved prevention and control engineering was proposed. The hazard of debris flow before and after the improvements in prevention and control engineering under different rainfall frequencies were studied to analyze the effectiveness of the improved prevention and control engineering. Results The results show that the Hanjia gully is located in the "8.8" Jiuzhaigou earthquake disturbance area, the static reserves of post-earthquake landslides and collapses are about 49.79 × 104 m3, and the debris flow sources are abundant, which leads to frequent debris flow during heavy rainfall. The high-hazard area is concentrated in the No. 1 retaining dam, and Fenghe Village and Pingsong Highway are in the low-hazard area under a rainfall event occurring every 10 years, and the existing prevention and control engineering can effectively prevent the debris flow disaster. Under a rainfall event occurring once in 50 years, Fenghe Village is in the high-hazard area of debris flow. The debris flow rushes out of the drainage channel and destroys the Pingsong Highway. The maximum mud depth in the accumulation area increases from 1.41 m to 3.14 m, the maximum velocity increases from 2.4 m/s to 3.65 m/s, and the accumulation area increases from 0.28 × 104 m2 to 5.41 × 104 m2. However, the existing prevention and control engineering methods cannot meet these requirements. After adopting improved prevention and control engineering, such as multistage retaining dams and cutting and straightening of drainage channels, the flow velocity of the debris flow in front of the two additional retaining dams becomes lower than that before the improvement, and the depth of mud in front of the additional retaining dams becomes higher than that before the improvement. The maximum velocity of the debris flow within 100 m of Dam No. 3 decreases by 29%, and the maximum mud depth increases by 413%. The maximum flow velocity in the first 100 m of Dam No. 2 decreases by 21%, the maximum mud depth increases by 175%, the maximum mud depth in the accumulation area is 3.9 m, and the maximum flow velocity is 3.4 m/s. The accumulation volume of debris flows is reduced by 50.2%, and the accumulation area is reduced by 86%. Conclusion Improved prevention and control engineering can effectively reduce the solid mass of debris flows and guide debris flow to discharge along drainage channels. The high-hazard area of the debris flow is concentrated in the drainage channel, and the control effect of the debris flow is remarkable. Significance The research results provide a scientific method for evaluating the effectiveness of debris-flow control engineering improvements and offer technical support for local debris-flow early warning systems
DESIGN AND OPTIMIZATION OF THE VARIABLE-DENSITY LATTICE STRUCTURE BASED ON LOAD PATHS
No full textLattice structure is more and more widely used in engineering by replacing solid structure. But its mechanical performances are constrained by the external shape if the unit cells are directly filled in the design domain, and the traditional topology optimization methods are difficult to give the explicitly mechanical guidance for the distribution of internal unit cells. In this paper, a novel design and optimization method of variable-density lattice structure is proposed in order to simultaneously optimize the external shape and the internal unit cells. First of all, the envelope model of any given structure should be established, and the load paths need to be visualized by the theory of load path. Then, the design criteria of external shape are established based on the principle of smoother load paths in the structure. An index of load flow capacity is defined to indicate the load paths density and to control the density distribution of unit cells, and a detailed optimization strategy is given. Finally, three examples of a cantilever plate, an L-shaped bracket and a classical three-point bending beam are used to verify the method. The results show that the models designed by the proposed method have better mechanical performances, lower material usage and less printing time
FATIGUE LIFE PREDICTION AND EXPERIMENTAL STUDY OF ALUMINUM ALLOY WHEEL HUB CONSIDERING DAMAGE ACCUMULATION (MT)
No full textAiming at the problem of fatigue life prediction of aluminum alloy wheel hub, a fatigue life prediction model considering damage accumulation is proposed and tested. The Finite Element Models of a wheel hub under bending fatigue test and radial fatigue test are established, and the main failure positions are studied by simulation analysis. The S-N curves of material and part are established by using the nominal stress method, and the average stress of the asymmetric cyclic load borne by the wheel hub is corrected by using the Morrow line. Considering the rotation process of the wheel hub, a theoretical model for predicting the fatigue life is constructed by using the linear cumulative damage theory. Taking an aluminum alloy wheel hub as an example, the life calculated by the theoretical model is 448.2 thousands revolutions. Compared with the fatigue life of 473.3 thousands revolutions given by the bending fatigue test, the error is about 5.6%, which verifies the effectiveness of the fatigue life prediction theoretical model
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