基于弯矩影响面方法的单向板移动荷载最不利位置研究

采用影响面的方法,运用matlab数值分析软件对移动荷载下板的弯矩变化进行了模拟分析。通过控制板的长短边比例,得出不同工况下移动荷载的最不利位置,同时对影响最不利位置的因素进行了相关的模拟研究,得出了长宽比越大的板,其受移动荷载的影响越小的结论。对今后具体的工程计算具有一定的参考意义。     

Non-coalescence and chain formation of droplets under an alternating current electric field

The dynamic behaviors of two droplets and droplet cluster under an alternating current (AC) electric field are investigated. Two droplets generally undergo transformation from complete coalescence to partial coalescence and finally to non-coalescence as the electric capillary number Ca_p increases. The critical electric capillary number Ca_pc for complete coalescence in the AC electric field remains unchanged and is twice as large as that in the direct current (DC) electric field when the frequency f ≥ 250 Hz. Charge transfer and reversal of electric field result in the reversal of the direction of electric force, which is the fundamental mechanism of non-coalescence of two droplets and chain formation in droplet cluster. The number of rebounds dramatically increases as f increases, promoting the stability of droplet chain. The droplet chains in the high-frequency AC electric field are longer and more stable than those in the low-frequency AC electric field.     

Experimental investigation of creep behavior of clastic rock in Xiangjiaba Hydropower Project

There are many fracture zones crossing the dam foundation of the Xiangjiaba Hydropower Project in southwestern China. Clastic rock is the main media of the fracture zone and has poor physical and mechanical properties. In order to investigate the creep behavior of clastic rock,triaxial creep tests were conducted using a rock servo-controlling rheological testing machine. The results show that the creep behavior of clastic rock is significant at a high level of deviatoric stress, and less time-dependent deformation occurs at high confining pressure. Based on the creep test results, the relationship between axial strain and time under different confining pressures was investigated, and the relationship between axial strain rate and deviatoric stress was also discussed. The strain rate increases rapidly, and the rock sample fails eventually under high deviatoric stress. Moreover, the creep failure mechanism under different confining pressures was analyzed. The main failure mechanism of clastic rock is plastic shear, accompanied by a significant compression and ductile dilatancy. On the other hand, with the determined parameters, the Burgers creep model was used to fit the creep curves. The results indicate that the Burgers model can exactly describe the creep behavior of clastic rock in the Xiangjiaba Hydropower Project.     

油品二元掺混黏度预测模型评价研究

为较好的控制和预测石油化工过程中油品掺混后的黏度,获得对于不同工艺情形的精度较高的掺混黏度预测模型,以黏度比为工况划分标准,相对误差的绝对值及工程允许误差为评价准则,评价了8种二元油品掺混黏度的预测模型。得到了各个模型在全黏度比1～106内的黏度预测特性。计算分析了各个模型的预测精度。按黏度比,对掺混黏度预测做了模型的优选。结果表明,Arrhenius、Bingham、Kendall等基本模型的预测结果波动及误差较大,不推荐使用,黏度比在1～103时优选Chevron模型,黏度比在104～105时优选Cragoe模型,而黏度比在105～106时各模型都超出允许范围,且波动及偏差较大,预测效果不好,亟待开发出一种适用模型。     

A 3D forming tool optimisation method considering springback and thinning compensation

In this paper, an enhanced numerical method for forming tool design optimisation in three-dimensional (3D) sheet metal forming applications is presented. The applied procedure enables a determination of appropriate forming tool geometry so that the manufacture of a sheet metal product inside specified tolerances would be ensured. In addition to the springback that occurs in the formed part after removal of the forming tools, the impact of the thinning of the sheet metal during the forming process is considered in the method, and both effects are correspondingly compensated for an iterative procedure. Computational efficiency in the E-DA-3D method is achieved mainly because the improved accuracy of the communicated data established corresponding interrelations between the discretised topologies used in the definition of the prescribed product geometry, the current tool geometry, and on this basis actually computed product geometry which is achieved by means of additional point topology mappings. The potential and effectiveness of the method is demonstrated by considering two cases of the forming tool design optimisation that are also experimentally validated.     

A novel Temperature–Humidity–Time defrosting control method based on a frosting map for air-source heat pumps

To improve the defrosting accuracy and the energy efficiency of the air-source heat pump (ASHP) under frosting and defrosting conditions, a novel Temperature–Humidity–Time (T–H–T) defrosting control method, based on a frosting map for the ASHP unit, is proposed in this paper. A field test was conducted for two heating seasons, to verify the feasibility and applicability of the T–H–T method. The advantages of the T–H–T method, compared to the conventional Temperature–Time (T–T) defrosting control method, are presented. In total, eight cases are shown in this paper. Cases 1 to 4 were chosen to reveal the T–H–T performance under different frosting conditions. It was found that no matter what kind of frosting conditions, defrosting was always initiated in a similar situation: ∼90% of the outdoor coil surface was covered by frost; the temperature difference between the compressor suction and discharge increased by ∼20%; and the heating capacity decreased by ∼30%. These results indicate that the T–H–T method can make an accurate decision under different frosting conditions. Cases 5a, 5b and Cases 6a, 6b were two groups of cases to compare the advantages of the T–H–T method against the conventional T–T method. Cases 5a and 5b were chosen for the non-frosting condition. It was found that the T–T method initiated the defrosting operation 31 times within 24 h. However, none of the defrosting operations was conducted for the T–H–T method. Cases 6a and 6b were chosen to compare these two methods under consecutive and variable frosting conditions. For the T–T method, 63% of the defrosting processes were found to be executed under conditions where defrosting was not necessary. However, for the T–H–T method, all the defrosting controls were found to be accurate and reasonable. These results indicated that the novel T–H–T method is suitable for the defrosting control of the ASHP, and has a more competitive performance than the conventional T–T method.     

Pressure transient analysis for asymmetrically fractured wells in dual-permeability organic compound reservoir of hydrogen and carbon

In this paper, a comprehensive semi-analytical model was presented to investigate pressure transient behavior for asymmetrically fractured wells in organic compound reservoir of hydrogen and carbon with dual-permeability behavior. Stehfest inversion algorithm can be used to transform it back into time domain to obtain pressure solution. The presented solution was validated well with numerical solutions. Flow characteristics for asymmetrically fractured wells in dual-permeability organic compound reservoir of hydrogen and carbon were divided into five regime. The effects of some important parameters on dimensionless pressure and its derivative curves were analyzed in details, including inter-porosity flow coefficient from matrix to natural fractures λ, storage coefficient ω, fracture asymmetry factor θ and permeability ratio κ. The presented model can be used to predict production performance and do well test analysis in the development of dual-permeability organic compound reservoir of hydrogen and carbon.     

Single phase transformerless wide range ac boost voltage regulator based on z-source network

This paper proposes a new type of voltage regulator based on single-phase z-source converter that compensates wide range voltage variations. This is not only capable of compensating variations at a much higher bandwidth but also boost the voltage level even twice that of input supply. The proposed system employs a pulse width modulation (PWM) z-source ac–ac converter along with a simple closed loop control. The input rms voltage can be sensed and divided by the desired value to find the instantaneous value of gain, which mathematically calculates the possible duty ratio of PWM switching signal based on the open loop characteristics of the converter. High speed IGBTs are used as bi-directional switch of the ac–ac converter and the circuit ultimately can easily and steadily maintain regulated voltage supply to the end user. The whole system operating principle and analysis are provided. Simulation results show the improvement of voltage disturbances both in voltage rise and fall conditions.     

热应力作用下LNG储罐外罐裂缝及失效时间分析

对于大型液化天然气储罐,内罐泄漏时,由于内外表面温差产生的巨大热应力对于外罐裂缝开展及储罐失效有非常重要的影响。为了获得外罐裂缝的开展规律以及储罐失效时间以便指导实际工程的设计与维护,利用传热学与弹塑性力学相关理论,提出了一种应力叠加方法,近似计算在内罐泄漏时外罐出现裂缝的内外温差,并且结合数值模拟结果进行对比分析,验证理论方法的准确性,确定裂缝开展规律,最终求得内罐从最不利泄漏点开始泄漏到外罐内侧混凝土开裂的储罐失效时间。结果表明:①内罐泄漏时,热应力巨大,不可忽略,热应力和其他荷载共同作用导致外罐产生大量裂缝,裂缝首先在外罐顶部内表面产生,并迅速向外表面开展,最终贯穿罐顶,导致储罐失效;②首次求得了储罐从内罐开始泄漏到外罐产生裂缝的最小时间,在此时间内采取有力措施及时处理,对控制事故发展、避免发生严重灾害具有重要意义。     

Adaptive noise cancellation based on EMD in water-supply pipeline leak detection

In water-supply pipeline leak detection and location, both the leak signals and blurred noises are closely related to the pipeline states and surroundings and most of the conventional noise-cancellation methods have to depend on the empirical parameters of either signals or noises. EMD (Empirical Mode Decomposition) is an adaptive signal decomposition method and is exclusive of base functions. A signal is decomposed into several IMFs (Intrinsic Mode Functions) in EMD, then the noise in a signal can be cancelled through removing uncorrelated IMFs. The existing EMD noise cancellation methods need to know the characteristics of either the wanted signal or the noise for rebuilding the noise-removed signal. However the characteristics of leak signals and noises are not fixed in various pipeline conditions, so the existing EMD noise cancellation methods can’t be directly applied in water-supply pipeline leak detection. This paper proposes an adaptive noise cancellation method based on EMD, in which the IMFs that don’t or less contain the components related to the leak can be removed through the cross-correlation between the IMFs and another signal collected at the either side of a suspect leak. In simulation analysis, the adaptive noise cancellation method can increase the SNRs (Signal to Noise Ratios) of leak signals as high as 16 dB. In processing practical pipeline vibro-acoustic signals, with the proposed method the peak of adaptive time delay estimate of leak signals, which determines the location of a leakage, becomes more distinguished, and thus the error of leakage location is improved.