Spectral Method for Solving Time Dependent Flow of Upper-Convected Maxwell Fluid in Tube

The ti me dependent flow of upper-convected Maxwell fluid in a horizontal circular pip e is studied by spectral method. The time dependent problem is mathematically re duced to a partial differential equation of second order. By using spectral meth od the partial differential equation can be reduced to a system of ordinary diff erential equations for different terms of Chebyshev polynomials approximations. The ordinary differential equations are solved by Laplace transform and the eige nvalue method that leads to an analytical form of the solutions.

Development of a Novel Parallel-spool Pilot Operated High-pressure Solenoid Valve with High Flow Rate and High Speed

High-pressure solenoid valve with high flow rate and high speed is a key component in an underwater driving system.However,traditional single spool pilot operated valve cannot meet the demands of both high flow rate and high speed simultaneously.A new structure for a high pressure solenoid valve is needed to meet the demand of the underwater driving system.A novel parallel-spool pilot operated high-pressure solenoid valve is proposed to overcome the drawback of the current single spool design.Mathematical models of the opening process and flow rate of the valve are established.Opening response time of the valve is subdivided into 4 parts to analyze the properties of the opening response.Corresponding formulas to solve 4 parts of the response time are derived.Key factors that influence the opening response time are analyzed.According to the mathematical model of the valve,a simulation of the opening process is carried out by MATLAB.Parameters are chosen based on theoretical analysis to design the test prototype of the new type of valve.Opening response time of the designed valve is tested by verifying response of the current in the coil and displacement of the main valve spool.The experimental results are in agreement with the simulated results,therefore the validity of the theoretical analysis is verified.Experimental opening response time of the valve is 48.3 ms at working pressure of 10 MPa.The flow capacity test shows that the largest effective area is 126 mm2 and the largest air flow rate is 2320 L/s.According to the result of the load driving test,the valve can meet the demands of the driving system.The proposed valve with parallel spools provides a new method for the design of a high-pressure valve with fast response and large flow rate.

Time lag characteristics of sap flow in seed-maize and their implications for modeling transpiration in an arid region of Northwest China

Plant capacity for water storage leads to time lags between basal stem sap flow and transpiration in various woody plants. Internal water storage depends on the sizes of woody plants. However, the changes and its influencing factors in time lags of basal stem flow during the development of herbaceous plants including crops remain unclear. A field experiment was conducted in an arid region of Northwest China to examine the time lag characteristics of sap flow in seed-maize and to calibrate the transpiration modeling. Cross-correlation analysis was used to estimate the time lags between stem sap flow and meteorological driving factors including solar radiation（R_s） and vapor pressure deficit of the air（VPD_（air））. Results indicate that the changes in seed-maize stem sap flow consistently lagged behind the changes in R_s and preceded the changes in VPD_（air） both on hourly and daily scales, suggesting that light-mediated stomatal closures drove sap flow responses. The time lag in the maize＇s sap flow differed significantly during different growth stages and the difference was potentially due to developmental changes in capacitance tissue and/or xylem during ontogenesis. The time lags between stem sap flow and R_s in both female plants and male plants corresponded to plant use of stored water and were independent of total plant water use. Time lags of sap flow were always longer in male plants than in female plants. Theoretically, dry soil may decrease the speed by which sap flow adjusts ahead of shifts in VPD_（air） in comparison with wet soil and also increase the speed by which sap flow adjusts to R_s. However, sap flow lags that were associated with R_s before irrigation and after irrigation in female plants did not shift. Time series analysis method provided better results for simulating seed-maize sap flow with advantages of allowing for fewer variables to be included. This approach would be helpful in improving the accuracy of estimation for canopy transpiration and conductance using meteorological measurements.

Modeling study on the flow patterns of gas–liquid flow for fast decarburization during the RH process

A water model and a high-speed video camera were utilized in the 300-t RH equipment to study the effect of steel flow patterns in a vacuum chamber on fast decarburization and a superior flow-pattern map was obtained during the practical RH process. There are three flow patterns with different bubbling characteristics and steel surface states in the vacuum chamber： boiling pattern（BP）, transition pattern（TP）, and wave pattern（WP）. The effect of the liquid-steel level and the residence time of the steel in the chamber on flow patterns and decarburization reaction were investigated, respectively. The liquid-steel level significantly affected the flow-pattern transition from BP to WP, and the residence time and reaction area were crucial to evaluate the whole decarburization process rather than the circulation flow rate and mixing time. A superior flow-pattern map during the practical RH process showed that the steel flow pattern changed from BP to TP quickly, and then remained as TP until the end of decarburization.

VISUALIZATION OF FLOW STRUCTURES IN A TURBULENT BOUNDARY LAYER USING A NEW TECHNIQUE

In this paper, an experimental investigation on the flow structures in a turbulent bounda- ry layer employing a special laser light sheet-Hydrogen bubble flow visualization technique is described. It is observed that the high/low speed streaks are directly related to the hairpin or horseshoe-like vortices. This observation can give a better understanding of the physical mechanism in the turbulent boundary layer.

FURTHER DISCUSSION ON STATISTICAL PROPERTIES OF ACTIVITY FLOW TIME IN PERT

In this paper attempts are made at answering the problems on the statistical properties of activity flow time in PERT raised by the late famous mathematician Hua Loo-keng.

Hybrid Discrete Harmony Search Algorithm for Flow Shop Scheduling with Limited Buffers

The flow shop scheduling problem with limited buffers( LBFSP) widely exists in manufacturing systems. A hybrid discrete harmony search algorithm is proposed for the problem to minimize total flow time. The algorithm presents a novel discrete improvisation and a differential evolution scheme with the jobpermutation-based representation. Moreover,the discrete harmony search is hybridized with the problem-dependent local search based on insert neighborhood to balance the global exploration and local exploitation. In addition, an orthogonal experiment design is employed to provide a receipt for turning the adjustable parameters of the algorithm. Comparisons based on the Taillard benchmarks indicate the superiority of the proposed algorithm in terms of effectiveness and efficiency.

Effects of relaxation time on start-up time for starting flow of Maxwell fluid in a pipe

Although the analytical solution of the starting flow of Maxwell fluid in a pipe has been derived for a long time, the effect of relaxation time λ on start-up time ts of this flow is still not well understood. Especially, there exist a series of jumps on the ts-λ. curve. In this paper we introduce a normalized mechanical energy by mode decomposition and mathematical analogy to describe the start-up process. An improved definition of start-up time is presented based on the normalized mechanical energy. It is proved that the ts-λ. curve contains a series of jumps if λ is larger than a critical value. The exact positions of the jumps are determined and the physical reason of the jumps is discussed.

A VARIATIONAL ANALYTICAL APPROACH TO TIME DEPENDENT FLOW OF OLDROYD B FLUID IN CIRCULAR TUBE

In the present investigation the time dependent flow of an Oldroyd fluid B in ahorizontal eylindrical pipe is stuided by the variational analytical approach developedby author. The tome dependent problem is mathematically reduced to a partialdifferential equation of third order. Using the improved variational approach due toKantorovich the partial differential equation can be reduced to a system of ordinarydifferential equations for different approximations. The ordinary differential equationsare solved by the method of the Laplace transform which is led to an analytical formof the solutions.

Fourier time spectral method for subsonic and transonic flows

The time accuracy of the exponentially accurate Fourier time spectral method（TSM） is examined and compared with a conventional 2nd-order backward difference formula（BDF） method for periodic unsteady flows. In particular, detailed error analysis based on numerical computations is performed on the accuracy of resolving the local pressure coefficient and global integrated force coefficients for smooth subsonic and non-smooth transonic flows with moving shock waves on a pitching airfoil. For smooth subsonic flows, the Fourier TSM method offers a significant accuracy advantage over the BDF method for the prediction of both the local pressure coefficient and integrated force coefficients. For transonic flows where the motion of the discontinuous shock wave contributes significant higherorder harmonic contents to the local pressure fluctuations,a sufficient number of modes must be included before the Fourier TSM provides an advantage over the BDF method.The Fourier TSM, however, still offers better accuracy than the BDF method for integrated force coefficients even for transonic flows. A problem of non-symmetric solutions for symmetric periodic flows due to the use of odd numbers of intervals is uncovered and analyzed. A frequency-searching method is proposed for problems where the frequency is not known a priori. The method is tested on the vortex shedding problem of the flow over a circular cylinder.

Numerical Simulation of ATPS Parachute Transient Dynamics Using Fluid-Structure Interaction Method

In order to simulate and analyze the dynamic characteristics of the parachute from advanced tactical parachute system(ATPS),a nonlinear finite element algorithm and a preconditioning finite volume method are employed and developed to construct three dimensional parachute fluid-structure interaction(FSI)model.Parachute fabric material is represented by membrane-cable elements,and geometrical nonlinear algorithm is employed with wrinkling technique embedded to simulate the large deformations of parachute structure by applying the NewtonRaphson iteration method.On the other hand,the time-dependent flow surrounding parachute canopy is simulated using preconditioned lower-upper symmetric Gauss-Seidel(LU-SGS)method.The pseudo solid dynamic mesh algorithm is employed to update the flow-field mesh based on the complex and arbitrary motion of parachute canopy.Due to the large amount of computation during the FSI simulation,massage passing interface(MPI)parallel computation technique is used for all those three modules to improve the performance of the FSI code.The FSI method is tested to simulate one kind of ATPS parachutes to predict the parachute configuration and anticipate the parachute descent speeds.The comparison of results between the proposed method and those in literatures demonstrates the method to be a useful tool for parachute designers.

Fabrication scheduling on a single machine to minimize the weighted sum of product completion time

In this paper, a fabrication scheduling problem concerning the production of components at a single manufacturing facility was studied, in which the manufactured components are subsequently assembled into a finite number of end products. Each product was assumed to comprise a common component to all jobs and a unique component to itself. Common operations were processed in batches and each batch required a setup time. A product is completed when both its two operations have been processed and are available. The optimality criterion considered was the minimization of weighted flow time. For this scheduling problem, the optimal schedules were described in a weignted shortest processing time first （WSPT） order and two algorithms were constructed corresponding to the batch availability and item availability, respectively.

Research on the Trusted Energy-Saving Transmission of Data Center Network

According to the high operating costs and a large number of energy waste in the current data center network architectures, we propose a kind of trusted flow preemption scheduling combining the energy-saving routing mechanism based on typical data center network architecture. The mechanism can make the network flow in its exclusive network link bandwidth and transmission path, which can improve the link utilization and the use of the network energy efficiency. Meanwhile, we apply trusted computing to guarantee the high security, high performance and high fault-tolerant routing forwarding service, which helps improving the average completion time of network flow.

Nature of Existence and Essence of Time in Existence

This study is based on the notion that every entity has two inseparable parts: the imperceptible existence and the perceptible body. Existence is comprised of space, time, and consciousness. These characteristics manifest in the perceptible forms of capability, activity, and awareness, respectively. The findings of this study suggest that physically (atoms), biologically (vegetation), psychologically (animals), and intellectually living entities (humans) have their own existences in the following elements: space (capability), time (activity), and consciousness (awareness). This study aims to discuss the context of time by visualizing the phenomenon in which the present penetrates the space fabric by touching consciousness and establishing self-sustaining life, termed as an entity. The second part of this study suggests that the negative and positive loops represent the future and the past in a sinusoidal wave, and the base line in between represents the continuous present. A small change occurs with each oscillation or wavelength, which increases entropy. The unit “change” occurs within one wavelength, which should be treated as the smallest unit of time. This unit may differ from the prevalent unit of time, which is measured based on duration.

Comparison of two projection methods for modeling incompressible flows in MPM

Material point method（MPM）was originally introduced for large deformation problems in solid mechanics applications.Later,it has been successfully applied to solve a wide range of material behaviors.However,previous research has indicated that MPM exhibits numerical instabilities when resolving incompressible flow problems.We study Chorin＇s projection method in MPM algorithm to simulate material incompressibility.Two projection-type schemes,non-incremental projection and incremental projection,are investigated for their accuracy and stability within MPM.Numerical examples show that the non-incremental projection scheme provides stable results in single phase MPM framework.Further,it avoids artificial pressure oscillations and small time steps that are present in the explicit MPM approach.

Approach of hybrid GA for multi-objective job-shop scheduling

In recent years,scholars have made many research results on job-shop scheduling(JSP)problem,especially in single objective such as the maximum completion time.But most of the actual system scheduling problems are more than one object.Therefore,the research of multi-objective scheduling problem is very important and meaningful.In this paper,we proposed a multi-objective scheduling model which adopts weighted sum method to optimize two important indexes(makespan and total flow time).Genetic algorithm(GA)has diversified global search ability,while simulated annealing(SA)combined with tabu search(TS)have intensified capabilities in local neighborhood search.To overcome the drawback of the GA,we proposed a new hybrid GA(NewHGA)which produces initial solutions by GA firstly,and then take SA operator incorporate TS operator to search in the local space.By adding the novel local search strategy,the diversity of solutions will be improved greatly so that it can ensure the algorithm jump out of the local optimal value.We test this algorithm using the benchmark instances of different sizes taken from the OR-Library,and the results show that the algorithm is efficient than another hybrid algorithm.

A Novel Criterion of Mixing Time in Gas-Stirred Ladle Systems

A novel criterion of mixing time in gas-stirred ladle systems was proposed in this paper. The essential difference between the previous criterion and the present one is that the former is based on the concentration itself while the latter is based on the variation rate of the concentration, which reflects the mixing efficiency directly. Experiment was carried out in an acrylic glass vessel with bottom blowing, and the tracer concentration was monitored by electrical conductivity probes. The mixing time obtained through the new criterion is approximately 20% less than that obtained through the 95% criterion, and the deviations of mixing times calculated from the new criterion are smaller than that from the previous one under the same conditions.

Evaluations of endoscopic vein harvesting in coronary artery bypass grafting surgery

Compared with the open saphenous vein harvesting （OVH）, there is a larger decrease in inci-sion complications of endoscopic vein harvesting （EVH）. Fewer studies were conducted to evaluate the quality of great saphenous vein （SVG） harvesting by these two methods. To apply transit time flow measurement （TTFM） to SVG grafts in coronary artery bypass grafting （CABG）, we properly evaluate the quality of SVG and surgical effect. Methods From January 2012 to August 2012, 38 cases underwent EVH and 16 cases underwent OVH. We recorded pulsatility index （PI）, mean graft flow （MGF） and diastolic flow （DF） of SVG grafts for statistical analysis. The dysfunctional grafts diagnostic criteria is PI 〉 5, MGF 〈 10 mL/min or DF 〈 50%. Result In terms of SVG grafts, no significant difference existed in the length of two groups （P = 0.2395）. EVH group har-vesting time was longer than OVH group （P = 0.0113）, but the incision length of EVH group was shorter （P = 0.0000） and it needed less suture time. EVH group presented no significant differences in incision complication rate from OVH group （P = 0.7055） within 1 month after surgery. TTFM data of well functioning grafts had no significant difference in the two groups （PI： 3.2 ± 1.0 vs. 2.9 ± 0.9, MGF： 34.7 ± 20.4 vs. 36.3 ± 19.2 mL / min, DF： 66.3% ± 10.6% vs. 68.5% ± 10.3%）. There was no significant difference in the rate of dysfunctional grafts in two groups （P = 0.7954） as well. The cause for tomosed the grafts with satisfactory effect. Conclusion vesting methods. The surgical effect and the quality of quality of SVG grafts can be reasonably evaluated by TYFM.