The Turbulent Schmidt Number for Transient Contaminant Dispersion in a Large Ventilated Room Using a Realizable k-εModel

Buildings with large open spaces in which chemicals are handled are often exposed to the risk of explosions.Computational fluid dynamics is a useful and convenient way to investigate contaminant dispersion in such large spaces.The turbulent Schmidt number(Sc_(t))concept has typically been used in this regard,and most studies have adopted a default value.We studied the concentration distribution for sulfur hexafluoride(SF_(6))assuming different emission rates and considering the effect of Sc_(t).Then we examined the same problem for a light gas by assuming hydrogen gas(H_(2))as the contaminant.When SF_(6) was considered as the contaminant gas,a variation in the emission rate completely changed the concentration distribution.When the emission rate was low,the gravitational effect did not take place.For both low and high emission rates,an increase in S_(ct) accelerated the transport rate of SF_(6).In contrast,for H_(2) as the contaminant gas,a larger S_(ct) could induce a decrease in the H_(2) transport rate.

Multi-point discharge model: study on corona discharge of double-ended needle in large space

Corona discharge, as a common means to obtain non-equilibrium plasma, can generally obtain high-concentration plasma by increasing discharge points to meet production needs. However,the existing numerical simulation models used to study multi-point corona discharge are all calculations of small-scale space models, which cannot obtain the distribution characteristics of plasma in large space. Based on our previous research, this paper proposes a hybrid model for studying the distribution of multi-point discharge plasma in large-scale spaces, which divides the computational domain and computes separately with the hydrodynamic model and the ion mobility model. The simulation results are verified by a needle–ball electrode device. Firstly, the electric field distribution and plasma distribution of the needle electrodes with single tip and double tips are compared and discussed. Secondly, the plasma distribution of the needle electrode with the double tip at different voltages is investigated. Both computational and experimental results indicate that the charged particle concentration and current of the needle electrode with double tips are both twice as high as those of the needle electrode with a single tip. This model can extend the computational area of the multi-point corona discharge finite element model to the sub-meter(25 cm) or meter level, which provides an effective means to study the plasma distribution generated by multiple discharge points in large-scale space.

Experimental study on thermal environment in large-space building with low sidewall air supply

The thermal environmental characteristics are experim-entally studied in terms of different air supply volumes and outdoor meteorological parameters in a large-space building which is air conditioned with a low sidewall air supply.The experimental results show that the indoor vertical temperature distributions under different condition are similar.The maximum vertical temperature difference（MVTD）is up to about 20 ℃,and it linearly changes with the sol-air temperature.The indoor vertical temperature gradients（VTGs）in the upper,central and lower zones are different.The influence of the sol-air temperature on the VTGs in the upper and the lower zones is greater than that in the central zone.The characteristics of the VTGs in the three zones affected by the air supply volume are the same as those affected by the sol-air temperature.Besides,because of the small air velocity,the predicted mean vote（PMV）on comfort in the occupied zone is slightly high and the air temperature difference between the head and the ankle is usually more than 3 ℃.

Design Schemes and Comparison Research of the End-effector of Large Space Manipulator

The end-effector of the large space manipulator is employed to assist the manipulator in handling and manipulating large payloads on orbit.Currently,there are few researches about the end-effector,and the existing end-effectors have some disadvantages,such as poor misalignment tolerance capability and complex mechanical components.According to the end positioning errors and the residual vibration characters of the large space manipulators,two basic performance requirements of the end-effector which include the capabilities of misalignment tolerance and soft capture are proposed.And the end-effector should accommodate the following misalignments of the mechanical interface.The translation misalignments in axial and radial directions and the angular misalignments in roll,pitch and yaw are ±100 mm,100 mm,±10°,±15°,±15°,respectively.Seven end-effector schemes are presented and the capabilities of misalignment tolerance and soft capture are analyzed elementarily.The three fingers-three petals end-effector and the steel cable-snared end-effector are the most feasible schemes among the seven schemes,and they are designed in detail.The capabilities of misalignment tolerance and soft capture are validated and evaluated,through the experiment on the micro-gravity simulating device and the dynamic analysis in ADAMS software.The results show that the misalignment tolerance capabilities of these two schemes could satisfy the requirement.And the translation misalignment tolerances in axial and radial directions and the angular misalignment tolerances in roll,pitch and yaw of the steel cable-snared end-effector are 30mm,15mm,6°,3° and 3° larger than those of the three fingers-three petals end-effector,respectively.And the contact force of the steel cable-snared end-effector is smaller and smoother than that of the three fingers-three petals end-effector.The end-effector schemes and research methods are beneficial to the developments of the large space manipulator end-effctor and the space docking mechanism.

Pressure from surrounding rock of three shallow tunnels with large section and small spacing

With the increasing traffic demand, the closely built three or more tunnels with large section play a significant role in the tunnel construction. However, the interaction among tunnels has important influences on the security and economy of tunnel engineering, and the calculation of pressure from the surrounding rock during the excavation is one of the problems that need to be solved urgently. Based on the practical engineering of three tunnels, the load model of three tunnels was proposed in consideration of the interaction and excavation sequence between tunnels. In comparison with the load model of single tunnel, the construction mechanical characteristics of the three tunnels were analyzed. The results show that the rock pressure of three tunnels calculated by the current tunnel design code is not reliable, and the interaction force increases with the spacing between tunnels.

Thermal stratification level of low sidewall air supply with air-conditioning system in large space

The thermal stratification level of low sidewall air supply system in large space was defined. Depending on the experiment of low sidewall air supply in summer 2008,the thermal stratification level was studied by simulation. Based on the simulation of experiment condition,the air velocity and vertical temperature distribution in a large space were simulated at different air-outlet velocities,and then the thermal stratification level line was obtained. The simulation results well match with the experimental ones and the average relative error is 3.4%. The thermal stratification level is heightened by increasing the air-outlet velocity with low sidewall air supply mode. It is concluded that when air-outlet velocity is 0.29 m/s,which is the experimental case,a uniform thermal environment in the higher occupied zone and a stable stratification level are formed. When the air-outlet velocity is low,such as 0.05 m/s,the thermal stratification level is too low and the air velocity is too small to meet the human thermal comfort in the occupied zone. So,it would be reasonable that the air-outlet velocity may be designed as 0.31 m/s if the height of the occupied zone is 2 m.

Investigation of Ancient and Large Tree Resources in Green Spaces of Urban Parks: A Case Study of Yunqizhujing Park in Hangzhou, China

Conservation of ancient and large trees in domestic and overseas cities was compared, ancient and large trees were regarded as important cultural relics playing an important role in optimizing urban natural environment and enriching urban humanistic and natural landscapes, and they were also important contents of urban garden works symbolizing urban parks. A case study was carried out Yunqizhujing Park to study conservation of ancient and large trees in park green spaces of Hangzhou City, solutions to current problems were proposed, and constructive suggestions were given for the conservation of ancient and large trees in urban park green spaces.

large Fock空间上Toeplitz算子的Fredholm性质

令ϕ是属于权函数类W,对于n维复空间ℂn上由ϕ诱导的large fock空间Fp(ϕ),记Fp(ϕ)=Lp(ϕ)⋂H(ℂn),其中H(ℂn)是ℂn上的解析函数全体。首先介绍了权函数类W的基本性质、Bergman空间上的覆盖定理并对再生核函数做出了估计。其次引入一个辅助算子Gl,并证明了Gl的有界性、Toeplitz算子Tf的Berezin变换和紧致性之间的关系以及Hankel算子Hf的有界性和紧致性。最后,给定0<p<∞,利用Toeplitz算子和Hankel算子的有界性和紧致性以及large Fock空间Fp(ϕ)的对偶理论,研究了Toeplitz算子Tf在Fp(ϕ)上具有Fredholm性质的充要条件是f的Berezin变换在整个n维复空间上有界且在无穷边界上远离原点,其中f是一个有界的消失平均震荡函数。

Energy consumption of large space atrium under nozzle outlet during winter season

Based on the thermal and velocity layer's theory,the experimental setup was established on large space atrium under nozzle outlet. A series of winter experiments were accomplished and the following conclusions could be drawn. At the sunny day of winter in Shanghai,the thermal and velocity layer are similar. The height of the both layer is 10-30 mm,and the temperature gratitude is 5-10 ℃ /m. Decreasing the angle of the nozzle outlet can increase the layer height dramatically. The maximum temperature difference of the occupant zone has relation with the angle of the nozzle outlet. The less the angle of the nozzle outlet is set,the greater the temperature difference is. The occupant temperature differences at these angles of the nozzle outlet are 5.1-4.4 ℃. The velocity of the wind is 0.02 and 0.17 m/s and they can accord with design demand. So,it can decrease the temperature gratitude by about 30% and it can save 10%-15% energy consumption.

Design of Mechanical Smoke Exhaust System in Large Space of Convention Center

The volumetric flow rate of smoke generated from the fire in large space often reaches to hundreds of thousands CMH because of extended floor height and as it’s more difficult to isolate the smoke to the limited area, comparing to normal-scale building, design and operation of effective smoke control system for large space is more than important. In this study, with the analysis model for such a large space as exhibition hall or conference room in conventional center, design of mechanical smoke exhaust system was conducted based on currently-available design standard which was then followed by numerical analysis of the design using 3D numerical analysis method. For conference room at 2.0 MW heat release rate, 99,173 CMH flow rate is required, if smoke layer is maintained at 60% of the floor height and for exhibition hall at 8.8 MW with 80% of floor height, flow rate required is 219,802 CMH, which are incorporated into the design. In view of 3D numerical analysis, accuracy of the design according to algebraic expression is sufficient.

Experimental Study on Indoor Thermal Stratification in Large Space by under Floor Air Distribution System (UFAD) in Summer

A ventilation method of down-supply up-return has grown popular in large space in recent years for comfort ventilation with low thermal load, especially in China, including gymnasium, factory space, and exhibition hall, etc. The undisturbed flow pattern in the space gives a gradient in temperature, and the vertical thermal stratification appears markedly in large space. The object for this paper is to understand the behaviour of an under floor air distribution system in a ventilated space. The thermal stratification characteristics in a real UFAD experimental space were measured. The effects of different supply conditions on the thermal stratification characteristics are investigated based on the experimental results. The relations between space air stratification and the control parameter is predicted. It can be indicated that there are 4 zones composing the vertical thermal stratification. And different zone has different control parameter.

Sequence Planning for On-Orbit Assembly of Large Space Truss Structures in a Multirobot Environment

An approach to sequence planning for on-orbit assembly of large space truss structures in a multirobot environment is presented. A hierarchical representation of large space truss structures at the structural volume element level and strut level is adopted. The representation of connectivity matrix and directed graph is respectively presented at the strut level and SVE level. The multirobot environment that consists of autonomous space robots and struts is supposed. Then the multirobot serial assembly strategy,assembly states,assembly tasks and assembly sequences are described. The assembly sequence planning algorithms at the strut level and SVE level are respectively discussed. The results of the simulations show that this approach is feasible and efficient. Two extensions of this approach include more accurate assessment of the efficiency representation and improvements in planning algorithm. In the future,the assembly sequence planning of more large space truss structures and complex multirobot environments and assembly tasks will be considered.

LARGE SIGNAL THEORY OF OROTRON IN CONSIDERATION OF SPACE CHARGE FIELD

An approximate formula of space charge field of orotron in rectangular coordinate system,when one of the boundaries is infinite, is derived. Using this model the self-consistant large signal interactionof orotron with space charge is calculated, and the effect of this charge on the performance of the device isdiscussed.

Analysis of the Impact of Large Constellations on the Space Debris Environment and Countermeasures

Large constellations have developed rapidly in recent years because of their unique advantages, but they will inevitably have a major negative impact on the space debris environment, leading to its deterioration. The key to mitigate the impact is the success rate and duration of the post-mission disposal(PMD) process. Aiming at solving this problem, this paper further studies the impact of large constellations on other space assets under different PMD strategies through simulation, and proposes corresponding strategies and suggestions for mitigation.According to One Web’s large constellation launch plan, the dangerous intersection of the large constellation with existing space assets at different stages of the constellations life cycle is calculated by simulation. Based on this, the influence of the large constellation operation on existing space assets at different times and strategies of PMD is analyzed. The conclusion shows that in the PMD stage, large constellations have the greatest impact on existing space assets;the PMD duration and number of satellites performing PMD at the same time are key factors to the degree of negative impact. The faster the PMD is, the less threat it poses to other spacecraft. More results and conclusions are still being analyzed.

Large Interactive Media Display and Its Influence on Transformation Urban Spaces from Neglecting to Action: The Case of Al-Thaqafa Street in Amman City

In 21st?century, media become the most important factor affecting the development of urban cities, including public places. As a result of the digital revolution, re-imaging and re-linkage public places by media are essential to create more interactions between public spaces and users, interaction media display, and urban screens, one of the most important defined media. This interaction can transform the urban space from being neglected to be more interactive space with users, specially the pedestrians. This paper aims to identify the effects of these new digital factors to transform public spaces, and the influences of large media display on the interaction between urban spaces and pedestrians. The paper focuses on Al-Thaqafa Street as one of the neglected spaces in Amman city, and attempts to analyse this street, explains its problems, and studies the influence of these new digital factors on its transformation, to be more active and vital by pedestrians.

Interaction Mechanism between Formation Process of Bank Collapse Disaster Chain and Territorial Space Utilization of Large Reservoirs

Number of reservoirs in China ranks the first in the world. Due to the complex geology, and superimposing rainfall and reservoir water fluctuation, the bank collapse chain is prone to disasters. The Yangtze River Reservoir is key geological disaster prevention area. Studying the process of reservoir disaster is significant because of the limited territorial space utilization. Scientific and technological issues, i.e., the mechanism of bank collapse disaster chain of large reservoirs, the interaction mechanism of bank collapse disaster chain and territorial space utilization, the early identification, monitoring technology and ecological prevention and control technology system of disaster chain, and the territorial space geological safety and control technology system are focused. We consider the material transformation, energy transfer and information transmission in disaster chain;adopt the survey, Space-Air-Ground integrated monitoring, theoretical analysis, numerical simulation and the multidisciplinary research methods;reveal the chain source development, evolution process of secondary and derivative disasters;explore the interaction mechanism of disaster chain and territorial space utilization;construct the system of early identification, monitoring, early warning, control and ecological preven-tion to achieve Emission Peak and Carbon Neutrality;provide theoretical and technical support for the territorial space geological safety, regulation and utilization of large reservoirs.

Characterization of Type p Banach Spaces by the Weak Law of Large Numbers

For weighted sums of the form?j=1kn anj Xnj\sum{_{j=1}^{k_(n)}}a_({nj})X_({nj})where{a_(nj),1?j?k_(n)↑∞,n?1}is a real constant array and{X_(aj),1≤j≤k n,n≥1}is a rowwise independent,zero mean,random element array in a real separable Banach space of typep,we establishL r convergence theorem and a general weak law of large numbers respectively,conversely,we characterize Banach spaces of typep in terms of convergence inr-th mean and probability for such weighted sums.

LARGE TIME ASYMPTOTIC BEHAVIOR OF THE COMPRESSIBLE NAVIER-STOKES EQUATIONS IN PARTIAL SPACE-PERIODIC DOMAINS

In this article, we study the large time behavior of the 3-D isentropic compressible Navier-Stokes equation in the partial space-periodic domains, and simultaneously show that the related profile systems can be described by like Navier-Stokes equations with suitable ＂pressure＂ functions in lower dimensions. Our proofs are based on the energy methods together with some delicate analysis on the corresponding linearized problems.

Large Solutions to the Generalized Debye-Hückel System in Fourier-Besov Spaces

The special structure in some coupled equations makes it possible to drop partial smallness assumption of the initial data to gain the global well-posedness.In this paper,we study the Cauchy problem for generalized Debye-Hückel system in Fourier-Besov spaces.Under more generalized index range,we obtain the global solution with small initial data and local solution with arbitrary initial.Besides,by constructing some weighted function,we prove that the global well-posedness still holds under the small assumption of the charge of initial data.Thus we show that although the initial densities and the hole in electrolytes are large,the equation is still global well-posedness.

Crack elongation and its width of large depth reinforced concrete beams

In order to meet the requirement of structural inspection,the crack spacing and crack width at various heights in the tensile zone of six large depth reinforced concrete beams were measured under several loading levels of serviceability state.The effects of the depth of normal section beams on the crack spacing and crack width were analyzed,and the modified model is proposed for calculating the average crack spacing by thinking about the depth of normal section,the reinforcement arrangement and the effective reinforcement ratio.The relationships of crack widths at any position in the tensile zone and at the reinforcement level on the side surface of beam were studied.By theoretical and statistical analysis,a method is proposed to calculate the ratios of crack widths between any position and the reinforcement level on the side surface of large depth reinforced concrete beams.