The Microcystis bloom that once disappeared from Donghu Lake, a shallow eutrophic Chinese lake,was successfully resumed with the use of the enclosure method. Seston and dissolved organic carbon (DOC)dynamics during th...The Microcystis bloom that once disappeared from Donghu Lake, a shallow eutrophic Chinese lake,was successfully resumed with the use of the enclosure method. Seston and dissolved organic carbon (DOC)dynamics during the Microcystis bloom were investigated with particular emphasis on the effect of three Chinese domestic fishes (silver carp, bighead carp and grass carp). The results showed that the change of chlorophyll a obviously reated to the fish species and its stocking density. Du to the relare of exracelular ogranic carbon and increased bacterial activity, DOC increased apparently after silver and bighead carps were introduced. POC/DOC dropped considerably in the enclosures containing silver and bighead carps and in the surrounding lake water, which implied that the bacterial acivity was more pronounced in such ecosystems. Statistical analytis indicated that the linear relationship between POC and chiorophyll a could reflect the state of algal growth and nutrient metabolism. It was expected that this study would provide some information on biomanipulation in the shallow eutrophic lakes.展开更多
In this article, we compute the enclosures eigenvalues (upper and lower bounds) using the quadratic method. The Schrodinger operator (A) (harmonic and anharmonic oscillator model) has used as an example. We study a ne...In this article, we compute the enclosures eigenvalues (upper and lower bounds) using the quadratic method. The Schrodinger operator (A) (harmonic and anharmonic oscillator model) has used as an example. We study a new technique to get more accurate bounds. We compare our results with Boulton and Strauss method.展开更多
The pathway and fate of heavy metals were studied in 10m3 enclosures at Xiamen Bay in 1985. The dissolved metals added are removed rather quickly during the first days, and their half-removal times ( t1/2) (d) are as ...The pathway and fate of heavy metals were studied in 10m3 enclosures at Xiamen Bay in 1985. The dissolved metals added are removed rather quickly during the first days, and their half-removal times ( t1/2) (d) are as follows: Pb 5. 4-5. 8, Hg 6. 7-14, Zn 11-22, Cu 16 - 29, and Cd 30-89. Zinc is transferred biologically to particles during phytoplankton bloom. The main Fate of added metals after 27 days is as follows; over 80% Cd and 60% Cu remain in dissolved phase, more than 60% Pb and 50% Hg transfer to settling settlement, while Zn is equally distributed in dissolved phase and settling settlement. The wall uptake is less than 2% of the total metals added. Organic materials play an essential role in the partition and the transfer of heavy metals in water column. Terrigenous and autochthonous particles show different affinities to different metals. Most heavy metals associate weakly with zooplankton. The Binding of Cd, Pb, Zn and Cu to the particles shows distinctive features related to the diagenetic alteration.展开更多
To investigate the effects of flow rate on phytoplankton dynamics and related environment variables,a set of enclosure experiments with different fl ow rates were conducted in an artificial lake. We monitored nutrient...To investigate the effects of flow rate on phytoplankton dynamics and related environment variables,a set of enclosure experiments with different fl ow rates were conducted in an artificial lake. We monitored nutrients,temperature,dissolved oxygen,p H,conductivity,turbidity,chlorophyll-a and phytoplankton levels. The lower biomass in all flowing enclosures showed that flow rate significantly inhibited the growth of phytoplankton. A critical flow rate occurred near 0.06 m/s,which was the lowest relative inhibitory rate. Changes in flow conditions affected algal competition for light,resulting in a dramatic shift in phytoplankton composition,from blue-green algae in still waters to green algae in flowing conditions. These findings indicate that critical flow rate can be useful in developing methods to reduce algal bloom occurrence. However,flow rate significantly enhanced the inter-relationships among environmental variables,in particular by inducing higher water turbidity and vegetative reproduction of periphyton( Spirogyra). These changes were accompanied by a decrease in underwater light intensity,which consequently inhibited the photosynthetic intensity of phytoplankton. These results warn that a universal critical flow rate might not exist,because the effect of flow rate on phytoplankton is interlinked with many other environmental variables.展开更多
Adding thin compartmental plates near the internal walls of enclosures has been nttmerically modeled using the lattice Boltzmann method. This practice was found to be an effective way to fitrther suppress the disadvan...Adding thin compartmental plates near the internal walls of enclosures has been nttmerically modeled using the lattice Boltzmann method. This practice was found to be an effective way to fitrther suppress the disadvantageous effects of heat leak, along with the application of insulation materials on the external surfaces. A modified extrapolation scheme for handling the thermal boundary of the thin plate was proposed and verified by comparison with the conventional coupled boundary scheme. The simulation of the natural convection during the cooling down processes and at steady states in the enclosure indicates that the existence of the plates leads to a higher cooling rate and a more favorable temperature uniformity. For a typical case, the one with plates takes 6% less time to reach the halfway point of the steady state and has 26% less temperature variance. Effects by the plates＇ positions and sizes were parametrically investigated, in order to find an optimal geometrical configuration. In addition, the fluid＇s intrinsic characteristics and the relative heat leak by using the Raylcigh number and Nussclt number, respectively, have been discussed in detail through hydrodynamic and convective heat transfer analyses.展开更多
A numerical study has been carried out to investigate the temperature distribution and the natural convection heat transfer in axisymmetric two-dimensional vertical saturated porous cylinder with steady state laminar ...A numerical study has been carried out to investigate the temperature distribution and the natural convection heat transfer in axisymmetric two-dimensional vertical saturated porous cylinder with steady state laminar flow. A comparison between two situations is done under the effect of MHD （magnetohydrodynamics） and radiation. In the two situations, the vertical walls of the cylinder are cooled with constant wall temperature and a constant heat generation subjected along the centerline of the cylinder. The first case for cylinder with insulated upper surface and cooled bottom surface while the second case for cylinder with cooled upper surface and insulated bottom surface. The governing equations used are continuity, momentum and energy equations which are transformed to dimensionless equations. The finite difference approach is used to obtain all the computational results using the MATLAB-7 programming. The parameters affected the system are Rayleigh number ranging within （102≤ Ra ≤104）, radiation parameter （0≤ Rd ≤ 2） and magnetohydrodynamics MHD （Mn） （0 ≤ Mn≤ 2）.The results show that the temperature of Case 1 is more than that in Case 2 at constant Ra, Mn and Rd while the value of the stream in Case 2 is greater than that in Case 1. Nu increase with the increase of Rd and increasing Mn caused the temperature to increase and the streamline dropped while Nu decreased. A correlation has been set up to give the average Nusselt number variation with Ra, Rd and Mn for which the results are found to be in good agreement with previously published researches.展开更多
The sound field driven by piping systems in enclosures may severely affect living comfort,which is frequently encountered in various engineering applications.Managing this sound field relies heavily on the available p...The sound field driven by piping systems in enclosures may severely affect living comfort,which is frequently encountered in various engineering applications.Managing this sound field relies heavily on the available prediction tools at hand,e.g.,the widely used finite element methods are computationally expensive due to the necessity to discretize entire space,analytical models,based on modal expansion method,may offer substantial advantages in terms of computational cost and efficiency.However,deriving eigenmodes of irregular enclosed spaces may be challenging,which impedes accurate and rapid predictions of the sound field in practical applications.This study presents an analytical framework aimed at rapidly and accurately predicting the interior sound field driven by the piping system vibrations in irregular enclosures.Vibration response of the piping system is obtained using the wave approach,and a line dipole source is idealized as the sound source of the piping system vibration.On the basis of eigenmodes of regular enclosures,the Kirchhoff-Helmholtz integral theorem(modal ex-pansion method for irregular enclosures)is introduced to account for the boundaries of irregular enclosures.This theoretical framework is validated through numerical simulations by finite element method and experiments,demonstrating high accuracy and significant efficiency advantages.The proposed method can be further employed to optimize radiated sound fields by tailoring the impedance of space walls or layout of piping systems.This study provides an efficient tool for predicting radiated sound field in general enclosures driven by vibration of piping systems,paving a new path for indoor acoustical optimization.展开更多
It is considered necessary that an additional term representing the direct sound be introduced into the classical normal mode solution of sound field in enclosures , to accord with practice and to make the formula mor...It is considered necessary that an additional term representing the direct sound be introduced into the classical normal mode solution of sound field in enclosures , to accord with practice and to make the formula more useful.展开更多
The classical normal-mode theory expresses the steady-state sound field in an enclosure produced by a sound source as a series of normal modes of vibration. Experimental facts are not often explained by this theory, a...The classical normal-mode theory expresses the steady-state sound field in an enclosure produced by a sound source as a series of normal modes of vibration. Experimental facts are not often explained by this theory, and it was conjectured that the normal-mode expression is not the complete solution of the wave equation in the enclosure, but only the reverberant part of it, and there should be an additional term representing the direct spherical radiation to make the solution complete. The problem is examined by critically reviewing the derivation of the normal-mode expression, and by theoretical analysis of the steady-state sound field in the room and experimental measurements therein. The conjecture is thus confirmed, and it is definitely shown that the sound field should contain the direct wave as well as the standing waves (normal modes) formed by the confinement of the boundary surfaces. Relevant mathematical expressions are derived.展开更多
In this paper, a concept of 'identical problems' of natural convection in enclosures is presented. A pair of problems of natural convection in enclosures is said to be identical if they look different in appea...In this paper, a concept of 'identical problems' of natural convection in enclosures is presented. A pair of problems of natural convection in enclosures is said to be identical if they look different in appearance but with appropriate selection of coordinates and appropriate definition of dimensionless variables for each problem, they will have identical geometric configurations and identical dimensionless governing equations and related boundary conditions. The identical characteristics of a pair of problems of natural convection in enclosures with an internal isolated island are demonstrated via dimensionless mathematical formulation and flow visualization results. Numerical computations are performed and the predicted streamlines agree with the flow visualization results. A number of other possible pairs of identical problems are also presented. Applications of the identical character are provided and assumptions under which the identical problems may exist are discussed.展开更多
Numerical computations are performed for the natural convection in circular enclosures with inner polygonal cylinders.The polygon surface and the outer envelope are at constant but different temperatures,A body-fitted...Numerical computations are performed for the natural convection in circular enclosures with inner polygonal cylinders.The polygon surface and the outer envelope are at constant but different temperatures,A body-fitted coordinate system is used,The coordinate system is generated via simple algebraic equations.The transformed governing equations are discretized on a control volume basis with power-law finite difference scheme.The SIMPLE-like algorithm is used to deal with the linkage between pressure and velocities.The numerical results are compared with the experimental data available in the literature,and the agreement between the numerical and experimental results are very good.展开更多
Emission characteristics of biogenic volatile organic compounds(BVOCs)from dominant tree species in the subtropical pristine forests of China are extremely limited.Here we conducted in situ field measurements of BVOCs...Emission characteristics of biogenic volatile organic compounds(BVOCs)from dominant tree species in the subtropical pristine forests of China are extremely limited.Here we conducted in situ field measurements of BVOCs emissions from representative mature evergreen trees by using dynamic branch enclosures at four altitude gradients(600-1690ma.s.l.)in the Nanling Mountains of southern China.Composition characteristics as well as seasonal and altitudinal variations were analyzed.Standardized emission rates and canopyscale emission factors were then calculated.Results showed that BVOCs emission intensities in the wet season were generally higher than those in the dry season.Monoterpenes were the dominant BVOCs emitted from most broad-leaved trees,accounting for over 70%of the total.Schima superba,Yushania basihirsuta and Altingia chinensis had relatively high emission intensities and secondary pollutant formation potentials.The localized emission factors of isoprene were comparable to the defaults in the Model of Emissions of Gases and Aerosols fromNature(MEGAN),while emission factors of monoterpenes and sesquiterpenes were 2 to 58 times of those in the model.Our results can be used to update the current BVOCs emission inventory in MEGAN,thereby reducing the uncertainties of BVOCs emission estimations in forested regions of southern China.展开更多
This study numerically investigates inclined magneto-hydrodynamic natural convection in a porous cavity filled with nanofluid containing gyrotactic microorganisms.The governing equations are nondimensionalized and sol...This study numerically investigates inclined magneto-hydrodynamic natural convection in a porous cavity filled with nanofluid containing gyrotactic microorganisms.The governing equations are nondimensionalized and solved using the finite volume method.The simulations examine the impact of key parameters such as heat source length and position,Peclet number,porosity,and heat generation/absorption on flow patterns,temperature distribution,concentration profiles,and microorganism rotation.Results indicate that extending the heat source length enhances convective currents and heat transfer efficiency,while optimizing the heat source position reduces entropy generation.Higher Peclet numbers amplify convective currents and microorganism distribution complexity.Variations in porosity and heat generation/absorption significantly influence flow dynamics.Additionally,the artificial neural network model reliably predicts the mean Nusselt and Sherwood numbers(Nu&Sh),demonstrating its effectiveness for such analyses.The simulation results reveal that increasing the heat source length significantly enhances heat transfer,as evidenced by a 15%increase in the mean Nusselt number.展开更多
Power integrated isolation structures play a crucial role in the field of power electronics,especially in silicon carbide(SiC)devices,where challenges such as high leakage current and insufficient voltage endurance ar...Power integrated isolation structures play a crucial role in the field of power electronics,especially in silicon carbide(SiC)devices,where challenges such as high leakage current and insufficient voltage endurance are prevalent.This paper introduces a novel isolation technology based on vanadium ion implantation,achieving high-performance SiC monolithic integration through deep energy level trapping engineering and three-dimensional composite isolation design.The core technologies include:semi-insulating layer+dielectric trench co-isolation,high-precision process control,high-temperature compatibility optimization,ultra-high breakdown field strength,support for 10kV class IGBT/MOSFET integration,and a 30-50%increase in chip area utilization,combining high performance with low-cost advantages.展开更多
The problem of active structural acoustic control in an enclosure using radiation mode is investigated. The response of the coupled enclosure is derived in terms of radiation modes. The potential energy in the enclosu...The problem of active structural acoustic control in an enclosure using radiation mode is investigated. The response of the coupled enclosure is derived in terms of radiation modes. The potential energy in the enclosure can be decomposed into independent parts and the radiation modes contribute to potential energy independently. The control strategy for minimizing first G radiation modes with large radiation efficiency is proposed, and the optimal model of control forces is presented. Finally, a numerical simulation for minimizing sound transmission into a rectangular enclosure using the proposed method is conducted. Simulation results indicate that one control force can control one radiation mode and controlling the first four-order radiation modes with four control forces can achieve significant potential energy reduction at the low frequency range.展开更多
Rangeland degradation is a serious problem throughout sub-Saharan Africa and its restoration is a challenge for the management of arid and semi-arid areas. In Lake Baringo Basin of Kenya, communities and individual fa...Rangeland degradation is a serious problem throughout sub-Saharan Africa and its restoration is a challenge for the management of arid and semi-arid areas. In Lake Baringo Basin of Kenya, communities and individual farmers are restoring indigenous vegetation inside enclosures in an effort to combat severe land degradation and address their livelihood problems. This study evaluated the impact of enclosure management on soil properties and microbial biomass, being key indicators of soil ecosystem health. Six reseeded communal enclosures using soil embankments as water-harvesting structures and strictly regulated access were selected, varying in age from 13 to 23 years. In six private enclosures, ranging from 3 to 17 years in age, individual farmers emulated the communal enclosure strategy and restored areas for their exclusive use. Significant decreases in bulk density, and increases in the soil organic carbon, total nitrogen and microbial biomass contents and stocks were found in the enclosures as compared with the degraded open rangeland. In the private enclosures, the impact of rehabilitation on the soil quality was variable, and soil quality was in general lower than that obtained under communal management. The significant increase of absolute stocks of carbon, nitrogen and microbial biomass compared to the degraded open rangeland indicates the potential for the restoration of soil quality through range rehabilitation. Over-sowing with indigenous legume fodder species could improve total nitrogen content in the soil and nutritional value of the pastures as well.展开更多
TEKO Enclosures公司推出可容纳所有类型小型电子装置的ENCLOS型机壳。典型应用包括：遥控和袖珍型仪表。这些通用机壳以黑色ABS(UL94HB)材料模铸而成，带有可以嵌入顶部凹陷处的铝质面板。该凹陷处也可用来安装薄膜小键盘或产品标签。...TEKO Enclosures公司推出可容纳所有类型小型电子装置的ENCLOS型机壳。典型应用包括：遥控和袖珍型仪表。这些通用机壳以黑色ABS(UL94HB)材料模铸而成，带有可以嵌入顶部凹陷处的铝质面板。该凹陷处也可用来安装薄膜小键盘或产品标签。这种产品有3种尺寸3．34英寸×2．85英寸，高度分别为0．98英寸、展开更多
Experimental study was conducted to determine the effect of velocity of axial fan,outlet vent height,position,area,and aspect ratio(h/w)of ventilated enclosure on convection heat transfer.Rectangular wooden ventilated...Experimental study was conducted to determine the effect of velocity of axial fan,outlet vent height,position,area,and aspect ratio(h/w)of ventilated enclosure on convection heat transfer.Rectangular wooden ventilated enclosure having top and front transparent wall was made up of Perspex for visualization,and internal physical dimensions of box were 200 mm×200 mm×400 mm.Inlet vent was at bottom while outlet vents were at the side and top wall.Electrically heated cylindrical heat source having 6.1 slenderness ratio was fabricated and hanged at the centre of the enclosure.To calculate heat transfer rates,thermocouples were attached to the inner surface of heat source with silica gel.Heat source was operated at constant heat flux in order to quantify the effect of velocity of air on heat transfer.It was observed that average Nusselt number was increased from 68 to 216 by changing velocity from 0 to 3.34 m/s at constant modified Grashof number i.e.5.67E+09.While variation in outlet height at the front wall did not affect heat transfer in forced convection region.However,Nusselt number decreased to 5%by changing the outlet position from top to the front wall or by 50%reduction in outlet area during forced convection.Mean rise in temperature of enclosure increased from 8.19 K to 9.40 K by increasing aspect ratio of enclosure from 1.5 to 2 by operating heat source at constant heat flux i.e.541.20 w/m^(2).展开更多
The hypertrophic subtropic Donghu Lake’s dense water bloom(of mainly Microcystis Anaabaena andOscillatoria)that occurred annually from the beginning of the 1970s, has disappeared since 1985. The infiuenceof planktivo...The hypertrophic subtropic Donghu Lake’s dense water bloom(of mainly Microcystis Anaabaena andOscillatoria)that occurred annually from the beginning of the 1970s, has disappeared since 1985. The infiuenceof planktivorous fishes (silver and bighead carps) on the water bloom was studied for three years usingthe enclosure method. The enclosures stocked densely with bighead and/or silver carp were free of waterbloom during the experimental period. The water bloom that appeared in the fish-free enclosures was completelyeliminated in 10-20 days by introduction of silver and/or bighead carp(grass carp was not effectivein controlling water bloom).This study showed clearly that grazing pressure by planktivorous fishes is a keyfactor in eliminating water bloom from the lake.展开更多
文摘The Microcystis bloom that once disappeared from Donghu Lake, a shallow eutrophic Chinese lake,was successfully resumed with the use of the enclosure method. Seston and dissolved organic carbon (DOC)dynamics during the Microcystis bloom were investigated with particular emphasis on the effect of three Chinese domestic fishes (silver carp, bighead carp and grass carp). The results showed that the change of chlorophyll a obviously reated to the fish species and its stocking density. Du to the relare of exracelular ogranic carbon and increased bacterial activity, DOC increased apparently after silver and bighead carps were introduced. POC/DOC dropped considerably in the enclosures containing silver and bighead carps and in the surrounding lake water, which implied that the bacterial acivity was more pronounced in such ecosystems. Statistical analytis indicated that the linear relationship between POC and chiorophyll a could reflect the state of algal growth and nutrient metabolism. It was expected that this study would provide some information on biomanipulation in the shallow eutrophic lakes.
文摘In this article, we compute the enclosures eigenvalues (upper and lower bounds) using the quadratic method. The Schrodinger operator (A) (harmonic and anharmonic oscillator model) has used as an example. We study a new technique to get more accurate bounds. We compare our results with Boulton and Strauss method.
文摘The pathway and fate of heavy metals were studied in 10m3 enclosures at Xiamen Bay in 1985. The dissolved metals added are removed rather quickly during the first days, and their half-removal times ( t1/2) (d) are as follows: Pb 5. 4-5. 8, Hg 6. 7-14, Zn 11-22, Cu 16 - 29, and Cd 30-89. Zinc is transferred biologically to particles during phytoplankton bloom. The main Fate of added metals after 27 days is as follows; over 80% Cd and 60% Cu remain in dissolved phase, more than 60% Pb and 50% Hg transfer to settling settlement, while Zn is equally distributed in dissolved phase and settling settlement. The wall uptake is less than 2% of the total metals added. Organic materials play an essential role in the partition and the transfer of heavy metals in water column. Terrigenous and autochthonous particles show different affinities to different metals. Most heavy metals associate weakly with zooplankton. The Binding of Cd, Pb, Zn and Cu to the particles shows distinctive features related to the diagenetic alteration.
基金Supported by the National Natural Science Foundation of China(Nos.51379146,51409190)the National Science Foundation for Post-Doctoral Scientists of China(No.2013M531218)
文摘To investigate the effects of flow rate on phytoplankton dynamics and related environment variables,a set of enclosure experiments with different fl ow rates were conducted in an artificial lake. We monitored nutrients,temperature,dissolved oxygen,p H,conductivity,turbidity,chlorophyll-a and phytoplankton levels. The lower biomass in all flowing enclosures showed that flow rate significantly inhibited the growth of phytoplankton. A critical flow rate occurred near 0.06 m/s,which was the lowest relative inhibitory rate. Changes in flow conditions affected algal competition for light,resulting in a dramatic shift in phytoplankton composition,from blue-green algae in still waters to green algae in flowing conditions. These findings indicate that critical flow rate can be useful in developing methods to reduce algal bloom occurrence. However,flow rate significantly enhanced the inter-relationships among environmental variables,in particular by inducing higher water turbidity and vegetative reproduction of periphyton( Spirogyra). These changes were accompanied by a decrease in underwater light intensity,which consequently inhibited the photosynthetic intensity of phytoplankton. These results warn that a universal critical flow rate might not exist,because the effect of flow rate on phytoplankton is interlinked with many other environmental variables.
基金Project supported by the National Natural Science Foundation of China （No. 51176112）
文摘Adding thin compartmental plates near the internal walls of enclosures has been nttmerically modeled using the lattice Boltzmann method. This practice was found to be an effective way to fitrther suppress the disadvantageous effects of heat leak, along with the application of insulation materials on the external surfaces. A modified extrapolation scheme for handling the thermal boundary of the thin plate was proposed and verified by comparison with the conventional coupled boundary scheme. The simulation of the natural convection during the cooling down processes and at steady states in the enclosure indicates that the existence of the plates leads to a higher cooling rate and a more favorable temperature uniformity. For a typical case, the one with plates takes 6% less time to reach the halfway point of the steady state and has 26% less temperature variance. Effects by the plates＇ positions and sizes were parametrically investigated, in order to find an optimal geometrical configuration. In addition, the fluid＇s intrinsic characteristics and the relative heat leak by using the Raylcigh number and Nussclt number, respectively, have been discussed in detail through hydrodynamic and convective heat transfer analyses.
文摘A numerical study has been carried out to investigate the temperature distribution and the natural convection heat transfer in axisymmetric two-dimensional vertical saturated porous cylinder with steady state laminar flow. A comparison between two situations is done under the effect of MHD （magnetohydrodynamics） and radiation. In the two situations, the vertical walls of the cylinder are cooled with constant wall temperature and a constant heat generation subjected along the centerline of the cylinder. The first case for cylinder with insulated upper surface and cooled bottom surface while the second case for cylinder with cooled upper surface and insulated bottom surface. The governing equations used are continuity, momentum and energy equations which are transformed to dimensionless equations. The finite difference approach is used to obtain all the computational results using the MATLAB-7 programming. The parameters affected the system are Rayleigh number ranging within （102≤ Ra ≤104）, radiation parameter （0≤ Rd ≤ 2） and magnetohydrodynamics MHD （Mn） （0 ≤ Mn≤ 2）.The results show that the temperature of Case 1 is more than that in Case 2 at constant Ra, Mn and Rd while the value of the stream in Case 2 is greater than that in Case 1. Nu increase with the increase of Rd and increasing Mn caused the temperature to increase and the streamline dropped while Nu decreased. A correlation has been set up to give the average Nusselt number variation with Ra, Rd and Mn for which the results are found to be in good agreement with previously published researches.
基金supported by the National Natural Science Foundation of China(Grant Nos.11632003,11972083,11991030,12372088,and U22B2078)Beijing Institute of Technology Research Fund Program for Young Scholars(Grant No.XSQD-202101010).
文摘The sound field driven by piping systems in enclosures may severely affect living comfort,which is frequently encountered in various engineering applications.Managing this sound field relies heavily on the available prediction tools at hand,e.g.,the widely used finite element methods are computationally expensive due to the necessity to discretize entire space,analytical models,based on modal expansion method,may offer substantial advantages in terms of computational cost and efficiency.However,deriving eigenmodes of irregular enclosed spaces may be challenging,which impedes accurate and rapid predictions of the sound field in practical applications.This study presents an analytical framework aimed at rapidly and accurately predicting the interior sound field driven by the piping system vibrations in irregular enclosures.Vibration response of the piping system is obtained using the wave approach,and a line dipole source is idealized as the sound source of the piping system vibration.On the basis of eigenmodes of regular enclosures,the Kirchhoff-Helmholtz integral theorem(modal ex-pansion method for irregular enclosures)is introduced to account for the boundaries of irregular enclosures.This theoretical framework is validated through numerical simulations by finite element method and experiments,demonstrating high accuracy and significant efficiency advantages.The proposed method can be further employed to optimize radiated sound fields by tailoring the impedance of space walls or layout of piping systems.This study provides an efficient tool for predicting radiated sound field in general enclosures driven by vibration of piping systems,paving a new path for indoor acoustical optimization.
文摘It is considered necessary that an additional term representing the direct sound be introduced into the classical normal mode solution of sound field in enclosures , to accord with practice and to make the formula more useful.
文摘The classical normal-mode theory expresses the steady-state sound field in an enclosure produced by a sound source as a series of normal modes of vibration. Experimental facts are not often explained by this theory, and it was conjectured that the normal-mode expression is not the complete solution of the wave equation in the enclosure, but only the reverberant part of it, and there should be an additional term representing the direct spherical radiation to make the solution complete. The problem is examined by critically reviewing the derivation of the normal-mode expression, and by theoretical analysis of the steady-state sound field in the room and experimental measurements therein. The conjecture is thus confirmed, and it is definitely shown that the sound field should contain the direct wave as well as the standing waves (normal modes) formed by the confinement of the boundary surfaces. Relevant mathematical expressions are derived.
文摘In this paper, a concept of 'identical problems' of natural convection in enclosures is presented. A pair of problems of natural convection in enclosures is said to be identical if they look different in appearance but with appropriate selection of coordinates and appropriate definition of dimensionless variables for each problem, they will have identical geometric configurations and identical dimensionless governing equations and related boundary conditions. The identical characteristics of a pair of problems of natural convection in enclosures with an internal isolated island are demonstrated via dimensionless mathematical formulation and flow visualization results. Numerical computations are performed and the predicted streamlines agree with the flow visualization results. A number of other possible pairs of identical problems are also presented. Applications of the identical character are provided and assumptions under which the identical problems may exist are discussed.
文摘Numerical computations are performed for the natural convection in circular enclosures with inner polygonal cylinders.The polygon surface and the outer envelope are at constant but different temperatures,A body-fitted coordinate system is used,The coordinate system is generated via simple algebraic equations.The transformed governing equations are discretized on a control volume basis with power-law finite difference scheme.The SIMPLE-like algorithm is used to deal with the linkage between pressure and velocities.The numerical results are compared with the experimental data available in the literature,and the agreement between the numerical and experimental results are very good.
基金supported by the National Natural Science Foundation of China (NSFC)Projects (Nos.42205105,42121004,and 42077190)the Science and Technology Project of Shaoguan (No.210811164532141)+3 种基金the National Key R&D Program of China (2022YFC3700604)the Science and Technology Program of Guangzhou City (No.202201010400)the Fundamental Research Funds for the Central Universities (No.21622319)the Research Center of Low Carbon Economy for Guangzhou Region (No.22JNZS50).
文摘Emission characteristics of biogenic volatile organic compounds(BVOCs)from dominant tree species in the subtropical pristine forests of China are extremely limited.Here we conducted in situ field measurements of BVOCs emissions from representative mature evergreen trees by using dynamic branch enclosures at four altitude gradients(600-1690ma.s.l.)in the Nanling Mountains of southern China.Composition characteristics as well as seasonal and altitudinal variations were analyzed.Standardized emission rates and canopyscale emission factors were then calculated.Results showed that BVOCs emission intensities in the wet season were generally higher than those in the dry season.Monoterpenes were the dominant BVOCs emitted from most broad-leaved trees,accounting for over 70%of the total.Schima superba,Yushania basihirsuta and Altingia chinensis had relatively high emission intensities and secondary pollutant formation potentials.The localized emission factors of isoprene were comparable to the defaults in the Model of Emissions of Gases and Aerosols fromNature(MEGAN),while emission factors of monoterpenes and sesquiterpenes were 2 to 58 times of those in the model.Our results can be used to update the current BVOCs emission inventory in MEGAN,thereby reducing the uncertainties of BVOCs emission estimations in forested regions of southern China.
基金Dean ship of Scientific Research at King Khalid University,Abha,Saudi Arabia,for funding this work through the Research Group Project(Grant No.RGP.2/610/45)funded by the Princess Nourah bint Abdulrahman University Researchers Supporting Project(Grant No.PNURSP2024R102),Princess Nourah bint Abdulrahman University,Riyadh,Saudi Arabia。
文摘This study numerically investigates inclined magneto-hydrodynamic natural convection in a porous cavity filled with nanofluid containing gyrotactic microorganisms.The governing equations are nondimensionalized and solved using the finite volume method.The simulations examine the impact of key parameters such as heat source length and position,Peclet number,porosity,and heat generation/absorption on flow patterns,temperature distribution,concentration profiles,and microorganism rotation.Results indicate that extending the heat source length enhances convective currents and heat transfer efficiency,while optimizing the heat source position reduces entropy generation.Higher Peclet numbers amplify convective currents and microorganism distribution complexity.Variations in porosity and heat generation/absorption significantly influence flow dynamics.Additionally,the artificial neural network model reliably predicts the mean Nusselt and Sherwood numbers(Nu&Sh),demonstrating its effectiveness for such analyses.The simulation results reveal that increasing the heat source length significantly enhances heat transfer,as evidenced by a 15%increase in the mean Nusselt number.
文摘Power integrated isolation structures play a crucial role in the field of power electronics,especially in silicon carbide(SiC)devices,where challenges such as high leakage current and insufficient voltage endurance are prevalent.This paper introduces a novel isolation technology based on vanadium ion implantation,achieving high-performance SiC monolithic integration through deep energy level trapping engineering and three-dimensional composite isolation design.The core technologies include:semi-insulating layer+dielectric trench co-isolation,high-precision process control,high-temperature compatibility optimization,ultra-high breakdown field strength,support for 10kV class IGBT/MOSFET integration,and a 30-50%increase in chip area utilization,combining high performance with low-cost advantages.
基金Supported by the National Natural Science Foundation of China(50375027,50575041)~~
文摘The problem of active structural acoustic control in an enclosure using radiation mode is investigated. The response of the coupled enclosure is derived in terms of radiation modes. The potential energy in the enclosure can be decomposed into independent parts and the radiation modes contribute to potential energy independently. The control strategy for minimizing first G radiation modes with large radiation efficiency is proposed, and the optimal model of control forces is presented. Finally, a numerical simulation for minimizing sound transmission into a rectangular enclosure using the proposed method is conducted. Simulation results indicate that one control force can control one radiation mode and controlling the first four-order radiation modes with four control forces can achieve significant potential energy reduction at the low frequency range.
基金the financial support provided by the Flemish Interuniversity Council (VLIR) of Belgium in favour of the first author
文摘Rangeland degradation is a serious problem throughout sub-Saharan Africa and its restoration is a challenge for the management of arid and semi-arid areas. In Lake Baringo Basin of Kenya, communities and individual farmers are restoring indigenous vegetation inside enclosures in an effort to combat severe land degradation and address their livelihood problems. This study evaluated the impact of enclosure management on soil properties and microbial biomass, being key indicators of soil ecosystem health. Six reseeded communal enclosures using soil embankments as water-harvesting structures and strictly regulated access were selected, varying in age from 13 to 23 years. In six private enclosures, ranging from 3 to 17 years in age, individual farmers emulated the communal enclosure strategy and restored areas for their exclusive use. Significant decreases in bulk density, and increases in the soil organic carbon, total nitrogen and microbial biomass contents and stocks were found in the enclosures as compared with the degraded open rangeland. In the private enclosures, the impact of rehabilitation on the soil quality was variable, and soil quality was in general lower than that obtained under communal management. The significant increase of absolute stocks of carbon, nitrogen and microbial biomass compared to the degraded open rangeland indicates the potential for the restoration of soil quality through range rehabilitation. Over-sowing with indigenous legume fodder species could improve total nitrogen content in the soil and nutritional value of the pastures as well.
文摘Experimental study was conducted to determine the effect of velocity of axial fan,outlet vent height,position,area,and aspect ratio(h/w)of ventilated enclosure on convection heat transfer.Rectangular wooden ventilated enclosure having top and front transparent wall was made up of Perspex for visualization,and internal physical dimensions of box were 200 mm×200 mm×400 mm.Inlet vent was at bottom while outlet vents were at the side and top wall.Electrically heated cylindrical heat source having 6.1 slenderness ratio was fabricated and hanged at the centre of the enclosure.To calculate heat transfer rates,thermocouples were attached to the inner surface of heat source with silica gel.Heat source was operated at constant heat flux in order to quantify the effect of velocity of air on heat transfer.It was observed that average Nusselt number was increased from 68 to 216 by changing velocity from 0 to 3.34 m/s at constant modified Grashof number i.e.5.67E+09.While variation in outlet height at the front wall did not affect heat transfer in forced convection region.However,Nusselt number decreased to 5%by changing the outlet position from top to the front wall or by 50%reduction in outlet area during forced convection.Mean rise in temperature of enclosure increased from 8.19 K to 9.40 K by increasing aspect ratio of enclosure from 1.5 to 2 by operating heat source at constant heat flux i.e.541.20 w/m^(2).
基金This work was supported by FEBL(State Key Laboratory for Freshwater Ecology and Biotechnology of China)fundsNational Natural Science Foundation of China (Grant NO.3937014)
文摘The hypertrophic subtropic Donghu Lake’s dense water bloom(of mainly Microcystis Anaabaena andOscillatoria)that occurred annually from the beginning of the 1970s, has disappeared since 1985. The infiuenceof planktivorous fishes (silver and bighead carps) on the water bloom was studied for three years usingthe enclosure method. The enclosures stocked densely with bighead and/or silver carp were free of waterbloom during the experimental period. The water bloom that appeared in the fish-free enclosures was completelyeliminated in 10-20 days by introduction of silver and/or bighead carp(grass carp was not effectivein controlling water bloom).This study showed clearly that grazing pressure by planktivorous fishes is a keyfactor in eliminating water bloom from the lake.
