Acoustic properties of sintered FeCrAlY foams with open cells (I): Static flow resistance

Open celled metal foams fabricated through the route of metal sintering are a new class of material that offers novel mechanical and acoustic properties. The metal sintering approach offers a cost-effective means for the mass-production of open-cell foams from a range of materials, including high-temperature steel alloys. The mechanical properties of open-celled steel alloy (FeCrAlY) foams have been characterized in previous studies, with focus placed on the influence of processing defects on stiffness and strength. In this work, the low-Reynolds number fluid properties of FeCrAlY foams were investigated both theoretically and experimentally. Specifically, the static flow resistance of the sintered foams important for heat transfer, filtration and sound absorption was modeled based on a cylinder and a sphere arranged in a periodic lattice at general incidence to the flow. Experimental measurements were subsequently carried out to validate theoretical predictions, with good agreement achieved. Supported by the National Basic Research Program of China (Grant Nos. 2006CB601202, 2006CB601204), the National 111 Project of China (Grant No. B06024), US Office of Naval Research (Grant No. N000140210117), the National Natural Science Foundation of China (Grant Nos. 10572111, 10632060), and the National Hi-Tech Research Development Program (Grant No. 2006AA03Z519)     

Thermoelastic properties of sandwich materials with pin-reinforced foam cores

Pin-reinforced foam is a novel type of sandwich core materials formed by inserting pins (trusses) into a foam matrix to create a truss-like network reinforced foam core. Upon loading, the pins deform predominantly by local stretching whilst the deformation of foam is governed by local bending. This paper presents a theoretical study on the thermoelasticity of pin-reinforced foam sandwich cores. To calculate the effective thermoelastic properties of pin-reinforced foam cores, the energy-based homogenization approach is employed to develop a micromechanicsbased model, calibrated by the existing experimental data. It is found that the stiffness of the sandwich core is mainly governed by pin reinforcements: the foam matrix contributes little to sandwich stiffness. Compared with traditional foam cores without pin reinforcements, the changes in in-plane thermal expansion coefficients are not vigorous as a result of pin reinforcements, while the throughthickness thermal expansion coefficient changes significantly. It is also demonstrated that it is possible to design materials with zero or negative thermal expansion coefficients under such a context. Supported by the National Basic Research Program of China (Grant No. 2006CB601202), the National Natural Science Foundation of China (Grant Nos. 10572111, 10632060), the National 111 Project of China (Grant No. B06024), the National High Technology Research Development Program (Grant No. 2006AA03Z519), the NPU Foundation for Fundamental Research, the Open Foundation of State Key Laboratory of Structural Analysis of Industrial Equipment (Grant No. GZ0701), and the NPU Foundation for Scientific Innovation     

The solidification of two-phase heterogeneous materials: Theory versus experiment

The solidification behavior of two-phase heterogeneous materials such as close-celled aluminum foams was analytically studied. The proposed analytical model can precisely predict the location of solidification front as well as the full solidification time for a two-phase heterogeneous material composed of aluminum melt and non-conducting air pores. Experiments using distilled water simulating the aluminum melt to be solidified (frozen) were subsequently conducted to validate the analytical model for two selected porosities (ɛ), ɛ=0 and 0.5. Full numerical simulations with the method of finite difference were also performed to examine the influence of pore shape on solidification. The remarkable agreement between theory and experiment suggests that the delay of solidification in the two-phase heterogeneous material is mainly caused by the reduction of bulk thermal conductivity due to the presence of pores, as this is the sole mechanism accounted for by the analytical model for solidification in a porous medium. Supported by the National Basic Research Program of China (“973” Project) (Grant Nos. 2006CB601202, 2006CB601203), the National Natural Science Foundation of China (Grant Nos. 10572111, 10632060), the National 111 Project of China (Grant No. B06024) and the National High-Tech Research and Development Program of China (“863” Project) (Grant No. 2006AA03Z519).     

Ultralight X-type lattice sandwich structure (II): Micromechanics modeling and finite element analysis

The methods of homogenization and finite elements are employed to predict the effective elastic constants and stress-strain responses of a new type of lattice structure, the X-structure proposed by the authors in a companion paper. It is shown that in most cases the predictions by the equivalent homogenization theory agree well with the experimental and 3-dimensional finite element calculated results. The theoretical and numerical study supports the argument that the X-structure is superior to the pyramid lattice structure in terms of mechanical strength. Supported by the National Basic Research Program of China (“973” Project) (Grant No. 2006CB601202), the National Natural Science Foundation of China (Grant Nos. 10632060, 10825210), the National “111” Project of China (Grant No. B06024) and the National High-Tech Research and Development Program of China (“863” Project) (Grant No. 2006AA03Z519)     

Development of Hydro-Informatic Modelling System and its application

The understanding of hydrological cycle is the core of hydrology and the scientific base of water resources management. Meanwhile, simulation of hydrological cycle has long been regarded as an important tool for the assessment, utilization and protection of water resources. In this paper, a new tool named Hydro-Informatic Modelling System (HIMS) has been developed and introduced with case studies in the Yellow River Basin in China and 331 catchments in Australia. The case studies showed that HIMS can be employed as an integrated platform for hydrological simulation in different regions. HIMS is a modular based framework of hydrological model designed for different utilization such as flood forecasting, water resources planning and evaluating hydrological impacts of climate change and human activities. The unique of HIMS is its flexibility in providing alternative modules in the simulation of hydrological cycle, which successfully overcome the difficulties in the availability of input data, the uncertainty of parameters, and the difference of rainfall-runoff processes. The modular based structure of HIMS makes it possible for developing new hydrological models by the users. Supported by the National Natural Science Foundation of China (Grant No. 40671031), National Key Basic Research Development Program of China (Grant Nos. G1999043601 and 2006CB403407) and National Key Technology R&D Program (Grant No. 2006BAB06N07)     

Acoustic properties of sintered FeCrAlY foams with open cells (II): Sound attenuation

Open-celled metal foams fabricated through metal sintering offers novel mechanical, thermal and acoustic properties. Previously, polymer foams were used as a means of absorbing acoustic energy. However, the structural applications of these foams are inherently limited. The metal sintering approach provides a cost-effective means for the mass-production of open-cell foams from a range of materials, including high-temperature steel alloys. The low Reynolds number fluid properties of sintered steel alloy (FeCrAlY) foams were investigated in a previous study. The static flow resistance of the foams was modeled based on a cylinder and a sphere arranged in a periodic lattice at general incidence to the flow, with the resulting predictions correlating well to measurements. The application of the flow resistance in an acoustic model is the primary focus of the present study. The predictions for the static flow resistance of the sintered foams are first used in a theoretical model to determine the characteristic impedances, as well as the propagation constants of the foams. Subsequently, the predicted acoustic performance of the foams is compared to experimental results. Finally, the design space for a simple acoustic absorber incorporating sintered foams is examined, with the effects of absorber size, foam selection, and foam spacing explored. Supported by the National Basic Research Program of China (Grant Nos. 2006CB601202, 2006CB601204), the National 111 Project of China (Grant No. B06024), US Office of Naval Research (Grant No. N000140210117), the National Natural Science Foundation of China (Grant Nos. 10572111, 10632060), and the National H-Tech Research and Development Program of China (Grant No. 2006AA03Z519)     

Development of ecohydrological assessment tool and its application

The development of Hydro-Informatic Modelling System (HIMS) provides an integrated platform for hydrological simulation. To extend the application of HIMS, an ecohydrological modeling system named ecohydrological assessment tool (EcoHAT) has been developed. Integrating parameter-management tools, RS (remote sensing) inversion tools, module-design tools and GIS analysis tools, the EcoHAT provides an integrated tool to simulate ecohydrological processes on regional scale, which develops a new method on sustainable use of water. EcoHAT has been applied to several case studies, such as, the Yellow River Basin, the acid deposition area in Guizhou province and the riparian catchment of Guanting reservoir in Beijing. Results prove that EcoHAT can efficiently simulate and analysis the ecohydrological processes on regional scale and provide technical support to integrated water resources management on basin scale. Supported by the National Key Technology R&D Program in the 11th Five-year Plan of China (Grant No. 2006BAB06B07), the National Natural Science Foundation of China (Grant No. 40671123), the National Basic Research Program of China (“973” Project) (Grant Nos. 2005CB422207, G19990436), and the National Hi-Tech Research and Development Program of China (“863” Project) (Grant No. 2006AA12Z145)     

The oscillatory damped behavior of double wall carbon nanotube oscillators in gaseous environment

The mechanical oscillatory behaviors of multiwall carbon nanotube oscillators in gaseous environment are investigated using the molecular dynamics method. The effects of ambient gas and temperature on intertube frictional force and oscillation frequency are analyzed. It is found that the intertube frictional force increases with the ambient gas density and temperature. Higher gas density and higher temperature cause a more rapid decay in the oscillation amplitude and an increase of the oscillation frequency. Compared to the vacuum environmental condition, the collision between gas atoms and the nanotube walls is a main ingredient leading to the increase of the energy dissipation. Gas damping may be the main reason for the failure of carbon nanotube oscillators working in gas environment. The ambient temperature also has an important effect on oscillations and low temperature is advantageous to sustain oscillations. Supported by the National Basic Research Program of China (“973”) (Grant No. 2006CB300404), the National Natural Science Foundation of China (Grant Nos. 50676019, 50775017), the Jiangsu Province Natural Science Foundation (Grant Nos. BK2006510, BK2007113), and the Research Funding for the Doctor Program from Chinese Educational Ministry (Grant No. 20050286019)     

Modeling and simulation for train control system using cellular automata

Train control system plays a key role in railway traffic. Its function is to manage and control the train movement on railway networks. In our previous works, based on the cellular automata (CA) model, we proposed several models and algorithms for simulating the train movement under different control system conditions. However, these models are only suitable for some simple traffic conditions. Some basic factors, which are important for train movement, are not considered. In this paper, we extend these models and algorithms and give a unified formula. Using the proposed method, we analyze and discuss the space-time diagram of railway traffic flow and the trajectories of the train movement. The numerical simulation and analytical results demonstrate that the unified CA model is an effective tool for simulating the train control system. Supported by the Program for Changjiang Scholars and Innovative Research Team in University (Grant No. IRT0605), the National Natural Science Foundation of China (Grant Nos. 60634010, 60776829), the Program for New Century Excellent Talents in University (Grant No. NCET-06-0074) and the Key Project of Ministry of Education of China (Grant No. 107007)     

Analyzing and evaluating the three-line rail traffic

In this paper, we propose a method to simulate the three-line rail traffic. The aim is to evaluate the carrying capacity of the three-line rail traffic by studying the rail traffic flow when the passenger flow is unsymmetrical. The simulation results demonstrate that under the unsymmetrical condition, the three-line rail traffic system has almost the same carrying capacity as that of a four-line rail traffic system. Compared with the four-line rail traffic system, the three-line rail traffic system has better utilization of rail line. As a result, building the three-line rail traffic system is a more economical and rational selection. Supported by the National Basic Research Program of China (Grant No. 2006CB705500), the Changjiang Scholars and Innovative Research Team in University (Grant No. IRT0605), the National Natural Science Foundation of China (Grant No. 60634010), New Century Excellent Talents in University (Grant No. NCET-06-0074), and the Key Project of Chinese Ministry of Education (Grant No. 107007)     

Research on cohesive sediment erosion by flow: An overview

Erosion of cohesive sediment by flow is a very complicated phenomenon occurring worldwide. Understanding and modeling of the erosion process are important for many issues such as the breaching of embankments, riverbank stability, siltation of harbors and navigation channels, service life of reservoirs, distribution of (heavy metal) pollutants and water quality problems. In the last few decades, numerous studies have been done on the erosion of cohesive sediment by flow. Nevertheless, the factors affecting the erosion resistance of cohesive sediment are still not fully understood and the knowledge of the physics of cohesive sediment erosion is inadequate, as a result the mathematical modeling of this erosion is far from satisfactory. In this paper an overview of the studies on the erosion resistance, erosion threshold and the erosion rate of cohesive sediment by flow is presented. The outcomes achieved so far from the studies and the existing problems have been analyzed and summarized, based on which recommendations are proposed for future research. Supported by the National Key Technology R&D Program of China (Grant Nos. 2006BAC14B02 and 2006BAB05B03) and the National Basic Research Program (973 Program) of China (Grant No. 2007CB714106)     

Filterbank implementation for multi-channel sampling in fractional Fourier domain

Reconstruction of a continuous time signal from its periodic nonuniform samples and multi-channel samples is fundamental for multi-channel parallel A/D and MIMO systems. In this paper, with a filterbank interpretation of sampling schemes, the efficient interpolation and reconstruction methods for periodic nonuniform sampling and multi-channel sampling in the fractional Fourier domain are presented. Firstly, the interpolation and sampling identities in the fractional Fourier domain are derived by the properties of the fractional Fourier transform. Then, the particularly efficient filterbank implementations for the periodic nonuniform sampling and the multi-channel sampling in the fractional Fourier domain are introduced. At last, the relationship between the multi-channel sampling and the filterbank in the fractional Fourier domain is investigated, which shows that any perfect reconstruction filterbank can lead to new sampling and reconstruction strategies. Supported by the National Natural Science Foundation of China for Distinguished Young Scholars (Grant No. 60625104), the National Natural Science Foundation of China (Grant Nos. 60890072, 60572094) and the National Key Basic Research Program Founded by MOST (Grant No. 2009CB724003)     

Dynamic simulation and optimization approach to construction diversion of hydraulic and hydroelectric projects

To solve the engineering and scientific problems in construction diversion and its simulation analysis, a complete scheme is presented. Firstly, the complex constraint relationship was analyzed among main buildings, diversion buildings and flow control. Secondly, the time-space relationship model of construction diversion system and the general block diagram-oriented simulation model of diversion process were set up. Then, the corresponding numerical simulation method and 3D dynamic visual simulation method were put forward. Further, the simulation and optimization platform of construction diversion control process was developed, integrated with simulation modeling, computation and visualization. Finally, these methods were applied to a practical project successfully, showing that the modeling process is convenient, the computation and the visual analysis can be coupled effectively, and the results conform to practical state. They provide new theoretical principles and technical measures for analyzing the control problems encountered in construction diversion of hydraulic and hydroelectric engineering under complex conditions. Supported by the National Basic Research Program of China (“973” Program) (Grant No. 2007CB714101), the National Key Technology R&D Program in the 11th Five year Plan of China (Grant No. 2006BAB04A13) and the National Science Fund for Distinguished Young Scholars of China (Grant No. 50525927)     

Rapid prediction method for nonlinear expansion process of medical vascular stent

A neural network model with high nonlinear recognition capability was constructed to describe the relationship between the deformation impact factors and the deformation results of vascular stent.Then,using the weighted correction method with the attached momentum term,the network training algorithm was optimized by introducing learning factor η and momentum factor ψ,so the speed of the network training and the system robustness were enhanced.The network was trained by some practi-cal cases,and the statisti...     

Application of time reversal mirror technique in microwave-induced thermo-acoustic tomography system

Microwave-induced thermo-acoustic tomography (MITAT) is a promising technique with great potential in biomedical imaging. It has both the high contrast of the microwave imaging and the high resolution of the ultrasound imaging. In this paper, the proportional relationship between the absorbed microwave energy distribution and the induced ultrasound source distribution is derived. Further, the time reversal mirror (TRM) technique based on the pseudo-spectral time domain (PSTD) method is applied to MITAT system. The simulation results show that high contrast and resolution can be achieved by the TRM technique based on PSTD method even for the received signals with very low signal-to-noise ratio (SNR) and the model parameter with random fluctuation. Supported by the National Natural Science Foundation of China (Grant No. 60771042), the National Hi-Tech Research and Development Program (“863” Project) (Grant No. 2007AA12Z159), 111 Project (Grant No. B07046), SiChuan Excellent Youth Foundation (Grant No. 08ZQ026-039), Program for New Century Excellent Talents in University of China and Program for Changjiang Scholars     

Ultralight X-type lattice sandwich structure (I): Concept,fabrication and experimental characterization

A new type of ultra-lightweight metallic lattice structure (named as the X-type structure) is reported. This periodic structure was formed by two groups of staggered struts in the traditional pyramid structure, and fabricated by folding expanded metal sheet along rows of offset nodes and then brazing the folded structure (as the core) with top and bottom facesheets to form sandwich panels. The out-of-plane compressive and shear properties of the X-type lattice sandwich structure were investigated experimentally and compared to those of the sandwich having a pyramidal truss core. It is found that the formation of the 2-dimensional staggered nodes can effectively make the X-type structure more resistant to inelastic and plastic buckling under both compression and shear loading than the pyramidal lattice truss. Obtained results show that the compressive and shear peak strengths of the X-type lattice structure are about 30% higher than those of the pyramidal lattice truss having the same relative density. Supported by the National Basic Research Program of China (“973” Project) (Grant No. 2006CB601202), the National Natural Science Foundation of China (Grant Nos. 10632060,10825210), the National “111” Project of China (Grant No. B06024) and the National High-Tech Research and Development Program of China (“863” Project) (Grant No. 2006AA03Z519)     

Classification of lying states for the humanoid robot SJTU-HR1

The humanoid robot SJTU-HR1’s concept is introduced and its characteristics tree is given. The basic states for SJTU-HR1 are proposed, including lying, sitting, standing and handstanding, abstracted from the daily exercises of human beings. The G _F (generalized function) set theory is exploited to achieve the kinematic characteristics of the interested EEs (end-effectors) of SJTU-HR1 for the lying states. Finally, the results show that the large amounts of states can be described using the abbreviations in a systematic manner. Although we have focused on the application of the G _F set theory to humanoid robots, particularly the SJTU-HR1, this methodology can also be applied to quadruped robots and hexapedal robots, especially when the desired tasks are complex. Supported by the Natural Basic Research Program of China (“973”) (Grant No. 2006CB705400), the National Natural Science Foundation of China (Grant Nos. 60534020, 30770538), Joint Research Fund for Young Scholars in China and Abroad (Grant No. 50728503), and the Graduate Innovation Foundation of Shanghai Jiao Tong University     

Molecular dynamics simulation of the test of single-walled carbon nanotubes under tensile loading

Molecular dynamics (MD) simulations were performed to do the test of sin-gle-walled carbon nanotubes (SWCNT) under tensile loading with the use of Bren-ner potential to describe the interactions of atoms in SWCNTs. The Young’s modulus and tensile strength for SWCNTs were calculated and the values found are 4.2 TPa and 1.40―1.77 TPa, respectively. During the simulation, it was found that if the SWCNTs are unloaded prior to the maximum stress, the stress-strain curve for unloading process overlaps with the loading one, showing that the SWCNT’s de-formation up to its fracture point is completely elastic. The MD simulation also demonstrates the fracture process for several types of SWCNT and the breaking mechanisms for SWCNTs were analyzed based on the energy and structure be-havior.     

Deformation behavior of Cu-12wt%Al alloy wires with continuous columnar crystals in dieless drawing process

The microstructure and mechanical properties of Cu-12wt%Al alloy wires which are composed of continuous columnar crystals after dieless drawing forming at drawing speed of 1.0―1.4 mm/s and deformation temperature of 600―900℃ were analyzed, and deformation behavior of the alloy during dieless drawing forming was experimentally investigated. The results showed that in the abovemen-tioned conditions, recrystallization phenomenon was not found during dieless drawing forming. When a drawing speed of 1.0 mm/s was...     

Incoherent scatter spectra due to HF heating in the low ionosphere region

The electron velocity distribution function and the incoherent scatter spectra during ionospheric heating in low ionosphere region are presented with consideration of the elastic collision between electrons and neural particles and the excitation of rotation energy level. The effects of pump frequency and electric fields on the spectra are discussed. With the increase of electric field, the non-Maxwellian feature is enhanced, and with the increase of heating frequency, the non-Maxwellian feature is weakened. The non-Maxwellian factor will bring a large error in ionosphere parameters, which must be considered in the inversion. Supported by the National Natural Science Foundation of China (Grant No. 40310223), the National Key Laboratory of Electromagnetic Environment (LEME), and National Key Technologies R&D Program of China (Grant No. 2006BAB18B06)