Super Layer Research Articles

Mechanical performance simulation and optimal design of carbon fiber composite B-pillar

This study primarily concentrates on the layer optimization and structural refinement of carbon fiber composite B-pillars. In the initial phase, an initial layer configuration for the carbon fiber composite material B-pillar was devised, followed by comprehensive finite element numerical simulations. The weight of the B-pillar was effectively diminished by 44.9% compared to its metal counterpart, while maintaining consistent performance across diverse operational conditions. Subsequently, an advanced layer thickness optimization model was formulated, incorporating the innovative ‘super layer’ concept. Integration of simulation software, such as ISIGHT and ABAQUS, facilitated the determination of optimal layer thickness and ratio for the composite material. The layer order was systematically optimized through the application of a discrete particle swarm optimization algorithm based on exchange order, adeptly addressing issues related to discontinuous design variables and potential combinations. The incorporation of a ply drop-off structure laying scheme was derived, resulting in an impressive weight reduction of 57.5%. In the final phase, adherence to NCAP side collision testing standards enabled a comprehensive evaluation, where in various indicators including deformation mode, intrusion amount, and intrusion speed were employed. The results substantiate that the composite B-pillar exhibits equivalent side impact resistance to the original metal B-pillar, ensuring robust passenger protection.

Research on the lightweight design and multilevel optimization method of B‐pillar of hybrid material based on side‐impact safety and multicriteria decision‐making

AbstractThis paper designs and optimizes a new structure hybrid material B‐pillar assembly. Establish a finite element analysis model for the side impact test of an electric vehicle to verify the model's accuracy. Construct a finite element model of the hybrid material B‐pillar assembly. Combined with the static performance analysis of the B‐pillar, the laminate design of the carbon fiber composite B‐pillar reinforcement plate and optimization. For the outer and inner panels of the B‐pillar, the surrogate model method and the multiobjective optimization method are combined to set 11 design variables and 13 responses. The optimal Latin hypercube design method was used to randomly sample each design variable and fit the radial basis function (RBF) approximate model. The modified second‐generation non‐dominated sorting genetic algorithm (MNSGA‐II) was used to carry out multiobjective optimization of the mixed material B‐pillar assembly, and the multicriteria decision‐making method was used to obtain the optimal solution for the Pareto solution set. A drop weight impact test was performed on the hybrid material B‐pillar assembly. The results showed that the peak collision force of the hybrid material B‐pillar was reduced by 43.7% compared with the original steel B‐pillar, the specific energy absorption was increased by 17.5%, and the side impact safety performance was better. After optimization, the weight of the mixed material B‐column was reduced by 26.44%. The improvement rates of the intrusion amount at P2 and the intrusion speed at P1 were 23.99% and 0.63%, respectively, and the lightweight effect and side impact safety were significantly improved.Highlights The finite element analysis parameters of carbon fiber composite materials were constructed through experiments, and the basis for simulation analysis under various working conditions of the B‐pillar based on performance‐driven optimization was established. A hybrid material B‐pillar design method is proposed, which consists of a variable‐thickness high‐strength steel B‐pillar outer plate, a variable‐thickness high‐strength steel B‐pillar inner plate, and a carbon fiber composite B‐pillar reinforcement plate. The super layer of the carbon fiber composite B‐pillar reinforcement plate was optimized and the laying plan of the carbon fiber composite B‐pillar reinforcement plate was determined. Performance‐driven optimization is adopted to realize the collaboration of multilevel design and optimization methods such as B‐pillar conceptual design, detailed design, and multiobjective optimization. A modified NSGA‐II algorithm was proposed and combined with the multicriteria decision‐making method and the entropy‐weighted gray relation analysis method to determine the Pareto optimal solution and the optimal design scheme for the mixed material B‐pillar.

Interlayer-expanded VS2 nanosheet: Fast ion transport, dynamic mechanism and application in Zn2+ and Mg2+/Li+ hybrid batteries systems

Currently, the development of polyvalent ions battery systems are still restricted by lacking suitable cathode materials with high energy density and long cycle life attributing to sluggish kinetic mechanism and of polyvalent ions. Herein, an effective inter-layer scaling strategy is proposed by using a simple hydrothermal method. The super layer spacing VS2 (∼1 nm) cathode dramatically improves electrochemical performance of zinc-ion batteries (ZIBs) and magnesium/lithium hybrid ion batteries (MLIBs). The specific discharge capacities of ZIBs and MLIBs are 450.7 and 488.8 mA h g−1 at current density of 0.1 A g−1 which are much higher than the same type of battery systems. Finally, the diffusion mechanism and the corresponding theoretical model is established by adopting first principles. In brief, the work provides an effective strategy for the large scale application of multivalent and hybrid batteries systems.

EVALUATION OF QUALITY OF POULTRY FEEDS SOLD IN KATSINA METROPOLIS, KATSINA STATE, NIGERIA

In Katsina metropolitan, a variety of poultry feeds are available, and the quality and standards of these feeds are critical for the production of eggs and meat. As a result, the quality of selected chicken feeds sold in Katsina metropolitan was assessed by performing proximate analysis using AOAC methodology. Super starter, grower concentrate, broiler finisher, broiler starter, broiler super starter, layer mesh, grower mesh, and layer concentrate were among the samples used. The percentage mean to standard deviation was used to express the findings. The crude protein content of the diets studied ranged from 0.46 ± 0.00 percent to, 8.24± 0.02 percent, ash content 6.31± 0.01 percent – 33.30± 0.04 percent, crude fiber content 1.03 ±0.00 percent – 3.21± 0.00 percent, lipid content 0.11± 0.00 percent, 2.30 ±0.00 percent, moisture content 4.28 ±0.25 – 6.66 ±0.78 percent, and carbohydrate content 51.78± 2.68 – 83.72 ±0.57 percent. Although there was variation in the mean and standard deviation levels among the samples analyzed, such variations were not statistically significant (P>0.05) according to a one-way analysis of variance (ANOVA) for the difference in the mean levels of parameters evaluated in eight samples.

EVALUATION OF QUALITY OF POULTRY FEEDS SOLD IN KATSINA METROPOLIS, KATSINA STATE, NIGERIA

In Katsina metropolitan, a variety of poultry feeds are available, and the quality and standards of these feeds are critical for the production of eggs and meat. As a result, the quality of selected chicken feeds sold in Katsina metropolitan was assessed by performing proximate analysis using AOAC methodology. Super starter, grower concentrate, broiler finisher, broiler starter, broiler super starter, layer mesh, grower mesh, and layer concentrate were among the samples used. The percentage mean to standard deviation was used to express the findings. The crude protein content of the diets studied ranged from 0.46 ± 0.00 percent to, 8.24± 0.02 percent, ash content 6.31± 0.01 percent – 33.30± 0.04 percent, crude fiber content 1.03 ±0.00 percent – 3.21± 0.00 percent, lipid content 0.11± 0.00 percent, 2.30 ±0.00 percent, moisture content 4.28 ±0.25 – 6.66 ±0.78 percent, and carbohydrate content 51.78± 2.68 – 83.72 ±0.57 percent. Although there was variation in the mean and standard deviation levels among the samples analyzed, such variations were not statistically significant (P>0.05) according to a one-way analysis of variance (ANOVA) for the difference in the mean levels of parameters evaluated in eight samples

Visualization of spatiotemporal data with different topology

Abstract. The availability of advanced technologies, the time of information society, and also the development of geographic information systems, have brought a lot of spatial data in most disciplines, which are carefully stored in recent decades and allow us spatiotemporal analysis and visualization. However, for long-term analyses and the synthesis of analysed data, including cartographic synthesis processes, it is a big problem when spatiotemporal data have different topologies at different times. And this does not only mean the correction of borders in the sense of clarification or other distinction. The problem is when, for example, the small administrative units is subject to significant temporal changes. Municipalities are divided and merged, while data are always stored for the topology of a particular year or period.The contribution presents a way to solve such a situation on the example of the Czech Republic. Data from 25 years’ period are adjusted so that it is possible to calculate and visualize long-term trends and analyses. In the case of the case study, these are spatial data of more than 6,000 municipalities, with changes in more than 200 cases during the observed period. In addition to the spatial component, there were also changes in identifiers, which are a common means of joining data. For example, when the name of the municipality was changed and the newly "created" municipality also received new identification code. All these problems are solved by the so-called "super layer", which represents aggregation to the smallest possible extent so that the analyses performed are carried out on the most detailed possible scale without missing data in partial periods.The project goal is to explore various geodemographic processes at a very detailed level, specifically at NUTS (Nomenclature of Territorial Units for Statistics) local administrative units 2 (LAU2) commonly used in European Union for statistical purposes. Our presented dataset/approach unified municipal administrative units allowing analyses of data as they change over time. We used a principle of "common spatial denominator", i.e. we used data aggregation into larger units with stable boundary.

Analysis and Optimization of Service Delay for Multiquality Videos in Multitier Heterogeneous Network With Random Caching

Aiming to minimize service delay, we propose a new random caching scheme in device-to-device (D2D)-assisted heterogeneous network. To support diversified viewing qualities of multimedia video services, each video file is encoded into a base layer (BL) and multiple enhancement layers (ELs) by scalable video coding (SVC). A super layer, including the BL and several ELs, is transmitted to every user. We define and quantify the service delay of multi-quality videos by deriving successful transmission probabilities when a user is served by a D2D helper, a small-cell base station (SBS) and a macro-cell base station (MBS). We formulate a delay minimization problem subject to the limited cache sizes of D2D helpers and SBSs. The structure of the optimal solutions to the problem is revealed, and then an improved standard gradient projection method is designed to effectively obtain the solutions. Both theoretical analysis and Monte-Carlo simulations validate the successful transmission probabilities. Compared with three benchmark caching policies, the proposed SVC-based random caching scheme is superior in terms of reducing the service delay.

Conductivity Fluctuation and Some Parameters of High temperature Superconductor Polycrystalline Y1Ba2Cu3O7−δ doped with Silver Nanoparticles

In this study, we report the effect of Ag nanoparticles doping on the dimensional fluctuations of superconducting order parameters, crystal structure, and some parameters of Y1Ba2Cu3O7−δ + × Ag (x = 0.0, 0.06, 0.1, 0.3, and 0.6 wt%) polycrystalline ceramics. By increasing the content of Ag in YBCO matrix, X-ray diffraction (XRD) with the Rietveld refinement technique revealed that the crystal lattice parameters changed and the orthorhombicity decreased slightly. Also, the increase of Ag wt% caused a decrease of superconducting transition temperatures (Tc) which are determined from the standard four-probe method and dropped abruptly. Aslamazov–Larkin (AL) model was used to analyze excess conductivity fluctuation. Lawerence–Doniach (LD) temperature named TLD which is responsible for the dimensional nature of fluctuation inside the grains is influenced by nano-silver combination in the compound. Crossover temperature from 2D to 3D (TLD) decreased in the mean-field region as a resultant dominance of 3D region by increasing of Ag in YBCO matrix. The decrease in zero-resistance critical temperature (Tc zero), zero-temperature coherence length along the c-axis ξc(0), and super layer length d values implies the degradation of inter-grain weak links, more disorder state of samples and unsettling of the mean free path for the charge carriers respectively with addition of silver nanoparticles. The calculations based on AL and LD model showed the highest anisotropy (γ = 1.34681) for the x = 0.6 sample. The size of the Ag ions, being larger compared to Cu ions, and the number of substitution sites affects the coupling between the CuO2 planes and that results in higher anisotropy. Critical magnetic fields Bc1(0), Bc2(0), and critical current density Jc(0) were indirectly calculated from the Ginzburg–Landau (GL) number and GL equations. By increasing the doping level of silver nanoparticle, these parameters were found to be higher in Ag-added YBCO samples compared to the pure Y123, meaning better intrinsic flux pinning properties of doped Y123. The silver nanoparticle inclusion reduces the grain size and increases the strength and hardness of the parent compound.

Single print optimisation of fused filament fabrication parameters

Single print optimisation (SPO) of process parameters, for the improvement of dimensional accuracy of an additively manufactured (AM) printed part with fused filament fabrication (FFF), is presented. A test object is sliced with different slicer parameters, as determined by a design of experiments (DOE) run table. The resulting files are merged into a single G-code file, which is used to perform a single print run. This prints the objects sequentially in super layers, where a super layer consists of several normal layers of sequentially printed parts limited by the printer Z-axis clearance. The test object is designed to be measured with accessible, affordable and easy-to-use dimensional measurement instruments. The goal of the optimisation is to improve the deposition of a single track, since all FFF objects are built up from several extrusions called tracks in the printer XY plane. The track height and width are key quantifiable measurands. Retraction effectiveness is also considered, with a qualitative response variable called stringing length. Ordinary least squares (OLS) regression is used to fit linear models to the three response variables. The bed level, as a function of X and Y coordinates, is used to improve part height accuracy. Track width is modelled with liquefier temperature and feed speed, whilst stringing length is modelled as a function of temperature. The models are verified by selecting an operation point which maximises print speed and minimises a cost function for the track width.

Fractionation of bio-oil produced from hydrothermal liquefaction of microalgae by liquid-liquid extraction

Fractionation of bio-oil is in favor of upgrading bio-oil to transport fuel or chemicals. The microalgae Dunaliella tertiolecta was hydrothermally liquefied to form a bio-oil, which was split into two layers during cooling: the lower layer contained organics with relatively high molar mass from 78 to 389 g mol−1, while the super layer with relatively low molar mass from 44 to 121 g mol−1. The lower layer of hydrothermally liquefaction (HTL) bio-oil was further fractionated into ethanol phase (oil 1) and dichloromethane phase (oil 2), and the super layer yielded 1 or 3-4 fractions of extracts (oil 3) via single-stage or multistage liquid-liquid extraction respectively. The compositions of each fraction were analyzed by GC-MS in detail. Dichloromethane, chloroform, cyclohexane, benzene, toluene, iso-octanol, petroleum ether, carbon tetrachloride, 1,1,1-trichloroethane, ethyl acetate were compared in terms of their extraction capabilities to organics of bio-oil. The results indicated the chloroform and dichloromethane have the highest comprehensive extraction capabilities. In multistage extraction, when dichloromethane was used as extractant, the extraction distribution ratio (calculated using COD, chemical oxygen demand) was 0.66 in first-stage, then sharply dropped with an increase in stage number, 2nd∼3rd stage extractions achieved the maximum extraction percentage (approximately 53%). That the optimum combination of chloroform, benzene and 1,1,1-trichloroethane fractionated the super layer of HTL bio-oil can obtain very low oxygen content fraction: hydrocarbons (purity of hydrocarbons: relative content 97.9%) from the 2nd stage of multistage extraction.

Modulating crack propagation in a multilayer stack with a super-layer

Abstract

New super junction lateral double-diffused metal-oxide-semiconductor field-effect transistor with the P covered layer

In order to design the lateral double-diffused metal-oxide-semiconductor field-effect transistor (LDMOS) with low loss required for a power integrated circuit, a new super junction LDMOS with the P covered layer which is based on the existing N buffered super junction LDMOS is proposed in this paper for the first time. The key feature of the proposed structure is that the P-type covered layer is partly above the N-type of the super junction layer, which is different from the N buffered super junction LDMOS. In this structure, the specific on-resistance of the device is reduced by using the high doped super junction layer; the problem of the substrate-assisted depletion which is produced due to the P-type substrate of the N-channel super junction LDMOS is eliminated by completely compensating for the charges of the N-type buffered layer and the P-type covered layer, thus improving the breakdown voltage. The charges of the N-type and P-type pillars are depleted completely. A new transmission path at the on-state is formed by N buffered layer to reduce the specific on-resistance, which is similar to the N buffered super junction LDMOS. However, the effect of N-type buffered layer of N buffered super junction LDMOS is not fully used. The drift region of the device is further optimized by the proposed device to reduce the specific on-resistance. The charge concentration of the N-type buffered layer in the proposed device is improved by the effect of charge compensation of the P covered layer. It is clear that high breakdown voltage and low specific on-resistance are realized in the proposed device by introducing the P-type covered layer and the N-type buffered layer. The results of the 3 D-ISE software suggest that when the drift region is on a scale of 10 μm, a specific on-resistance of 4.26 mΩ·cm2 obtained from P covered super junction LDMOS by introducing P covered layer and N buffered layer is reduced by about 59% compared with that of conventional super junction LDMOS which is 10.47 mΩ·cm2, and reduced by about 43% compared with that of N Buffered super junction LDMOS which is 7.46 mΩ·cm2.

Design of Gastroretentive Floating Bilayer Tablets of Metformin and Glimepiride

The present study involves designing and development of a bilayer tablet of Metformin HCl (MET) and Glimepiride (GLP) to offer immediate release of GLP and gastroretentive layer of MET. Bilayer tablets containing two layers i.e. immediate release layer formulated using super disintegrant Sodium starch glycolate and gastroretentive layer formulated with polymers like HPMC K4M and HPMC K100M to modulate the biphasic drug release. Wet granulation method was employed to formulate bilayer tablets. Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM) were used for physicochemical compatibility and stability studies of the tablets. Accelerated stability studies were followed in compliance with ICH guidelines. The in vitro release profile shows desired biphasic release behavior after storage at accelerated condition (40°C± 2°C and 75%RH ± 5% RH) for 6 months. Biphasic drug release pattern was successfully achieved through the formulation of bilayer tablets that are stable and capable of releasing the drug over 12 hrs.

Chemical composition study of high-k La-silicate gate stacks at sub-nanometer scale

La-based high-k oxides as gate dielectrics are promising for the complementary metal–oxide–semiconductor (CMOS) devices. We investigated the chemical compositions across a TaN/LaSiO/Si gate stack at sub-nanometer scale with electron energy loss spectroscopy (EELS) mapping, Z-contrast imaging, high-resolution transmission electron microscopy (HRTEM) imaging, and other tools. The interfaces in the gate stack were shown to maintain their integrity even after post annealing. The alloying between La2O3 and SiO2 to form LaSiO depended on the annealing conditions. To the as-deposited sample, a La–O super atomic layer structure was observed and La was in lower oxidation states as it diffused deeper into SiO2. The LaSiO thickness only increased slightly after post annealing and the gate stack showed the required thermal stability. All the results make TaN/LaSiO/Si a promising choice for transistor gate stacks. The combination of EELS mapping and other techniques is very useful in the chemical composition study of gate stacks at ultra-high spatial resolution.

The Roof Broken Mechanism of Fully Mechanized Coal Face with Super Thick and Loose Layer

In view of the study insufficient of the broken rule and mechanism and feature of coal face with super thick and loose layer that crushed coal face hydraulic support, The broken rule and mechanism and feature of coal face with super thick and loose layer in LONGDONG Mine are studied and the fracture development and abscission layer growth and caving characteristics in the process of are analysed by use of theoretical analysis and physical simulation experiment and numerical simulation analysis. The study comes to the conclusion that super thick and loose layer are with caving arch structure that are different from conventional roof broken feature.the broken mechanical model of super thick and loose layer are established and the coal face caving arch parameters of super thick and loose layer are determined by use of mining rock mechanics theory.

Use of stress-engineered material layers for the measurement of interfacial fracture toughness of nanoscale thin films

A new technique employing stress-engineered material layers for the measurement of interfacial fracture toughness of nanoscale thin films has been developed. This technique has been implemented to measure the interfacial fracture toughness of patterned Titanium (Ti) film on a Silicon (Si) substrate. This test employs a stress-engineered super layer deposited on Ti to provide the energy for the delamination propagation of Ti thin film from the Si substrate. The amount of energy available for the delamination propagation is varied by depositing a selectively-etchable thin release layer between the film strips and the substrate. By designing a decreasing area of the release layer, it is possible to arrest the delamination at a given location, and the interfacial fracture toughness or the critical energy release rate can be found at the location where the delamination ceases to propagate. For Ti film with thickness of 90 nm, the results show that the interfacial fracture toughness of Ti/Si ranges from 3.45 to 5.70 J/m² when the mode mixity increases from 6.8 to 38.4°. The methodology presented in this paper is generic in nature, and can be used to measure the process-dependent interfacial fracture toughness of various nanoscale thin film interfaces.

Studies on the toxic effects of pentachlorophenol on the biological activity of anaerobic granular sludge

In order to explore the pathway of the anaerobic biotreatment of the wastewater containing pentachlorophenol (PCP) and ensure the normal operation of Upflow Anaerobic Sludge Blanket (UASB) reactor, the anaerobic sludge under different acclimation conditions were selected to seed and start up UASB reactors. Anaerobic toxicity assays were employed to study the biological activity, the tolerance and the capacity to degrade PCP of different anaerobic granular sludge from UASB reactors. Results showed that the anaerobic granular sludge acclimated to chlorophenols (CPs) could degrade PCP more quickly (up to 9.50 mg-PCP g −1 TVS d −1). And the anaerobic granular sludge without acclimation to CPs had only a little activity of degrading PCP (less than 0.07 mg-PCP g −1 TVS d −1). Different PCP concentrations (2, 4, 6, 8 mg L −1) had different inhibition effects on glucose utilization, volatile fatted acidity (VFA)-degrading and methanogens activity of PCP degradation anaerobic granular sludge, and the biological activity declined with the increase in PCP concentration. The methanogens activity suffered inhibition from PCP more easily. The different acclimation patterns of seeded sludge had distinctly different effects on biological activity of the degradation of PCP of anaerobic granular sludge from UASB reactors. The biological activity of the anaerobic granular sludge acclimated to PCP only was also inhibited. This inhibition was weak compared to that of anaerobic granular sludge acclimated to CPs, further, the activity could recover more quickly in this case. In the same reactor, the anaerobic granular sludge from the mid and base layers showed higher tolerance to PCP than that from super layer or if the sludge is unacclimated to CPs, and the corresponding recovery time of the biological activity in the mid and base layers were short. Acetate-utilizing methanogens and syntrophic propinate degraders were sensitive to PCP, compared to syntrophic butyrate degraders.

Single-sample decohesion test: mechanics and implementation

The Single-Sample Decohesion Test (SSDT), developed by the authors, eliminates shortcomings of current interfacial fracture toughness testing methods. In this approach, a highly stressed super layer is used to drive delamination and create any mode mix at the crack tip. SSDT uses the change in crack surface area to vary the available energy per unit area for crack growth and thus to bound the steady state interfacial fracture toughness. Therefore, this technique uses a single sample to measure the interfacial fracture toughness and maintains the advantages of the original decohesion test: (1) SSY conditions, (2) micro-electronics and MEMS representative interfaces, and (3) ability to generate any mode mix. Critical to the usefulness of this test is the availability of a mechanics based analytical model to calculate the test site energy release rate. The test sites are cantilevered thin film strips, which undergo large, nonlinear deflection, consist of multilayered materials, are subject to in-plane biaxial loading, have varying in-plane dimensions, and can be loaded from pure shear to pure peel. In this paper, one dimensional and linear and nonlinear classical laminate plate theories are compared to a finite element representation of the SSDT test site. The regions of applicability of linear and nonlinear analytical models are discussed and nonlinear effects such as the importance of capturing the bifurcation of curvature are highlighted. Application of the nonlinear plate theory model to the test is shown and interfacial fracture toughness results are provided for a Ti/Si interface at several mode mixes.

Interfacial Fracture Toughness Measurement of a Ti/Si Interface

Titanium adhesive layers are commonly used in microelectronic and MEMS applications to help improve the adhesion of other metal layers to a silicon substrate. Such Ti/Si interfaces could potentially delaminate under externally applied mechanical loads, thermally induced stresses, or process-induced intrinsic stresses or a combination of these different loads. In order to design against delamination, knowledge of the interfacial fracture toughness of the Ti/Si interface is necessary. However, interfacial fracture toughness data for such interfaces is not widely available in the open literature, in part due to the difficulty in measuring the strength of thin film interfaces. The Modified Decohesion Test (MDT), a new test developed by the authors, has been used to characterize the mode mix dependent interfacial fracture toughness of a Ti/Si interface. In this approach, a highly stressed super layer is used to drive delamination and generate any mode mix at the crack tip. MDT uses the change in crack surface area to vary the available energy per unit area for crack growth and thus to bound the interfacial fracture toughness. Therefore, this technique uses a single sample to measure the interfacial fracture toughness. Since the deformations remain elastic, a mechanics-based solution can be used to correlate test parameters to the energy release rate. Common IC fabrication techniques are used to prepare the sample and execute the test, thereby making the test compatible with current microelectronic or MEMS facilities. Using the MDT, interfacial fracture toughness (Γ) bounds were found for a Ti/Si interface at three mode mixes. At a mode mix of 19.5 deg, 5.97J/m2⩽Γ⩽7.87J/m2, at a mode mix of 23 deg, 9.32J/m2⩽Γ⩽10.42J/m2, and at a mode mix of 30 deg, 12.70J/m2⩽Γ⩽17.02J/m2.

Statistical properties of a d-type rough wall boundary layer in a transitionally rough and a fully rough regime.

In order to investigate the low Reynolds number effects on the turbulent structures of a d-type rough wall boundary layer, the statistical properties in a transitionally rough and a fully rough regime have been examined experimentally. The measurements associated with the turbulent production rate, probability distributions, higher-order moments and energy spectra were made in the range of momentum thickness Reynolds numbers of Rθ=700 to 5140. The local equilibrium state can be recognized for a wide Reynolds number range down to Rθ=700. The probability distributions and the higher-order moments including Reynolds shear stress flux show that the ejection events due to positive high amplitude of υ fluctuating component play a dominant role on the turbulent transport process in the inner layer of the present rough wall flow for a transitionally rough regime of Rθ≤2000. The low Reynolds number effect on the outer layer, which enlarges the contorted surface of the viscous super layer, is found for the Reynolds number range Rθ≤800.