Lag Phenomenon Research Articles

Study on the microstructure and liquid–solid correlation of Al–Mg alloys

ABSTRACTBased on the available structural models and theories of electrical resistivity (ER) of liquid alloys, the structure and the liquid–solid correlation of Al (100-x) Mgx (x = 0, 10, 20, 30, 40, 50) alloys have been qualitatively studied by measuring the ER during the heating/cooling process using the direct-current (DC) four-probe method, as well as by characterizing the solidification morphology and testing the hardness. The result shows that the ER of Al–Mg alloys increases with the increasing temperature and the Mg content; thermal state and history have an effect on the solidification structure and properties: the ER of Al–Mg alloys exhibits a lag phenomenon of structure change during the heating/cooling process. A higher heating/cooling rate contributes to the more obvious relaxation effect of ER and the more uniform structure. Furthermore, higher pouring temperature (PT) leads the melts and solidification structure to be more homogeneous, which increases the hardness.

Investigation on Shear Lag Phenomenon in RCC Framed Tube Structures

Investigation on Shear Lag Phenomenon in RCC Framed Tube Structures

Some aspects of interactive dynamic stability of thin-walled trapezoidal FGM beam-columns under axial load

The present paper deals with a dynamic interactive response of FG beam-columns subjected to in-plane pulse loading when the shear lag phenomenon and distortional deformations are taken into account. The structures are assumed to be simply supported at the ends. In order to obtain the equations of motion of individual plates, the classical laminate plate theory (CLPT) has been modified in such a way that it additionally accounts for all components of inertial forces. Thin-walled trapezoidal FGM beam-columns are considered. A dynamic interaction of the global mode with the lowest primary local buckling mode and the secondary local mode has been analysed. Attention has been drawn to some unexpected aspects related to the fact that a two- and three-modal approach has been assumed in the analysis of dynamic interactive buckling.

Effect of Relative Stiffness of Beam and Column on the Shear Lag Phenomenon in Tubular Buildings

Effect of Relative Stiffness of Beam and Column on the Shear Lag Phenomenon in Tubular Buildings

Finite Element Investigation on Shear Lag in Composite Concrete-Steel Beams with Web Openings

In this paper, effective slab width for the composite beams is investigated with special emphasis on the effect of web openings. A three dimensional finite element analysis, by using finite element code ANSYS, is employed to investigate shear lag phenomenon and the resulting effective slab width adopted in the classical T-beam approach. According to case studies and comparison with limitations and rules stipulated by different standards and codes of practice it is found that web openings presence and panel proportion are the most critical factors affecting effective slab width, whereas concrete slab thickness and steel beam depth are less significant. The presence of web opening reduces effective slab width by about 21%. Concentrated load produces smaller effective slab width when compared with uniformly distributed and line loads. Generally, standard codes of practice overestimate effective slab width for concentrated load effect, while underestimate effective slab width for uniformly distributed and line load effect. Based on the data available, sets of empirical equations are developed to estimate the effective slab width in the composite beams with web openings to be used in the classical T-beam approach taking into account the key parameters investigated. 
 

Effects of head deformation on aerodynamic characteristics of spinning vehicle

Slight deformation of head influences the aerodynamic characteristics of head, after-body, and tail fins of spinning vehicle. The influence of head deformation was analyzed by the DES method. The results reveal that the frequency of interference on the after-body and fins caused by head deformation is different with the spin frequency of vehicle. It is more important that the interference caused by the head deformation has a lag phenomenon, which is related to the flow velocity and the spin rate of the vehicle. The normal force coefficient and side force coefficient of spinning vehicle with deformed head rise as the rotational speed of vehicle increases, and lag behind that in low spin rate conditions. In high Mach number conditions, the fluctuation magnitude of aerodynamic characteristics of spinning vehicle with deformed head is larger than those in low Mach number conditions.

Symplectic Analysis of the Shear Lag Phenomenon in a T-Beam

AbstractThe principal purpose of this paper is to develop a new analytical method for the shear lag problem of T-beams. The flange slab of a T-beam is simplified into a plane stress plate. A system of Hamilton dual equations of the flange slab using symplectic elasticity theory can be obtained. Analytical solutions of the flange slab under uniform or linear shear force applied on the entire slab length are obtained by solving the equation. Based on the solution, the cause of the positive shear lag and negative shear lag phenomenon are studied in this paper. Theoretical research indicates that the method is superior for analyzing the shear lag phenomenon. The analytical solution has been validated by comparison with the beam solution and FEM solution of a cantilever T-beam subjected to a uniform load.

Heat transfer analysis and second degree burn prediction in human skin exposed to flame and radiant heat using dual phase lag phenomenon

Heat transfer through fabric-human skin system subjected to high intensity flame as well as radiant heat exposure has been analyzed in this work. Experiments are performed to determine heat transfer through four different fabric samples. Temperature distributions across various skin layers are obtained numerically using Dual Phase Lag Model of Bio-heat Transfer (DPLMBT) while considering temperature dependent blood perfusion rate in dermis and subcutaneous layers. Wave phenomenon is observed inside human skin. Second degree burn time is obtained using Henriques’ burn integral relation. Second degree burn times are compared with experimental results where Stoll’s criterion is used. It is concluded that present results are more realistic compared to the prediction using Stoll’s criterion. It is recommended to use DPLMBT to analyze heat transfer inside human skin subjected to such small duration of high level heat flux exposure. It is observed that temperature distribution and hence second degree burn time depends significantly on the values of heat flux and temperature gradient phase lags.

The Effect of RC Core on Rehabilitation of Tubular Structures

In the present study, the effect of core on shear lag phenomenon in tubular structures is investigated. Three different tubular structure models including model without core, model with central core and model with central core but eliminated in last 15 stories have been analyzed. A shear lag index is defined for evaluating these models. From examination of the results, the effective influence of core for improving the behavior of framed-tube structures has been concluded. The influence of core in reduction of shear lag in first story is estimated by 5%. Investigating the shear lag phenomenon of columns on web frame, it could be revealed that in top story the positive and negative shear lag phenomena have been occurred simultaneously.

An Empirical Study on Time Lag Phenomenon Regarding Summertime Indoor Thermal Environments in the Domestic Buildings of Different Construction Types in Hot-Humid Climate Zone

In the empirical case studies of the seven detached house buildings situated in Yilan, Taiwan in a hot and humid climate, this research conducted the actual measurements and analysis of the Summertime Indoor and Outdoor thermal environment parameters in order to accomplish the research of Time Lag Phenomenon of Summertime Indoor Temperature and Humidity in the Buildings of Light (Composite) Constructions and Heavy (Reinforced Concrete) Constructions. Firstly, it indicated that given the condition of doors and windows in closed positions, there would be Time Lag Phenomenon for both of the indoor Temperature and Humidity measurements in domestic buildings. The Temperature Time Lag for Heavy Construction Buildings had a duration of around three hours, almost as twice that of the figure for Light Construction Buildings. There was a significant correlation between Quantity of Interior Finishes and Humidity Time Lag inside domestic buildings, whereas the bigger the Quantity of Interior Finishes, the longer the Humidity Time Lag. Secondly, it also showed that given the condition of doors and windows in opened positions, there was almost zero Time Lag for both of the domestic indoor Temperature and Humidity measurements. Last but not least, generally speaking, the Ratio of Indoor/Outdoor Diurnal Temperature Range of Light Construction Buildings were higher than that of Heavy Construction Buildings. In particular, given the condition of doors and windows in opened positions with natural ventilation in summertime, it was slightly cooler inside the Light Construction Domestic Buildings than the Heavy Construction Domestic Buildings.

창호 블라인드와 상변화물질 적용에 의한 냉방 에너지 사용량 절감효과에 대한 검토 연구

This study looks into changing building energy use by application of phase change material (PCM). PCM does not need extra energy for operation and is used for reducing building energy use and, CO2 output by displaying semi-permanent effects after installation. It also is able to avoid the maximum electric power time-zone by inducing a time lag phenomenon of cooling and heating loads with high thermal capacity using latent heat. To verify the efficiency of blinds and PCM, tests about the PCM operation mechanism using air conditioning machinery and nocturnal panel cooling were done. In the test results of the case using PCM installation, a blind angle with machinery air conditioning and nocturnal panel cooling at the same time shows a 22 percent energy saving effect against general space. The test results of each case were compared and analyzed based on the blind and window opening settings. Finally, the energy reduction of existing buildings using PCM application was reviewed based on the final measurement results.

Thermal properties of biomass tar at rapid heating rates

Gasification of biomass tar by pyrolysis is a valuable source for renewable energy, providing chemicals, a precursor to carbon material and potentially a raw material for liquid fuel. In this research, experimental studies via thermal gravimetric analysis (TGA) of biomass tar were implemented at three rapid heating rates (i.e., 10 K/min, 50 K/min, 100 K/min, respectively) in a nitrogen atmosphere. On the basis of analytical methods utilized in thermal dynamics and physical chemistry, the results showed that the thermogravimetric curve (TG) of the biomass moved in a high-temperature direction with an increase in the heating rate. The greater the heating rate, the steeper the curve and the lower the resolution, the lag phenomenon of the temperature being more significant. Concurrently, a differential thermal analysis (DTA) was one of the methods employed to study the relationship between the temperature difference and the temperature or time of the tested substance and a reference substance. The peak temperature and maximum reaction rate of the differential thermal analysis curve (DTA) increased as the heating rate, the volatiles and the molecular residence time of the biomass was shortened at a higher heating rate, thereby potentially inhibiting the generation of carbon and increasing the production and yield of liquid fuel. Keywords: biomass tar, liquid fuel, rapid heating rate, thermal dynamics, pyrolysis, gasification, renewable energy DOI: 10.3965/j.ijabe.20140702.012 Citation: Zhang H, Zhang K, Zhou X H, Hu J J, Jing Y Y, Liu S Y. Thermal properties of biomass tar at rapid heating rates. Int J Agric & Biol Eng, 2014; 7(2): 101－107.

Abnormal dynamic behavior in a ferroelectric bilayer film

Based on the Landau–Khalatnikov equation of motion, the switching dynamic behavior (including switching time, hysteresis loop and remanent polarization) of a ferroelectric bilayer film with surface transition layer within each constituent thin film and an interfacial coupling between two thin films has been first studied. The results show that the serious lag phenomenon of the hysteresis loop of the bilayer film occurs due to the strong strength of the interfacial coupling. It is interesting to note that there is a critical point, which is an equilibrium point of two contrary actions of the surface transition layer and interfacial coupling. The abnormal behavior of the switching time and remanent polarization in the bilayer film is attributed to the competition of the surface transition layer and interfacial coupling.

An Experimental Study and Analysis of Full Process of External Prestressing CFRP Concrete Box Girder

A full rang of external prestressing CFRP concrete box girder flexural performance have been tested. Crack distribution, deflection,strain distribution, stress increment of external CFRP have been measured. The results demonstrate that that as the load increase, the shear lag phenomenon on the upper and bottom plate of the box girder is more significantly; There is a certain friction Loss on the interface between CFRP and two steering block which arrange in the mid-span. If suitable element models and material constitutive laws are chose, the ANSYS program may simulate the fully flexural experimental process of the box girder, the result is well agree with the experimental result.

Single Trench SiON Waveguide TE-TM Mode Converter

A TE-TM mode converter fabricated in a single trench SiON waveguide is described. The device has the advantage that only single masking and etching process is needed to fabricate it. We discuss the design of the mode converter from the view point of fabrication tolerance. The single trench structure is fabricated using the reactive ion-etch lag phenomenon. A 97% TE-TM mode conversion (extinction ratio=15 dB) is demonstrated at a wavelength of 1.27μm . An excess loss is measured to be 0.8 dB.

Transport mechanism of desorbed gas in coalbed methane reservoirs

Abstract The gas-liquid two-phase flow and mass transfer principle shows that the diffusion caused by concentration difference only happens in a single-phase fluid; gas-liquid two-phase diffluent solution happens in the way of dissolution; and gas-liquid two-phase insoluble or semi- soluble solution flows under differential pressure driving. These facts demonstrate that the transport of desorbed gas through matrix pores is the flow, and it doesn't conform to Fick law. The dissolution, diffusion, nucleation and bubble processes of desorbed gas through depressurization are studied, and the nonlinear flow model of free gas from matrix pores to the cleat and fracture system is established based on force analyses of the gas bubble and the gas column. Research shows that a small amount of desorbed gas diffuses by dissolution; most of them becomes nucleation and bubble, and then flows to the coal cleat and fracture system under the pressure difference driving; considering the existence of the pressure difference between the matrix pores and cleats, the pressure in coal matrix will reduce more slowly, the investigated radius will be shorter, and the outflow lag phenomenon of desorbed gas will appear. The dynamic reserve should be calculated not by using cleat pressure but by the pressure in coal matrix. The mechanism of enhanced methane recovery by CO2 injection is not only replacement but displacement. Improved methane recovery can be obtained by optimizing the production pressure difference, it is not reasonable that the lower formation pressure gives higher methane recovery.

Kinetics Investigation of RIE Lag Phenomenon by GaAs ICP Etching

In this paper, according to the relationships of the etch-rate with the FWs from 2μm to 100μm and of the etch-rate changes with etch-time for a particular FW, obtained by our experiments, a possible etching process model were proposed. When the etch-time was relatively short, it was the reaction limited process. With the etch-time going on, the fresh reactive gas was difficult to get through the etching trench to the fresh reaction interface, the etch-rate decreased, which was called the residual removing limited process. Our mathematic fitting results proved the above etching model and pointed that for the reaction limited process, the etch depth linearly increase with the etch time. While it got into the residual removing limited process, the etch-rate decreased.

Prediction of the tensile capacity of cold formed angles experiencing shear lag

The present study deals with the shear lag phenomenon in cold formed angles under tension, which are connected on one leg. A new expression for shear lag factor which represents the net section reduction coefficient has been suggested in the present paper. The proposed expression based on the regression analysis of 108 experimental results reported in the literature is validated by experiments involving net section failure in angles under tension. Totally 18 experiments were carried out on single angles fastened with bolts to the gusset plates under tension loaded upto net section rupture mode of failure. The experimental test parameters considered are number of bolts, pitch and shear lag distances and ratio of connected leg length to unconnected leg length. The tensile capacities are evaluated by various specifications such as AS/NZS:4600:2005, NAS:2001, AISC:2005, BS:5950-Part5:1998, IS:800-2007 and the proposed equation. A comparative study of tensile capacities predicted based on various codes and the experiment results is presented in this paper. For the tested range of specimens, both NAS:2001 and AISC:2005 standards over-predicted the capacities for all the specimens. The IS:800-2007 and AS/NZS 4600:2005 predictions are good for the specimens with three bolted connections and unconservative in the case of specimen with two bolts. Both BS:5950-Part-5:1998 and the proposed equation for IS:801 predict good estimate of the tensile capacity of cold formed angle members. The proposed equation for cold formed steel tension members, which is in the same format of IS:800 (2007) (Indian code for Hot rolled steel design), has been demonstrated to be good.

Theoretical analysis on expansion mechanism in carbon dioxide expander

The expansion mechanism inside carbon dioxide expander is analyzed theoretically in this paper. The mechanism analysis of metastable equilibrium indicates that there is a potential barrier during phase change process. That is to say energy is required to overcome the potential barrier when the new interface is formed from primary phase. The superheat of liquid is the impetus of phase change and has an exponential decrease with the increase of the saturated temperature of fluid. The analysis also indicates that there is a critical radius during the phase change process. The bubble will grow up when its radius is larger than the critical value, otherwise, will disappear. When considering the metastable phase change, calculation of P and V during expansion process indicates that the phase-change will be delayed with the decline of pressure, which is called lag phenomenon. The phase-change delay time decreases with the increase of initial temperature. When the initial temperature is close to the critical temperature, the delay time is close to zero. The phase-change delay brings energy losses, which decrease with the increase of initial temperature and its decrease ratio also has a decrease trend. When the initial pressure is 10 MPa, the energy loss will be 1.06 W with an initial temperature of 10°C while 0.34 W with that of 20°C.

How common are invasion-induced ecosystem impacts?

It would be an exaggeration to argue that most invasions produce ecosystem impacts, and the term should be reserved for cases in which many species in an ecosystem are affected. However, certain facts suggest that true ecosystem impacts are more common than is normally assumed. First, the term “ecosystem impact” has often been reserved for cases in which the nutrient regime or nutrient cycling is affected, whereas physical structural and other changes in ecosystems ought to be included. Second, as with all ecology, very few systems and species have been studied relative to all those that exist, so it is likely that many ecosystem impacts remain to be detected. Third, there are many types of impacts, many are idiosyncratic, many are subtle, and many are indirect, so it is likely that many impacts have simply not been recognized even in studied systems. Finally, the frequency of the lag phenomenon in invasions implies that at least some existing non-native species that are currently having little or no impact will eventually have much greater ones. These facts suggest that, even if it would be an overstatement to say that most invasions cause ecosystem impacts, it would not be more of an overstatement than the common assertion that very few introduced species have any significant impact.