Values Of Load Ratio Research Articles

Building thermal load management through integration of solar assisted absorption and desiccant air conditioning systems: A model-based simulation-optimization approach

Performance of standalone air-conditioning systems is affected while simultaneously handling both sensible and latent building loads. Model-based simulation and optimization is one of the best ways to analyze system's performance under load fluctuations at the initial design stages. Therefore, in the current study, seasonal transient simulations of an Integrated Absorption Desiccant System are carried out using TRNSYS to handle sensible (10.94 kW peak) and latent (4.44 kW peak) cooling load separately. Radiant cooling with chilled water from an absorption chiller mainly handles sensible cooling load, while the latent load is achieved by a solid desiccant dehumidification system. Initially, key components of the system are modeled in TRNSYS including a flat plate solar collector system, desiccant wheel, heat recovery wheel, and absorption chiller. Afterwards, the integrated model is coupled with GenOpt to optimize the solar fraction and thermal coefficient of performance by varying collector area, flow rate in the collector loop, flow rate in load side loop, and volume of storage tank. The resulted optimized value of solar fraction is 57.50%, and COPth is 0.55 for standalone absorption system, whereas the solar fraction of 56.20%, COPth of 1.52 are achieved for IADS. In addition, the effects of load variation in terms of sensible to latent load ratio on regeneration heat required for both IADS and conventional desiccant system are also analyzed. A critical value of load ratio of 0.75 is also observed in terms of heat regeneration requirements to compare the both systems. The proposed approach and analysis will be very helpful for HVAC designers for optimal system performance through separate load handling, especially at the initial design stage.

Calibration of nasgro equation for mixed-mode loading using experimental and numerical data

A procedure to calibrate the NASGRO equation in a high yield-strength steel under mixed-mode loading (I + II) is presented. The calibration consists in obtaining the material parameters known as C, m, p and q. The procedure is based on experimental and numerical results. The experimental tests were used to characterize the material and obtain fatigue crack growth data. For the fatigue tests, tapered double cantilever beam (TDCB) specimens with different maximum load and load ratio values were used. Through the numerical analysis, the stress intensity factors, the crack growth direction and the crack path coordinates were calculated. The numerical analysis was performed using XFEM and the maximum energy release rate criterion. The calibrated model allows predicting the number of load cycles with an RMS value of less than 5%, compared with the experimental results.

Characterization of fatigue delamination growth under mode I and II: Effects of load ratio and load history

The study of fatigue delamination growth in composite materials aims to develop a slow-growth approach for composite materials that would provide conservative and reliable results. The present work focuses on the study of the load ratio effect on fatigue crack growth at constant amplitude and on the effect of variable amplitude loading on crack propagation. With this in mind, a Crack Driving Force (CDF) is chosen to attempt to overlap delamination growth curves obtained from different load ratio values for mode I and mode II. It is shown that the CDF collects the effect of the load ratio on the crack growth curves and allows to build a crack growth master curve for mode I and II. Variable amplitude loads are then considered for delamination propagation in mode I. However, variable amplitude loads bring to light a load history effect during fatigue crack growth that the CDF does not take into account.

10.30: Mechanical response of steel structures in fire: Influence of different material and creep models

ABSTRACTThe paper deals with the influence of viscous creep of steel on the behaviour of steel structures during fire. Two stress‐strain relationships for structural steel, combined with Harmathy's explicit model of viscous creep at elevated temperatures, are presented in the paper: (i) bilinear stress‐strain relationship and (ii) modified Poh's stress‐strain relationship. The presented models have been implemented in self‐developed software Pozar for numerical analysis of mechanical response of planar steel frames in fire. Further on results are validated against experimental ones published by Rubert and Schaumann, 1985. The numerical results, obtained with stress‐strain relationship according to the Eurocode 3, are added for comparison. It is shown that all tested models give satisfactory results for small load ratios. Poh's stress‐strain relationship in combination with Harmathy's model of viscous creep and newly proposed coefficients give the best results among the tested models with explicitly considered viscous creep. However, none of the considered models give good agreement with the experiment at high values of load ratio. Furthermore, the comparison between the different material and creep models is conducted for three heating regimes, namely linear heating regime and fast and slow natural fire development. A prominent influence of the employed material model on the final midspan displacements is observed.

Axial crushing of triaxially braided composite tubes at quasi-static and dynamic rates

This paper presents the results of an experimental investigation into the behaviour of braided CFRP tubes subjected to quasi-static and dynamic axial crushing. Tubes of six different geometries, with round, rectangular or square cross-sections, with 2–4 plies of triaxial braids, were tested. Two types of square tubes were also tested with a plug initiator. Comparisons were made by examining the failure modes, load-displacement curves, specific energy absorption (SEA), and the ratio of the peak load to the average progressive crush load. When tested without a plug initiator, the crush characteristics of these tubes differed significantly under the two loading rates. Under quasi-static crush, tubes showed a greater tendency to fail in an unstable manner, characterized by global buckling, folding of the walls and crushing at both ends of the tube. Therefore, quasi-static crush testing should be used with caution when evaluating dynamic response of a structure. In dynamic testing, seven out of the eight configurations failed in a stable manner, with damage initiating at the bottom and propagating up the length of the tube in a splaying type failure mode. The smaller square and the round tubes performed the best, displaying higher SEA and lower load ratio values.

Separation of 2,4,6-trinitrophenol from aqueous solution by liquid–liquid extraction method: Equilibrium, kinetics, thermodynamics and molecular dynamic simulation

In this paper, the equilibrium and kinetic studies on the extraction of 2,4,6-trinitrophenol (picric acid) (0.021–0.061kmolm−3) using Amberlite LA2, a secondary amine (ALA2: 0.118–0.588kmolm−3) dissolved in a polar active solvent, methyl-iso-butyl ketone (MIBK) are performed. Also, the temperature effect (293.2±1K, 303.2±1K and 313.2±1K) on the extraction mechanism and efficiency is evaluated. Thermodynamic parameters like the change in entropy and enthalpy are determined. From the values of loading ratio (Z<0.5), it is inferred that the amine molecule form 1:1 complex with the acid molecule in the organic phase. The mass transfer coefficient (kL=3.1×10−5ms−1) of picric acid in MIBK is determined. The Hatta number is calculated, and observed to vary in the range of 0.0032–0.0054, indicating that there is a very slow chemical reaction taking place between the acid and the amine molecule in the bulk of the organic phase. The reaction order is estimated to be 0.9w.r.t picric acid, and 0.6w.r.t ALA2 with rate constants of 14.95×10−6 (kmolm−3)−0.5s−1, and 8.94×10−7(kmolm−3)−0.5s−1, for forward and backward reaction, respectively. Kinetic and potential energies of components during reactive extraction have been determined by molecular dynamic modeling.

Buckling Behaviour of the Delaminated Sandwich Plates under Combined Loads

In the paper, a methodology to evaluate the influence of the central circular delamination on the buckling and postbuckling behaviour of the sandwich plates under shear and compression loading, used in ship hull structure, is presented. The parametric calculus was done for various values of loading ratios. The numerical tests on the delaminated plates are presented. Sandwich composite plates containing central delaminations are analyzed with respect to combined boundary shear and axial compression buckling. Finally, the graphical results for all values of loading ratio are presented.

Damage Assessment of Threaded Connections based on an Advanced Material Model and Local Concepts

In the actual guidelines, for example the German VDI guideline 2230 [1] or the EUROCODE 3 [2], the fatigue assessment of bolted connections and bolts is based on the nominal stress approach. The FKM guideline for analytical strength assessment [3] does not include concepts for a threaded connection, it refers to the existing guidelines as [1]. At present there does not exist any guideline, which provides a damage assessment for general threaded connection by applying local concepts. In the present paper the basics of such a concept are outlined. The investigated metal is 34CrNiMo6, which is generally used for screw threads. The experimental determination of the local stress-strain behaviour in mechanically threaded connections is practically not feasible and needs a numerical approach. This numerical attempt consists of two main tasks, namely the description of the material properties and finite element (FE) analysis. The first one is concerned with the identification of material parameters, which are necessary for the FE analysis, especially for the advanced material model. The experimental work is given by determining the initial monotonic stress- strain curve, the initial unloading curve, the cyclic stress relaxation and cyclic creep. The parameter identification is accomplished using the software MATLAB, which includes the essential nonlinear optimization algorithms. The obtained parameters are entered in the FE software, which is used for the further FE analysis. The distinctive features of the FE analysis are the nonlinearity, especially nonlinear material behaviour, nonlinear contact algorithms and the consideration of large deformations, the high number of load steps and the various load ratio values (R = 0.06 and R = 0.71). The results of the FE analysis are used for the assessment of threaded connections. The damage assessment is realized with the local strain approach based on the damage parameters PSWT and PJ. Finally the result of the simplified method according to Schneider is applied on a high preloaded bolt connection (R = 0.71) and compared with the result achieved with the advanced material model.

Characteristics of bifurcation and buckling load of space truss in consideration of initial imperfection and load mode

This study investigated characteristics of bifurcation and critical buckling load by shape imperfection of space truss, which were sensitive to initial conditions. The critical point and buckling load were computed by the analysis of the eigenvalues and determinants of the tangential stiffness matrix. The two-free-nodes example and star dome were selected for the case study in order to examine the nodal buckling and global buckling by the sensitivity to the eigen buckling mode and the analyses of the influence, and characteristics of the parameters as defined by the load ratio of the center node and surrounding node, as well as rise-span ratio were performed. The sensitivity to the imperfection of the initial shape of the two-free-nodes example, which occurs due to snapping at the critical point, resulted in bifurcation before the limit point due to the buckling mode, and the buckling load was reduced by the increase in the amount of imperfection. The two sensitive buckling patterns of the numerical model are established by investigating the displaced position of the free nodes, and the asymmetric eigenmode greatly influenced the behavior of the imperfection shape whether it was at limit point or bifurcation. Furthermore, the sensitive mode of the two-free-nodes example was similar to the in-extensional basis mechanism of a simplified model. The star dome, which was used to examine the influence among several nodes, indicated that the influence of nodal buckling was greater than that of global buckling as the rise-span ratio was higher. Besides, global buckling is occurred with reaching bifurcation point as the value of load ratio was higher, and the buckling load level was about 50%–70% of load level at limit point.

Reactive Extraction of Pyridine Carboxylic Acids with N, N-Dioctyloctan-1-Amine: Experimental and Theoretical Studies

The paper represents the equilibrium study on reactive extraction of pyridine-3-carboxylic acid (NA) and pyridine-4-carboxylic (iNA) acid from aqueous solution by N, N-dioctyloctan-1-amine (TOA) dissolved in five different diluents [dodecane, methyl benzene, decan-1-ol, 4-methylpentan-2-one (MIBK), and chloroform] at constant temperature of 298 ± 1 K. According to an experimental study, the extraction ability of diluents with TOA is found to be in the order of chloroform > decan-1-ol > MIBK > methyl benzene > dodecane for both acids. The highest extraction efficiency in terms of the distribution coefficient (K D) is found to be 45.15 and 25.79 for NA (0.12 mol · dm−3) and iNA (0.03 mol · dm−3), respectively. The values of loading ratio, Z (between 0.194 and 0.512) for both acids indicate the formation of 1:1 acid-TOA complexes in the organic phase. The values of the equilibrium constants (K 11) are determined from the experimental data using mass action law. These estimated values of K 11 are compared with the predicted values of K 11 from relative basicity and linear solvation energy relationship (LSER) models. The LSER model predicts the K 11 with an error limit of ±3% for NA and ±2% for iNA.

Numerical-based fatigue assessment of cylindrical pressure vessel having girth weld misalignment at varying load ratios

Finite element (FE)-based numerical study of a pressurised cylindrical pressure vessel containing 50% weld misalignment at the cylinder-to-cylinder junction is performed. The work evaluates the effect of misalignment on fatigue behaviour of the pressure vessel for different load ratios to quantitatively analyse its impact in terms of fatigue life and maximum anticipated damage. Fatigue life sensitivity to varying loads is also analysed by extrapolating the fatigue life results for 50% to 150% of applied FE load. Results from an ideally perfect weld are also obtained for comparative analysis. Results of FE analysis show significant effect of misalignment on fatigue properties of the cylinder which is more prominent at higher values of load ratio.

Comparative Study on Reactive Extraction of Picolinic Acid with Six Different Extractants (Phosphoric and Aminic) in Two Different Diluents (Benzene and Decan-1-ol)

The equilibrium study on reactive extraction of picolinic acid by six different extractants (phosphoric and aminic) dissolved in two different diluents (benzene and decane-1-ol) is carried out to evaluate the performance of extractants and diluents. The extraction ability in terms of the distribution coefficient (K D) is found to be in the order of tri-n-octylamine (TOA) ≥ tri-n-dodecylamine (TDDA) > di-2-ehylhexyl phosphoric acid (D2EHPA) > tri-n-butyl phosphate (TBP) > tri-octyl methyl ammonium chloride (Aliquat 336) > tri-n-octyl phosphine oxide (TOPO) with both diluents. Decan-1-ol is found to be the better solvating medium for the acid-extractant complexes. A mathematical model based on mass action law is employed to estimate the values of partition coefficient (P) and dimerization constant (D) in physical extraction, and equilibrium extraction constants (K E) in chemical extraction. The values of loading ratios (Z) less than 0.5 imply the formation of (1:1) acid:extractant solvates in the organic phase. Decan-1-ol with TOA is the most effective solvation medium with K D, max = 9 at 0.01 kmol · m−3 of picolinic acid and K E = 19.448 m3 · kmol−1.

An experimental study of loading parameters effect on fatigue crack closure in 12NC6 steel

In this paper, the fatigue crack closure (FCC) phenomenon was experimentally revealed using the back face strain gauges technique. The effects of the loading parameters on FCC have been investigated on 12NC6 heat treated steel. Four yield stresses values have been tested. The loading conditions were chosen to have the stress intensity factor range ΔK between 17 and 30MPam with four load ratio values: 0.05–0.1–0.3 and 0.5. In this study, the closure stress intensity factor Kcl is approximately constant for all load ratio values (R). The expression describing the evolution of the closure parameter U is obtained as a function of both the R and Kmax.

Turbulence modulation for gas – particle flow in vertical tube and horizontal channel using four-way Eulerian–Lagrangian approach

Turbulence modulation of gas–solid flow in vertical tube and horizontal channel in dilute and moderately dense suspensions is investigated numerically using a four way Eulerian–Lagrangian approach. Low Reynolds number k–l model is used for analyzing the fluid phase motion. A new model is presented based on a source-term formulation, which can predict fluid phase turbulence augmentation due to the presence of large particles and damping of turbulence due to small particles in the core of the channel and tube. Particle–particle and particle–wall collisions are simulated based on a deterministic approach, and coupling terms representing the fluid–particle interactions are also taken into account. The predicted fluid mean velocity and turbulence intensity profiles are in good agreement with the available experimental data. Additional numerical simulation results for variation of the eddy viscosity, turbulence production and dissipation are also presented for different values of loading ratios.

Modelling and adaptive control of small capacity chillers for HVAC applications

Abstract An adaptive controller for single and uneven tandem scroll compressor, packaged air-cooled water chillers is described. The designed controller allows to substantially increase the energy performance of the system, as well as to achieve excellent regulation performances in process applications. The controller parameters are adapted on the basis of estimates of the plant thermal load, that are computed by using a Kalman filter. An ad hoc approach is used to define a relay control logic, which is based on a numerical optimization procedure. To support controller design, a detailed simulation environment is developed and validated on an experimental facility. Performance of the algorithm is described with both simulation and experimental data. At low part load ratio values the proposed algorithm grants a 0.6–0.7 K improvement in the regulation performance in terms of supply water temperature standard deviation and mean supply water temperature deviation. The unit energy efficiency improvement with respect to supply water temperature control varies from 7.3% to 3.0% while the experimental seasonal energy efficiency rating improvement is 9.1%.

Gas–solid turbulent flow and heat transfer with collision effect in a vertical pipe

A turbulent gas–solid suspension upward flow in a vertical pipe is simulated numerically using Eulerian–Lagrangian approach. Particle–particle and particle–wall collisions are simulated based on deterministic approach. The influence of particle collisions on the particle concentration, mean temperature and fluctuating velocities are investigated. Numerical results are presented for different values of loading ratios. The profiles of particle concentration, mean velocity and temperature are shown to be flatter by considering inter-particle collisions, while this effect on the gas mean velocity and temperature is not significant. It is demonstrated that the effect of inter-particle collisions have a dramatic influence on the particle fluctuation velocity. It is shown that the profiles of particle concentration and particle velocity are flattened due to inter-particle collisions and this effect becomes more pronounced with increasing loading ratio. Also, the attenuation of turbulence by inter-particle collisions in the core region of the pipe is increased by increasing loading ratio.

The equation of the second portion of the fatigue fracture kinetic diagram for various additional load ratios

The second portion of the fatigue fracture kinetic diagram is described by a reliable equation with additional load ratios R in the case of the crack-tip closure effect and by the Forman equation for the values of load ratio R* in the case without the crack closure effect. We have obtained the analytical dependence of the effective range of the stress intensity factor ΔKeff on the nominal range ΔKR for the first part of the second portion of the fatigue fracture kinetic diagram (ΔK1-2,R≤ΔKR≤ΔKfcl,R) with various load ratios.

A study of the helical effect on the thread connection by three dimensional finite element analysis

The three-dimensional finite element analysis of bolted joints with finite sliding deformable contact has been studied, and the helical and friction effect on the load distribution of each thread is analyzed. It shows the analytical analysis by Yamamoto’s method reaches a lower value of load ratio than the finite element analysis at the first thread. The load distribution on each thread between axisymmetrical model and three-dimensional model are provided. Hence, although increasing the coefficient of friction and decreasing the lead angle may improve the load distribution slightly, for 1-inch 16UNF bolt joints, the error of load ratio at the first thread in axisymmetrical finite element model is 12% with respect to three-dimensional analysis.

Performance of Skidder Tires in Swamps — Comparison between Statistical and Neural Network Models

Tractive performance of a rubber-tired skidder operating on soft organic soil in the Coastal Plain region of North Carolina was determined for three tire sizes inflated at each of three inflation pressures (69, 103, and 172 kPa). The tractive pull/dynamic load ratio values were low (= 0.32) for all tire size/inflation pressure combinations and, when plotted against the travel reduction, appeared to be dependent on the tire inflation pressure.

Traction and Rolling Resistance of a Dual-Tired Skidder on Wetland

ABSTRACT ROLLING resistance and tractive performance of a skidder equipped with dual tires operating on soft soil in the Coastal Plain region of North Carolina were determined for six tire inflation pressure combinations (TIPC). The rolling resistance increased with the increase in dynamic load for all pressures. The mean line pull, P, increased linearly with the tree load, WL (P = 0.62 WL). The tractive pull/dynamic load ratio values were low and when plotted against the slip appeared to be independent of the tire inflation pressure indicating that the tires performed like rigid wheels on soft, deformable surfaces.