A new model of first-order magnetocaloric materials with experimental validation

The use of new mathematical models to represent first-order magnetocaloric materials is reported. Three mathematical models with differing strengths and weaknesses are assessed. The material models are implemented in a numerical model to predict the cyclical performance of a magnetocaloric regenerator. Predictions using both measured and modeled material are compared. A prototype is used to confirm the predictions of the model as well as confirm performance trends related to the variables being investigated. The numerical model with measured and mathematically represented materials shows good correlation to experimental tests. The result is a new and useful method of representing magnetocaloric materials that can accurately predict results over a range of cyclical parameters.     

Impedance of the eddy-current displacement probe: the transformer model

A new approach to calculation of the impedance of the eddy-current displacement probe is presented. It is based on the transformer model of the probe-to-target coupling. The usual method of calculating the impedance by solving for the electromagnetic field distribution in the probe and the conductive target involves solution of integral equations. Instead, a simpler approach is possible by modeling the probe-to-target coupling as a loaded transformer, involving only linear ac circuit analysis and elliptic integrals (readily available in MATHCAD, MATLAB, etc.). The model transformer has single primary and multiple secondary windings. The primary winding models the probe coil, while the distributed Eddy current's circulation paths are modeled by multiple secondary windings. The target active area (the eddy current's carrying area) is divided into concentric rings. Each ring is modeled as a single-turn secondary loaded with the ring impedance. Simulation shows that division of the target active area into a moderate number of rings (16) is sufficient for very good accuracy of the model. Accuracy was checked by comparison of the simulated transfer curve of the displacement transducer to the measured transfer curve of the actual transducer. The agreement between the model and the measurement is very good. The model can be used to investigate the influence of various coil shapes and target materials on linearity and sensitivity of the eddy-current displacement transducer.     

混响的混合高斯概率密度建模

混合高斯模型能够有效地拟合混响背景的一维概率密度分布。常用的混合高斯概率密度模型参数估计方法是EM迭代算法,但这种算法的主要缺点是估计精度过分依赖于初始值。而GreedyEM算法通过往混合模型中不断地加入高斯分量,能很好地解决这一问题。文章将多维图象处理中的GreedyEM算法加以合理简化,并给出模型自动定阶方法,从而成功应用于水声混响的一维混合高斯模型建模中。实验结果表明:应用新算法能从混响接收数据中准确拟合其概率密度曲线,并且能适应不同的数据长度,具有很好的通用性。     

Influence of pore geometry on the effective response of porous media

The generalized method of cells (GMC) is used to study the influence of pore geometry on the effective elastic properties and inelastic response of porous materials. Periodic microstructures with four distinct pore geometries are studied and the results for effective elastic properties are compared with several other available models and experimental results. Predictions for the inelastic response of porous alumina are presented for tensile loading, as a function of pore geometry and pore volume fraction, with the inelastic behavior of the bulk material modeled using a unified visco-plasticity theory. All results are presented for discrete pore shape and discrete porosity. It is shown that pore geometry can have a significant influence on both elastic and inelastic response, that pore geometry can be associated with parameters from other models, and that the generalized method of cells is an efficient, flexible and reliable method of analysis for such problems.     

Models for organics removal from vinasse from ethanol production

Global ethanol production generates almost 100 billion liters per year of a high-strength liquid waste called vinasse. One sustainable method of treating vinasse using environmental biotechnology is anaerobic digestion, which generates biogas that can be used as a renewable energy resource. Although a number of models have been developed for predicting biogas generation rates, no previous study has modeled liquid organic removal rates for vinasse treatment. The goal of this research was thus to develop models for predicting liquid-phase organic removal rates for anaerobic treatment of vinasse. 6-L laboratory-scale batch reactors were filled with vinasse of six different compositions and operated at three different mesophilic temperatures (30, 35, 40 °C). Biochemical and chemical oxygen demand (BOD and COD) were measured over time using Standard Methods 5210B and 5220C. Based on data collected, multiple linear regression equations (R² = 0.79 and 0.94) were developed to predict first-order rate constants k_BOD and k_COD as functions of temperature and vinasse composition (initial values of nitrogen, potassium, phosphorous, and sulfur). The first-order models developed require a small number of readily available input parameters. They apply to treatment of vinasse from ethanol produced from corn and milo; future work can test their applicability to ethanol produced from other feedstocks. The models can be used for sizing/design of reactors for anaerobic treatment of vinasse.     

FRP-confined concrete under axial cyclic compression

One important application of fiber reinforced polymer (FRP) composites in construction is as FRP jackets to confine concrete in the seismic retrofit of reinforced concrete (RC) structures, as FRP confinement can enhance both the compressive strength and ultimate strain of concrete. For the safe and economic design of FRP jackets, the stress–strain behavior of FRP-confined concrete under cyclic compression needs to be properly understood and modeled. This paper presents the results of an experimental study on the behavior of FRP-confined concrete under cyclic compression. Test results obtained from CFRP-wrapped concrete cylinders are presented and examined, which allows a number of significant conclusions to be drawn, including the existence of an envelope curve and the cumulative effect of loading cycles. The results are also compared with two existing stress–strain models for FRP-confined concrete, one for monotonic loading and another one for cyclic loading. The monotonic stress–strain model of Lam and Teng is shown to be able to provide accurate predictions of the envelope curve, but the only existing cyclic stress–strain model is shown to require improvement.     

基于本构模型的发泡聚乙烯缓冲特性曲线研究

目的 建立EPE本构模型,并基于本构模型研究EPE缓冲系数-最大应力曲线。方法 通过静态压缩实验得到EPE应力-应变曲线,利用三次Bezier曲线拟合实验曲线,根据拟合曲线求得缓冲系数,从而得到缓冲系数-最大应力曲线。结果 利用三次Bezier曲线拟合得到了EPE分段本构模型,基于本构模型建立了EPE分段缓冲系数-最大应力曲线参数方程。本构模型、基于本构模型建立的EPE缓冲系数-最大应力曲线均收敛于分段点（0.3,0.1075）,且当拟合应力值为0.4529 MPa时,得到缓冲系数最小值（5.0362）。结论 利用三次Bezier曲线拟合得到的应力-应变曲线与实验曲线有很好的拟合度,分别基于本构模型建立的和由实验数据得到的2条EPE缓冲系数-最大应力曲线有较好的拟合度,基于三次Bezier曲线拟合的本构模型研究EPE缓冲特性曲线是可行的。     

Evaluation of models for tube material characterization with the tube bulging test in an industrial setting

It is now well recognized that the material data obtained from a tensile test is less appropriate than those from a Tube Bulging Test (TBT) for a finite element simulation of tube hydroforming. However, the manufacturers still use classical data (often tensile test data) for designing metal operations due to the lack of standard for the TBT and a more complex post processing analysis of experimental measures. Getting the hardening curve from the tube bulging test requires the use of an analytical or numerical model. In this paper, three models for post-processing measures obtained from the TBT are compared based on the same experimental procedure. Thanks to a preliminary step, consisting of the validation of the analytical models through the use of finite element simulations of the TBT, it highlights that the results obtained for the local (stress and strain) and global components (the thickness distribution along the tube and the deformed tube profile) are very close, whatever the models. The test configuration (die radius and free length) seems to have no significant impact on the resulting stress-strain curve for the three models. The three models are used for post processing tube bulging tests performed on AISI304, INCONEL and Copper tubes validating their capacity for tube characterization on different materials. Finally, this study demonstrates that the Boudeau-Malécot Model can be used to obtain hardening curve from TBT without a loss of accuracy compared to more complex post-processing models and with an important gain of quality compared to tensile test.     

Refutational theorem proving for hierarchic first-order theories

We extend previous results on theorem proving for first-order clauses with equality to hierarchic first-order theories. Semantically such theories are confined to conservative extensions of the base models. It is shown that superposition together with variable abstraction and constraint refutation is refutationally complete for theories that are sufficiently complete with respect to simple instances. For the proof we introduce a concept of approximation between theorem proving systems, which makes it possible to reduce the problem to the known case of (flat) first-order theories. These results allow the modular combination of a superposition-based theorem prover with an arbitrary refutational prover for the primitive base theory, whose axiomatic representation in some logic may remain hidden. Furthermore they can be used to eliminate existentially quantified predicate symbols from certain second-order formulae.     

Modeling of nonlinear responses for reciprocal transducers involving polarization switching

Nonlinearities and hysteresis effects in a reciprocal PZT transducer are examined by use of a dynamical mathematical model on the basis of phase-transition theory. In particular, we consider the perovskite piezoelectric ceramic in which the polarization process in the material can be modeled by Landau theory for the first-order phase transformation, in which each polarization state is associated with a minimum of the Landau free-energy function. Nonlinear constitutive laws are obtained by using thermodynamical equilibrium conditions, and hysteretic behavior of the material can be modeled intrinsically. The time-dependent Ginzburg-Landau theory is used in the parameter identification involving hysteresis effects. We use the Chebyshev collocation method in the numerical simulations. The elastic field is assumed to be coupled linearly with other fields, and the nonlinearity is in the E-D coupling. We present numerical results for the reciprocal-transducer system and identify the influence of nonlinearities on the system dynamics at high and low frequency as well as electrical impedance effects due to tuning by a series inductance. It is found that nonlinear effects are not important at high frequencies (1 MHz) subject to high-input voltages, but they become important under high-voltage and off-resonance conditions.     

Numerical prediction of load–displacement behaviors of adhesively bonded joints at different extension rates and temperatures

The present work focuses on simulation of nonlinear mechanical behaviors of adhesively bonded DLS (double lap shear) joints for variable extension rates and temperatures using the implicit ABAQUS solver. Load–displacement curves of DLS joints at nine combinations of extension rates and environmental temperatures are initially obtained by conducting tensile tests in a UTM. The joint specimens are made from dual phase (DP) steel coupons bonded with a rubber-toughened adhesive. It is shown that the shell–solid model of a DLS joint, in which substrates are modeled with shell elements and adhesive with solid elements, can effectively predict the mechanical behavior of the joint. Exponent Drucker-Prager or Von Mises yield criterion together with nonlinear isotropic hardening is used for the simulation of DLS joint tests. It has been found that at a low temperature (−20 °C), both Von Mises and exponent Drucker-Prager criteria give close prediction of experimental load–extension curves. However, at a high temperature (82 °C), Von Mises condition tends to yield a perceptibly softer joint behavior, while the corresponding response obtained using exponent Drucker-Prager criterion is much closer to the experimental load–displacement curve.     

On Using a Dual Bound Approach to Characterize the Yield Behaviour of Porous Ductile Materials Containing Void Clusters

Two constitutive models for porous ductile materials are employed together to predict the yield behaviour of ductile materials containing void clusters. In this dual bound approach, the upper and lower bound constitutive models of Gurson (1977) and Sun and Wang (1989) are each evaluated in order to obtain upper and lower estimates for the material behaviour. By combining these two solutions, a predictive band can be created to capture the experimental variation in the yielding behaviour. Although these constitutive models have been derived with the assumption of a periodic void distribution, real materials contain void clusters that can significantly alter the onset of yielding and fracture. Therefore it is of great interest to determine if using dual constitutive models can produce an acceptable first-order approximation of the yielding behaviour in these materials. In the present work, the upper and lower bound yield loci are superimposed over numerical data available in the literature for the yielding of materials containing void clusters. It is shown that the dual bound approach is able to capture the material behaviour over a wide range of practically encountered stress triaxialities.     

改进的灰色模型在光催化数据预测中的应用

光催化去除水中污染物的研究通常得到的是小样本的离散数据,利用拟一级动力学模型对实验结果进行模拟和分析,有时拟合效果较差,且无法用于数据预测.本研究在离散灰色预测模型(DGM(1,1))的基础上,考虑数据的非线性特征并结合等维信息替代思想建立了非线性动态离散灰色模型(EDGM(1,1,α)),利用该模型对三元复合材料Bi...     

Multivariable control-oriented modeling of a direct expansion (DX) air conditioning (A/C) system

A dynamic mathematical model for a DX A/C system has been developed. The dynamic model, written in state-space representation which was suitable for designing multivariable control, was linearized at steady state operating points. The linearized model has been validated by comparing the model simulation results with the experimental data obtained from an experimental DX A/C system. The simulated results agreed well with the experimental data, suggesting that the model developed was able to capture the transient characteristics of the DX A/C system modeled. It is expected that the model developed can be useful in designing a multi-input multi-output (MIMO) controller to simultaneously control indoor air temperature and humidity in a space served by a DX A/C system.     

Determination of ionisation energies and attempt-to-escape factors using thermally stimulated conductivity

A procedure for determining an arbitrary distribution of activation energies (E) and attempt-to-escape frequencies (s) from overlapping contributions to thermoluminescence (TL) or thermally stimulated conductivity (TSC) is described. For the case of no retrapping, i.e. first order kinetics, the glow curve can be described by a two-dimensional Fredholm equation representing a superposition of Randall-Wilkins first-order peak shapes. The solution to this equation gives the distribution of trapping energies and attempt-to-escape-frequency factors necessary to obtain the TL or TSC peak shape. Analysis of simulated TL/TSC data for trap distributions distributed in both E and s demonstrates that the arbitrary E and s values can be determined from the solution of the Fredholm equation. The procedure is demonstrated for experimental TSC data from gamma-irradiated Al2O3:C.     

Modelling the fracture of cementitious materials

The crack band and the fictitious crack line models of the fracture process zone in cementitious materials are discussed. The two methods are quite similar. However, the fictitious crack model is shown to lend itself to a simple K-superposition method which makes use of known analytical expressions. This method is shown to give very similar results to a finite-element analysis of the fictitious crack model and has the advantage that it can be programmed for a personal computer. The predictive capability of the fictitious crack model is demonstrated by comparison of the experimental load-deflection curve for a small notch bend mortar specimen with a theoretical curve calculated from data obtained from larger beams. It is suggested that the RILEM test method for the determination of the fracture energy should be used also to establish a bilinear stress-displacement relationship for the strain-softening of the fracture process zone.     

Two-step method for preparation of NaA-X zeolite blend from fly ash for removal of cesium ions

Pure zeolites can be synthesized from silica extracts obtained from fly ash by alkaline leaching. The extraction potential of industrial by-product fly ash was investigated under repeated fusion process conditions. The amount of extracted silica was 131.43 g/kg ash while the amount extracted alumina was limited to 41.72 g/kg ash. The results of zeolite synthesis from the Si-bearing extracts demonstrated that pure zeolites with high cation exchange capacity (4.624 meq/g) can be produced. The sorption potential of synthesized A-X zeolite blend for the removal of cesium ions has been investigated. The influences of pH, contact time and temperature have been reported. Thermodynamic parameters such as changes in Gibbs free energy (DeltaG degrees), enthalpy (DeltaH degrees) and entropy (DeltaS degrees) were calculated. A comparison of kinetic models applied to the sorption data was evaluated for pseudo first-order, pseudo second-order and homogeneous particle diffusion models. The results showed that both the pseudo second-order and the homogeneous particle diffusion models were found to best correlate the experimental rate data.     

Temperature effects on creep behavior of continuous fiber GMT composites

The effects of temperature on the tensile creep of continuous random fiber glass mat thermoplastic composite (GMT) have been studied following an accelerated characterization procedure. The objectives of this work are twofold. First, is to obtain a long-term creep model using time–temperature superposition (TTS) that can represent behavior within the linear viscoelastic regime (up to 20 MPa) at room temperature. The second is to develop a non-linear viscoelastic model that accounts for a wide range of stresses and temperatures. Creep and recovery tests were carried out for a stress range between 20 and 60 MPa over a temperature range of room temperature to 90 °C. TTS was applied to obtain a master curve which was curve fitted to a nine-term Prony series. It was found that material generally behaved non-linearly for all stresses and temperature. For stresses up to 50 MPa, the non-linear viscoelastic behavior due to temperature can be reasonably modeled by only the time–temperature shift factors from TTS. At 60 MPa, however, the non-linear parameters have to be modeled as a product of stress and temperature dependent functions. The model predictions are in good agreement with the experimental results at most stress and temperature levels. The creep curves predicted at higher temperatures especially at 60 MPa tend to underestimate at longer times.