FD Model Research Articles

Supporting design knowledge exchange by converting models of functional decomposition

The concept of technical function is used with different meanings in the engineering domain. This ambiguity hampers the exchange of design knowledge across functional modelling approaches. This paper investigates three issues relevant to handling this communication problem. First, it provides a clarification of engineering meanings of function and functional decomposition (fd) models. Secondly, it presents an assessment of the benefits of co-existing functional conceptualisations. Thirdly, following the positive outcome of this assessment, it presents a conceptual strategy to exchange design knowledge across modelling approaches. This strategy does so by converting models of fd across approaches. It is shown that the proposed conversion strategy is able to retain design knowledge that is lost when using another methodology for the conversion of fds. This paper ends by identifying a future research agenda for model conversions.

Numerical Simulation of Thermal Stress Fields of Steel Casting

Many defects relative to stress occur during the complicate casting process, such as hot tearing, residual stress concentration and distortion. Modeling of casting thermal stress during casting solidification process is of great significance to predict and analyze casting stress defects. Involving too many complex influencing factors, the stress simulation is very difficult and retains a hot spot of macro simulation in foundry engineering. Currently most researchers adopt integrated FDM/FEM method, i.e. using finite difference method (FDM) to calculate solidification and heat transferring, while finite element method (FEM) to simulate stress. Some universal commercial FEA packages are usually adopted. This study has tried two kinds of approaches to simulate casting thermal stress. One is based on ANSYS, a well-known powerful FEA analysis software. Another is to develop an independent own copyrighted casting stress simulation system based on FDM. The routes of these two methods were given respectively. To calibrate the simulation system, a stress frame sample and a real practical casting were simulated and pouring experiment was also carried on. The results of simulation were in agreement with the experiment results and practical cases. It indicates that these two approaches can all meet demands. When adopting FDM method, thermal analysis and stress analysis can use the same FD model, which can avoid the nodes matching between different models and reduce the errors of thermal load transferring. It makes the simulation of fluid-flow field, temperature field and stress field unify into one model. This system takes full advantages of mature FDM technology and can be used to simulate the forming of residual stress and predict the occurrence of hot tearing.

Theoretical comparison of hydrodynamic diffusion layer models used for dissolution simulation in drug discovery and development

The effective hydrodynamic diffusion layer thickness ( h eff) of a drug particle dissolving into an agitated fluid is of great importance for oral absorption simulation. The purpose of the present study was to: (1) introduce a h eff estimation method based on the fluid dynamic theory (FD model), and (2) compare the FD model with the non-FD-based approximation models previously reported by Hintz and Johnson (HJ model) and Wang and Flanagan (WF model). In the FD model, the relative velocity of a particle suspended in an agitated fluid was estimated from the terminal slip velocity and the microeddy effect. For small particles (particle radius ( r p) < ca. 15 μm), the HJ, WF and FD models resulted in the similar h eff values, whereas they resulted in different h eff values for large particles ( r p > ca. 15 μm). One of the merits of the FD model is that it provides the a priori theoretical estimation of h eff from particle radius, drug density, agitation strength, fluid viscosity, and diffusion coefficient. The hydrodynamic conditions in the gastrointestinal (GI) tract differ among human and animals, the GI sites, and fasted/fed conditions, etc. Therefore, the FD model could provide a more comprehensive and sophisticated simulation of oral absorption.

Markov-chain Monte Carlo Estimation of Permeability Coefficients From in Vivo Human Exposure to Aqueous Chloroform

P-644 Introduction: The standard US EPA protocol for estimating dermal exposure to contaminants in water depends upon a dataset derived from in vitro experiments using human cadaver skin. Few experimental investigations of dermal availability have been conducted in vivo in humans. One class for which multiple human in vivo experiments have been reported is volatile organic compounds (VOCs), for which the primary indicator of absorption is concentration in breath. However, because exhalation only represents a small fraction of total absorption, a model must be used to estimate total dermal permeation. Little attention has been paid in the scientific literature to the effect of alternate skin models on performance of the resulting PBPK model. Three versions of a skin model are considered here: a continuously stirred tank reactor (CSTR) in which the VOC concentration is uniform throughout the skin; a true membrane model which simulates concentration gradients in skin by a finite-difference scheme (FD); and an approximate membrane model which is a modified CSTR model that matches theoretical membrane results for certain conditions (STL). Comparison of permeability coefficients (Kp) derived from these in vivo results to the corresponding in vitro estimate is undertaken here. Methods: The three dermal models were constructed in the Object-Pascal program BlackBox (Oberon Microsystems, Switzerland) and compiled in WinBUGS 1.4 (Imperial College & Medical Research Council, UK). Real-time breath sampling data from the Gordon et al (1998) chloroform study were input to the model, and Markov-Chain Monte Carlo (MCMC) analysis was used to determine the posterior distribution of the apparent skin Kp. Population-based posterior distributions of Kp were generated at 30°C, 35°C, and 40°C for both genders using all three dermal models. Results: The posterior distributions of Kp displayed substantial inter-model differences. The FD and STL models produced consistently higher estimates of Kp in both genders. The female subjects exhibit lower Kp's at 30°C and 35°C despite being comparable to the males at 40°C. Discussion and Conclusions: The three skin models yield different results with respect to MCMC-generated Kp estimates. In general, results from the STL model closely resemble that of the true membrane FD model, and are computationally much less demanding, while the CSTR model does a poor job of fitting the real-time data. In vivo Kp estimates from the FD and STL models at 30°C are very similar to the value generated by the in vitro experiments (which were conducted at roughly that temperature). At higher temperatures in vivo Kp's are noticeably elevated. This work was supported by US EPA via cooperative agreement R-82963201. Material presented here has not been reviewed by EPA and no Agency endorsement should be inferred. JAS was also partially supported via CDC/NIOSH Training Grant T42/CCT010418-11.

N-H···S Hydrogen Bonds in a Ferredoxin Model

The Fe4S4 complex {(CH3)3NCH2CONH2}2[Fe4S4((tBuS)4] (1) was synthesized to replicate the ferredoxin active site with a subset of its N-H...S hydrogen bonds. The two cationic counterions mimic the polypeptide backbone of ferredoxin (Fd) as amide hydrogen-bond donors to sulfur atoms of the iron-sulfur cluster. X-ray crystallographic data show that the organic sulfur (Sgamma) of one tert-butylthiolate ligand and one inorganic sulfur of the cluster core serve as N-H...S hydrogen-bond acceptors. The cluster core of complex 1 is tetragonally elongated in contrast to that of Fd, which is tetragonally compressed. This is the first observation of an elongated [Fe4S4]2+ cluster core. Additionally, this is the first synthetic Fd model in which N-H...S hydrogen bonding to a cluster has been achieved.

New AGILD EMS Electromagnetic Field Modeling

The Electromagnetic Stirring (EMS) technology has wide applications in the metal continuous casting. Stirring consists of exciting variable magnetic field in metal liquid, the magnetic field generates induction current. The induction current in the metal flow interacts with magnetic filed to generate EM force, which makes perfect motion to improve casting. The EM force strength is proportional with square of the magnetic field strength. The key of the optimized control of EMS is to adjust several parameters for best EM force and deep magnetic penetration. In this paper, we present a new AGILD EMS modeling. We use Maxwell magnetic field differential equation to replace the reduced magnetic field equation. We present new volume magnetic differential integral equation and new boundary strip magnetic field differential integral equation which are proposed by XIe and Li in GLGEO. According to the new AGILD EM modeling in [1], we developed 3D AGILD EMS modeling. Our AGILD EMS modeling does not need any complex boundary condition. The matrix equations are decomposed by GILD parallel processes. Therefore, our AGILD EMS modeling is fast and accurate without any boundary error. Our AGILD EMS modeling can simulate multiple strands and EMSs together. The simulation shows that the AGILD EMS modeling is very powerful tool for the design of excellent EMS system in Billent/Bloom and metal continuous casting system. The simulation is performed by using GLGEO’s new GL[2-4] and AGILD EMS modeling software. The EMS is an established technology and installed in Billet, Bloom and metal casters. The stirring consists of exciting variable magnetic field which is penetrating in the steel, iron, and metal liquid. The magnetic field generates induction electric current in the metal liquid. The induction current in the metal liquid interacts with the magnetic field to generate EM force which drives the metal liquid flow motion such that the casting is perfectly performing. The casting quality is improved by reduced segregation and porosity through transformation to an equiaxed solidification structure. The steel and iron productions are increasing due to the increased casting speeds. The temperature and carbon component are key factors for high quality steel. The magnetic field penetrating distribution depends on the material properties and high temperature. Moreover, the electromagnetic properties depend on the temperature. The temperature difference between outer and insider of the caster mold is very large. We consider the magnetic conductivity be space variable. The reduced magnetic field equation is no longer to govern this case. In this paper, we use the magnetic field Maxwell equation to replace the reduced magnetic equation. Moreover, we present a new strip magnetic field differential integral equation which is proposed by Xie and Li in [1]. We use the new strip integral equation on the double layered boundary and the magnetic field Garlekin equation in the internal domain to construct the AGILD EMS modeling for the metal continuous casting. It has more advantages over FEM and FD modeling. The AGILD and GL EMS modeling, GL and AGILD nondestructive testing, GL and AGILD heating modeling, and GL and AGILD heavier viscosity flow modeling for the continuous casting are developed by Xie and Li in GLGEO. Many EM research works on motor need the condition that the magnetic resistivity monotone increasedly depends on the magnetic induction. It is very strong and unpractical condition. In practice, magnetic resistivity is not monotone increasing but has a minimum point at B = B0. Our nonlinear FEM EM modeling [10-12] are available for the above practical condition, i.e. the magnetic resistivity is not monotone increasing. We prove that if H(B) monotone increasedly depends on B, the nonlinear FEM is convergent. Because H(B) = υ(B)B, so, we only need that υ(B)B monotone increasedly depends on the B, which is widely generalized. Moreover, the H(B)’s monotone property is the practical physical property. Our nonlinear FEM magnetic DC modeling is briefly described in this paper. The organization of the paper is as follows. We present the new strip differential integral equation in the section 2 which is proposed in [1]. The double layered collocation FEM equation for the magnetic field is

Structural Dynamic Responses with Generalised Explicit Finite Difference Models

Finite Difference method is one of the most commonly used numerical methods. Conventional finite difference method is convenient for describing problems and easy understanding. In this paper, two explicit finite difference models for large deformation of several material characteristics are developed. The models are capable of handling impulsive and constant load, impact and gravitational force, etc. Their capabilities to handle relatively complex shapes such as a T-joint, circular wheel, etc. which are not possible to deal with using classical FD models, are presented and discussed. A robust method is developed to describe the general stress-strain relationship, such as elastic-perfectly plastic, elastic-strain hardening, and multiple modulii elastic and plastic. The effects of strain rate, Hysteresis and Bauschinger are also included. Comparisons between the computational results from the new models and results from published data in the literature are made.

Finite-difference computation of head-related transfer functions for human hearing

Modeling the head-related transfer function (HRTF) is a key to many applications in spatial audio. To understand and predict the effects of head geometry and the surrounding environment on the HRTF, a three-dimensional finite-difference model has been developed for the head-related impulse response. A perfectly matched layer (PML) is used to absorb outgoing waves at the truncated boundary of an unbounded medium. An external source is utilized to decrease the computational domain size. This numerical model has been validated by analytical solutions for a spherical head model. The FD code is then used as a computational tool to predict the HRTF for various scenarios. In particular, a simplified spherical head model is compared to a realistic head model up to about 7 kHz. The HRTF is also computed for a realistic head model in the presence of a wall. It is demonstrated that this FD model can be a useful tool for spatial audio applications.

Full nonlinear closure for a hydrodynamic model of transport in silicon

The increasing miniaturization of modern electronic devices requires an accurate modelization of transport in semiconductors. This is of great importance for describing phenomena such those due to hot electrons, i.e., the conditions very far from thermodynamic equilibrium caused by strong electric fields and field gradients. The most general approach to the simulation of charge transport in semiconductors employes the semiclassical Boltzmann transport equation ~BTE! coupled with Poisson equation. A numerical solution of such system of equations with traditional techniques is extremely complex, and then approximate methods based on kinetic and fluid dynamic ~FD! models are often preferred. The most accurate kinetic description is given by Monte Carlo ~MC! methods, which can take into account explicitly both the band structure and the various scattering phenomena. 1,2 This method permits us to compute directly all the quantities relative to transport ~such as the distribution function, density of carriers, velocity, mean energy, and so on! but at a cost of long computation times and stochastic noise in data. The results obtained from MC simulations permit us also to calculate transport coefficients , which are used as an input to more simplified FD models. Other kinetic approaches are based on the choice of particular forms of the nonequilibrium distribution function of carriers. Common examples are the simple shifted Maxwellian 3 or an expansion of the distribution in spherical harmonics. 4 The cylindrical symmetry constraint in momentum space and the reduced number of terms of the expansion that can be practically used do not permit, however, to describe transport properties of carriers in conditions very far from equilibrium. 5

A Monte Carlo model of fd and Pf1 coat proteins in lipid membranes

A Monte Carlo Dynamics simulation was used to investigate the behavior of filamentous bacteriophage coat proteins in a model membrane environment. Our simulation agrees with the previous experimental observations that despite the low sequence similarity between the major coat proteins of Pf1 and fd bacteriophages, their structure in the membrane environment is very similar. These results support the hypothesis that the hydrophobic effect exerts an important influence on membrane protein structure. The model may also be used for modeling the insertion and transport processes in protein-membrane systems. The example of fd protein was also used as a test of sensitivity of our model to temperature, thickness of the hydrocarbon phase, and simulation time. In all cases, the results were independent (over the tested range) of the particular values of the parameters.

Structure of [2Fe-2S] ferredoxin I from Equisetum arvense at 1.8 A resolution.

Ferredoxin I (Fd I) from Equisetum arvense is an iron-sulfur protein composed of 95 amino-acid residues and one [2Fe-2S] cluster. It crystallized in the space group P2(1), a = 30.4, b = 57.4, c = 47.5 A and beta = 78.7 degrees with two molecules per asymmetric unit. X-ray diffraction data up to 1.8 A resolution were collected by using a Rigaku four-circle diffractometer. The initial model of Fd I, which was derived by the molecular replacement method using a structure of the Fd I from the blue-green alga Aphanothece sacrum, was refined by molecular dynamics simulation and a least-squares minimization with stereochemical restraints. Positional parameters and isotropic temperature factors for 1420 non-H protein atoms and 183 water molecules were refined on 13 838 observed structure factors (F(o) > sigma(Fo)) between 10.0 and 1.8 A resolution. The final Rfactor was 17.0%, and the standard deviation of atomic position estimated by Luzzati plot [Luzzati (1952). Acta Cryst. 5, 802-810] was 0.2 A. The electron-density map was well defined for the two independent molecules except for the N-terminal residue and the three C-terminal residues. Equivalent Calpha atoms of two independent molecules in the asymmetric unit were superposed by the least-squares method with root-mean-square deviations of 0.26 A. Reasonable structural differences were observed at a polypeptide segment having few intramolecular interactions. Highly flexible regions of the molecule were assigned from the structural differences between the two independent molecules in the crystal and the distribution of temperature factors along the polypeptide chain.

Molecular models and structural comparisons of native and mutant class I filamentous bacteriophages: Ff (fd, f1, M13), If1 and IKe

The filamentous bacteriophages are flexible rods about 1 to 2 microns long and 6 nm in diameter, with a helical shell of protein subunits surrounding a DNA core. The approximately 50-residue coat protein subunit is largely alpha-helix and the axis of the alpha-helix makes a small angle with the axis of the virion. The protein shell can be considered in three sections: the outer surface, occupied by the N-terminal region of the subunit, rich in acidic residues that interact with the surrounding solvent and give the virion a low isoelectric point; the interior of the shell, including a 19-residue stretch of apolar side-chains, where protein subunits interact mainly with each other; and the inner surface, occupied by the C-terminal region of the subunit, rich in basic residues that interact with the DNA core. The fact that virtually all protein side-chain interactions are between different subunits in the coat protein array, rather than within subunits, makes this a useful model system for studies of interactions between alpha-helix subunits in a macromolecular assembly. We describe molecular models of the class I filamentous bacteriophages. This class includes strains fd, f1, M13 (these 3 very similar strains are members of the Ff group), If1 and IKe. Our model of fd has been refined to fit quantitative X-ray fibre diffraction data to 30 A resolution in the meridional direction and 7 A resolution in the equatorial direction. A simulated 3.3 A resolution diffraction pattern from this model has the same general distribution of intensity as the experimental diffraction pattern. The observed diffraction data at 7 A resolution are fitted much better by the calculated diffraction pattern of our molecular model than by that of a model in which the alpha-helix subunit is represented by a rod of uniform density. The fact that our fd model explains the fd diffraction data is only part of our structure analysis. The atomic details of the model are supported by non-diffraction data, in part previously published and in part newly reported here. These data include information about permitted or forbidden side-chain replacements, about the effect of chemical modification, and about spectroscopic experiments.(ABSTRACT TRUNCATED AT 400 WORDS)

Temperature transients on engine combustion chamber walls—IV. Application of the finite-difference model to surface thermocouples and wall deposits

The FD computational code developed in Part I ( Int. J. Mech. Sci. 33, 775 (1991) [1]) has the capability of handling composite walls having different material layers. This characteristic of the FD model is used to study the effects of thermocouple thickness and material type, as well as substrate material type on surface thermocuple readings. Later, the effects of wall deposits on surface thermocouple readings and engine heat transfer are explained.

Temperature transients on engine combustion chamber walls—III. Application of the finite-difference model to various metal and ceramic walls

The FD code developed, explained in Part I ( Int. J. Mech. Sci. 33, 775 (1991) [1]), is applied to various metal and ceramic walls to observe the possible surface temperature swings and heat flux levels in an operating diesel engine. The effects of the coolant-side boundary condition and enhanced gas heat transfer coefficient (htc) are also investigated. Finally, the paper deals with linking the FD model to detailed steady-state engine thermal resistance models, and its implementation in engine cycle simulation programs.

Rheological properties of internal viscosity models with stress symmetry

Internal viscosity models (IVM) for dilute-solution polymer dynamics differ in how they define the deformational force Fd which includes φ, the IV coefficient, and in how they treat polymer rotational velocity Ω. Here, the handling of angular momentum is shown to be crucial. A torque balance in simple shear flow at shear rate G leads to stress symmetry and specification of Ω(G) which differs greatly from the conventional Ω = G/2. This determines the G dependence of viscosity η and normal stress coefficient ζ. There are also implications of a transition in rotational behavior as φ approaches a critical value. Predictions of η(G), ζ(G), and η*(ω) are presented for two versions of Fd: one derived recently by the authors and one being most commonly used at present. Limiting cases for high and low φ, and for high and low G and ω, are discussed. Some differences exist between predictions of the two Fd models, but these are surprisingly minor.

Rheological properties of internal viscosity models with stress symmetry

AbstractInternal viscosity models (IVM) for dilute‐solution polymer dynamics differ in how they define the deformational force Fd which includes φ, the IV coefficient, and in how they treat polymer rotational velocity Ω. Here, the handling of angular momentum is shown to be crucial. A torque balance in simple shear flow at shear rate G leads to stress symmetry and specification of Ω(G) which differs greatly from the conventional Ω = G/2. This determines the G dependence of viscosity η and normal stress coefficient ζ. There are also implications of a transition in rotational behavior as φ approaches a critical value. Predictions of η(G), ζ(G), and η*(ω) are presented for two versions of Fd: one derived recently by the authors and one being most commonly used at present. Limiting cases for high and low φ, and for high and low G and ω, are discussed. Some differences exist between predictions of the two Fd models, but these are surprisingly minor.