Lumped models for transient thermal analysis of multilayered composite pipeline with active heating

In this study, improved lumped parameter models were proposed for transient thermal analysis of multilayered composite pipeline with active heating, which is essential for flow assurance design and operating strategies of deepwater subsea pipelines. Improved lumped models for transient heat conduction in multilayered composite pipelines were based on two-points Hermite approximations for integrals. The transient energy equation for the bulk temperature of the produced fluid was transformed into a set of ordinary differential equations in time by using a finite difference method. The coupled system of ordinary differential equations for average temperatures in the solids and bulk temperature of the fluid at each longitudinal discretization point along the pipeline was solved by using an ODE solver. With the proposed method, we analyzed the transient heat transfer in stainless steel-polypropylenestainless steel sandwich pipes (SP) with active electrical heating. Convergence behaviors of the average temperature of each layer and the bulk temperature of the produced fluid calculated by using the improved lumped models (H0,0/H1,1 and H1,1/H1,1 approximations) against the number of grid points along the pipelines were presented. Case studies were performed to investigate the effect of the linear rate of power input and the average velocity on the bulk temperature distribution of the produced fluid.Indisponível

Structure-function relationship study of a loop structure in allosteric behaviour and substrate inhibition of Lactococcus lactis prolidase

Lactococcus lactis, prolidase (Llaprol) hydrolyzes Xaa-Pro dipeptides. Since Xaa-Pro is known as bitter peptides, Llaprol is potentially applicable to reduce bitterness of fermented foods. Llaprol shows allosteric behaviour and substrate inhibition, which are not reported in other prolidases. Computer models of Llaprol based on an X-ray structure of non-allosteric Pyrococcus furiosus prolidase showed that a loop structure (Loop32-43) is located at the interface of the protomers of this homodimeric metallodipeptidase. This study investigated roles of four charged residues (Asp36, His38, Glu39, and Arg40) of Loop32-43 in Llaprol using a combination of kinetic examinations of ten mutant enzymes and their molecular models. Deletion of the loop structure by Δ36-40 mutant resulted in a loss of activity, indicating Loop32-43 is crucial for the activity of Llaprol. D36S and H38S exhibited 96.2 % and 10.3 % activity of WT, whereas little activities (less than 1.0 % of WT activity) were observed for mutants E39S, D36S/E39S, R40S, R40E, R40K and H38S/R40S. These results implied that Glu39 and/or Arg40 play critical role(s) in maintaining the catalytic activity of Llaprol. These observations suggested that the loop structure is flexible and this attribute, relying on charge-charge interactions contributed by Arg40, Glu39 and Lys108, is important in maintaining the activity of Llaprol. When the loop takes a conformation close to the active site (closed state), Asp36 and His38 at the tip of the loop can be involved in the catalytic reaction of Llaprol. The two active mutant prolidases (D36S and H38S) resulted in modifications of the unique characteristics; the allosteric behaviour was not observed for D36S, and H38S Llaprol showed no substrate inhibition. D36E/R293K, maintaining the negative charge of position 36 and positive charge of position 293, still possessed the allosteric behaviour, whereas the loss of the charges at these positions (D36S of this study and R293S of a previous study (Zhang et al., 2009 BBA-Proteins Proteom 1794, 968-975) eliminated the allosteric behaviour. These results indicated the charge-charge attraction between Asp36 and Arg293 is important for the allostery of Llaprol. In the presence of either zinc or manganese divalent cations as the metal catalytic centre, D36S and H38S enzymes also showed different substrate preferences from WT Llaprol, implying the influence of Asp36 and His38 on the substrate binding. D36S and H38S also showed higher activities at pH 5.0 to 6.0, in which range WT Llaprol steeply decreased its activity, indicating Asp36 and His38 are involved in the active centre and influence the microenvironment of catalytic His296. The above observations are attributed to modifications of their local structure in the active centre since the temperature dependency and thermal denaturing temperature indicated little effects on the overall structure of the Llaprol mutants. From these results, we concluded that the unique behaviours of Llaprol are correlated to Loop32-43 and Asp36 and His38 on it. When Loop32-43 takes a closed conformation, Asp36 interacts with Arg293 via charge-charge attraction to form an allosteric subsite. The saturation of the allosteric site with substrates further allowed the communications of His38 with S1 site residues to complete the active site. When the substrate concentration becomes higher than it is required to saturated productive S1' site, His38, Phe190 and Arg293 would resemble the residue arrangement of S1' site residues (His292, Tyr329, and Arg337) and bind to the proline residue of substrates. This non-productive binding would prevent the conformational change of Loop32-43, which further results in the substrate inhibition. For further confirmation of this mechanism, crystallographic studies will be conducted. In this thesis, we have indentified the conditions to produce crystals of Llaprol proteins

Dynamic response of clamped axially moving beams: Integral transform solution

The generalized integral transform technique (GITT) is employed to obtain a hybrid analytical–numerical solution for dynamic response of clamped axially moving beams. The use of the GITT approach in the analysis of the transverse vibration equation leads to a coupled system of second order differential equations in the dimensionless temporal variable. The resulting transformed ODE system is then solved numerically with automatic global accuracy control by using the subroutine DIVPAG from IMSL Library. Excellent convergence behavior is shown by comparing the vibration displacement of different points along the beam length. Numerical results are presented for different values of axial translation velocity and flexural stiffness. A set of reference results for the transverse vibration displacement of axially moving beam is provided for future co-validation purposes.Indisponível

Dynamic Behavior of Axially Functionally Graded Pipes Conveying Fluid

Dynamic behavior of axially functionally graded (FG) pipes conveying fluid was investigated numerically by using the generalized integral transform technique (GITT). The transverse vibration equation was integral transformed into a coupled system of second-order differential equations in the temporal variable. The Mathematica’s built-in function, NDSolve, was employed to numerically solve the resulting transformed ODE system. Excellent convergence of the proposed eigenfunction expansions was demonstrated for calculating the transverse displacement at various points of axially FG pipes conveying fluid. The proposed approach was verified by comparing the obtained results with the available solutions reported in the literature. Moreover, parametric studies were performed to analyze the effects of Young’s modulus variation, material distribution, and flow velocity on the dynamic behavior of axially FG pipes conveying fluid

Improved lumped models for transient combined convective and radiative cooling of multi-layer composite slabs

Improved lumped parameter models were developed for the transient heat conduction in multi-layer composite slabs subjected to combined convective and radiative cooling. The improved lumped models were obtained through two-point Hermite approximations for integrals. Transient combined convective and radiative cooling of three-layer composite slabs was analyzed to illustrate the applicability of the proposed lumped models, with respect to different values of the Biot numbers, the radiationconduction parameter, the dimensionless thermal contact resistances, the dimensionless thickness, and the dimensionless thermal conductivity. It was shown by comparison with numerical solution of the original distributed parameter model that the higher order lumped model (H1,1/H0,0 approximation) yielded significant improvement of average temperature prediction over the classical lumped model. In addition, the higher order (H1,1/H0,0) model was applied to analyze the transient heat conduction problem of steel-concrete-steel sandwich plates.Indisponível

Dynamic behavior of pipes conveying gas–liquid two-phase flow

In this paper, the dynamic behavior of pipes conveying gas–liquid two-phase flow was analytically and numerically investigated on the basis of the generalized integral transform technique (GITT). The use of the GITT approach in the analysis of the transverse vibration equation lead to a coupled system of second order differential equations in the dimensionless temporal variable. The Mathematica's built-in function, NDSolve, was employed to numerically solve the resulting transformed ODE system. The characteristics of gas–liquid two-phase flow were represented by a slip-ratio factor model that was devised and used for similar problems. Good convergence behavior of the proposed eigenfunction expansions is demonstrated for calculating the transverse displacement at various points of pipes conveying air–water two-phase flow. Parametric studies were performed to analyze the effects of the volumetric gas fraction and the volumetric flow rate on the dynamic behavior of pipes conveying air–water two-phase flow. Besides, the normalized volumetric-flow-rate stability envelope for the dynamic system was obtained.Indisponível

Factors that Undermine International Students’ Decision to Choose China as Work Destination: An Exploratory Study

Recently, China has become one of the top leading destinations in Asia and fifth global host destination for international students from across the globe. Unlike the developed countries, China is not an attractive work destination for those global students graduating from Chinese universities. This study aims to explore the determinants of de-motivation for international students to choose China as work destination. This research  leads  to  expand  the  understanding of  the  various  elements  that  support students’  decision  with  regards  to  choosing  a  study  destination. The questionnaires were distributed personally at international students’ dormitories of various universities in Wuhan to ensure the highest response. The results shows that 64 percent responded that Chinese economy is growing but 74 percent of the respondents mentioned that they do not want to stay for seeking jobs after graduation and 80 percent of the respondents were not to start their own business in China. One of the reasons was that majority of students was legally bound to go back to their countries after graduation as they were on scholarships. Policy suggestions will be directed in the light of these results. This research also, exploring that contribution of growing countries as not only senders, but also recipients of international students. Keywords: de-motivation, international graduates, work destinatio

Exact solution of bending problem of clamped orthotropic rectangular thin plates

The generalized integral transform technique (GITT) is employed to obtain an exact solution for the bending problem of fully clamped orthotropic rectangular thin plates. The use of the GITT approach in the analysis of the transverse deflection equation leads to a coupled system of fourth order differential equations (ODEs) in the dimensionless longitudinal spatial variable. The resulting transformed ODE system is then numerically solved by making use of the subroutine DBVPFD from IMSL Library. Numerical results with automatic global accuracy control are obtained for different values of aspect ratio. Critical comparisons with previously reported numerical results are performed with excellent agreement. A set of reference results for clamped orthotropic rectangular plates is also provided for future covalidation purposes, which are verified by those obtained from the general-purpose finite element software package ABAQUS.Indisponível