Studies on gasketed flange joints under bending with anisotropic Hill plasticity model for gasket

The behavior of a gasketed flange joint under bending loads has been studied by three dimensional finite element analysis (FEA) and experiments. The in-plane and bending stiffness of spiral wound gaskets are considered using anisotropic Hill plasticity material model. The variation in bolt axial force of joints under bending load predicted by the finite element analysis compares well with the experimental results. The contact stress distribution obtained have significant variation in the pattern from the previous material models and consistent with the results of Bouzid [1] regarding flange rotation.     

环形通道内强化传热综合热力性能分析及评价

针对强化换热元件的综合热力性能分析和评价问题，建立了环形通道内强化传热综合能力性能分析方程，并以纵掠针肋套管换热元件强化传热为例介绍了其应用。     

Performance of hot water systems with tanks in series

It is usual to extract hot water from a storage tank, using displacement by cold water from the mains; this causes the temperature of the outgoing hot water to decrease with time. In order to alleviate this undesirable feature a number of tanks in series may be employed. In this communication the effect of number of tanks on the outlet temperature of hot water, has been analytically investigated; it has been assumed that the only heat exchange, taking place in the tanks is on account of flow of water. The considerations in this analysis are similar to those made by Rabinovich and Fert [1] and Rabinovich [2], for a system of tanks in a solar collector loop without any outflow of water. Thus the analysis is best applicable when hot water is extracted at a fast rate, so that the gain or loss of heat by other mechanisms is negligible, compared to that due to the flow of water. The analysis should also be applicable to shallow solar ponds, Sodha et al. [3], and built in storage water heaters, Sodha et al. [4].     

A parametric model for axial and bending stress concentration factors in API drillstring threaded connectors

This paper presents a study of the variation of stress concentration factor in threaded connectors due to application of external axial and bending loads. The study is based on a hybrid modelling technique previously developed to conduct such analysis. The paper considers the case of API threaded connectors used in drill string applications and uses a particular FEA sub-modelling method of calculating stress concentration factors. The method is used to conduct a parametric study on the effect of geometric thread parameters on axial and bending stress concentration factors.     

New results on control of multibody systems which conserve angular momentum

A planar system of rigid bodies interconnected by one degree of freedom rotational joints is considered. This multibody system is referred to as a multilink, and the rigid bodies are referred to as links. The angular momentum of the multilink is conserved but is not necessarily zero. We show that if the number of links is at least four, then periodic joint motions can make the absolute orientation of a specified base link track exactly a specified function of time whose time derivative is periodic. This result on the use of periodic joint motions for orientation tracking extends previous work [15], [20], [22] on using periodic joint motions for rest-to-rest reorientation. It has interesting physical consequences. Specifically, in the case of non-zero angular momentum periodic joint motions can maintain the orientation of the base link constant. In the case of zero angular momentum periodic joint motions can change the orientation of the base link at a specified angular rate. We also demonstrate that if the multilink consists of at least three links, then for any value of the angular momentum joint motions can reorient the multilink arbitrarily over anarbitrary time interval. This result extends similar results in [15] for zero angular momentum and in [20] that apply for nonzero angular momentum but not for an arbitrary time interval. In terms of their control-theoretic aspects, the problems treated in the paper can be viewed as controllability problems for a class of nonlinear control system with time-dependent drift.     

Molecular engineering of Diketopyrrolopyrrole-based photosensitizer for solution processed small molecule bulk heterojunction solar cells

New symmetrical low band-gap small molecule materials, DPP-bis[ter-3HT-TPA] and DPP-bis[ter-3HT] as novel derivatives of Diketopyrrolopyrrole-thiophene with/without triphenylamine (TPA) end group have been synthesized and characterized. And the effects of TPA moiety were investigated. Compared to DPP-bis[ter-3HT], DPP-bis[ter-3HT-TPA] shows red-shifted absorption and significantly higher molar absorption coefficient. And the HOMO level of DPP-bis[ter-3HT-TPA] is elevated than DPP-bis[ter-3HT]. Moreover, DPP-bis[ter-3HT-TPA] exhibited one order higher hole mobility than DPP-bis[ter-3HT], suggesting that TPA contributes to a better hole mobility. The bulk-heterojunction photovoltaic devices with DPP-bis[ter-3HT-TPA] showed better efficiencies than DPP-bis[ter-3HT], showing the best power-conversion efficiency (PCE) of 1.5% (±0.12) under 100 mW/cm² with a short-circuit current (J_sc)=5.73 mA/cm², a fill factor (FF)=0.45, and an open-circuit voltage (V_oc)=0.59 mV.     

冲刷作用下砂土地层中桩的侧向力学性质分析

  [目的]  冲刷是在水流以及波浪作用下土体流失的一个过程,它通常发生在桥梁、港口码头、以及海岸平台等结构的基础周围,造成基础的承载力下降,危及上部结构的安全。目前在分析桩的侧向力学行为时,只考虑了冲刷深度对桩的侧向承载力的影响,而忽略了冲刷形成的冲刷孔的影响。事实上,冲刷孔的几何形状不仅包括冲刷深度、还包括了冲刷孔的宽度以及冲刷孔的坡度。目前,工程设计中广泛采用的侧向桩分析方法,即p-y曲线方法无法考虑冲刷孔三维几何形状对桩的侧向力学性质的影响。  [方法]  针对这个问题,文章提出了一种修正的p-y曲线方法以用于分析砂土地层中桩在冲刷作用下的侧向力学响应。  [结果]  该方法改进了基于锲形体破坏模型的Reese p-y曲线法,从而能考虑冲刷孔三维几何形状的影响。将计算得到的结果与三维有限差分数值分析的结果进行了比较,验证该修正方法的可靠性。  [结论]  计算结果表明:在冲刷孔的几何形状参数里,冲刷深度对桩的侧向力学性质的影响最大,其次是冲刷孔的宽度与坡度。忽略冲刷孔几何形状的影响,桩在地面位置的侧向位移会增加49%～68%。     

Emission characteristics and heat release rate surrogates for ammonia premixed laminar flames

Ammonia is a carbon-free fuel that has the potential to meet increasing energy demand and to reduce CO₂ emissions. In the present work, the characteristics of pollutant emissions in ammonia premixed laminar flames are investigated using one-dimensional simulations, and heat release rate (HRR) surrogates for ammonia combustion are proposed. Both atmospheric and high-pressure conditions were considered, and four representative mechanisms for ammonia combustion were employed. It is shown that the total emission of NO and NH₃ achieves a minimum around an equivalence ratio (?) of 1.1 under atmospheric conditions, and there is no noticeable emission of NO and NH₃ for ? = 1.1 ~ 1.5 under high-pressure conditions. Three HRR surrogates, [NH₃][OH], [NH₂][O], and [NH₂][H], were proposed based on the analysis of HRR and elementary reaction profiles. The performance of HRR surrogates was found to vary with equivalence ratios. For example, with the Miller mechanism, [NH₃][OH], [NH₂][O], and [NH₂][H] have the best performance under atmospheric conditions at ? = 1.15, 0.95 and 1.05, respectively, and under high-pressure conditions at ? = 1.11, 0.87 and 0.96, respectively. Similar conclusions can also be drawn with other mechanisms. These findings provide valuable insights into emission control and flame identification of ammonia combustion.     

Validation of a three-dimensional viscous–inviscid interactive solver for wind turbine rotors

MIRAS is a newly developed computational model that predicts the aerodynamic behavior of wind turbine blades and wakes subject to unsteady motions and viscous effects. The model is based on a three-dimensional panel method using a surface distribution of quadrilateral singularities with a Neumann no penetration condition. Viscous effects inside the boundary layer are taken into account through the coupling with the quasi-3D integral boundary layer solver Q³UIC. A free-wake model is employed to simulate the vorticity released by the blades in the wake. In this paper the new code is validated against measurements and/or CFD simulations for five wind turbine rotors, including three experimental model rotors [20–22], the 2.5 MW NM80 machine [23] and the NREL 5 MW virtual rotor [24]. Such a broad set of operational conditions and rotor sizes constitutes a very challenging validation matrix, with Reynolds numbers ranging from 5.0⋅10⁴ to 1.2⋅10⁷.     

Pinch locations at heat capacity flow-rate disturbances of streams for minimum utility cost heat exchanger networks

The work deals with heat exchanger network (HEN) targeting under heat capacity flow-rates of streams disturbances. In particular, the aim is to calculate all pinches that can exist in a HEN with utilities of minimum cost when stream heat capacity flow-rates (CPs) are allowed to change within given ranges. It is assumed that the disturbances are stochastic. The knowledge of pinches at certain as well uncertain data is of great importance in designing HENs. For instance, Pinch Technology is based on pinch phenomenon and its influence on HEN operation and design. In case of parameter disturbances, this is even more important since additional application in HEN’s control (see e.g. [1], [2]). It is worthnoting that in case of disturbances, pinches behave in very complex manner as it was shown in [1], [2], [3], [4], [5]. A rigorous approach has been developed for calculating all feasible locations of pinches that can occur in minimum utility cost of HENs operating at varying heat capacity flow-rates of process streams. The method is based on recursive solution of mixed-integer linear programming (MILP) optimisation model that requires quite moderate number of binary variables. Examples of method application and analysis of results are presented in the work.     

Numerical study of experimental feasible heat release rate markers for NH3–H2-air premixed flames

Ammonia (NH₃) and hydrogen (H₂) as carbon-free fuels have attracted much attention for combustion applications in recent years. Co-firing ammonia with hydrogen provides a solution to overcome the extremes in the reactivities of both pure ammonia and hydrogen fuels. Heat release rate (HRR) is one of the most important quantities in the study of turbulent combustion, but direct measurement of local HRR is not experimentally feasible. In this study, we explored several quantities, [NH], [O], and the gradient of [OH] (Grad [OH]) as potential experimentally feasible HRR markers for NH₃–H₂-air premixed flames using numerical simulations. The performance of these quantities over a wide range of equivalence ratios and H₂ blending ratios have been examined, and some key reactions have been identified to explain the corresponding variations of the correlation for [NH] and [O]. It is concluded that the [NH] and Grad [OH] can be used in general as a suitable HRR marker for NH₃–H₂-air premixed flames, and the use of [NH] is especially recommended for lean flame conditions. A strategy that slightly shifts the [NH] and Grad [OH] profiles to overlap the corresponding HRR shows a further improvement on the performance of [NH] and Grad [OH]. The use of [O] can be considered for rich flame conditions while cautions are needed for conditions with high H₂ blending ratios.     

Derivation of ‘γ’ parameter from limit load expression of cracked component to evaluate J–R curve

Experimental evaluation of the J-integral requires the ‘η_pl’ function, proposed by Rice et al. [Progress in flaw growth and fracture toughness testing (1973) 231], to multiply the area under the load vs. plastic load-line-displacement curve. However, the J-integral, thus evaluated, requires modification if crack growth occurs. A ‘γ’ term was proposed by Hutchinson and Paris [Elastic–plastic fracture (1979) 37] and later generalised by Ernst et al. [Fracture mechanics (1979) 581] and Ernst and Paris [Techniques of analysis of load–displacement records by J-integral methods (1980)] to correct the J-integral to account for crack growth. The η_pl and γ functions are available for very few geometries under specific loading conditions. A limit load-based general expression of η_pl was given by Roos et al. [Int J Pres Ves Piping 23 (1986) 81], but no such expression is available for γ functions. The advantage of having limit load-based general expressions for η_pl and γ functions is that the limit load for a particular geometry subjected to a specific loading condition is easily available in the open literature. In the present paper, a limit load-based general expression for the γ function is derived. The general expression is then validated by deriving the known γ functions of various geometries subjected to various loading conditions, which are available in the open literature. The general expressions are then used to derive new η_pl and γ functions for same pipe and elbow geometries with various crack configurations under different loading conditions, for which no solutions are available in the open literature. Finally, experiments have been carried out on 200 mm nominal bore (NB) elbows with throughwall circumferential cracks under in-plane bending moment. The proposed new expressions of η_pl and γ functions for this geometry are used to obtain the J–R curve from the experimental load vs. load-line-displacement and load vs. crack growth data.     

Redox state-dependent changes in the crystal structure of [NiFeSe] hydrogenase from Desulfovibrio vulgaris Hildenborough

Hydrogenases are enzymes that can potentially be used in bioelectrical devices or for biological hydrogen production, the most studied of which are the [NiFe] type. Most [NiFe] hydrogenases are inactivated by oxygen and the few known O₂-tolerant enzymes are hydrogen-uptake enzymes, unsuitable for hydrogen production, due to strong product inhibition. In contrast, the [NiFeSe] hydrogenases, where a selenocysteine is bound to the nickel, are very attractive alternatives because of their high hydrogen production activity and fast reactivation after O₂ exposure. Here we report five high-resolution crystallographic 3D structures of the soluble form of the [NiFeSe] hydrogenase from Desulfovibrio vulgaris Hildenborough in three different redox states (oxidized as-isolated, H₂-reduced and air re-oxidized), which revealed the structural changes that take place at the active site during enzyme reduction and re-oxidation. The results provide new insights into the pathways of O₂ inactivation in [NiFe], and in particular [NiFeSe], hydrogenases. In addition, they suggest that different enzymes may display different oxidized states upon exposure to O₂, which are probably determined by the protein structure.     

Two-photon laser-induced fluorescence measurement of CO in turbulent non-premixed bluff body flames

Detailed measurements of reactive and passive scalars in axisymmetric bluff-body flames of CH₄/H₂, CH₄/air, and CO/H₂ have been reported in the past [1] and have been used in several studies directed at developing and validating turbulent combustion models [2], [3], [4], [5]. Comparisons of measured and modeled results for flames with CH₄/H₂ as fuel have shown significant disagreement in the mass fractions of CO, with the Raman scattering measurements of [CO] being much higher than the modeling calculations. Previously published data [1] were collected using the Raman scattering technique for all major species including CO. Raman scattering measurements of [CO] in methane flames suffer from laser-excited interference from higher hydrocarbons formed on the fuel-rich side of the reaction zone. It is well established [6], [7], [8] that measurements of [CO] based on two-photon laser-induced fluorescence (TPLIF) can provide much better accuracy than those based on Raman scattering in methane and natural gas flames.Keywords: Bluff body; CO; LIF; Raman; Flame     

海上风电钢管桩水平承载力计算方法研究

  [目的]  p-y曲线法在计算钢管桩水平位移时的桩身受力状态有明显优势。  [方法]  开发了一套新的p-y曲线自动提取程序,根据提取的剪力用三次样条曲线进行拟合,然后一次求导得到p。  [结果]  研究表明:该方法提高计算精度的同时,降低了使用者的经验要求,方便工程推广使用。  [结论]  针对桂山海上风电场项目的大直径单桩基础现场试桩结果进行三维有限元分析,验证了该提取方法在桩土相互作用分析中的可靠性。     

The determination of JIC for polyethylene pipe using non-standard arc-shaped specimen

In this paper, a test method for polyethylene pipe material is given. The feasibility of this test method using a non-standard specimen design is verified by three-point bending. Moreover, using three kinds of non-standard arc-shaped specimens, the J_IC values of polyethylene pipe material are calculated employing finite element analysis and experimental method. It is shown that the test method proposed is feasible for testing polyethylene pipe material using non-standard arc-shaped specimens and non-standard arc-shaped tension specimens with X/W=0.5, however, tests with non-standard arc-shaped tension specimens with X/W=0 appear to produce unreliable results compared to the other two non-standard specimens.     

Yield load solutions of heterogeneous welded joints

The aim of this paper is to establish yield load solutions when the materials inhomogeneity within the weld is present, which is usually the case in repair welding. The effect of yield strength mismatch of welded joints performed with different geometry on the yield load value has been investigated in the context of single edge notched fracture toughness specimen subjected to bending SE(B) using the finite element method. The crack was located in the center of the weld and the two most important geometrical parameters were identified as: crack length ratio a/W as well as slenderness of the welded joint, which were systematically varied. One practical and four additional combinations of filler materials, with the same portion of overmatched part and undermatched part of the weld, were analyzed, and plane strain FE solutions for the case when the crack is located in the overmatched half of the heterogeneous weld were obtained.     

A simple method for pulse-echo thermal wave imaging of arbitrary-shaped subsurface scatterers in heterogeneous materials

We present a simple, general and computationally fast numerical method for pulse-echo thermal wave imaging of arbitrary-shaped subsurface scatterers in heterogeneous materials. In this method, the thermal wave theory is employed to determine the initial temperature distribution inside the materials shortly after pulse-heat is applied. Then a technique, Effective Parameters for Interfacial Cells (EPIC), developed in connection with heat conduction [1–3], electrostatics [4–5] and incompressible fluid flow [6], is extended to allow calculation of transient surface temperature distribution. The method is simpler and computationally faster than other numerical methods. We present representative results which could be used for non-destructive testing of subsurface defects.     

Relation of opposed flow (creeping) flame spread with extinction/ignition

Zheng, Wichman, and Benard [1] provided the motivation for addressing and revisiting modeling issues in opposed flow (creeping) flame spread over melting materials. Their approach is compared here with an earlier one [2], [3], [4] and [5]. Specifically, the theoretical underpinnings of flame-spread are discussed in relation to analytical and similarity interpretation of numerical results and experiments. The focus is on the significance and selection of the forward thermal length in the solid and on the most appropriate energy balance near the flame front for deducing material properties from experiments. Finally, (a) an expression for the speed of flame spread in opposed flow over melting materials obtained from the present analysis is compared with previous analytical results in [1] and (b) a fresh look at the critical conditions for flame spread is presented.     

Evaluating the level and nature of sustainable development for a geothermal power plant

The paper provides for an evaluation of the potential level and nature of sustainable development of the Sabalan geothermal power plant in NW Iran, to be operational in 2011. The paper achieves this by applying a mathematical model of sustainable development developed by the author (re: Phillips [17], [18]), in respect to the Environmental Impact Assessment (EIA) conducted by Yousefi et al. [13] using the Rapid Impact Assessment Matrix (RIAM) methodology (re: Pastakia [15]; Pastakia and Jensen [16]). Using a model application methodology developed for the RIAM, the results indicated that the nature of sustainable development for Sabalan was considered to be very weak (S = 0.063). This was due to the imbalance between negative environmental impacts and positive socio-economic impacts deriving from the project. Further, when placed into context with a similar set of results obtained from the EIA of the Tuzla geothermal power plant by Baba [35] also using the RIAM methodology, then the similarities between the results obtained raises some legimate questions as to the sustainable development credentials of geothermal power production.