Real-life experiences with flow-induced vibration

A number of occurrences of flow-induced vibration in the power-generating industry are presented, many in nuclear plant where all incidents/problems have to be reported. Specifically, cases of (i) vortex-induced vibration (VIV), (ii) fluidelastic instability in cylinder arrays, (iii) axial and (iv) annular-flow-induced vibration, (v) leakage-flow instability and (vi) shell-type ovalling are discussed. For items (ii), (v) and (vi), a few words on the mechanisms underlying the vibration are provided.     

On the boundedness and the stability properties of solution of certain fourth order differential equations

This paper investigates equation(1)in two cases:(i)P≡0,(ii)P(≠O)satisfies|P(t,x,y,z,ω)|≤(A |y| |z| |ω|)q(t),where q(t)is a nonnegative function of t.For case(i)the asymptotic stability in the large of the trivial solution x=0 is investigatedand for case(ii)the boundedness result is obtained for solutions of equation(1).Theseresults improve and include several well-known results.     

Mixing state of individual carbonaceous particles during a severe haze episode in January 2013, Nanjing,China

Chemical composition, hourly counts, and sizes of atmospheric carbonaceous particles were measured to investigate their mixing state on clear and hazy days. 623,122 carbonaceous particles with sizes 0.2–2.0 μm was analyzed using a single-particle aerosol mass spectrometer from 1st to 17th January 2013. Particle types included biomass/biofuel burning particles (biomass), element carbon (EC-dominant) particles that were also mixed with biomass/biofuel burning species (EC-biomass) or secondary species (EC-secondary), organic carbon (OC), internally mixed OC and EC (OCEC), ammonium-containing (ammonium) and sodium-containing (sodium) particles. On clear days the top ranked carbonaceous particle types were biomass (48.2%), EC-biomass (15.7%), OCEC (11.1%), and sodium (9.6%), while on hazy days they were biomass (37.3%), EC-biomass (17.6%), EC-secondary (16.6%), and sodium (12.7%). The fractions of EC-secondary, ammonium (10%), and sodium particle types were elevated on hazy days. Numbers of EC-secondary particles were more than four times those on clear days (4.1%). Thus, carbonaceous particles mixed with ammonium, nitrate and sulfate during aging and transport, enhancing their light extinction effects and hygroscopic growth under high relative humidity on hazy days, further reducing visibility. Our real-time single-particle data showed that changes to mixing state had a significant impact on light extinction during haze events in Nanjing.     

Vapour-diffusion assisted growth of oriented or-cobalt hydroxide thin films

Layered ,α-cobalt hydroxides Co(OH) 1.65Cl0.35.0.5H2O (1), Co(OH) 1.75(NO3)0.25.0.1H2O (2) with unique macro- and microscale morphologies have been synthesised by a low temperature, ammonia-controlled vapour-diffusion method. The materials have thin film morphologies and were characterized by X-ray powder diffraction (XRD) and field emission scanning electron microscopy (FESEM).     

(Q)SAR modelling of nanomaterial toxicity: A critical review

There is increasing recognition that some nanomaterials may pose a risk to human health and the environment. Moreover, the industrial use of the novel engineered nanomaterials (ENMs) increases at a higher rate than data generation for hazard assessment; consequently, many of them remain untested. The large number of nanomaterials and their variants (e.g., different sizes and coatings) requiring testing and the ethical pressure towards nonanimal testing means that in a first instance, expensive animal bioassays are precluded, and the use of (quantitative) structure–activity relationships ((Q)SARs) models as an alternative source of (screening) hazard information should be explored. (Q)SAR modelling can be applied to contribute towards filling important knowledge gaps by making best use of existing data, prioritizing the physicochemical parameters driving toxicity, and providing practical solutions for the risk assessment problems caused by the diversity of ENMs. This paper covers the core components required for successful application of (Q)SAR methods to ENM toxicity prediction, summarizes the published nano-(Q)SAR studies, and outlines the challenges ahead for nano-(Q)SAR modelling. It provides a critical review of (1) the present availability of ENM characterization/toxicity data, (2) the characterization of nanostructures that meet the requirements for (Q)SAR analysis, (3) published nano-(Q)SAR studies and their limitations, (4) in silico tools for (Q)SAR screening of nanotoxicity, and (5) prospective directions for the development of nano-(Q)SAR models.     

A review: Acoustic emission,a tool for composite-materials studies

The technique of acoustic emission has two broad applications areas. The first is nondestructive evaluation. The second is as a tool in studies or research which are not fundamentally directed towards acoustic emission. It is this second application with which we are concerned here. Acoustic emission is a very useful tool in this role because of its high sensitivity, real-time capability, volume-monitoring approach, and sensitivity to any process or mechanism which generates sound waves. This paper presents a comprehensive review of areas where acoustic emission (AE) has been used for materials studies on composite materials. The following fields, among others, will be covered: (1) time-dependent composite properties, (2) impact studies, (3) correlation of AE with stress level, (4) application to matrix cure studies, (5) relationship of AE-detected damage to other measures of damage, (6) studies of the effects of matrix material, (7) application to differences in second phase, (8) interface studies, (9) AE and dimensional stability, (10) AE applied to orientation studies, and (11) environmental effects. This review will emphasize the roles that AE can play as a tool for the materials scientist: (1) discovery of damage mechanisms, (2) characterization of damage progression with increasing time or stress, (3) optimization of fabrication variables, and (4) reduction in the numbers of test specimens required in various studies.     

Scaling mixing during miscible displacement in heterogeneous porous media

This paper discusses scaling of mixing during miscible flow in heterogeneous porous media. In large field systems dispersivity appears to depend on system length due to heterogeneities. Three types of scaling are discussed to investigate the heterogeneous effects. Dimensional analysis of mixing during flow through geometerically scaled heterogeneous models is illustrated using measured dispersion. Fractal analysis of mixing in statistically scaled heterogeneous porous media is discussed. Analog scaling of pressure transients in heterogeneous porous media is suggested as an in-situ method of estimating dispersion.Notation L Length - M mass - t time, (1) indicates dimensionless - a dispersivity (L) - V local velocity (L/t) - c concentration (l). - v velocity (L/t) - C₁ fluid compressibility (Lt²/M) - v time averaged velocity (LJt) - D dispersion VA) - W width (L) - D fractional dimension (1) - x coordinate (L) - d Euclidean dimension (1) - Y Y=In \-k (l) - \-d average particle size (L) - y coordinate (L) - g acceleration due to gravity (L/t2) - _c fractal cutoff (L) - \-k average permeability (L2) - viscosity (LM/t) - L length (L) - porosity (1) - L correlation scale (1/L) - density (N/L³) - N Number of sites (l) - ² variance (dimension depends on variable) - p pressure (W/t²L) - spectral exponent (l) - [R] randomnumber (1) - r radius (L) - t time (t)     

Synthesis of submicron-sized composite particles with unique morphology by emulsifier-free seeded emulsion copolymerization

Polystyrene （PSt） microspheres with diameter of 375 nm to be used as the seeds for seeded emulsion polymerization were prepared via emulsion polymerization using potassium persulfate （KPS） as initiator in ethanol-water mixed solvents. Emulsifier-free seeded emulsion copolymerization of styrene （St） with acrylonitrile （AN） was carried out in the presence of poly（ethylene glycol） monomethoxymonomethacrylate （PEGm） macromonomer as reactive stabilizer and 2,2＇-azobisisobutyronitrile （AIBN） as initiator to obtain submicron-sized PEGm graft poly（styrene-coacrylonitrile） （PEGm-g-PSAN） composite particles with unique morphology. Scanning electron microscopy （SEM） indicated that St and AN together contributed to forming the unusual morphology. The concentration of St and AN, total monomer concentration, initiator type and the monomer adding method remarkably affected the morphology of the composite polymer particles.     

RDX/TNT、HMX/TNT炸药Dn(κ)关系研究

研究了不同配比HMX/TNT炸药的Dn()关系,并与不同配比RDX/TNT 炸药的Dn()关系进 行了对比。结果表明,配比相同时HMX/TNT炸药Dn()关系曲线总是在RDX/TNT炸药Dn()关系曲线 上方;RDX/TNT和HMX/TNT炸药的Dn()关系曲线随着炸药中TNT含量增加而下移。引入变量Rt 分 别将两种混合炸药的Dn()关系推广为Dn(,Rt)关系,给定变量Rt 就可以通过Dn(,Rt)关系得出相应未标 定的Dn()关系,Dn(,Rt)关系不仅可以减少实验标定次数,并且能满足DSD方法计算精度要求。     

Extension and characterization of pressure-sensitive molecular film

Pressure-sensitive paint (PSP) has the potential as a diagnostic tool for pressure measurement in high Knudsen number regime because it works as a so-called “molecular sensor”. However, there are few reports concerning application of PSP to micro-devices, because conventional PSPs are too thick owing to polymer binders. In our previous work, we adopted the Langmuir–Blodgett (LB) technique to fabricate the pressure-sensitive molecular film (PSMF) using Pd(II) Mesoporphyrin IX (PdMP), which has pressure sensitivity only in the low pressure range (below 130 Pa). In this study, aiming for pressure measurement under an atmospheric pressure condition, we have constructed four samples of PSMFs composed of Pt(II) Mesoporphyrin IX (PtMP), Pt(II) Mesoporphyrin IX dimethylester (PtMPDME), Pt(II) Protoporphyrin IX (PtPP) and Cu(II) Mesoporphyrin IX dimethylester (CuMPDME) as luminescent molecules. The pressure sensitivity of those PSMFs was measured, and it was clarified that the pressure sensitivity of PSMF-PtMP is the highest among the four samples. Moreover, the temperature dependency of PSMF-PtMP was investigated, and we found that the temperature dependency of PSMF is dominated not by the oxygen diffusion in the layer, but by non-radiative deactivation process of excited luminescent molecules.     

粘性土(红土)中游离氧化铁含量对其工程地质性质的影响

通过试验, 本文就游离氧化铁在粘性土尤其是红土中富积含量的变化对土体工程地质性质产生的影响及其规律性做了初步研究。     

超细氧化铁对TNT炸药爆热的影响

利用均匀沉淀法制备得到纳米级氧化铁,研究了不同粒度的氧化铁颗粒对TNT炸药爆热的影响。结果表明:随着氧化铁颗粒度的减小,它与TNT组成的混合炸药的爆热得到有效的提高。     

Hydrothermal synthesis of star-like and dendritic PbS nanoparticles from new precursors

Lead sulfide (PbS) nanostructures with different morphologies and particle sizes were obtained via a simple hydrothermal reaction between lead (II) salicylate (Pb(Hsal)₂) and thiourea (tu). Reaction products were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet-visible (UV–vis) and Fourier transform infrared (FT-IR) spectroscopy. Morphology of the product, varying from star-like to dendritic, depends on the mole ratio of tu to (Pb(Hsal)₂), pH, and reaction time.     

Nonlinear oscillations and boundary value problems for Hamiltonian systems

We prove the existence of solutions of various boundary-value problems for nonautonomous Hamiltonian systems with forcing terms $$\begin{gathered} \dot x(t) = H'_p (t, x(t), p(t)) + g(t), \hfill \\ \dot p(t) = - H'_x (t, x(t), p(t)) - f(t). \hfill \\ \end{gathered} $$ Among these problems is the existence of T-periodic solutions, namely those satisfying x(t+T)=x(t) and p(t+T)+p(t). A special study is made of the classical case, where H(x, p)=1/2 |p|²+V(x). In the case of parametric oscillations, where (f, g)=(0, 0) and t ? H(t, x, p) is T-periodic, we give a lower bound for the true (minimal) period of the T-periodic solution (x, p) produced by our method, and we prove the existence of an infinite number of subharmonics.     

An inverse heat conduction problem of estimating boundary fluxes in an irregular domain with conjugate gradient method

A Boundary Element Method (BEM)-based inverse algorithm utilizing the iterative regularization method, i.e. the Conjugate Gradient Method (CGM), is used to solve the Inverse Heat Conduction Problem (IHCP) of estimating the unknown transient boundary heat flux in a multi-dimensional domain with arbitrary geometry. Results show that the advantages of applying the CGM in the inverse calculations lie in that the major difficulties in (i) choosing a suitable quadratic norm, (ii) determining a proper regularization order and (iii) determining the optimal smoothing (or regularization) coefficient in the conventional Regularization Method (RM) are avoided. Received on 27 October 1997     

A Parallel 3D Unsteady Flow Analysis in an Asymmetrically Constricted Vessel

In this study, parallel computation of unsteady incompressible flow in an asymmetrically constricted 3D vessel has been presented. A time accurate cell centered finite volume method (FVM) in conjunction with pseudo-compressibility technique and Roe's flux difference splitting of nonlinear terms has been employed for solving the Navier-Stokes (NS) equations on the multiple instruction multiple data (MIMD) machine VPP700. The influence of Reynolds' number ( Re ) and the Strouhal number ( St ) on flow dynamic factors like wall pressure (WP), wall shear stress (WSS), central axis velocity (CAV), etc., have been analyzed. Three-dimensional (3D) features in the formation and detachment of separation zones, which are sensitive to both Re and St have been noticed on the diverging wall of the constriction.     

Synthesis of submicron-sized composite particles with unique morphology by emulsifier-free seeded emulsion copolymerization

Polystyrene (PSt) microspheres with diameter of 375 nm to be used as the seeds for seeded emulsion polymerization were prepared via emulsion polymerization using potassium persulfate (KPS) as initiator in ethanol-water mixed solvents.Emulsifier-free seeded emulsion copolymerization of styrene (St) with acrylonitrile (AN) was carried out in the presence of poly(ethylene glycol) monomethoxymonomethacrylate (PEGm)macromonomer as reactive stabilizer and 2,2'-azobisisobutyronitrile (AIBN) as initiator to obtain submicron-sized PEGm graft poly(styrene-co-acrylonitrile) (PEGm-g-PSAN) composite particles with unique morphology.Scanning electron microscopy (SEM) indicated that St and AN together contributed to forming the unusual morphology.The concentration of St and AN,total monomer concentration,initiator type and the monomer adding method remarkably affected the morphology of the composite polymer particles.     

流变学研究的若干问题

本文综述了1988年8月第10届国际流变学会议部分大会邀请报告及分组报告的下列几个领域内容:①分子动力学;②光学流变测量;⑧血液的动态测量;④数值仿真;⑤钻探油井;⑥强化采油;⑦减阻;⑧聚合物挤压成形加工;⑨食品流变学.     

A uniform high-order method for a singular perturbation problem in conservative form

A uniform high order method is presented for the numerical solution of a singular perturbation problem in conservative form. We firest replace the original second-order problem (1.1) by two equivalent first-order problems (1.4), i.e., the solution of (1.1) is a linear combination of the solutions of (1.4). Then we derive a uniformly O(h~m+1)accurate scheme for the first-order problems (1.4), where m is an arbitrary nonnegative integer, so we can get a uniformly O(h~m+1) accurate solution of the original problem (1.1) by relation (1.3). Some illustrative numerical results are also given.     

Elastoplastische Stoffgleichungen für trockenen Sand

Übersicht Es werden inkrementelle Stoffgleichungen für trockenen Sand unter Berücksichtigung der Bezugsinvarianz (J 1), der Koordinateninvarianz (J 2) und der Einheiteninvarianz (J 3) entwickelt. Dabei sind die acht folgenden Stoffannahmen zugrundegelegt worden: Es liegt ein sogenannter einfacher Stoff vor (A 1), das Stoffunktional ist geschwindigkeitsunabhängig (A 2), das Stoffunktional ist stetig (A 3), die Fließgrenze hängt homogen von den Spannungen ab (A 4), im elastischen Bereich gilt das Hookesche Gesetz (A 5), die Fließregel hängt homogen von den Spannungen ab (A 6), durch Deformationszyklen kann einer Probe keine Energie entzogen werden (A 7), die Cauchy-Spannungen sind Zustandsparameter (A 8).Explizite Ausdrücke werden für isotropes Material angegeben und mit (z. T. eigenen) Versuchsergebnissen verglichen. Die Fließgrenze ist ein konvexer Kegel, der weder Kreisnoch Sechseckquerschnitt aufweist. Die Fließregel genügt nur für die deviatorischen Komponenten einer Normalitätsbedingung, während für die Volumenänderungen eine Dilatanzfunktion eingeführt wird. Je nach Dichte findet bei Gestaltänderung Kontraktion bzw. Expansion und plastische Verfestigung bzw. Entfestigung statt. Abschließend wird ein theoretisches Modell zur Erfassung anisotroper Zustände im Sand entwickelt.

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Summary Incremental constitutive equations for dry sand satisfying the frame invariance (J 1), the coordinate invariance (J 2) and the unit invariance (J 3) are developed from the following constitutive assumptions: sand is a simple material (A 1), the constitutive functional is velocity independent (A 2), the constitutive functional is continuous (A 3), the flow condition is a homogeneous function of stress (A 4), within the elastic range Hooke's law holds (A 5), the flow rule is a homogeneous function of stress (A 6), it is impossible to drag energy from a sample by cyclic deformation (A 7), the Cauchy stresses are state parameters (A 8).Explicit expressions are given for isotropic material and compared with (partly new) test results. The flow condition is a convex cone, being neither hexagonal nor circular. The flow rule satisfies a normality condition for the deviatoric components, whereas a dilatancy function is introduced for volume changes. Depending on density deformation is accompanied by contraction and plastic hardening or expansion and softening, respectively. Finally, a theoretical model for anisotropic states in sand is proposed.

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Gekürzte Fassung einer von der Fakultät für Bauingenieur- und Vermessungswesen der Universität (TH) Karlsruhe genehmigten Habilitationsschrift.