Free Vibrations of Taut Cable with Attached Damper. I: Linear Viscous Damper

Free vibrations of a taut cable with an attached linear viscous damper are investigated in detail using an analytical formulation of the complex eigenvalue problem. This problem is of considerable practical interest in the context of stay-cable vibration suppression in bridges. An expression for the eigenvalues is derived that is independent of the damper coefficient, giving the range of attainable modal damping ratios and corresponding oscillation frequencies in every mode for a given damper location without approximation. This formulation reveals the importance of damper-induced frequency shifts in characterizing the response of the system. New regimes of behavior are observed when these frequency shifts are large, as is the case in higher modes and for damper locations further from the end of the cable. For a damper located sufficiently near the antinode in a given mode, a regime of solutions is identified for which the damping approaches critical as the damper coefficient approaches a critical value. A regime diagram is developed to indicate the type of behavior in each mode for any given damper location.     

Axisymmetric Submerged Intrusion in Stratified Fluid

This paper presents the results of laboratory experiments conducted to study the spreading rates of axisymmetric intrusive gravity currents produced by a constant inflow into a stratified body of water. The experiments were conducted over a wide range of initial parameters. A balance of the forces that drive and retard the flow indicate that the intrusion is characterized by four spreading regimes: (1) the radial jet; (2) the radial momentum flux balanced by the inertia force; (3) the pressure (buoyancy) force balanced by the inertia force; and (4) the pressure force balanced by the interfacial drag (“viscous force”). The experimental results seem to confirm the derived spreading relations. The paper makes three significant contributions. It resolves theoretically and experimentally the existing conflict regarding the proper radial growth of the intrusion in the inertia-buoyancy regime. In addition, it relates the observed transition from the inertia-buoyancy regime to viscous buoyancy regime. It does so using scaling arguments to find the length and time scales for this transition. The paper also gives extensive experimental evidence for the spreading relationships in the inertia-buoyancy and viscous-buoyancy regimes, and it facilitates the determination of the corresponding experimental coefficients.     

Partition of manganese during the proeutectoid ferrite transformation in steel

The late stages of the isothermal proeutectoid ferrite reaction in Fe-C-Mn have been investigated theoretically and experimentally. For the growth of grain-boundary allotriomorphs three temporal regimes must be recognized. In the early regime the grain-size is infinite with respect to the diffusion length of carbon so the growth is parabolic. The middle regime involves the cumulative impingement of the carbon fields from opposite sides of the grains. This regime ends as the carbon activity approaches substantial uniformity through the ferrite and austenite. The final stage involves the extremely slow approach of the manganese towards uniform activity as well. These temporal regimes must be further subdivided into high and low super saturation regions. In the low supersaturation region segregation of manganese must occur at all times, while in the high supersaturation region it must occur significantly only for late times. The growth rates and the diffusion profiles for the third temporal regime have been calculated on a local equilibrium model and compared with the metallographic and microprobe results for alloys within the two regions of supersaturation. The agreement between theory and experiment is in all cases good.     

Localization of plastic flow: spatial vs temporal instabilities

The initiation of unstable plastic deformation associated with dynamic strain ageing in controlled load rate tests has been studied. Experimental measurements on an AlMgSi alloy show the existence of two regimes of instability: temporal and spatial. The initiation of the instability is found to occur by the growth of spatially uniform (temporal) strain rate oscillations. At a larger strain, spatial strain localization is found to develop. The existence of an intermediate regime of purely temporal instability is confirmed by a (linear) stability analysis, taking into account stress triaxiality due to non-uniform deformation. Interaction between adjacent material elements via dislocation cross-slip is also considered. Both effects are shown to cause a delay in the onset of spatial instabilities relative to purely temporal instabilities.     

应力比对J55钢级疲劳裂纹断口形貌的影响

借助疲劳试验机及SEM,研究了应力比对J55钢级疲劳裂纹扩展性能的影响,并对断口形貌进行分析。结果表明:随着应力比增大,进入快速裂纹扩展区的ΔK变小;对于应力比0.1,低Paris区断裂模式为沿晶体学平面发生的穿晶断裂,Paris线性部分为由双滑移机制控制的疲劳条带断裂,高Paris区为疲劳条带断裂和延性静态断裂相结合的断裂模式;应力比为0.3、0.5与应力比为0.1的断裂模式相似;对于应力比0.7,沿晶体学平面发生穿晶断裂模式贯穿整个Paris区。     

Creep deformation properties of creep strength enhanced ferritic steels

Creep deformation properties of creep strength enhanced ferritic steels were investigated. Good linear relationships between creep strain vs. time and creep rate vs. time were observed within a transient stage in a double logarithmic plot. It was appropriately expressed by a power law rather than exponential law, logarithmic law and Blackburn’s equation. With decrease in stress, a magnitude of creep strain at the onset of accelerating creep stage decreased from about 2% in the short-term to less than 1% in the long-term. Life fraction of the time to specific strain of 1% creep strain and 1% total strain, to time to rupture tended to increase with decrease in stress. A time to 1% total strain, that is a parameter for design of high temperature components, was observed in the transient creep stage in the short-term regime, however, it shifted to the accelerating creep stage in the long-term regime. Difference in stress dependence of the minimum creep rate was observed in the high- and low-stress regimes with a boundary condition of 50% of 0.2% offset yield stress. Stress dependence of the minimum creep rate in the high stress regime was equivalent to a strain rate dependence of flow stress observed in tensile test, and a magnitude of stress exponent, n, in the high stress regime decreased with increase in temperature from 20 at 550°C to 10 at 700°C. On the other hand, n value in the low stress regime was about 5, and creep deformation in the low stress regime was considered to be controlled by dislocation climb.     

Radiobiological modeling of combined targeted 131I therapy and total body irradiation for treatment of disseminated tumors of differing radiosensitivity

PURPOSE: A model is presented for calculating combinations of targeted 131I and total body irradiation, followed by bone marrow rescue, in the treatment of tumors of different radiosensitivity. The model is used to evaluate the role of the total body irradiation component in the optimal combination regime as a function of the radiosensitivity of the tumor cells. METHODS AND MATERIALS: A microdosimetric model was used to calculate absorbed dose in small tumors and micrometastases when uniformly targeted by the radionuclide 131I. Cell kill was calculated from absorbed dose using an extended version of the linear quadratic model. The addition of varying total doses of total body irradiation, assuming 2 Gy fractions, was also calculated using the linear quadratic model. The net cell kill from combined modality (targeted 131I and total body irradiation) was computed for varying proportions of the two components, for a range of tumor sizes, restricting the total radiation dose to within tolerance for a full-course TBI regime (approximately 14 Gy total) in all cases. The calculations were repeated for a range of presumed tumor uptakes of the targeting agent and for a range of tumor radiosensitivities, typical of those reported for tumor cells of differing type in culture. Optimal regimes were identified as those predicted to yield a high probable tumor cure rate (evaluated using a Poisson statistical model) for all tumor sizes. RESULTS: The analysis supports earlier model studies which predicted that systemic combination treatment with targeted 131I and total body irradiation would be superior to either component used alone. The intrinsic tumor radiosensitivity is found to be a factor which influences the optimal combination of the 131I and external beam total body irradiation components. The total body irradiation component is greater in optimal regimes treating radio-resistant than radiosensitive tumors. However, an obligatory total body irradiation component is also predicted for more radiosensitive tumors; the analysis suggests that the total body irradiation component should in no circumstances be less than 2 x 2 Gy, whilst practical arguments exist in favor of higher doses. CONCLUSION: Total body irradiation is an obligatory component for effective systemic treatment of disseminated malignant tumors to which 131I can be selectively targeted. Clinical studies applying this strategy to the treatment of neuroblastoma by 131I targeted by meta-iodo-benguanidine (mIBG), total body irradiation and bone marrow rescue are now in progress.     

Application of fuzzy sets and neural network theory to the numerical pattern recognition of bubble flow and jet flow

The injection of gas into a liquid is associated with two characteristic flow regimes: bubble flow and jet flow. In metallurgy, these flow regimes are of interest with respect to refractory lifetime and mass transfer. The flow regimes were investigated in the systems water-air and ethanol-air by monitoring the bottom vibrations of a cold model. The vibrations were analyzed by numerical pattern recognition. The nominal Mach number of 1.1 is the criterion for the transition from bubble flow to jet flow. A numerical pattern recognition system which is able to distinguish between the flow regime below and above the nominal Mach number of 1.1, just by analyzing the vibration signal, is presented. This task can be accomplished in spite of the use of different liquids, nozzle diameters and liquid heights. As a classificator, both a fuzzy k nearest neighbour algorithm and a neural network were employed successfully. Fuzzy logic was found to be especially useful for describing the different flow regimes.     

A load perturbation method of examining dynamic strain ageing

Load perturbation tests carried out on a 6063 AlMgSi alloy under load rate control verify the predictions of a constitutive model proposed earlier to describe the mechanical response in the dynamic strain ageing regime. The verification is based on a comparison of the measurements with the analytical solution of linearized constitutive equations for small perturbations as well as with numerical solutions for the full nonlinear constitutive model. The possibility of using this type of perturbative testing for accurate determination of the onset of plastic instability is discussed.     

The effect of cyanide and lead ions on the cementation rate,stoichiometry and morphology of silver in cementation from cyanide solutions with zinc powder

The cementation of silver on zinc powder from solutions with a wide concentration range of cyanide has been investigated in the absence and presence of lead ions through stirred reactor batch tests and scanning electron microscopy studies on the cementation product. The concentration of cyanide ions affected the morphology of the product, the nature of cementation reaction and the cementation kinetics. Three cyanide-dependent concentration regimes have been identified: a low cyanide concentration regime in which silver cementation followed an ion-exchange type reaction taking place at the zinc/aqueous solution interface, and the silver deposited around the zinc particle in a uniform growth; a high cyanide concentration regime, as in plant practices, in which the cementation of silver followed an overall chemical reaction involving the evolution of hydrogen and a one-to-one molar silver-to-zinc stoichiometry (In this regime, both the anodic oxidation and the cathodic reduction reactions occurred at distinct interfaces and the silver deposited in a dense-branching morphology.), and an intermediate cyanide concentration regime which is a transition between the two previous regimes. In the low and intermediate regimes, lead and cyanide ions did not affect the morphology of the cemented silver, but increased the silver cementation kinetics owing to Zn(OH)₂ instability. Within the high cyanide concentration regime, lead ions did not appreciably change the cementation kinetics. They modified the pattern of the silver deposit from a dense-branching to a dendritic morphology.     

Physical Simulation of New Desulphurization Technology Using Pulsed and Rotary Stirring-Injection

The contrast experiment of different stirring modes,which includes a new type of stirring-injection with the method of pulse and rotation,and the initial one-way stirring method,is done through physical simulation in the laboratory.The stirring methods of pulse and rotation are of two kinds.One is pulsed and rotary stirrer with positive and opposite directions.The other is pulsed and rotary stirrer with rotation-stop-rotation.The results show that the stirring mode of pulse and rotation has better effects than the one-way stirring method.The specific effects are that the mixing time of the melting bath is apparently shortened,the number of grains involved in the liquid surface is increased,and the residence time of air bubble in water is doubled.     

Dorsoventral patterning in the Drosophila retina by wingless

The eye imaginal disc displays dorsal-ventral (D-V) and anterior-posterior polarity prior to the onset of differentiation, which initiates at the intersection of the D-V midline with the posterior margin. As the wave of differentiation progresses anteriorly, additional asymmetry develops as ommatidial clusters rotate coordinately in opposite directions in the dorsal and ventral halves of the disc; this forms a line of mirror-image symmetry, the equator, which coincides with the D-V midline of the disc. How D-V pattern is established and how it relates to ommatidial rotation are unknown. Here we address this question by assaying the expression of various asymmetric markers under conditions that lead to ectopic differentiation, such as removal of patched or wingless function. We find that D-V patterning develops gradually and that wingless plays an important role in setting up this pattern. We show that wingless is necessary and sufficient to induce dorsal expression of the gene mirror prior to the start of differentiation and also to restrict the expression of the WR122 marker to differentiating photoreceptors near the equator. In addition, we find that manipulations in wingless expression shift the D-V axis of the disc as evidenced by changes in the expression domains of asymmetric markers, the position of the site of initiation and the equator, and the pattern of epithelial growth. Thus, Wg appears to coordinately regulate multiple events related to D-V patterning in the developing retina.     

Dynamic Aeroelastic Instabilities of an Aircraft Wing with Underwing Store in Transonic Regime

The research used the transonic small disturbance theory to better understand the dynamic aeroelastic phenomena and factors that affect the onset of flutter and store induced limit-cycle oscillations (LCO) in the transonic regime. Several parametric studies of the flutter and LCO of an aircraft wing with underwing store in the transonic regime were conducted, as well as an investigation of the effect of inclusion of store aerodynamics on the onset of flutter. The flutter sensitivity was analyzed for the following store parameters: (1) location of underwing store center of gravity with respect to aerodynamic root chord; (2) location of underwing store along the span of the wing; and (3) underwing clearance (pylon length). The parametric studies indicated that as the store center of gravity is moved fore of the elastic axis, the flutter velocity of the wing increased. Also, as the store is moved towards the aerodynamic tip chord, the flutter velocity of the wing decreased. The research work also concluded that as the underwing clearance is increased, the flutter velocity of the wing decreased. In addition to these results, it also helped in understanding that addition of store aerodynamics had no significant influence on the flutter velocity of the wing. Also, studies were conducted to identify the onset of LCO for different configurations of underwing store and flight regimes (unmatched analysis), thereby identifying the parameters that induce LCO. The sensitive parameters that affect flutter and LCO are identified.     

Postbuckling of Moderately Thick Imperfect Rings under External Pressure

A fully nonlinear finite-element analysis for postbuckling response of a moderately thick imperfect ring under applied hydrostatic pressure is presented. The fully nonlinear theory employed here, in contrast to the von Karman approximation generally prevalent in the existing literature, for a moderately thick ring does not, on employment of the conventional Love–Kirchhoff hypothesis (originally developed for the small deflection regime), automatically guarantee vanishing of the transverse normal and shear strains in the large deflection regime. A curved six-node element, based on an assumed quadratic displacement field (in the circumferential coordinate), employs a two-dimensional hypothesis, known as linear displacement distribution through thickness theory, to capture the effect of the transverse shear/normal (especially, shear) deformation behavior. Numerical results show that even for a sufficiently thin ring, the conventional nonlinear theory, based on von Karman approximation, produces an error on the order of 10%.     

Sintering behavior and strength properties of stomatological porcelain—Titanium nickelide composite materials

The sintering behavior and strength properties of stomatological porcelain—titanium nickelide composites were investigated. The dependence of porosity, linear and volumetric changes, phase composition and structure on sintering time and temperature, component concentrations, and initial porosity have been determined. It was shown that density changes are the result of a competition between shrinkage and volumetric growth. An optimal regime of sintering to ensure open porosity and high strength is recommended. Siberian Physico-Technical Institute, Tomsk. Translated from Poroshkovaya Metallurgiya, Nos. 7–8(402), pp. 31–36, July–August, 1998.     

Vibration of Tensioned Beams with Intermediate Damper. I: Formulation, Influence of Damper Location

Exact analytical solutions are formulated for free vibrations of tensioned beams with an intermediate viscous damper. The dynamic stiffness method is used in the problem formulation, and characteristic equations are obtained for both clamped and pinned supports. The complex eigenfrequencies form loci in the complex plane that originate at the undamped eigenfrequencies and terminate at the eigenfrequencies of the fully locked system, in which the damper acts as an intermediate pin support. The fully locked eigenfrequencies exhibit “curve veering,” in which adjacent eigenfrequencies approach and then veer apart as the damper passes a node of an undamped mode shape. Consideration of the evolution of the eigenfrequency loci with varying damper location reveals three distinct regimes of behavior, which prevail from the taut-string limit to the case of a beam without tension. The second regime corresponds to damper locations near the first antinode of a given undamped mode shape; in this regime, the loci bend backwards to intersect the imaginary axis, and two distinct nonoscillatory decaying solutions emerge when the damper coefficient exceeds a critical value.     

Analytical Solution of the Burgers Equation for Simulating Translatory Waves in Conveyance Channels

A Burgers equation model (BEM) for simulating translatory waves in conveyance channels is extracted from the Saint-Venant equations for small perturbations in initial uniform flow. The present study improves upon the previous model and presents analytical solutions for the simulation of translatory waves occurring in conveyance channels. The BEM is reduced to the linear diffusion equation using the Cole–Hopf transformation and then solved by means of the Green’s function assuming an infinite domain. The simulation studies performed show that the BEM results are comparable to those of the Saint-Venant equations for small perturbations in the initial uniform flow conditions and for Froude numbers within the subcritical region. The BEM could be useful for flood routing and for simulating release of water from a reservoir into a conveyance channel when the flow perturbation is small.     

Tensile instability in creep damaging solids

Tensile instability in creep damaging bars subject to geometrical and/or material non-uniformities is investigated for the constant load and constant stress tests provided the longwavelength approximation is maintained. The constitutive model employed in the study is valid for the moderate stress-elevated temperature regime which is dominated by completely creep constrained cavity growth. Two definitions of instability are used to study initial rates of imperfection growth and imperfection growth through failure. The first is concerned with the immediate response to a disturbance (stability in the small) while the second is related to a loss of correspondence between increments of perturbed and unperturbed field variables. A linearized stability analysis based on the first definition reveals that, like the pure viscous creep case, the deformation is unstable however, in contrast to viscous creep, the characteristic time for neck growth is much shorter. A nonlinear analysis based on the second definition associates the onset of instability with fracture occurring at a finite area but infinite local section strain. Histories of strain and area differences reveal the tendency for a highly localized neck to form, however this is countered by stability loss (fracture) at a finite area.     

Dose Dependence of Strength After Low-Temperature Irradiation in Metallic Materials

This study intends to review and characterize the low-temperature (<473 K [200 °C]) irradiation-hardening behaviors in metallic materials and to propose new interpretations on the dose dependence of strength, particularly in the prehardening and saturation regimes. The analysis of results of yield stress-dose curves indicate that four dose-dependence regimes exist: the prehardening, main hardening, saturation, and embrittlement regimes. The semilog plots of yield stress vs dose data revealed that the prehardening regime displaying zero hardening or softening was common at least for the alloys with low-dose data available. It was observed that the dose range of the prehardening regime increased with the strength of material, which indicates that slower initiation in irradiation hardening is expected when strength is higher. For the majority of the metallic materials analyzed, it was reconfirmed that the exponent of the power-law hardening function was evaluated to be about 0.5 in the main hardening regime and about 0.1 in the saturation regime. In these positive hardening regimes, the low strength pure metals such as Fe, Ta, Cu, and Zr displayed lower hardening exponents. The minimum dose to the saturation of irradiation hardening was in the range of 0.003 to 0.08 dpa, depending on the category of materials. It was also reaffirmed that there exists a strong relationship between the saturation in irradiation hardening and the occurrence of plastic instability at yield.