The vibration behavior of wind turbine blades (WTB) must be thoroughly investigated to avert undesirable dynamical phenomena under working conditions. This paper sets out an experimental frequency ...analysis of a rotating, scaled-down, segmented WTB. The purpose of the present work is twofold: (1) to devise a suitable experiment for the modal identification of a rotating component, when no rotor-specific test equipment is available, and (2) to validate a recently developed theoretical model for the dynamics of segmented wind turbine blades, through the modal parameters of the test blade identified for a given range of spinning velocity. The 3D fused deposition modeling technology was used to manufacture the blades segments, assembled with a steel threaded shaft and nut. A speed-controlled motor is used to scrutinize the influence of the rotation velocity on the blades modal parameters. To identify the blades modal frequencies and damping ratios, the eigensystem realization algorithm method was implemented. At rest, the blades natural frequencies were adjusted based on the additional assembly stiffness generated by the nut tightening torque. Because the modal identification of rotating components using conventional test equipment is a difficult task, a significant feature in this paper, beyond the obtained results, is the proposed original experimental technique to investigate the flapwise (out-of-plane) dynamical behavior of the rotating blades. The experimental results are compared with previous theoretical results, as a function of the blades spinning velocity, showing the significant influence of the rotation speed on the segmented WTB dynamical behavior, in agreement with the theoretical predictions.
In this paper, numerical and experimental modal analysis of a segmented wind turbine blade assembled with a steel threaded shaft and a nut are presented. The blade segments are built by a 3D printer ...using ABS material. The experimental modal parameters identification has been achieved using the Eigen system Realization Algorithm (ERA) method for different values of the blade segments assembly force caused by the nut tightening torque. Furthermore, a three dimensional finite element model has been built using DTK18 three node triangular shell elements in order to model the blade and the threaded shaft structure, taking into account the additional stiffness caused by the nut tightening torque. This study covers the blade segments assembly force effects on the rotating blade vibration characteristics. The numerical model is adjusted and validated by the identified experimental results. This work highlights the significant variation of the natural frequencies of the segmented wind turbine blade by the assembling load of the segments versus blade rotating speed.
In this paper, a new method for identifying the dynamical parameters of local constraining supports such as mass, stiffness, and damping was developed through combining the measured frequency ...transfer functions and structural modification techniques. Since measurement noise often leads to erroneous identifications, regularization techniques have been implemented to reduce noise amplification in the inverse problem. The developed technique has been validated by numerical tests on a multi-supported flexible structure, which can be seen as an idealized electricity generator rotor shaft. The results are satisfactory for noise-free data as well as under realistic noise levels. The sensitivity of the identified support features to noise levels is asserted through a parametric study
Background Both natural history and treatment outcome of hepatitis B virus (HBV) infection are influenced by genotypes and viral load. Information about factors determining HBV genotype distribution ...and viraemia in HIV/HBV-co-infected patients is scarce. Methods All HIV-positive patients living in Europe and Argentina recruited in EuroSIDA (1994–2006) were tested for serum HBV surface antigen (HBsAg). Chronic carriers were further characterized virologically at one central laboratory. Variables influencing HBV genotype distribution and viraemia were assessed using logistic regression. Results From 16 505 HIV patients enrolled in EuroSIDA, 1179 (7.1%) were HBsAg positive, of whom 474 had specimens that allowed inclusion in the virological substudy. Overall 293 (62%) were treated with anti-HBV active antiretroviral drugs at the time of testing. Hepatitis delta virus superinfection was recognized in 14% and hepatitis C virus (HCV) antibodies in 27%. Serum HBV DNA was detectable in 315 (66.5%) and HBV genotyping gave results in 170 (35.9%) patients. HBV genotype distribution was as follows: A (72.9%), D (17.1%), G (1.8%), E (1.2%), F (1.2%) and C (0.6%); another 5.9% were co-infected with multiple HBV genotypes. In the multivariate analysis, the best predictor of HBV genotype A infection was risk exposure other than intravenous drug use, whereas predictors for detectable HBV viraemia were lower CD4 counts and lack of HCV antibodies. Conclusion A substantial proportion of HIV-positive patients with chronic hepatitis B show detectable HBV viraemia despite being treated with anti-HBV active antiretroviral drugs (mainly lamivudine). Low CD4 counts were associated with an independent higher risk of detectable HBV viraemia, which supports an earlier introduction of antiretroviral therapy, including anti-HBV drug(s) more potent than lamivudine.
Most systems consist on dynamical substructures connected at a number of constraining points. Moreover, constraints often display intermittent contact phenomena, such as arising from clearance ...supports. A significant difficulty when computing time-domain responses is the manner to enforce such coupling constraints. Here, we explore the Udwadia-Kalaba (U-K) formulation, which has been very seldom used in this context. By extending the basic U-K analytical framework, we address continuous flexible subsystems modelled by their unconstrained modes and coupled through the highly nonlinear intermittent point-constraints. For continuous flexible systems, a modal U-K formulation is implemented such that the constraint is applied when contact is detected at the clearance location. A crucial aspect is that constraint violations must be prevented, not only at the acceleration level, but also at the velocity and displacement levels, in order to avoid computational drift. This is achieved through a constraint violation correction method. For single gap-constraints, a convenient formulation is obtained, in which the constraint matrix is pre-computed prior to the simulation time-loop and applied whenever an intermittent contact is detected, leading to an efficient computation of vibro-impact responses. For systems with several intermittent constraints, an essential difficulty within the context of the proposed formulation is that every possible combination of contact/non-contact conditions is expressed by a different constraint matrix. A pragmatic solution is to keep track of the current system contact configuration and rebuild the constraint matrix whenever a change in the constraint state is detected. We formulate and illustrate such computational strategy, as applied to random-excited multi-supported beams with a significant number of clearance supports. Results are compared with dynamical computations performed using a classic penalty technique for enforcing the nonlinear support constraints, emphasizing the viability of the proposed technique for performing predictive analysis of flexible structures with multiple clearance supports.
In view of the large variability on therapeutic response and the multiple factors associated to tamoxifen (TAM) metabolic activation, this study aimed to evaluate the effect of CYP2D6 and CYP3A4 ...phenotypes, drug interactions, and vitamin D exposure on TAM metabolism in a group of breast cancer patients.
Trough blood samples were collected from 116 patients. TAM and metabolites endoxifen (EDF), N-desmethyltamoxifen, and 4-hydroxytamoxifen (HTF) were measured in plasma by liquid chromatography-tandem mass spectrometry. CYP2D6 and CYP3A4 phenotyping were obtained according to dextromethorphan/dextrorphan and omeprazole/omeprazole sulfone metabolic ratios, measured by high-performance liquid chromatography in plasma collected 3 hours after oral administration of 33 mg of dextromethorphan and 20 mg of omeprazole. Vitamin D3 was measured in plasma by high-performance liquid chromatography-ultraviolet. Data on concomitant use of drug considered as CYP2D6 and CYP3A4 inhibitor or inducer and vitamin D supplementation were recorded.
About 20% of patients had reduced CYP2D6 metabolic activity and 7% CYP3A4 impaired metabolism. EDF levels diminished proportionally to the reduction of CYP2D6 metabolic activity (poor metabolizer 2.79 ng·mL, intermediate metabolizer (IM) 5.36 ng·mL, and extensive metabolizer 10.65 ng·mL, P < 0.01). Median plasma levels of TAM (161.50 ng·mL) and HTF (1.32 ng·mL) in CYP2D6 IM/CYP3A4 poor metabolizer patients were higher (P < 0.05) than those from CYP2D6 IM/CYP3A4 extensive metabolizer patients (122.07 ng·mL and 0.61 ng·mL, respectively). Seasons contributed to the interpatient variability of EDF and HTF levels; summer concentrations were 24% and 42% higher compared with winter. Vitamin D3 was not associated to CYP3A4 metabolic activity, indicating that other mechanisms might be involved in the relation between TAM metabolism and vitamin D exposure.
CYP3A4 contributes to the bioactivation of TAM through formation of HTF and becomes increasingly important in case of reduced or absent CYP2D6 activity. EDF and HTF exposure were associated to seasonal variations, with considerable higher plasma concentrations during summer.
Taro Colocasia esculenta (L.) Schott is a root crop which is an important staple food in many regions of the world, producing 10.5 million tonnes on 1.4 million hectares a year. The crop is ...cultivated in wet (rain fed) or irrigated conditions, requiring on average 2,500 mm water per year, and in many countries it is cultivated in flooded plots. It is estimated that taro production could decrease by 40% as a result of the increase in drought and other severe events. In this work, thirty three accessions, including local cultivars, selected and hybrid lines were submitted to long duration drought stress and screened for tolerance. Twelve physiological, morphological and agronomic traits were measured at harvest, and subject to multivariate analysis. Stress indices, Water Use Efficiency and Factorial Analysis were useful for discriminating accessions regarding drought tolerance and yield stability, and drought tolerant and susceptible cultivars were identified. Our results confirm that different taro cultivars have different drought avoidance and tolerance strategies to cope with water scarcity. Better yield performers minimised biomass and canopy loss, while tolerance was observed in cultivars that presented low potential yield, but efficiently transferred resources to enhance corm formation. Among the 33 accessions, two local cultivars showed high yield stability and could be considered as suitable parents for breeding programs, while two others are well adapted to drought, but with overall low yield potential.
For achieving realistic numerical simulations of bowed string instruments, based on physical modeling, a good understanding of the actual friction interaction phenomena is of great importance. Most ...work published in the field including our own has assumed that bow/string frictional forces behave according to the classical Coulomb stick–slip model, with an empirical velocity-dependent sliding friction coefficient. Indeed, the basic self-excited string motions (such as the Helmholtz regime) are well captured using such friction model. However, recent work has shown that the tribological behavior of the bow/string rosin interface is rather complex, therefore the basic velocity-dependent Coulomb model may be an over-simplistic representation of the friction force. More specifically, it was suggested that a more accurate model of the interaction force can be achieved by coupling the system dynamical equations with a thermal model which encapsulates the complex interface phenomena. In spite of the interesting work performed by Askenfelt
32, a direct measurement of the actual dynamical friction forces without disturbing the string motion is quite difficult. Therefore, in this work we develop a modal-based identification technique making use of inverse methods and optimization techniques, which enables the identification of the interface force, as well as the string self-excited motion, from the dynamical reactions measured at the string end supports. The method gives convincing results using simulated data originated from nonlinear computations of a bowed string. Furthermore, in cases where the force identifications are very sensitive to errors in the transfer function modal parameters, we suggest a method to improve the modal frequencies used for the identifications. Preliminary experimental results obtained using a basic bowing device, by which the string is excited with the stick of the bow, are then presented. Our identifications, from the two dynamical string reactions, are consistent as attested by the comparison of the two available versions of the string dynamical motion and of the friction force. Furthermore, the method seems adequate to investigate the interface force for the bowed string.
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