Wim Desmet

A large-scale multicentre study of patient skin doses in interventional cardiology: dose–area product action levels and dose reference levels

For 318 patients in 8 different Belgian hospitals, the entire skin-dose distribution was mapped using a grid of 70 thermoluminescence dosimeters per patient, allowing an accurate determination of the maximum skin dose (MSD). Dose-area product (DAP) values, exposure parameters and geometry, together with procedure, patient and cardiologist characteristics, were also registered. Procedures were divided into two groups: diagnostic procedures (coronary angiography) and therapeutic procedures (dilatation, stent, combined procedures (e.g. coronary angiography + dilatation + stent)). The mean value of the MSD was 0.310 Gy for diagnostic and 0.699 Gy for therapeutic procedures. The most critical projection for receiving the MSD is the LAO90 (left anterior oblique) geometry. In 3% of cases, the MSD exceeded the 2 Gy dose threshold for deterministic effects. Action levels in terms of DAP values as the basis for a strategy for follow-up of patients for deterministic radiation skin effects were derived from measured MSD and cumulative DAP values. Two DAP action levels are proposed. A first DAP action level of 125 Gy cm(2) corresponding to the dose threshold of 2 Gy would imply an optional radiopathological follow-up depending on the cardiologists decision. A second DAP action level of 250 Gy cm(2) corresponding to the 3 Gy skin dose would imply a systematic follow-up. Dose reference levels - 71.3 Gy cm(2) for diagnostic and 106.0 Gy cm(2) for therapeutic procedures - were derived from the 75 percentile of the DAP distributions. As a conclusion, we propose that total DAP is registered in patients record file, as it can serve to improve the follow-up of patients for radiation-induced skin injuries.

An experimental procedure for the determination of wake-airfoil interaction noise parameters

Wake-airfoil interaction noise is a concern for many applications such as contra-rotating open rotors, aeroengine rotor-stator interaction and high density wind-farms. In this study we propose a measurement procedure, based on the implementation of low-cost electret microphones flush-mounted on the surface of an airfoil subjected to incoming rotating wakes. This methodology is applied on the characterization of the chord-wise distribution of unsteady pressure jump. This paper demonstrates that the electret microphones can provide high measurement repeatability on a broad range of frequencies and that they can be applied to engineering measurements. The electrets are applied to a rotor-wakeairfoil interaction case, where aerodynamic quantities, e.g. wall-pressure fluctuation and propagation velocity are compared with results from linearized airfoil theory. It is shown that he correct electrets phase calibration allows the computation of the perturbation propagation velocity along the airfoil chord. Correlation levels between the wall pressure jump and the far-field noise are established for different frequencies and regions of the airfoil. The measured wall pressure fluctuations were used as input for Curle’s analogy for far-field noise prediction, and the results were compared with measurements, showing good agreement. Finally, the upstream wake flow velocity was measured by means of hot-wire anemometry and the resulting space-averaged incoming flow velocity fluctuation were used as input for an unsteady panel code. In this case, the predicted wall pressure fluctuation and the far-field noise are compared showing both also good agreement.

A nondestructive method to verify the glenosphere-baseplate assembly in reverse shoulder arthroplasty

BACKGROUNDnGlenoid dissociation is a rare postoperative complication in reverse shoulder arthroplasty that has severe consequences for the patient and requires revision in most cases. A mechanically compromised Morse taper is hypothesized to be the main cause of this complication, with bony impingements and soft tissue interpositioning being cited as the most important problems. Intraoperative assessment of the taper assembly is challenging. Current methods require applying considerable torque to the glenosphere or relying on radiographs.nnnMATERIALS AND METHODSnThis in vitro study demonstrates how the assembly quality can be accurately determined in a nondestructive way by exploiting the implant-specific relation between screw and Morse taper characteristics by measuring the angular rotation-torque curve.nnnRESULTSnThe feasibility of the method is demonstrated on 2 reverse implant models. Several data features that can statistically discriminate between optimal and suboptimal assemblies are proposed.nnnCONCLUSIONnSuboptimal assemblies can be detected using the method presented, which could easily be integrated in the current surgical workflow. Clinical recommendations based on the methods rationale are also presented, allowing detection of the most severe defect cases with surgical instruments currently in use.

Structural Health Monitoring Considerations on Offshore Wind Turbine Models

The growth of wind turbines in terms of power capacity and rotor diameter size has driven the research toward new studies and ideas. Nowadays high potential sites on land have already been taken and offshore locations need to be exploited taking advantage of the stronger wind. In 2009 a 5 MW concept has been proposed by NREL in order to be considered as the reference wind turbine for the next years. In 2013 a new reference model has been introduced by DTU Wind Energy, a 10 MW wind turbine. Both offshore wind turbines have been modeled by using an aeroelastic code and several simulations have been carried on with the main objective of developing advanced health monitoring techniques. As the first step to perform Structural health Monitoring (SHM) is the identification of the most sensitive parameters to structural degradation, advanced data analysis were developed. Methods such as the Multi-Blade Coordinate (MBC) transformation and the Harmonic Power Spectrum (HPS) have been validated and combined with Operational Modal Analysis to identify the modal parameters of the turbine in operational conditions, including sensors on the tower, blades and nacelle. Once the model and analysis techniques have been validated, damages have been introduced by adding lumped masses and by reducing the blades and/or the tower stiffness. Some SHM considerations have been drawn by analyzing the so-called whirling modes. They are due to the rotation of the blades and they can be observed only after that a pre-processing technique has been applied. They have been highlighted because they seem to be very sensitive to the introduction of small damages. doi: 10.12783/SHM2015/350

The Dynamic Behavior Induced by Different Wind Turbine Gearbox Suspension Methods Assessed by Means of the Flexible Multibody Technique

The continuous demand for increase in power output for new wind parks under strict cost constraints, the greater wind resource at elevation and the desire for fewer machines per Mega-Watt to reduce operations resulted in a demand for bigger turbines. The drive train is an important component in realizing reliable and robust wind turbines. This paper investigates a geared wind turbine. In this type a gearbox is used to convert the low rotor speed to the required high generator speed. In the market several solutions are available to constrain the gearbox in the nacelle. The used configuration significantly determines the gearbox response to rotor loads and the transmission of gearbox vibrations to the turbine. This paper investigates the effectiveness of three configurations: the three point mounting, the double bearing configuration and the hydraulic damper system. The flexible multibody modeling technique can be used to accurately characterize gearbox dynamics. The goal of this work is to use an experimentally validated multibody model of a wind turbine drive train to characterize the ability of the three configurations to minimize the introduction of non-torque loads in the gearbox and the ability to isolate the gearbox vibrations from the rest of the turbine.Copyright