Analysis Of Reflected Wave Research Articles

Non-invasive Determination of Aortic Mechanical Properties and Their Effects on Left Ventricular Function Following Endovascular Abdominal Aneurysm Repair

BackgroundIncreased pulse-wave velocity (PWV) entails elevated arterial stiffness and is associated with adverse cardiovascular outcomes. Previous studies have shown PWV increases following endovascular aneurysm repair (EVAR). Animal models suggest elevated PWV following endograft deployment occurs in conjunction with decreased aortic compliance and increased aortic impedance. This could lead to unwanted effects on left ventricular (LV) function. This study evaluates the early implications of EVAR on aortic mechanics and associated LV function.Materials and methodsProspective observational study of elective EVAR for abdominal aneurysm. Transesophageal echocardiography was used to acquire LV flow and function, as well as images of the ascending aorta. Speckle tracking echocardiography (STE) software analysis allowed for determination of aortic volume change throughout the cardiac cycle. Aortic mechanics (including compliance, impedance and reflected wave analysis) and left-ventricular function (including cardiac output, hydraulic load and diastolic function) were measured pre- and post-endograft deployment.ResultsEndograft deployment resulted in no significant increase in aortic impedance. It did alter the timing of reflected waves in the aorta, with a greater positive wave being reflected during systole. This increased the hydraulic load on the LV with corresponding statistically non-significant trends for decreasing cardiac output and LV diastolic function.DiscussionSTE represents an emerging imaging modality for aortic biomechanical assessment. The increased PWV seen following EVAR may not reflect the same aortic biomechanical pathophysiology as in the non-surgical population with measures of increased arterial stiffness. The stiffer endograft does not appear to acutely increase aortic impedance, though it does alter the timing of reflected waves which may have negative effects on LV function.

Hydrodynamic response of the WEC sub-system of a novel hybrid wind-wave energy converter

Multiple marine resources are usually available in the same area and synergies between the different users of these resources exist. Multipurpose platforms, which combine more than one of these renewable resources, have been proposed as a sustainable approach. One type of multipurpose platforms is the hybrid wind-wave systems, in which a single platform combines the exploitation of offshore wind and wave energy. In this paper a novel hybrid system that integrates an oscillating water column (OWC) wave energy converter (WEC) with an offshore wind turbine on a monopile substructure is considered. The main objective of this paper is to define and test a simplified version of the WEC sub-system of this hybrid energy converter. An experimental campaign was carried out to characterise the hydrodynamic response of a 1:37.5 scale model of the WEC sub-system under regular and irregular waves. On the basis of the data from the experimental campaign, the hydrodynamic response of the WEC sub-system is characterised in four steps: (i) through an incident and reflected wave analysis (IRWA), to characterise the interaction between the device and the waves; (ii) through the capture width ratio, to study the performance of the device; (iii) through response amplitude operators (RAOs) of the free surface elevation and pneumatic pressure inside the OWC chamber, to study the effects of the incident waves on the device response; and (iv) through the wave run-up on the device. The results from this multifaceted analysis lead to the proof of concept of this novel hybrid system, supporting its feasibility to be combined with offshore wind substructures; but also to characterise its behaviour and interaction with the wave field, essential to full understanding of the benefits of hybrid systems.

Analysis of the Explosive Internal Impact on the Barriers of Building Structures

Work issues concern the safety of construction in relation to the hazards arising from explosion of the explosive charge located inside the building. The algorithms proposed in the paper for determining the parameters of the overpressure wave resulting from the detonation of clustered explosive charges, determine the basis for numerical simulation analyzes. Determination of the maximum value of peak pressure on the wave forehead of an internal explosion is presented on the basis of reflected wave analysis. Changeability in time of the internal explosion action describes the overpressure phase only. The analysis of the load caused by the internal explosive charge detonation was carried out under conditions of the undisturbed standard atmosphere. A load determination algorithm has been developed, taking into account the geometrical characteristics of the building barriers and the rooms as well as the parameters of environment in which the detonation occurs. The way of taking into account the influence of venting surfaces, i.e. windows, doors, ventilation ducts, on the overpressure wave parameters, was presented. Discloses a method to take into account the effect of the surface relief, i.e. windows, doors, air ducts, pressure wave parameters. Modification of the method for explosive overpressure determination presented by Cormie, Smith, Mays (2009), was proposed in the paper. This modification was developed on the basis of substitute impulse analysis for multiple overpressure pulses. In order to take into account the pressure distribution of explosive gases on the barrier surface, the method of modification the relationship for determination the changeability over time and space of the pressure of explosive gases, was presented. For this purpose, the changeability of the pressure wave angles of incidence to the barrier and the distance of the explosive charge to any point on the surface of the barrier, was taken into account. Based on the developed procedure, the overpressure changeability over time was determined for selected measurement points of the reference room. A comparative analysis of the determined loadings with experimental results and theoretical results of other authors, taken from the original work of Weerhiejm et al. (2012), was carried out.

Surface analysis of oxygen free electrolytic-copperX-band accelerating structures and possible correlation to radio frequency breakdown events

X-band accelerator structures meeting the next linear collider design requirements have been found to suffer vacuum surface damage caused by rf breakdown, when processed to high electric-field gradients. Improved understanding of these breakdown events is desirable for the development of structure designs, fabrication procedures, and processing techniques that minimize structure damage. rf reflected wave analysis and acoustic sensor pickup have provided breakdowns localization in rf structures. Particle contaminations found following clean autopsy of four rf-processed traveling wave structures have been catalogued and analyzed. Their influence on rf breakdown, as well as that of several other material-based properties, are discussed.