State-Space Dynamic Substructuring with the Transmission Simulator Method

Dynamic substructuring is a technique to simplify the analysis of complex structures. The vibrational problems of the constituent substructures are analysed and solved individually and their solutions are then assembled to form the global solution. In experimental dynamic substructuring, at least one of the constituent substructures lis identified experimentally. The coupling interfaces are commonly simplified in such syntheses, which can result in poor prediction quality in many applications. The transmission simulator was introduced to address this problem. Transmission simulators are well-modelled parts attached to the interface of the substructures to be coupled. This allows for distributed interfaces and a relaxation of the coupling conditions by using the transmission simulator\u27s analytical modes as a basis for the coupling equations, at the cost of adding a decoupling step to the substructuring problem. In this paper, the transmission simulator method is translated to the state-space substructuring domain. The methodology is applied to the Society for Experimental Mechanics\u27 substructuring focus group\u27s Ampair A600 test bed in form of experimental-analytical substructuring. The Ampair wind turbine\u27s hub is used as the transmission simulator and is modelled with finite elements while the three blades, individually attached to the real hub, are experimentally identified. The three experimental blade hub systems are then coupled and two finite element hubs decoupled from the system, using the derived method. Finally, this system is compared to a directly measured hub with three blades by means of frequency response functions and modal properties

Internal consistency and convergent validity of the International Spinal Cord Injury Quality of Life Basic Data Set at discharge from first rehabilitation

Study design This study is a cross-sectional analysis using data from the Swiss Spinal Cord Injury Cohort Study. Objectives To examine internal consistency and convergent validity of the International Spinal Cord Injury Quality of Life Basic Data Set (QoL-BDS) at discharge from first inpatient rehabilitation. Setting The study was performed at four rehabilitation centers in Switzerland. Methods Participants were Swiss residents aged over 16 years newly diagnosed with traumatic or non-traumatic spinal cord injury (SCI). Measures included the QoL-BDS, World Health Organization Quality of Life (WHOQOL) items, Hospital Anxiety and Depression Scale (HADS), and Spinal Cord Independence Measure III (SCIM). Results A total of 495 participants were included. In all, 57% had a traumatic SCI, 71.1% a motor complete SCI, and 33.3% had tetraplegia. Mean age was 53 (SD = 16.4) years and 68% were male. No floor or ceiling effects were found. Inter-correlations were strong (0.73-0.80) and Cronbach's alpha was good (0.88). QoL-BDS mean scores were 6.4 (SD = 2.2) for life satisfaction, 5.8 (SD = 2.4) for physical health, 6.9 (SD = 2.4) for psychological health, and 6.4 (SD = 2.1) for total QoL. Correlations with reference measures were strongest for QoL-BDS total and WHOQOL general quality of life (r = 0.67), QoL-BDS physical health and WHOQOL health and daily activities (r = 0.64 and 0.53), and QoL-BDS psychological health and HADS depression and anxiety (r = -0.64 and -0.69). SCIM correlated weakly with all QoL-BDS items. Conclusions The QoL-BDS revealed no floor or ceiling effects and demonstrated good internal consistency and convergent validity in individuals with SCI assessed at discharge from first rehabilitation. This study supports the clinical routine use of the QoL-BDS

Correlation of velocity and susceptibility in patients with aneurysmal subarachnoid hemorrhage

In many cerebral grey matter structures including the neocortex, spreading depolarization (SD) is the principal mechanism of the near-complete breakdown of the transcellular ion gradients with abrupt water influx into neurons. Accordingly, SDs are abundantly recorded in patients with traumatic brain injury, spontaneous intracerebral hemorrhage, aneurysmal subarachnoid hemorrhage (aSAH) and malignant hemispheric stroke using subdural electrode strips. SD is observed as a large slow potential change, spreading in the cortex at velocities between 2 and 9 mm/min. Velocity and SD susceptibility typically correlate positively in various animal models. In patients monitored in neurocritical care, the Co-Operative Studies on Brain Injury Depolarizations (COSBID) recommends several variables to quantify SD occurrence and susceptibility, although accurate measures of SD velocity have not been possible. Therefore, we developed an algorithm to estimate SD velocities based on reconstructing SD trajectories of the wave-front's curvature center from magnetic resonance imaging scans and time-of-SD-arrival- differences between subdural electrode pairs. We then correlated variables indicating SD susceptibility with algorithm-estimated SD velocities in twelve aSAH patients. Highly significant correlations supported the algorithm's validity. The trajectory search failed significantly more often for SDs recorded directly over emerging focal brain lesions suggesting in humans similar to animals that the complexity of SD propagation paths increase in tissue undergoing injury

A Consistency Analysis of Phase-Locked-Loop Testing and Control-Based Continuation for a Geometrically Nonlinear Frictional System

Two of the most popular vibration testing methods for nonlinear structures are control-based continuation and phase-locked-loop testing. In this paper, they are directly compared on the same benchmark system, for the first time, to demonstrate their general capabilities and to discuss practical implementation aspects. The considered system, which is specifically designed for this study, is a slightly arched beam clamped at both ends via bolted joints. It exhibits a pronounced softening-hardening behavior as well as an increasing damping characteristic due to the frictional clamping. Both methods are implemented to identify periodic responses at steady-state constituting the phase-resonant backbone curve and nonlinear frequency response curves. To ensure coherent results, the repetition variability is thoroughly assessed via an uncertainty analysis. It is concluded that the methods are in excellent agreement, taking into account the inherent repetition variability of the system

Spreading depolarization and angiographic spasm are separate mediators of delayed infarcts

In DISCHARGE-1, a recent Phase III diagnostic trial in aneurysmal subarachnoid haemorrhage patients, spreading depolarization variables were found to be an independent real-time biomarker of delayed cerebral ischaemia. We here investigated based on prospectively collected data from DISCHARGE-1 whether delayed infarcts in the anterior, middle, or posterior cerebral artery territories correlate with (i) extravascular blood volumes; (ii) predefined spreading depolarization variables, or proximal vasospasm assessed by either (iii) digital subtraction angiography or (iv) transcranial Doppler-sonography; and whether spreading depolarizations and/or vasospasm are mediators between extravascular blood and delayed infarcts. Relationships between variable groups were analysed using Spearman correlations in 136 patients. Thereafter, principal component analyses were performed for each variable group. Obtained components were included in path models with a priori defined structure. In the first path model, we only included spreading depolarization variables, as our primary interest was to investigate spreading depolarizations. Standardised path coefficients were 0.22 for the path from extravascular bloodcomponent to depolarizationcomponent (P = 0.010); and 0.44 for the path from depolarizationcomponent to the first principal component of delayed infarct volume (P < 0.001); but only 0.07 for the direct path from bloodcomponent to delayed infarctcomponent (P = 0.36). Thus, the role of spreading depolarizations as a mediator between blood and delayed infarcts was confirmed. In the principal component analysis of extravascular blood volume, intraventricular haemorrhage was not represented in the first component. Therefore, based on the correlation analyses, we also constructed another path model with bloodcomponent without intraventricular haemorrhage as first and intraventricular haemorrhage as second extrinsic variable. We found two paths, one from (subarachnoid) bloodcomponent to delayed infarctcomponent with depolarizationcomponent as mediator (path coefficients from bloodcomponent to depolarizationcomponent = 0.23, P = 0.03; path coefficients from depolarizationcomponent to delayed infarctcomponent = 0.29, P = 0.002), and one from intraventricular haemorrhage to delayed infarctcomponent with angiographic vasospasmcomponent as mediator variable (path coefficients from intraventricular haemorrhage to vasospasmcomponent = 0.24, P = 0.03; path coefficients from vasospasmcomponent to delayed infarctcomponent = 0.35, P < 0.001). Human autopsy studies shaped the hypothesis that blood clots on the cortex surface suffice to cause delayed infarcts beneath the clots. Experimentally, clot-released factors induce cortical spreading depolarizations that trigger (i) neuronal cytotoxic oedema and (ii) spreading ischaemia. The statistical mediator role of spreading depolarization variables between subarachnoid blood volume and delayed infarct volume supports this pathogenetic concept. We did not find that angiographic vasospasm triggers spreading depolarizations, but angiographic vasospasm contributed to delayed infarct volume. This could possibly result from enhancement of spreading depolarization-induced spreading ischaemia by reduced upstream blood supply.Peer Reviewe

State-Space Substructuring with Transmission Simulator

The dynamic substructuring focus group of SEM organizes sessions on experimental substructuring each IMAC conference and has been doing so for a number of years. Over the last decade, the use of so-called transmission simulators has trended within the community. Transmission simulators are well-modeled parts that fit to the interface of the substructures to be coupled to allow distributed interfaces and relaxation of the coupling conditions by the transmission simulator’s analytical modes at the cost of adding a decoupling step to the substructuring problem. In this paper, the transmission simulator concept is adapted to state-space substructuring. Experimental-analytical substructuring of the focus group benchmark structure, the Ampair A600 wind turbine, is used to verify the methodology