Poul Henning Kirkegaard

Can architectural design alter the physiological reaction to psychosocial stress? A virtual TSST experiment

Is has long been established, that views to natural scenes can a have a dampening effect on physiological stress responses. However, as people in Europe, Canada and North America today spent 50-85% of their time indoors, attention might also be paid to how the artificial man-made indoor environment influences these mechanisms. The question that this study attempts to start addressing is therefore whether certain design, characteristics of indoor spaces can make a difference to the physiological stress response as well. Using a virtual version of the Trier Social Stress Test, in which the space is computer generated and properties of the space therefore can be systematically varied, we measured saliva cortisol and heart rate variability in participants in a closed room versus a room with openings. As shown by a significant linear contrast interaction between groups and TSST conditions, participants in the closed room responded with more pronounced cortisol reactivity to stress induction, and continued to show higher levels throughout recovery, compared to participants in the open room. No differences were found regarding any part of the autonomic nervous system.

Boundary element method solution in the time domain for a moving time-dependent force

Abstract The problem of a moving time dependent concentrated force on the surface of an elastic halfspace is of interest in the analysis of traffic generated noise. The Boundary element method (BEM) is superior to the Finite element method (FEM) in solving such problems due to its inherent ability so satisfy the radiation conditions exactly. In this paper a model based on the BEM is formulated for the solution of the mentioned problem. A numerical solution is obtained for the 2D plane strain case, and comparison is made with the results obtained from a corresponding FEM solution with an impedance absorbing boundary condition.

Operational Modal Analysis and Wavelet Transformation for Damage Identification in Wind Turbine Blades

This study demonstrates an application of a previously proposed modal and wavelet analysis-based damage identification method to a wind turbine blade. A trailing edge debonding was introduced to an SSP 34-m blade mounted on a test rig. Operational modal analysis was conducted to obtain mode shapes for undamaged and damaged states of the blade. Subsequently, the mode shapes were analyzed with one-dimensional continuous wavelet transformations for damage identification. The basic idea of the method is that structural damage will introduce local mode shape irregularities which are captured in the continuous wavelet transformation by significantly magnified transform coefficients, thus providing combined damage detection, localization, and size assessment. It was found that due to the nature of the proposed method, the value of the identification results highly depends on the number of employed measurement points. Since a limited number of measurement points were utilized in the experiments, only certain damage-sensitive modes, in which pronounced damage-induced mode shape changes occur, are applicable for valid identification of the damage.

DAMAGE LOCALIZATION AND QUANTIFICATION OF EARTHQUAKE EXCITED RC-FRAMES

SUMMARY In the paper a recently proposed method for damage localization and quantification of RC-structures from response measurements is tested on experimental data. The method investigated requires at least one response measurement along the structures and the ground surface acceleration. Further, the two lowest time-varying eigenfrequencies of the structure must be identified. The data considered are sampled from a series of three RC-frame model tests performed at the structural laboratory at Aalborg University, Denmark during the autumn of 1996. The frames in the test series were exposed to two or three series of ground motions of increasing magnitude. After each of these runs the damage state of the frame was examined and each storey of the frame were classified into one of the following six classifications: undamaged, cracked, lightly damaged, damaged, severely damaged or collapse. During each of the ground motion events the storey accelerations were measured by accelerometers. After application of the last earthquake sequence to the structure the frames were cut into pieces and each of the beams and columns was statically tested and damage assessment was performed using the obtained sti⁄nesses. The damage in the storeys determined by the suggested method was then compared to the damage classification from the visual inspection as well as the static tests. It was found that especially in the cases where the damage is concentrated in a certain area of the structure a very good damage assessment is obtained using the suggested method. ( 1998 John Wiley & Sons, Ltd.

On Structural Health Monitoring of Wind Turbine Blades

The aim of the present paper is to provide a state-of-the-art outline of structural health monitoring (SHM) techniques, utilizing temperature, noise and vibration, for wind turbine blades, and subsequently perform a typology on the basis of the typical 4 damage identification levels in SHM. Before presenting the state-of-the-art outline, descriptions of structural damages typically occurring in wind turbine blades are provided along with a brief description of the 4 damage identification levels.

Dynamic Double Curvature Mould System

The present paper describes a concept for a reconfigurable mould surface which is designed to fit the needs of contemporary architecture. The core of the concept presented is a dynamic surface manipulated into a given shape using a digital signal created directly from the CAD drawing of the design. This happen fast, automatic and without production of waste, and the manipulated surface is fair and robust, eliminating the need for additional, manual treatment. Limitations to the possibilities of the flexible form are limited curvature and limited level of detail, making it especially suited for larger, double curved surfaces like facades or walls, where the curvature of each element is relatively small in comparison to the overall shape.

Prediction of Global and Localized Damage and Future Reliability for RC Structures subject to Earthquakes

This paper deals with the prediction of global and localized damage and the future reliability estimation of partly damaged reinforced concrete structures under seismic excitation. Initially, a global maximum softening damage indicator is considered based on the variation of the eigenfrequency of the first mode due to the stiffness and strength deterioration of the structure. The hysteretic behaviour of the first mode is modeled by a Clough and Johnston hysteretic oscillator with degrading elastic restoring force. The linear parameters of the model are assumed to be known, measured before the arrival of the first earthquake by non-destructive vibration tests or by means of structural analysis. The previous excitation and displacement response time series are employed for the identification of the instantaneous softening using an ARMA model. The hysteresis parameters are updated after each earthquake. The proposed model is next generalized for a MDOF system. Using the calibrated model for the structure and the global damage state, the global damage in a future earthquake can then be estimated when a suitable earthquake simulation model is applied. The performance of the SDOF hysteretic model is illustrated on RC frames which were tested by Sozen and his associates.

Wavelet Transformation for Damage Identification in Wind Turbine Blades

The present paper documents a proposed modal and wavelet analysis-based structural health monitoring (SHM) method for damage identification in wind turbine blades. A finite element (FE) model of a full-scale wind turbine blade is developed and introduced to a transverse surface crack. Hereby, post-damage mode shapes are derived through modal analysis and subsequently analyzed with continuous two-dimensional wavelet transformation for damage identification, namely detection, localization and assessment. It is found that valid damage identification is obtained even when utilizing the mode shape of the first structural blade mode. However, due to the nature of the proposed method, it is also found that the accuracy of the damage assessment highly depends on the number of employed measurement points.

Patients Light Preferences in Hospital Wards: related to light atmosphere in Danish homes

When designing Danish hospitals in the future, patients, staff and guests are in focus and it is especially important to design an environment with knowledge of users sensory and functionally needs. Likewise, focus should be on how hospital wards can support patients’ experiences or maybe even how it can have a positive influence on the recovery process. The present paper introduces the human perspective and the Danish cultural approach in illuminating homes and how it can contribute to innovative lighting design at hospitals. The importance of having a holistic approach to lighting design is introduced based on the theory by Gernot Bohmes i.e. “concept of atmosphere” dealing with the effect of experiencing atmosphere. The aim of this study for design of a lighting concept for wards is to get qualified information on patients light preferences for light atmosphere by studying the everyday use of light in homes. This explorative study displays the preferred light atmosphere in Danish homes in the age group of 60–85 years old people. With an anthropologically approach to the subject using semi structured interviews, the goal is to explore preferences for light atmosphere when the user are in the control of the light and get inspiration on how they create a private sphere. The purpose is also through this analyse to display cultural trends of illuminating homes, therefore, the paper will introduce the design lighting concept for wards based on different everyday situation activities from a hospital ward.

Load Identification of Offshore Platform for Fatigue Life Estimation

The lifetime of an offshore platform is typically governed by accumulated fatigue damage. Thus, the load time history is an essential parameter for prediction of the lifetime of the structure and its components. Consequently, monitoring of structural loads is of special importance in relation to re-assessment of offshore platforms. Structural monitoring systems (SMS’s) on offshore structures typically consist of a set of sensors such as strain gauges, accelerometers, wave radars and GPS’s, however direct measuring of the actual loading is usually not feasible. One approach is to measure the loads indirectly by monitoring of the available dynamic responses of the structure. This work investigates the possibility for using an economically beneficial, model-based load estimation algorithm for indirect measuring of the loading forces acting on the offshore structure. The algorithm is based on the reduced order model of the structure and the discrete Kalman filter which recursively estimates unknown states of the system in real time. As a test-case, the algorithm is designed to estimate the equivalent total loading forces of the structure. The loads are estimated from noised displacement measurements of a single location on the topside of the offshore structure. The method is validated using simulated data for two wave loading cases: regular and irregular wave loadings.