A comprehensive study of the delay vector variance method for quantification of nonlinearity in dynamical systems

Although vibration monitoring is a popular method to monitor and assess dynamic structures, quantification of linearity or nonlinearity of the dynamic responses remains a challenging problem. We investigate the delay vector variance (DVV) method in this regard in a comprehensive manner to establish the degree to which a change in signal nonlinearity can be related to system nonlinearity and how a change in system parameters affects the nonlinearity in the dynamic response of the system. A wide range of theoretical situations are considered in this regard using a single degree of freedom (SDOF) system to obtain numerical benchmarks. A number of experiments are then carried out using a physical SDOF model in the laboratory. Finally, a composite wind turbine blade is tested for different excitations and the dynamic responses are measured at a number of points to extend the investigation to continuum structures. The dynamic responses were measured using accelerometers, strain gauges and a Laser Doppler vibrometer. This comprehensive study creates a numerical and experimental benchmark for structurally dynamical systems where output-only information is typically available, especially in the context of DVV. The study also allows for comparative analysis between different systems driven by the similar input

A parametric study: Frame analysis method for masonry arch bridges

The predictability of masonry arch bridges and their behaviour is widely considered doubtful due to the lack of knowledge about the conditions of a given masonry arch bridge. The assessment methods for masonry arch bridges are MEXE, ARCHIE, RING and Frame Analysis Method. The material properties of the masonry and fill material are extremely difficult to determine accurately. Consequently, it is necessary to examine the effect of load dispersal angle through the fill material, the effect of variations in the stiffness of the masonry, the tensile strength of the masonry mortar continuum and the compressive strength of the masonry mortar continuum. It is also important to understand the effect of fill material on load dispersal angle to determine their influence on ratings. In this paper a series of parametric studies, to examine the sensitivity of assessment ratings to the various sets of input data required by the frame analysis method, are carried out

Perception of safety of cyclists in Dublin city

In recent years, cycling has been recognized and is being promoted as a sustainable mode of travel. The perception of cycling as an unsafe mode of travel is a significant obstacle in increasing the mode share of bicycles in a city. Hence, it is important to identify and analyze the factors which influence the safety experiences of the cyclists in an urban signalized multi-modal transportation network. Previous researches in the area of perceived safety of cyclists primarily considered the influence of network infrastructure and operation specific variables and are often limited to specific locations within the network. This study explores the factors that are expected to be important in influencing the perception of safety among cyclists but were never studied in the past. These factors include the safety behavior of existing cyclists, the users of other travel modes and their attitude toward cyclists, facilities and network infrastructures applicable to cycling as well as to other modes in all parts of an urban transportation network. A survey of existing cyclists in Dublin City was conducted to gain an insight into the different aspects related to the safety experience of cyclists. Ordered Logistic Regression (OLR) and Principal Component Analysis (PCA) were used in the analysis of survey responses. This study has revealed that respondents perceive cycling as less safe than driving in Dublin City. The new findings have shown that the compliance of cyclists with the rules of the road increase their safety experience, while the reckless and careless attitudes of drivers are exceptionally detrimental to their perceived safety. The policy implications of the results of analysis are discussed with the intention of building on the reputation of cycling as a viable mode of transportation among all network users.postprin

Physical Modelling of Offshore Wind Turbine Foundations for TRL (Technology Readiness Level) Studies

Offshore wind turbines are a complex, dynamically sensitive structure due to their irregular mass and stiffness distribution, and complexity of the loading conditions they need to withstand. There are other challenges in particular locations such as typhoons, hurricanes, earthquakes, sea-bed currents, and tsunami. Because offshore wind turbines have stringent Serviceability Limit State (SLS) requirements and need to be installed in variable and often complex ground conditions, their foundation design is challenging. Foundation design must be robust due to the enormous cost of retrofitting in a challenging environment should any problem occur during the design lifetime. Traditionally, engineers use conventional types of foundation systems, such as shallow gravity-based foundations (GBF), suction caissons, or slender piles or monopiles, based on prior experience with designing such foundations for the oil and gas industry. For offshore wind turbines, however, new types of foundations are being considered for which neither prior experience nor guidelines exist. One of the major challenges is to develop a method to de-risk the life cycle of offshore wind turbines in diverse metocean and geological conditions. The paper, therefore, has the following aims: (a) provide an overview of the complexities and the common SLS performance requirements for offshore wind turbine; (b) discuss the use of physical modelling for verification and validation of innovative design concepts, taking into account all possible angles to de-risk the project; and (c) provide examples of applications in scaled model tests

Improvement of Engineering Properties of Peat with Palm Oil Clinker

The aim of this study is to investigate the effects of Palm Oil Clinker (POC) added as a stabilizer forimproving the strength of peat. Cement and POC are added into peat up to 50% of the maximum dry unitweight. Treated peat achieved higher dry unit weight, almost 2.5 times as compared to untreated peat.Unconfined compressive strength (UCS) of treated peat is also investigated for soaked and unsoakedconditions. The results show that curing time improved the unconfined compressive strength of treatedsample and increased by a factor of 20 and 11 for unsoaked and soaked conditions after 28 days ofcuring, respectively. The treated samples added with POC can be related to an increase in unconfinedcompressive strength for long time curing

Feasibility of energy harvesting from vertical pedestrian-induced vibrations of footbridges for smart monitoring applications

The present work is meant at contributing to the innovation of the current methodologies for pedestrian bridge monitoring. Specifically, the use of vibrational energy harvesters for self-powered wireless structural monitoring of footbridges is here advanced for the first time, and a novel sensorless strategy is also proposed to survey remotely their serviceability conditions. In this perspective, comprehensive computer-aided numerical investigations are initially conducted to obtain statistical estimates of the electrical energy generated from a composite piezoelectric cantilever beam subjected to the vertical footbridge response under the passage of walkers. In doing so, randomness related to the pedestrians' dynamics and footbridges with different modal features are taken into account. An investigation based on experimental data is finally presented. In detail, one case study is concerned with a footbridge prone to large vibrations due to quasi pedestrian–structure resonance condition while the second one deals with a stiffer footbridge experiencing low excitation levels. Ultimately, this study indicates that energy harvesting from vertical pedestrian-induced vibrations can be a promising strategy for footbridges monitoring, and it provides useful design guidelines in this regard

Vibration-based leak detection and monitoring of water pipes using output-only piezoelectric sensors

While access to potable water remain one of the grand challenges of the modern world, water distribution pipelines continue to degrade globally and pose a problem in overcoming this challenge. There is a need for data-driven decision-making in relation to identifying structurally degraded pipelines, typically used in water distribution, through monitoring and subsequent assessment in a smart manner. This explains the growing attention the area of leak and damage detection in water pipes. This paper presents the conception, development and experimental validation of a novel technology for leak detection in water pipes using sensors made from piezoelectric materials that converts strain from vibration into electrical energy. These monitors are self-powered and hence has the potential to be deployed more easily than those requiring external power to run. The paper details the fabrication and characterization of the sensors, the experimental design which details the design of a benchmark test rig developed and the test procedure to ensure repeatability. The paper subsequently demonstrates how harvested energy signatures are aligned to the location and extent of damage in the pipe by experimentally introducing leakage in the pipe. It presents the results from tests conducted to validate the idea. The conclusions and recommendations provide insights and directions into more extensive applications for these types of sensors for monitoring of our built infrastructure. It is expected that this paper will form an experimental benchmark for future work on this topic