Innovations in dynamic test restraint systems

Recent launch system development programs have led to a new generation of large scale dynamic tests. The variety of test scenarios share one common requirement: restrain and capture massive high velocity flight hardware with no structural damage. The Space Systems Lab of McDonnell Douglas developed a remarkably simple and cost effective approach to such testing using ripstitch energy absorbers adapted from the sport of technical rockclimbing. The proven system reliability of the capture system concept has led to a wide variety of applications in test system design and in aerospace hardware design

Condition Monitoring Technologies for Synthetic Fiber Ropes - a Review

This paper presents a review of different condition monitoring technologies for fiber ropes. Specifically, it presents an overview of the articles and patents on the subject, ranging from the early 70’s up until today with the state of the art. Experimental results are also included and discussed in a conditionmonitoring context,where failuremechanisms and changes in physical parameters give improved insight into the degradation process of fiber ropes. From this review, it is found that automatic width measurement has received surprisingly little attention, and might be a future direction for the development of a continuous condition monitoring system for synthetic fiber ropes

Condition Monitoring Technologies for Steel Wire Ropes – A Review

In this research, we review condition-monitoring technologies for offshore steel wire ropes (SWR). Such ropes are used within several offshore applications including cranes for load handling such as subsea construction at depths up to 3-4000 meters, drilling lines, marine riser tensioner lines and anchor lines. For mooring, there is a clear tendency for using fiber ropes. Especially for heavy-lift cranes and subsea deployment, winches with strong ropes of up to 180 mm in diameter may be required, which has a considerable cost per rope, especially for large water depths. Today’s practice is to discard the rope after a predetermined number of uses due to fatigue from bending over sheaves with a large safety factor, especially for systems regulated by active heave compensation (AHC). Other sources of degradation are abrasion, fretting, corrosion and extreme forces, and are typically accelerated due to undersized or poorly maintained sheaves, groove type, lack of lubrication and excessive load. Non-destructive testing techniques for SWR have been developed over a period of 100 years. Most notably are the magnetic leakage techniques (electromagnetic methods), which are widely used within several industries such as mining and construction. The content reviewed in this research is primarily the developments the last five years within the topics of electromagnetic method, acoustic emissions (AE), ultrasound, X- and γ-rays, fiber optics, optical and thermal vision and current signature analysis. Each technique is thoroughly presented and discussed for the application of subsea construction. Assessments include ability to detect localized flaws (i.e. broken wire) both internally and externally, estimated loss of metallic cross sectional area, robustness with respect to the rough offshore environment, ability to evaluate both rope and end fittings, and ability to work during operation

Exploration of torsional actuation and twist to writhe transition in nanostructured hydrogels

Torsional artificial muscles are a branch of actuators that react to a stimulus by rotating. This rotation is driven by a change in volume and mechanical properties such as modulus and was shown to be extremely large in the case of twisted fibers due to their helical geometry. The following thesis introduces a new method of fabrication of nanofiber yarns and nanocomposites with the aim of making hydrogel torsional catch actuators that combine responsiveness to pH changes and a high torsional output as well as a systematic approach to the modeling of their behavior using the single helix theory

Development of design tool for statically equivalent deepwater mooring systems

Verifying the design of floating structures adequately requires both numerical simulations and model testing, a combination of which is referred to as the hybrid method of design verification. The challenge in direct scaling of moorings for model tests is the depth and spatial limitations in wave basins. It is therefore important to design and build equivalent mooring systems to ensure that the static properties (global restoring forces and global stiffness) of the prototype floater are matched by those of the model in the wave basin prior to testing. A fit-for-purpose numerical tool called STAMOORSYS is developed in this research for the design of statically equivalent deepwater mooring systems. The elastic catenary equations are derived and applied with efficient algorithm to obtain local and global static equilibrium solutions. A unique design page in STAMOORSYS is used to manually optimize the system properties in search of a match in global restoring forces and global stiffness. Up to eight mooring lines can be used in analyses and all lines have the same properties. STAMOORSYS is validated for single-line mooring analysis using LINANL and Orcaflex, and for global mooring analysis using MOORANL and Orcaflex. A statically equivalent deepwater mooring system for a representative structure that could be tested in the Offshore Technology Research Center at Texas A&M University is then designed using STAMOORSYS and the results are discussed

Modelling and Prediction of the Effects of Dynamic Responses of Tall Buildings on an Elevator System

Vibrations on a high rise building often influence all elevator components and affect the ride quality of the elevator car. The lateral and longitudinal vibrations of the suspension and compensating ropes can occur and the lateral and longitudinal vibrations at the elevator car may take place. The ropes in the elevator system can be characterized by low and high frequency modes and they are lightly damped. The elevator system in a high rise building is composed of suspension and compensating ropes, which are the pivotal components of the elevator system. An important feature of the ropes in the elevator system is that they have a time varying length. However, the rate in which the length changes can be considered as small and as a result dynamic characteristics of the system vary slowly during the elevator car travel. The design methodology of an elevator system requires a thorough dynamic analysis in order to predict the dynamic loads and to evaluate the response of the system during various operational modes. This response may be caused by a number of sources of excitation. The main source of excitation this study is focused on is the excitation coming from the wind loading on the high rise building. Wind loading on a building structure causes high displacements at the top of the building structure, exciting all of the components of the elevator system. The main excitation from the building structure to the suspension and compensating ropes are the displacements at the machine room level. The other sources of excitation are coming from the building interface which is used to guide the elevator car and counterweight along the elevator shaft during travel. The building interface consists of guide rails and roller guides. The lateral vibration of the elevator car can result from the roller guide vibrations or due to the guide rail segments being misaligned. These various sources of excitation may lead to an adverse dynamic behaviour of the elevator system due to its nonlinear and nonstationary nature. Due to the time varying length of the ropes in the elevator system the mass and the stiffness of the system change and consequently its dynamic characteristics such as frequencies, damping ratios and mode shapes are affected. The aim of this research is to develop and to validate a computer model of the elevator system to predict the dynamic responses of the ropes in an elevator system due to the vibrations of a high-rise building under wind loading, when the elevator system is stationary and in motion. The three objectives of this thesis are to develop a mathematical and computer model of the elevator system to understand the behaviour of the ropes in the elevator system under the influence of the building vibrations caused by wind action, to develop an experimental programme involving a lift testing tower facilities and/or alternative tall building sites, in order to validate the computer model through experimental testing, and to develop a computer software tool as an executable program on Windows operating system to predict the behaviour of the ropes in the elevator system based on the final mathematical models of a stationary and moving elevator system. The experimental testing was conducted at the National Lift Tower in Northampton using an experimental rig. A set of experiments were developed and various measurements were carried out. The equations that accurately describe the motion of the mass-rope suspension system in the rig were derived. The mathematical model takes into account the stationary and nonlinear nature of the mass rope suspension system in the rig. The linear and nonlinear resonance phenomena were predicted through simulation and they were compared with the experimental results. The equations of motion that describe the elevator system comprised of the elevator car, compensating sheave, and counterweight connected by the suspension and compensating ropes were derived. A method to account for the nonstationary and nonlinear nature of the elevator system was developed. The linear and nonlinear phenomena were observed. The nonstationary and nonlinear behaviour of the ropes in the elevator system was demonstrated through simulation. The results showed that nonlinear coupling in the lateral in plane and out of plane directions of the suspension and compensating ropes can generate modal interaction between the elevator car, compensating sheave, and counterweight. Thus, the displacements of the elevator car, compensating sheave, and counterweight can be predicted

A new method of termination for heavy-duty synthetic rope fibres

Termination of heavy-duty synthetic fibre ropes has long been an issue of concern in marine environments. Recent serious rope accidents and new requirements for lighter ropes with better performance in mooring lines have encouraged industry to look for new methods for increasing line performance using existing ropes. One way of increasing rope performance is to use efficient methods for rope termination. This is why the main objective of this study has been to investigate a new method for rope termination. Rope failure usually happens inside or very close to termination due to high stress concentration areas. The new method, "The Vaseghi Stress Relief Socket", has been proposed to improve the high stress concentration areas inside sockets and move failure points along the rope. The new method has increasedthe tensile performance of existing ropes up to 13%. It should also be addedthat the ropes in this study are mainly used in marine environmentsfor mooring oil platforms. Considering the results of the tensile and cycling tests, The Vaseghi Stress Relief Socket, proved a great potential for replacement of existing methods of termination e.g. the splice. It should also be noted that the reproduction of the socket termination is more consistent than that of other methods of termination. Tensile properties of ropes using `The Vaseghi Stress Relief Socket' were initially a matter of concern, for rope termination is the most important feature of ropes.In fact, if there is a termination failure in tensile tests, the rope will not be considered efficient for mooring purpose even though its other performancesare excellent. Load cycling was the second property that was considered. Acoustic Emission monitoring was performed to find out the relation between the load-extension behaviour of the rope using The Vaseghi stress Relief socket and the AE signals. Finally, the finite element modelling of socket helped to investigate the stress concentration areas in the socket to optimise the amount of the reinforcing material and identify the weak point areas in the socket, which could lead to further research studies for new designs

Development of Non-Destructive Testing by Eddy Currents for Highly Demanding Engineering Applications

Defect detection with Non-Destructive Testing (NDT) is essential in accidents prevention, requiring R&TD to generate new scientific and procedural knowledge for new products with high safety requirements. A current challenge lies in the detection of surface and sub-surface micro defects with NDT by Eddy Currents (EC). The main objective of this work was the development of applied research, technological innovation and experimental validation of EC customized systems for three highly demanding inspection scenarios: micro defects in tubular geometries; brazed joints for the automotive industry; and high-speed moving composite materials. This objective implied starting from the scientific fundamentals of NDT by EC to design and simulate EC probes and the prototypes developed were tested in industrial environment, reaching a TRL ≈ 5. Another objective, of a more scientific and disruptive nature, was to test a new technique for the creation of EC in the materials to be inspect, named Magnetic Permeability Pattern Substrate (MPPS). This technique consists on the development of substrates/films with patterns of different magnetic permeabilities rather than the use of excitation bobbin coils or filaments of complex geometry. The experimental results demonstrated that the prototypes developed for the three industrial applications studied outperformed the state of the art, allowing the detection of target defects with a very good signal-to-noise ratio: in tubular geometries defects with depth of 0.5 mm and thickness of 0.2 mm in any scanning position; in the laser brazed weld beads pores with 0.13 mm diameter and internal artificial defects 1 mm from the weld surface; in composite materials defects under 1 mm at speeds up to 4 m/s and 3 mm lift-off. The numerical simulations assisted the probe design, allowing to describe and characterize electrical and magnetic phenomena. The new MPPS concept for the introduction of EC was validated numerically and experimentally

Numerical and Experimental Study of Shared Mooring Systems for Prototype Floating Wind Farms

Paper V is excluded in the paper due to copyright. Paper VI and VIII is excluded from the dissertation until they are published.Conventional mooring systems represent a substantial portion of the cost of a floating offshore wind farm (FOWF). The concept of shared mooring was initially proposed to reduce the overall usage of mooring lines and the number of anchors required by connecting adjacent floating offshore wind turbines (FOWTs) in an FOWF. Although such a concept offers cost-saving potential, extra complexity has been introduced to the floating system as the platform motions of FOWTs are coupled. To demonstrate the feasibility of shared mooring systems, it is of great interest and importance to understand the fundamental influence of shared mooring systems on the dynamic characteristics of FOWFs. Limited research has been conducted concerning detailed dynamic analyses of shared mooring systems and experimental investigations of FOWFs. This thesis addresses this knowledge gap by conducting numerical and experimental studies on prototype dual-spar FOWFs with shared mooring systems. Extensive investigations are carried out considering various shared mooring configurations, different turbine spacings and water depths, and varying mooring properties, configurations, and load scenarios. In the numerical study, a modeling method is developed for shared mooring systems utilizing Irvine’s elastic catenary theory for hanging cables, which serves as the basis for the mooring stiffness linearization and eigenvalue analysis of FOWFs with shared mooring systems. For a dual-spar FOWF, a shared line connecting two FOWTs is the basic shared mooring configuration. The influence of the shared line on the system’s natural periods and eigenmodes are investigated through a comparison to a single spar FOWT. The investigation reveals the significant influence of the shared line on the natural periods of surge and sway degrees of freedom (DOFs) of the spar platforms due to the dominance of mooring stiffness in the relevant terms of restoring stiffness. Moreover, the natural periods of these DOFs are found to be sensitive to variations in the mooring properties of both the single lines connecting the FOWTs to the seabed and the shared line connecting adjacent FOWTs. The basic shared mooring configuration is then modeled with a numerical simulation tool to perform fully coupled time-domain simulations under varying environmental conditions (ECs). A comparison with a single spar FOWT demonstrates larger motion ranges and dynamic motions of FOWTs in the FOWF, along with higher tension levels in the single lines. The shared line experiences high dynamic tension and snap load events. The studied mooring layout displays sensitivity to loading directions due to its inherent asymmetry. An alternative shared mooring system is considered by connecting neighboring FOWTs to a shared tethered buoy and by replacing the single lines of the FOWTs with hanging lines connected to individual tethered buoys. Through dynamic analyses under various load scenarios and comparison against the basic shared mooring configuration, it is concluded that the proposed tethered-buoy shared mooring system can achieve a significant reduction in tension levels across all mooring lines and alleviate potential threats associated with snap loads, with a trade-off for increased mean offset and dynamic motions of the FOWTs. Therefore, the proposed tethered-buoy shared mooring system is a preferred solution for future applications involving inter-array cables, where the excursion restrictions of FOWTs become less critical. A hydrodynamic model test campaign is conducted for dual-spar FOWFs with different shared mooring systems. Decay tests are carried out, and regular and irregular wave tests are performed under various ECs. Detailed physical modeling of the FOWTs and shared mooring systems are documented. Through a comparison to the results of a previously tested single spar FOWT, the findings from the numerical study are verified. A clump weight is introduced at the midpoint of the shared line in the basic shared mooring configuration, and its effects are investigated through a comparative analysis where the natural periods, motion response, and mooring tension before and after the inclusion of the clump weight are analyzed. The added clump weight leads to a decrease in the natural periods of horizontal DOFs and reduced dynamic motions of the FOWTs. Despite an increase in the pretension of all mooring lines, dynamic tension in these lines is reduced, and a reduced number of snap load events in the shared line is observed. In summary, this thesis investigates shared mooring systems for prototype dualspar FOWFs by numerical and experimental approaches. A quasi-static modeling method of shared mooring systems is developed and applied. The dynamic characteristics of FOWFs with five shared mooring configurations are revealed, and the station-keeping performance of the FOWF systems are highlighted in the comparison. These research outcomes augment the current understanding of and expand the existing knowledge base related to shared mooring systems. The analysis methods developed and employed in this study can be further utilized in the design and optimization of FOWFs.publishedVersio

Impact of Ear Occlusion on In-Ear Sounds Generated by Intra-oral Behaviors

We conducted a case study with one volunteer and a recording setup to detect sounds induced by the actions: jaw clenching, tooth grinding, reading, eating, and drinking. The setup consisted of two in-ear microphones, where the left ear was semi-occluded with a commercially available earpiece and the right ear was occluded with a mouldable silicon ear piece. Investigations in the time and frequency domains demonstrated that for behaviors such as eating, tooth grinding, and reading, sounds could be recorded with both sensors. For jaw clenching, however, occluding the ear with a mouldable piece was necessary to enable its detection. This can be attributed to the fact that the mouldable ear piece sealed the ear canal and isolated it from the environment, resulting in a detectable change in pressure. In conclusion, our work suggests that detecting behaviors such as eating, grinding, reading with a semi-occluded ear is possible, whereas, behaviors such as clenching require the complete occlusion of the ear if the activity should be easily detectable. Nevertheless, the latter approach may limit real-world applicability because it hinders the hearing capabilities.</p