19 research outputs found
Definitive Design of Interactive Hand and Wrist Exoskeleton for Post-Stroke Rehabilitation at Home
Get PDFBackground: Stroke recovery would benefit tremendously if patients could continue their therapy at home while, for many patients, this requires a therapy device that helps them to overcome the hyper-flexion of wrist/fingers that is limiting their ability to open and use their hand. Objective: To develop an interactive hand/wrist exoskeleton for post-stroke rehabilitation, that provides adaptive extension assistance at the wrist/fingers, interfaces with motivational games based on activities of daily-life, and can be used independently by patients at home. Methods: Passive/active hand/wrist exoskeletons have been developed that provide the required interaction/assistance. They have been evaluated by therapists in clinical settings and used at home by 24 patients in three countries (for six weeks, ~15 [minutes/day] of active gaming). We used those experiences to create the definitive design of the SCRIPT hand/wrist exoskeleton. Results: The hand/wrist exoskeleton is able to deal with joint misalignments by its wrist/finger mechanisms such as spring-loaded self-aligning double parallelogram at the wrist, and individual hinged cantilevers with adjustable springs at the fingers/thumb for both extension assistance. Potentiometers at the wrist/finger/thumb measure flexion/extension which provide the interaction torque/forces via multiplying by the stiffness of the springs. The signals are used to interact with motivation games and to measure therapy progress. Conclusion: Using technical/clinical evaluations, we improved on our initial design that had limitations in range of motion, measurement accuracy and maximum applicable assistance, while also reducing setup and device calibration times, since our definitive design of the interactive hand/wrist exoskeleton for post-stroke rehabilitation at home is a compromise between complexity and functionality
Feasibility of reconstructing the glenohumeral center of rotation with a single camera setup
Get PDFBackground: An accurate estimation of the glenohumeral joint center of rotation (CoR) is important during alignment of braces and exoskeletons, as a misalignment will introduce undesired forces on the human body. The aim of this research was to develop a new method to estimate the glenohumeral CoR and register the location to the body using a single camera and two printed markers. Methods: During shoulder anteflexion, the arm roughly describes an arc in the sagittal plane, with the glenohumeral joint in the center. Two binary square-fiducial ArUco markers were secured to the upper arm and the scapula, their position and orientation were obtained, and a sphere was fitted to the coordinates of the arm marker. The sphere center position was then registered on the skin. The accuracy was assessed with a test bench with a known rotational center. The repeatability was assessed in vivo with five healthy participants. Results: The mean absolute offset between the true CoR of the test bench and the fitted sphere centers across multiple trials was 2.7 mm at a velocity of 30 degrees/s, and 2.5 mm at 60 degrees/s. The root mean squared distance from the estimated sphere centers after each trial to the mean sphere center across all trials per participant was 5.1 mm on average for the novice examiner and 5.2 mm for the expert examiner. Conclusions: The proposed method is able to accurately and precisely estimate the glenohumeral CoR
Performance-based seismic analysis of an anchored sheet pile quay wall
No full textPorts are civil works which have a major societal and economic importance. Quay structures are infrastructural elements of primary significance for the functioning of a port system. The ability to economically design quay structures with sufficient seismic resistance is therefore of great importance when situated in areas that are prone to earthquakes. Conventional seismic design is force-based i.e. that structures are designed to have sufficient capacity to withstand a pseudo-static seismic design force. This methodology is associated with no insight in the performance of the structure when exceeding the pseudo-static limit equilibrium state and uneconomic design due to the demand that the structure can resist a very high seismic design force without deforming. A more advanced alternative is Performance-Based Design (PBD) methodology. In this methodology the key design parameters for the seismic performance of structures are stress states and deformations of soil and structure, rather than just a seismic design force. Furthermore it recognizes that varying amounts of permanent deformations associated with different degrees of (repairable) damage are allowable. The present study is embedded in the topic of performance-based seismic design of quay structures. Typical quay types are gravity-based quay walls, sheet pile quay walls and pile-deck structures. The observed trend in seismic quay design is that gravity and sheet pile type structures (i.e. retaining walls) are associated with areas with zero to low seismicity while pile-deck structures are generally the preferred solution in areas with higher seismicity. This can be explained by more favourable seismic performance (i.e. more deformation capacity) of pile-deck structures compared to retaining walls. In line with this trend it is found that PBD methodology is developed to significant lesser extent for retaining walls (especially anchored sheet pile walls) than for pile-deck structures. Therefore the present study focuses on performance-based seismic design of anchored sheet pile quay walls. In the seismic design methodology there are generally three levels of seismic analysis available, i.e. simplified analysis (pseudo-static), simplified dynamic analysis and dynamic analysis. Simplified analysis of anchored sheet pile quay walls is associated with conventional design methodology. Simplified dynamic analysis can be used to obtain a first estimate of permanent-displacement of a structure after exceeding limit equilibrium, based on an assumed failure mode. This type of analysis has to be made more suitable for anchored sheet pile quay walls. In dynamic analysis the seismic behaviour of a structure can be simulated by means of finite element software. Experience has shown that it is desirable to consider sheet pile quay walls in a less conservative way in (preliminary) seismic design for which pseudo-static methodology is commonly applied. Therefore the general objective of the present study is to propose improvements on (simplified) seismic design methodologies for anchored sheet pile quay walls by considering deformation behaviour. For this purpose a research methodology is developed in which pseudo-static, permanent-displacement and FE analysis are employed, calibrated with an experimental reference case that considers a typical anchored sheet pile quay wall. The reference case is taken from a conference paper. It reports on a shake table test under centrifugal gravity which is performed on a scale model of an existing sheet pile quay wall with a batter pile anchor. The quay is situated in homogeneous soil that consists of coarse densified sand. Due to the soil condition liquefaction effects are prevented. Sequential seismic loading of increasing severity is applied during the shake table testing. Measurement results that are reported in the reference case paper comprise bending moments in the sheet pile wall, normal forces in the anchor rod and horizontal displacements of the sheet pile wall. For simplified analysis a calibrated D-SHEET PILING model of the reference case anchored sheet pile quay wall is created. Through an iterative pseudo-static calculation procedure in which D-SHEET PILING and reference case dynamic bending moment results are fitted, it is attempted to find a deformation-based seismic load reduction for structural forces in the sheet pile wall that can be applied in pseudo-static design methodology. For simplified dynamic analysis an analytical limit equilibrium model is developed, based on the failure behaviour of the reference case. The goal of this model is that it can compute the critical acceleration of the anchored quay structure and estimate the sheet pile forces at this critical state. These abilities are validated with PLAXIS 2D and checked with the reference case measurements respectively. Six accelerograms in the reference case soil column, obtained with equivalent linear site-response analysis (with SHAKE2000), are combined with the computed critical acceleration for permanent-displacement (sliding-block) analysis. For dynamic analysis a calibrated PLAXIS 2D model of the reference case anchored sheet pile quay wall is created. Dynamic performance of the PLAXIS 2D model is validated with SHAKE2000 by comparing site-response analysis results of both models. Pseudo-static and pseudo-dynamic calculations are applied to obtain the critical acceleration. Dynamic calculations with six bedrock motions are carried out to simulate the reference case experiment. PLAXIS 2D calculation results are used to validate simplified and simplified dynamic analysis results and to gain insight in the seismic failure behaviour of the anchored sheet pile quay wall. Approaches for (simplified) performance-based seismic analysis of a typical anchored sheet pile quay wall are proposed as a result of the research. For pseudo-static methodology a deformation-based seismic load reduction for structural forces in the sheet pile wall is proposed. For the present reference case it is concluded that a reduction in the range of 45% to 50% is allowable. For simplified dynamic analysis a limit equilibrium model is proposed to compute the critical acceleration of the present quay structure and to estimate sheet pile forces at this critical state. It is concluded that the ability of the limit equilibrium model is satisfactory. Although subjected to uncertainty, permanent-displacement analysis results indicate that the sliding-block analysis, originally developed for embankments, is possibly not suitable for anchored sheet pile quay walls. For dynamic analysis it is concluded that PLAXIS 2D is able to compute the reference case failure behaviour reasonably well, despite some computational setbacks. Complementary is the conclusion that PLAXIS 2D pseudo-static approach proves to be suitable to determine the critical acceleration of an anchored sheet pile structure in contrast to pseudo-dynamic approach which appears less suitable for that matter. In addition the performance-based design principle is linked to the present study so that an idea about the seismic performance limits of anchored sheet pile quay walls in quantitative terms can be provided. As a result of the present study findings it is recommended to perform more extensive research on the ability of permanent-displacement analysis to evaluate the amount of sliding displacement of an anchored sheet pile quay wall. In line with this recommendation it is found that further research on site-response analysis is desirable in the application of simplified dynamic and dynamic analysis. In general it is recommended to create more seismic test cases with different setups for a broader validity of the present results, to develop a seismic test case for the Groningen earthquake situation, to add measurement instrumentation to new and existing structures for verification of research results and to make such (raw) measurement data available to the public.Hydraulic Structures & Flood RiskHydraulic EngineeringCivil Engineering and Geoscience
Developing scenarios for the European plastics industry based on the uncertainties of shale gas
No full textTechnology, Policy and ManagementValues Technology and InnovationManagement of Technolog
Synthese en karakterisering van poly(meth)acrylaten en poly(meth)acryiaat/urethaan netwerken
No full textApplied SciencesTechnologie van Macromoleculaire Stoffe
Effect of compaction and soil moisture on the effective permeability of sands for use in methane oxidation systems
No full textEffective gas permeability is an important parameter in the design of methane oxidation systems, governing diffusive oxygen ingress and the spatial spread of landfill gas. The influences of soil texture, compaction, soil moisture and the resulting air filled porosity on the gas permeability were researched by performing pressure loss experiments on two loamy sands, currently in use as methane oxidation layer material. These experiments mimicked the influence of the intrinsic soil properties, the construction method (compaction) and the local climate (soil moisture) on the soils’ permeability. In both soils, effective and specific permeability were strongly impacted by the level of soil compaction, whereas increasing moisture contents had little effect in one of the soils, only reducing effective permeability when a certain threshold was exceeded. In the other soil, structure-forming processes induced by the addition of water led to an increase in both effective and specific permeability with increasing moisture. It is concluded that the spatial spread of the landfill gas in the gas distribution layer is predominantly affected by texture and compaction of the overlying methane oxidation layer. In terms of methane oxidation system design, the choice of material and construction method have more impact on gas permeability than seasonal changes in soil moisture in moderate climates. Furthermore, air filled porosity on its own is not adequate to estimate the effective permeability of loamy sand for methane oxidation layers. Further research should address the estimation of effective gas permeability based upon soil texture, bulk density and soil moisture combined.Geo-engineerin
Reliability Based Design Optimization on Quay Walls by re-calculating partial factors
No full textIn the years to come, the Netherlands will face a substantial challenge as over 1,500 kilometers of aging quay walls and sheet pile walls approach the end of their technical lifespan. Infrastructure managers anticipate that the necessary replacements will necessitate investments amounting to billions of euros. Moreover, this task carries a significant environmental footprint, notably in terms of CO2 emissions. The construction work required for these replacements will also result in disruptions and reduced accessibility, inconveniencing users.This study addresses two pivotal aspects. Firstly, it focuses on enhancing the design aspects of new structures and optimizing costs, with a specific focus exploring how these enhancements can ease the financial challenges faced by infrastructure managers. Secondly, it investigates the safety of existing structures and explores ways to maximize their loadbearing capacity while maintaining safety standards. The expected outcomes of this study promise improved design aspects, cost-efficiency, and enhanced safety measures.Quay walls can fail due to various mechanisms. This research investigates three primary causes: yielding of soil, yielding of quay wall and anchor yielding. Quay walls illustrate the complexities of soil-structure interaction. To address this, models were developed in both Plaxis and D-Sheet Piling. D-Sheet Piling was the preferred choice due to its computational speed. The reliability analysis was conducted with Probabilistic Toolkit. Considering the calculation methods, First Order Reliability Method (FORM) was employed, emphasizing in efficient computational results in contrast to the Monte-Carlo approach.In the first aspect, the partial factors were recalculated and compared them with the existing EC partial factor approach. To optimize the current design methodology, the retaining height of the structure was adjusted based on its reliability index. Additionally, the maximum anchor force required was re-evaluated for the structure. This procedure has been conducted for two scenarios, considering and not considering model uncertainty.Furthermore, an analysis was conducted to understand how altering the retaining height can lead to reduced steel usage, subsequently impacting costs and CO2 emissions. In the second aspect, it was pursued to enhance the structure’s performance by introducing a factor "n" across four distinct scenarios: 1. Simultaneously increasing all loads. 2. Increasing the surcharge loads on the terrain. 3. Increasing the bollard load. 4. Raising the final excavation level in front of the quay wall. While this study aligns with the extensive body of research in the field of civil engineering, It seeks to offer a new and sustainable approach on understanding quay wall design, focusing specifically on the designers’ viewpoint. Through the exploration of innovative design frameworks and approaches, this research seeks to make a valuable contribution to the long-term sustainability of quay wall structures. It aims to redefine our approach to accessibility and safety in these crucial structures. The comprehensive investigations conducted throughout this study provide an enhanced comprehension of quay wall design, reliability, and the optimization of performance.Geo-Engineerin
