Exercise-Based Injury Prevention in Child and Adolescent Sport: A Systematic Review and Meta-Analysis
- Authors: Rossler, Roland , Donath, Lars , Verhagen, Evert , Junge, Astrid , Schweizer, Thomas , Faude, Oliver
- Date: 2014
- Type: Text , Journal article
- Relation: Sports Medicine Vol. 44, no. 12 (2014), p. 1733-1748
- Full Text: false
- Reviewed:
- Description: Background: The promotion of sport and physical activity (PA) for children is widely recommended to support a healthy lifestyle, but being engaged in sport bears the risk of sustaining injuries. Injuries, in turn, can lead to a reduction in current and future involvement in PA and, therefore, may negatively affect future health as well as quality of life. Thus, sports injury prevention is of particular importance in youth. Objective: The aim of this systematic review was to quantify the effectiveness of exercise-based injury prevention programs in child and adolescent sport in general, and with respect to different characteristics of the target group, injury prevention program, and outcome variables. Data Sources: An Internet-based literature search was conducted in six databases (CINAHL, Cochrane, EMBASE, ISI Web of Science, PubMed, SPORTDiscus) using the following search terms with Boolean conjunction: (sport injur* OR athletic injur* OR sport accident*) AND (prevent* OR prophylaxis OR avoidance) AND (child* OR adolescent OR youth). Study Selection: Randomized controlled trials and controlled intervention studies in organized sport, published in English in a peer-reviewed journal, analyzing the effects of an exercise-based injury prevention program in athletes younger than 19 years of age. Data Extraction: Two reviewers evaluated eligibility and methodological quality. Main outcome extracted was the rate ratio (RR). Statistical analyses were conducted using the inverse-variance random effects model. Results: Twenty-one trials, conducted on a total of 27,561 athletes (median age 16.7 years [range 10.7-17.8]), were included. The overall RR was 0.54 (95% CI 0.45-0.67) [p < 0.001]. Girls profited more from injury prevention than boys (p = 0.05). Both prevention programs with a focus on specific injuries (RR 0.48 [95% CI 0.37-0.63]) and those aiming at all injuries (RR 0.62 [95% CI 0.48-0.81]) showed significant reduction effects. Pre-season and in-season interventions were similarly beneficial (p = 0.93). Studies on programs that include jumping/plyometric exercises showed a significant better (p = 0.002) injury preventive effect (RR 0.45 [95 % CI 0.35-0.57], Z = 6.35, p < 0.001) than studies without such exercises (RR 0.74 [95% CI 0.61-0.90], Z = 3.03, p = 0.002). Conclusions: The results provide good evidence and clearly demonstrate beneficial effects of exercise-based injury prevention programs in youth sports as they can result in statistically significant and practically relevant injury reduction. In particular, multimodal programs including jumping/plyometric exercises can be recommended. However, there is a considerable lack of data for children (under 14 years of age) and for individual sports in general. Future research should include these groups and focus on the effect of specific exercises and compliance.
DEM modeling of particle breakage in silica sands under one-dimensional compression
- Authors: Shi, Danda , Zheng, Lin , Xue, Jianfeng , Sun, Jing
- Date: 2016
- Type: Text , Journal article
- Relation: Acta Mechanica Solida Sinica Vol. 29, no. 1 (2016), p. 78-94
- Full Text: false
- Reviewed:
- Description: A Discrete Element Method (DEM) model is developed to study the particle breakage effect on the one-dimensional compression behavior of silica sands. The 'maximum tensile stress' breakage criterion considering multiple contacts is adopted to simulate the crushing of circular particles in the DEM. The model is compared with published experimental results. Comparison between the compression curves obtained from the numerical and experimental results shows that the proposed method is very effective in studying the compression behavior of silica sands considering particle breakage. The evolution of compression curves at different stress levels is extensively studied using contact force distribution, variation of contact number and particle size distribution curve with loading. It is found that particle breakage has great impact on compression behavior of sand, particularly after the yield stress is reached and particle breakage starts. The crushing probability of particles is found to be macroscopically affected by stress level and particle size distribution curve, and microscopically related to the evolutions of contact force and coordination number. Once the soil becomes well-graded and the average coordination number is greater than 4 in two-dimension, the crushing probability of parent particles can reduce by up to 5/6. It is found that the average contact force does not always increase with loading, but increases to a peak value then decreases once the soil becomes more well-graded. It is found through the loading rate sensitivity analysis that the compression behavior of sand samples in the DEM is also affected by the loading rate. Higher yield stresses are obtained at higher loading rates. © 2016 The Chinese Society of Theoretical and Applied Mechanics.
Commercial golf glove effects on golf performance and forearm muscle activity
- Authors: Sorbie, Graeme , Darroch, Paul , Grace, Fergal , Gu, Yaodong , Baker, Julien , Ugbolue, Ukadike
- Date: 2017
- Type: Text , Journal article
- Relation: Research in Sports Medicine Vol. 25, no. 4 (2017), p. 451-461
- Full Text: false
- Reviewed:
- Description: The study aimed to determine whether or not commercial golf gloves influence performance variables and forearm muscle activity during golf play. Fifteen golfers participated in the laboratory based study, each performing 8 golf swings with a Driver and 7-iron whilst wearing a glove and 8 without wearing the glove. Club head speed, ball speed and absolute carry distance performance variables were calculated. Surface electromyography was recorded from the flexor digitorum superficialis and extensor carpi radialis brevis on both forearm muscles. Club head speed, ball speed and absolute carry distance was significantly higher when using the Driver with the glove in comparison to the Driver without the glove (p < 0.05). No significant differences were evident when using the 7-iron and no significant differences were displayed in muscle activity in either of the conditions. Findings from this study suggest that driving performance is improved when wearing a glove.
CFRP repaired welded thin-walled cross-beam connections subject to in-plane fatigue loading
- Authors: Xiao, Zhigang , Zhao, Xiao
- Date: 2012
- Type: Text , Journal article
- Relation: International Journal of Structural Stability and Dynamics Vol. 12, no. 1 (2012 2012), p. 195-211
- Full Text: false
- Reviewed:
- Description: Cracked cross-beam connections made of thin-walled rectangular hollow sections (RHS) are repaired with carbon fiber-reinforced polymer (CFRP) sheets. Constant amplitude fatigue experiments are conducted on the repaired specimens. A pilot test is conducted on a T-connection of square hollow sections (SHS) to explore the effective method of applying CFRP. Due to the peeling effect at the corner region of the SHS-to-SHS connection, early debonding happens in the pilot test that only results in a slight extension in fatigue life. In the following experiments of repairing RHS-to-RHS cross-beam connections, circumferential or transverse restraining CFRP patches are applied in the corner region that prevents early debonding successfully and leads to significant increase in fatigue life. Finally, an improvement is made with the addition of steel strengthening plates that increase both the flexural stiffness and fatigue life of the cracked specimens significantly. The proposed retrofitting method may be useful for repairing other similar fatigue-cracked welded tubular connections.
Improving the efficiency of LPG Compression Ignition Engines for Passenger Cars through Waste Heat Recovery
- Authors: Boretti, Alberto
- Date: 2012
- Type: Text , Journal article
- Relation: SAE International Journal of Fuels and Lubricants Vol. 4, no. 2 (2012), p. 223-236
- Full Text: false
- Reviewed:
- Description: The turbocharged direct injection lean burn Diesel engine is the most efficient now in production for transport applications with full load brake efficiencies up to 40 to 45% and reduced penalties in brake efficiencies reducing the load by the quantity of fuel injected. The secrets of this engine's performances are the high compression ratio and the lean bulk combustion mostly diffusion controlled in addition to the partial recovery of the exhaust energy to boost the charging efficiency. The major downfalls of this engine are the carbon dioxide emissions and the depletion of fossil fuels using fossil diesel, the energy security issues of using foreign fossil fuels in general, and finally the difficulty to meet future emission standards for soot, smoke, nitrogen oxides, carbon oxide and unburned hydrocarbons for the combustion of the fuel injected in liquid state and the lack of maturity the lean after treatment system. LPG is an alternative fuel with a better carbon to hydrogen ratio therefore permitting reduced carbon dioxide emissions. It flashes immediately to gaseous form even if injected in liquid state for a much cleaner combustion almost cancelling some of the emissions (even if unfortunately not all of them) of the diesel and it permits a much better energy security within Australia. The paper presents a passenger car diesel engines converted to LPG. In this engine the efficiency is then improved recovering the waste heat. This recovery has impacts on both the in cylinder fuel conversion efficiency and the efficiency of the after treatment. Results of engine performance simulations are performed for a in-line four cylinder 1.6 litres LPG CI passenger car engine with a power turbine following the turbine of the turbocharger or an heat exchanger to recover the exhaust (and other) waste heat and compared with the experimental results for the diesel without waste heat recovery. © 2011 SAE International.
Reachability and controllability of linear switched impulsive systems
- Authors: Liu, Chao , Han, Qi , Li, Chuandong , Zhang, Qun
- Date: 2013
- Type: Text , Journal article
- Relation: IET Control Theory and Applications Vol. 7, no. 9 (2013), p. 1294-1299
- Full Text: false
- Reviewed:
- Description: This study investigates the reachability and controllability of linear switched impulsive systems in which impulsive component is independent of switching among different subsystems. Some crucial geometrical criteria are established. The authors present the fact that the reachable sets and the controllable sets may not be subspaces, if impulsive matrices are singular. While impulsive matrices are reversible, the reachable and controllable subspaces can be determined by two proposed subspace algorithms. The authors also point out that the reachable or controllable subspace is an invariant subspace of the considered systems. Finally, two simple corresponding examples are discussed to illustrate the correctness and effectiveness of the proposed theoretical results. © The Institution of Engineering and Technology 2013.
- Description: C1
Coupled DEM-LBM simulation of internal fluidisation induced by a leaking pipe
- Authors: Cui, Xilin , Li, Jun , Chan, Andrew , Chapman, David
- Date: 2014
- Type: Text , Journal article
- Relation: Powder Technology Vol. 254, no. (2014), p. 299-306
- Full Text: false
- Reviewed:
- Description: This paper presents a numerical study of soil fluidisation induced by local leakage from a buried pipe using the coupled discrete element and lattice Boltzmann approach (DEM–LBM). The behaviour of the system is studied using different flow rates and initial bed heights. The excess pore pressure distribution and the soil behaviour due to a localised leak are investigated and compared with previous experimental findings. The comparison indicates that DEM–LBM is capable of capturing the leakage–soil interaction at the particle scale. Moreover, as the flow distribution is found to be one-dimensional in the radial direction rather than one-dimensional in the vertical direction, an extension to the Ergun flow equation is derived and the numerically measured fluidising pressure shows good agreement with this analytical solution. In addition, as indicated by the numerical results and the derived analytical solution, the relationship between fluidising pressure and pipe buried depth as well as leak size is also established. The simulation results suggest that DEM–LBM is a promising tool to carry out further studies into the internal fluidisation phenomenon.
Could targeted exercise programmes prevent lower limb injury in community Australian football?
- Authors: Andrew, Nadine , Gabbe, Belinda , Cook, Jill , Lloyd, David , Donnelly, Cyril , Nash, Clare , Finch, Caroline
- Date: 2013
- Type: Text , Journal article
- Relation: Sports Medicine Vol. 43, no. 8 (2013), p. 751-763
- Relation: http://purl.org/au-research/grants/nhmrc/565900
- Relation: http://purl.org/au-research/grants/nhmrc/565907
- Full Text:
- Reviewed:
- Description: Background: Australian football is a popular sport in Australia, at both the community and elite levels. It is a high-speed contact sport with a higher incidence of medically treated injuries when compared with most other organized sports. Hamstring injuries, ligament injuries to the knee or ankle, hip/groin injuries and tendinopathies are particularly common and often result in considerable time lost from sport. Consequently, the prevention of lower limb injuries is a priority for both community and elite Australian football organizations. There is considerable literature available on exercise programmes aimed at reducing lower limb injuries in Australian football and other running-related sports. The quality and outcomes of these studies have varied considerably, but indicate that exercise protocols may be an effective means of preventing lower limb injuries. Despite this, there has been limited high-quality and systematic evaluation of these data. Objective: The aim of this literature review is to systematically evaluate the evidence about the benefits of lower limb injury prevention exercise protocols aimed at reducing the most common severe lower limb injuries in Australian football. Methods: The Cochrane Central Register of Controlled Trials, the Cochrane Bone Joint and Muscle Trauma Group Specialized Register, MEDLINE and other electronic databases were searched, from January 1990 to December 2010. Papers reporting the results of randomized controlled trials (RCTs), quasi-RCTs, cohort and case-control studies were extracted. Primary outcomes were injury reduction or risk factor identification and/or modification. Secondary outcomes were adherence to any trialled interventions, injury severity and adverse effects such as secondary injuries and muscle soreness. The methodological quality of extracted manuscripts was assessed and results were collated. Results: Forty-seven papers were identified and reviewed of which 18 related to hamstring injury, eight related to knee or ankle ligament injury, five related to tendon injury and four were hip or groin injury related. Another 12 papers targeted general lower limb injuries. Most (n = 27 [57 %]) were observational studies, investigating injury risk factors. Twenty reported the results of intervention trials. Of these, 15 were efficacy trials reporting the effects of an intervention in reducing injury rates, four were biomechanical interventions in which the impact of the intervention on a known injury risk factor was assessed and one reported changes in injury risk factors as well as injury rates. The strength of the evidence base for exercise programmes for lower limb injury prevention was found to be limited, primarily due to the research methods employed, low adherence to interventions by the study participants and a lack of statistical power. Limited evidence obtained from a small number of RCTs suggests that balance and control exercises might be efficacious in preventing ankle ligament injuries and a programme involving a combination of balance and control exercises, eccentric hamstring, plyometrics and strength exercises could be efficacious in preventing all lower limb injuries. Conclusions: Overall, the evidence for exercise programmes as an efficacious lower limb injury prevention strategy is predominantly restricted to studies addressing injury aetiology and mechanisms. The findings of this review highlight the need to develop and test interventions in well designed population-based trials with an emphasis on promoting intervention uptake and adherence and, hence, intervention effectiveness. The results of this review can inform the development of the components of a future lower limb injury prevention exercise protocol for community-level Australian football. © 2013 Springer International Publishing Switzerland. Funded by the NHMRC.
- Description: 2003011215
Instrumentation and motivations for organised cycling: : The development of the cyclist motivation instrument (CMI)
- Authors: Brown, Trent , O'Connor, Justen , Barkatsas, Anastasios
- Date: 2009
- Type: Text , Journal article
- Relation: Journal of Sports Science and Medicine, vol. 8, no. 2, Asist Group, p. 211-218
- Full Text:
- Description: ‘Serious leisure’ cycling has developed as a reinterpretation of the traditional form of the sport. This short term, informal, unstructured and unconventional conceptualisation represents a challenge to participant numbers in the mainstream sport. The purpose of this study was twofold: (i) to ascertain the cultural, subcultural and ecological factors of participation in this new conceptualised form enabling clubs, associations and governments to a deeper understanding about participants practices and (ii) as an ongoing validation to previous qualitative work (see O’Connor and Brown, 2005). This study reports on the development and psychometric properties (principal components analysis, confirmatory factor analysis) of the Cyclists’ Motivation Instrument. Four hundred and twenty two cyclists (371 males, 51 females) who were registered members of the state competitive cycling body completed a fifty-one item instrument. Five factors were identified: social, embodiment, self-presentation, exploring environments and physical health outcomes and these accounted for 47.2% of the variance. Factor alpha coefficients ranged from .63 to .88, overall scale reliability was .92, suggesting moderate to high reliability for each of the factors and the overall scale.
Epidemiology of facial injuries in sport
- Authors: Black, Amanda , Eliason, Paul , Patton, Declan , Emery, Carolyn
- Date: 2017
- Type: Text , Journal article
- Relation: Clinics in Sports Medicine Vol. 36, no. 2 (2017), p. 237-255
- Full Text: false
- Reviewed:
- Description: Facial injuries can pose a large health burden for athletes, potentially resulting in time loss and surgery. This article reviews the incidence, common mechanisms, and risk factors of facial injuries in several sports globally. Estimates of facial injury rates are complicated by a lack of, or inconsistent, reporting on specific types of injury. Much of the epidemiologic literature is based on hospital-based injury surveillance and there is a paucity of literature examining sport-specific risk factors. Future research should focus on prospective injury surveillance methodologies with consistent injury definitions examining risk factors and the effectiveness of facial injury prevention efforts.
A reliability-based design optimization model for electricity power networks
- Authors: Ezzati, Ghasem
- Date: 2015
- Type: Text , Journal article
- Relation: Dynamics of Continuous, Discrete and Impulsive Systems Series B: Applications and Algorithms Vol. 22, no. 5 (2015), p. 339-357
- Full Text: false
- Reviewed:
- Description: Significant attentions have recently been attracted by electricity power net- works where many optimization models are applied to optimize distributed power. Many optimization models are available for electricity networks that mainly take into accoun- t total cost. Reliability related issues of electricity networks are also considered in the literature. However, there is a lack to formulate a reliability-based design optimization (RBDO) model of these networks. An RBDO model is introduced in this paper to deal with probabilistic constraints in an optimization model for electricity networks. In our suggested approach, an optimization problem is firstly solved to find optimal parameters of the network. Then, the optimal solution is adjusted using an RBDO problem. Our main aim is to minimize an extra cost that is experienced by considering reliability. It is expected to have a higher extra cost for a lower failure probability. © 2015 Watam Press.
Left ventricular speckle tracking-derived cardiac strain and cardiac twist mechanics in athletes : A systematic review and meta-analysis of controlled studies
- Authors: Beaumont, Alexander , Grace, Fergal , Richards, Joanna , Hough, John , Oxborough, David , Sculthorpe, Nicholas
- Date: 2017
- Type: Text , Journal article
- Relation: Sports Medicine Vol. 47, no. 6 (2017), p. 1145-1170
- Full Text: false
- Reviewed:
A review of instrumented equipment to investigate head impacts in sport
- Authors: Patton, Declan
- Date: 2016
- Type: Text , Journal article , Review
- Relation: Applied Bionics and Biomechanics Vol. 2016, no. (2016), p. 1-17
- Full Text:
- Reviewed:
- Description: Contact, collision, and combat sports have more head impacts as compared to noncontact sports; therefore, such sports are uniquely suited to the investigation of head impact biomechanics. Recent advances in technology have enabled the development of instrumented equipment, which can estimate the head impact kinematics of human subjects in vivo. Literature pertaining to head impact measurement devices was reviewed and usage, in terms of validation and field studies, of such devices was discussed. Over the past decade, instrumented equipment has recorded millions of impacts in the laboratory, on the field, in the ring, and on the ice. Instrumented equipment is not without limitations; however, in vivo head impact data is crucial to investigate head injury mechanisms and further the understanding of concussion. © 2016 Declan A. Patton.
A novel error indicator and an adaptive refinement technique using the scaled boundary finite element method
- Authors: Song, Chongmin , Ooi, Ean Tat , Pramod, Aladurthi , Natarajan, Sundararajan
- Date: 2018
- Type: Text , Journal article
- Relation: Engineering Analysis with Boundary Elements Vol. 94, no. (2018), p. 10-24
- Full Text: false
- Reviewed:
- Description: In this paper, an adaptive refinement strategy based on the scaled boundary finite element method on quadtree meshes for linear elasticity problems is discussed. Within this framework, the elements with hanging nodes are treated as polygonal elements and thus does not require special treatment. The adaptive refinement is supplemented with a novel error indicator. The local error is estimated directly from the solution of the scaled boundary governing equations. The salient feature is that it does not require any stress recovery techniques. The efficacy and the robustness of the proposed approach are demonstrated with a few numerical examples.
A scaled boundary finite element formulation over arbitrary faceted star convex polyhedra
- Authors: Natarajan, Sundararajan , Ooi, Ean Tat , Saputra, Albert , Song, Chongmin
- Date: 2017
- Type: Text , Journal article
- Relation: Engineering Analysis with Boundary Elements Vol. 80, no. (2017), p. 218-229
- Full Text: false
- Reviewed:
- Description: In this paper, a displacement based finite element framework for general three-dimensional convex polyhedra is presented. The method is based on a semi-analytical framework, the scaled boundary finite element method. The method relies on the definition of a scaling center from which the entire boundary is visible. The salient feature of the method is that the discretizations are restricted to the surfaces of the polyhedron, thus reducing the dimensionality of the problem by one. Hence, an explicit form of the shape functions inside the polyhedron is not required. Conforming shape functions defined over arbitrary polygon, such as the Wachpress interpolants are used over each surface of the polyhedron. Analytical integration is employed within the polyhedron. The proposed method passes patch test to machine precision. The convergence and the accuracy properties of the method is discussed by solving few benchmark problems in linear elasticity. © 2017 Elsevier Ltd
Acoustic emission source location on large plate-like structures using a local triangular sensor array
- Authors: Aljets, Dirk , Chong, Alex , Wilcox, Steven , Holford, Karen
- Date: 2012
- Type: Text , Journal article
- Relation: Mechanical Systems and Signal Processing Vol. 30, no. (2012), p. 91-102
- Full Text: false
- Reviewed:
- Description: A new acoustic emission (AE) source location method was developed for large plate-like structures, which evaluates the location of the source using a combined time of flight and modal source location algorithm. Three sensors are installed in a triangular array with a sensor to sensor distance of just a few centimeters. The direction from the sensor array to the AE source can be established by analysing the arrival times of the A 0 component of the signal to the three sensors whilst the distance can be evaluated using the separation of S 0 and A 0 mode at each sensor respectively. The close positioning of the sensors allows the array to be installed in a single housing. This simplifies mounting, wiring and calibration procedures for non-destructive testing (NDT) and structural health monitoring (SHM) applications. Furthermore, this array could reduce the number of sensors needed to monitor large structures compared to other methods. An automatic wave mode identification method is also presented. © 2012 Elsevier Ltd.
A 2-year prospective study of injury epidemiology in elite Australian rugby sevens : Exploration of incidence rates, severity, injury type, and subsequent injury in men and women
- Authors: Toohey, Liam , Drew, Michael , Finch, Caroline , Cook, Jill , Fortington, Lauren
- Date: 2019
- Type: Text , Journal article
- Relation: American Journal of Sports Medicine Vol. 47, no. 6 (2019), p. 1302-1311
- Full Text: false
- Reviewed:
- Description: Background: Injuries are common in rugby sevens, but studies to date have been limited to short, noncontinuous periods and reporting of match injuries only. Purpose: To report the injury incidence rate (IIR), severity, and burden of injuries sustained by men and women in the Australian rugby sevens program and to provide the first longitudinal investigation of subsequent injury occurrence in rugby sevens looking beyond tournament injuries only. Study Design: Descriptive epidemiology study. Methods: Ninety international rugby sevens players (55 men and 35 women) were prospectively followed over 2 consecutive seasons (2015-2016 and 2016-2017). All medical attention injuries were reported irrespective of time loss. Individual exposure in terms of minutes, distance, and high-speed distance was captured for each player for matches and on-field training, with the use of global positioning system devices. The IIR and injury burden (IIR × days lost to injury) were calculated per 1000 player-hours, and descriptive analyses were performed. Results: Seventy-three players (81.1%) sustained 365 injuries at an IIR of 43.2 per 1000 player-hours (95% CI, 43.0-43.3). As compared with male players, female players experienced a lower IIR (incidence rate ratio, 0.91; 95% CI, 0.90-0.91). Female players also sustained a higher proportion of injuries to the trunk region (relative risk, 1.75; 95% CI, 1.28-2.40) but a lower number to the head/neck region (relative risk, 0.58; 95% CI, 0.37-0.93; P =.011). The majority (80.7%) of subsequent injuries were of a different site and nature than previous injuries. A trend toward a reduced number of days, participation time, distance, and high-speed distance completed before the next injury was observed after successive injury occurrence. Conclusion: Female players have a lower IIR than male players, with variation of injury profiles observed between sexes. With a surveillance period of 2 years, subsequent injuries account for the majority of injuries sustained in rugby sevens, and they are typically different from previous types of sustained injuries. After each successive injury, the risk profile for future injury occurrence appears to be altered, which warrants further investigation to inform injury prevention strategies in rugby sevens.
Effect of grain bonding on the stability of a borehole drilled through low cemented formations
- Authors: Hashemi, Sam , Melkoumian, Nouné , Xu, Chaoshui
- Date: 2012
- Type: Text , Conference paper
- Relation: 7th Australasian Congress on Applied Mechanics, ACAM 2012 p. 884-894
- Full Text: false
- Reviewed:
- Description: Achieving an in-depth understanding of the behaviour of low cemented formations such as running sands around a cylindrical borehole is of significant importance in identifying stability problems, designing adequate borehole supports and choosing an efficient drilling method. This paper presents numerical investigations on failure modes of unsupported vertical cylindrical boreholes drilled through weak formations, i.e. low cemented sands where the movement of individual grains is not restricted by sufficient cementation. Distinct element method (DEM) was used for this study. The method enables to simulate sand grains and control normal and shear bonding between them. To simulate actual condition surrounding a borehole at a depth of 80m, a 2m × 2m × 2m cube made up of spherical particles with diameters ranging from 5mm to 70mm was constructed and analysed in the DEM code, PFC3D. The results showed that stress concentration developed in the ground due to the presence of a borehole leads to the formation of a damage zone around that borehole. When there is not sufficient bonding between the sand grains, the interaction between them results in their movement towards the borehole and the eventual collapse of the borehole wall. The effect of fluid flow on stability of boreholes has been studied as well. The cementation between sand grains is mainly caused by the presence of clay particles in the formation. The bonding strength between sand grains is an intrinsic or micro property of the bonding material and is very difficult to measure in laboratory conditions. The results obtained from current research will help to evaluate the effect of particle bonding on the mechanical behaviour of low cemented formations and develop methods to assess borehole stability during and after drilling through such formations.
Crack propagation modelling in concrete using the scaled boundary finite element method with hybrid polygon-quadtree meshes
- Authors: Ooi, Ean Tat , Natarajan, Sundararajan , Song, Chongmin , Ooi, Ean Hin
- Date: 2017
- Type: Text , Journal article
- Relation: International Journal of Fracture Vol. 203, no. 1-2 (2017), p. 135-157
- Full Text: false
- Reviewed:
- Description: This manuscript presents an extension of the recently-developed hybrid polygon-quadtree-based scaled boundary finite element method to model crack propagation in concrete. This hybrid approach combines the use of quadtree cells with arbitrary sided polygons for domain discretization. The scaled boundary finite element formulation does not distinguish between quadtree cells and arbitrary sided polygons in the mesh. A single formulation is applicable to all types of cells and polygons in the mesh. This eliminates the need to develop transitional elements to bridge the cells belonging to different levels in the quadtree hierarchy. Further to this, the use of arbitrary sided polygons facilitate the accurate discretization of curved boundaries that may result during crack propagation. The fracture process zone that is characteristic in concrete fracture is modelled using zero-thickness interface elements that are coupled to the scaled boundary finite element method using a shadow domain procedure. The scaled boundary finite element method can accurately model the asymptotic stress field in the vicinity of the crack tip with cohesive tractions. This leads to the accurate computation of the stress intensity factors, which is used to determine the condition for crack propagation and the resulting direction. Crack growth can be efficiently resolved using an efficient remeshing algorithm that employs a combination of quadtree decomposition functions and simple Booleans operations. The flexibility of the scaled boundary finite element method to be formulated on arbitrary sided polygons also result in a flexible remeshing algorithm for modelling crack propagation. The developed method is validated using three laboratory experiments of notched concrete beams subjected to different loading conditions.
Extraction and processing of real time strain of embedded FBG sensors using a fixed filter FBG circuit and an artificial neural network
- Authors: Kahandawa, Gayan , Epaarachchi, Jayantha , Wang, Hao , Canning, John , Lau, Alan
- Date: 2013
- Type: Text , Journal article
- Relation: Measurement: Journal of the International Measurement Confederation Vol. 46, no. 10 (2013), p. 4045-4051
- Full Text:
- Reviewed:
- Description: Fibre Bragg Grating (FBG) sensors have been used in the development of structural health monitoring (SHM) and damage detection systems for advanced composite structures over several decades. Unfortunately, to date only a handful of appropriate configurations and algorithm sare available for using in SHM systems have been developed. This paper reveals a novel configuration of FBG sensors to acquire strain reading and an integrated statistical approach to analyse data in real time. The proposed configuration has proven its capability to overcome practical constraints and the engineering challenges associated with FBG-based SHM systems. A fixed filter decoding system and an integrated artificial neural network algorithm for extracting strain from embedded FBG sensor were proposed and experimentally proved. Furthermore, the laboratory level experimental data was used to verify the accuracy of the system and it was found that the error levels were less than 0.3% in predictions. The developed SMH system using this technology has been submitted to US patent office and will be available for use of aerospace applications in due course. © 2013 Elsevier Ltd. All rights reserved.