1,411 research outputs found
Control of flash gas bypass mac system with emphasis on start-ups and transients
No full textFlash Gas Bypass (FGB) approach has the benefits of eliminating refrigerant maldistribution and reducing refrigerant pressure drop across the evaporator. Most of the previous research on flash gas bypass focused on performance improvement in steady state and demonstrated that compared to direct expansion mode (DX), FGB mode have better performance. However, the control strategy of FGB system and dynamic behavior during start-ups and transients were not yet clearly defined and investigated. In this paper, a novel control strategy has been proposed for an automobile air conditioning system operating in flash gas bypass mode with R134a as the refrigerant. This research aims at understanding FGB system performance in dynamic and transient load conditions using Sporlan electronic flow controls.
This research identified three important issues for FGB system start-up process: size of bypass valve, size of FGB tank and control strategy for system operation. Although the exact sizing of both valve and FGB tank would be different from system to system, this study gave a basic guideline and a practical example of choosing corresponding components. More importantly, an innovative control strategy was implemented to make sure FGB system could be well-functioned under different working conditions in both start-up and transient scenarios automatically.
The proposed control strategy utilized an electronic expansion valve (EV) for the control of subcooling from condenser outlet and a bypass valve(BV) for superheat from compressor inlet. Both start-up and transient system behaviors were studied. Transients include changes in air mass flow rate on evaporator side, face velocity on condenser side and compressor speed. The experimental results showed that the proposed cycle control strategy was found to be able to provide reliable control to the system.Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2017-02-28 without embargo termsThe student, Yueming Li, accepted the attached license on 2016-12-07 at 14:55.The student, Yueming Li, submitted this Thesis for approval on 2016-12-07 at 15:00.This Thesis was approved for publication on 2016-12-08 at 14:25.DSpace SAF Submission Ingestion Package generated from Vireo submission #10469 on 2017-02-28 at 15:03:38Made available in DSpace on 2017-03-01T15:49:31Z (GMT). No. of bitstreams: 2
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Previous issue date: 2016-12-0
Efficient aeroelastic reduced order model with global structural modifications
No full textTime domain aeroelastic analysis has high computing costs when using computational fluid dynamics. These costs become prohibitive when the structural model undergoes large changes from the baseline design, as within an aircraft design process. To overcome this realistic challenge, we have developed, implemented, and demonstrated an efficient method that is robust in the presence of global modifications of the structure. The method consists of: a) a reduced order model of the linearized Navier-Stokes equations generated around an aeroelastic equilibrium that depends, in turn, on the structural model; b) an approximate structural dynamic reanalysis method valid for global modifications of the structure; and c) a mechanism to exchange information between fluid and structural solvers without need for calculating at each iteration of the structural design an eigenvalue problem of the modified structure. The resulting aeroelastic reduced order model is demonstrated for the AGARD 445.6 wing, and material properties are varied up to 100% from their original values. It is found that: a) predictions of the time domain aeroelastic response and of the flutter speed are accurate for all modifications of the structure; and b) the computational efficiency of the proposed aeroelastic reduced order model is linearly proportional to the number of structural configurations considered. The method, therefore, is ideally suited for optimization and uncertainty studies
Computational fluid dynamics-based aero-servo-elastic analysis for gust load alleviation
No full textGust load alleviation using computational fluid dynamics as source of the aerodynamic predictions is carried out in the time domain. To this goal, an aero-servo-elastic reduced order model is generated. The model capitalises on two key aspects: a dimensional reduction through proper orthogonal decomposition, further enhanced via balanced truncation; and an analytically derived mechanism to reproduce the gust effects in the reduced order model. The compact model in state-space form thus obtained was then used for control design synthesis. Assuming information on the structural motion only is accessible for feedback, a linear quadratic regular was designed, first, on the reduced model, and then validated on the large computational model. Resultsare presented for two configurations: an aerofoil and the modified AGARD 445.6 wing, both with a trailing-edge control surface. Studies are presented for the gust response to discrete gusts and continuous turbulence. In particular, for the latter, the standard deviation of the loads and the structural motion was reduced as much as 77%
In situ growth of CuO on porous geopolymer spheres as green catalysts for enhanced peroxymonosulfate-activated degradation of Orange I
No full textIn this study, in situ growth of CuO on the surface of porous geopolymer catalyst spheres (GC) was prepared through a simple method for the activation of peroxymonosulfate (PMS) to degrade Orange I (OI) in water. GC-0.01 exhibited an excellent performance with more than 95% degradation of OI within 30 min. The effects of PMS concentrations, catalyst dosage, Cl−, HCO3−, and humic acid (HA) on OI degradation in the GC-0.01/PMS system were systematically investigated. The study of the mechanism showed that PMS combined with the catalyst to generate complexes on the surface of the spheres, which could degrade OI through an electron transfer pathway. In addition, a variety of reactive oxygen species, mainly 1O2, were also present in the GC-0.01/PMS system, which could also degrade OI. This work provides new insight into the application of oxide-modified geopolymers in the activation of PMS for water purification applications
An efficient implementation of transonic aeroelastic tailoring based on a reduced-order model using structural dynamic reanalysis method
No full textDue to fuel efficiency, advanced aerodynamic and structural concern, more and more composite materials used in aircraft desgin. In composite structure aeroelastic tailoring process, an accurate and efficient method to evaluate the aeroelastic stability is very required. The traditional CFD-based POD/ROM has been shown its accuracy and efficiency for transonic aeroelastic analysis at fixed system. In aeroelastic tailoring process, in order to meet the requirements of aeroelastic performance, the parameters of the composite structure need to be modified repeatedly and the aerodynamic model have to be reconstructed. However, these reconstruction procedures take a considerable time, and greatly increasing the time cost of the aircraft design. To develop a more efficient composite structure aeroelastic tailoring method, starting with improving the efficiency of aeroelastic performance evaluation, this paper propose an approximate aeroelastic characteristics evaluation method based CFD-based POD/ROM by introducing the structural dynamic reanalysis method. The improved AGARD 445.6 composite wing was employed to verify the accuracy and efficiency of the proposed method. The results show that the proposed evaluation method can not only accurately predict the aeroelastic response of the structure, but also greatly improving the efficiency of transonic composite structure aeroelastic tailoring.</p
Variables influencing radiological fracture healing in children with femoral neck fractures treated surgically: A review of 177 cases
No full textPurpose: This study aimed: (1) to determine the probability of and the amount of time needed to achieve fracture healing in children with displaced femoral neck fractures (FNFs) treated surgically; and (2) to determine which factors can affect both the probability of and the amount of time needed to achieve radiological fracture healing in those patients. Hypothesis: Pediatric FNFs require longer time to achieve union than previously reported. Methods: We retrospectively reviewed the data of 177 children (mean age 10.5 ± 3.9 years) with FNFs treated surgically. Risk factors, including age, sex, laterality, the mechanism of injury, the initial displacement severity, the type of fracture, the time to reduction, the reduction method, the fixation method and the reduction quality, were recorded. Furthermore, the presence of a comminuted medial or posterior cortex on anteroposterior (AP) or lateral radiographs was also recorded. Results: A total of 172 hips (97.2%) achieved radiological fracture healing during the follow-up period. Severe initial displacement, a comminuted cortex on the AP or lateral radiographs and poor reduction quality significantly increased the time needed to achieve radiological fracture healing (p < 0.05). Cox regression analysis indicated that the cumulative probability of achieving fracture healing increased linearly during the first 6 months and then plateaued, with a monthly increase of less than 5%. The severity of initial displacement, presence/absence of comminution on the medial or posterior cortex, and reduction quality were factors influencing the probability of achieving fracture healing within the first 6 months after injury (p < 0.05). Conclusions: Radiological union of displaced pediatric FNFs treated surgically increases linearly during the first six month after surgery and then it tends to plateau. Risk factors for nonunion are severe initial displacement, poor reduction quality and the presence of comminuted medial or posterior cortex on AP or lateral radiographs; the same factors are associated with a longer time to achieve fracture healing. Level of evidence: III
Effect of the Number, Size, and Location of Cannulated Screws on the Incidence of Avascular Necrosis of the Femoral Head in Pediatric Femoral Neck Fractures: A Review of 153 Cases
No full textBackground: The correlation between the number, size, and location of cannulated screws and the incidence of avascular necrosis (AVN) in children with femoral neck fractures treated surgically is uncertain. Methods: We retrospectively reviewed 153 children (mean age: 10.6±3.7 y) with femoral neck fractures treated by internal fixation with 2 (n=112) or 3 (n=41) cannulated screws. The severity of initial displacement was divided into incomplete (type I) and complete (type II, angulation <50 degrees; type III, angulation >50 degrees) fractures. The diameter of the screw was measured and recorded as a percentage of the femoral neck width. The distance (D) between the mid-point of each screw at the base (B) of the femoral neck and at the tip (T) of each screw and the superior and anterior cortices of the femoral neck, respectively, were measured on anteroposterior (AP) and lateral (L) radiographs. Values were expressed as the ratio between the measured distance and the width of the femoral neck (BDAP%, TDAP%, BDL%, and TDL%). The correlation between the number, size, and location of the screws and AVN was analyzed. Results: Patients with type II of initial displacement treated with 2 cannulated screws had a lower AVN rate (21.4%) than those treated with 3 screws (44.8%) (P=0.027). Screw diameter (19%) in patients with AVN was larger than (17%) in patients without AVN (P<0.001); patients with AVN had a lower BDAP% (48.6%) than those without AVN (56.4%) (P<0.001). Screw size and BDAP% were risk factors for AVN (P<0.05). Further, screw diameter >16.5% and BDAP% <51.6% of the femoral neck width were the cutoff values for an increased AVN rate (P<0.05). Conclusions: Patients treated with 2 cannulated screws showed a lower rate of AVN than patients treated with 3 screws. Screws of larger size and screws closer to the piriformis fossa on AP radiographs increased the risk of AVN in children with femoral neck fractures treated surgically. Level of Evidence: Level III
Factors influencing outcomes of pelvic osteotomy for residual acetabular dysplasia following closed reduction in patients with developmental dysplasia of the hip
No full textAffiliations Expand
PMID: 37610089 DOI: 10.1097/BPB.0000000000001117
Abstract
To investigate the factors influencing outcome of pelvic osteotomy (PO) for residual acetabular dysplasia (RAD) following closed reduction (CR) in patients with developmental dysplasia of the hip (DDH). We retrospectively reviewed 91 patients (95 hips) with DDH who underwent PO for RAD. Tönnis grade, Acetabular index, Center Edge Angle, Reimer's Index (RI), and avascular necrosis of the femoral head (AVN) were assessed. Hips were divided into satisfactory (Severin I/II) and unsatisfactory group (Severin III/IV). Finally, 87 hips (91.5%) had satisfactory and 8 (8.5%) unsatisfactory outcomes. The RI before PO was significantly higher in unsatisfactory (49.6 ± 9%) than in satisfactory group (30.6%±11.8%). All patients without AVN had satisfactory outcome, while it was 78.9% of patients with AVN. Logistic regression analysis showed that higher AVN grade and RI before PO were risk factors for unsatisfactory outcome. Satisfactory outcome was obtained in all hips with RI < 33% before PO, while it was 79.5% if RI > 33% before PO (79.5%). There was no difference in the satisfactory rate between patients undergoing open reduction (66.7%) and those not undergoing (83.3%). The rate of satisfactory outcome in patients undergoing femoral osteotomy (63.6%) was lower than those without it (100%). In patients with RAD following CR, good outcome can be expected after PO alone. AVN and preoperative RI > 33% are risk factors for poor outcome. Additional open reduction and femoral osteotomy do not significantly improve outcome of PO in patients with preoperative RI > 33%.
Copyright © 2023 Wolters Kluwer Health, Inc. All rights reserved.To investigate the factors influencing outcome of pelvic osteotomy (PO) for residual acetabular dysplasia (RAD) following closed reduction (CR) in patients with developmental dysplasia of the hip (DDH). We retrospectively reviewed 91 patients (95 hips) with DDH who underwent PO for RAD. Tönnis grade, Acetabular index, Center Edge Angle, Reimer's Index (RI), and avascular necrosis of the femoral head (AVN) were assessed. Hips were divided into satisfactory (Severin I/II) and unsatisfactory group (Severin III/IV). Finally, 87 hips (91.5%) had satisfactory and 8 (8.5%) unsatisfactory outcomes. The RI before PO was significantly higher in unsatisfactory (49.6 ± 9%) than in satisfactory group (30.6%±11.8%). All patients without AVN had satisfactory outcome, while it was 78.9% of patients with AVN. Logistic regression analysis showed that higher AVN grade and RI before PO were risk factors for unsatisfactory outcome. Satisfactory outcome was obtained in all hips with RI < 33% before PO, while it was 79.5% if RI > 33% before PO (79.5%). There was no difference in the satisfactory rate between patients undergoing open reduction (66.7%) and those not undergoing (83.3%). The rate of satisfactory outcome in patients undergoing femoral osteotomy (63.6%) was lower than those without it (100%). In patients with RAD following CR, good outcome can be expected after PO alone. AVN and preoperative RI > 33% are risk factors for poor outcome. Additional open reduction and femoral osteotomy do not significantly improve outcome of PO in patients with preoperative RI > 33%
Is there an alternative to the Delbet-Colonna classification? Introduction and reliability assessment of a new classification system for paediatric femoral neck fractures: preliminary results
No full textAbstract
Purpose The purpose of this study was to introduce a new classification system for pediatric femoral neck fractures (PFNFs) and to evaluate its reliability.
Methods Two hundred and eight unilateral PFNFs (mean patient age: 9.0 ± 4.8 years) were included. Based on preoperative radiographs, the new classification system distinguished PFNFs without anterior or posterior translation (Type I), PFNFs with anterior (Type II) or posterior (Type III) translation, PFNFs with a comminuted medial or posterior column (Type IV), and subtrochanteric femoral fractures (SFFs; Type V). Radiographs were evaluated twice with an interval of two weeks by 19 raters with different specialties, experiences and geographical origins. The results were compared with a selection of 50 patient age-matched unilateral PFNFs and SFFs (mean patient age: 9.1 ± 4.9 years). These were graded twice by the same graders according to the Delbet-Colonna (D-C) classification.
Results Four radiologists and 15 pediatric orthopedic surgeons from Europe and Asia graded the radiographs. Fair agreement was found between radiologists (κ = 0.296 ± 0.01) and surgeons (κ = 0.3 ± 0.005) (P = 0.17), although more experienced surgeons performed better than less experienced ones; a similar fair assessment was found for raters from Europe (κ = 0.309 ± 0.021) and Asia (κ = 0.3 ± 0.006) and for type II, III and IV fractures; the κ value in the first evaluation (0.309) was similar to that in the second evaluation (0.298). The overall κ value of the D-C classification subtypes was significantly higher (0.599 ± 0.217) than that of the new classification, 0.326 ± 0.162 (t = 3.190 P = 0.005).
Conclusions The new classification system showed fair reliability relative to the D-C classification. The reliability of the new classification system was not affected by the specialty or geographic origin of the rater or the evaluation round, only by rater experience level. The concordance was worse for PFNFs with anterior or posterior translation or with a comminuted medial or posterior columns.Purpose: The purpose of this study was to introduce a new classification system for paediatric femoral neck fractures (PFNFs) and to evaluate its reliability. Methods: Two hundred and eight unilateral PFNFs (mean patient age: 9.0 ± 4.8 years) were included. Based on preoperative radiographs, the new classification system distinguished PFNFs without anterior or posterior translation (Type I), PFNFs with anterior (Type II) or posterior (Type III) translation, PFNFs with a comminuted medial or posterior column (Type IV), and subtrochanteric femoral fractures (SFFs; Type V). Radiographs were evaluated twice with an interval of two weeks by 19 raters with different specialties, experiences and geographical origins. The results were compared with a selection of 50 patient age-matched unilateral PFNFs and SFFs (mean patient age: 9.1 ± 4.9 years). These were graded twice by the same graders according to the Delbet-Colonna (D-C) classification. Results: Four radiologists and 15 paediatric orthopaedic surgeons from Europe and Asia graded the radiographs. Fair agreement was found between radiologists (κ = 0.296 ± 0.01) and surgeons (κ = 0.3 ± 0.005) (P = 0.17), although more experienced surgeons performed better than less experienced ones; a similar fair assessment was found for raters from Europe (κ = 0.309 ± 0.021) and Asia (κ = 0.3 ± 0.006) and for type II, III and IV fractures; the κ value in the first evaluation (0.309) was similar to that in the second evaluation (0.298). The overall κ value of the D-C classification subtypes was significantly higher (0.599 ± 0.217) than that of the new classification, 0.326 ± 0.162 (t = 3.190 P = 0.005). Conclusions: The new classification system showed fair reliability relative to the D-C classification. The reliability of the new classification system was not affected by the specialty or geographic origin of the rater or the evaluation round, only by rater experience level. The concordance was worse for PFNFs with anterior or posterior translation or with a comminuted medial or posterior columns
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