Annual performance evaluation of a hybrid concentrated solar-micro gas turbine based on off-design simulation.

As the adoption of solar hybrid systems continues to rise due to their potential to compensate for the fluctuation of solar irradiation, it becomes imperative to accurately evaluate their performance, considering the variation of off-design conditions. This paper introduces a detailed analysis method for evaluating the annual performance of a solar-MGT system under transient boundary conditions for a whole-year operation range. A hybrid system of a micro gas turbine, recuperator, and solar dish is considered, and an off-design simulation model is developed and verified with available experimental results. Two different configurations for a recuperated cycle are considered, and simulations are conducted for a test case in Pretoria, SA. The results for Jun.21 and Dec.21 as low and high solar energy days are reported with more details to compare the configurations and demonstrate the effect of ambient temperature on the heat loss of the solar receiver and the overall performance of the system. The alternative configuration reduces heat loss with a lower temperature receiver but has higher fuel consumption compared to the conventional configuration. Operating strategies for different hours of operation from 1 h to 24 h per day are simulated for 365 days, based on real meteorological data, and compared with the operating in solar available hours. It is shown that the whole-year simulation of the system considering the variation of boundary conditions can change the estimation of fuel consumption by 25 %.

Effect of the core bone engaged length on the BASHTI fixation strength, an in-vitro study on bovine tendons using identical-density surrogate bones.

BACKGROUND: BASHTI is an implant-less anterior cruciate ligament (ACL) reconstruction technique, which resolves the problems caused by implants such as interference screws. This study aims to investigate the effect of the drill bit and tendon's diameter on the Core Bone Engaged Length (CBEL) and the fixation strength. CBEL is the length of core bone which has a full engagement with both tunnel and graft at the same time. METHODS: 60 in-vitro tests were conducted for 6, 7, 8, and 9 mm tendon sizes with a 10 mm bone tunnel. In this study bovine tendons and dummy bone blocks were used to model the fixation. Drill bits were used to extract the core bone for securing the auto-graft. A three-stage tensile test including a force-controlled cyclical preloading of 10-50 N with a frequency of 0.1 Hz for 10 cycles, followed by the main force-controlled cyclical loading of 50-200 N with a frequency of 0.5 Hz for 150 cycles, and immediately a displacement-controlled single cycle pull-out load with a rate of 20 mm/min were carried out to discover the fixation strength of each sample. RESULTS: The 6 mm group had the greatest CBEL. However, all cases in this group failed in loadings below 200 N, which is the minimum required strength after ACL reconstruction. The fixation strength of cases with more than 200 N fixation strength for 7, 8, and 9 mm tendon diameters were 275 ± 42, 330 ± 110, and 348 ± 93 N, respectively, showing insignificant difference between groups (P-value = 0.45). Nevertheless, CBELs for these groups were 16.6 ± 3.4, 9.6 ± 2.4, and 11.7 ± 3.8 mm, respectively, implying a significant increase in CBEL in the 7 mm group than that for 8 and 9 mm groups (P-value = 0.002 and 0.049, respectively). CONCLUSION: Results showed that CBEL could assess the quality of BASHTI technique. However, CBEL was an inverse function of tendon compression, so it was not an independent parameter to determine BASHTI strength. Also, the CBEL of 7 mm group which fulfilled the 200 N threshold was higher than that of 8 and 9 mm groups, so its healing process speed may be higher, which is recommended for a future study in this field.

Sheathed fixation improves BASHTI technique in an anterior cruciate ligament reconstruction.

Bone and Site Hold Tendon Inside (BASHTI) technique is an implant-less surgical methodology used for anterior cruciate ligament (ACL) reconstruction. It has some clinical advantages, such as speeding up the healing process. Since the force required to insert the core bone inside the tunnel may damage the core bone and affect the fixation process, the study aims to investigate the strength of fixation of BASHTI technique using proposed sheathed core bones. Experimental tests were performed to evaluate the biomechanical strength of the fixation. Synthetic bone combined with bovine tendons as a graft was used. Polymers were used to create the sheath for mechanical testing. The results showed that fixation strength and stiffness in PTFE sheath with 0.1 mm were 343.86 N and 114.62 N/mm and in PVC sheath with similar thickness, 235.95 N, and 93.36 N/mm. Subsequently, 0.2 mm PTFE sheaths were tested in two different sections: incomplete fixation and complete fixation. The strength and stiffness of the first section were 221.6 N and 66.99 N/mm and for the second section 420.02 N and 126.16 N/mm. Using sheath facilitates the fixation process in BASHTI technique. The 0.1 mm PTFE sheath and 0.2 mm PTFE sheath with complete fixation provide higher fixation strength than other groups. The outcome showed that engaged length has a direct effect on the fixation strength. The BASHTI technique offers an implant-less organic ACL reconstruction method that can improve the fixation method and speed up the healing process.

An Experimental Analysis to Determine the Load-Bearing Capacity of 3D Printed Metals.

Reverse engineering is conducted based on the analysis of an already existing product. The results of such an analysis can be used to improve the functioning of the product or develop new organizational, economic, information technology, and other solutions that increase the efficiency of the entire business system, in particular 3D printed products. Therefore, the main aim of this research is to focus on evaluation of the load-bearing capacity of already existing 3D printed metals in order to see their suitability for the intended application and to obtain their relevant mechanical properties. To this end, 3D printed metallic bars with almost square cross-sections were acquired from an external company in China without any known processing parameters, apart from the assumption that specimens No. 1-3 are printed horizontally, and specimens No. 4-7 are printed vertically. Various experiments were conducted to study microstructural characteristics and mechanical properties of 3D printed metals. It was observed that specimens No. 1-6, were almost similar in hardness, while specimen No. 7 was reduced by about 4.5% due to the uneven surface. The average value of hardness for the specimens was found to be approximately 450 HV, whereas the load-extension graphs assessed prior point towards the conclusion that the specimens' fractured in a brittle status, is due to the lack of plastic deformation. For different specimens of the 3D printed materials, the main defects were identified, namely, lack of fusion and porosity are directly responsible for the cracks and layer delamination, prevalent in SLM printed metals. An extensive presence of cracks and layer delamination prove that the printing of these metallic bars was completed in a quick and inaccurate manner, which led to higher percentages of lack of fusion due to either low laser power, high scan speed, or the wrong scan strategy.

Early post-operative performance of an anatomically designed hybrid thread interference screw for ACL reconstruction: A comparative study.

Although the anterior cruciate ligament (ACL) reconstruction using interference screw is a well-accepted surgical procedure, patients still suffer graft failure in the initial rehabilitation phase. Graft fixation stability of a newly designed anatomical hybrid thread tapered interference screw (AHTTIS) was compared with a conventional standard one (CSIS) by conducting in-vitro mechanical tests. According to the CSIS manufacturer's instruction, eight tapered bone tunnels, matching AHTTIS geometry, and eight straight cylindrical tunnels were drilled in artificial bone blocks. Bovine tendon grafts were fixed using AHTTIS and CSIS in their corresponding bone tunnels. Each graft was subjected to a pre-load, a dynamic cyclic sinusoidal tensile load, and a tensile pullout load. Aggregate graft displacement relative to the bone tunnel under dynamic cyclic load, load corresponding to a 3 mm displacement; load and displacement at yield and ultimate failure of the graft; and graft-bone-screw stiffness resulted from pullout tests were recorded. There were no significant differences between recorded parameters of the two groups, except the graft displacements relative to the bone tunnel at ultimate failure load (8.35 ± 3.03 mm versus 5.28 ± 1.37 mm) and at the yield point (7.73 ± 3.02 mm versus 4.59 ± 1.25 mm) (P < 0.05), which were both significantly greater for the AHTTIS group. Considering all tests were made in the worst-case scenario of fixation of an interference screw, i.e., the employed synthetic bone just mimicked cancellous bone, graft fixation with the AHTTIS is practical. However, in the case of employing high strain rate loads on AHTTIS, further considerations are needed to reduce the side effect of slippage of the graft.

Detection and Analysis of Corrosion and Contact Resistance Faults of TiN and CrN Coatings on 410 Stainless Steel as Bipolar Plates in PEM Fuel Cells.

Bipolar Plates (BPPs) are the most crucial component of the Polymer Electrolyte Membrane (PEM) fuel cell system. To improve fuel cell stack performance and lifetime, corrosion resistance and Interfacial Contact Resistance (ICR) enhancement are two essential factors for metallic BPPs. One of the most effective methods to achieve this purpose is adding a thin solid film of conductive coating on the surfaces of these plates. In the present study, 410 Stainless Steel (SS) was selected as a metallic bipolar plate. The coating process was performed using titanium nitride and chromium nitride by the Cathodic Arc Evaporation (CAE) method. The main focus of this study was to select the best coating among CrN and TiN on the proposed alloy as a substrate of PEM fuel cells through the comparison technique with simultaneous consideration of corrosion resistance and ICR value. After verifying the TiN and CrN coating compound, the electrochemical assessment was conducted by the potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) tests. The results of PDP show that all coated samples have an increase in the polarization resistance (Rp) values (ranging from 410.2 to 690.6 Ω·cm2) compared to substrate 410 SS (230.1 Ω·cm2). Corrosion rate values for bare 410 SS, CrN, and TiN coatings were measured as 0.096, 0.032, and 0.060 mpy, respectively. Facilities for X-ray Diffraction (XRD), Scanning Electron Microscope (FE-SEM, TeScan-Mira III model and made in the Czech Republic), and Energy Dispersive X-ray Spectroscopy (EDXS) were utilized to perform phase, corrosion behavior, and microstructure analysis. Furthermore, ICR tests were performed on both coated and uncoated specimens. However, the ICR of the coated samples increased slightly compared to uncoated samples. Finally, according to corrosion performance results and ICR values, it can be concluded that the CrN layer is a suitable choice for deposition on 410 SS with the aim of being used in a BPP fuel cell system.

Bone density may affect primary stability of anterior cruciate ligament reconstruction when organic core bone plug fixation technique used.

PURPOSE: Core Bone Plug Fixation (CBPF) technique is an implant-less methodology for ACL reconstruction. This study investigates the effect of bone density on CBPF stability to identify the bone quality that is likely to benefit from this technique. METHODS: Artificial blocks with 160 (Group 1), 240 (Group 2), and 320 (Group 3) kg/m3 densities were used to simulate human bone with diverse qualities. These groups are representative of the elderly, middle age and young people, respectively. A tunnel was made in each test sample using a cannulated drill bit which enabled harvesting the core bone plug intact. Fresh animal tendon grafts were prepared and passed through the tunnel, so the core bone was pushed in to secure the tendon. The fixation stability was tested by applying a cyclic load following by a pullout load until the failure occurred. The selected group was compared with interference screw fixation technique as a gold standard method in ACL reconstruction. RESULTS: The Group 2 stiffness and yield strength were significantly larger than Group 1. The graft slippage of Group 1 was significantly less than Group 3. The ultimate strengths were 310 N and 363 N, in Groups 2 and 3, significantly larger than that of Group 1. The ultimate strength in fixation by interference screw was 693.18 N, significantly larger than the bone plug method. CONCLUSIONS: The stability of CBPF was greatly affected by bone density. This technique is more suitable for young and middle-aged people. With further improvements, the CBPF might be an alternative ACL reconstruction technique for patients with good bone quality. CLINICAL RELEVANCE: The CBPF technique offers an implant-less organic ACL reconstruction technique with numerous advantages and likely would speed up the healing process by using the patient's own bones and tissues rather than any non-biologic fixations.

Effect of Geometry on the Fixation Strength of Anterior Cruciate Ligament Reconstruction Using BASHTI Technique.

The goal of this study is to investigate the effects of tendon and cannulated drill bit diameter on the strength of the bone and site hold tendon inside (BASHTI) fixation technique for an anterior cruciate ligament (ACL) reconstruction. Bovine digital tendons and Sawbones blocks were used to mimic the ACL reconstruction. Mechanical strength of the specimens was measured using a cyclic loading continued by a single cycle pullout load until failure to simulate the real postsurgical loading conditions. Finally, failure modes of specimens and ultimate failure load were recorded. The maximum possible tendon surface strain (i.e., tendon compression [TC]) for tendon diameters of 6, 7, 8, and 9 mm were 0.73, 0.8, 0.7, and 0.65, respectively. Eighty per cent of the specimens with tendon diameter of 6 mm and 20% of specimens with tendon diameter of 7 mm failed on the torn tendon. All samples with larger tendon diameters (i.e., 8 and 9 mm) failed on the fixation slippage. The maximum fixation strength according to the most suitable core bones for 6, 7, 8, and 9 mm tendons were 148 ± 47 N (core 9.5 mm), 258 ± 66 N (core 9.5 mm), 386 ± 128 N (core 8.5 mm), and 348 ± 146 N (core 8.5 mm), respectively. The mode of tendon failure was significantly influenced by the tendon diameter. Also, an increase in TC raised the fixation strength for all tendon diameters; however, tendon over compression decreased the fixation strength for the 8 mm tendon group. Finally, an empirical equation was proposed to predict BASHTI fixation strength.

A multi-objective approach to optimize the weight and stress of the locking plates using finite element modeling.

This paper aims to identify an optimum bone fracture stabilizer. For this purpose, three design variables including the ratio of the screw diameter to the plate width at three levels, the ratio of the plate thickness to the plate width at three levels, and the diameter of the bone at two levels were selected for analysis. Eighteen 3D verified finite element models were developed to examine the effects of these parameters on the weight, maximum displacement and maximum von Mises stress of the fixation structure. Considering the relations between the inputs and outputs using multivariate regression, a genetic algorithm was used to find the optimal choices. Results showed that the diameter of the bone and the amount of load applied on it did not have a significant effect on the normalized stresses on the structures. Furthermore, in all ratio of the plate thickness to the plate width, as the ratio of the screw diameter to the plate width increased, the amount of stress on the structure decreased. But, by further increasing the ratio of the screw diameter to the plate width, the amount of stress on the structure increased. On the other hand, by increasing the value of the ratio of the plate thickness to the plate width, the maximum amount of stress on the structure decreased. Finally, optimal solutions in terms of the weight and the maximum amount of stress on the structure were presented.

Comparison of mechanical properties in interference screw fixation technique and organic anterior cruciate ligament reconstruction method: a biomechanical study.

BACKGROUND: Bone and Site Hold Tendon Inside (BASHTI) technique is an organic implant-less technique for anterior cruciate ligament (ACL) reconstruction with some clinical advantages, such as speeding up the healing process, over implantable techniques. The study aims to compare the mechanical properties of BASHTI technique with the conventional interference screw technique. METHODS: To investigate the mechanical properties, 20 in-vitro experimental tests were conducted. Synthetic dummy bone, along with fresh digital bovine tendons, as a graft, were used for experiments. Three loading steps were applied to all specimens, including a preconditioning, a main cyclic, and a pull-out loading. RESULTS: The mechanical characters of an interference screw technique using an 8 mm tendon diameter, including fixation strength, average cyclic stiffness (ACS), and average pull-out stiffness (APS) were found to be 439 ± 132 N, 10.3 ± 5.3 kN/mm, and 109 ± 40 N/mm, respectively. In the case of an interference screw using a 9 mm tendon, the fixation strength, ACS, and APS were obtained 549 ± 87 N, 10.3 ± 4.7 kN/mm, and 91 ± 13 N/mm, respectively. In parallel, the fixation strength, APS, and ACS of BASHTI technique using an 8 mm tendon were 360 ± 123 N, 3.3 ± 0.6 kN/mm, and 79 ± 27 N/mm, respectively, while, for 9 mm tendon 278 ± 103 N, 2.4 ± 1.2 kN/mm, and 111 ± 40 N/mm, were reported for fixation strength, APS, and ACS respectively when BASHTI technique was used. CONCLUSION: About 50% of interference screw samples showed superior mechanical properties compared to BASHTI technique, but in another half of the samples, the differences were not significant (N.S.). However, due to organic advantages of BASHTI technique and lower cost, it could be used as a substitute for interference screw technique, especially where fast recovery is expected.

Can the body slope of interference screw affect initial stability of reconstructed anterior cruciate ligament?: An in-vitro investigation.

BACKGROUND: Superior biomechanical performance of tapered interference screws, compared with non-tapered screws, with reference to the anterior cruciate ligament (ACL) reconstruction process, has been reported in the literature. However, the effect of tapered interference screw's body slope on the initial stability of ACL is poorly understood. Thus, the main goal of this study was to investigate the effect of the interference screw's body slope on the initial stability of the reconstructed ACL. METHODS: Based on the best screw-bone tunnel diameter ratios in non-tapered screws, two different tapered interference screws were designed and fabricated. The diameters of both screws were equal to bone tunnel diameter in one-third of their length from screw tip, then they were gradually increased by 1mm, in the lower slope (LSTIS), and 2 mm, in the higher slope (HSTIS) screws. To simulate the ACL reconstruction, sixteen soft tissue grafts were fixed, using HSTIS and LSTIS, in synthetic bone blocks. Through applying sub-failure cyclic incremental tensile load, graft-bone-screw construct's stiffness and graft laxity in each cycle, also through applying subsequent step of loading graft to the failure, maximum load to failure, and graft's mode of failure were determined. Accordingly, the performance of the fabricated interference screws was compared with each other. RESULTS: HSTIS provides a greater graft-bone-screw construct stiffness, and a lower graft laxity, compared to LSTIS. Moreover, transverse rupture of graft fibers for LSTIS, and necking of graft in the HSTIS group were the major types of grafts' failure. CONCLUSIONS: HSTIS better replicates the intact ACL's behavior, compared to LSTIS, by causing less damage in graft's fibers; reducing graft laxity; and increasing fixation stability. Nonetheless, finding the optimal slope remains as an unknown and can be the subject of future studies.

An analysis of the biomechanics of interference screw fixation and sheathed devices for biceps tenodesis.

BACKGROUND: This study aimed to evaluate the differences in biomechanical properties of biceps tenodesis when performed with sheathed versus unsheathed screws and also to investigate the effect of altering the pre-tension. METHODS: Tenodesis was performed in an in vitro model using biomechanical test blocks and ovine tendons. Blocks were allocated to 1 of 5 groups which varied by method of tenodesis and cyclical loading protocol: Group A, Biosure PK screw (10-100 N), Group B: 7-8 mm Biosure Sync and Biosure PK screw (10-100 N), Group C: Biosure PK screw (10-70 N), Group D: Biosure PK (20-100 N), and Group E: custom sheath and Biosure PK screw (10-100 N). If tenodeses remained intact after 500 cycles maximum load to failure testing was performed. FINDINGS: 30% of tenodeses in Group A failed prior to 500 cycles whereas none failed in the sheathed device groups (P=0.02). Using a sheathed device prevented mal-rotation. However, tenodeses in Group B were more likely to fail immediately distal to the tenodesis at a load below the anticipated maximum load to failure suggesting tendon damage during fixation. Using the custom sheath, which did not have sharp edges, resulted in a statistically significant increased maximum load to failure in Group E (348 N) when compared to Group A (228 N, mean difference 120 N, P=0.01) and Group B (253N, mean difference 95 N, P=0.0007). INTERPRETATION: Sheathed devices prevent mal-rotation and increase stiffness and maximum load to failure. This is further improved by reducing tendon damage at the time of tenodesis.

Mechanical assessment of two different methods of tripling hamstring tendons when using suspensory fixation.

PURPOSE: To investigate two different methods of suture fixation and tendon behaviour when using an Endobutton and a tripled tendon. METHODS: Thirty bovine tendons and foam blocks were randomly allocated to three groups: group 1: The tendon was doubled through 40-mm Endobutton; group 2: Tripled tendon--whip-stitched with No. 2 Ultrabraid, passed through an Endobutton and third limb secured to the loop via seven knots; and group 3: Tripled tendon--whip-stitched with No. 2 Fibreloop and fixed as group 2. A tunnel matching the graft diameter was drilled through the block. The graft was passed through the tunnel and fixed with an interference screw. The constructs were cycled at 1 Hz from 10 to 50 N for 10 cycles followed by 50-250 N at 1 Hz for 500 cycles. Load-to-failure test was then carried out at a rate of 20 mm/min. A custom digital image capture technique was used to measure and calculate displacement, strain and stress. Statistical analysis was carried out using Kruskal-Wallis test and paired t test. RESULTS: There was no statistical significant difference between ultimate tensile strength (UTS) (P = 0.35) and yield load (0.41) between the 3 groups. The mean displacement of the third tendon limb in group 2 was 4.8 mm and in group 3, 1.5 mm. Displacement was not statistically significant (P = 0.07). The mean stress in the third limb versus the doubled portion of tendon in group 2 was 0.4 ± 0.02 versus 4.8 ± 0.52 MPa and in group 3, 0.5 ± 0.03 versus 5.2 ± 0.52 MPa. CONCLUSIONS: In this biomechanical study, there was no mechanical difference in the overall properties between a doubled and tripled tendon graft. Significant cyclic elongation occurred in the third limb of the tripled tendon in comparison with the doubled portioned. Further work is needed to determine whether these mechanical findings translate to clinical practice. Caution should be used when tripling hamstring grafts. In particular, tripling small grafts provides no biomechanical advantage immediately and possibly long term, thus potentially increasing the risk of failure.

Measurement of an intact knee kinematics using gait and fluoroscopic analysis.

A method has been introduced in this paper to measure the kinematics of a knee joint and to use it as a boundary condition to model the knee's mechanical behaviour. A mobile C-Arm fluoroscopy system (Ziehm Vision R) and a CCD camera were used for the measurement of a patient's knee kinematics. The fluoroscopic images were recorded with 12 fps and then sent to Matlab software (Mathworks, Natick, MA, USA) for image processing. In parallel, CT scan images of the knee bones were used to create the 3D anatomical geometry of the knee by aid of Mimics software (Materialise NV). However, the geometrical model of the two medial and lateral menisci was generated from MRI data. The 3D geometrical model of the knee was then sent to Abaqus finite element software (Simulia Dassault Systems) to analyse the knee joint contact loads by introducing the boundary condition which was obtained from fluoroscopic images. The finite element model was used to evaluate the stress distribution on the cartilages during the gait. The result was then compared with the experimental data of gait analysis. The comparison between the results showed a close agreement between the two outcomes.

Post-operative assessment of an implant fixation in anterior cruciate ligament reconstructive surgery.

The objective of this paper is to numerically simulate the behaviour of an anterior cruciate ligament (ACL) reconstructed knee using interference screw fixation under a single cycle loading or a cyclic loading test and to compare the numerical results with experimental tests using porcine samples of knee joint. A hyper-elastic material model was used to model the tendon graft and evaluate its elongation during continuous and cyclic tensile loading. The rigidity of the interference screw fixation was also examined using the finite element based numerical model. The finite element model uses the benefit of an anatomical 3D geometry of the tibial bone and tendon graft which was created from a CT scan of a patient.

Estimating Young's modulus of zona pellucida by micropipette aspiration in combination with theoretical models of ovum.

The zona pellucida (ZP) is the spherical layer that surrounds the mammalian oocyte. The physical hardness of this layer plays a crucial role in fertilization and is largely unknown because of the lack of appropriate measuring and modelling methods. The aim of this study is to measure the biomechanical properties of the ZP of human/mouse ovum and to test the hypothesis that Young's modulus of the ZP varies with fertilization. Young's moduli of ZP are determined before and after fertilization by using the micropipette aspiration technique, coupled with theoretical models of the oocyte as an elastic incompressible half-space (half-space model), an elastic compressible bilayer (layered model) or an elastic compressible shell (shell model). Comparison of the models shows that incorporation of the layered geometry of the ovum and the compressibility of the ZP in the layered and shell models may provide a means of more accurately characterizing ZP elasticity. Evaluation of results shows that although the results of the models are different, all confirm that the hardening of ZP will increase following fertilization. As can be seen, different choices of models and experimental parameters can affect the interpretation of experimental data and lead to differing mechanical properties.

Post-operative analysis of ACL tibial fixation.

The main aims of the study were to describe the mechanical behaviour of the bone and tendon graft in ACL reconstruction. We also wanted to evaluate the stresses upon the tendon and try to relate these to modes of healing observed in animal studies. An MRI scan of a knee from a 22-year-old male patient, 3 months post ACL reconstruction, was used to generate a finite element model for assessing the stresses on the tendon and bone. A 200 N force, equivalent to the force during normal gait, was placed on the graft and the stress distribution recorded. The maximum stress was found on the tendon graft at the proximal end of the tibial tunnel. Direct tendon healing, which has been observed in animal studies, maybe as a result of the increased stress in this area.