bluuebunny/crossref_metadata_2025 huggingface dataset:
Improved GT Fleet Performance Evaluations by Considering Installed Compressor Blading Clearances
Authors: Wäsle J. , Cameron D. , Schabacker J.
Published: July 2013

The product development process for gas turbines relies upon the understanding of the existing engine fleet. For this reason, performance measurement data are regularly collected. The processed data show a remaining scatter, which complicates the direct use of the fleet evaluation results. This scatter can be attributed to e.g. the measurement chain, existing hardware condition, and hardware installation. To understand the true engine performance, the contributing factors behind the scatter must be addressed.

This paper describes the influence of compressor blading clearances on gas turbine performance. Fleet evaluation results are first presented. The scatter in the resulting parameters (i.e.: compressor efficiency and mass flow rate, turbine efficiency) cannot be explained simply by uncertainty in the performance measurement data. Therefore, an empirical model has been developed which correlates measured compressor clearances with deviations in component efficiencies in order to understand the end effect on engine performance.

The evaluation shows a correlation between the weighted average clearances and compressor blading efficiencies. Thus, one of the contributors to the data scatter has been identified and quantified by using the empirical model and statistical analysis. The result demonstrates a method to reduce uncertainties in the fleet data and consequently improve the component understanding.
How Combined Cycle Configuration is Impacted by Current Power Market Requirements
Authors: Zachary Justin
Published: July 2013

In the past 20 years, the equipment manufacturers have made significant strives to develop better and more cost effective products: gas turbines, steam turbines, Heat Recovery Steam Generators (HRSG), water treatment, fuel treatment equipment etc. Consequently, the Combined Cycle Power Plants (CCPP) have become, due to many technological breakthroughs, the most efficient form of electrical power generation from fossil fuel, reaching or exceeding net efficiencies of 60%. We are also witnessing a substantial penetration of Renewable in the power generation mix. The Renewable intermittent nature of generation associated with new grid requirements for spinning reserves and/or frequency control must be considered when new CCPP are conceptually designed.

The paper will examine several CCPP configurations, involving one, two, and three gas turbines. Substantial improvements in the efficiency are usually associated with an increased gas turbines electrical output. Various scenarios of plant configurations with targeted, sensible level of integration will be examined.

The challenges of major equipment selection (gas turbines, heat recovery steam generator steam turbines, heat sink) for each of the configurations will be examined from an EPC (Engineering, Procurement, Construction) Contractor perspective, based on the lessons learned from the development and execution of more than 30 advanced CCPPs.

A special emphasis will be given to the strategy of providing the CCPP with fast start-up, capability, rapid load changes, without negatively impacting part-load efficiencies and emissions. The effect of plant configuration on plant reliability, maintenance requirements and recommended spare parts will also be discussed.

Finally the paper describes the lessons learned, in plant configuration selection that can be successfully employed on future projects through judicious equipment selection at the development phase, design optimization and proper project management at the execution phase.
On the Stability of Transonic Compressor With Wet Compression and Blade Tip Water Injection
Authors: Luo Mingcong , Zheng Qun , Sun Lanxin , Deng Qingfeng , Chen Jiyou , Wang Jie , Bhargava Rakesh K.
Published: July 2013

The rotor blade tip leakage flow and associated formation of the tip leakage vortex and interaction of the tip leakage vortex with the shockwave, particularly in the case of a transonic compressor rotor have significant impact on the compressor performance and its stability. Air injection upstream of the compressor rotor tip has been shown to improve compressor performance and enhance its stability. The air required for rotor blade tip injection is generally taken from the later stages of the compressor thus causing penalty on the gas turbine performance. In this study, effects of water injection at the rotor tip with and without the wet compression on the compressor performance and its stability have been examined. To achieve the stated objectives, the well tested transonic compressor rotor stage, NASA rotor stage 37, has been numerically simulated.

The evaluation of results on various performance parameters such as total pressure ratio, inlet flow capacity and adiabatic efficiency combined with contours of total pressure losses, entropy, Mach No., and temperature including limiting streamlines, shows that the blade tip water injection could help in reducing low energy region downstream of the shockwave and strength of the tip leakage vortex with the compressor operating at its rotating stall boundary condition. The extent of reduction depends on the droplet size, injection flow rate and its velocity. Furthermore, results show that combined case of the blade tip water injection and the wet compression could provide better stall margin enhancement than the blade tip water injection case.
Evaluation of Design Performance of the Semi-Closed Oxy-Fuel Combustion Combined Cycle
Authors: Yang H. J. , Kang D. W. , Ahn J. H. , Kim T. S.
Published: July 2013

This study aims to present various design aspects and realizable performance of the natural gas fired semi-closed oxy-fuel combustion combined cycle (SCOC-CC). Design parameters of the cycle are set up on the basis of component technologies of today’s state-of-the-art gas turbines with a turbine inlet temperature between 1400°C and 1600°C. The most important part in the cycle analysis is the turbine cooling which affects the cycle performance considerably. A thermodynamic cooling model is introduced to predict the reasonable amount of turbine coolant to maintain the turbine blade temperature of the SCOC-CC at the levels of those of conventional gas turbines. Optimal pressure ratio ranges of the SCOC-CC for two different turbine inlet temperature levels are searched. The performance penalty due to the CO2 capture is examined. Also investigated are the influences of the purity of oxygen provided by the air separation unit on the cycle performance. A comparison with the conventional combined cycle adopting a post-combustion CO2 capture is carried out taking into account the relationship between performance and CO2 capture rate.
Exergy Analysis of a Hybrid Micro Gas Turbine Fuel Cell System Based on Existing Components
Authors: Bakalis D. P. , Stamatis A. G.
Published: July 2013

A hybrid system based on an existing recuperated microturbine and a pre-commercially available high temperature tubular solid oxide fuel cell is modeled in order to study its performance. Individual models are developed for the microturbine and fuel cell generator and merged into a single one in order to set up the hybrid system. The model utilizes performance maps for the compressor and turbine components for the part load operation. The full and partial load exergetic performance is studied and the amounts of exergy destruction and efficiency of each hybrid system component are presented, in order to evaluate the irreversibilities and thermodynamic inefficiencies. Moreover, the effects of various performance parameters such as fuel cell stack temperature and fuel utilization factor are investigated. Based on the available results, suggestions are given in order to reduce the overall system irreversibility. Finally, the environmental impact of the hybrid system operation is evaluated.
Experimental and Numerical Studies on a New Type of Spray Axial-Flow Fan
Authors: Li Jing-yin , Han Qiang , Niu Zi-ning , Xi Guang
Published: July 2013

A new spray axial-flow fan with a ring-shaped spray-generating device in the upstream of the rotor is proposed in this paper. The characteristics of the new spray axial-flow fan were tested in detailed according to the international performance test standard. The experimental results showed that the characteristics of the new fan operating with working fluid which having a high water-air mass ratio have been improved obviously, compared with those of the existing spray fan with the conventional spray-generating device. The new spay fan considerably expands the limit on the water-air mass ratio of the working fluid, beyond which the motor of the spray fan may be over loaded, due to its much lower decrease slope of total pressure efficiency and much lower increment slope of shaft power against the increase in the water-air mass ratio of the working fluid. In addition, its utilization factor of sprayed water also increases obviously. Numerical investigations on this new fan with working fluid under the air phase or the mixed air-water phase were also conducted. The results indicated that the numerical results agree well with the experimental data with air as the working fluid. This verified the validity of computational models. However, the numerical results using the discrete phase model available in the Fluent program for the mixed air-water working fluid showed an evident deviation from the experimental results. The numerical simulations underestimate the deteriorating effect of the characteristics of the spay fan with water added, which means it cannot well simulate and analyze the complex flow filed inside the spay fan. Further research is needed to explore the mechanism for the deteriorated characteristics of the spray fan.
Modelling Contra-Rotating Turbomachinery Components for Engine Performance Simulations: The Geared Turbofan With Contra-Rotating Core Case
Authors: Alexiou A. , Roumeliotis I. , Aretakis N. , Tsalavoutas A. , Mathioudakis K.
Published: July 2013

This paper presents a method of modelling contra-rotating turbomachinery components for engine performance simulations. The first step is to generate the performance characteristics of such components. In this study, suitably modified one-dimensional mean line codes are used. The characteristics are then converted to three-dimensional tables (maps). Compared to conventional turbomachinery component maps, the speed ratio between the two shafts is included as an additional map parameter and the torque ratio as an additional table. Dedicated component models are then developed that use these maps to simulate design and off-design operation at component and engine level.

Using this approach, a performance model of a geared turbofan with a Contra-Rotating Core (CRC) is created. This configuration was investigated in the context of the European program NEWAC (NEW Aero-engine core Concepts). The core consists of a seven-stage compressor and a two-stage turbine without inter-stage stators and with successive rotors running in opposite direction through the introduction of a rotating outer spool. Such a configuration results in reduced parts count, length, weight and cost of the entire HP system. Additionally, the core efficiency is improved due to reduced cooling air flow requirements.

The model is then coupled to an aircraft performance model and a typical mission is carried out. The results are compared against those of a similar configuration employing a conventional core and identical design point performance. For the given aircraft-mission combination and assuming a 10% engine weight saving when using the CRC arrangement over the conventional one, a total fuel burn reduction of 1.1% is predicted.
Conceptual Mean-Line Design of Single and Twin-Shaft Oxy-Fuel Gas Turbine in a Semi-Closed Oxy-Fuel Combustion Combined Cycle
Authors: Sammak Majed , Genrup Magnus , Thorbergsson Egill , Grönstedt Tomas
Published: July 2013

The aim of this study was to compare single- and twin-shaft oxy-fuel gas turbines in a semi-closed oxy-fuel combustion combined cycle (SCOC-CC). This paper discussed the turbomachinery preliminary mean-line design of oxy-fuel compressor and turbine. The conceptual turbine design was performed using the axial through-flow code LUAX-T, developed at Lund University. A tool for conceptual design of axial compressors developed at Chalmers University was used for the design of the compressor. The modeled SCOC-CC gave a net electrical efficiency of 46% and a net power of 106 MW. The production of 95% pure oxygen and the compression of CO2 reduced the gross efficiency of the SCOC-CC by 10 and 2 percentage points, respectively. The designed oxy-fuel gas turbine had a power of 86 MW. The rotational speed of the single-shaft gas turbine was set to 5200 rpm. The designed turbine had four stages, while the compressor had 18 stages. The turbine exit Mach number was calculated to be 0.6 and the calculated value of AN2 was 40·106 rpm2m2. The total calculated cooling mass flow was 25% of the compressor mass flow, or 47 kg/s. The relative tip Mach number of the compressor at the first rotor stage was 1.15. The rotational speed of the twin-shaft gas generator was set to 7200 rpm, while that of the power turbine was set to 4500 rpm. Twin-shaft turbine designed with five turbine stages to maintain the exit Mach number around 0.5. The twin-shaft turbine required a lower exit Mach number to maintain reasonable diffuser performance. The compressor turbine was designed with two stages while the power turbine had three stages. The study showed that a four-stage twin-shaft turbine produced a high exit Mach number. The calculated value of AN2 was 38·106 rpm2m2. The total calculated cooling mass flow was 23% of the compressor mass flow, or 44 kg/s. The compressor was designed with 14 stages. The preliminary design parameters of the turbine and compressor were within established industrial ranges. From the results of this study it was concluded that both single- and twin-shaft oxy-fuel gas turbines have advantages. The choice of a twin-shaft gas turbine can be motivated by the smaller compressor size and the advantage of greater flexibility in operation, mainly in off-design mode. However, the advantages of a twin-shaft design must be weighed against the inherent simplicity and low cost of the simple single-shaft design.
Combustor and Single-Stream Jet Noise Prediction for a Newly Designed Turbojet Engine by Using Semi-Empirical Methods
Authors: Barbosa João Roberto , Dezan Daniel Jonas
Published: July 2013

Research is being carried out at the Technological Institute of Aeronautics to provide the support for the design of high performance gas turbines, including noise prediction by means of theoretical and empirical methods. Emphasis is given to new engines noise prediction, to anticipate problems at very early design stage and to take the necessary actions to guarantee that the engine noise is below the imposed limits. Noise prediction is part of the high fidelity engine performance prediction computer program, which provides the designer, at any time during the design phases, with information on the noise levels generated by each component and by the engine. Research indicates that the combustor and the propelling nozzle are major noise sources, so that these two components of a turbojet engine were dealt with in this work. The far-field one-third octave band sound pressure levels, (SPL), and overall sound pressure level (OASPL) are calculated, for several observer positions and engine rotational speeds. A 5 kN turbojet engine under development serves as the basis for the noise prediction. The influence of the observer position on SPL and OASPL for steady engine operation, as well as the effect of the engine rotational speeds on the engine noise generated by the combustor and the propelling nozzle are presented, which are in agreement with the noise of similar engines. Ground reflection and atmospheric attenuation were not considered. A high fidelity engine performance prediction computer code incorporates the noise prediction methodology whose results are reported in this paper.
CO2 Capture From Air-Blown Gasification-Based Combined Cycles
Authors: Giuffrida Antonio , Romano Matteo C. , Lozza Giovanni
Published: July 2013

This paper focuses on an air-blown gasification-based combined cycle where CO2 is removed from the coal-derived gas before fuelling the combustion turbine. On the basis of public information from Mitsubishi Heavy Industries (MHI), the air-blown gasifier was modeled and its performance was investigated by the authors in a previous study. Here, with reference to a possible IGCC power plant with such a gasification technology, the possibility of removing CO2 from the coal-derived fuel gas is considered. The main differences between the two IGCCs, without and with CO2 capture, are gas used for coal loading (N2 or CO2), the layout of the syngas cooling and treatment sections (owing to the presence of watergas shift reactions and CO2 absorption process) and the composition of the fuel used in the combustion turbine. The results highlight that IGCC efficiency reduces by about 10.8% points when realizing CO2 capture, mainly due to the steam consumption in shift reactors and CO2 solvent regeneration and to power consumption for CO2 compression. However, the calculated efficiency penalty is in line with the values typical of IGCCs with oxygen-blown gasifier and CO2 capture.

The power balances of the assessed cases are reported in detail and the main technical issues are discussed in the paper. The results of a sensitivity analysis are also reported to assess the effects of different steam to carbon ratios in the shift reactors.
Oxy-Fuel Turbomachinery Development for Energy Intensive Industrial Applications
Authors: Hollis Rebecca , Skutley Patrick , Ortiz Carlos , Varkey Vijo , LePage Danise , Brown Barry , Davies Daniel , Harris Mark
Published: July 2013

Future fossil-fueled power generation systems will require emission control technologies such as carbon capture and sequestration (CCS) to comply with government greenhouse gas regulations. The three prime candidate technologies which permit carbon dioxide (CO2) to be captured and safely stored include pre-combustion, post-combustion capture and oxy-fuel (O-F) combustion. For more than a decade Clean Energy Systems, Inc. (CES) has been designing and demonstrating enabling technologies for oxy-fuel power generation; specifically steam generators, hot gas expanders and reheat combustors.

Recently CES has partnered with Florida Turbine Technologies, Inc. (FTT) and Siemens Energy, Inc. to develop and demonstrate turbomachinery systems compatible with the unique characteristics of oxy-fuel working fluids. The team has adopted an aggressive, but economically viable development approach to advance turbine technology towards early product realization. Goals include short-term, incremental advances in power plant efficiency and output while minimizing capital costs and cost of electricity.

Phase 2 of this development work has been greatly enhanced by a cooperative agreement with the U.S. Department of Energy (DOE). Under this program the team will design, manufacture and test a commercial-scale intermediate-pressure turbine (IPT) to be used in industrial O-F power plants. These plants will use diverse fuels and be capable of capturing 99% of the produced CO2 at competitive cycle efficiencies and cost of electricity. Initial plants will burn natural gas and generate more than 200MWe with near-zero emissions.

To reduce development cost and schedule an existing gas turbine engine will be adapted for use as a high-temperature O-F IPT. The necessary modifications include the replacement of the engine’s air compressor with a thrust balance system and altering the engine’s air-breathing combustion system into a steam reheating system using direct fuel and oxygen injection.

Excellent progress has been made to date. FTT has completed the detailed design and issued manufacturing drawings to convert a Siemens SGT-900 to an oxy-fuel turbine (OFT). Siemens has received, disassembled and inspected an SGT-900 B12 and ordered all necessary new components for engine changeover. Meanwhile CES has been working to upgrade an existing test facility to support demonstration of a “simple” oxy-fuel power cycle. Low-power demonstration testing of the newly assembled OFT-900 is expected to commence in late 2012.
Performance Evaluation of a 5 kN Gas Turbine Based on Specially Designed Components
Authors: Tomita Jesuíno Takachi , Bringhenti Cleverson , Barbosa João Roberto , Martins Vitor Alexandre Carlesse
Published: July 2013

The design of a small gas turbine in the range of 5 kN thrust / 1.2 MW shaft power is being made in association with industry, aiming at distributed power generation and cogeneration. The gas turbine was constructed and its gas generator is being prepared for development tests. The results will be used for the final specification of the power section. The gas turbine design has been carried out using indigenous software, developed specially to fulfill the requirements of the engines design, as well as the support for validation of research work. The work reported in this paper deals with the design methodology of a 5:1 pressure ratio, 5-stage axial flow compressor with VIGV and a single stage axial flow turbine. These components were designed and their maps synthesized and fed to the gas turbine performance simulation program. The engine performance results were analyzed and verified. The calculated behavior compares with similar engines’, indicating they are qualitatively correct.
Intimal Thickening Sourced From Low Wall Shear Stress in Human Left Coronary Artery Was Observed by Optical Coherence Tomography
Authors: Suo Jin , McDaniel Michael , Eshtehardi Parham , Dhawan Saurabh S. , Timmins Lucas H. , Jo Hanjoong , Taylor Robert W. , Samady Habib , Giddens Don
Published: July 2013

The high resolution of optical coherence tomography (OCT) may offer improved description of luminal surfaces and intimal thickening in human coronary arteries by comparison to other imaging modalities, such as intravascular ultrasound (IVUS). We investigated the left anterior descending (LAD) coronary artery of a patient using both OCT and IVUS methods and found an asymmetrical distribution of intimal thickness (IT) around the lumen circumference in the OCT images, whereas the IVUS images showed a lumen with no asymmetry in IT. We reconstructed a 3D coronary artery model from the OCT slices that represented the morphological details of local luminal surfaces accurately and used this to simulate the pulsatile flow field in the model employing computational fluid dynamics (CFD). The pulsatile wall shear stress (WSS) distribution on the LAD surface was derived, and time-averaged WSS was computed. The data for IT and WSS distributions in the LAD segment were compared, and a linear inverse relationship between IT and WSS was found; higher WSS (> 25±5 dynes per square centimeter) favors thinner intima (< 0.12±0.05 millimeters) and lower WSS (< 12±5 dynes per square centimeter) favors thicker intima (> 0.33±0.05 millimeters). The enhanced spatial resolution of OCT offers an improved imaging technique for developing CFD models and assessing early atherosclerosis in patients with coronary artery disease.
Eddy Current Detection of Cancer in Surgically Excised Tissue
Authors: Sequin Emily K. , McFerran-Brock Jennifer , West Joseph , Subramaniam Vish
Published: July 2013

In current clinical practice, a patient usually undergoes a diagnostic computer tomography (CT) scan for evaluation of specific presenting symptoms. The presence of cancer is then confirmed by a diagnostic biopsy or at surgical exploration by histopathologic analysis. Suspicious finding on the diagnostic CT scan may be followed by an 18F FDG (Fluorodeoxyglucose radiolabeled with 18F) positron emission tomography (PET) scan. In a majority of cases, these pre-operative CT and PET scans are used to identify the approximate location of the tumor(s) before surgical intervention. Surgery remains the most effective means of treating solid malignancies despite advances in chemotherapy and radiation therapy [1].
Changes in the COP Trajectory After Use of a CAD and FEA Designed Orthotic
Authors: Rizza Robert , Liu Xue-Cheng , Thometz John , Lyon Roger , Tassone Channing , Van Valin S.
Published: July 2013

Following Ponseti casting, a new modality has been successfully developed to prevent clubfoot from recurrence in ambulating children. The new modality utilizes a non-traditional approach in the design and construction of customized dynamic pedorthtoses [1]. This approach implements dynamic plantar pressure data, as well as computer aided design (CAD) and finite element analysis (FEA).
Effect of Transvascular Fluid Exchange for Nonlinear, Biphasic Analyses of Flow-Controlled Infusion in Brain
Authors: Smith Joshua H. , Starkweather Kathleen A. , García José Jaime
Published: July 2013

Convection-enhanced delivery (CED) is a means to deliver therapeutic agents directly into brain tissue. Since CED often results in a rather significant interstitial fluid pressure, it is possible that infusions could result in a loss of fluid to the vasculature. While previous studies have included the effects of transvascular fluid exchange, they did so under the assumption of rigidity of the tissue [1, 2] or without considering its effect on the transport of the infused agent [3]. Recently, we proposed a spherical, biphasic model for constant flow-rate infusions that considers nonlinear stress-strain curves under finite deformation and nonlinear variation of hydraulic conductivity with deformation [4]. We have incorporated the effect of transvascular fluid exchange into this model and have studied the implications of variations in the vascular permeability, which may be of interest for improving drug delivery by CED.
Adipocytes Respond to Mechanical Stretch by Producing More Lipids
Authors: Shimon Naama , Shaharabani-Yosef Orna , Zaretsky Uri , Gefen Amit
Published: July 2013

Obesity is a leading preventable cause of mortality and morbidity worldwide, with increasing prevalence in adults as well as in children [1]. Authorities often view obesity as one of the most serious public health problems of the 21st century. Treating obesity is aimed at decreasing the amount of excessive adipose tissue by changing the balance between intake and expenditure of energy, via physical exercise, diet control or both, under the assumption that if there are no hormonal disorders present, the obesity is caused by calorie consumption that is not counterbalanced by sufficient calorie burn.
A Method for Quantitative Analysis of the Kinematics of Fibroblast Migration in a Monolayer Wound Model
Authors: Topman Gil , Sharabani-Yosef Orna , Gefen Amit
Published: July 2013

A wound healing assay is simple but effective method to study cell migration in vitro. Cell migration in vitro was found to mimic migration in vivo to some extent [1,2]. In wound healing assays, a “wound” is created by either scraping or mechanically crushing cells in a monolayer, thereby forming a denuded area. Cells migrate into the denuded area to complete coverage, and thereby “heal” the wound. Micrographs at regular time intervals are captured during such experiments for analysis of the process of migration.
Mechanics of the Cephalopod Chromatophore Layer: Structural Characterization of Cephalopod Chromatophores
Authors: Kirkwood Keith M. , Bell George , Kuzirian Alan M. , Hanlon Roger T. , Wetzel Eric D.
Published: July 2013

Cephalopods are a class of mollusks that include cuttlefish, octopus, and squid1 that are capable of adaptive display capabilities. The cephalopods unique adaptable appearance is enabled by a sequence of thin layers in their soft and stretchable skin2 that allows them to quickly change color (Figure 1a), pattern, iridescence and texture (with the exception of the squid)3. Two layers in the skin are responsible for this remarkable ability (Figure 1b). The chromatophore layer, located beneath the transparent epidermis layer, is a layer of thousands of pigmented chromatophore organs that are yellow, red, or brown. Below this layer is a sequence of structural reflectors called iridophores that reflect spectra from near-IR to short-wavelength blues and greens1,4. The combination of chromatophore pigments and structural reflectors allows the cephalopod to display dynamic patterning in complex combinations of color, iridescence, brightness, and polarity. The design of the chromatophore organs and the dermal layer are the focus of this investigation.
A Multi-Scale Collagen Turn-Over Model for Soft Biological Tissues With Application to Abdominal Aortic Aneurysm Growth
Authors: Martufi Giampaolo , Gasser T. Christian , Auer Martin
Published: July 2013

Collagen is a structural protein responsible for the mechanical strength, stiffness and toughness of biological tissues like skin, tendon, bone, cornea, lung and vasculature. In the present study we considered the enlargement of the aneurysm as a consequence of a pathological degradation and synthesis of collagen, i.e. malfunction of collagen turn-over. Consequently, the vascular wall is modeled by an (inert) matrix material representing the elastin, which is reinforced by a dynamic structure of bundles of collagen. Specifically, collagen is formed by a continuous stress-mediated process: deposited in the current configuration and removed by a constant degradation rate. Finally the micro-plane concept is used for the Finite Element implementation of the constitutive law. The model proposed within this study has a strong biological motivation and is able to capture both non-linear mechanics of aortic tissue and saline feature of AAA growth. Besides that, the micro-plane approach allows a straight forward FE implementation and preliminary results indicate its numerical robustness.
Stress-Strain Profile of Carotid Plaque With and Without Juxtaluminal Hemorrhage/Thrombus: A Possible Mechanism for Subsequent Cerebrovascular Events
Authors: Teng Zhongzhao , Sadat Umar , Gillard Jonathan H.
Published: July 2013

Patients suffering from a transient ischemic attack (TIA) are at high risk of a stroke or recurrent TIA, with about half of all recurrent events during the seven days after a TIA occurring in the first 24 hours. These events are usually caused by thromboembolization from ruptured carotid atherosclerotic plaques. Large trials have shown that carotid endarterectomy benefits patients with high grade carotid stenosis, but the risk-to-benefit ratio was less clear-cut for symptomatic patients with moderate stenosis (50–69%). Therefore, identification of high-risk plaques within this group could significantly decrease the ratio.
Tricuspid Valve Annulus Tension
Authors: Bhattacharya Shamik , He Zhaoming
Published: July 2013

Functional tricuspid regurgitation is a direct outcome of right ventricular dilatation and tricuspid annulus dilatation. The mechanism underlying functional tricuspid regurgitation is believed to be multifactorial and related to abnormalities in right ventricular volume, function and shape. Changes in the right ventricle geometry may lead to alterations in the positions of the papillary muscles (PM) of the tricuspid valve (TV). PM displacement happens in right ventricular dilatation but its correlation with tricuspid annulus dilatation is still unknown. The unique structure and orientation of tricuspid PM has role to play in TV annulus mechanics and right ventricular mechanics (Fig.1). It has been already shown that annulus tension (AT) is a parameter to evaluate left ventricular function that, previously, was evaluated via the left ventricular geometry and pressure [1–3].
Biotransport Education: Thermal Therapies
Authors: Pearce John
Published: July 2013

Thermal therapies are important clinical modalities in patient treatment that range from long term lower temperature heating for physical therapy and tumor hyperthermia therapy to very high temperature extremely short term heating for surgery. Heat sources that are typically applied include surface contact conduction heat transfer devices, lasers, and electromagnetic field sources from 500 kHz to 2.45 GHz. Their analysis using the classical bioheat equation has proven to be an effective and useful approach to treatment planning, experiment modeling, and new device development efforts.
Plaque Growth Functions Combining Wall Stress, Flow Shear Stress and Morphology May Provide Better Prediction for Atherosclerosis Progression: 3D FSI Studies Based on In Vivo Serial MRI
Authors: Yang Chun , Canton Gador , Yuan Chun , Hatsukami Tom , Tang Dalin
Published: July 2013

Atherosclerotic plaque progression involves biological, structural and mechanical factors. Previous work has shown that initiation and early progression of atherosclerotic plaque correlate negatively with flow wall shear stresses [1–2]. However, plaque growth functions based on patient-specific data to predict future plaque growth are lacking in the current literature. Six plaque growth functions based on fluid-structure-interaction (FSI) models and in vivo serial magnetic resonance image (MRI) data were proposed for progression prediction. This is to test the hypothesis that combining plaque morphology, plaque wall maximum principal stress (WS), strain (WSN) and flow maximum shear stress (FSS) could better predict plaque progression.
Determination of Human Carotid Atherosclerotic Plaque Material Properties Non-Invasively Using In Vivo Cine and 3D Magnetic Resonance Imaging and Image-Based Modeling Techniques
Authors: Liu Haofei , Canton Gador , Yuan Chun , Ferguson Marina , Yang Chun , Billiar Kristen , Tang Dalin
Published: July 2013

Atherosclerotic plaque rupture is believed to be associated with high critical stress exceeding plaque cap material strength. In vivo magnetic resonance image (MRI)-based computational models have been introduced to calculate critical plaque stress and assess plaque vulnerability [1–5]. However, accuracy of computational stress predictions is heavily dependent on the data used by the models. Patient-specific plaque material properties are desirable for accurate stress predictions but are not currently available. In this paper, non-invasive in vivo Cine and 3D multicontrast MRI data and modeling techniques were combined to obtain patient-specific plaque material properties to improve model prediction accuracies. A 2D human carotid plaque model was used to demonstrate impact of material stiffness on computational stress predictions.
Functional Imaging of the Proximal Femur Using Shape Template and a Bone Mineral Density Image
Authors: Väänänen Sami P. , Isaksson Hanna , Jurvelin Jukka S.
Published: July 2013

Measurement of bone mineral density (BMD) by DXA (dual-energy X-ray absorptiometry) is generally considered to be the clinical gold standard to diagnose osteoporosis. However, BMD alone is only a moderate predictor of fracture risk. Finite element analyses (FEA) of bone mechanics can contribute to a more accurate prediction of fracture risk (Cody et al. 1999). However, CT imaging is relatively expensive and inflicts larger radiation doses on the patient.
Impact of Articulation Geometry on Contact Mechanics in Total Ankle Replacement Design
Authors: Dharia Mehul A. , Bischoff Jeff E. , Gillard Duane , Wentorf Fred , Mroczkowski Matt
Published: July 2013

Total ankle replacement designs have evolved since their introduction in the mid 1970s. While the first-generation total ankle replacement (TAR) designs had unacceptably high failure rates, recent designs have demonstrated improved outcomes [1]. Two philosophies are commonly used in TAR design: mobile-bearing and fixed-bearing. Unlike mobile-bearing designs which have two articulating surfaces, fixed-bearing designs have only one articulating surface. While fixed-bearing designs have lower risk of dislocation than mobile-bearing designs, the single articulation feature can produce higher contact stress on the articulating surface, increasing the potential for polyethylene wear [1, 2].
Planar Biaxial Characterization of Human Coronary and Carotid Arteries for Computational Modeling
Authors: Kural Mehmet H. , Tang Dalin , Zheng Jie , Billiar Kristen L.
Published: July 2013

Finite element analyses (FEA) provide contributions to clinical cardiovascular applications such as assessment of plaque vulnerability, the mechanical optimization of balloon angioplasty and stent deployment. However, FEA-predicted stresses for physiological and pathological states are dependent heavily on the accuracy of material models utilized. Thus, developing accurate quantitative descriptions for the multiaxial mechanical behavior of blood vessels is essential for developing accurate computational models for arterial stiffness.
The Potential of Prolonged Tissue Culture to Reduce Stress Generation and Retraction in Engineered Heart Valve Tissues
Authors: van Vlimmeren Marijke A. A. , Driessen-Mol Anita , Oomens Cees W. J. , Baaijens Frank P. T.
Published: July 2013

Heart valve tissue engineering (TE) relies on extracellular matrix production by cells seeded into a degrading scaffold material. Valves are cultured constraint with the leaflets attached to each other for 4 weeks [1]. The seeded cells naturally exert traction forces to their surroundings and due to an imbalance between scaffold, tissue and these traction forces, stress is generated within the tissue, which is good for tissue formation and architecture. However, during culture it causes tissue compaction, resulting in leaflet flattening, and at time of implantation, the leaflets are separated and the generated stress causes retraction of the leaflets (fig 1). This retraction on its turn results in loss of functionality.
A Textbook and Other Resources for Teaching Challenge-Based Biotransport
Authors: Roselli Robert J. , Diller Kenneth R.
Published: July 2013

An important outcome of the VaNTH ERC for Bioengineering Education Technologies is direct evidence of the effectiveness of challenge-based learning. This is a form of active learning that is based on the principle that the most effective learning environment is not only knowledge-centered, but is also learner-centered, assessment-centered and community-centered. Challenges presented in such a learning environment are most effective when they are based on real life applications that are of interest to the learner, but require the learner to extend his/her knowledge base before the challenge can be solved. By design, some of the necessary knowledge is gained outside the classroom and some is gleaned by student activities conducted inside the classroom. An objection to the use of active learning raised by some instructors is that less material can be covered in the classroom than in a traditional lecture-based course. Although this is true, it is not true that less material can be covered in an active learning course than in a lecture-only course. Instead, concepts that are easy to grasp can be moved to out-of-class activities, allowing more in-class time for the more difficult concepts. We have developed resources that can assist instructors of biotransport to begin adopting the challenge-based approach.
Shear Stress Effects on the Inflammation and Thrombogenic State of Baboon Endothelial Outgrowth Cells
Authors: Ankeny Randall F. , Nerem Robert M.
Published: July 2013

Endothelial progenitor cells (EPCs) are believed to play an important role in the injury response of the human vasculature. Sudies have shown how EPCs are activated and play roles in tumor and hindlimb ischemia nevascularization[1,2]. Furthermore, EPCs are increased after surgical procedures and localized to vascular grafts and denuded arteries[2,3]. EPCs have also garnered immense interest in the field of tissue engineering due to their ease of isolation and their high prolifierative rate[2].
Targeting Ovarian Cancer Cells With Rapidly Biodegradable L-Tyrosine Polyphosphate Nanoparticles Decorated With Folate
Authors: Ditto Andrew J. , Robbishaw Nikki K. , Panzner Matthew J. , Youngs Wiley J. , Yun Yang H.
Published: July 2013

Chemotherapy employs toxic chemicals to kill rapidly dividing cells. Examples of FDA approved antineoplastic drugs include cisplatin, doxorubicin, and paclitaxel. Since most of these drugs are nonspecific, they also damage normal tissues as well as the aberrant tumors. As a result, non-specific therapies have multiple side effects, which include myelosuppression, mucositis, alopecia, nephrotoxicity, and genotoxcity. In order to minimize these issues, researchers have begun to conjugate antineoplastic chemicals with targeting moieties or encapsulate drugs into nanoparticles decorated with compounds, peptides, or proteins that recognize specific cellular receptors, which are upregulated by the neoplastic cells. The targeting moieties aid in the accumulation of these drugs within the blood vessels of carcinomas, while keeping concentrations low in the systemic circulation. Thus, targeted delivery systems are able to minimize the unwanted side effects and increase the efficacy of chemotherapies.
Initial Stress in Biomechanical Models of Atherosclerotic Plaques
Authors: Speelman L. , Akyildiz A. C. , Wentzel J. J. , van Brummelen E. H. , Jukema J. , Poelmann R. E. , van der Steen A. F. W. , Gijsen F. J.
Published: July 2013

Rupture of the cap of an atherosclerotic plaque is instigated when the stresses in the cap due to the blood pressure exceed the local cap strength. Image based computational finite element models of atherosclerotic plaques are widely used to compute stresses in the fibrous cap. These models are often based on pressurized geometries. The shape of the plaque is determined by the blood pressure at the time of imaging, and thus contains initial stresses (IS) and strains, which are generally ignored in plaque stress studies.
Degree of Retrograde Flow and Its Effect on Local Hemodynamics and Plaque Distribution in an Aortic Regurgitation Murine Model of Atherosclerosis
Authors: Hoi Yiemeng , Van Doormaal Mark , Zhou Yu-Qing , Zhang Xiaoli , Henkelman R. Mark , Steinman David A.
Published: July 2013

Previously, Zhou et al. [1] presented a novel mouse model of aortic valve regurgitation (AR) to explore the effect of altered hemodynamics on atherogenesis. In these ldlr−/− mice with AR, extensive atherosclerotic plaque was found along the naturally lesion-free descending thoracic (DTAo) and abdominal aorta (AbAo), with distinct spatial distributions suggestive of a strong local hemodynamic influence (Fig. 1, top). Doppler ultrasound measurement showed that both DTAo and AbAo of the AR mice experienced an oscillatory flow pattern induced by the diastolic retrograde flow, as opposed to the consistent antegrade flow found in the non-AR mice. The study also suggested that the fraction of the DTAo surface covered by lesions tends to increase with the absolute diastolic retrograde Time-Velocity Integral (TVI) as measured from the Doppler ultrasound.
In Vitro Study of the C2-C7 Sheep Cervical Spine
Authors: DeVries Nicole A. , Gandhi Anup A. , Fredericks Douglas C. , Smucker Joseph D. , Grosland Nicole M.
Published: July 2013

Due to the limited availability of human cadaveric specimens, animal models are often utilized for in vitro studies of various spinal disorders and surgical techniques. Sheep spines have similar geometry, disc space, and lordosis as compared to humans [1,2]. Several studies have identified the geometrical similarities between the sheep and human spine; however these studies have been limited to quantifying the anatomic dimensions as opposed to the biomechanical responses [2–3]. Although anatomical similarities are important, biomechanical correspondence is imperative to understand the effects of disorders, surgical techniques, and implant designs. Some studies [3–5] have focused on experimental biomechanics of the sheep cervical functional spinal units (FSUs). Szotek and colleagues [1] studied the biomechanics of compression and impure flexion-extension for the C2-C7 intact sheep spine. However, to date, there is no comparison of the sheep spine using pure flexion-extension, lateral bending, or axial rotation moments for multilevel specimen. Therefore, the purpose of this study was to conduct in vitro testing of the intact C2-C7 sheep cervical spine.
Design Optimization of Rotary Blood Pumps: Alternatives to Anticoagulation Therapy
Authors: Girdhar Gaurav , Xenos Michalis , Chiu Wei-Che , Alemu Yared , Lynch Bryan , Jesty Jolyon , Slepian Marvin , Einav Shmuel , Bluestein Danny
Published: July 2013

Mechanical circulatory support (MCS) devices such as the ventricular assist devices (VADs) provide life saving short-term bridge-to-transplant solutions (1) to a large proportion of patients who suffer from chronic heart failure. Although hemodynamically efficient, such devices are burdened with high incidence of thromboembolic events due to non-physiological flow past constricted geometries where platelets (the principal cellular clotting elements in blood) are exposed to elevated shear stresses and exposure times (2) — requiring mandatory anticoagulation. We recently developed an optimization methodology — Device Thrombogenicity Emulator (DTE)(3) — that integrates device specific hemodynamic stresses (from numerical simulations) with experimental measurements of platelet activation. The DTE was successfully applied by our group to measure / optimize the thromboresistance of mechanical heart valves (MHV) (3, 4).
Mucus Clearance: An Experimental and Numerical Study
Authors: Hu Yingying , Bian Shiyao , Grotberg James B.
Published: July 2013

Mucus in a human lung has non-Newtonian properties such as shear-thinning, yield stress, and viscoelasticity. Rheological changes of mucus may greatly affect its ability to function as a lubricant, selective barrier, and the body’s first line of defense against infection (Lai 2009). Patients with COPD, asthma, or cystic fibrosis often have mucus hyper-secretion. Mucus plugging can cause total airway obstruction (Kant 2007). If mucus is too thick, for example in severe bronchitis or cystic fibrosis where the sputum viscosity can be more than 105 times that of water, patients experience great difficulty in mucus clearance, resulting in bacterial overgrowth (Lai 2009). The understanding of the mechanisms involved in mucus clearance is far from complete. For instance, the relation is not known between the non-Newtonian properties of the mucus layer and ciliary function in thickened mucus (Button 2008).
Dynamic Numerical and Experimental Evaluation of Trileaflet Polymer Prosthetic Heart Valves
Authors: Claiborne Thomas E. , Xenos Michalis , Girdhar Gaurav , Alemu Yared , Sheriff Jawaad , Slepian Marvin , Pinchuk Leonard , Jesty Jolyon , Einav Shmuel , Bluestein Danny
Published: July 2013

Valvular heart disease (VHD) continues to be a significant public health issue with an estimated 1–2% of the population affected [1]. Currently, VDH is primarily treated at the end stages with open-heart surgical replacement of the diseased valve with either a tissue or mechanical prosthetic heart valve (PHV), each having deficiencies including low durability and high thrombosis respectively. Polymer trileaflet PHVs have been designed to mimic the native aortic valve (AV) hemodynamics while being more durable and less thrombogenic than current PHVs. Recent advances in polymers and its applications for polymer PHVs, including transcatheter PHVs or use in the Total Artificial Heart (TAH) (Fig. 1), encourage further research and development [2–4]. Paramount to polymer PHV progress is proving equivalence to commercially available FDA approved PHVs.