A ventricular assist device (VAD), which is a miniaturized axial flow pump from the point of view of mechanism, has been designed and studied in this report. It consists of an inducer, an impeller, and a diffuser. The main design objective of this VAD is to produce an axial pump with a streamlined, idealized, and nonobstructing blood flow path. The magnetic bearings are adapted so that the impeller is completely magnetically levitated. The VAD operates under transient conditions because of the spinning movement of the impeller and the pulsatile inlet flow rate. The design method, procedure, and iterations are presented.
The VAD's performance under transient conditions is investigated by means of computational fluid dynamics (CFD). Two reference frames, rotational and stationary, are implemented in the CFD simulations.
The inlet and outlet surfaces of the impeller, which are connected to the inducer and diffuser respectively, are allowed to rotate and slide during the calculation to simulate the realistic spinning motion of the impeller. The flow head curves are determined, and the variation of pressure distribution during a cardiac cycle (including systole and diastole) is given. The axial oscillation of impeller is also estimated for the magnetic bearing design. The transient CFD simulation, which requires more computer resources and calculation efforts than the steady simulation, provides a range rather than only a point for the VAD's performance. Because of pulsatile flow phenomena and virtual spinning movement of the impeller, the transient simulation, which is realistically correlated with the in vivo implant scenarios of a VAD, is essential to ensure an effective and reliable VAD design.
From the.Mechanical and Aerospace Engineering Department, Virginia Artificial Heart Institute, University of Virginia, Charlottesville, VA; †Biomedical Engineering Department, Virginia Artificial Heart Institute, University of Virginia, Charlottesville, VA; and the ‡Utah Artificial Heart Institute, Salt Lake City, UT. Presented in part at ASAIO-ISAO Joint Conference, June 19–21, 2003, Washington, DC. Correspondence: Xinwei Song, 122 Engineer's Way, Mechanical & Aerospace Department, University of Virginia, Charlottesville, VA 22903.
Claiming approximately 945,836 lives in the year 2000, cardiovascular disease (CVD) is the number one killer in the world. It is estimated that approximately 4.8 million people in the United States have congestive heart failure (CHF), a clinical syndrome that involves severe ventricular dysfunction and ultimately leads to a reduction in cardiac output. Approximately 40,000 patients with CHF die each year, and as many as 250,000 deaths are a result of CHF related illnesses. According to statistical estimations, approximately 400,000 new CHF cases are diagnosed each year in the United States. These patients with cardiac failure follow a significant regimen of cardiac medications and often require heart transplantation. Because there is a limited number of donor hearts available each year (approximately 2,500), many such patients with CHF may not survive the lengthy waiting period for a donor heart.
Patients with CHF often need mechanical circulatory support (MCS) as a bridge to transplantation and even as a long-term destination therapy. MCSs have been researched and developed for decades and fall into three main categories: total artificial heart (TAH), volume displacement blood pump (DBP), and rotary blood pump (RBP). The TAH aims to completely replace the native heart with a pulsatile MCS. DBP and RBP are the ventricular assist devices (VAD) that merely assist the native ventricle to pump blood through the body and, therefore, reduce its workload.
DBPs are typically pulsatile blood flow support devices with flexible membranes or pusher plate design including a multitude of valves. In contrast, RBPs provide continuous blood flow via a centrifugal or axial flow design with no membranes or valves. Up to 2003, there were three MCSs that had received U.S. Food and Drug Administration (FDA) approval and could be used for a designated therapy: Thoratec VAD, HeartMate LVAS (left ventricular assist system), and Novacor LVAS.
Several MCSs were undergoing clinical trials. VADs have been proven to provide effective supplemental circulatory support to patients with cardiac failure. An estimated 35,000–70,000 people in the United States could benefit from long-term MCSs each year. To provide a viable MCS option as long-term therapy for these patients with cardiac failure and an improvement over currently available devices, the present authors designed a fully implantable axial flow RBP with a magnetically levitated impeller for the adult population. The Virginia Artificial Heart Institute (VAHI) has developed several prototypes of continuous flow centrifugal left ventricular assist devices (LVADs) with magnetically levitated impellers for long-term use for patients with CHF.
The most recent and successful prototype, the HeartQuest CF4b, is currently undergoing animal testing at the Utah Artificial Heart Institute. The CF4b pump has been implanted in a series of four calves for 30–60 days and in one calf for approximately 110 days. The calves performed well on the treadmill with the pump support; they did not show an increase in plasma free hemoglobin over the support duration, and they had no fibrin split products or d-dimers in the circulating blood (indicative of thrombosis) that had been broken down with the fibrolysin enzymes.
The experiences gained from this successful centrifugal design effort were helpful in developing an axial flow blood pump. Even though the advantages and disadvantages of axial versus centrifugal VADs are still in dispute, the present authors believe that there are a number of advantages of the axial flow design as compared with the centrifugal configuration, especially for a totally magnetically suspended impeller. The centrifugal pump presents a geometry that is not easily implanted to a calf or a human because of its inflow and outflow port locations. The magnetically levitated impeller design for a centrifugal RBP generates a secondary blood flow path through the clearances between the pump housing and the rotating impeller.
This secondary flow path may create possibilities of flow stagnation and high shear stresses, which could lead to hemolysis and possible thrombosis. In contrast to centrifugal VADs, the magnetically levitated impeller design for the present authors' axial flow pump does not include a secondary blood flow path. Furthermore, axial pumps have better anatomic fit because of their compact sizes and tubular configurations. As a result, axial flow pumps require less time to implant, thereby decreasing the cost and invasiveness of the procedure. The main design objective of the present authors' axial flow pump, named the LEV-VAD, is to produce a pump with a streamlined, idealized, one pass, nonobstructing blood flow path that can deliver 100 mm Hg pressure rise at 6 L/min volume flow rate. As previously mentioned, the LEV-VAD includes an impeller that is suspended entirely by magnetic bearings (MBs).
This suspension design allows the impeller to avoid any contact with the pump's internal housing. This design also reduces regions of stagnant and high shear flow that normally surround a fluid or pivot bearing by allowing for larger clearances between the rotor and housing. Unlike traditional mechanical bearings, MBs have no moving parts in contact; thus they do not wear over time and consequently have a longer operational lifetime. The bearing Hall sensors provide information that aids in the control of the impeller's position and movement.
Novel algorithms that have been developed and tested over years will be implemented to deduce the pump operating flow rate and pressure rise by monitoring the electrical power to the bearings. Illustrates the LEV-VAD design including magnetic bearings and motor components. Materials and Methods Pump Design Theory Turbo machines involve an energy transfer between the rotor and the flowing fluid. In the axial pump, the impeller receives energy from an external electric motor and imparts the energy to the fluid. Basic design expression for an axial pump is a form of Newton's law of motion applied to the fluid traversing the rotor, which states that the torque on the impeller is equal to the changing rate of the angular momentum of fluid.
Defines the torque ( T) as a function of mass flow rate ( m), the radii ( r 1 and r 2), and the tangential absolute velocities ( V u1 and V u2). Performance curves are frequently plotted using a pair of dimensionless variables described above, such as curve or curve. Additionally, dimensionless variables are commonly used to select the type of machine and to determine the impeller size and geometry according to the operating requirements. For example, displays the copy of empirical diagrams for selection of machine and initial guess of pump dimension based upon the specific speed Ω s.
High efficiency axial pumps correspond to the range of specific speed of 2.5–5.5. The particular speed specific diameter plot (Cordier diagram) shows the optimum relation between the operating speed and pump dimensions, allowing for high efficiencies.
The impeller geometry, including impeller tip and root diameters, annular flow area, blade number, and inlet and outlet blade angles (β 1, β 2) can be determined by the specific diameter based upon some other empirical charts and formulas. An axial pump so selected and designed would be expected to have a high efficiency.
Generally, the blades have shapes or profiles similar to those of airfoils: they are thin, cambered, and streamlined. Design Objectives and Criteria The design process of an axial flow RBP is far more complex than that of a typical industrial axial flow pump. Blood pump designers must consider a number of specific design requirements besides pump performance, such as implantability, blood compatibility, durability, and MBs feasibility.
To achieve an implantable pump, the overall size of the device becomes the central focus and the most important constraint during the design phase. Designing a pump with high efficiency and lower power consumption helps to minimize the size of the motor, thereby reducing the overall size of the RBP.
Also, a miniaturized blood pump would reduce device related infections and could eliminate the need for an abdominal surgical pocket. Because, for the same head and capacity requirements, the pump operational speed is inversely proportional to the pump's size, a smaller pump corresponds to a higher rotational speed of the rotor. Unfortunately, a higher rotor speed implies a higher value of shear stress, which could have a traumatic effect on blood. Therefore, the second important constraint becomes the rotor rotational speed and the clearance gaps between the rotor and the stationary housing. The larger the clearance gaps, the smaller the shear stress value under a given rotational speed.
However, wider clearance gaps create more challenges to the MB designs. The blood pump should be a nonthrombogenic device. Fundamentally, blood needs to be constantly in motion to avoid clotting and thrombosis. The smooth, nonobstructing flow path through the pump should be ideal to maintain a continuous wash over all surfaces and to avoid recirculation or stagnant flow regions that would encourage deposition of platelets. Additionally, platelet activation is far more sensitive to high shear flow conditions. A combination of smooth flow path and proper flow pattern near surfaces can reduce potential deposition and activation of the coagulation cascade. Durability is the main motive for using MBs in the present authors' LEV-VAD designs.
MBs have an expected lifetime of 15–20 years and are more reliable than mechanical bearings. Another advantage over mechanical bearings is that blood can wash over surfaces to avoid stagnation. In addition, mechanical bearings generate more shear stress near the touch points. On the other hand, MBs need extra space to locate the permanent magnets and coils. The fluid forces and moments on the impeller and more detailed information on the fluid field are required to design the stiffness and control capability of MBs. Also, the VADs with MBs need more percutaneous wires as compared with those with pivot or fluid bearings.
Depending upon the diversity of patients and the level of their physical exertion, the axial RBP must be able to operate over a wide range of flow conditions. Designed to operate at a single, best efficiency operating point, blood pumps quite frequently are required to perform at off design conditions. The robust motor and suspension system and its control system must be able to successfully and quickly respond to these flow condition adjustments by varying pump rotational speed. The design of the LEV-VAD requires a multidisciplinary consideration of traditional hydraulic analyses, MB design and its control system, and hematologic performance criteria. Compromises must be explored among those design elements to obtain the best overall performance. Gives the insight of design objectives and considerations.
Design Iterations The flowchart illustrated in presents the general design procedure of an axial blood pump with magnetically suspended impeller. A baseline analysis was completed first by means of classic pump design formulas and empirical diagrams to obtain an initial pump geometry.
Based upon that, a CFD model was generated, and an initial MB design was executed. The detailed information of fluid field exposed the deficiencies of the initial design and provided the fluid forces and moments for optimizing MB design. The CFD fluid path and MB designs will greatly affect the overall pump geometric parameters.
A number of design iterations have been performed to reach the prototype stage for manufacture and bench tests. It should be noted that a proper mechanical design does not necessarily create an ideal VAD prototype. Unfeasibility or extremely high cost of manufacture, coverage by existing patents, or absence of innovation could abort a desirable design.
Elaborates the design iterations that the present authors experienced before the final design. A configuration with inducer, impeller, and diffuser has been adopted. The inducer straightens the flow and removes prerotation of the fluid before the fluid reaches the impeller region, which makes the design of the impeller much easier. The simple geometry of inducer provides the possibility to optimally locate the active magnetic bearings (AMBs) without increasing the VAD's overall size.
The impeller accelerates speed of the fluid and transforms the rotational energy imparted by the motor to the kinetic energy of the fluid. The stagger angle of the blade should gradually increase along the flow direction; otherwise, flow separation would likely occur. Unlike the simple velocity distribution at the discharge of inducer, the existing angular velocity and nonuniformity of axial velocity at the trailing edge of the impeller blades make the design of the diffuser extremely challenging. The diffuser converts the kinetic energy of the fluid to the desired pressure energy and thus must be designed to avoid recirculation, minimize resistance to flow, and allow for manufacturability. Because of the great curvature, three diffuser blades are finally adopted in the LEV-VAD for ease of manufacturing.
Last Version: LEV-VAD The last version, named LEV-VAD, reached desirable fluid, magnetic, and hematologic performances. The LEV-VAD measures approximately 100 mm in length and 30 mm in diameter.
Shows the blade angle (Beta on the ordinate) distributions along the axis in impeller section at different spans. The blade angle is measured from the axial to the tangential direction.
The M-Prime on the abscissa represents the radius normalized distance along the meridional curve. The blade angle is designed to change gradually. Shows the pump's configuration and the CFD model of the LEV-VAD. The fluid enters the inducer, the impeller, and the diffuser sequentially.
The axial gaps between inducer and impeller and the impeller and diffuser are both 1 mm. The main geometric parameters for inducer, impeller, and diffuser blades are given in. The inducer's fluid dynamic function is to feed the impeller straightly, so both its inlet and outlet blade angles are zero degree, which means that the inducer blades are parallel to the axis.
The inlet angles of impeller and diffuser blades are designed to be tangent to the fluid incident angle to avoid the vortex and reduce the friction and energy loss. They are relatively large because of the high rotational speed of the impeller. Counter-clockwise is specified as positive; clockwise is specified as negative. The diffuser blade outlet angle is designated as zero degree to minimize the angular component of fluid speed and, thereby, eliminate the swirl at the pump discharge. The length and height of blades are largely dependent upon the design and requirements of MBs. CFD Analysis CFD Software. This study used four software programs: BladeGen, TurboGrid, Build, and TASCflow, which are commercial software available through ANSYS Corp.
(Canonsburg, PA, U.S.A.) BladeGen is an interactive turbomachinery design program for Windows platform, which allows easy graphical manipulation of the complicated impeller or diffuser design parameters and configurations. It easily isolates one or more parameters, which helps to create complicated blade configurations.
For example, it is able to change the blade height while keeping the hub and shroud profiles constant, or modify the stagger angle without changing the blade angle. With an impeller or diffuser design, BladeGen exports the proper data files defining the hub, shroud, and blade profiles to TurboGrid. TurboGrid is an interactive hexahedral grid generation system, specifically designed for turbomachinery. It is preprogrammed with several templates tailored to the complex curvatures of various types of turbines, compressors, and pumps. TurboGrid provides a graphical user interface (GUI) for manipulating the total number and distribution law of mesh seeds. This functionality allows for optimization of the grid through iterations, such as the grid amount within the boundary layer, and the location of nearest grid to wall surface. From this, TurboGrid generates a well distributed grid for computation in the final program, TASCflow, which is the fluid Navier-Stokes CFD solver and postprocessor.
Build, which is a generic grid generator, is used to define and generate mesh for all regions in the pump except the blade regions. The entire computational grid must include no negative volumes or twisted elements. It must have acceptable skew angles (generally 15° and. Computational Efforts for Transient Simulations. Because of the complex blade curvatures, the CFD model of LEV-VAD involves a rather dense and complicated mesh algorithm. Tascflow provides some beneficial recommendations for grid quality based upon a substantial number of computational experiences and experimental test comparisons for various types of turbo machines.
For instance, it suggests the y+ value of first grid near to walls as 2, and the number of grids within the boundary layer as 10–15 for the low Reynold number regions in blade passages. To satisfy these grid generation criteria and thereby reach acceptable computation accuracy, the inducer, impeller, and diffuser have 74,700, 200,000, and 77,800 grids, respectively. The LEV-VAD CFD model, which has approximately 352,500 total grids, requires at least 370 M RAM for running a steady flow simulation.
Illustrates a quantitative insight for the computational cost and resource. As compared with the steady state flow simulations, the transient calculations entail far more in computational resources. The memory allocation for a transient computation, with the same CFD model, requires three to eight times that for a steady computation, depending upon the iterative strategy selected. These additional computational requirements for the transient study coupled with the already large CFD model in general leads to an extremely computationally intensive set of simulations. Because of the high rotational speed and the small dimension of the pump, the computational time step must be very small.
For example, if the rotational speed of the four blade impeller is 7,000 RPM, it takes approximately 2.1 ms for the impeller to spin one pitch. To capture more information about the flow field from the movement of the blades, the present authors selected an incremental time step of 0.42 ms. This time step allows for 200 time-points to be computed, recorded, and processed for a single heartbeat with normal period of 0.8 seconds. The postprocess, which reads the information from each transient result file, is time consuming, as well.
Results Pump Performance Two transient components are examined simultaneously in this report. One component relates to the time varying boundary conditions (TVBC): the pulsed inlet flow rate. The other aspect is related to the transient rotational sliding interfaces (TRSI) between the rotational and stationary reference frames. They have different mechanisms that bring about the subsequent transient effects. The period of TVBC is 0.8 seconds corresponding to the native heartbeat, and flow rate variation is selected from simulative data of representative patients with CHF who would be considered prime LVAD candidates. The period of TRSI case is directly decided by the rotational speed, such as 2.1 ms for 7,000 RPM.
The time step was set as 0.42 ms for a total of 250 time-points to complete one heartbeat without any effects of initial conditions. For each time step, the impeller rotates approximately 18°. Demonstrates the static pressure distribution across the pump at five sequential time steps during a single period for a constant rotational speed of 7,000 RPM and a periodic inflow rate with the average volume flow rate of 6 L/min. The pressure is increasing spatially smoothly and temporally gradually, which indicates that the designs of blades and flow path are desirable. The pressure field, especially around the interface between impeller and diffuser, changes obviously at different time-points. Illustrates the correlation of volume flow rate and head rise of LEV-VAD, i.e., the Q-P curve, during a heartbeat.
The relation of pressure rise and flow rate demonstrates hysteresis, as expected, to form a closed loop curve. The maximum difference of pressure rises is approximately 55 mm Hg. The static pressure rises ranged from approximately 80–180 mm Hg, depending upon the absolute flow rate and its gradient. The peak head rise occurred at the end of native heart diastole, when the volume flow rate of blood through the VAD is at a minimum and when this peak would be expected. The forces exerted on the impeller are essential to the magnetic suspension designs.
After the fluid dynamics simulation was completed, three vector components of fluid forces can be determined by summing the individual contributions at all element surfaces on the impeller's walls. Because of the axially symmetrical configuration of the impeller, the radial force is relatively small and below 0.15 N. The axial force, however, which could be as large as 5.5 N, is a critical parameter for a successful magnetic suspension design. Displays the axial forces on the impeller.
The direction of the axial force is the conventional negative z direction because the pressure in the back clearance is larger than the pressure in the passages. The axial force increased as expected theoretically with a decrease in flow rate or an increase in rotational speed. Oscillations of the axial force with even transient intervals can also be observed in.
This oscillation phenomenon resulted from the TRSI simulations allowing the impeller blades to virtually rotate. After each rotation, the interface components between two reference frames are updated with respect to the location of the impeller at that time. This detailed transient simulation is more similar to in vivo operating conditions and thereby more realistic than the steady state simulation.
Furthermore, it can provide more information to validate the level of shear stress in the pump and to predict the level of blood trauma. The maximum shear stress of approximately 350 Pa occurred when the impeller blades encountered the diffuser blades angularly.
The loci are around the tip of impeller blades at pressure side and the root of diffuser blades at the suction side. Dynamic investigation of the shear stress level makes the pump design more reliable and effective. Comparison With Experiments Once the CFD design is finished, a Solidworks file is created for the manufacturer to build a physical model to test the pump performance. A plastic model is used to conduct particle image velocimetry (PIV) tests, and the velocity and pressure distributions and fluid forces can be measured in laboratory.
With the plastic materials, MBs are replaced by mechanical bearings. The tolerance of measurement of the flow rate is within ± 1% based upon the manufacturer's certification and calibration experiments conducted before the formal tests with the same working fluid. The tolerance of pressure measurement is within ± 2 mm Hg. Because the spinning speed of the impeller is too fast for comparing the response time of the measuring machine, it is impossible to conduct corresponding measurements for TRSI cases. The measurements for TVBC cases hopefully can be performed with the help of a heart simulator in the future. The steady numerical CFD results agree well with the measurements over the entire range of operational conditions tested. The maximum discrepancy between CFD simulations and PIV measurements is less than 20% and occurs at a flow rate of 4 L/min and 6,000 RPM.
Generally, the discrepancy is less than 10%. Axial Oscillation of Impeller The transient CFD simulation of the fluid field in the LEV-VAD provides information regarding the pressure difference across the whole pump as it varies with time. The time varying axial fluid force, which is approximately equal to the product of pressure difference and axial cross section area, can be calculated and estimated. Under the action of this force, the impeller moves forward until the MBs produce a restoring force that could overcome the axial fluid force. The fluid force and counter-restoring force may create an axial oscillation or vibration of impeller in the internal cavity of VAD. The amplitude of this vibration is also variable, whereas the maximum displacement of the vibration caused by the extreme fluid forces would be critical for the magnetic suspension design. Note that blood is a viscous fluid whose viscosity is approximately 3.5 times higher than that of water; therefore the oscillatory motion of the impeller experiences a damping influence from the fluid's presence.
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The force analysis is drawn in. When the impeller moves toward the inlet, the magnetic force and damping force from blood are opposite to the fluid force. The total force exerted on the rotor is equal to the product of the mass and the acceleration of impeller. Here, A: axial cross section area of impeller C: damping coefficient of blood, 0.5 N s/m D: displacement of impeller S f: Stiffness of magnetic bearing, 12 N/mm in this design ΔP: pressure difference between the impeller, calculated by transient CFD simulations. The velocity and acceleration of impeller are obtained by solving. The balance location during the operation is moved toward the inlet by 0.4 mm. The maximum amplitude of vibration is approximately 0.2 mm, which requires the axial gap between the leading edges of the impeller blades and the stationary trailing edges of inducer blades at least 0.2 mm to prevent the impeller from hitting the inducer.
The TASCflow has the capability to run a moving grid case. The mesh topology and number of grids remain constant whereas the volume of elements and coordination of grids vary during the calculations. With the movement of the impeller, the grids at one end are compressed and those at the other end are expanded. However, the large amount of memory required disables the moving grid computation. Fortunately, we can evaluate the effect of the impeller's axial oscillation on the pump performance by bench tests. The experimental results by the plastic pump described previously showed that there is little difference in pump performance for different axial locations of the impeller. This indicates that the pump performance is not sensitive to the location of the impeller.
Discussion The LEV-VAD design history and iterations have been described in this report. Conventional pump design approach and empirical formulas helped to establish the initial blood pump model.
Detailed CFD simulations are followed to investigate the fluid field and pump performance and to finalize the pump design. The general blood pump design procedure and strategy presented in this report are found helpful. A transient simulation study of the LEV-VAD, including TVBC and TRSI, was implemented by means of CFD technology. The variations in pressure rise and forces on the impeller under transient conditions were determined. The relation of pressure rise and flow rate demonstrates hysteresis. The variations of pump performance caused by the rotating position of impeller have been observed. Transient results indicated that the shear stress level was underestimated in steady studies.
TRSI is highly recommended in the CFD simulation of blood pump for blood compatibility studies. The transient simulations, which require more computational efforts and sources, give more detailed information for pump performances and prove to be essential to ensure a reliable and effective design. The axial oscillation of the impeller in the magnetic field has been described and investigated. Results indicate that the oscillated motion of the impeller is less important to pump performance but is critical for MBs design. The approaches introduced in this report enable a complete computational evaluation of the VAD's performance under transient flow conditions. This analysis provides insight into the pump's performance under dynamic flow conditions, which are realistic when considering in vivo implant scenarios and can generally be applied in the design process of VADs.
Future research efforts will focus on PIV measurements for the LEV-VAD prototype and comparisons of such measurements to the transient flow computational predictions.
. Dietz, Brian J.; VanDyk, Steven G.; Predmore, Roamer E. 2000-01-01 The Moderate Resolution Imaging Spectrometer (MODIS) optical instrument for NASA Goddard will measure biological and physical processes on the Earth's surface and in the lower atmosphere. A key component of the instrument is an extremely accurate scan mirror motor/encoder assembly. Of prime concern in the performance and reliability of the scan motor/encoder is bearing selection and lubrication. This paper describes life testing of the bearings and lubrication selected for the program. Mobley, Jeffrey; Robertson, Michael; Hodges, Charles 2016-01-01 Sierra Nevada Corporation’s Space Systems performed bearing life testing for the Scan Mirror Motor/Encoder Assembly (SMMA), part of the Scan Mirror Assembly on-board the Aerosol Polarimetry Sensor (APS) on the NASA Glory Spacecraft.
The baseline bearing life test duration extended beyond the launch date for the Glory Spacecraft; a risk that the program was willing to undertake with the understanding that if any anomalies or failures occurred before the required life was achieved, then the mission objectives or operating profile could be modified on orbit to take those results into account. Even though the Glory Spacecraft failed to reach orbit during its launch in March of 2011, the bearing life testing was continued through a mutual understanding of value between Sierra Nevada Corporation and our customer; with a revised goal of testing to failure rather than completing a required number of life cycles. Life testing thus far has not only exceeded the original mission required life, but has also exceeded the published test data for Cumulative Degradation Factor (CDF) from NASA/CR-2009-215681. Many lessons were learned along the way regarding long life testing. The bearing life test has been temporarily suspended due to test support equipment issues. 1985-01-01 Selected geophysical problems associated with the concept of continental drift as an incidental corollary of plate movement are discussed. The problems include the absence of a suitable plate-driving mechanism for plates with continental leading edges, the absence of the low-velocity zone under shields, and continental roots of 400 to 700 km depths.
It is shown that if continental drift occurs, it must use mechanisms not now understood, or that it may not occur at all, plate movement being confined to ocean basins. 2009-05-01 rotor was supported by ceramic ball bearings on the coupling end, and the test hybrid bearing at the other end. A magnetic bearing is utilized to.supported by ceramic ball bearings on the coupling end, and the test hybrid bearing at the other end.
A magnetic bearing is utilized to apply loads to the.Rotor The test rotor was made of 718 Inconel steel, with a bearing span of 308.6 mm (12.149 in.) between a set of ceramic support ball bearings and. Thompson, Linda B.; Flowers, Cecil E.
1991-01-01 Layered specimens readily made in standard sizes for tensile and other tests of mechanical properties. Standard specimen of metal ordinarily difficult to plate to standard grip thickness or diameter made by augmentation with easier-to- plate material followed by machining to standard size and shape. Thompson, Linda B.; Flowers, Cecil E. 1991-01-01 Layered specimens readily made in standard sizes for tensile and other tests of mechanical properties.
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Standard specimen of metal ordinarily difficult to plate to standard grip thickness or diameter made by augmentation with easier-to- plate material followed by machining to standard size and shape. Gunderson, Katelyn; Aitchison, Lindsay 2014-01-01 The overall objective of these experiments is to test the dust-resistant seal on the high performance glove disconnect system (HPGD), to analyze the response of the bearing to lunar regolith simulant effects. Shea, James Herbert 1989-01-01 Discussed are two techniques that can be used to directly test the theory that the plates which make up the crust of the earth are still moving. Described are the use of satellite laser ranging and very long baseline interferometry. Samples of data and their analysis are provided. (CW). Allaire, P.
E.; Mikula, A.; Banerjee, B.; Lewis, D. W.; Imlach, J. 1993-01-01 A magnetic thrust bearing can be employed to take thrust loads in rotating machinery. The design and construction of a prototype magnetic thrust bearing for a high load per weight application is described.
The theory for the bearing is developed. Fixtures were designed and the bearing was tested for load capacity using a universal testing machine. Various shims were employed to have known gap thicknesses. A comparison of the theory and measured results is presented.
Allaire, P. E.; Mikula, A.; Banerjee, B.; Lewis, D. W.; Imlach, J. A magnetic thrust bearing can be employed to take thrust loads in rotating machinery. The design and construction of a prototype magnetic thrust bearing for a high load per weight application is described. The theory for the bearing is developed.
Fixtures were designed and the bearing was tested for load capacity using a universal testing machine. Various shims were employed to have known gap thicknesses. A comparison of the theory and measured results is presented.
Vlcek, Brian L.; Hendricks, Robert C.; Zaretsky, Erwin V. 2003-01-01 Monte Carlo simulations combined with sudden death testing were used to compare resultant bearing lives to the calculated hearing life and the cumulative test time and calendar time relative to sequential and censored sequential testing. A total of 30 960 virtual 50-mm bore deep-groove ball bearings were evaluated in 33 different sudden death test configurations comprising 36, 72, and 144 bearings each. Variations in both life and Weibull slope were a function of the number of bearings failed independent of the test method used and not the total number of bearings tested. Variation in L10 life as a function of number of bearings failed were similar to variations in lift obtained from sequentially failed real bearings and from Monte Carlo (virtual) testing of entire populations. Reductions up to 40 percent in bearing test time and calendar time can be achieved by testing to failure or the L(sub 50) life and terminating all testing when the last of the predetermined bearing failures has occurred. Sudden death testing is not a more efficient method to reduce bearing test time or calendar time when compared to censored sequential testing.
Trombley, Arthur; Fan, Titan; LaBudde, Robert 2011-01-01 The level of total aflatoxin contamination was analyzed in naturally contaminated and spiked samples of corn and peanut using the Aflatoxin Plate Kit. This kit is an enzyme-linked immunosorbent assay (ELISA) suitable for rapid testing of grains and peanuts. The assay was evaluated for ruggedness and linearity of the standard curve.
The test kit results were then statistically evaluated for accuracy, precision, and correlation to a validated HPLC method (AOAC 994.08). The results were verified by an independent laboratory. Keith, Theo G., Jr.; Jansen, Mark 2004-01-01 The main proposed research of this grant were: to design a high-temperature, conical magnetic bearing facility, to test the high-temperature, radial magnetic bearing facility to higher speeds, to investigate different backup bearing designs and materials, to retrofit the high-temperature test facility with a magnetic thrust bearing, to evaluate test bearings at various conditions, and test several lubricants using a spiral orbit tribometer. A high-temperature, conical magnetic bearing facility has been fully developed using Solidworks. The facility can reuse many of the parts of the current high-temperature, radial magnetic bearing, helping to reduce overall build costs. The facility has the ability to measure bearing force capacity in the X, Y, and Z directions through a novel bearing mounting design.
The high temperature coils and laminations, a main component of the facility, are based upon the current radial design and can be fabricated at Texas A&M University. The coil design was highly successful in the radial magnetic bearing. Vendors were contacted about fabrication of the high temperature lamination stack. Stress analysis was done on the laminations. Some of the components were procured, but due to budget cuts, the facility build up was stopped. Gibson, John 1992-01-01 Proposed fixture for mounting large ball bearings during tests facilitates application of variable, known radial loads, and prevent gross movement of bearing radial or axial directions.
Load applied through Belleville spring washers to collar restrained by carrier ring. Load applied smoothly because collar and outer race of bearing flex in carrier ring. Inner race mounted on shaft rotated during application load. Gibson, Howard; Moore, Chip; Thom, Robert 2000-01-01 The Marshall Space Flight Center has a unique test rig that is used to test and develop rolling element bearings used in high-speed cryogenic turbopumps. The tester is unique in that it uses liquid hydrogen as the coolant for the bearings. This test rig can simulate speeds and loads experienced in the Space Shuttle Main Engine turbopumps.
With internal modifications, the tester can be used for evaluating fluid film, hydrostatic, and foil bearing designs. At the present time, the test rig is configured to run two ball bearings or a ball and roller bearing, both with a hydrostatic bearing. The rig is being used to evaluate the lifetimes of hybrid bearings with silicon nitride rolling elements and steel races. Gibson, Howard; Moore, Chip; Thom, Robert 2000-01-01 The Marshall Space Flight Center has a unique test rig that is used to test and develop rolling element bearings used in high-speed cryogenic turbopumps.
The tester is unique in that it uses liquid hydrogen as the coolant for the bearings. This test rig can simulate speeds and loads experienced in the Space Shuttle Main Engine turbopumps. With internal modifications, the tester can be used for evaluating fluid film, hydrostatic, and foil bearing designs. At the present time, the test rig is configured to run two ball bearings or a ball and roller bearing, both with a hydrostatic bearing. The rig is being used to evaluate the lifetimes of hybrid bearings with silicon nitride rolling elements and steel races. 2010-10-01. 46 Shipping 2 2010-10-01 false Production test plate requirements.
57.06-1 Section 57.06-1 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING WELDING AND BRAZING Production Tests § 57.06-1 Production test plate requirements. (a) Production test plates shall. 2011-10-01.
46 Shipping 2 2011-10-01 false Production test plate requirements. 57.06-1 Section 57.06-1 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING WELDING AND BRAZING Production Tests § 57.06-1 Production test plate requirements. (a) Production test plates shall. 2012-10-01. 46 Shipping 2 2012-10-01 false Production test plate requirements. 57.06-1 Section 57.06-1 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING WELDING AND BRAZING Production Tests § 57.06-1 Production test plate requirements.
(a) Production test plates shall. 2013-10-01. 46 Shipping 2 2013-10-01 false Production test plate requirements. 57.06-1 Section 57.06-1 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING WELDING AND BRAZING Production Tests § 57.06-1 Production test plate requirements.
(a) Production test plates shall. 2014-10-01. 46 Shipping 2 2014-10-01 false Production test plate requirements.
57.06-1 Section 57.06-1 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING WELDING AND BRAZING Production Tests § 57.06-1 Production test plate requirements. (a) Production test plates shall. Dirusso, Eliseo; Brown, Gerald V. 1992-01-01 Experiments were performed on a Hybrid Magnetic Bearing designed for cryogenic applications such as turbopumps.
This bearing is considerably smaller and lighter than conventional magnetic bearings and is more efficient because it uses a permanent magnet to provide a bias flux. The tests were performed in a test rig that used liquid nitrogen to simulate cryogenic turbopump temperatures. The bearing was tested at room temperature and at liquid nitrogen temperature (-320 F). The maximum speed for the test rig was 14000 rpm. For a magnetic bearing stiffness of 20000 lb/in, the flexible rotor had two critical speeds. A static (nonrotating) bearing stiffness of 85000 lb/in was achieved.
Magnetic bearing stiffness, permanent magnet stiffness, actuator gain, and actuator force interaction between two axes were evaluated, and controller/power amplifier characteristics were determined. The tests revealed that it is feasible to use this bearing in the cryogenic environment and to control the rotor dynamics of flexible rotors when passing through bending critical speeds. The tests also revealed that more effort should be placed on enhancing the controller to achieve higher bearing stiffness and on developing displacement sensors that reduce drift caused by temperature and reduce sensor electrical noise.
E.; Scibbe, H. W.; Wisander, D. 1973-01-01 Ball bearings with lead- and lead-alloy-coated retainers were operated in liquid hydrogen at 30,000 rpm under a thrust load of 400 lb. Bearing lives were compared using different: (1) lead- and lead-alloy coatings, (2) coating thicknesses, (3) substrate materials, (4) retainer locating surfaces, and (5) plating techniques. Longer bearing run times were achieved using retainers with a lead-tin-copper alloy coating electroplated onto a leaded-bronze material and an aluminum-bronze alloy. Thirty percent of the bearings tested achieved the desired objective of 10 hours. All of the lead-alloy coated retainers exceeded this objective.
A coating thickness of at least 0.0014 in. Was used for all bearings exceeding the 10-hour goal. Machin, Ricardo A.; Evans, Carol T. 2013-01-01 On the 29th of February 2012 the Orion Capsule Parachute Assembly System (CPAS) project attempted to perform an airdrop test of a boilerplate test article for the second time. The first attempt (Cluster Development Test 2, July 2008) to deliver a similar boilerplate from a C-17 using the Low Velocity Air Drop (LVAD) technique resulted in the programmer parachute failing to properly inflate, the test article failing to achieve the desired test initiation conditions, and the test article a total loss.
This paper will pick up where the CDT-2 failure investigation left off, describing the test technique that was adopted, and outline the modeling that was performed to gain confidence that the second attempt would be successful. The second boiler plate test (Cluster Development Test 3-3) was indeed a complete success and has subsequently been repeated several times, allowing the CPAS project to proceed with the full scale system level development testing required to integrate the hardware to the first Entry Flight Test vehicle as well as go into the Critical Design Review with minimum risk and a mature design. Huang, Junejei; Chang, Chihui 1992-10-01 Instead of using lenses or mirrors as a null compensator, the construction of the zone plate interferometer is used to accomplish the null test. By choosing the focal length of the zone plate according to the radius of curvature and conic constant of the test surface, the conventional zone plate interferometer is modified to be a null test of concave conicoids. To test convex conicoids, an imaging lens is added between the zone plate and the test surface. As long as the zone plate is perfectly imaged into the center of the curvature of the test surface, a null test of convex conicoids is the same as that of concave ones.
Rosenlieb, J. 1985-01-01 A test rig was designed to evaluate the performance of a spherical roller bearing with a geared outer ring operating under conditions similar to those of a planet bearing in a helicopter transmission.
The configuration is an extension of the widely accepted four-square gearbox arrangement. It provides for testing of two bearings simultaneously with outer ring rotation, misalignment, diametrically opposed loading through the gear teeth, and under race lubrication.
Instrumentation permits the measurement of inner and outer ring temperature, bearing drag torque, degree of misalignment, outer ring speed, cage speed, and applied load. PAJUNEN, A.L. 2000-04-03 The purpose of this test is to verify that the Shortened Fuel Canister Hook with Certified Scale (i.e. Weigh Station) can be used to weigh an empty canister from the Canister Well and the empty Primary Cleaning Machine (PCM) Strainer Basket from the process table.
Drawing H-1-84835, 'Canister Handling Hook for Fuel Retrieval System Process Table,' provides details of the Shortened Fuel Canister Hook. It is also necessary to verify that the grid plate can be lifted and tilted over a canister in the canister well. This testing shall be performed before N Reactor fuel is processed through the FRS in Phase 3.
The Phase 3 Test will repeatedly weigh fuel and scrap canisters and the PCM strainer basket containing N Reactor fuel (Pajunen, et. Advance testing of this weigh station will ensure that accurate fuel weight data can be recorded in the Phase 3 Test.
This document satisfies the requirements EN-6-031-00, ' Testing Process' for a test plan, test specification and test procedure.
Picturedictionary-tutorial.pdf - Picture Dictionary: A Tutorial 1 4/3/2007. In this tutorial, we show the “PD Tutorial Test-case” project as an example for you to follow, but Download our bladegen tutorial eBooks for free and learn more about bladegen tutorial. These books contain exercises and tutorials to improve your practical skills, at all levels!
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