Carriage Speed Research Articles

Comparison Of Full-Scale PIV Measurements With CFD Simulations Of A Ship Propeller Inflow

Flow around the ship's hull and specifically the inflow conditions of the propeller(s) critically influence the propeller efficiency and cavitation behaviour. In a typical single-propeller vessel, the hull of the ship creates a velocity deficit in the top part of the propeller disk. This creates suitable conditions for cavitation, which is the main source of noise and vibration both inside the vessel as well as in the marine environment. Recently, two measurement campaigns were performed using a novel full-scale stereo-PIV device built to measure flows around vessels sailing at sea. During the first campaign, performed in one of MARIN's basins, the device was commissioned. The second campaign was performed during a sea trial; it resulted in propeller inflow data that can be used for validating CFD codes. The uncertainty of the PIV measurements was assessed using both campaigns. In the basin, uncertainty bias could be determined by comparing the PIV results with the carriage speed. At sea, the random part of uncertainty was determined by quantifying the standard deviation of the mean velocity for all three velocity components in the wake peak area of the propeller inflow. Overall, the uncertainty was found to be acceptably small, given the scale of the measurement and the necessity to work with naturally occurring seeding particles in the sea. CFD calculations of the same full-scale flow were performed using an in-house flow solver. The CFD results predicted the propeller RPM and the delivered power measured during the full-scale trial well, which gives confidence in the ability of CFD to predict ship trial performance. The comparison of the flow fields was good, with the PIV results demonstrating that full-scale PIV can be done reliably, and that the CFD is able to capture the major features of the flow in the considered area. For a large part of the flow field, the CFD was within the measurement uncertainty band. The wake peak was slightly underpredicted, which may be related to roughness effects on the boundary layer thickness.

Influence of Backpack Carriage and Walking Speed on Muscle Synergies in Healthy Children.

Four to five muscle synergies account for children's locomotion and appear to be consistent across alterations in speed and slopes. Backpack carriage induces alterations in gait kinematics in healthy children, raising questions regarding the clinical consequences related to orthopedic and neurological diseases and ergonomics. However, to support clinical decisions and characterize backpack carriage, muscle synergies can help with understanding the alterations induced in this condition at the motor control level. In this study, we investigated how children adjust the recruitment of motor patterns during locomotion, when greater muscular demands are required (backpack carriage). Twenty healthy male children underwent an instrumental gait analysis and muscle synergies extraction during three walking conditions: self-selected, fast and load conditions. In the fast condition, a reduction in the number of synergies (three to four) was needed for reconstructing the EMG signal with the same accuracy as in the other conditions (three to five). Synergies were grouped in only four clusters in the fast condition, while five clusters were needed for the self-selected condition. The right number of clusters was not clearly identified in the load condition. Speed and backpack carriage altered nearly every spatial-temporal parameter of gait, whereas kinematic alterations reflected mainly hip and pelvis adaptations. Although the synergistic patterns were consistent across conditions, indicating a similar motor pattern in different conditions, the fast condition required fewer synergies for reconstructing the EMG signal with the same level of accuracy.

Design, Development and Commissioning of the Boldrewood Towing Tank – A Decade of Endeavour

The process of design, build and eventual commissioning of the towing tank on the Boldrewood Innovation Campus is described. The design brief required a facility that would have a capability to test models at a commercial scale but that would be effective as teaching environment for the next generation of Naval Architects as well as providing a flexible space for future fundamental research. Each of these provided their own challenges but the eventual solution of a 138 m long, 3.5 m deep, 6 m wide facility has more than met the initial aspirations. Equipped with 12 independent 0.5 m wavemaking flaps at the West end, a passive beach at the East end, a deployable side beach along the South wall for post run wave absorption and a monocoque Aluminium alloy carriage, the Boldrewood towing tank has now been successfully operating for more than a year. The carriage position and speed are controlled by a twin winch arrangement using a laser positioning system and low embodied energy composite cables. The carriage can reach a maximum speed of 10 m/s with controllable acceleration rates and can have up to four constant speed phases per run. Initial commissioning results and comparisons with benchmark data for the KCS hull confirm the accuracy and repeatability of the facility. In particular, the position and speed of the carriage are known to a high level of precision. To date research and consultancy work has spanned the performance of high speed vessels, uncrewed underwater and surface vessels, wave energy and tidal current systems, floating platforms for wind turbines, performance sport work for sailing, kayaking, rowing and swimming, open water propeller tests as well as conventional displacement vessel testing for self-propulsion and resistance. All ship science and maritime engineering students use the facility as part of their taught modules in every year of their programme as well as for individual, MSc and group projects as appropriate. It has also made a strong impact on the many thousands of visitors a year to the campus for science and engineering open days.

Research on dynamic characteristics of the turnover system of rail belt conveyor

The rail belt conveyor is a new bulk material conveying system that combines the advantages of traditional belt conveyors and railway systems. However, the turnover system, which is a key part of the carriage’s direction-changing mechanism, experiences severe vibration and impact problems that affect its performance and reliability. In this study, a dynamic model of the carriage-rail coupling in the turnover system is established, and the vibration characteristics of the rail are analyzed. The influence of carriage speed, wheelbase, and wheel diameter on the vibration acceleration of the rail is investigated. The results show that higher carriage speeds intensify the vibration response of the rail when the carriage leaves the turnover wheel. The wheel diameter has a significant effect on the vibration acceleration, especially at high speeds. Additionally, the wheelbase affects the vibration acceleration, with smaller wheelbases resulting in more prominent effects. The established dynamic model is validated using measured data, providing insights into the dynamic behavior of the turnover system in rail belt conveyors.

Increasing load carriage and running speed differentially affect the magnitude, variability and coordination patterns of muscle forces

The study aims to investigate the effects of different loads and speed during running on inter- and intra-individual muscle force amplitudes, variabilities and coordination patterns. Nine healthy participants ran on an instrumentalized treadmill with an empty weight vest at two velocities (2.6 m/s and 3.3 m/s) or while carrying three different loads (4.5, 9.1, 13.6 kg) at 2.6 m/s while kinematics and kinetics were synchronously recorded. The major lower limb muscle forces were estimated using a musculoskeletal model. Muscle force amplitudes and variability, as well as coordination patterns were compared at the group and at the individual level using respectively statistical parametric mapping and covariance matrices combined with multidimensional scaling. Increasing the speed or the load during running increased most of the muscle force amplitudes (p < 0.01). During the propulsion phase, increasing the load increased muscle force variabilities around the ankle joint (modification of standard deviation up to 5% of body weight (BW), p < 0.05) while increasing the speed decreased variability for almost all the muscle forces (up to 10% of BW, p < 0.05). Each runner has a specific muscle force coordination pattern signature regardless of the different experimental conditions (p < 0.05). Yet, this individual pattern was slightly adapted in response to a change of speed or load (p < 0.05). Our results suggest that adding load increases the amplitude and variability of muscle force, but an increase in running speed decreases the variability. These findings may help improve the design of military or trail running training programs and injury rehabilitation by progressively increasing the mechanical load on anatomical structures.

Virtual PMM captive tests using OpenFOAM to estimate hydrodynamic derivatives and vessel maneuverability

This study reveals the significance of hydrodynamic derivatives derived at the different Froud number (Fr) in accurately predicting of a vessel's turning-circle maneuvers through solving the maneuvering modeling group (MMG) model. The computed turning-circle diameter showed a good agreement with the model test results, with less than 4% difference observed when using the hydrodynamic derivatives derived at Fr = 0.201. However, at Fr = 0.26, a significant difference was observed, which could be attributed to the use of lower values of maximum sway amplitude ymax and maximum yaw rate rmax′. The hydrodynamic characteristics of a maneuvering vessel may not be fully reflected, with the high displacement of the straight surging motion dominating the results. In this study, a set of virtual planar motion mechanism (PMM) captive tests is numerically conducted on a bare container ship hull model using an open-source code OpenFOAM. The virtual PMM captive test cases involve different maximum sway amplitude, maximum yaw rates, and Fr, achieved by varying sway amplitudes, heading angles, and the carriage speeds, respectively. The obtained numerical results are reconstructed as Fourier series (FS) equations to derive hydrodynamic derivatives employing the single run (SR) method. A system-based method is adopted to predict vessel's turning-circle maneuverability in calm water by employing the MMG mathematical model.

Estimating marksmanship performance during walking while maintaining weapon aim

Marksmanship performance while moving is a critical skill among tactical athletes due to the high demands of their occupational duties. Qualifications for dynamic marksmanship performance are not standardized across tactical athlete groups, which may limit comprehensive assessment of tactical athlete performance for situational awareness and adaptability to an unpredictable environment. Although static marksmanship performance provides foundational information on skills and level of ability, research is lacking on factors that influence dynamic marksmanship performance to best prepare tactical athletes for duties. The purpose of this study was to identify whether static marksmanship performance, speed of movement, load carriage, and biomechanical factors while ‘shooting on the move’ influenced dynamic marksmanship performance. Twenty-four male tactical athletes (22 active-duty Army Soldiers, two civilian SWAT operators; age: 23.83 ± 5.47 years; height: 1.80 ± 0.08 m; weight: 81.04 ± 7.87 kg) participated; final analyses did not include data from the two civilian operators to maintain sample homogeneity. Tactical athletes completed static and dynamic (‘shoot on the move’) marksmanship tasks under three load conditions: (1) no load (NL), (2) half kit (HK) of 11.34 kg, and (3) full kit (KIT) of 22.68 kg. Dynamic marksmanship was completed under three speed conditions: (1) self-selected slow speed, (2) standard speed, and (3) self-selected fast speed. Hip, knee, and ankle kinematics were collected via wireless inertial measurement units. Spatiotemporal parameters were collected via optical detection system. Marksmanship performance (accuracy) was collected via open-air acoustic target scoring and mean radial error (MRE) was calculated for both static and dynamic marksmanship tasks. Linear mixed-effects models were fit with dynamic MRE as the outcome variable with fixed effects of static MRE, load condition, speed condition, kinematics, and spatiotemporal parameters, adjusting for body mass. Alpha level was set a priori at p ≤ 0.10. The final statistical model included fixed effects of static MRE, load condition, speed condition, and time spent in double limb support. Static MRE (p < 0.01) and time spent in double limb support (p = 0.01) were significant factors. For each 1 cm increase in static MRE there was a 0.66 cm increase in dynamic MRE. For every 1% increase in time spent in double limb support while ‘shooting on the move’ there was a 0.13 cm increase in dynamic MRE. Findings from this study highlight that tactical athletes who have larger static stance MRE and spend a longer time in double limb support during a gait cycle exhibit an increase in MRE during ‘shoot on the move’ trials. Overall, dynamic shooting accuracy is not affected by lower extremity joint angles, load carriage, or speed of movement. Although strong relationships are known between gait speed, load, and lower extremity kinematics, the differences in tactical gait compared to normal gait and multi-task paradigm that likely favors marksmanship accuracy seem to present novel movement characteristics unique to occupational gait. Further investigation is warranted to identify other potential factors that may improve or worsen dynamic marksmanship performance.

Numerical analysis of interaction between sea ice and propeller based on coupled DEM-FEM model

When a ship navigates through ice-covered seas, the interaction between sea ice and propellers damages the propeller blades. A coupled discrete element method (DEM)-finite element method (FEM) model was developed to investigate the interaction between an ice block and a propeller. The ice block and ice-class propeller were simulated using the sphere-based DEM and hexahedral solid elements of the FEM, respectively. According to the mechanical mechanism of the ice-blade interaction, the compressive strength of sea ice is the most important parameter for the simulation. The bonding strength between the element was determined by the element size and compressive strength of the sea ice material through uniaxial tests. Then, the ice-propeller interaction was simulated using the proposed DEM-FEM model. The convergence of the proposed numerical model was verified. For simulating the ice-propeller milling process, four parameters, i.e., carriage speed, cut depth, rotational speed, and ice strength, were investigated to analyze the ice load and dynamic response of the propeller. Finally, considering the randomness of the ice-propeller interaction with the real condition, a numerical simulation of ice-propeller interaction during backward sailing of the ship was established, and the random characteristics of the ice load on the blades were analyzed.

Nonlinear dynamic model for linear guideway with crowning subjected to external load in five directions

The motion accuracy of linear guideway is adversely affected by ball passage vibration (BPV) when rolling balls within carriage move in a loop. Reduced vibration amplitude can be realized by a carriage with crowning design by now. However, few dynamic models are availability for the BPV analysis when linear guideway is subjected to actual external load in five directions. In this paper, a nonlinear dynamic model is proposed to investigate the periodic micro fluctuation of linear guideway with crowning subjected to load in five directions. The idea of coordinate transformation is adopted for the easier derivations of time-dependent and piecewise restoring force function. The different contact states of each ball are described in detail due to load distribution. The numerical simulation is employed to deal with equation of motion and discuss the effects of ball grouping, external load, preload and carriage speed. Experiment is also conducted for the verification of proposed model. The analytical model developed here is promising to clarify the mechanism of BPV from a dynamic perspective and serve the walking parallelism accuracy monitoring of linear guideway.

Indirect Monitoring of Frequencies of a Multiple Span Bridge Using Data Collected from an Instrumented Train: A Field Case Study.

In this paper, a field study is carried out to monitor the natural frequencies of Malahide viaduct bridge which is located in the north of Dublin. The bridge includes a series of simply supported spans, two of which collapsed in 2009 and were replaced. The replaced spans are stiffer than most of the others and these differences resulted in higher natural frequencies. An indirect bridge monitoring approach is employed in which acceleration responses from an instrumented train are used to estimate the natural frequencies of each span of the viaduct showing the locations of the two replaced spans with higher stiffness. For the indirect approach, an Ensemble Empirical Mode Decomposition (EEMD)-based Hilbert Huang Transform (HHT) technique is employed to identify the natural frequency of each span. This is carried out by analysing the Instantaneous Frequencies (IFs) from the calculated intrinsic mode functions. The average of the IFs calculated using 41 runs of the instrumented train (with varying carriage mass and speed for each run) are used to estimate the natural frequencies. To assess the feasibility of the indirect approach, a bespoke set of direct measurements was taken using accelerometers attached successively on each span of the viaduct. The free and forced vibrations from each span are used to estimate the first natural frequencies. The frequencies obtained from drive-by measurements are compared to those from direct measurements which confirms the effectiveness of indirect approaches. In addition, the instantaneous amplitudes of the drive-by signals are used to indicate the location of the stiffer spans. Finally, the accuracy and robustness of the indirect approaches for monitoring of multi span bridges are discussed.

Developing an Automated Monitoring System for Cable Yarding Systems

Cable yarders are often the preferred harvesting system when extracting trees on steep terrain. While the practice of cable logging is well established, productivity is dependent on many stand and terrain variables. Being able to continuously monitor a cable yarder operation would provide the opportunity not only to manage and improve the system, but also to study the effect on operations in different conditions.This paper presents the results of an automated monitoring system that was developed and tested on a series of cable yarder operations. The system is based on the installation of a Geographical Navigation Satellite System (GNSS) onto the carriage, coupled with a data-logging unit and a data analysis program. The analysis program includes a set of algorithms able to transform the raw carriage movement data into detailed timing elements. Outputs include basic aspects such average extraction distance, average inhaul and outhaul carriage speed, but is also able to distinguish number of cycles, cycle time, as well as break the cycles into its distinct elements of outhaul, hook, inhaul and unhook.The system was tested in eight locations; four in thinning operations in Italy and four clear-cut operations in New Zealand, using three different rigging configuration of motorized slack-pulling, motorized grapple and North Bend. At all locations, a manual time and motion study was completed for comparison to the data produced by the newly developed automated system. Results showed that the system was able to identify 98% of the 369 cycles measured. The 8 cycles not detected were directly attributed to the loss of GNSS signal at two Italian sites with tree cover. For the remaining 361 cycles, the difference in gross cycle time was less than 1% and the overall accuracy for the separate elements of the cycle was less than 3% when considered at the rigging system level. The study showed that the data analyses system developed can readily convert GNSS data of the carriage movement into information useful for monitoring and studying cable yarding operations.

Experimental assessment of a 100 W prototype horizontal axis tidal turbine by towing tank tests

In the present research, the performance of a prototype tidal turbine is evaluated via towing tank tests. The examined model is a three-bladed horizontal axis with a 1.15 m diameter. Previously, we studied the hydrodynamic behavior of this turbine and calculated the hydrodynamic coefficients using a numerical approach. Thus, this work concentrates on overwhelming the challenges, from manufacturing and assembling to data acquisition and power storage. The turbine is tested under various conditions namely: pitch angle, electrical load, carriage speed, and immersion depth to improve efficiency. Our experiment indicated the turbine performance to be the best being close to the surface of the water at different flow speeds. The optimum electrical load was found to be 20 Ω adding 16–40% to efficiency. By fixing the optimum load and tip immersion depth, the maximum efficiency of the whole rotor achieved around 0.265 at less than 0.56 m/s as towing speed while at the speed of 1.1 m/s, the maximum output power was more than 120 W having the pitch of the blades fixed at 20.4°.

Parametric Modeling of SAW Process using Genetic Algorithms Based Technique

The main aim of the present work paper is to apply a novel and efficient evolutionary technique in modeling welding responses which is very essential in subsequent optimization of the welding process. Submerged arc welding (SAW) being a highly efficient welding process owing to deep penetrant weld and smooth finish is used for the process modeling in the present research study. An empirical relationship is established between the significant input welding parameters and bead geometrical parameters (responses) by using a potential modeling tool namely, gene expression programming (GEP). Thus GEP gives the optimized model expressions to relate the responses to selected inputs. The various input parameters selected are Voltage, electrode wire feed, carriage speed and tube-end to work distance. These are altered to predict the responses namely, reinforcement, penetration and width of the bead. The models obtained have high correlation coefficients thus indicating the effectiveness of the GEP algorithm.

Optimization of hardness of weld in submerged arc welding

If a high quality of welding joint in thick metal is required, submerged arc welding process is preferably used. There are several welding input process parameters which influence the quality of the weld. Some important input process parameters in the case of submerged arc welding process are welding current, welding voltage, wire feed and carriage speed. A lot of researches are working to have the optimum values of these parameters but the problem is unsolved yet and requires more attentive work. In this work 16 welded joints were used for training a C++ program applying the artificial neural networks. Nine other welded joints were used for testing and validating the program. This work predicts the required values of input process parameters to obtain the optimum values of hardness of the work pieces if the values of input process parameters i.e. current, voltage feed and speed are known. The sensitivity analysis was also carried out to see the effect of different input process parameters on hardness of the work pieces.

Survey of the near wake of an axial-flow hydrokinetic turbine in the presence of waves

Flow field results are presented for the near-wake of an axial-flow hydrokinetic turbine in the presence of surface gravity waves. The turbine is a 1/25 scale, 0.8 m diameter, two bladed turbine based on the U.S. Department of Energy's Reference Model 1 tidal current turbine. Measurements were obtained in the large towing tank facility at the U.S. Naval Academy with the turbine towed at a constant carriage speed and a tip speed ratio selected to provide maximum power. The turbine has been shown to be nearly scale independent for these conditions. The selected wave form was intended to represent oceanic swell encountered off the U.S. eastern seaboard. The resulting model wave is a deep water wave, in terms of relative depth, traveling with the “current”, in the opposite direction of the towing carriage. Velocity measurements were obtained using a submersible, planar particle image velocimetry (PIV) system at streamwise distances of up to two diameters downstream of the rotor plane. PIV ensembles were obtained for phase locked conditions with the reference blade at the horizontal position. Phase averaged results for no-wave and wave conditions are presented for comparison showing further expansion of the wake and shear layer in the presence of waves as compared to the no-wave case. When ensembles are selectively sampled on the wave phase, a high degree of coherency is shown to remain and the wake width is shown to undulate with the passing of the wave, with the vertical displacement range on the same order as that of a particle under similar conditions. The impact of waves on turbine tip vortex helical structure is also examined. Waves are shown to change the location of adjacent helices. In the streamwise direction, this changes the pitch of the helix, shown in previous studies to affect the downstream wake recovery distance. In the vertical direction, depending on the wave-induced flow field at the time they were created, vortices are forced outward, into the mean flow or inward, into the wake core, potentially enhancing kinetic energy transport and accelerating the re-energization process.

Efficient Fabrication of Polycaprolactone Scaffolds for Printing Hybrid Tissue-Engineered Constructs.

Hybrid constructs represent substantial progress in tissue engineering (TE) towards producing implants of a clinically relevant size that recapitulate the structure and multicellular complexity of the native tissue. They are created by interlacing printed scaffolds, sacrificial materials, and cell-laden hydrogels. A suitable biomaterial is a polycaprolactone (PCL); however, due to the higher viscosity of this biopolymer, three-dimensional (3D) printing of PCL is slow, so reducing PCL print times remains a challenge. We investigated parameters, such as nozzle shape and size, carriage speed, and print temperature, to find a tradeoff that speeds up the creation of hybrid constructs of controlled porosity. We performed experiments with conical, cylindrical, and cylindrical shortened nozzles and numerical simulations to infer a more comprehensive understanding of PCL flow rate. We found that conical nozzles are advised as they exhibited the highest shear rate, which increased the flow rate. When working at a low carriage speed, conical nozzles of a small diameter tended to form-flatten filaments and became highly inefficient. However, raising the carriage speed revealed shortcomings because passing specific values created filaments with a heterogeneous diameter. Small nozzles produced scaffolds with thin strands but at long building times. Using large nozzles and a high carriage speed is recommended. Overall, we demonstrated that hybrid constructs with a clinically relevant size could be much more feasible to print when reaching a tradeoff between temperature, nozzle diameter, and speed.

Microstructural influence on damping for Friction stir welded Aluminum plates

Friction Stir Welding (FSW) is a solid state welding process. in which a rotating tool moves along the butted surfaces of rigidly clamped plates to form the weld. The speed of rotation, the axial load, feed rate and the type of tool influences the structural properties of the weld. An experimental study was carried out on Marine grade aluminum plates by varying the carriage speed, rotor speed and tools. A parametric study was carried out using three sets of carriage speed, rotor speed and tools. Further the FSW welded plates were analyzed for strength using universal testing machine. From the test results best, intermediate and worst cases were separated out based on the tensile strength and strain. One of the contributing factors towards this variability could be the sensitivity of friction coefficient. This results in improper heating and material distribution across advancing and retreating side. The microstructure of the welds was analyzed using. Next the influence of these microstructural grain properties on macroscopic damping behavior was analyzed by carrying out a modal testing on the welded structure. Understanding the damping behavior is helpful in characterizing the vibration of the structure. Sensitivity analyses on the variations in the damping for different natural frequencies were carried out. The study clearly indicated a sensitivity of damping on the microstructural properties the FSW welded plates.

Improving a methodology of theoretical determination of the frame and directing forсes in modern diesel trains

The method for determining the directing force was improved, taking into consideration the effect of transverse creep forces and the angle of the directing force inclination to the vertical axis. It was established that when determining the directing force, it is necessary to check the gap between the wheel flange and the rail head which is difficult to realize without computer simulation. When determining the frame force on the axle of the wheel set, a comprehensive approach was adopted taking into account geometric irregularities of the track path, both in vertical and horizontal planes; longitudinal and transverse creep forces at the point of the wheel-rail contact and influence of adjacent wheel sets of the diesel train car. Dependences of the frame and directing forces on speed of the carriage movement and the value of amplitude of the horizontal irregularity of the rail track were obtained. It was established that when moving in the straight section of the track, an increase in speed from 0 m/s to 50 m/s results in a rise in the value of the frame force: up to 8.3 kN for the first wheel set and 19.37 kN for the second wheel set and the directing force up to 31.38 kN for the first wheel set and up to 46.83 kN for the second wheel set. The increase in amplitude of the horizontal irregularity of the track, which is one of the primary causes of occurrence of forced oscillations of the carriage section above the springs also leads to an increase in numerical values of the forces of interaction of the rolling stock with the rail track. All this can bring about an increased power influence of the wheel set on the track and a negative impact on the basic criteria of traffic safety. Influence of the carriage movement speed on the value of transverse creep forces was studied. It has been established that with an increase in the carriage speed from 0 m/s to 50 m/s, these forces grow from 0 to 15.75 kN for the 1 st wheel set and from 0 to 29.22 kN for the 2 nd wheel set. This indicates impermissibility of neglecting the transverse creep forces when determining the directing force. Comparison of numerical values of the directing force determined by different methodologies was performed. It has been established that the methodology used in conducting forensic examination of railroad accidents may result in underestimation of fulfillment of the derailing condition. At the same time, calculations according to the formula improved in this study give an opportunity to obtain the results most approximate to the real operation conditions. Comparison of the experimental and theoretical calculated values of the frame force acting on the first wheel set of the diesel train car was made and their practical coincidence was shown. Discrepancy of the compared values of the frame force was within 7.2 %

Formability Improvements of DP 1180 Subjected to Continuous-Bending-Under-Tension

There continues to be a desire to incorporate advanced high strength steels (AHSS) into automotive and other applications in order to reduce the overall weight of the final product. However, these materials exhibit limited ductility prior to fracture and require high forming forces. One means to address these concerns, at least in a laboratory setting, is by subjecting the material to continuous-bending-under-tension (CBT). In this procedure, a set of three rollers reciprocate over the gauge length of the specimen while the material is continuously pulled in tension. The adjustable parameters during CBT testing are the roller depth, the crosshead velocity (which applies the continuous, tensile force to the specimen), and the carriage speed for the reciprocating rollers (which is typically set to the highest value possible while maintaining a safe process). The formability improvements obtained through CBT processing are decreased applied force and increased elongation to fracture. The latter is achieved by assuring that during the CBT process the entire gauge length elongates to the maximum possible value before fracture occurs. Past research has shown that the concentrated deformation in the fracture location of a tensile specimen is similar to the deformation over the entire gauge length of a CBT processed specimen. In this paper, a parameter space study of the DP 1180 AHSS is conducted in order to determine the optimal roller depth and crosshead velocity to achieve the maximum formability improvements for this material. The results demonstrate a promising means to improve displacement (approximately four times over that in simple tension) prior to fracture for this AHSS when subjected to CBT processing.

Survey of the near wake of an axial-flow hydrokinetic turbine in quiescent conditions

Abstract Flow field results are presented for the near-wake of an axial flow hydrokinetic turbine in quiescent flow conditions. The turbine is a 1/25 scale, 0.8 m diameter, two bladed turbine modeled after the Sandia National Laboratory Reference Model 1 Tidal Current Turbine. All measurements were obtained in the large towing tank facility at the United States Naval Academy with the turbine towed at a constant carriage speed and a tip speed ratio corresponding to maximum power production. The turbine is scale independent with respect to lift and very slightly dependent with respect to drag for these conditions ( R e c @ 0.7 R ≈ 4 × 10 5 ). The wake velocity field data was obtained using a two-dimensional particle image velocimetry (PIV) system. PIV ensembles were obtained for phase locked conditions. This paper focuses on characterizing the velocity and the mean flow structure in the near wake. Specifically, the downstream evolution of coherent tip vortices shed by the rotor blades were examined. Vortex aperiodicity was shown to increase with downstream distance. The streamwise spacing between adjacent vortex cores was shown to be constant within a diameter downstream of the rotor. Further downstream, significant vortex filament interaction was observed, including leapfrogging. This interaction is thought to be the primary mechanism for wake breakdown and re-energization.