Predicted vs Measured Initial Camber in Precast Prestressed Concrete Girders

Prestressing of concrete is the introduction of permanent internal stresses in a structure or system in order to improve its performance. Concrete is strong in compression but weak in tension. The tensile strength of concrete is approximately 10% of the concrete’s compressive strength. Prestressing strands helps counteract this by introducing compressive stress in the area that will experience tensile stress because of the service load. In precast prestressed concrete girders, strands are placed in the bottom flange of the girder. These strands are tensioned to approximately 75% of their ultimate tensile capacity. After placing the concrete and after the required compressive strength has been achieved, the strands are cut and the tension forces transfer from the strands to the concrete. This creates a large compressive stress in the bottom flange. The eccentricity of the pretensioned strands in the prestressed concrete girders creates a bending moment that causes the girder to deflect upward, and this is called camber. This camber is reduced by the downward deflection of the girder due to the girder self-weight. Camber in prestressed concrete girders is effected by several factors, such as the girder’s cross sectional properties, concrete material properties, strand stress, ambient temperature, and relative humidity. Some methods of predicting camber use the initial camber that occurs immediately after cutting the strands to predict the camber at the time of girder erection. There are many sources of errors in predicting camber in a concrete girder including the differences in the actual and the design value of concrete properties and of strand stress. In this study, the difference between the measured and the predicted initial camber will be investigated on six AASHTO Type VI girders. The initial camber was predicted using the simple elastic analysis. The measured initial camber was then compared with the design camber. The difference between using the gross section properties and the transformed section properties to predict camber was quantified. Actual concrete properties including compressive strength, elastic modulus and unit weight were used to assess the current design method. Camber obtained from the actual, measured concrete properties will be called the predicted camber in this study. The effect of using the actual and the design elastic shortening losses on the estimation of the initial camber was also quantified

Slotted variable camber flap

Variable camber actuator assemblies broaden the range of speeds at which lift to drag performance is maximized for slotted flap wings. Lift is improved over a broader range of cruising speeds by varying wing camber with rotational flap movements that do not introduce wing slots and induced drag. Forward flaps are secured to forward flange links which extended from, and are a part of forward flap linkage assemblies. The forward flaps rotate about flap pivots with their rotational displacement controlled by variable camber actuator assemblies located between the forward flaps and the forward flange links. Rear flaps are held relative to the forward flaps by rear flap linkage assemblies which may act independently from the forward flap linkage assemblies and the variable camber actuator assemblies. Wing camber is varied by rotating the flaps with the variable camber actuator assemblies while the flaps are in a deployed or tucked position. Rotating the flaps in a tucked position does not introduce significant wing surface discontinuities, and reduces aircraft fuel consumption on most flight profiles

Flight test results from a supercritical mission adaptive wing with smooth variable camber

The mission adaptive wing (MAW) consisted of leading- and trailing-edge variable-camber surfaces that could be deflected in flight to provide a near-ideal wing camber shape for any flight condition. These surfaces featured smooth, flexible upper surfaces and fully enclosed lower surfaces, distinguishing them from conventional flaps that have discontinuous surfaces and exposed or semiexposed mechanisms. Camber shape was controlled by either a manual or automatic flight control system. The wing and aircraft were extensively instrumented to evaluate the local flow characteristics and the total aircraft performance. This paper discusses the interrelationships between the wing pressure, buffet, boundary-layer and flight deflection measurement system analyses and describes the flight maneuvers used to obtain the data. The results are for a wing sweep of 26 deg, a Mach number of 0.85, leading and trailing-edge cambers (delta(sub LE/TE)) of 0/2 and 5/10, and angles of attack from 3.0 deg to 14.0 deg. For the well-behaved flow of the delta(sub LE/TE) = 0/2 camber, a typical cruise camber shape, the local and global data are in good agreement with respect to the flow properties of the wing. For the delta(sub LE/TE) = 5/10 camber, a maneuvering camber shape, the local and global data have similar trends and conclusions, but not the clear-cut agreement observed for cruise camber

Variable camber rotor study

Deployment of variable camber concepts on helicopter rotors was analytically assessed. It was determined that variable camber extended the operating range of helicopters provided that the correct compromise can be obtained between performance/loads gains and mechanical complexity. A number of variable camber concepts were reviewed on a two dimensional basis to determine the usefulness of leading edge, trailing edge and overall camber variation schemes. The most powerful method to vary camber was through the trailing edge flaps undergoing relatively small motions (-5 deg to +15 deg). The aerodynamic characteristics of the NASA/Ames A-1 airfoil with 35% and 50% plain trailing edge flaps were determined by means of current subcritical and transonic airfoil design methods and used by rotor performance and loads analysis codes. The most promising variable camber schedule reviewed was a configuration with a 35% plain flap deployment in an on/off mode near the tip of a blade. Preliminary results show approximately 11% reduction in power is possible at 192 knots and a rotor thrust coefficient of 0.09. The potential demonstrated indicates a significant potential for expanding the operating envelope of the helicopter. Further investigation into improving the power saving and defining the improvement in the operational envelope of the helicopter is recommended

Benjamin Britten's Six Metamorphoses After Ovid: tracing the trajectory of its popularity, and the factors that make this piece important to this day

Access to thesis permanently restricted to Ball State community onlyBenjamin Britten’s Six Metamorphoses After Ovid, Opus 49 is, arguably, one of the most popular pieces written for unaccompanied oboe. It is regularly programmed and performed by amateurs, students, and professionals worldwide. The purpose of this creative project was to trace the trajectory of the Six Metamorphoses from its first performance at the Aldeburgh Festival on June 14, 1951, until the present day and the factors that have contributed to it becoming a seminal piece of oboe literature. Researching dissertations, journal articles, and conducting interviews with both oboists and composers it is clear that the Six Metamorphoses After Ovid has been influential on the number of solo oboe works available today. Britten’s compositional effectiveness in his use of mythological characters, taken from the ancient Roman poet Pūblius Ovidius Nāsō’s literary work Metamorphoses, is a main factor in the popularity of this piece. Included in this paper is a description of each mythological character, the technical nuances of each movement, and interviews with oboe pedagogues that support this information.Thesis (M.M.

Variable-camber systems integration and operational performance of the AFTI/F-111 mission adaptive wing

The advanced fighter technology integration, the AFTI/F-111 aircraft, is a preproduction F-111A testbed research airplane that was fitted with a smooth variable-camber mission adaptive wing. The camber was positioned and controlled by flexing the upper skins through rotary actuators and linkages driven by power drive units. The wing camber and control system are described. The measured servoactuator frequency responses are presented along with analytical predictions derived from the integrated characteristics of the control elements. A mission adaptive wing system chronology is used to illustrate and assess the reliability and dependability of the servoactuator system during 1524 hours of ground tests and 145 hours of flight testing

Influence of thickness and camber on the aeroelastic stability of supersonic throughflow fans: An engineering approach

An engineering approach was used to include the nonlinear effects of thickness and camber in an analytical aeroelastic analysis of cascades in supersonic acial flow (supersonic leading-edge locus). A hybrid code using Lighthill's nonlinear piston theory and Lanes's linear potential theory was developed to include these nonlinear effects. Lighthill's theory was used to calculate the unsteady pressures on the noninterference surface regions of the airfoils in cascade. Lane's theory was used to calculate the unsteady pressures on the remaining interference surface regions. Two airfoil profiles was investigated (a supersonic throughflow fan design and a NACA 66-206 airfoil with a sharp leading edge). Results show that compared with predictions of Lane's potential theory for flat plates, the inclusion of thickness (with or without camber) may increase or decrease the aeroelastic stability, depending on the airfoil geometry and operating conditions. When thickness effects are included in the aeroelastic analysis, inclusion of camber will influence the predicted stability in proportion to the magnitude of the added camber. The critical interblade phase angle, depending on the airfoil profile and operating conditions, may also be influenced by thickness and camber. Compared with predictions of Lane's linear potential theory, the inclusion of thickness and camber decreased the aerodynamic stifness and increased the aerodynamic damping at Mach 2 and 2.95 for a cascade of supersonic throughflow fan airfoils oscillating 180 degrees out of phase at a reduced frequency of 0.1

Numerical analysis of a variable camber rotor blade as a lift control device

A new rotor configuration called the variable camber rotor was numerically investigated as a lift control device. This rotor differs from a conventional (baseline) rotor only in the blade aft section. In this configuration, the aft section or flap is attached to the forward section by pin joint arrangement, and also connected to the rotor control system for the control of rotor thrust level and vectoring. Pilot action to the flap deflection controls rotor lift and tip path plane tilt. The drag due to flaps is presented and the theoretical result correlated with test data. The assessment of payoff for the variable camber rotor in comparison with conventional (baseline) rotor was examined in hover. The variable camber rotor is shown to increase hover power required by 1.35%, but such a minimal power penalty is not significant enough to be considered a negative result. In forward flight, the control needs of the variable camber rotor were evaluated

Sail optimization for upwind sailing: application in a Tornado, the Olympic class catamaran.

A study of a boat’s motion is carried out in order to analyze the aerodynamic properties of the optimal sail for obtaining the maximum velocity when sailing to windward. The mechanics study shows the optimal CL and CD for a given sail and how the shape of the aerodynamic polar of the sail should be. A parametrical analysis of the aerodynamics of a sail is then carried out varying the maximum camber, position of the maximum camber in the chord direction and position of the maximum camber in the mast direction. The parametric analysis is done numerically with a vortex lattice method (VLM) and experimentally in a wind tunnel. The results show that the influence of the relevant parameters studied can be reduced to the variation of two parameters, A and B, defining the polar of the sail, CD = B + A2CL 2; and the influence of parameters A and B on the maximum VMG obtainable are calculated