Occurrence of Libellulid Dragonflies (Odonata: Libellulidae) in Southeastern Michigan and Adjacent Essex County, Ontario

During 1994-1995 extensive field work was conducted in southeastern Michigan in an attempt to assess the species population and composition of libellulid dragonflies. Additional field work was conducted on dragonflies from southwestern Ontario migrating into southeastern Michigan. Comparisons were made with the species listed for this area 37 years earlier in Kormondy (1958) anticipating changes due to wetland reductions and the effects of pesticides. With one exception, all species listed in Kormondy were observed. Ad- ditionally, one species, unknown from this area as of 1958, was encountered

Discovery of an Isolated Population of \u3ci\u3eAnax Longipes\u3c/i\u3e in Michigan (Odonata: Aeshnidae)

Anax longipes is a large aeshnid dragonfly previously unknown from Michigan. Adults and larvae were found in abundance at a series of experimental ponds within the E.S. George Reserve in Livingston County, Michigan

Nonlinear displacement analysis of advanced propeller structures using NASTRAN

The steady state displacements of a rotating advanced turboprop are computed using the geometrically nonlinear capabilities of COSMIC NASTRAN Rigid Format 4 and MSC NASTRAN Solution 64. A description of the modified Newton-Raphson algorithm used by Solution 64 and the iterative scheme used by Rigid Format 4 is provided. A representative advanced turboprop, SR3, was used for the study. Displacements for SR3 are computed for rotational speeds up to 10,000 rpm. The results show Solution 64 to be superior for computating displacements of flexible rotating structures. This is attributed to its ability to update the displacement dependent centrifugal force during the solution process

Effects of mistuning on bending-torsion flutter and response of a cascade in incompressible flow

The effect of small differences between the individual blades (mistuning) on the aeroelastic stability and response of a cascade were studied. The aerodynamic, inertial, and structural coupling between the bending and torsional motions of each blade and the aerodynamic coupling between the blades was considered. A digital computer program was developed to conduct parametric studies. Results indicate that the mistuning has a beneficial effect on the coupled bending torsion and uncoupled torsion flutter. On forced response, however, the effect may be either beneficial or adverse, depending on the engine order of the forcing function. The results also illustrate that it may be feasible to utilize mistuning as a passive control to increase flutter speed while maintaining forced response at an acceptable level

Effects of structural coupling on mistuned cascade flutter and response

The effects of structural coupling on mistuned cascade flutter and response are analytically investigated using an extended typical section model. This model includes both structural and aerodynamic coupling between the blades. The model assumes that the structurally coupled system natural modes were determined and are represented in the form of N bending and N torsional uncoupled modes for each blade, where N is the number of blades and, hence, is only valid for blade dominated motion. The aerodynamic loads are calculated by using two dimensional unsteady cascade theories in the subsonic and supersonic flow regimes. The results show that the addition of structural coupling can affect both the aeroelastic stability and frequency. The stability is significantly affected only when the system is mistuned. The resonant frequencies can be significantly changed by structural coupling in both tuned and mistuned systems, however, the peak response is significantly affected only in the latter

Coupled bending-bending-torsion flutter of a mistuned cascade with nonuniform blades

A set of aeroelastic equations describing the motion of an arbitrarily mistuned cascade with flexible, pretwisted, nonuniform blades is developed using an extended Hamilton's principle. The derivation of the equations has its basis in the geometric nonlinear theory of elasticity in which the elongations and shears are negligible compared to unity. A general expression for foreshortening of a blade is derived and is explicity used in the formulation. The blade aerodynamic loading in the subsonic and supersonic flow regimes is obtained from two dimensional, unsteady, cascade theories. The aerodynamic, inertial and structural coupling between the bending (in two planes) and torsional motions of the blade is included. The equations are used to investigate the aeroelastic stability and to quantify the effect of frequency mistuning on flutter in turbofans. Results indicate that a moderate amount of intentional mistuning has enough potential to alleviate flutter problems in unshrouded, high aspect ratio turbofans

Flutter of swept fan blades

The effect of sweep on fan blade flutter is studied by applying the analytical methods developed for aeroelastic analysis of advance turboprops. Two methods are used. The first method utilizes an approximate structural model in which the blade is represented by a swept, nonuniform beam. The second method utilizes a finite element technique to conduct modal flutter analysis. For both methods the unsteady aerodynamic loads are calculated using two dimensional cascade theories which are modified to account for sweep. An advanced fan stage is analyzed with 0, 15 and 30 degrees of sweep. It is shown that sweep has a beneficial effect on predominantly torsional flutter and a detrimental effect on predominantly bending flutter. This detrimental effect is shown to be significantly destabilizing for 30 degrees of sweep

Range Extension of \u3ci\u3eStylogomphus Albistylus\u3c/i\u3e (Odonata: Gomphidae) for the Upper Peninsula of Michigan

Larvae, exuviae, and teneral adults of Stylogomphus albistylus (Hagen) were collected from Mountain Stream, within the boundaries of the Huron Mountain Club, in the Upper Peninsula of Michigan (Marquette County). This represents the first published report of this species from the Upper Peninsula of Michigan, and only the second recorded site for the state of Michigan

Aeroelastic characteristics of a cascade of mistuned blades in subsonic and supersonic flows

The effects of mistuning on flutter and forced response of a cascade in subsonic in subsonic and supersonic flow were investigated. The aerodynamic and structural coupling between the bending and torsional motions and the aerodynamic coupling between the blades were studied. It is shown that frequency mistuning always has a beneficial effect on flutter. For the cascade considered, the potential for raising flutter speed is greater in subsonic than in supersonic flow. Preliminary results for structural damping mistuning show that there are no additional benefits over adding damping mistuning may have either a beneficial or an adverse effect on forced response, depending on the engine order of the excitation and Mach number