differential detection of duobinary cpfsk differential detection of duobinary cpfsk is analyzed to determine its performance as an alternative to other incoherent bandwidth efficient detection schemes it is shown that a bpsk differential receiver can correctly detect a duobinary msk signal when precoding differential encoding is employed at the transmitter the effects of intersymbol interference due to if filtering at the receiver are analyzed for a gaussian and a 4th order butterworth if filter furthermore nonredundant error correction is shown to be feasible for differential detection of duobinary msk and a method of analyzing the performance of the error correction receiver is presented

determination of the mutual radiation resistances of a rectangular plate and their impact on the radiated sound power abstract the mutual radiation resistances resulting from cross modal coupling have been mostly excluded from sound power calculations on the belief or premise that either for some reasons they have an insignificant impact on the power radiation or consideration of them can be an enormous computational burden in this paper the characteristics of the mutual radiation resistances are investigated of a simply supported rectangular plate it is shown that once the self radiation resistances or the so called modal radiation efficiencies have been calculated the mutual radiation resistances can be readily obtained at virtually no cost of equal importance because no approximation is made the present formulation is fully accurate in the entire frequency range an asymptotic expression is also derived for large modal wavenumbers numerical results are presented to illustrate the spectral characteristics of the mutual radiation resistances and the corresponding impact on the radiated sound power

optimum gaussian filter for differential detection of msk an optimum predetection gaussian bandpass filter for differential detection of msk is derived theoretically with numerical techniques the optimum product of bandwidth b and bit duration t compromising the noise reduction effect with the intersymbol interference effect is calculated at a given bit error rate ber it is shown that the optimum bt product is 1 21 with 4 02 db degradation at 10 6ber where the degradation is defined as the increase in e b n 0 relative to ideal coherent detection of msk

real analytic actions of lattices this paper introduces a new approach to the study of lattice actions on compact manifolds the group sl n z acts by real analytic di eomorphisms on the sphere sny1 via the action on the space of in nite rays based at 0 2 r we believe this action is minimal in the following sense conjecture i any smooth action of a nite index subgroup of sl n z n 2 on a compact r manifold factors through a nite group action if r ny 1

error rate performance of digital fm mobile radio with postdetection diversity an analysis of bit error rate ber in a binary digital fm system with postdetection diversity is presented expressions for the average ber due to additive white gaussian noise awgn random fm noise and delay spread in the multipath channel are derived for reception using differential demodulation dd and frequency demodulation fd assuming independent fading signals calculated results for msk show that the ber performance is strongly dependent on the rms delay bit duration ratio and that the delay spectrum shape is of no importance when the receiver predetection filter product is optimized for the effect of awgn the effect of fading correlation on the diversity improvement is also analyzed for a two branch case with multiplicative rayleigh fading signals expressions for the average ber due to awgn and random fm noise are derived calculated results are shown for the average ber due to random fm noise assuming a horizontally spaced antenna system at a mobile station it is shown that the use of small antenna spacings leads to a diversity improvement greater than that obtainable for the case of independent awgn

smooth classification of cartan actions of higher rank semisimple lie groups and their lattices let g be a connected semisimple lie group without compact factors whose real rank is at least 2 and let g be an irreducible lattice we provide a c classification for volume preserving cartan actions of an d g also if g has real rank at least 3 we provide a c classification for volume preserving multiplicity free trellised anosov actions on compact manifolds

noncoherent block demodulation of msk with inherent and enhanced encoding it is shown that there is a close relation between known noncoherent minimum shift keying msk demodulation structures such as envelope and differential receivers and schemes derived from the noncoherent maximum likelihood block estimation n mlbe principle when the observation interval is increased the performance of msk with n mlbe tends to that of binary coherently detected orthogonal binary frequency shift keying a new demodulation strategy reduced block noncoherent estimation rbne is introduced and shown to improve the performance of noncoherent msk beyond that of coherently detected orthogonal fsk when rbne is used with msk and the observation interval is increased the performance approaches that of antipodal signaling the key feature of all these structures is multisymbol noncoherent processing with exploitation of the msk inherent coding properties induced by its phase continuity the use of binary block codes for msk with n mlbe is considered it is shown that simple binary block codes with low bandwidth expansion that exploit the inherent msk memory can give significant gains

a state space coupling method for fluid structure interaction analysis of plates a state space coupling method is presented for the direct solution of fluid loaded natural frequencies and mode shapes of plates this method expands the frequency dependent term in the rayleigh integral in a power series on circular frequency after factoring out the frequency term from the integrands integration involved in setting up the acoustic impedance coefficient matrices is confined to a frequency independent part the acoustic impedance coefficient matrices are therefore frequency independent and can be coupled directly with the structural matrix into a canonical state space form to yield the fluid loaded modes via the direct eigenvalue analysis a fluid loaded stiffened plate is involved to demonstrate the method numerical results of the fluid loaded natural frequencies mode shapes and modal damping ratios are given to show the efficacy of the state space coupling method

coupled finite element boundary element approach for fluid structure interaction a new computational capability is described for calculating the sound pressure field radiated or scattered by a harmonically excited submerged arbitrary three dimensional elastic structure this approach called nashua couples a nastranfinite element model of the structure with a boundary element model of the surrounding fluid the surface fluid pressures and normal velocities are first calculated by coupling the finite element model of the structure with a discretized form of the helmholtz surfaceintegral equation for the exterior fluid after generation of the fluid matrices most of the required matrix operations are performed using the general matrix manipulation package available in nastran farfield radiated pressures are then calculated from the surface solution using the helmholtz exterior integral equation the overall capability is very general highly automated and requires no independent specification of the fluid mesh an efficient new out of core block equation solver was written so that very large problems could be solved the use of nastran as the structural analyzer permits a variety of graphical displays of results including computer animation of the dynamic response the overall approach is illustrated and validated using known analytic solutions for submerged spherical shells subjected to both incident pressure and uniform and nonuniform applied mechanical loads

a numerical method for the computation of the resonance frequencies and modes of a fluid loaded plate application to the transient response of the system in previous papers we have shown that the time response of a fluid loaded structure can be expressed in terms of the resonance modes of the fluid structure system we first show the efficiency of such a representation by comparing numerical predictions to experimental results the main objective of this paper is to consider the numerical aspects of this representation namely the computation of the coupling term in the variational equation and the computation of the resonance frequencies and modes three methods are proposed to compute the resonance frequencies an iterative technique a warburton approximation and a perturbation technique light fluid approximation numerical results are presented to compare these three methods for air and water loading the last part of the paper discusses the choice of the number of resonance modes which is required to obtain a representation of the transient radiated pressure with a sufficient accuracy

free vibrations of annular plates coupled with fluids abstract the natural frequencies of annular plates on an aperture of an infinite rigid wall and in contact with a fluid on one side are theoretically obtained by using the added mass approach the fluid is assumed to be incompressible and inviscid and the velocity potential describes its irrotational motion the hankel transform is applied to solve the fluid plate coupled system boundary conditions are expressed by integral equations mode shapes are first assumed not to be modified by the fluid accurate numerical results are given for different plate boundary conditions they are suitable for engineering applications the accuracy of the assumed modes approach is theoretically studied by using the rayleigh ritz method that removes the simplifying hypothesis that dry and wet mode shapes are the same eigenfunctions of the plate vibrating in vacuum are assumed as admissible functions and the rayleigh quotient for coupled vibration is used to obtain a galerkin equation it was found that the fundamental mode and frequency for all the plate boundary conditions considered is well estimated by the assumed modes approach higher modes are computed with less accuracy by this formula and for some enhanced applications the rayleigh ritz approach is necessary

krylov subspace methods for reduced order modeling in circuit simulation the simulation of electronic circuits involves the numerical solution of very large scale sparse in general nonlinear systems of differential algebraic equations often the size of these systems can be reduced considerably by replacing the equations corresponding to linear subcircuits by approximate models of much smaller state space dimension in this paper we describe the use of krylov subspace methods for generating such reduced order models of linear subcircuits particular emphasis is on reduced order modeling techniques that preserve the passivity of linear rlc subcircuits

an advanced computational method for radiation and scattering of acoustic waves in three dimensions the method proposed in this paper provides a computational method for implementing the helmholtz integral formula for acoustic radiation and scattering problems associated with arbitrary shaped three dimensional bodies in particular an isoparametric element formulation is used in which both the surface geometry and the acoustic variables on the surface of the body are represented by second order shape functions within the local coordinate system a general formula for the surface velocity potential and the exterior field is derived this result is applicable to nonsmooth bodies i e it includes the case where the surface may have a nonunique normal e g at the edge of a cube test cases are shown involving spherical cylindrical and cubical geometry

an improved state space method for coupled fluid structure interaction analysis this paper presents an improved state space method for incorporating fluid structure interaction into structural acoustic analyses giordano and koopmann j a giordano and g h koopmann state space boundary element finite element coupling for fluid structure interaction analysis j acoust soc am 98 363 372 1995 introduced a state space approach for the coupled analysis of fluid loaded structures giordano s method employed a third order interpolation of the fluid impedance coupled with state space formalism permitting the direct eigenvalue analysis of the coupled system and thereby yielding the fluid loaded modes and natural frequencies this is in contrast to the common technique of sweeping through a range of frequencies so as to identify the natural frequencies and mode shapes the original state space approach yielded system matrices of order 4n where n is the number of degrees of freedom in the underlying model where giordano s method employed an interpolation based on surface velo

double symbol error rates for differential detection of narrow band fm this paper evaluates the double symbol error rate average probability of two consecutive symbol errors in differentially detected narrow band fm numerical results are presented for the special case of msk with a gaussian if receive filter it is shown that not unlike similar results previously obtained for the single error probability of such systems large inaccuracies in predicted performance can occur when intersymbol interference is ignored

modal parameter estimation for fluid loaded structures from reduced order models a model reduction method is developed to estimate modal parameters of fluid loaded structures the method uses a matrix free formulation of rational krylov projection to construct reduced order models of the fluid loaded structures from forced responses at selected interpolation frequencies due to small sizes of the reduced order models eigenpairs of the associated eigenvalue problems are available at a very low computational cost resonance frequencies modal damping ratios and mode shapes of the original systems are recovered from the forced responses and the eigenpairs of the reduced order models nonphysical modes introduced by the model reduction process are filtered out by a modal damping ratio test and double checked by the condition number of the dynamic stiffness matrix efficiency and accuracy of the present method are demonstrated on a benchmark model of a water loaded plate clamped in a baffle

state space boundary element finite element coupling for fluid structure interaction analysis state space coupling is a new approach for handling computational fluid structure interaction problems in the low to medium frequency range the method is based on standard boundary element bem and finite element fem discretizations of the acoustic and structural domains respectively the implicit frequency dependence of a traditional acoustic impedance matrix is made explicit through a power series expansion on circular frequency and considering time harmonic motion once expanded the acoustic energy of the fluid is directly coupled to that of the structure via hamilton s principle the coupled system is then recast in a canonical state space form which is also in the form of a standard eigenvalue problem solution of this system produces a series of complex eigenvalues and eigenvectors which represent a modal decomposition of the fluid loaded structure biorthogonality properties of the state space eigensystem allow for an uncoupled modal solution of the forced problem results for a submerged spherical shell and a finite plate in an infinite ridged baffle are given to illustrate the state space approach

differential versus limiter discriminator detection of narrow band fm the error probability performance of differential detection of narrow band fm is determined and compared with the analogous results for limiter discriminator detection of the same modulation it is shown that over a large class of benign and hostile environments e g gaussian if filter 1 leq bt leq 3 h leq 1 awgn partial band noise jamming the differential detector offers no theoretical performance advantage over the limiter discriminator receiver with integrate and dump postdetection filtering

vibroacoustic response of an eccentric hollow cylinder abstract the linear 3d elasticity theory in conjunction with the classical method of separation of variables and the translational addition theorem for cylindrical wave functions are employed to investigate the three dimensional steady state sound radiation characteristics of an arbitrarily thick eccentric hollow cylinder of infinite length submerged in an unbounded ideal acoustic medium and subjected to arbitrary time harmonic on surface mechanical drives the spatial fourier transform along the shell axis and fourier series expansion in the circumferential direction are utilized to obtain a formal integral expression for the radiated pressure field in the frequency domain the method of stationary phase is subsequently implemented to evaluate the integral for an observation point in the far field the analytical results are illustrated with numerical examples in which air filled water submerged concentric and eccentric steel cylinders are driven by harmonic concentrated radial and transverse surface loads effects of excitation and cylinder eccentricity on the far field radiated pressure amplitudes directivities are discussed and contributions from pseudo rayleigh whispering gallery and axially guided waves are examined through selected spatial dispersion patterns limiting cases are considered and the validity of results is established with the aid of a commercial finite element package as well as by comparison with the data in the existing literature

an analytical solution for the self and mutual radiation resistances of a rectangular plate it is widely accepted that for an arbitrary acoustic wavenumber the radiation resistance of a simply supported rectangular plate has to be calculated through numerical integration in this study an analytical solution for the self and mutual radiation resistances is obtained in the form of the power series of the non dimensional acoustic wavenumber unlike the previous analytical or asymptotic solutions it is not subject to any of the restrictions usually imposed upon the acoustic wavenumber a few numerical examples are given simply to verify the solution and elucidate the reliance of the self and mutual radiation resistances on the acoustic wavenumber and the plate aspect ratio it is shown that the present formulae are extremely efficient by cutting the cpu time by orders of magnitude in comparison with the traditional numerical integration scheme this investigation successfully fills the long existing gap in solutions for the moderate wavenumbers that are often of primary concern in an acoustic analysis