Accelerating the Induced Dimension Reduction method using spectral information

The Induced Dimension Reduction method (IDR(s)) (Sonneveld and van Gijzen, 2008) is a short-recurrences Krylov method to solve systems of linear equations. In this work, we accelerate this method using spectral information. We construct a Hessenberg relation from the IDR(s) residual recurrences formulas, from which we approximate the eigenvalues...

Acoustic communication experiments in the Westerschelde shipping lane using direct-sequence spread spectrum signals

Spread-spectrum underwater acoustic communication signals were broadcast in the vicinity of a busy shipping lane. Four spreading code lengths were applied, leading to bit rates between 65 and 667 bit/s in the passband between 10 and 14 kHz. Excellent results are obtained for a track over a predominantly flat bathymetry, whereas communication...

Shallow-water acoustic communication with high bit rate BPSK signals

BPSK signals have been defined for transmission through a shallow-water acoustic communication channel. The signals were accompanied by two displaced carriers to facilitate carrier recovery. To correct for the adverse effects of time spreading, a pseudo-random learning sequence was transmitted ahead of the communication signal. The signal...

The ROBLINKS underwater acoustic communication experiments

Within the EU-MAST III project ROBLINKS waveforms and algorithms have been developed to establish robust underwater acoustic communication links with high data rates ín shallow water. To evaluate the signalling schemes a wide range of experiments has been performed during a sea trial that has been held in May 1999 in the North Sea, off rhe Dutch...

Analysis of shallow-water acoustic communication channel

This paper analyses the physical characteristics of the acoustic channel during the ROBLINKS underwater communication experiments. It is demonstrated that marginal changes of the sound speed profile have profound effect on the propagation in the shallow- water environment, and hence on the quality of acoustic communication links. Further, the...

Advances in the ROBLINKS project on long-range shallow-water robust acoustic communciation links

Within the ROBLINKS project waveforms and algorithms have been developed to establish robust underwater acoustic communication links with high data rates in shallow water. To evaluate the signalling schemes, a wide range of experiments has been performed during a sea trial that has been held in May 1999, in the North Sea, off the Dutch coast....

The parallel computation of the smallest eigenpair of an acoustic problem with damping

Acoustic problems with damping may give rise to large quadratic eigenproblems, which require efficient and parallelizable solution algorithms. This paper describes such an algorithm: the Jacobi-Davidson solution method for quadratic eigenproblems. In particular, it describes its parallelization according to the Bulk Synchronous Programming model...

Singular vectors and estimates of the analysis-error covariance metric

An important ingredient of ensemble forecasting is the computation of initial perturbatinos. Various techniques exist to generate initial perturbations. All these aim to produce an ensemble that, at initial time, reflects the uncertainty in the initial condition. In this paper a method for computing singular vectors consistent with current...

The Finite Element Discretization for Stream-Function Problems on Multiply Connected Domains

The no-normal-flow condition states that the stream-function is constant at solid boundaries. For multiply connected domains these (unknown) constants differ per boundary and must be determined from integral conditions. This complicates discretization and solution of the problem considerably. In this paper we describe a simple, elegant, and...

An analysis of element-by-element preconditioners for nonsymmetric problems

A group of preconditioners for systems of linear equations arising from finite element discretization, which is of increasing interest, is the class of element-by-element preconditioners. These preconditioners allow the solution of a system without the need to assemble the global stiffness matrix. The success of a preconditioner depends on how...