Allan Peter Engsig-Karup

Technical University of Denmark | DTU · Department of Applied Mathematics and Computer Science

The use of model-based numerical simulations of wave propagation in rooms for engineering applications requires that acoustic conditions for multiple parameters are evaluated iteratively, which is computationally expensive. We present a reduced basis method (RBM) to achieve a computational cost reduction relative to a traditional full-order model (...

We propose and demonstrate a new approach for fast and accurate surrogate modelling of urban drainage system hydraulics based on physics-guided machine learning. The surrogates are trained against a limited set of simulation results from a hydrodynamic (HiFi) model. Our approach reduces simulation times by one to two orders of magnitude compared to...

We present a scalable 2D Galerkin spectral element method solution to the linearized potential flow radiation problem for wave induced forcing of a floating offshore structure. The pseudo-impulsive formulation of the problem is solved in the time-domain using a Gaussian displacement signal tailored to the discrete resolution. The added mass and dam...

The use of epidemic modelling in connection with spread of diseases plays an important role in understanding dynamics and providing forecasts for informed analysis and decision-making. In this regard, it is crucial to quantify the effects of uncertainty in the modelling and in model-based predictions to trustfully communicate results and limitation...

Estimating the hydrodynamic characteristics of bodies interacting with ocean waves is of key importance in ocean engineering. Solving the wave-structure interaction problem has been a topic of research for many years, especially using linearized potential flow theory which generally captures the majority of the physics for typical marine structures...

The development of efficient and accurate numerical methods for simulating realistic sound in virtual environments—such as computer games and VR/AR—has been an active research area for the last decades. However, handling dynamic scenes with many moving sources is still challenging due to intractable storage requirements and extensive computation ti...

Submitted to IWWWFB 2022. This abstract describes our recent work on employing reduced-order modelling (ROM) to solve fully nonlinear potential flow equations (FNPF) to achieve faster turn-around time than a full order model (FOM) based on the spectral element method (SEM) [1]. We propose a PODGalerkin based model-order reduction approach to reduc...

Submitted to IWWWFB 2022. Simulation of water waves and taking into account the sea floor to estimate sea states are important for the design of offshore structures. We propose a new high-order accurate pseudospectral method for solving the incompressible Navier-Stokes equations with a free surface. The work is motivated by the lack of high-order a...

Submitted to IWWWFB 2022. See the published version. Estimating the hydrodynamic characteristics of bodies interacting with ocean waves is of key importance in ocean engineering. Solving the wave-structure interaction problem has been a topic of research for many years, especially using linearized potential flow theory which generally captures th...

Realistic sound is essential in virtual environments, such as computer games and mixed reality. Efficient and accurate numerical methods for pre-calculating acoustics have been developed over the last decade; however, pre-calculating acoustics makes handling dynamic scenes with moving sources challenging, requiring intractable memory storage. A phy...

Realistic sound is essential in virtual environments, such as computer games and mixed reality. Efficient and accurate numerical methods for pre-calculating acoustics have been developed over the last decade; however, pre-calculating acoustics makes handling dynamic scenes with moving sources challenging, requiring intractable memory storage. A phy...

During the COVID-19 pandemic, Denmark has pursued a mass testing strategy culminating in the testing of 12.167 individuals per 100,000 inhabitants per day during the spring of 2021. The strategy included free access to COVID-19 testing, and since 2021, compulsory documentation for negative tests or vaccination has been required for access to workpl...

The estimation of extreme loads from waves is an essential part of the design of offshore wind turbines. Standard design codes suggest either to use simplified methodologies based on regular waves, or to perform fully-nonlinear computations. The former may not provide an accurate representation of the real extreme waves, while the latter is too com...

In the political decision process and control of COVID-19 (and other epidemic diseases), mathematical models play an important role. It is crucial to understand and quantify the uncertainty in models and their predictions in order to take the right decisions and trustfully communicate results and limitations. We propose to do uncertainty quantifica...

During the Covid-19 pandemic, Denmark has pursued a unique mass testing strategy culminating in testing of more than 8,000 citizens per 100,000 inhabitants per day in the Spring 2021. The strategy includes free access to Covid-19 testing and since 2021, compulsory documentation for negative test or vaccination for access to workplace, educational i...

It is well known that input data uncertainty has a major influence on the correctness of room acoustic simulations. This paper proposes a comprehensive framework for experimental validation and uncertainty quantification in room acoustic simulations. The sources of uncertainty in room acoustic simulations are many, but especially the boundary condi...

We present a Spectral Element Fully Nonlinear Potential Flow (FNPF-SEM) model developed for the simulation of wave-body interactions between nonlinear free surface waves and impermeable structures. The solver is accelerated using an iterative p-multigrid algorithm. Two cases are considered: (i) a surface piercing box forced into vertical motion cre...

In marine offshore engineering, cost‐efficient simulation of unsteady water waves and their nonlinear interaction with bodies are important to address a broad range of engineering applications at increasing fidelity and scale. We consider a fully nonlinear potential flow (FNPF) model discretized using a Galerkin spectral element method to serve as...

No PDF available ABSTRACT The absorption properties of room surfaces have a major influence on the acoustics of rooms. In wave-based room acoustic simulations it is common practice to model room surfaces using a local-reaction approximation, instead of modeling the full extended-reaction behavior. However, previous research has indicated that the l...

No PDF available ABSTRACT This study presents a new model order reduction technique applied to room acoustic simulations using a high-order numerical scheme based on the spectral element method. The goal is to efficiently simulate iterative design processes in room acoustics, where the room acoustics with different boundary absorption properties ar...

Numerical methods can be used to simulate wave propagation in rooms, with applications in virtual reality and building design. Such methods can be highly accurate but computationally expensive when simulating high frequencies and large domains for long simulation times. Moreover, it is common that solutions are sought for multiple input parameter v...

This paper investigates the optimization of second-order control signals required to produce stable non-linear, deep-water waves using a wedge-shaped, plunger-type wave generator. Both numerical and experimental methods are utilized. A fully non-linear and dispersive potential flow (FNPF) solver developed at DTU is used for the numerical work, foll...

This paper presents ISOPE’s 2020 comparative study on the interaction between focused waves and a fixed cylinder. The paper discusses the qualitative and quantitative comparisons between 20 different numerical solvers from various universities across the world for a fixed cylinder. The moving cylinder cases are reported in a companion paper as part...

Epidemic models are often used without taking into account continuous age-dependent effects, limiting its use to study homogeneous subgroups in a population. An obstacle for using continuous age-dependent epidemic compartment models is the need for efficient numerical solution procedures. In this work, we propose an efficient space and time third-o...

In environmental acoustics and in room acoustics, many surfaces exhibit extended-reaction (ER) behavior, i.e., their surface impedance varies with the angle of the incident sound wave. This paper presents a phenomenological method for modeling such angle dependent surface impedance properties in time-domain wave-based simulations. The proposed meth...

The estimation of extreme loads from waves is an essential part of the design of an offshore wind turbine. Standard design codes suggest to either use simplified methods based on regular waves, or to perform fully nonlinear computations. The former might not provide an accurate representation of the extreme waves, while the latter is computationall...

This paper presents an equivalent fluid model (EFM) formulation in a three-dimensional time-domain discontinuous Galerkin finite element method framework for room acoustic simulations. Using the EFM allows for the modeling of the extended-reaction (ER) behavior of porous sound absorbers. The EFM is formulated in the numerical framework by using the...

We present a massively parallel and scalable nodal Discontinuous Galerkin Finite Element Method (DGFEM) solver for the time-domain linearised acoustic wave equations. The solver is implemented using the libParanumal finite element framework with extensions to handle curvilinear geometries and frequency dependent boundary conditions of relevance in...

In marine offshore engineering, cost-efficient simulation of unsteady water waves and their nonlinear interaction with bodies are important to address a broad range of engineering applications at increasing fidelity and scale. We consider a fully nonlinear potential flow (FNPF) model discretized using a Galerkin spectral element method to serve as...

This paper presents an equivalent fluid model (EFM) formulation in a 3D time-domain dis-continuous Galerkin finite element method framework for room acoustic simulations. Using the EFM allows for the modeling of the extended-reaction (ER) behavior of porous sound absorbers. The EFM is formulated in the numerical framework by using the method of aux...

This abstract presents our progress in the development of a fully nonlinear potential ow solver capable of modelling wave-structure and wave-bottom interactions. The numerical method is based on a finite difference method with a sigma-transform in the vertical direction, as presented in Bingham and Zhang (2007), and boundary conditions are imposed...

Mooring systems exhibit high failure rates. This is especially problematic for offshore renewable energy systems, like wave and floating wind, where the mooring system can be an active component and the redundancy in the design must be kept low. Here we investigate how uncertainty in input parameters propagates through the mooring system and affect...

Nonlinear model predictive control (NMPC) often requires real-time solution to optimization problems. However, in cases where the mathematical model is of high dimension in the solution space, e.g. for solution of partial differential equations (PDEs), black-box optimizers are rarely sufficient to get the required online computational speed. In suc...

We present a new stabilised and efficient high-order nodal spectral element method based on the Mixed Eulerian Lagrangian (MEL) method for general-purpose simulation of fully nonlinear water waves and wave-body interactions. In this MEL formulation a standard Laplace formulation is used to handle arbitrary body shapes using unstructured – possibly...

Extended-reaction modeling in wave-based simulations This paper presents a general method for modeling extended-reaction surface impedance boundary conditions in time-domain wave-based room acoustic simulations. A sound field separation technique is used to separate the sound field at a boundary into its incident and reflected components, in each t...

We apply optimal control to operational optimization to a model of a real oil reservoir, SOLSORT, located in the Danish North Sea. The oil reservoir model is a partial differential equation system that is simulated using a commercial oil reservoir simulator (Eclipse 300). The numerical optimization is conducted using an optimization software tool c...

In environmental acoustics and in room acoustics, many surfaces exhibit extended-reaction (ER) behavior, i.e., their surface impedance varies with the angle of the incident sound wave. This paper presents a phenomenological method for modeling such angle dependent surface impedance properties in time-domain wave-based simulations. The proposed meth...

Many widely used numerical algorithms for option pricing and instrument valuation in finance are computationally expensive. In this work, we explore a means to lower this computational cost by considering a data-driven option pricing approach based on artificial neural networks (ANNs). We consider ANNs for both creating a function approximation of...

POST-CONFERENCE ISOPE 2018 CONTRIBUTION: A 3D fully nonlinear potential flow (FNPF) model based on an Eulerian formulation is presented. The model is discretized using high-order prismatic - possibly curvi-linear - elements using a spectral element method (SEM) that has support for adaptive unstructured meshes. The paper presents details of the FNP...

Results from Blind Test Series 1, part of the Collaborative Computational Project in Wave Structure Interaction (CCP-WSI), are presented. Participants, with a range of numerical methods, simulate blindly the interaction between a fixed structure and focused waves ranging in steepness and direction. Numerical results are compared against correspondi...

This paper presents a wave-based numerical scheme based on a spectral element method, coupled with an implicit-explicit Runge-Kutta time stepping method, for simulating room acoustics in the time domain. The scheme has certain features which make it highly attractive for room acoustic simulations, namely a) its low dispersion and dissipation proper...

We present a depth-integrated Boussinesq model for the efficient simulation of nonlinear wave-body interaction. The model exploits a ‘unified’ Boussinesq framework, i.e. the fluid under the body is also treated with the depth-integrated approach. The unified Boussinesq approach was initially proposed by Jiang [26] and recently analysed by Lannes [2...

We present a fully nonlinear potential flow (FNPF) model for simulation of wave-body interaction in three spatial dimensions (3D) and apply it to the case of an axi-symmetric point absorber. The FNPF model is discretized is space by a C 0 spectral element method (SEM) using high-order prismatic-possibly curvilinear-elements. This SEM-FNPF model is...

Nonlinear model predictive control (NMPC) often requires real-time solution to optimization problems. However, in cases where the mathematical model is of high dimension in the solution space, e.g. for solution of partial differential equations (PDEs), black-box optimizers are rarely sufficient to get the required online computational speed. In suc...

We consider a non-overlapping domain decomposition approach to approximate the solution of elliptic boundary value problems with high contrast in their coefficients. We propose a method such that initially local solutions subject to Robin boundary conditions in each primal subdomain are constructed with (locally conservative) finite element or fini...

Near-well flow analysis is an important tool for gaining detailed insight of the flow behaviour and for improving well design and production optimization of real reservoirs. One challenge of accurate numerical modelling of the flow field in the vicinity of the well is related to the scale disparity factor in space and time. The numerical scale gap...

The need for advanced time-domain simulators for improved offshore engineering analysis is growing with the continued improvement in computational resources. In line with this trend, we consider a fully nonlinear potential flow (FNPF) model discretised with a stabilised Galerkin Spectral Element Method (SEM) [5] addressing the stability problems an...

Results from Blind Test Series 1, part of the Collaborative Computational Project in Wave Structure Interaction (CCP-WSI), are presented. Participants , with a range of numerical methods, simulate blindly the interaction between a fixed structure and focused waves ranging in steepness and direction. Numerical results are compared against correspond...

Nonlinear wave-body problems are important in renewable energy, especially in case of wave energy converters operating in the near-shore region. In this paper we simulate nonlinear interaction between waves and truncated bodies using an efficient spectral/hp element depth-integrated unified Boussinesq model. The unified Boussinesq model treats also...

Nonlinear wave-body problems are important in renewable energy, especially in case of wave energy converters operating in the near-shore region. In this paper we simulate nonlinear interaction between waves and truncated bodies using an efficient spectral/hp element depth-integrated unified Boussinesq model. The unified Boussinesq model treats also...

The focus of this paper is on the parallel scalability of a distributed multigrid framework, known as the DTU Compute GPUlab Library, for execution on large heterogeneous supercomputers. We demonstrate near-ideal weak scalability for a high-order fully nonlinear potential flow (FNPF) time domain model on the Oakridge Titan supercomputer, which is e...

Near-well flow analysis is an important tool for gaining detailed insight of the flow behaviour and for improving well design and production optimization of real reservoirs. One challenge of accurate numerical modelling of the flow field in the vicinity of the well is related to the scale disparity factor in space and time. The numerical scale gap...

We present recent progress on the development of a new fully nonlinear potential flow (FNPF) model for estimation of nonlinear wave-body interactions based on a stabilised unstructured spectral element method (SEM). We introduce new proof-of-concepts for forced nonlinear wave-body interaction in two spatial dimensions to establish the methodology i...

Breather solutions to the nonlinear Schrödinger equation have been put forward as a possible prototype for rouge waves and have been studied both experimentally and numerically. In the present study, we perform high resolution simulations of the evolution of Peregrine breathers in finite depth using a fully non-linear potential flow spectral elemen...

We present recent progress on the development of a new fully nonlinear potential flow (FNPF) model for estimation of nonlinear wave-body interactions based on a stabilised unstructured spectral element method (SEM). We introduce new proof-of-concepts for forced nonlinear wave-body interaction in two spatial dimensions to establish the methodology i...

Breather solutions to the nonlinear Schrödinger equation have been put forward as a possible prototype for rouge waves and have been studied both experimentally and numerically. In the present study, we perform high resolution simulations of the evolution of Peregrine breathers in finite depth using a fully nonlinear potential flow spectral element...

A wave-based numerical scheme for simulating room acoustics, based on the spectral element method, is presented. This method possesses qualities, such as high-order accuracy and geometrical flexibility, which make it very suitable for accurate and cost-effective room acoustic simulations of complex geometries of any size and shape. Various numerica...

We present a spectral/hp element method for a depth-integrated Boussinesq model for the efficient simulation of nonlinear wave-body interaction. The model exploits a 'unified' Boussinesq framework, i.e. the flow under the body is also treated with the depth-integrated approach, initially proposed by Jiang [25] and more recently rigorously analysed...

PRE-CONFERENCE ISOPE 2018 CONTRIBUTION: For the assessment of experimental measurements of focused wave groups impacting a surface-piecing fixed structure, we present a new Fully Nonlinear Potential Flow (FNPF) model for simulation of unsteady water waves. The FNPF model is discretized in three spatial dimensions (3D) using high-order prismatic -...

For improved prediction of subsurface flows and correct representing of the uncertainties of geostatistical properties, we use the framework of Bayesian statistical interface in combination with the Markov Chain Monte Carlo (MCMC) method which needs many fine-scale simulations. Hence it is essential to apply cheap screening stages, such as coarse-s...

The spectral/hp element method combines the geometric flexibility of the classical h-type finite element technique with the desirable numerical properties of spectral methods, employing high-degree piecewise polynomial basis functions on coarse finite element-type meshes. The spatial approximation is based upon orthogonal polynomials, such as Legen...

Our goal is to achieve numerical efficiency for large scale reservoir simulation with acceptable accuracy for uncertainty quantification and production optimization problems. For efficiency, we use wavelet based upscaling, which is a physics-based model order reduction technique and propose a time-adaptive simulation to consider long time steps for...

Algebraic multiscale (AMS) solvers for subsurface reservoir simulation have been developed to converge to the fine scale solution of large-scale highly heterogeneous problems. In such solvers, a localisation assumption that neglects flux on edges of dual volumes influences the accuracy and the efficiency of the method. We propose a new technique to...

As a FinTech software provider, SimCorp delivers financial calculations for risk analysis and pricing of financial instruments to many financial institutions world-wide. Speed of execution of pricing kernels is key in order to live up to the requirements of modern portfolio management practices. These place an emphasis on real-time advanced analyti...

In many cases, room acoustics are neglected during the early stage of building design. This can result in serious acoustical problems that could have been easily avoided and can be difficult or expensive to remedy at later stages. Ideally, the room acoustic design should interact with the architectural design from the earliest design stage, as a pa...

A major challenge in next-generation industrial applications is to improve numerical analysis by quantifying uncertainties in predictions. In this work we present a formulation of a fully nonlinear and dispersive potential flow water wave model with random inputs for the probabilistic description of the evolution of waves. The model is analyzed usi...