# Nils Reidar B. Olsen's research while affiliated with Norwegian University of Science and Technology and other places

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## Publications (58)

The dependency of the friction factor on the flow direction was investigated experimentally in a milled scale model of an unlined rock blasted tunnel under pressurized flow conditions by reversing the flow direction. The experimental data were used to highlight the significance of anisotropic roughness structures and variations in the cross-section...

The friction loss in a part of the rock-blasted unlined tunnel of the Litjfossen hydropower plant in Norway was determined from experimental and numerical studies. Remote sensing data from the prototype tunnel provided the input data for both the numerical model and the construction of a 1:15 scale model with an innovative milling approach. The num...

Soil slides can occur when the water level in a lake or a reservoir is lowered. This may take place in situations when a reservoir is flushed to remove sediments. The current study describes a three-dimensional numerical model used for the simulation of reservoir flushing that includes the slide movements. The geotechnical failure algorithms start...

A numerical model was used to compute the formation of a braided channel system. The model calculated the water flow field from the fully 3D Navier-Stokes equations on a non-orthogonal unstructured adaptive grid. The sediment transport was computed from the Engelund-Hansen formula. A free surface algorithm based on local pressure gradients was used...

Consecutive bends making up meandering rivers induce complex three-dimensional currents (Blanckaert et al., 2013, Kasvi et al., 2017). These secondary currents will have strong effect on suspended sediments esp. closest to the bed. In this study, we investigate the capability of a numerical model in terms of reproducing water flow and the spatial p...

Friksjonstap i tunneler beregnes vanligvis med Mannings eller Darcy-Weissbachs formler. I disse formlene inngår det en friksjonsfaktor som må bestemmes. Dette kan gjøres med kalibrering hvis en har tilgjengelige kalibreringsdata. Ellers må faktoren bestemmes på andre måter. I vårt prosjekt har vi beregnet friksjonsfaktoren i en 120 m lang råsprengt...

Purpose
The purpose of the current study was to present a 3D computational fluid dynamics (CFD) model that can be used to predict long-term (11 years) bed changes in a reservoir due to sedimentation and dredging and that can be done with a reasonable computational time (18 h) on a desktop computer.
Materials and methods
The numerical model solved...

Numerical algorithms are presented for modeling bank failures during reservoir flushing. The algorithms are based on geotechnical theory and the limit equilibrium approach to find the location and the depth of the slides. The actual movements of the slides are based on the solution of the Navier-Stokes equations for laminar flow with high viscosity...

A numerical model is presented that compute the geometrical dimensions and movement of downstream migrating antidunes. The model solves the Navier-Stokes equations together with the k-epsilon turbulence model to find the water flow field over the bedforms. A two-dimensional width-averaged grid is used. The bed elevation changes are computed by solv...

The simulation of sediment transport by three-dimensional modelling is linked with the question how accurate such models are. The current paper provides a test where detailed field measurements of velocities and bed elevation changes over a three-month period from a prototype reservoir are compared with simulation results. The SSIIM software was us...

Four algorithms are described for computing a steady free water surface with the solution of the three-dimensional (3D) Navier-Stokes equations. The numerical methods are used in hydraulic engineering cases, typically spillways and river modelling. The algorithms were tested against a laboratory experiment of a v-shaped broad-crested weir. The comp...

This study presents a calibration method of horizontal acoustic Doppler current profilers (H-ADCP), based on 3D Computational Fluid Dynamics (CFD) simulations. Rigidly mounted H-ACCPs are currently used to continuously monitor water discharges. In this study three instruments were employed at separate sites in an unlined rock-blasted hydro power tu...

The current study focuses on the application of a three-dimensional numerical model for the prediction of morphological bed changes. The sediment deposition in a reservoir during a 10-year-flood was investigated and the results of the simulation were validated with data derived from a physical model study. Because of the small grain sizes in the pr...

The prediction of cohesive sediment transport requires numerical models which include the dominant physico-chemical processes of fine sediments. Mainly in terms of simulating small scale processes, flocculation of fine particles plays an important role since aggregation processes affect the transport and settling of fine-grained particles. Floccula...

The results of modeling in river engineering are an elementary prerequisite for river management, especially sediment transport, and are consequently of fundamental importance. Therefore, the aim of this paper is to analyze the flow field in the Iffezheim reservoir and to investigate the sensitivity of hydraulic and numerical parameters (e.g. time...

There are quite a few studies investigating low Reynolds number turbulence models for predicting the near-wall flow over smooth walls. However, analogous work over rough walls is sparse despite the fact that many flows of practical interest, particularly in geophysical flows and hydraulic engineering, are over rough walls. This paper presents a pri...

The three-dimensional numerical model SSW was used to compute suspended sediment distribution and deposition pattern in a hydropower reservoir. The study also included three-dimensional measurements of suspended sediments in the reservoir using the LISST-SL instrument. The measurement device is based on a laser-diffraction method and measures conce...

The waterway counts as a main and costly part of a hydro power project. Excavating tunnels for waterways by rock-blasting is a rapid method compared to utilizing tunnel boring machines (TBM). However the variation in cross-section geometry and surface roughness that arises in unlined rock-blasted tunnels results in a considerable increase in head l...

A fully three-dimensional numerical model for reservoir flushing has been tested against field measurements for the Angostura reservoir in Costa Rica. The numerical program solves the Reynolds-averaged Navier–Stokes (RANS) equations in three-dimensions and uses for discretization the finite-volume method together with a second-order upwind scheme....

Upstream migration of fish through circular culverts is often prevented by velocities in the barrel being higher than that of the natural channel. In this investigation a computational fluid dynamic (CFD) model has been used to test the effects of various spoiler baffle geometries in culverts of varying size to reduce water velocity and increase wa...

Sediments filling reservoirs is a common problem in the world today, with an estimated 1% of the capacity of hydropower reservoirs being lost annually through sedimentation. One of the most used techniques for reducing this problem is reservoir flushing. During a flood, the water level is drawn down, causing increased velocities, therefore facilita...

To predict the magnitude of flushed out sediments and to predict where in the reservoir erosion takes place is still a challenge in engineering. Physical models are often used to get knowledge of the success of an upcoming flushing. In this study a numerical program is presented as an alternative. The used CFD code solves the RANS-equations in thre...

Quite some effort has been put into the development of low Reynolds
number turbulence models to enhance predictions of the near wall flow
over smooth walls. Despite the success of these models analogous models
for the flow over rough walls are sparse. Based on a high resolution
large-eddy simulation of the flow over a bed artificially roughened by...

A three-dimensional computational fluid dynamics model is applied to predict local scour around an abutment in a rectangular laboratory flume. When modeling local scour, steep bed slopes up to the angle of repose occur. To predict the depth and the shape of the local scour correctly, the reduction of the critical shear stress due to the sloping bed...

In many situations the design of culverts prevents the upstream migration of fish because water velocity in the barrel is greater than that of the natural channel. One way to reduce the water velocity within the culvert is to install spoiler baffles on the base. The current investigation uses a three-dimensional numerical tool to examine the influe...

Two computational fluid dynamics (CFD) codes, Flow-3D and SSIIM 2, have been used to calculate the water flow over a trapezoidal broad-crested weir. The two programs apply different algorithms for making the grid and computing the free water surface. Flow-3D uses the Volume of Fluid (VOF) method with a fixed grid, while SSIIM 2 uses an algorithm ba...

A three-dimensional numerical model was used to compute the water flow and the sediment deposition for a 100-year flood in the delta of Lake Oyeren in Norway. The model solved the Reynolds-averaged Navier-Stokes (RANS) equations with the k-epsilon turbulence model on a three-dimensional unstructured grid. The sediment transport was computed solving...

A three-dimensional numerical model was applied to compute uniform and nonuniform sediment transport and bed deformation in an S-shaped laboratory channel located at the University of Innsbruck, where detailed measurements of the velocity field and bed elevation changes were made. The channel had two bends, a trapezoidal cross section, and a slope...

Secondary currents play a significant role in open channel flows. They directly influence the primary mean flow field, transport and mixing processes and the transversal alternation of bed shear stress. In this paper the flow field in a straight open channel with a rectangular geometry is calculated using two different numerical models. One solves...

Annular flumes are a commonly used type of test rig for laboratory studies on cohesive sediment transport as the flow is generated in a way designed not to interfere with flocculation. A major characteristic of the annular flow are distinct secondary currents, i.e. the flow field is clearly three-dimensional. The hydraulics of two open annular flum...

A three-dimensional (3-D) numerical model with standard k–ε turbulence closure has been applied to model the transport and mixing of solute in a large-scale laboratory channel. The channel is meandering with self-formed cross-sectional shape. Simulation accuracy was evaluated through comparison of computed and measured temporal concentration curves...

A fully three-dimensional non-hydrostatic model was applied to compute the water flow and morphodynamic processes in a laboratory flume. The experiments provided data for bed deformation and grain sorting processes in a 180? channel bend. The data were used to investigate the performance of different sediment transport approaches. The original van...

A 3D numerical model was used to compute the discharge distribution in the channel branches of Lake Oyeren's delta in Norway. The model solved the Navier Stokes equations with the k - epsilon turbulence model on a 3D unstructured grid. The bathymetry dataset for the modelling had to be combined from different data sources. The results for three dif...

This study evaluates the use of two Computational Fluid Dynamics (CFD) techniques in calculating the three-dimensional flow and bed shear stress distribution in a regulated river reach near Trondheim, Norway. The two different CFD codes being used in this study are: one commercial FLOW-3D and an in-house program, SSIIM, developed by the third autho...

Turbulent flow in a meandering channel is computed with two Computational Fluid Dynamics (CFD) codes solving the Navier–Stokes equations by employing different turbulence closure approaches. The first CFD code solves the steady Reynolds-Averaged Navier–Stokes equations (RANS) using an isotropic turbulence closure. The second code is based on the co...

The flow of water in a three-dimensional sand trap is calculated by a numerical model, using a finite volume method to solve the Navier-Stokes equations for three dimensions on a general non-orthogonal grid. The k- turbulence model is used to solve the Reynolds- stress term. The diffusion/convection equation for the sediment concentration is solved...

The stage-discharge curve for a complex spillway geometry has been computed with a three-dimensional numerical model. The model solved the Reynolds-averaged Navier-Stokes equations using the k-epsilon turbulence model. An orthogonal fixed grid was used, where the cells could be wet, dry or partially wet. A volume-of-fluid method was used to compute...

The bed changes in a section of the river Danube were computed using a 3-D computational fluid dynamics model. A time series of discharges during the flood in 2002 was used. The results compared reasonably well with regular bed level surveys before and after the flood. The Danube River section was 6 km long and located between Vienna and the Austri...

The present study investigated the use of computational fluid dynamics (CFD) in predicting the formation, development, and migration of free-forming meander bends. The three-dimensional CFD model computed water flow and sediment transport in alluvial channels and predicted vertical and horizontal bed changes. Different algorithms and parameters wer...

Using a three-dimensional finite volume code with standard k-ε turbulence closure the hydraulic impact of willow stands (Salix alba and Salix fragilis) on the velocity distribution was modelled. The additional hydraulic resistance of the willow stands was modelled separately to the bed resistance using a drag force term that was introduced into the...

A three-dimensional numerical model was used for calculating the velocity and bed level changes over time in a 90° bended channel. The numerical model solved the Reynolds-averaged Navier-Stokes equations in three dimensions to compute the water flow and used the finite-volume method as the discretization scheme. The k-ε model predicted the turbulen...

This paper describes the sedimentological studies for the Angostura Power Plant, Costa Rica. The plant, in operation since October 2000, is located in the middle basin of the Reventazon River, and has a reservoir of about 15x10 6 m 3. The river up to the project site has a drainage area of 1463 km 2 , with large slopes and high precipitation, excee...

Validation of a three-dimensional finite volume code solving the Navier–Stokes equations with the standard k-epsilon turbulence model is conducted using a high quality and high spatial resolution data set. The data set was collected from a large-scale meandering channel with a self-formed fixed bed, and comprises detailed bed profiling and laser Do...

This paper attempts to compare the accuracy of a two-dimensional (2D) depth-averaged code (TELEMAC-2D) and a three-dimensional (3D) code (SSIIM) in the numerical simulation of free surface flows. Assessment was conducted using benchmark data collected from a meandering compound channel at the UK EPSRC Flood Channel Facility. For both codes a standa...

A three-dimensional CFD model was used to compute the formation of the meandering pattern in an initially straight alluvial channel. The numerical model was based on the finite volume method using an unstructured grid with dominantly hexahedral cells. The k-ε model was used to predict turbulence and the SIMPLE method was used to compute the pressur...

This paper attempts to compare the accuracy of a two-dimensional (2D) depth-averaged code (TELEMAC-2D) and a three-dimensional (3D) code (SSIIM) in the numerical simulation of free surface flows. Assessment was conducted using benchmark data collected from a meandering compound channel at the UK EPSRC Flood Channel Facility. For both codes a standa...

Velocity distributions in channels partially covered with vegetation have been computed using a three dimensional model. The Navier-Stokes equations were solved, using the SIMPLE method and the k-ε turbulence model. The vegetation was modeled as vertical cylinders. A formula for the drag force on the vegetation was included as a sink term in the Na...

A three-dimensional numerical model was used to model water circulation and spatial variation of temperature in Lake Sperillen in Norway. A winter situation was simulated, with thermal stratification and ice cover. The numerical model solved the Navier-Stokes equations on a 3D unstructured non-orthogonal grid with hexahedral cells. The SIMPLE metho...

Headworks in rivers with severe sediment transport can suffer from poor sediment control and poor techniques for removal of the sediments in the withdrawn water. Reliable physical modelling of the phenomena involved has always been a problem. These facts, often combined with relaxed operational attention, invariably lead to the blocking of intakes,...

Paper presented at The Seventh International Conference on HydroScience and Engineering (ICHE)hosted by the College of Engineering at Drexel Univeristy on September 10-13, 2006 in Philadelphia, Pennsylvania. The conference theme was IT in the Field of HydroSciences. It included several mini-symposia that emphasized IT topics in HydroSciences and th...

Velocity distributions in channels partially covered with vegetation have been computed using a three dimensional model. The Navier-Stokes equations were solved, using the SIMPLE methodandthe k- ε turbulence model. The vegetation was modeled as vertical cylinders. A formula for the drag force on the vegetation was includedas a sink term in the Navi...

## Citations

... The scale-model tests were designed to investigate the effect of the wall rock roughness on head losses and the friction factor in the tunnels [34,35]. It was therefore decided to construct models of rather straight tunnel sections to avoid the additional influence of bends, alcoves, and partial linings. ...

... Railway tunnels are playing an increasing role in mountainous roads with complex terrain [1,2]. However, the entrance section of highway tunnels is shallowly buried and the surrounding rock is broken. ...

... Due to these simplifying assumptions, but also because of the general limitation of numerical models, it is not possible to accurately predict channel avulsion and erosion through previously deposited cohesive sediments (Hajek and Wolinsky 2012;Liang et al. 2015). Furthermore, channel bank failure depends on the sediment type, moisture content, and seepage processes (Luppi et al. 2009;Rinaldi and Nardi 2013;Olsen and Haun 2020). Therefore, bank failure cannot be simulated with a numerical setup for reservoir sedimentation due to fine particle deposition. ...

... They have been applied to explain some poorly understood phenomena in natural braided rivers, such as avulsions [8,9]; discuss the essential factors controlling the complex processes in braided rivers; and test hypotheses that are difficult to be verified in natural rivers [10,11]. Previous studies have reviewed the existing numerical models for braided river simulation [3,5,[12][13][14][15][16][17]. ...

... An earlier study by Olsen and Haun [19] also used a numerical model to compute the sediment slides at the banks of the Bodendorf reservoir. However, they used a much ...

... To minimize sediment deposition and ensure sustainable reservoir operation, it is essential to quantify and accurately predict sedimentation processes. State-of-the-art tools for predicting reservoir sedimentation are two (2d) or three (3d) dimensional numerical models coupling hydrodynamics and sediment transport (Haun et al. 2013;Hanmaiahgari et al. 2018;Olsen and Hillebrand 2018;Khorrami and Banihashemi 2021). ...

... Kennedy, 1961Kennedy, , 1963Engelund, 1970;Hayashi, 1970;Parker, 1975;Colombini, 2004;Andreotti et al., 2012;Charru et al., 2013), and computationally (e.g. Giri and Shimizu, 2006;Bohorquez and Ancey, 2016;Doré et al., 2016;Olsen, 2017), commonly assuming two-dimensional bedforms. However, it is known that two-dimensional (2D) dunes and antidunes with uniform transverse crests evolve into three-dimensional (3D) forms. ...

... Olsen (2009) considered the main advantage of the SSIIM program to model sediment transport in troughs with a moving bottom with complex geometry. The program was used in calculations of water, and sediment flows through the sedimentation reservoir (Agrawal 2005, Singh et al. 2007, local erosion at the pillars (Abouzeid et al. 2006) and below the overflow (Hämmerling et al. 2013), as well as accumulation of sediments in the retention reservoir (Zhang et al. 2013) or erosion below it (Zhang et al. 2016). ...

... The solution method and the numerical algorithms described here had previously been tested on several different flow problems (Wilson et al., 2003). The main reason for using this model in the present study was that its ability to compute the formation of antidunes. ...

... Accordingly, 3D numerical models can provide a more precise assessment of morphological processes in shallow reservoirs (Esmaeili et al. 2017). In this work, the fully three-dimensional numerical model SSIIM 2 (Sediment Simulation In Intakes with Multiblock option) (Olsen 2014) is used for hydro-morphodynamic simulations, which has been proven to yield reliable results in the field of reservoir sedimentation/flushing studies (Haun & Olsen 2012;Hillebrand et al. 2017;Mohammad et al. 2020). This software solves the Reynolds-averaged Navier-Stokes (RANS) equations together with the continuity equation (Equations (1) and (2)). ...