Utdanning

Programmer:

BSc i Petroleumslogistikk og Økonomi 

MSc in Sustainable Energy Logistics

Kurs:

PET101 Olje- og gassindustrien (7.5 ECTS, Bachelor)

LOG400 Logistics planning in energy sector (7.5 ECTS, Bachelor)

LOG410 Offshore energy logistics (7.5 ECTS, Bachelor) 

LOG775 Energy analytics and sustainable technologies (7.5 ECTS, Master) 

LOG776 Economics of Energy Value Chains (7.5 ECTS, Master)

LOG777 Business cases in energy logistics (7.5 ECTS, Master) 

LOG778 Offshore Energy Logistics Planning (7.5 ECTS, Master) 

LOG904-114 Game theory applied in Logistics (2.5, Master) 

LOG904-116 Upstream offshore oil and gas logistics (2.5 ECTS, Master)

LOG904-180 Offshore wind logistics (2.5 ECTS, Master)

LOG904-183 Energy transition (2.5 ECTS, Master)

 

Avhandlinger:

PhD:

År

Kandidat

Tittel

Veileder

Pågående, siden 2024 Pedro Lopes Offshore chemicals integrated supply planning under uncertainty Irina Gribkovskaia, Paulo Ribas

Pågående, siden 2023

Vladislav Klyuev

Helicopter transportation offshore under uncertainty

Irina Gribkovskaia, Paulo Ribas, Rafael Martinelli

Pågående, siden 2021

Tsimafei Nemytau

Horizontal collaboration in supply vessel planning

Irina Gribkovskaia, Gilbert Laporte, Yauhen Kisialiou

Pågående, siden 2020

Gaute Slettemark

Offshore helicopter personnel transportation and emergency response planning

Irina Gribkovskaia, Katerina Shaton

2020

Markus Brachner

Evaluating and optimizing emergency preparedness for offshore personnel transport in the Arctic Region

Lars Magnus Hvattum, Berit Helgheim

2019

Yauhen Kisialiou

Periodic supply vessel planning under uncertainty

Irina Gribkovskaia, Gilbert Laporte

2017

Katerina Shaton

Essays on upstream gas transport infrastructure planning and appraisal

Arild Hervik

2017

Yury Redutskiy

Oilfield infrastructure design in offshore oil and gas production

Kjetil Haugen, Irina Gribkovskaia

2015

Ellen Karoline Norlund

Green transportation planning in offshore supply

Irina Gribkovskaia

2012

Fubin Qian

Helicopter routing in the Norwegian oil industry: Minimization of risk for passenger transportation

Irina Gribkovskaia

2010

Bjørnar Aas

Supply base management

Stein Wallace

2010

Alexander Shyshou

Vessel planning in offshore oil and gas operations

Irina Gribkovskaia

 

Master:

 

År

Kandidat Tittel Veileder

Bedrift / Område

2024

Gjestvang, Christian Enstad

How the logistics flow for materiel out to offshore installations at the base in Kristiansund (Vestbase) can be improved

Bjørnar Aas

Erfaringsbasert Forsvaret

2023

Bye, Kristine Haram

Knowledge and capabilities of incumbent Norwegian oil and gas companies contributing to gaining competitive advantage through sustainable business model innovation: a single case study of Odfjell Technology

Maria Morgunova; Paulo Ribas

Sustainable Energy

2023

Dzaparov, Stepan

The environmental impact of shipping in the Arctic zone: Development of the methodology for emissions estimation and analysis

Irina Gribkovskaia

Sustainable Energy

2023

Kizenkov, Vladislav

Adaptive large neighborhood search with Reinforcement learning modification in periodic supply vessel planning problem

Irina Gribkovskaia,; Tsimafei Nemytau

Equinor

2023

Kolotkov, Aleksei

Dynamic repositioning of offshore emergency rescue vessels based on offshore personnel helicopter flight schedule

Irina Gribkovskaia

Equinor

2023

Poshta, Yaraslau

Simulation model for evaluation of weekly helicopter flight plans with operational modifications

Irina Gribkovskaia,; Tsimafei Nemytau

Equinor

2023

Talkachou, Maksim

Construction of offshore helicopters flight schedules with a fair allocation of flight slots

Irina Gribkovskaia,; Tsimafei Nemytau

Equinor

2023

Xue, Manru

Short-term scheduling of support vessels in wind farm maintenance

Paulo Ribas

Sustainable Energy

2022

Adukule, Arnold

Supply vessel routing optimization with multiple time windows

Paulo C. Ribas

Sustainable Energy

2022

Klyuev, Vladislav

Helicopter planning and periodic flight scheduling in offshore personnel transportation

Irina Gribkovskaia

Equinor

2022

Lapitskaya, Sviatlana

Coalitional game theory with uncertainty in helicopter personnel transportation planning

Katerina Shaton, Irina Gribkovskaia

Equinor

2022

Mandryk Mikalai; Vysotski, Andrei

Analysis of vessel assignment strategies in operational supply vessel planning under uncertainty

Irina Gribkovskaia,; Tsimafei Nemytau

Equinor

2022

Matsioula, Dimosthenia Efstathia

Supply Chain Strategies : Trade-off between costs, time, and emissions on the upstream part of the oil & gas industry

Katerina Shaton,; Sergei Teryokhin

Sustainable Energy

2022

Mikheeva, Valeriia

Planning and optimization of the petroleum products distribution network

Anna Konovalenko,; Lars M. Hvattum

Sustainable Energy

2022

Ouslimani, Adnane

Operational planning in helicopter personnel transportation in offshore upstream losgistics

Irina Gribkovskaia

Sustainable Energy, Equinor

2022

Rolland, Veronica Wichstrøm

Implementation of additive manufacturing technology as a risk mitigation and supply chain performance improvement strategy: A single case study of the Norwegian oil and gas industry

Bjørnar Aas

 

2022

Skriabin, Anton

Analysis of throughput of the Northern Sea Route

Irina Gribkovskaia

Sustainable Energy

2022

Strukov, Mikhail

Analysis of the Northeast Passage transit traffic using transshipment hubs with simulation

Irina Gribkovskaia

Sustainable Energy

2021

Belski, Andrei; Salashenka, Veranika

Optimal positioning of area emergency response vessels

Irina Gribkovskaia

Equinor

2021

Havnsund, Karoline

Supply vessels in ensuring resilience within social ecosystems: a case of offshore field project development in the North Sea

Antonina Tsvetkova

Petroleum Logistics

2021

Hoff, Marte; Kristiansen, Siv Agnete

"Hvordan kan Equinor lykkes med å redusere mengden kvalitetsavvik relatert til varestrømmen på forsyningsbasene?" - Et case-studie av kvalitetsavviksprossessen ved forsyningsbasene i Equinor med henblikk på hvordan oppnå kontinuerlig forbedring

Bjørnar Aas

Erfaringsbasert, Equinor

2021

Pishchalava, Ahata; Stsefanovich, Kanstantsin

Analysis of horizontal cooperation in offshore supply vessel and personnel helicopter transportation planning

Irina Gribkovskaia

Equinor

2021

Tserakh, Ivan

Periodic planning of offshore helicopter transportation

Irina Gribkovskaia

Equinor

2020

Abbasi Seidabad, Omid; Savin, Vladyslav

Operational supply vessel routing with pickups and deliveries of multiple commodities under weather influence

Irina Gribkovskaia

Petroleum Logistics

2020

Ali, Sahab

The concept of energy efficiency technologies in the upstream petroleum industry: A literature review

Yury Redutskiy

Petroleum Logistics

2020

Gambhir, Lubhit

Enterprise risk management in the Norwegian petroleum sector in the Arctic

Yury Redutskiy

Petroleum Logistics

2020

Grahl, David; Kleiven, Ane

Offshore logistics operations on the Norwegian Continental Shelf: challenges and solutions

Antonina Tsvetkova

 

2020

Hetland, Torbjørn; Strandkleiv, Martin Dommersnes

Analysis of operational modifications for platform supply vessel voyages

Irina Gribkovskaia

Equinor

2020

Pham, Ngoc Lan Thanh

Integrated decision-making on the utilization of capacities throughout the push segment of vertically integrated petroleum companies

Yury Redutskiy

Petroleum Logistics

2020

Rubchenia, Darya

Fleet sizing for maritime inventory routing problem in the petroleum industry with stochastic optimization

Arild Hoff

Petrobras

2019

Angelova, Angelina; Zamiatkin, Vladislav

Socio-economic appraisal of the gas infrastructure development in the Barents Sea.

Katarina Shaton

Petroleumslogistikk

2019

Anobil, Peter; Bruce-Cobbold, Joseph

Downstream supply chain design of petrochemical /oil companies: A case of GOIL.

Halvard Arntzen

Petroleumslogistikk

2019

Arabadzhi, Bogdan

Operational supply vessel planning with varying demands from installations.

Irina Gribkovskaia

Equinor

2019

Baradaka, Ivan

Development og a distribution network for fuel products in Belarus

Irina Gribkovskaia

 

2019

Camitz-Leidland, Cecilie Maria; Vysochyna, Anastasiia

Integration of decision-making on safety system design.

Yury Redutskiy

Petroleumslogistikk

2019

Chuhunou, Vadzim; Huseinava, Natassia

Operational supply vessels planning with varying demands and weather uncertainty

Irina Gribkovskaia

Equinor

2019

Drob, Anastasiya

Fleet combination analysis in the Brazilian petroleum industry.

Arild Hoff

Petrobras

2019

Dybdahl, Hendrik

Engineering contractor’s and production operator’s perspectives on employee scheduling for oil and gas facilities maintenance in remote locations.

Yury Redutskiy

Petroleumslogistikk

2019

Effah-Kesse, Doris

The use of surveillance tools in enhancing safety and security across offshore installations. A case study of oil and gas companies in Ghana.

Bjørnar Aas

Petroleumslogistikk

2019

Kamalitdinov, Artur; Vinogradov, Artem

Logistical analysis of the Arctic European railway transportation system.

Irina Gribkovskaia

Petroleumslogistikk

2019

Kukharava, Lidziya; Zabrodski, Illia

Fleet sizing for pipe lay support vessels.

Irina Gribkovskaia

Petrobras

2019

Solvang, Espen André Bareksten

Investigating the lead time and planning of OCTG in an upstream supply chain: A case study of Equinor`s logistical centre.

Bjørnar Aas

Equinor

2019

Zakhtarenka, Anton

Analysis of horizontal cooperation in crude oil maritime transportation to onshore terminals.

Irina Gribkovskaia

Petrobras

2018

Agyemang, Benjamin Opoku

Risk analysis in supply vessel operations in Ghana.

Yury Redutskiy

Petroleumslogistikk

2018

Akbar, Ali

Risk management perspective on employee scheduling for maintenance of automated safety systems for remotely located oil & gas facilities.

Yury Redutskiy

Petroleumslogistikk

2018

Anderson, Kristanna Tunga

Safety system design and maintenance planning for oil and gas facilities located in remote areas.

Yury Redutskiy

Petroleumslogistikk

2018

Babayev, Farid; Mujahid, Muhammad Moosa

A descriptive study of offshore floating wind energy: A case study of Alpha Wind Energy project at Hawaii, USA.

Bjørnar Aas

Petroleumslogistikk; Alpha Wind Energy

2018

Baghirov, Javid

The use of drones in oil and gas logistics.

Bjørnar Aas

Petroleumslogistikk

2018

Chuprova, Alena

Analysis of infrastructure and factors influencing the operational environment of the Northern Sea Route and their future impact on possible transit.

Odd I. Larsen

Petroleumslogistikk

2018

Kjenne, Fredrik

Effektivisering av krevende logistikkoperasjoner: En case-studie av interntransportens ikkeverdiskapende aktiviteter ved Hammerfest LNG

Bjørn Guvåg

Equinor ASA - Erfaringsbasert master.

2018

Moskaleva, Katerina; Pekarskaya, Tatsiana

Supply vessel planning problem with demand uncertainty.

Irina Gribkovskaia

Equinor ASA

2017

Akkuzhina, Elvira

Fleet size and location inventory routing problem for LPG distribution company.

Alina Kovalenko

Petroleumslogistikk

2017

Bekken, Lasse Halvorsen; Strømme, Fredrik Sørøy

Pricing natural gas value chain emissions - A scenario-based case study of the Norwegian Barents Sea.

Arild Hervik

Petroleumslogistikk

2017

Bjørneset, Hans Martin

Applicability of logistics performance metrics for a subsea entrepreneur entering new markets.

Yauhen Maisiuk

Petroleumslogistikk

2017

Dahlen, Odin Kvalvåg; Kleiven, Andreas Møll

Horizontal cooperation in upstream logistics material supply on the Norwegian Continental Shelf: a conceptual framework.

Irina Gribkovskaia

Petroleumslogistikk, Statoil

2017

Dar, Muarif Sana; Ibrahim, Mohamed Salaheldin

Optimization model for drilling fluid circulation system: A case study from Edvard Grieg field.

Bjørnar Aas

Petroleumslogistikk - Lundin-Norway AS. Petroleum Logistics.

2017

Eliseussen, Kristian; Sola, Carolina

Key performance indicators in Statoil's drilling supply chain.

Harald Hjelle

Statoil ASA

2017

Kibarov, Dmitrii

Yamal LNG project: searching for optimal number of carriers.

Bjørnar Aas; Ludmila Studenikina

Petroleum Logistics

2017

Mukhamedzhanov, Roman

Evaluation of schedules robustness for tactical supply vessel planning under weather uncertainty and demand variability with simulation.

Yauhen Maisiuk

Petroleum Logistics

2017

Sannes, Petter; Wreczycki, Patrick Adam

A case study related to petroleum activity in the Barents Sea - Important key factors when Lundin Norway AS considers supply base location based on the activity scenario in 2030.

Bjørnar Aas

Lundin Norway AS - Petroleum Logistics

2017

Sætre, Torbjørn

Kan en mer Lean håndtering av utgående vareflyt bidra til redusert snutid for fartøy?

Bjørnar Aas

Statoil ASA - Erfaringsbasert master

2016

Almiashev,  Rushan

An adaptive large neighborhood search heuristic for periodic supply vessel planning problem.

Irina Gribkovskaia

Statoil ASA

2016

Anderson, Kristanna Tunga; Oancea, Luiza

Analysis of urgent deliveries in upstream petroleum logistics - A case study of Haltenbanken area.

Bjørnar Aas

Statoil ASA

2016

Golyzhnikova, Daria

Mathematical modelling of safety instrumented system for pipeline infrastructure planning.

Yury Redutskiy

Petroleum Logistics

2016

Larsen, Katrine

Analysis of disruptions in supply vessel voyages: case study.

Yauhen Maisiuk

Statoil ASA - Erfaringsbasert master

2016

Marder, Elena

Heuristic for robust periodic supply vessel planning.

Irina Gribkovskaia

Statoil ASA

2015

Grimstad, Henriette Indreeide; Ørving, Tale

Analysis of information flow in base-to-base transportation. A case study of Bring Offshore & Energy.

Bjørnar Aas

Bring Cargo Offshore and Energy

2015

Kvie, Magn Stian

Requirements for a logistics information system in the oil and gas industry – A case study for Statoil.

Bjørn Jæger

Statoil ASA. Erfaringsbasert master

2015

Liasnoi, Aliaksei

Periodic supply vessel planning with flexible departures and coupled vessels.

Irina Gribkovskaia

Statoil ASA

2015

Nester, Anton; Veselkova, Daria

Servicing small gas fields and solving gasification problems of remote sparsely populated areas in Eastern Siberia using LNG transportation.

Øyvind Halskau, Yury Scherbanin

 

2015

Pettersen, Tonje

Lean i integrert aktivitetsplanlegging.

Per Engelseth

AS Norske Shell / Draugen. Erfaringsbasert master

2014

Dzeravianka, Anastasiya

The use of the Northern Sea Route for the transportation of gas from Norway to Asia.

Irina Gribkovskaia

 

2014

Guldbrandsen, Vegard

Evaluation of HOLD solution: A case study of the upstream supply chain of Norne.

Bjørnar Aas

Statoil ASA

2014

Hubin, Aliaksandr

Evaluation of supply vessel schedules robustness with a posteriori improvement.

Irina Gribkovskaia

Statoil ASA

2014

Kapranov, Maksim

Development of decision support system for evaluation of speed optimization strategies in supply vessel planning under weather uncertainty.

Irina Gribkovskaia

Statoil ASA

2014

Rusten, Heidi Eriksen

Challenges concerning VAT and customs duty for National Oilwell Varco Norway in production countries and transaction costs concerning this.

Bjørnar Aas

National Oilwell Varco Norway AS - Erfaringsbasert master

2014

Taknæs, Tommy

Improving information management for increased supply chain performance.

Bjørnar Aas

Erfaringsbasert master

2013

Anfimau, Mikhail

Algorithms for construction of multi-base supply vessel schedules.

Irina Gribkovskaia

Statoil ASA

2013

Bezlepkina, Elena; Bosomykina, Olga

Simulation model for supply vessels fleet sizing with wave-dependent speed loss.

Irina Gribkovskaia

BP

2013

Bue, Louise; Torvik, Runa

Mapping information flow: A Case study of an upstream supply network.

Per Engelseth; Berit Helgheim

Vestbase AS

2013

Bukhautsova, Darya

Multi-base supply vessel planning with mathematical models.

Irina Gribkovskaia

 

2013

Kukareko, Kiril

Virtual warehousing in offshore oil and gas platforms' supply chain.

Nils Jacob Berland

NorSea Group AS

2013

Petkevich, Yevgheni

Algorithms for takeoff and landing risk minimization in offshore helicopter transportation.

Irina Gribkovskaia

Statoil ASA

2013

Rubinat Hernandez, Victor

Generation of supply vessels schedules with models.

Irina Gribkovskaia

Statoil ASA

2013

Sørli, Isa Merete

Evaluation of robustness of supply vessel sailing plans with simulation.

Irina Gribkovskaia

Statoil ASA

2013

Volikova, Elena

Speed optimization in supply vessel planning under weather uncertainty.

Irina Gribkovskaia

Statoil ASA

2012

Abdollahi, Vahid

Fuel consumption reduction in offshore supply vessel planning.

Irina Gribkovskaia

Statoil ASA

2012

Aliakseyeu, Pavel

Simulation model for evaluation of reaction strategy on stochastic factors in platform supply vessel fleet sizing problem.

Irina Gribkovskaia

Statoil ASA

2012

Anne Stine Volsdal

Base-to-base transport: model split and emissions analyses.

Irina Gribkovskaia

Statoil ASA

2012

Barysavets, Tatsiana; Mikhailau, Mikalai

Emissions reduction in offshore supply vessels planning.

Irina Gribkovskaia

Statoil ASA

2011

Hesthag, Malin; Stormyr, Lisa

Improving Linjebygg Offshore's warehouse logistics

Bjørnar Aas

Linjebygg Offshore AS

2011

Karalkova, Anastasiya; Kilcheuskaya, Katsiaryna

X2X: new conceptual solution on the edge of information systems and supply chain management.

Bjørnar Aas

X2X project

2011

Panamarenka, Katsiaryna

Minimization of emissions in periodic supply vessel planning through speed optimization.

Irina Gribkovskaia

Statoil ASA

2011

Storøy, Olga

Optimization of condensate transportation from the Nyhamna processing plant (Ormen Lange Field).

Bjørnar Aas

Norske Shell AS

2010

Brathaug, Nikolai Vedde; Sagbakken, Øyvind

An analysis of the planning horizon for logistics activities at the Heidrun offshore installation.

Bjørnar Aas

Statoil ASA

2010

Haram, Trygve; Xu, Binqiang

A case study of express transport  in Shell's upstream supply chain.

Bjørnar Aas

AS Norske Shell

2010

Onyia, Beltus Nnanyelugo; Osuma, Olawande

Logistics challenges involved in constructing of operating facilities in emga - projects (A Case study of cost overrun in Snøhvit LNG Project).

Arild Hervik

Snøhvit (Statoil ASA)

2010

Urke, Frederik Knoblauch

Collaborative port allocation - An experiment with collective intelligence in a modern supply chain.

Nils Jacob Berland

Vestbase AS

2010

Wang, Lijie; Zhang, Tingting

The value of flexibility at petroleum industry: Real Options for gas hub development.

Arild Hervik

Norske Shell AS

2009

Ahmad, Zubair

Design of an information architecture for information exchange related to quay allocation at Vestbase – Kristiansund.

Nils Jacob Berland

Vestbase AS

2009

Aneichyk, Tatsiana

Simulation model for strategic fleet sizing and operational planning in offshore supply vessels operations.

Irina Gribkovskaia

StatoilHydro AS

2009

Arica, Emrah; Vuvunikian, Milena

Optimization models for the integrated steel plant within the Gas-Mat research project.

Irina Gribkovskaia

GasMat project

2009

Siarhei Tsitou

Comparison of metaheuristics for the single vehicle pickup and delivery routing problem with multiple commodities

Irina Gribkovskaia

StatoilHydro ASA

2009

Maisiuk, Yauhen

Development of a generic dynamic discounted cash flow analysis tool for investment in the GasMat Park.

Irina Gribkovskaia

GasMat project

2008

Eugen Sopot

Tabu search heuristic for the multiple vehicle routing problem with pickups and deliveries

Irina Gribkovskaia

SatatoilHydro ASA

2008

Arne Gjengstø and Sigurd Vaksvik

Single vehicle pickup and delivery problem with multiple commodities and visit windows

Irina Gribkovskaia

StatoilHydro ASA

2008

Johansen, Hans Thomas; Ovesen, Torgeir Hoem

Spare parts optimization for the gas export compressors on the Ormen Lange project.

Kjetil Haugen

A/S Norske Shell

2008

Liu, Xiaohuan

Location based competitive advantage: The analysis of Vestbase in Kristiansund.

Arild Hervik

Vestbase AS

2008

Morkemo, Eirik-André Lund; Öztürk, Sadi

Fleet size planning for anchor handling vessels at StatoilHydro.

Irina Gribkovskaia

StatoilHydro AS

2007

Akselvoll, Arne Borch; Zouari, Ahmed

Multi-commodity pickup and delivery supply vessel routing for Statoil: Analysis and modelling.

Irina Gribkovskaia

Statoil ASA

2007

Arhaug, Solveig Lena Myrvold

Analysis of capacity utilization of supply vessels serving oil and gas installations fram Mongstadbase.

Irina Gribkovskaia

Norsk Hydro ASA

2007

Meek, Per Arne Fagervoll; Furu, Gunhild

Application of supplier networks in project supply chain management – a study of the Ormen Lange project.

Berit Helgheim

Norsk Hydro / Norske Shell

2007

Mironovs, Aleksejs

The impact of RFID technology on the load carrier fleet management at the supply base in Kristiansund.

Bjørnar Aas; Anne Karin Wallace

Statoil ASA

2007

Sund, Arthur; Walquist, Jørgen K.

Gas infrastructure developments in the Norwegian Sea: Can real option values alter the optimal decision?

Arild Hervik

Petroleumsdirektoratet

2007

Årsheim, Kai Frode

Measuring performance of PSV strategies in offshore drilling campaigns.

Øyvind Halskau; Bjørnar Aas

AS Norske Shell

2006

Bjørshol, Christer; Tan, Ren

An analysis of the logistics chain of a mobile rig: A case study of Transocean Searcher.

Stein Wallace; Bjørnar Aas

Statoil ASA

2006

Alexander Shlopak

Pickup and delivery single vehicle routing problem with capacitated customers.

Irina Gribkovskaia

Statoil ASA

2006

Aliaksandr Shyshou

A single vehicle routing problem with deliveries and selective pickups.

Irina Gribkovskaia

Statoil ASA

2006

Shi, Xuemei; Xia, Feng

Transport planning under uncertainty.

Stein Wallace

Statoil ASA, Forsyningsbase Kristiansund

2005

Følsvik, Kjell Vidar; Horky, Rene

The Heidrun offshore platform - its internal logistics and some external issues.

Stein Wallace

Statoil ASA

2005

Martin Vlçek

Heuristic algorithms for the single vehicle pickup and delivery problem and none-simultaneous services.

Irina Gribkovskaia

Statoil ASA

2005

Rodrigues, Tony Anskar

Future scenarios on Vestbase AS.

Harald Hjelle

Vestbase AS

2005

Stranden, Jan Kristian; Vestad, Einar;

Optimizing the supply chain for supply vessels at Vestbase.

Ola Bø; Kai A. Olsen

Statoil ASA

2004

Moxness, Trygve Weidemann

Noen strategiske allianser for å bedre containerflyten til Statoil.

Stein Wallace

Statoil ASA

2003

Aas, Bjørnar; Senkina, Erna

En analyse av forsyningskjeden for bore- og brønnmateriell til Heidrunplattformen.

Kjetil Haugen

Statoil ASA, Forsyningsbase Kristiansund

2003

Pedersen, Roy

Styringsstruktur i oljeindustrien.

Arnt Buvik

Oljeindustrien