Petri Varsta - Academia.edu (original) (raw)

Papers by Petri Varsta

Research paper thumbnail of Bending response of web-core sandwich beams

Composite Structures, Jun 1, 2006

This paper presents a new analytical solution for the bending response of a web-core sandwich bea... more This paper presents a new analytical solution for the bending response of a web-core sandwich beam. The beam is a transverse cut from the sandwich plate. The method is based on the plane frame analysis, where the response of the beam is divided into local and global components. The ClebschÕs method is used to calculate the deflection of the face plates. The validation of the plane frame method is carried out with FE-analyses based on the shell element formulation. Also a comparison is made with the method based on homogenized beam. Periodic stress distributions in the face plates are revealed with the plane frame analysis and are supported by the FE-analysis. The existing methods based on homogenized beam are not able to predict these stresses. The plane frame analysis can benefit the development of the theory related to web-core sandwich plate.

Research paper thumbnail of Ship-Ice Contact and Design Loads

In this paper recent developments to model ship-ice contact and to evaluate design ice loads are ... more In this paper recent developments to model ship-ice contact and to evaluate design ice loads are summarised. The focus is on first year ice appearing annually in the Baltic Sea. The most important parameters to specify characteristics of ice cover for winter navigation purposes are presented. Observations on ship-ice contact suggest that the contact has a line-like nature. This concept is summarised and it's implications to structural design are discussed. An equivalent level ice thickness approach which includes the effect of ridges on the ice loads is described. The effect of ship parameters on the load level, based on the physical background for ice loads on different parts of a ship hull is given. A method to estimate the life-time ice loads on different parts of the hull of a vessel navigating in the Baltic Sea is developed, and the calculated loads are compared with measured long-term ice loads onboard MS KEMIRA, MS ARCTURUS and IB SISU. Finally the risk of damage caused by ice loads on ships in the Baltic Sea is discussed.

Research paper thumbnail of A ship in compressive ice.Analysis of the ice failure process.Concluding report from the joint Russian-Finnish project in 1991-1993

Research paper thumbnail of European Research in Marine Structures

Transactions of the Society of Naval Architects and Marine Engineers, 2011

 Users may download and print one copy of any publication from the public portal for the purpose... more  Users may download and print one copy of any publication from the public portal for the purpose of private study or research.  You may not further distribute the material or use it for any profit-making activity or commercial gain  You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.

Research paper thumbnail of Numerical and experimental investigation on the collision resistance of the X-core structure

Ships and Offshore Structures, Mar 1, 2012

Research paper thumbnail of Failure Process of Ice Edge Caused by Impact with Ship's Side

A survey of existing ice edge failure models is made, and some suggestions to improvements in the... more A survey of existing ice edge failure models is made, and some suggestions to improvements in these models are presented. The observed failure process of ice plate under various loading conditions is described. The process is then divided into physically different details such as crushing, shearing and bending, based on literature survey and observations made at sea. Results from tests made with fresh water beams are reported, and determination of compressive elastic constants of columnar grained fresh water ice is dealt with. Order from NSFI as No. 19954.

Research paper thumbnail of Sea Transport in Ice-Covered Waters

Sea transport in the Arctic regions represents just a small part of the world's total shippin... more Sea transport in the Arctic regions represents just a small part of the world's total shipping, not least because of the difficult environmental conditions encountered in these areas. Winter navigation started about a hundred years ago in the sub-arctic sea areas, where ice cover exists only during the winter months. Navigation in the Arctic proper began about a half century ago. The sailing period increases from year to year with the final goal obviously being year round traffic at a tolerable cost. This phase was reached in the Baltic in the early 1970s. The paper aims to give a general idea of the basic questions in polar sea transport systems. The demand for transportation and the influence on cargo handling systems and ship technology are discussed. However, details of technical solutions are, as far as possible, avoided.

Research paper thumbnail of Full scale observations of ship performance in ice

Research paper thumbnail of Ship-ice contact and design ice loads

Research paper thumbnail of International Conference on Education and Professional Development of Engineers in Maritime Industry, December 7th-8th 2011, Newcastle, UK

Research paper thumbnail of This is an electronic reprint of the original article. This reprint may differ from the original in pagination and typographic detail

This paper investigates the influence of weld rotation stiffness on the global bifurcation buckli... more This paper investigates the influence of weld rotation stiffness on the global bifurcation buckling strength of laser-welded web-core sandwich plates. The study is carried out using two methods, the first is the equivalent single-layer theory approach solved analytically for simply supported plates and numerically for clamped plates. First-order shear deformation theory is used. The second method is the three-dimensional model of a sandwich plate solved with finite element method. Both approaches consider the weld through its rotation stiffness. The weld rotation stiffness affects the transverse shear stiffness. Plates are loaded in the web plate direction. Four different cross-sections are considered. Weld stiffness is taken from experimental results presented in the literature. The results show a maximum of 24% decrease in buckling strength. The strength was affected more in plates with high reduction of transverse shear stiffness and high bending stiffness. Furthermore, clamped plates were influenced more than simply supported. The intersection between buckling modes shifted towards higher aspect ratios, in the maximum case by 24%. The results show the importance of considering the deforming weld in buckling analysis.

Research paper thumbnail of Fatigue Strength between Arc and Laser Hybrid Welded Joints

Research paper thumbnail of Modelling of Impact Between Ship Hull and Ice

Research paper thumbnail of On the Ice Trial of a 14500 DWT Tanker on the Gulf of Bothnia

This tanker is described under the main headings of (i) time and test area, (ii) ice pressure, (i... more This tanker is described under the main headings of (i) time and test area, (ii) ice pressure, (iii) speed measurements, (iv) power measurements, (v) ice measurements, (vi) turning test, and (vii) relationship between ice pressure and structural response of the ship. The results are tabulated and illustrated by graphs and histograms.

Research paper thumbnail of Structural Ice Loads in the Baltic

Research paper thumbnail of On Plastic Design of an Ice-Strengthened Frame

Research paper thumbnail of Some finite element estimates of ship collision event

Proceedings of the 11th International Congress of the International Maritime Association of the Mediterranean, Lisbon, Portugal, 26-30 September 2005, 2006

Research paper thumbnail of Ship collision as criteria in ship design

Advanced Ship Design for Pollution Prevention, 2010

Research paper thumbnail of European Research in Marine Structures

 Users may download and print one copy of any publication from the public portal for the purpose... more  Users may download and print one copy of any publication from the public portal for the purpose of private study or research.  You may not further distribute the material or use it for any profit-making activity or commercial gain  You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.

Research paper thumbnail of Long Term Measurements of Ice Pressure and Ice Induced Stresses on the Icebreaker Sisu in Winter 1978

The paper describes the measuring system onboard the icebreaker including the data collector syst... more The paper describes the measuring system onboard the icebreaker including the data collector system, ice pressure gauges, strain gauges, and the calibration of the ice pressure gauges. The weather and ice conditions in the Baltic during the winter of 1978 are stated. The following results of the measurements are discussed: Daily pressure maxima. Daily recordings. Statistical analysis. Influence of external conditions, and connection between ice pressure and ice-induced stress. Order from NSFI as No. 19966.

Research paper thumbnail of Bending response of web-core sandwich beams

Composite Structures, Jun 1, 2006

This paper presents a new analytical solution for the bending response of a web-core sandwich bea... more This paper presents a new analytical solution for the bending response of a web-core sandwich beam. The beam is a transverse cut from the sandwich plate. The method is based on the plane frame analysis, where the response of the beam is divided into local and global components. The ClebschÕs method is used to calculate the deflection of the face plates. The validation of the plane frame method is carried out with FE-analyses based on the shell element formulation. Also a comparison is made with the method based on homogenized beam. Periodic stress distributions in the face plates are revealed with the plane frame analysis and are supported by the FE-analysis. The existing methods based on homogenized beam are not able to predict these stresses. The plane frame analysis can benefit the development of the theory related to web-core sandwich plate.

Research paper thumbnail of Ship-Ice Contact and Design Loads

In this paper recent developments to model ship-ice contact and to evaluate design ice loads are ... more In this paper recent developments to model ship-ice contact and to evaluate design ice loads are summarised. The focus is on first year ice appearing annually in the Baltic Sea. The most important parameters to specify characteristics of ice cover for winter navigation purposes are presented. Observations on ship-ice contact suggest that the contact has a line-like nature. This concept is summarised and it's implications to structural design are discussed. An equivalent level ice thickness approach which includes the effect of ridges on the ice loads is described. The effect of ship parameters on the load level, based on the physical background for ice loads on different parts of a ship hull is given. A method to estimate the life-time ice loads on different parts of the hull of a vessel navigating in the Baltic Sea is developed, and the calculated loads are compared with measured long-term ice loads onboard MS KEMIRA, MS ARCTURUS and IB SISU. Finally the risk of damage caused by ice loads on ships in the Baltic Sea is discussed.

Research paper thumbnail of A ship in compressive ice.Analysis of the ice failure process.Concluding report from the joint Russian-Finnish project in 1991-1993

Research paper thumbnail of European Research in Marine Structures

Transactions of the Society of Naval Architects and Marine Engineers, 2011

 Users may download and print one copy of any publication from the public portal for the purpose... more  Users may download and print one copy of any publication from the public portal for the purpose of private study or research.  You may not further distribute the material or use it for any profit-making activity or commercial gain  You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.

Research paper thumbnail of Numerical and experimental investigation on the collision resistance of the X-core structure

Ships and Offshore Structures, Mar 1, 2012

Research paper thumbnail of Failure Process of Ice Edge Caused by Impact with Ship's Side

A survey of existing ice edge failure models is made, and some suggestions to improvements in the... more A survey of existing ice edge failure models is made, and some suggestions to improvements in these models are presented. The observed failure process of ice plate under various loading conditions is described. The process is then divided into physically different details such as crushing, shearing and bending, based on literature survey and observations made at sea. Results from tests made with fresh water beams are reported, and determination of compressive elastic constants of columnar grained fresh water ice is dealt with. Order from NSFI as No. 19954.

Research paper thumbnail of Sea Transport in Ice-Covered Waters

Sea transport in the Arctic regions represents just a small part of the world's total shippin... more Sea transport in the Arctic regions represents just a small part of the world's total shipping, not least because of the difficult environmental conditions encountered in these areas. Winter navigation started about a hundred years ago in the sub-arctic sea areas, where ice cover exists only during the winter months. Navigation in the Arctic proper began about a half century ago. The sailing period increases from year to year with the final goal obviously being year round traffic at a tolerable cost. This phase was reached in the Baltic in the early 1970s. The paper aims to give a general idea of the basic questions in polar sea transport systems. The demand for transportation and the influence on cargo handling systems and ship technology are discussed. However, details of technical solutions are, as far as possible, avoided.

Research paper thumbnail of Full scale observations of ship performance in ice

Research paper thumbnail of Ship-ice contact and design ice loads

Research paper thumbnail of International Conference on Education and Professional Development of Engineers in Maritime Industry, December 7th-8th 2011, Newcastle, UK

Research paper thumbnail of This is an electronic reprint of the original article. This reprint may differ from the original in pagination and typographic detail

This paper investigates the influence of weld rotation stiffness on the global bifurcation buckli... more This paper investigates the influence of weld rotation stiffness on the global bifurcation buckling strength of laser-welded web-core sandwich plates. The study is carried out using two methods, the first is the equivalent single-layer theory approach solved analytically for simply supported plates and numerically for clamped plates. First-order shear deformation theory is used. The second method is the three-dimensional model of a sandwich plate solved with finite element method. Both approaches consider the weld through its rotation stiffness. The weld rotation stiffness affects the transverse shear stiffness. Plates are loaded in the web plate direction. Four different cross-sections are considered. Weld stiffness is taken from experimental results presented in the literature. The results show a maximum of 24% decrease in buckling strength. The strength was affected more in plates with high reduction of transverse shear stiffness and high bending stiffness. Furthermore, clamped plates were influenced more than simply supported. The intersection between buckling modes shifted towards higher aspect ratios, in the maximum case by 24%. The results show the importance of considering the deforming weld in buckling analysis.

Research paper thumbnail of Fatigue Strength between Arc and Laser Hybrid Welded Joints

Research paper thumbnail of Modelling of Impact Between Ship Hull and Ice

Research paper thumbnail of On the Ice Trial of a 14500 DWT Tanker on the Gulf of Bothnia

This tanker is described under the main headings of (i) time and test area, (ii) ice pressure, (i... more This tanker is described under the main headings of (i) time and test area, (ii) ice pressure, (iii) speed measurements, (iv) power measurements, (v) ice measurements, (vi) turning test, and (vii) relationship between ice pressure and structural response of the ship. The results are tabulated and illustrated by graphs and histograms.

Research paper thumbnail of Structural Ice Loads in the Baltic

Research paper thumbnail of On Plastic Design of an Ice-Strengthened Frame

Research paper thumbnail of Some finite element estimates of ship collision event

Proceedings of the 11th International Congress of the International Maritime Association of the Mediterranean, Lisbon, Portugal, 26-30 September 2005, 2006

Research paper thumbnail of Ship collision as criteria in ship design

Advanced Ship Design for Pollution Prevention, 2010

Research paper thumbnail of European Research in Marine Structures

 Users may download and print one copy of any publication from the public portal for the purpose... more  Users may download and print one copy of any publication from the public portal for the purpose of private study or research.  You may not further distribute the material or use it for any profit-making activity or commercial gain  You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.

Research paper thumbnail of Long Term Measurements of Ice Pressure and Ice Induced Stresses on the Icebreaker Sisu in Winter 1978

The paper describes the measuring system onboard the icebreaker including the data collector syst... more The paper describes the measuring system onboard the icebreaker including the data collector system, ice pressure gauges, strain gauges, and the calibration of the ice pressure gauges. The weather and ice conditions in the Baltic during the winter of 1978 are stated. The following results of the measurements are discussed: Daily pressure maxima. Daily recordings. Statistical analysis. Influence of external conditions, and connection between ice pressure and ice-induced stress. Order from NSFI as No. 19966.