Tractive performance of an underwater tracked vehicle based on soil-track interaction

Transcription

1 Tractive performance of an underwater tracked vehicle based on soil-track interaction Literature review & Research plan Geotechnical & Geoenvironmental Engineering Laboratory 서울대학교 SEOUL NATIONAL UNIVERSITY

2 CONTENTS 1 2 Introduction Literature review 3 Research plan 4 Summary 2

3 1. Introduction 3

4 Background Development of underwater tracked vehicle for heavy construction work With the expansion of the underwater construction market, - subsea plants - offshore wind farms - subsea cables & pipelines the demand of underwater construction vehicle of which weight is up to 30tonf has been increased. New installed capacity of offshore wind turbines (The world wind energy association, 2012) Tracked vehicle guarantees - low contact pressure - high tractive force -4-

5 Background How tracked vehicle travels on the seabed Paved road Vehicle displacement (dd) - Vehicle displacement is equal to track displacement. - Tractive performance relies on engine power. Seabed (off-road) Vehicle displacement (dd) & Slip displacement (i ) - Vehicle displacement is equal to the difference btw track displacement and slip displacement. - Tractive performance does not solely rely on engine power. - Tractive performance potential is limited by the soil thrust determined from soil-track interaction. -5-

6 Background What happen within the soil-track interface Vehicle weight Vehicle displacement Vehicle weight Travel direction Track displacement Bottom thrust Traction (=soil thrust) Slip displacement (i ) Shearing action Soil thrust (=Traction) - A shearing action takes place on the soil-track interface, which results in the development of slip displacement and soil thrust. - Soil thrust increases with slip displacement and approaches a constant value(the max. soil thrust). - After reaching at the max. soil thrust, shear failure occurs within the soil-track interface, leading to vehicle idling (track displacement = slip displacement). -6- Traction (=soil thrust) Soil thrust = Bottom thrust + 2 Max. soil thrust Slip displacement (i )

7 Background Thrust-slip displacement relationship *** - Evaluation of soil thrust-slip displacement relationship is a key factor to assess the tractive performance of tracked vehicle. - Soil thrust is the traction force exerted at the soiltrack interface. - Soil thrust-slip displacement relationship is a function of shear strength parameters of the soil and track system configuration. Traction (=soil thrust) Slip displacement (i ) Max. soil thrust Soil thrust = Bottom thrust + 2 However, - Most of the studies carried out previously have not taken soil-track interaction into consideration. - Existing theoretical models (thrust-slip displacement relationship) have not sufficiently considered important parameters including track shape, track spacing and side thrust. -7-

8 Topic of the presentation Research topic : Evaluation of tractive performance of an underwater tracked vehicle, based on soil-track interaction preliminary study This presentation focuses on : literature review on tractive performance of an tracked vehicle - Existing theoretical model - Experimental studies + Research plans -8-

9 2. Literature review Tractive performance of an tracked vehicle 9

10 Existing theoretical model (Thrust-slip displacement) Shear plane theory (Bekker, 1956; Wong, 1984, 1989; Park et al., 2000) Vehicle weight Travel direction Thrust = (sssssssss ssssssssssss) dddd Traction (=soil thrust) Bottom thrust Soil thrust = Bottom thrust + 2 Traction (=soil thrust) Max. soil thrust = (sssssssss sssssssssssssss) dddd Slip displacement (i ) -10- = ττ bb ddaa bb + 22 ττ ss ddaa ss where, ττ bb, ττ ss : shear stress on the bottom and on the side AA bb, AA ss : contact area on the bottom and on the side - Shear stress was defined as a function of slip displacement, obeyed the Mohr-Coulomb criterion. - Bottom thrust can be expressed as ττ bb ddaa bb. - developed by the grousers has not been clearly investigated. ex) ττ = ττ mmmmmm (1 exp 1 jj KK ) j : shear displacement, K : shear displacement at ττ mmmmmm Bekker, 1956; Wong 1984, 1989 did not consider Park et al., 2000 considered as a frictional force exerted by active earth pressure

11 Existing theoretical model (Thrust-slip displacement) Compression-Sliding approach (Grecenko, , 2010, 2011) Vehicle weight Travel direction Frictional force Soil block compression Traction (=soil thrust) Thrust = SSoooooo bbbbbbbbbb cccccccccccccccccccccc + FFrrrrrrrrrrrrrrrrrr ffffffffff = FF gg /AA gg + WWff tt where, FF gg, AA gg : shear stress on the bottom and on the side WW, ff tt : contact area on the bottom and on the side Traction (=soil thrust) Soil thrust = Soil block compression + Frictional force Max. soil thrust = (sssssssss sssssssssssssss) dddd Compression stage Transition point Sliding stage Slip displacement (i ) - Soil thrust exerted by soil block compression accompanied with frictional force(compression stage). - Soil block is sheared off and slides along the soiltrack interface after transition point(sliding stage). - The max. soil thrust is (sssssssss sssssssssssssss) dddd, the same as shear plane theory. - developed by the grousers has not been clearly investigated. Grecenko, , , 2010, 2011 only considered cohesion of the soil -11-

12 Existing theoretical model (Thrust-slip displacement) Limitations of existing theoretical model : Existing models have only dealt with simple shapes of track systems. Bottom thrust Bottom thrust? Bottom thrust - Existing model has not sufficiently considered important parameters including track shape and track spacing. - has not been fully understood and theoretically defined. Bekker, 1956; Wong 1984, 1989 did not consider Park et al., 2000 considered as active earth pressure Grecenko, , , 2010, 2011 only considered cohesion of the soil - It is not sure what happen between each track systems (the interference effect). -12-

13 Experimental studies Experimental evaluation of tractive performance (Park, 1996; Park et al., 2000; Hong and Choi, 2001; Choi et al., 2003; Grecenko, ; Liu et al., 2008; Moreland et al., 2012; ect.) In order to overcome the limitations of existing theoretical model, - Tractive performance of tracked vehicle has been experimentally investigated under various track system configurations (grouser height, grouser spacing, ect.). - Soil thrust-slip displacement curves were obtained from the test results. - Each soil thrust obtained from each test condition was compared, suggesting optimized track system configurations for specific soil conditions. Optimized track configuration (a) Park et al., 2000 (b) Grecenko, Experimental tests set-up -13- Liu et al., 2008 Soil thrust-slip displacement curves

14 Experimental studies Limitations of previous studies : Most of the studies have not taken soil-track interaction into account, but rather focused on the mechanical configuration of tracks. Traction (=soil thrust)? Max. soil thrust Focusing Slip displacement (i ) Theoretical model? - Most of previous studies evaluated tractive performance of tracked vehicle by means of the max. soil thrust. - While traveling, tracked vehicle develops soil thrust not exceeding the max. soil thrust in a typical situation. - Theoretical model being able to be utilized in practical field ground conditions has not been investigated. -14-

15 3. Research plan 15

16 Research plan Development of modified thrust-slip displacement model (New model) Bottom thrust? Bottom thrust Existing models (shear plane theory or CS approach) - - The interference effect Theoretical study Track model experiments Modification of existing thrust-slip displacement model and evaluation of tractive performance of underwater tracked vehicle -16-

17 Research plan How to develop the modified thrust-slip displacement model? a. Performing the track model experiments under various test conditions (soil properties, grouser shape, grouser spacing, etc.) d l Soil properties h The interference b. Evaluation of experimental thrust-slip displacement curves c. Comparing the test results with existing models and modifying them based on theoretical soil mechanics Traction (=Soil thrust) Measured Fitted Thrust =ff(ii, cc,, ll, dd, hh, FF aaaaaaaaaa, eeeeee. ) Slip displacement(i) -17-

18 4. Summary 18

19 Summary I. Tractive performance of underwater tracked vehicle - Being limited by the soil thrust determined from soil-track interaction - Being evaluated by means of soil thrust-slip displacement relationship II. The studies carried out previously - Having not sufficiently defined the important parameters including side thrust and the interference effect. - Being limited to be utilized in practical field ground conditions III. Based on the theoretical study and track model test results, - Modification of existing thrust-slip displacement model (New model) - Evaluation of tractive performance of underwater tracked vehicle in practical field ground conditions -19-

20 THANK YOU Any question? 서울대학교 SEOUL NATIONAL UNIVERSITY