model tests of new type of anchors in centrifuge using

Model Tests of New Type of Anchors in Centrifuge using Wireless Smart Sensors Networks 135

Model Tests of New Type of Anchors in Centrifuge using Wireless Smart Sensors Networks

by Toshi-ichi Tachibana Member* Rubens Ramires Sobrinho* Tsugukiyo Hirayama Member**

Summary

The present paper describes tests performed with models inside centrifuge apparatus as a special tool for analysis and design of foundation elements applied in offshore structures. By using wireless smart sensors technology in physical model test inside centrifuges, significant improvements in the parameters determination will be possible for first time in Brazil. The centrifuge modeling has been used to address geotechnical problems in offshore engineering area, in order to avoid misinterpreting results commonly observed in reduced model tests. Herein it is also presented a modeling example of a special type of anchor known as ''turtle anchor”, developed by CENPES-PETROBRAS, which has already been used in real cases. A comprehensive series of tests in conventional scale has been performed on turtle anchors; however, the results did not bring numerical information about contact stress between soil and anchor, due to difficulties in evaluating the bearing capacity and deformation.

1. Introduction

Nowadays, in order to carry out real or model tests, there are many options of electric systems and sensors available. These systems are still cable dependant, therefore higher installation time and greater cable lengths are required at the industrial plant, increasing installation overall cost. The communication between the sensor element and data acquisition system and control (DAQC) has been limited and dependant on wires and cables since long time. This limitation also occurs because the communication is carried out by manufacturer's protocols, which implies high costs. Now, these systems are arousing interest due to the decrease or even elimination of cables usage, minimizing cost.

Progress is more significant when access to the measurement networks takes place by means of wireless technology, allowing faster reading of the process variables or the monitoring of test conditions. The current evolution enables creating wireless smart sensor networks to be used in several applications.

It comprises activities such as tests with reduced scale model inside centrifuges. Two works which used Wireless Smart Sensors Networks (WSSN) inside centrifuges can be detached (Cheekiralla, 2004; Wilson et al., 2004), although the conclusion of Cheekiralla's work indicates failures in its use. The reduced scale model test inside centrifuges was performed by IPT- (Technological Research Institute of São Paulo) centrifuge unit

through the use of conventional instrumentation technology, such as data acquisition system and control (DAQC) and cables for data transfer. In some cases, results obtained are hard to interpret or understand, and repetitions of tests are possibly required. The previous estimates obtained by numeric modeling are not comparable to tests results. In many cases it was necessary to develop auxiliary devices to reduce the instrumentation effects during the study evolution.

Thus, the wireless technology was employed in the actual study, using the IPT centrifuge. The acquired experience with wireless technology, today, is possible to be transferred to UENF – State University of Norte Fluminense Darcy Ribeiro – where major Brazilian centrifuge is installed.

2. Basic considerations of modeling

The study of phenomena associated with the behavior of foundation elements has been often hampered by difficulties in carry out a series of field tests due to its high cost and complexity.

The use of physical models is an old practice in the engineering area and it has been improved by the development of electro-electronics sensors, allowing precise measurement of stress and strains.

Thus, in recent years, the amount and quality of information obtained from these tests on models has substantially increased as a result of the improvement of instrumentation and systems for processing data.

The models are a physical representation, in reduced scale, which are tested and analyzed, using laws of similarity employed to interpret the results.

Particularly for the study of geotechnical problems, the physical model represents an important tool because, given its smaller size, it is possible to consider the ground homogeneity and mass forces. It is also feasible to consider the model characteristics that can influence its behavior.

University of São Paulo

＊ Yokohama National University

原稿受理平成年月日

Model Tests of New Type of Anchors in Centrifuge

using Wireless Smart Sensors Networks

by Toshi-ichi Tachibana, Member*　　Rubens Ramires Sobrinho*

Tsugukiyo Hirayama, Member**

Recceived 5th Aug. 2011

　日本船舶海洋工学会論文集　第 14 号　 2011 年 12 月　 136

In practice, it is observed that the use of very small scales presents difficulties in manufacturing and instrumentation. Larger models are easier to build but, in general, they require bigger and more sophisticated equipment, in particular those used for loadings.

Models can be employed to evaluate theories and their generalizations to several cases, through simulations in three-dimensional scale. The result accuracy can be affected by many factors, such as materials properties, model manufacturing, manufacturing tolerance control, loading techniques, measurement methods, and results interpretation.

The models must be designed and examined in accordance with the laws of similarity between them and its prototypes.

The laws of similarity are based on modeling theory and they are derived from dimensional analysis of the physical phenomena involved.

Scale factors for independent parameters are chosen and the same factor must be considered for others parameters.

In order to ensure that the phenomena observed in models are mimicking the prototype behavior, it is necessary to meet the similarity requirements. Geometric similarity is easy to be achieved, but full similarity is very difficult to attain. In such cases, it is necessary to justify the differences, checking their influences on parameters and results.

In general, geotechnical problems involve water flow (pore pressure dissipation in this case), which affects strains and stresses of soil-element interface, in a level below that of prototypes. Unit scale of stress, using the same materials, can only be achieved by using centrifuges. The choice of model materials must consider stress limits, stiffness, rupture mechanisms, the influence of temperature and humidity, the effect of loading speed as well as size and form.

The success of experimental results depends on precision and reliability of measurements. In order to achieve the same precision of prototype tests, they must contemplate at least the scale factor applied to instruments in model simulations. Tests with models can be improved by the use of statistical analysis in data interpretation and appropriate instrumentation. Model instrumentation includes identifying amounts to be measured, selecting measurement sensors, and their installation and calibration process.

Table 1 presents a list of main physical amounts involved in modeling process.

The scale factors between model and prototype, for a scale reduction of 1:N is presented in Table 2 (Portugal, 1999).

In case of water flow, it can be demonstrated that the scale factor for time is N-1. By adopting N-1, the similarity condition is obtained, but the modeling law for the fluid speed cannot be fulfilled or is violated. It would be necessary therefore to use a liquid with different dynamic viscosity in order to avoid violating this law (Portugal, 1999).

The study of offshore foundations in actual scale would demand many material resources, beyond a place of appropriate dimension and with similar geological-geotechnical characteristics. Thus, the use of reduced models is an important tool to evaluate the phenomenon related to the installation process, which can be reproduced in smaller scale and conditions closer to homogeneity in terms of ground parameters. Tests in reduced models, especially those that deal with bearing capacity of foundation, have been mostly performed for academic purposes.

Table 1: Physical quantities Quantity Unit

Lenght L Force F Time T Mass F L-1 T2 Stress F L-2 Strain --

Acceleration LT-2 Linear Displacement L

Elastic Modulus FL-2

Table 2: Scale factors in physical model (Portugal, 1999) Quantity Scale Factor

Lenght N-1 Time N-1/2 Speed N-1/2

Acceleration 1 Mass N-3 Force N-2

Stress, Pressure N-1

Costs and difficulties inherent to modeling are roadblocks to its use in a larger scale. When measurement of pore-pressures are required, care with the instrumentation must guide the tests, since any instrumentation of significant size, immersed in the ground soil mass, can behave as reinforcement element. Moreover, scale effects are important if they violate some modeling laws and when tests with models become surpassed due to the analysis of prototype behavior. In order to evaluate results, studies on the influence of scale effect can be conducted by accomplishing a series of tests regarding phenomenon in different scales. This is known as modeling of the models.

In a study of bearing capacity of foundation using reduced physical models, some factors require special attention: the dimensions and geometry of a model, the stress level in the model and in the ground. While analyzing pore-pressure dissipation, time scale effects must be considered. Likewise, in order to reproduce the same stress level existing in the field using a centrifuge, this special piece of equipment enables real case simulation under increased gravity accelerations, and appears as an alternative. Few are the available centrifuges in Brazil (IPT - Technological Research Institute in São Paulo State has one, developed in partnership with FAPESP – São Paulo State Research Foundation) and its use is still focused on academic research. It is certainly a promising tool for technological innovations in the geotechnical area.

3. Physics of modeling

According to dimensional analysis presented by Portugal (1999), there are two identical geometric systems in physical modeling, where parameters indicated by ´*´ imply relation between model and prototype:


In practice, it is observed that the use of very small scales presents difficulties in manufacturing and instrumentation. Larger models are easier to build but, in general, they require bigger and more sophisticated equipment, in particular those used for loadings.

Models can be employed to evaluate theories and their generalizations to several cases, through simulations in three-dimensional scale. The result accuracy can be affected by many factors, such as materials properties, model manufacturing, manufacturing tolerance control, loading techniques, measurement methods, and results interpretation.

The models must be designed and examined in accordance with the laws of similarity between them and its prototypes.

The laws of similarity are based on modeling theory and they are derived from dimensional analysis of the physical phenomena involved.

Scale factors for independent parameters are chosen and the same factor must be considered for others parameters.

In order to ensure that the phenomena observed in models are mimicking the prototype behavior, it is necessary to meet the similarity requirements. Geometric similarity is easy to be achieved, but full similarity is very difficult to attain. In such cases, it is necessary to justify the differences, checking their influences on parameters and results.

In general, geotechnical problems involve water flow (pore pressure dissipation in this case), which affects strains and stresses of soil-element interface, in a level below that of prototypes. Unit scale of stress, using the same materials, can only be achieved by using centrifuges. The choice of model materials must consider stress limits, stiffness, rupture mechanisms, the influence of temperature and humidity, the effect of loading speed as well as size and form.

The success of experimental results depends on precision and reliability of measurements. In order to achieve the same precision of prototype tests, they must contemplate at least the scale factor applied to instruments in model simulations. Tests with models can be improved by the use of statistical analysis in data interpretation and appropriate instrumentation. Model instrumentation includes identifying amounts to be measured, selecting measurement sensors, and their installation and calibration process.

Table 1 presents a list of main physical amounts involved in modeling process.

The scale factors between model and prototype, for a scale reduction of 1:N is presented in Table 2 (Portugal, 1999).

In case of water flow, it can be demonstrated that the scale factor for time is N-1. By adopting N-1, the similarity condition is obtained, but the modeling law for the fluid speed cannot be fulfilled or is violated. It would be necessary therefore to use a liquid with different dynamic viscosity in order to avoid violating this law (Portugal, 1999).

The study of offshore foundations in actual scale would demand many material resources, beyond a place of appropriate dimension and with similar geological-geotechnical characteristics. Thus, the use of reduced models is an important tool to evaluate the phenomenon related to the installation process, which can be reproduced in smaller scale and conditions closer to homogeneity in terms of ground parameters. Tests in reduced models, especially those that deal with bearing capacity of foundation, have been mostly performed for academic purposes.

Table 1: Physical quantities Quantity Unit

Lenght L Force F Time T Mass F L-1 T2 Stress F L-2 Strain --

Acceleration LT-2 Linear Displacement L

Elastic Modulus FL-2

Table 2: Scale factors in physical model (Portugal, 1999) Quantity Scale Factor

Lenght N-1 Time N-1/2 Speed N-1/2

Acceleration 1 Mass N-3 Force N-2

Stress, Pressure N-1

Costs and difficulties inherent to modeling are roadblocks to its use in a larger scale. When measurement of pore-pressures are required, care with the instrumentation must guide the tests, since any instrumentation of significant size, immersed in the ground soil mass, can behave as reinforcement element. Moreover, scale effects are important if they violate some modeling laws and when tests with models become surpassed due to the analysis of prototype behavior. In order to evaluate results, studies on the influence of scale effect can be conducted by accomplishing a series of tests regarding phenomenon in different scales. This is known as modeling of the models.

In a study of bearing capacity of foundation using reduced physical models, some factors require special attention: the dimensions and geometry of a model, the stress level in the model and in the ground. While analyzing pore-pressure dissipation, time scale effects must be considered. Likewise, in order to reproduce the same stress level existing in the field using a centrifuge, this special piece of equipment enables real case simulation under increased gravity accelerations, and appears as an alternative. Few are the available centrifuges in Brazil (IPT - Technological Research Institute in São Paulo State has one, developed in partnership with FAPESP – São Paulo State Research Foundation) and its use is still focused on academic research. It is certainly a promising tool for technological innovations in the geotechnical area.

3. Physics of modeling

According to dimensional analysis presented by Portugal (1999), there are two identical geometric systems in physical modeling, where parameters indicated by ´*´ imply relation between model and prototype:

Where m and p imply the model system and prototype system and l* and t* are scale factors for length and time, respectively. In model, the velocity vector at any given point is: Thus: Or: Thus, the velocity scale factor is: In model, the acceleration vector at any given point is expressed by: From equations (2) and (5): Then: The distributions of mass will be also similar if: Where mm and mp refers to the mass of homologue parts, in model system and prototype, respectively, and m* is scale factor.

Applying the Newton’s Second Law, we obtain: Replacing the terms, we obtain: Where F* represents scale factor of the forces.

In physical modeling, the materials behavior can be represented by two different ways: conventional physical modeling and centrifuges physical modeling.

In the conventional physical modeling the models are tested under normal gravitational field.

The centrifuges physical modeling, to create artificial gravity forces in models for the tests.

Portugal (1999) describes that it is possible to submit the model under stronger gravitational field and achieve one tension field that complies with mechanical and complete similarity with prototype.

3.1 Centrifuge physical modeling

Considering that (i) the centrifuge physical modeling technique and

proceedings are equal to conventional physical modeling,

(ii) geometric scale factor reduction is imposed and (iii) model tests are performed under the artificial

acceleration field N times higher than normal gravitational acceleration field, where N (≧1) is the geometric reduction factor, we obtain:

(iv)

If the materials of models were identical the prototype, ρ*=1, we obtain:

Force as result of enhanced gravity: If we choose a＊=N and equations (6), (9), and (10), we will get:

Niyama (1992) referred in his thesis that Galileo was the first who applied the modern scale analysis and employed the notion of critical tension cr * = l * *, where l is the length, the specific weight, resulting in the following expression:

Where ρ is specific mass and g is earth gravity acceleration. This expression represents the physical condition for prototype and its reduced scale model.

The works of Niyama (1992) indicates that in continuous medium, the equilibrium equations are validated if the expression above is taken into consideration. Portugal (1999) thesis presents the equilibrium equation of one continuous:


Where: σij, the components of the tensor of total tension; gi, the components of the force vector (mass); δi, the components of the displacement vector; ρ, volumetric mass of the constituted material.

The equation (19) is presented in dimensional form and It can be transformed into non dimensional one:

The variables x1, σ1 and t represent fundamental dimensions, where σi is the main component of the tensor of total tension (i=1, 2, 3).

Dimensional equilibrium formulation with (11) dimensional constant components allows modeling law applied to the model and in accordance with similarity requirements to the prototype.

If the model and the prototype are geometric similar and equal values of products in model and prototype apply, we obtain:

From (26), we get:

From equation (27) and (25) we obtain the following equation (28):

This is the fundamental modeling law applied for problems of static equilibrium.

In soils, the model can be constituted by same materials employed in prototypes, where ρ* =1. Test is desirable at same tension level where σ* = 1. From equation (1) and (13):

The main purpose to test in centrifuge is to increase acceleration at same proportional linear scale N.

4. Centrifuge description

This apparatus consists of two reinforced containers rotated by one electrical motor, with a rotation-controlled system, exerting a force on the model proportionally to N times the gravitational force. The main features of the equipment are: • Nominal diameter: 1500 mm;

• Acceleration: 200 g (g: acceleration of gravity); • Rotation: 451 rpm (revolutions per minute).

The centrifuge arm (Figure 1) is symmetrical to its rotational axis (vertical direction). The steel structure is suspended 38 cm above the ground and fixed to the ground by metallic anchors. Neoprene plates are used to isolate the machine from external vibrations.

The centrifuge side walls are made of steel and filled with sand in order to avoid empty regions. Under normal testing conditions, centrifuge rotates perfectly balanced, with the model placed in one of the container and the counterweight in the other one. The containers are made of steel, measuring 250 x 300 x 130mm.

Figure 2 shows all centrifuge systems while Figure 3 shows a photo of IPT’s centrifuge.

Figure 1: Arm assembly – IPT/FAPESP Centrifuge

Figure 2: IPT/FAPESP Centrifuge Systems

Figure 3: IPT/FAPESP Centrifuge photo


Where: σij, the components of the tensor of total tension; gi, the components of the force vector (mass); δi, the components of the displacement vector; ρ, volumetric mass of the constituted material.

The equation (19) is presented in dimensional form and It can be transformed into non dimensional one:

The variables x1, σ1 and t represent fundamental dimensions, where σi is the main component of the tensor of total tension (i=1, 2, 3).

Dimensional equilibrium formulation with (11) dimensional constant components allows modeling law applied to the model and in accordance with similarity requirements to the prototype.

If the model and the prototype are geometric similar and equal values of products in model and prototype apply, we obtain:

From (26), we get:

From equation (27) and (25) we obtain the following equation (28):

This is the fundamental modeling law applied for problems of static equilibrium.

In soils, the model can be constituted by same materials employed in prototypes, where ρ* =1. Test is desirable at same tension level where σ* = 1. From equation (1) and (13):

The main purpose to test in centrifuge is to increase acceleration at same proportional linear scale N.

4. Centrifuge description

This apparatus consists of two reinforced containers rotated by one electrical motor, with a rotation-controlled system, exerting a force on the model proportionally to N times the gravitational force. The main features of the equipment are: • Nominal diameter: 1500 mm;

• Acceleration: 200 g (g: acceleration of gravity); • Rotation: 451 rpm (revolutions per minute).

The centrifuge arm (Figure 1) is symmetrical to its rotational axis (vertical direction). The steel structure is suspended 38 cm above the ground and fixed to the ground by metallic anchors. Neoprene plates are used to isolate the machine from external vibrations.

The centrifuge side walls are made of steel and filled with sand in order to avoid empty regions. Under normal testing conditions, centrifuge rotates perfectly balanced, with the model placed in one of the container and the counterweight in the other one. The containers are made of steel, measuring 250 x 300 x 130mm.

Figure 2 shows all centrifuge systems while Figure 3 shows a photo of IPT’s centrifuge.

Figure 1: Arm assembly – IPT/FAPESP Centrifuge

Figure 2: IPT/FAPESP Centrifuge Systems

Figure 3: IPT/FAPESP Centrifuge photo

5. Test performed with wireless technology (“Wireless Smart Sensors Network”)

Experience gained during tests on suction piles enabled the implementation of a new research project focused on the behavior of a new foundation solution for offshore structures, named turtle anchor. It is a special anchor, which has a format similar to a turtle, driven into the soil. Three different models were constructed (see Figure 4). Table 3 shows the main characteristics of models and prototypes, with different structural arrangement and the same height. The model was designed to withstand 150 g acceleration during the centrifuge tests. Table 4 presents the weight force for each model and related prototype.

Figure 4: Turtle anchor models

(*) Weight force (N2) , where N is the scale factor

Testing assemblage started by pouring soil into centrifuge container. This undrained soil had cohesion of 15 kPa, water content of 33.4 %, and cone penetration of 7 mm at lab level. Soil grains and water were mixed, in order to attain the parameters mentioned above.

The soil mass was disposed into the container in layers of 4 cm each.

Tests were performed for each layer in order to reveal water content and cone penetration. This procedure was aimed to prevent air from entering the soil, consequently, ensure soil mass homogeneity.

When soil achieved 13 cm height inside the container, 10 cm of water was poured on the soil mass, simulating the water sea level. Then, an anchor model and all the apparatus were installed before starting the test (Figure 5).

At the end of each test, an undisturbed Shelby sample was removed from the box, and all soil tests were repeated to confirm

that conditions were kept unchanged during the centrifuge action. Monitoring sensors comprised of a tilt sensor, a load cell, a

small motor, and an encoder, utilized a wireless system, developed by Ramires (2007) (Figures 6 and 7).

Figure 5: “Turtle anchor” model

Dragging and pulling out forces were simulated using load cells with 350 Ω resistance strain gauges in a full bridge arrangement. Forces up to 600 N could be measured with this device.

The motor had an encoder system with 15,000 resolution points. It was able to simulate a 1.15 mm/s pulling out velocity, which corresponds to 4.14 mm/s at prototype level.

Some special pulleys were placed on the container in order to ensure that horizontal forces on anchor models reproduces what happens in real situation.

Two different software applications were developed in order to record data testing. The first one was C based language, and the second one was based on LabVIEW package. These two software applications were executed simultaneously, in order to avoid communication noises.

Figure 6 – Evaluation module (Chipcon, 2003)

Figure 7 – Wireless smart sensors applied in tests


Figures 8 and 9 shows one of the tests performed.

Figure 8 – “Turtle anchor” during test

Figure 9: Pictures taken during testing

Table 5 presents results of tests in centrifuges and Table 6, Figures 10 up to 12 show the same values for the prototype conditions, obtained from the reduced modeling tests.

Prototype forces were obtained by using a scale factor of N2. For displacements, the scale factor is N, and for tilt angles it is equal to the unity.

Visual observations of the results in centrifuge indicated that:

anchor 1 is not stable when submitted to horizontal forces. It penetrates some centimeters in soil mass, but only the back part of model was undergrounded. This anchor probably suffered a strong influence of the sensor and cables masses, installed near its back part;

anchor 2 also presented unstable behavior during pulling out, which was confirmed at the "flight end" by the position of anchor model in the box;

anchor 3 proved to be the one with the best behavior. A 56º penetration angle was measured during testing, providing this model with stronger dragging resistance. A stable situation was noticed at the end of tests, showing that the geometry of anchor 3 is suitable for situations in which horizontal forces act over anchors.

Figure 10 –Anchor 1 displacement in soil


Figure 12 – Anchor 3 displacement in soil


Figures 8 and 9 shows one of the tests performed.

Figure 8 – “Turtle anchor” during test

Figure 9: Pictures taken during testing

Table 5 presents results of tests in centrifuges and Table 6, Figures 10 up to 12 show the same values for the prototype conditions, obtained from the reduced modeling tests.

Prototype forces were obtained by using a scale factor of N2. For displacements, the scale factor is N, and for tilt angles it is equal to the unity.

Visual observations of the results in centrifuge indicated that:

anchor 1 is not stable when submitted to horizontal forces. It penetrates some centimeters in soil mass, but only the back part of model was undergrounded. This anchor probably suffered a strong influence of the sensor and cables masses, installed near its back part;

anchor 2 also presented unstable behavior during pulling out, which was confirmed at the "flight end" by the position of anchor model in the box;

anchor 3 proved to be the one with the best behavior. A 56º penetration angle was measured during testing, providing this model with stronger dragging resistance. A stable situation was noticed at the end of tests, showing that the geometry of anchor 3 is suitable for situations in which horizontal forces act over anchors.



Figure 12 – Anchor 3 displacement in soil

6. Comclusions

This paper presented examples of tests in centrifuges, in particular, offshore foundation elements. These foundation solutions have been used in offshore structures, particularly in marine oil and gas production systems.

It is well known that it is very difficult, costly and dangerous to perform tests in real scale, especially in deep water situations.

Costs involved in this activity also represent a major concern for companies and designers. Consequently, centrifuge seems to be a suitable tool to simulate and analyze the behavior of new solutions, bringing valuable information about bearing capacity, displacements, and stability of foundation elements.

Wireless instrumentation methodology developed for current research, intended to protect data against communication failure, and achieved 100% of efficiency, ensuring that proposed method is superior to traditional one from level of detail availability and reliability perspective, turning centrifuge tests more attractive for offshore structure related studies.

Acknowledgement The tests were performed by IPT and EPUSP, financially

supported by FAPESP. Today, many tests are performed at UENF Laboratory too, and it's possible to offer results with more accuracy, attending several applications today and in a near future.

References Campos, G.C., Campos, E. P.; Medeiros Jr., C.J. (2006) “Utility of the reduced physical models of the boundary

analysis for turtle anchors”. In: III Congress Geotechnical Brazilian-Portugal, p. 429-434.

Cheekiralla, S. M. S. L. (2004); “Development of a Wireless Sensor Unit for Tunnel Monitoring”, Thesis (Master Science) in Civil Engineering Department and Ambient of the MIT – Massachusetts Institute of Technology; USA.

CHIPCON ( 2003); Quick StartInstructions CC1010DK Development Kit;. Norway

Niyama S, (1992); “Contribution to the study of the bushing in the open ended piles driven” – Doctoral thesis - Escola Politécnica – University of São Paulo,

Niyama S., Gobara W., Dionysus A., JR, Alvim F.M.,Ramires R., Tachibana L.S. 1994 “Development of the First Prototype Geotechnical Centrifugefor IPT”, COBRANSEF X- X Congress Brazilian Soil Mechanics and Foundation Engineering, Foz do Iguaçu

Portugal, J.A. (1999).; Physical Modelling with Centrifuge. Portugal, 241 p. Doctoral Thesis – Lisboa College Technician Institute.

Ramires R.S, Tachibana T(2000 ) “Methodology for soil behavior analysis for marine Offshore Structures through reduced Model,”. Proceedings of the XVIII National Maritime Transportation, Shipbuilding and Offshore, Brazilian Society of Naval Engineering, Rio de Janeiro - Brazil

Ramires, R.S. (2007); Method for data protection against communication failures in

wireless smart sensors networks. 2007. Doctoral Thesis – Escola Politécnica – University of São Paulo, São Paulo, Brazil, 326 p.,

Wilson, D. W.; Weber. G. H.; Slankard, T.; Hamann, B.; Kutter, B. L.(2004);

Visualization in Experimental Earthquake Engineering,. CITRIS Workshop on Sensor, Sensor Networks and Sensor Applications, University California Davis, USA.

model tests of new type of anchors in centrifuge using

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