Louis Lamarche

Numerical Study of Thermal Behavior of a Wind Turbine Nacelle Operating in a Nordic Climate

This article presents a numerical method for investigating the thermal behavior of a wind turbine nacelle operating in a Nordic climate. External air flow around the nacelle and rotor as well as internal air flow through the nacelle are described using the Reynolds-averaged Navier-Stokes equations. The energy equation is used to account for heat transfer effects. The standard k − ε model is chosen for the closure of time-averaged turbulent flow equations. The rotor is modeled using the actuator-disk concept. An unstructured control-volume finite-element method is employed to solve the resulting governing equations. This article focuses on the effects of external air temperature, wind velocity, and the heat rate released by an electrical generator on the spatial distribution of the temperature inside the nacelle. It is found that, to maintain an acceptable temperature level within the nacelle during summer, the amount of air mass rate flowing through the nacelle should be adjusted properly as a function of wind velocity and external temperature. During winter, the nacelle should be well insulated and the air should be well stirred to obtain nearly uniform temperature distribution within the nacelle.

Backstepping adaptive position control for robotic manipulators

The paper presents a general approach for the design of an adaptive position control for a robotic system by the backstepping strict-feedback technique. The advantage of this control technique is that it imposes desired properties of stability by fixing the candidate Lyapunov functions initially, then by calculating the other functions in a recursive way. The adaptation of the parameters is made by the direct adaptive method. The results obtained by using this control method, which is valid for various types of robotic architectures, are very satisfactory when applied to a three d.o.f robot consisting of one prismatic axis (axis 1), and two others rotary axes. The results show that the robot follows exactly the triangular trajectory assigned to him. The trajectory tracking errors are negligible. Simulation results are included in order to evaluate the tracking performances and the global stability of the controlled system, and to justify the reliability of the proposed control technique.

Backstepping passivity adaptive position control for robotic manipulators

This paper presents a general approach for the design of an adaptive position control for robotic systems by the backstepping passivity strict-feedback technique. The advantage of this control technique is that it imposes desired stability properties by fixing for a given output, the storage, input and stabilizing functions with each recursive step of the system. Parameter estimation is made by the direct adaptive technique. The results obtained by using this control method, which is valid for various types of robotic architectures, are very satisfactory when applied to a four d.o.f robot consisting of one prismatic axis (axis 1) and three other rotary axes. The performance of the controller is illustrated by simulation results showing the tracking of a triangular trajectory. The results show that the robot follows exactly the triangular trajectory. The trajectory tracking errors are negligible.

An integrated computer-aided optimization system for process planning

Abstract Designing a manufacturing operation is a major activity of process planning, especially in the case of processes requiring a comprehensive selection of the operating parameters. This activity includes three hierarchical stages : procedure design, schedule design, and tolerance design. A new approach for process modelling and optimization has been devised to address the problems to solve at each stage. The methodology is based on sequential experimentation to model the feasible domain of the process and on a direct search technique to optimize for quality and process robustness. An integrated computer-aided system has been designed to manage the manufacturing data and the strategies for optimization and variation reduction. Applications to various manufacturing processes are presented.

Study of potential nonconformities of a new recreation center building's envelope

This article presents a building envelopes analysis in order to verify the compliance with mandatory provisions of the Model National Energy Code for Buildings in Canada (MNECB 1997). Because some of the requirements are «not met», investigations were carried out to provide justifications in order to prove that the building can be considered as an exception to the mandatory provisions of MNECB. Therefore, we evaluate the impact of three (3) potential nonconformities of the buildings walls on the building energy performance. In regards to article 3.1.1.1.4 of MNECB, there is an exception if it can be proved that permanent process (like heat recovery of refrigeration compressors) can produce at all times enough heat that no other heating source is required. First of all, by using simulation, we were able to indicate that almost all buildings heating will be provided by energy recovery from ice rinks refrigeration systems (99.2%). Secondly, by using an energy analysis carried out with HEAT2 software, we can show that the increase of heating energy demand caused by the 3 studied walls is very low. This represents an increase of the heating energy demand of only 0.2%, and this, regardless of the heat recovery process. Because the nonconforming wall sections are small (0.97% of the envelope area), this mainly explains the minor impact in terms of building performance. In conclusion, according to the results obtained, we were able to recommend the building for consideration as an exception to the mandatory provisions of MNECB.

Multiple source ground heat storage

Sharing geothermal borefields is usually done with each borehole having the same inlet conditions (flow rate, temperature and fluid). The objective of this research is to improve the energy efficiency of shared and hybrid geothermal borefields by segregating heat transfer sources. Two models are briefly presented: The first model allows the segregation of the inlet conditions for each borefields; the second model allows circuits to be defined independently for each leg of double U-tubes in a borehole. An application couples residential heat pumps and arrays of solar collectors. Independent circuits configuration gave the best energy savings in a symmetric configuration, the largest shank spacing and with solar collectors functioning all year long. The boreholes have been shortened from 300 m to 150 m in this configuration.

Simplified optimization method for preliminary design of HVAC system and real building application

HVAC systems (heating, ventilation, and air conditioning) are recognized as the greatest energy consumers in commercial and institutional buildings. Generally, designers use common sense, historical data, and subjective experience in designing these systems; this includes the number of systems chosen and the grouping of the zones served by these systems. HVAC energy efficiency is not an easily calculable criterion during the selection of these systems; usually the first selection criterion is the weakest investment cost. In this article, we present a simplified optimization method for preliminary design of HVAC system using the zones’ daily profile loads. A global load ratio is applied as an optimization function. The global load ratio represents the relationship between the systems real load and its possible maximum load for a given period. The variables for the optimization problem are: (i) grouping of the zones served by the systems and (ii) number of systems serving the building. Type of system was preselected for the present study, but this could also serve as an optimization variable. The correlations between global load ratio and energy consumption were shown using an office building. Then, this method was applied on an existing institutional building and compared with the detailed optimization method. In the second method, the HVAC energy consumption, calculated using DOE-2 software, was used as the optimization function. The comparison made among the existing, reference, and optimized buildings (all sharing the same constraints) have yielded significant energy savings for HVAC energy consumption. A life cycle cost analysis has also been done to estimate savings in terms of investment, operation and maintenance costs. These savings depend upon building configuration, the constraints imposed, the types of HVAC systems selected, and the control strategies for these systems.

Une méthode simple d'adaptation des maillages pour le calcul des écoulements compressibles

ABSTRACT This work presents some recent results on the solution of compressible flows using a simple adaptive mesh method and finite element code. This method consists of mesh enrichment and mesh derefinement procedures, and is based upon a special finite element residual norm. The residual norm provides a reliable indicator of regions to be adapted and hence to improve the quality of the solution. The paper presents the finite element formulation used, a modified Delaunay triangulation of arbitrary planar domains and the algorithms related to their adaptivity. Several numerical examples are presented which demonstrate the performance of our methods in solving compressible high speed flows.